Peas are a leguminous agricultural crop.
- Economic importance
- History of the crop
- Cultivation areas and yields
- Chemical composition and nutritional value
- Botanical description
- Biological features
- Crop rotation
- Fertilizer system
- Crop care
- Weed control
- Storage and post-processing
- Resource-saving intensive technology
- Abiotic stresses
- Seed production
Peas account for about 80% of all sown areas of leguminous crops in Russia. Peas are of food, fodder and agrotechnical importance in agriculture.
There are three main types of pea crop production:
- plants that produce well-developed, juicy but immature seeds (English, garden, grape, and green peas are terms referring to plants of this type. The early involvement of English breeders in the cultivation of peas is thought to be the origin of the term “English” peas);
- plants that produce immature, juicy, edible pods (beans) with seeds Peas harvested fresh as immature pods and seeds are known as sugar or snow peas;
- plants producing fully developed, mature, dry seeds.
Pea seeds are digestible and highly palatable. Mature, unripe seeds (green peas) and green beans (vegetable varieties) are used for food purposes. Peas, in addition to being used fresh, are frozen, canned and dehydrated.
Dried peas are reconstituted by soaking and used directly or further processed by canning. When processed dry, the seed shells are removed. The intact or split seeds are used in soups and are also ground into a powder.
Green peas contain 25-30% sugars, vitamins A, B1, B2 and C, minerals. Pea seeds contain 23-30% protein.
In some Eastern countries the tender shoots of peas are used as greens.
Because of their high protein content, good amino acid balance and high digestibility, dried field peas are mainly used as animal feed. Pea-grass mixtures are grown for silage, green fodder and hay. 1 kg of green matter equals 0.13 fodder units and contains 25 g of digestible protein. 1 kg of seeds is equal to 1.17 fodder unit and contains 180-240 g of protein. 1 kg of hay contains up to 13% protein. Pea meal is used in livestock farming as a concentrated feed for livestock. Shredded grain, chaff and green mass are used for fodder purposes. Earlier pea straw was used as a fodder. Its protein content amounted to 6-8%, and 1 kg contained 0.23 fodder units and 31 g of digestible protein. Recently, it has been used more often as an organic fertilizer.
Pea plants are capable of nitrogen fixation: 1 ha of crops can remain up to 50-70 kg/ha. In rotation it is a good preceding crop for many crops. Due to the short vegetation period peas are well suited as an intermediate, vapor-intensive crop or for green fertilizer.
History of the crop
The wild progenitor of the pea is unknown, and opinions differ as to its possible origin. According to one view, central Asia, Abyssinia, and the Mediterranean basin are the primary centers and the Middle East is the secondary center. According to another view, the Mediterranean Sea basin is the primary center and the Middle East and the central Ethiopian plateau are the secondary centers. In the domestic theory, with reference to archaeological excavations, the homeland of sown peas is assumed to be the regions of Western Asia, i.e. Transcaucasia, northwest of Iran, mountainous Turkmenistan, Afghanistan and India, where small-seeded forms were grown. Large-seeded forms of peas, according to N.I. Vavilov, originate from the second center – the Eastern Mediterranean.
Peas are one of the oldest crops, even in the Stone Age 20,000 years ago they were used as food. The charred remains of pea seeds have been identified as being 7,000 to 9,000 years old.
According to archaeological excavations in Chernovtsy and Ivano-Frankovsk regions in Eastern Europe peas appeared probably in the III-II millennium BC. In Russia it is known from VI-VIII centuries.
By the Bronze Age (c. 3000 BC) it was used by the inhabitants of Central Europe, and primitive seeds have been found in areas inhabited by the Swiss lake people and in the caves of central Hungary. Peas were known to the Greeks and Romans, and these early species are first mentioned in England after the Norman Conquest (1066 AD).
Fresh peas were popular in the 19th century, when English breeders developed improved varieties, and in some parts of the world these varieties are called English peas.
Dry peas were also widely cultivated in 19th century Europe and the United States. Dry peas were also widely grown in smaller subsistence systems, but the most significant development of varieties came from the introduction of mechanical harvesting equipment, first (for dry peas) threshing machines and then combine harvesters, and for fresh peas, the harvesting machine known as the viner.
Cultivation areas and yields
Dried peas are most commonly grown on a large industrial scale in Europe, especially in France. Most are grown for the animal feed market. In comparison, production is smaller in the UK, but peas are grown for high quality human consumption and for export. The U.S. and Canada together are very large producers of dried peas, again mainly for animal feed, although a significant amount is used as food ingredients.
The largest producing country is Canada, with 2.5 million tons; China and the Russian Federation produce on average about 1 million tons, and France, India, and the United States each produce 0.5 million tons of dried peas per year.
In 1980 peas were cultivated on about 15 million hectares in the world with an average yield of 1.4 t/ha; by the end of the twentieth century they accounted for 7 million hectares or 4.2% of the total legume crop area. The gross grain yield is 12 million tons or 5.3% of the total grain legume production at an average yield of 1.8 t/ha.
Production of dried field peas is more than three times that of fresh peas. The leading dry pea production countries in 1994 were France, Russia, Ukraine, China, and Canada with approximately 3.4 million, 2.5 million, 2.5 million, 1.5 million, and 1.4 million tons, respectively. India’s production of 579,000 tons was also significant. Production from all of the former Soviet Union republics accounted for nearly 36% of global production of 14.5 million tons of dried peas in 1994, and France separately supplied about 23% of the total. These production volumes do not necessarily mean domestic consumption, since part of the production goes for export and for livestock feed.
The area under crops in the USSR was 5 million hectares in 1983. In Russia at the beginning of the 2000s, the area was 0.5 million hectares or 42% of the area of leguminous crops. The gross output is 1.2 mln tons or 66.7% of the grain yield of this group, with the average yield of 1.2-1.4 t/ha.
Peas are cold-resistant, early maturing, undemanding to the soil. In Russia peas are grown in most regions of the world, up to 65° N. latitude. (early maturing varieties grow as early as 68° N), but the main crops are concentrated in the Central Black Earth zone and the central part of the Non-Black Earth zone, in Tatarstan, Chuvashia, Mordovia, Bashkiria, and in the northern Caucasus. In the former USSR, it is also cultivated in the forest-steppe and right-bank Ukraine, Belarus and the Baltics.
Thanks to the development of early maturing and drought-resistant varieties, pea crops have spread in Western and Eastern Siberia, the Urals, and Kazakhstan. However, because of its poor drought tolerance and susceptibility to pea bruchus, it is rarely grown in the southern and southeastern regions. In Central Asia and Transcaucasia, wintering varieties of peas are sown in autumn.
Among leguminous crops, peas are one of the leading crops by yield. High yields were obtained at the Novoanninskiy variety plot in Volgograd Region and amounted to 6.43 t/ha. Under optimal growing conditions, peas can produce high yields on large areas. For example, in 1982. in Korenevsky district of Krasnodar Krai (collective farm “Pobeda”) the seed yield was 4.52 t/ha (sowing area 138 ha); in Alexandrovsky district of Stavropol Krai (collective farm “Komsomolets”) – 3.24 t/ha (700 ha); in Yalchinsky district of Chuvashia (collective farm “Pobeda”) – 2.92 t/ha (640 ha); in Ruzaevsky district of Kokchetav region (in the state farm “Valikhanovsky”, Kazakhstan) – 3.79 t/ha (630 ha).
Of the two major commercial pea species, the peas grown in most temperate agricultural areas of the world are those intended to be harvested fresh, frozen, or canned (known as vining peas or green peas).
The main factors limiting production are weather conditions, soil type, and availability of processing plants.
Europe with nearly 38% and North America with 28% of total world production are by far the leading producers of green peas. The United States produces about 25%; most of this production goes into processing.
The largest European producers of frozen peas are the United Kingdom at 155,000 tons, France at 190,000 tons, Belgium at 69,000 tons, and Spain at 62,000 tons per year. The U.S. is also a major producer, producing about 260,000 tons per year.
Chemical composition and nutritional value
Typical nutritional value of frozen green peas (data from British Growers Association and U.S. Department of Agriculture Standard Reference SR27), per 100 g of cooked product, without added salt:
- caloric value – 327 kJ;
- protein – 5.2 g;
- total carbohydrates – 14.3 g (4.7 g as sugars);
- dietary fiber – 5,5 g;
- sodium – 72 mg;
- vitamin C – 9.9 mg.
Nutritional value of dried peas (USDA Standard Reference SR21 data), per 100 g of product in boiled form:
- caloric value – 494 kJ;
- protein – 8.3 g;
- total carbohydrates – 21.1 g (2.9 g as sugars);
- dietary fiber – 8.3 g;
- sodium – 2,0 mg;
- iron – 1.3 mg;
- folate – 65 mg.
As ingredients or components for animal and fish feeds, peas are well-known sources of protein and energy, although low in some sulfur amino acids. Peas have a total protein content between soybean meal and grains. As with all raw materials, total crude protein (calculated as nitrogen x 6.25) varies between crops, growing conditions, and year; however, on average, protein values remain standard, and feed manufacturers use established values for peas of about 21%. In studies of commonly grown pea varieties, very few differences in protein levels were found between pea varieties (Bastianelli et al., 1995) or pea and bean varieties (Houdijk et al., 2013).
Nutritional value of forage (combined) peas:
- dry matter – 86%;
- oil – 1.0%;
- starch – 44.6%;
- cellulose – 5.2%;
- minerals – 3.0%;
- protein – 20,7%;
- amino acids:
- lysine, 1.51%;
- methionine – 0.91%;
- cysteine – 0.48%;
- threonine – 0.79%;
- thiamine – 0,20%;
- valine, 0.97%.
The nutritional value of soybeans (Hy-Pro) is given for comparison:
- dry matter, 86%;
- oil – 1.9%;
- cellulose, 6.0%;
- minerals – 6.4%;
- protein – 54.3%;
- amino acids:
- lysine, 2.92%;
- methionine – 0.65%;
- cysteine – 1.35%;
- threonine – 1.86%;
- thiamine – 0.65%;
- valine, 2.27%.
The composition of amino acids in peas depends on the total protein content and the ratio of various proteins. Lysine levels are intermediate between soybean meal and cereals, which is essential nutrition for non-ruminants, but peas do not contain enough amino acids sulfur or tryptophan.
Starch is the most abundant component of peas, about 500 g/kg, and is a valuable source of energy for livestock. The average oil content is low (less than 2%). The composition of this oil is similar to that of grain crops, mainly triglycerides, polyunsaturated in nature with a predominance of linoleic acid.
In Europe, the most commonly grown white-flowered peas contain only low levels of trypsin inhibitors, although varieties containing 7 mg to 10 mg are sometimes found, which is not considered too high for animal feed.
Many studies have investigated the value of peas and beans as a protein source for livestock, and it is recognized that peas and beans can be used in nutritionally balanced diets for many ruminants and non-ruminants and can completely replace soybean meal without detrimental effects on livestock performance. In addition, the increasing use of de-fed beans in aquaculture for salmon farming in Norway and Scotland will gradually replace the need for fishmeal in diets.
Disposal of straw after pea consolidation may be a problem in some cases, but increasingly pea straw is now being used as feed for sheep and cattle. With a higher protein content and less fiber, pea straw has a higher nutritional value than cereal straw. In terms of quality, it is intermediate between cereal straw and good grass hay (Mould et al., 2001; Ellwood, 2004).
The nutritive value of pea haulm for animal feed:
- dry matter – 88.8%;
- crude protein – 8.2%;
- crude fiber – 36.3%;
- lignin – 7.2%;
- ash – 9,8%;
- gross energy – 18 MJ/kg.
Domestication resulted in a division into seed, fodder, and vegetable species; edible forms of peas with pods are thought to be recent.
Modern varieties of garden peas are the opposite of the primitive forms, which had a coarse, tough and slightly bitter seed shell. Modern varieties also differ from the wild species in their large seeds and short, compact growth. Although they are grown less frequently, some tall, small-seeded varieties are still cultivated.
The edible species of chick peas are commonly known as snow pea, sugar pea, or Chinese pea; they have been given botanical status as P. sativum saccharatum. Another edible pod species, designated as P. sativum N&Y. macrocarpon, is known as sugarcrisp peas. The main characteristics of each species are a juicy pod wall and very slow seed development. Sugar snap peas are a relatively new species and have fleshy and juicy edible pods that are very similar to bean pods, unlike the flat, broad and thin-walled sugar snap peas. The pods of each type usually remain relatively juicy, even when some seed enlargement occurs, because the fibrous parchment layer of the inner wall of the fruit is not formed.
Field or dried peas (pelushka) are grown to produce mature dried seeds and are generally considered an agronomic field crop. The previous classification of field peas as Pisum arvense does not fit, and this crop is not different from P. sativum.
Peas (Pisum L.) are represented by several species, the main of which is the cultivated pea (P. sativum L.) – polymorphic, the most common species. It includes subspecies:
- pea common sowing (Pisum sativum) – with white flowers, light single-colored spherical (in some forms wrinkled) seeds of white, pink, green, yellow color with light scars, weight of 1000 pieces 150-340 g;
- field peas, or pelushka, (Pisum arvense) – with red-purple flowers and dark, usually mottled angular seeds with small indentations and brown or black welt; stipules have red anthocyanin (purple) spots; peels are gray-green, black or brown.
Peas are an herbaceous annual with a relatively short growing season.
Pea sowing is subdivided into a peeling variety and a sugar pea variety. Pea peeling varieties have a tough parchment layer in the walls of the bean, and are grown mainly for grain. Sugar varieties do not have a parchment layer; beans in their green state can be used for food purposes and are grown mainly for vegetables.
Field peas (pelushka) have fodder value, less often as a green fertilizer, and are grown for seed, hay, and green fodder. It may be cultivated on poor sandy and peaty soils, is very early maturing, and its seed production is stable even in the north, for example, in Vologda and the Komi Republic.
The root system is taprooted, penetrates to a depth of 80-150 cm, with numerous lateral roots, located mainly in the arable horizon, is not very strongly developed.
The stem is rounded, tetrahedral, hollow inside except for the base, easily lodged. Stem length depends on variety and growing conditions, varying from 25 cm to 250-300 cm, usually 80-100 cm. Usually the stems are not self-bearing, and branching is limited.
The growth pattern varies from indeterminant, vining and climbing types to determinant bush or dwarf forms.
The stem is simple within the fruiting part, on which flowers and beans are located more or less evenly The stem of bent varieties is flatly thickened in the upper part, the nodes are close, flowers and beans are crowded; the lower part of the stem, from the root neck to the first flower or bean, has the usual structure, easily lodging.
The number of unproductive nodes of the main stem up to the first flower is a varietal trait and characterizes the duration of the growing season. The number of unproductive nodes begins at the first underdeveloped scale-like leaf above the root neck.
The nodes bearing a flower or a bean are called productive or fertile nodes. The number of fertile nodes is largely determined by the growing conditions.
The leaves are alternate. Leaf types range from varieties with extensive leaflets to varieties with almost all leaflets turned into tendrils; the latter forms are known as leafless.
Leaves are compound (semi-pinnate), usually consisting of a petiole, 2-3 pairs of leaflets followed by an unpaired number of tendrils (3-5, sometimes 7) and leaflets. Pea leaflets are larger than the leaflets, semi-serrate, about 1/3 with a serrated edge. Spleaves of pea have purple spot.
The whiskers are modified leaflets with which the pea plant clings to any support. As a result, the lodging pea stalk is able to grow upright.
Rarely, pea leaves may have no tendrils, ending in an unpaired leaflet. Such a leaf is called an unpaired leaf, sometimes an acacia leaf. Also, a pea leaf may be leafless or mustachy. In this case, the leaf consists of a petiole, turning into a many-branched main vein, ending with tendrils, leaves are absent. In very rare cases the main leaf vein extensively branched ends in three to five very small leaflets without tendrils. It is botanically correct to call such a leaf type multiply unpaired.
Leaflets of pea plants vary in shape: oblong, ovate, obovate, transitional from ovate to broadly ovate, broadly ovate, inversely broadly ovate and rounded. Leaflet shape and color is commonly established at the level of the first to second fruiting node. The definition of the leaflet shape includes the nature of the leaflet edge: full-edged, serrated, serrated, serrated-toothed, interrupted-toothed, interrupted-toothed, crenulated.
Leaflet color is a varietal trait, although it is subject to variability depending on the age of the plant and leaf, soil fertility, and fertilizers applied. The coloration is yellowish-green, light green, green, dark green, and grayish-green.
Leaf stalks and leaves usually have a silvery grayish mosaic pattern made up of spots of varying size, which are more pronounced on leaf stalks. The size of the spots and the density of the mosaic are a varietal trait, and their absence or very dense mosaic are found in quite rare forms of peas.
The pea plant, except for rare forms, is covered with a waxy coating (cuticular layer). It is also rare to have a very strong waxy patina.
The genetic control of many pea leaf traits is well defined. The homozygous recessive gene af (afila) results in plants without leaves and with a large number of tendrils. The gene tl leads to plants with additional leaves and no tendrils, and the gene st leads to reduced strap-like buds and small leaves. This set of genes and several others can be genetically manipulated to produce a wide variety of leaf shapes. Leafy af and afst forms have improved stability because the tendrils are intertwined and provide mutual support. Leafless varieties are also less affected by insects and diseases because of improved drying conditions in the leaf canopy. However, modified forms with fewer or no leaves are generally less productive for fresh pea production except for very high plant density, which compensates for the low leaf area index. Aphelial varieties produce less light-colored fruit than leafy varieties because of greater light penetration under the canopy.
Peduncles emerge from the axils of bracts and bear 1-3 flowers.
The inflorescence is a brush; in fascira forms of peas, the inflorescence is a false umbrella.
The flower is oviparous, moth-like, and consists of five petals: a sail, two wings, and a boat, formed by the fusion of two petals. At the junction, the boat-like petals usually form an outgrowth called a keel. The sail is inversely broadly ovate or narrowed, cut at the bottom. Flower coloration in varieties of grain or vegetable peas is usually white, but may be pink, purple, or mixed.
The flowers of field peas are usually purple.
Self-pollination usually occurs before the flowers are fully open, so the frequency of cross-pollination is very low.
The fruit is a multiseeded pod, usually with 3-10 seeds, consisting of two leaves, each of which develops from a single carpel (fruiting leaf). The number of seeds in the pod varies greatly from variety to variety, although usually 5-6. Two to five fruiting nodes are formed on the stem. Seed ripening begins with the beans of the lower nodes.
Modern varieties usually have at least two beans (pods) per node, and some varieties have several beans on each fruiting node. Agronomic practices and the environment affect bean establishment and bean number, as high plant density reduces the number of beans per unit area.
The structure of the bean flaps is used to distinguish between husked, sugar and semi-sugar forms of peas. Inside the pea pods of husked forms, there is a firm parchment layer consisting of 2-3 layers of woody (lignified) and 1-2 rows of non-trunken cells. In sugar forms, bean flaps are devoid of the parchment layer; in semisugar forms, the parchment layer is poorly developed or partially developed in separate sections. The presence of the parchment layer causes the beans to crack easily when drying out, while its absence causes poor threshing ability of the seeds.
When the beans mature and dry out, they have a natural tendency to open up and release seeds. Modern breeding attempts to limit this feature to reduce seed loss before harvest.
The bean can be shaped:
- straight, with a blunt, pointed or retracted apex;
- slightly curved, with a blunt or pointed apex;
- curved, with a blunt or pointed apex;
- sickle-shaped – with a pointed tip;
- concave with a blunt tip.
Sugar snap pea varieties also have distinct (the width of bean flaps is slightly greater than the diameter of the seed and, therefore, the flaps fit tightly around the seed during ripening) and sword-shaped (the width of bean flaps is much greater than the diameter of the seed) varieties.
The color of the immature bean is a varietal trait and is light green, green, and dark green. The color of the mature bean is light green or light yellow.
Bean size is divided into: small – 3-4.5 cm long, medium – 4.5-6.0, large – 6-10 and very large – 10-15 cm.
Seeds are attached alternately to the sides of the fused carpels. Bean size, like seed number, is a stable characteristic of a variety, but bean size and seed number vary between varieties.
The number of seeds in the pod (pod fulfillment) varies: small – 3-4 pcs., medium – 5-6 and large – 7-12. The arrangement of seeds in the pod may be different: almost not touching each other; touching, but not compressing each other; very compressed – as if sticking together 2-6 seeds together (caterpillar arrangement).
A pea seed is a berry (zap. Rubatzky) consisting of two large seedpods surrounding the embryo and closed by the seed coat (testis). Pea seeds are characterized by hypogeal germination, and the seedpods usually do not shed the seed coat.
The surface of vegetable pea seeds is wrinkled or intermittently wrinkled. Seed coloring in white-flowered forms depends on the color of seed buds peeping through the translucent, almost colorless seed coat. In rare cases, the seed skin of pea plants has some greenish or yellowish spots. The seed pods come in blue-green, pale green, yellow, orange-yellow, yellow-green (bicolor, yellow areas interspersed with green), green, dark green, olive, brown or reddish brown, with speckled or marbled spots.
Vegetable peas are characterized by mostly green, bluish-green seeds, sometimes yellow-green, yellow, and very rarely olive seeds. The green seeds of some varieties fade easily, turning white or yellow when ripening and drying in the light. In yellow-seeded varieties, if prematurely stopped growing and ripening from heat, color formation is disrupted, with the seeds becoming green.
Mature smooth seeds are characterized by rapid and higher starch accumulation and lower sugar content than wrinkled seeds. The floury texture of smooth pea seeds is due to the high starch content. Varieties with smooth seeds, especially field peas, tolerate cold better than varieties with wrinkled seeds.
Varieties with wrinkled seeds are most commonly processed through freezing while smooth-seeded varieties are canned. However, varieties with wrinkled seeds are also increasingly canned. In the past, processors preferred to use dark-colored peas for freezing and light-colored peas for canning; this distinction is less common nowadays. Small peas are preferred for processing. In general, small peas are peas 3.5-5 mm in diameter, medium peas 5-7 mm, and large peas over 7 mm. Another indicator is the weight of seeds per 1,000 seeds. The weight of a thousand seeds varies from 90 g to 400 g. A thousand fresh peas weighing less than 150 g are considered small, 150-250 g medium, and over 250 g large. There is an opinion that small peas (petite pois) are sweeter and more tender than large peas. Within the same variety, large peas are usually less tender than small peas, but between varieties, size is not an indicator of tenderness.
Seed germination begins shortly after imbibition begins. Seed cotyledons represent embryonic respiratory tissue, since there is no separate organ in the seed to store nutrients. After imbibition is complete, the starch contained in the embryo cells begins to be converted into sucrose, which then becomes available as an energy source for the embryo axis. The embryonic axis then elongates, ruptures the testis, and becomes visible as a developing radicle or root. Later, the apical part of the embryo develops as a plumula, rises upward, and appears above the soil surface. The cotyledons remain underground (hypogeal germination), where they continue to supply nutrients to the developing germ until the plumula grows and forms a primary set of leaves.
The pea plant does not support itself particularly efficiently because the stems are inherently weak. Ancient relatives of modern pea varieties were mostly prostrate, with extensive stem growth. However, the ability of the pea plant to stand more upright is a major concern for breeders of modern varieties. Usually there is one main stem from each plant, but the number of pods at the node and on the plant varies from variety to variety. In some cases, there may be one or more axillary stems, but the leaves and flowers have the same structure. As the stem develops, a leaf forms from the axillary meristem, called a node. Leaves develop at each node, starting at about the sixth node and up. As the stem lengthens, more and more leaves develop on it, and the space between the nodes is called the internode. At each node there are large stems. Each section of the stem consisting of an internode, a leaf, and a meristem is called a phytomer (Nougarede and Rondet, 1973). Each compound leaf consists of a petiole with four to six pairs of pinnate leaflets and ends in three tendrils. The pea leaf has a cuticle of wax on the upper surface, and the color of the leaf can vary from yellow-green to dark blue-green, depending on the variety. Recently, the general morphology of the plant has been altered to improve agricultural adaptation, and many modern varieties derived from breeding mutants have different stem, leaf, and tendril characteristics. Varieties have been bred in which the stem has been greatly reduced and all the leaves have been transformed into tendrils. These “aphila” varieties are called leafless peas, but the productivity of these varieties is generally inferior to traditional peas with leaves. Further breeding work has made it possible to develop varieties with normal-sized stems that retain the characteristics of aphylla. These “semi leafless” aphylla types are now represented by varieties of both dry peas and creeping peas. A number of varieties used commercially have normal or more pinnate leaflets.
Peas have a thin tap root that can penetrate to a depth of 80 cm and less well developed lateral roots. The roots grow in cracks in the soil and have a weak ability to penetrate compacted layers.
As a legume, peas have nodules on their roots containing nitrogen-fixing bacteria (Rhizobium leguminosarum) that provide the plant with sufficient nitrogen throughout its life. The nodules vary with age and growth conditions. They are irregularly shaped, about 2.0-5.0 mm in diameter, and usually densely arranged along the tap root. They are white at first, but as the plant matures, they discolor and fade. When young, healthy, and active, they are usually bright pink, but when opened, they show a red coloration caused by the pigment legaemoglobin. The bacteria benefit by having a stable environment and a supply of carbohydrates provided by the plant.
Thus, peas are able to use enough nitrogen for their growth and also provide a residual level of nitrogen in the soil after harvest, which then becomes available for the next crop. In temperate climates, these are likely to be cereals, and the residual nitrogen significantly reduces the need to apply the full rate of nitrogen fertilizer. This favors rotations that include legume crops, thereby reducing the total nitrogen input to the system.
The onset of flowering is thought to depend on photoperiod and temperature, but the number of nodes and the inherent earliness of the plant also determine at which node the first flowers appear. In modern pea varieties, flowering begins at a predetermined node, thereby providing a known ripening time to aid and plan the harvesting operation. The number of flower or reproductive nodes varies by genotype, but most peas sown in spring have six to eight flower nodes that produce pods. In more indeterminant genotypes, the influence of environmental conditions may be more pronounced as the stem continues to elongate, producing more reproductive nodes. Plant density also affects stem length, as stem length and number of reproductive nodes can double at very low plant densities.
There are a number of genotypes that exhibit different flower coloration. Flowers that are self-pollinated can be white, pink, purple, or bicolor, depending on the variety. White-flowered peas usually produce green or yellow seeds, while colored peas produce brown or mottled seeds. Usually only white-flowered peas are grown for freezing or canning, although some markets exist for colored varieties, both for human consumption and for specialized pet food.
Flower development occurs linearly along the stem as daytime temperatures accumulate, and this occurs continuously under a wide range of environmental conditions; however, during periods of slower growth, such as due to low temperatures, the rate of development may slow down. The onset of flowering is also influenced by the photoperiod: the longer the length of day that plants experience after emergence, the earlier flower set (Berry and Aitken, 1979), and this may also depend on the cultivar (Lejeune-Henault et al., 1999).
Pea flowers contain anthers and stigmas, and the pollen matures before the flower opens. Inside the flower is a stamen consisting of a filament and anthers, and a pistil containing a stigma (stigma) and ovary. As the flower develops, the anthers extend to the stigma and pollen is carried inside the flower, and self-pollination occurs before the petals are fully opened. As the fertilized ovary expands, the walls lengthen and the pod becomes open. The remnants of the flower petals remain at the tip of the pod until they dry out and fall off.
Heat demand is low, cold-resistant.
Germination can occur in a wide range of soil temperatures, starting from 1-2°C. Biological minimum is +4 … +5 °C. The optimum temperature for emergence of seedlings is 6-12°C (according to other data, 20°C Rubatzky). Above 25°C germination percentage decreases.
Sprouts survive frosts as low as -4 … -8 °C. Inflorescences and pods are more susceptible to frost damage than leaves and stems; young plants are more resistant to low temperatures.
Generative organs are formed and flowering occurs at average daily air temperatures of +6 … +7°C.
Heat demand varies in ontogenesis and is one of the main characteristics of pea agroecological groups.
The optimum average temperature for vegetative growth is 13 to 18°C.
High temperatures during flowering and grain ripening, as well as dry winds, have a negative effect on yields. Above 29°C, growth is virtually halted.
Cultivated in the south are winter and winter hardy forms capable of surviving mild winters.
Forage pea varieties are more frost-resistant.
Frosts of -2 … -3 °C during the fruiting period may cause beans to freeze.
The correlation between the number of nodes to the first flower, growing temperatures, and time to harvest maturity is very high; it is useful for planning sowing and harvest periods. Heat units (degree-days) are also widely used to predict harvest timing for peas destined for processing. For peas, a base temperature of 4°C (where degree-days begin) with an upper limit of 29°C is usually the range for calculating accumulated heat units. Plant growth is negligible at temperatures below or above this range and therefore has little effect on accumulated heat units.
Based on the results of growth and performance tests, varieties are determined by their heat unit requirements. Early-blooming varieties require only 1,000 heat units to reach crop maturity, while late-blooming varieties may require more than 1,600. Generally, early-blooming varieties are day-neutral; late-blooming varieties are accelerated by the long day. Moderately high temperatures also shorten the time to bloom, but temperatures above 30°C can cause flower or ovary to miscarry. Moderate diurnal fluctuations in temperature usually improve plant growth.
Peas are a relatively moisture-loving crop. They are sensitive to moisture prior to flowering. According to other data, peas have relatively low moisture requirements, and depending on seasonal conditions, 75-150 mm of water is often sufficient; many pea-producing regions rely entirely on rainfall.
Seeds require 110-115% water of seed weight (100-110% of seed volume) to swell and germinate. Thanks to the rapid growth of the root system, which reaches a depth of 30 cm two weeks after the appearance of seedlings, the moisture accumulated in the soil during the winter period, provides normal plant growth in the first third of the growing season.
It is a bit more drought-resistant than fodder beans, vetch, lupine, but less so than chickpea, mayola and lentil.
Transpiration coefficient is 400-600 (400-450). Water requirements are reduced by 10% with good phosphorus-potassium nutrition.
The main amount of moisture is spent on transpiration to regulate the temperature of plants, that moisture supply is especially important during hot weather with temperatures above 28-30 ° C.
The most important critical periods of the growing season in relation to moisture are the budding period (5-7 days before flowering) and the beginning of bean formation. If there is a lack of moisture at this time, the crop decreases as a result of flower shedding, the formation of small grains, through the grains. Prolonged lack of moisture adversely affects plant growth and development, and the quality of green peas decreases sharply.
Peas are sensitive to excess moisture, so waterlogging should be avoided, especially during the flowering stage. The most moisture-sensitive periods are just before flowering and also during pod growth. Excessive and prolonged moisture leads to lower yields and even plant death. Leafless pea varieties have a higher tolerance to soil moisture than regular leafy forms. Rain or watering during flowering can increase disease incidence. Excess moisture in heavy soils, especially at low temperatures, leads to strong vegetative mass development, rotting of leaves and beans, root system die-off, development of fungal diseases, and an extended growing season.
Peas are light-loving plants with long daylight hours. For this reason, the growth and development of peas in northern areas is a little faster.
Early maturing varieties are less responsive to day length.
Pea plants require intense light. Shading reduces photosynthesis, causing loss of flowers and ovaries, especially in lodged plants below. Therefore, dense sowing or heavy overgrowth with weeds dramatically reduces yields.
Peas can be grown on many types of soil, from light sandy loam to heavy clay.
Peas are demanding to soil fertility and moisture, as they have time to form a large ground mass with a relatively weak root system.
Optimal soils are chernozems of medium cohesion, well moistened and limestoned, gray forest, cultivated sod-podzolic, chestnut, sandy loam, light and medium loamy soils, covered with 0.8-1.0 depth moraine loam.
Dense, heavy, light sandy, acidic, solonetzic, boggy soils with groundwater occurrence less than 60-80 cm are not suitable.
Optimal agrochemical parameters of soil: pH 5.6-6.0 (by other recommendations, pH 6-8; also 6.0-7.5); humus content of at least 2%, labile phosphorus and exchangeable potassium of at least 150-170 mg/kg soil. Peas do not grow well in sour soils. If soil pH is high, manganese deficiency is sometimes observed.
Poor drainage and soil compaction greatly reduce productivity and increase susceptibility to root diseases.
Peas are an annual early-ripening spring crop. There are also wintering forms cultivated in the south.
The growing season varies from 60 to 140 days depending on cultivar and growing conditions.
Plants are self-pollinated, but in hot and dry years, open flowering is possible and some cross-pollination occurs.
Peas grow slowly during their early stages of development so controlling weeds is very important.
Root tubers are formed 7 to 10 days after sprouting (from the phase of 5 to 8 leaves).
Maximum growth is observed from the beginning of flowering to the beginning of ripening.
Flowering lasts 10 to 30 days, and 6 to 8 days in drought conditions. Movement of plastic substances from leaves and stems to seeds is completed in the phase of proteinous ripeness, at which moisture content is 35-40% at the beginning of the phase, and 20-25% at the end of the phase.
Early-ripening varieties produce flowers after five or six nodes have formed. Some late varieties flower after 15 or more nodes have been formed. The number of non-fruiting nodes is a fairly constant characteristic of the variety. Flowers are produced sequentially, starting with the lowest flower-bearing node and progressing as the nodes develop.
Large-scale commercial production of green peas for freezing and canning requires more careful planning and management at all stages of growing and harvesting. Given the capital investment, the limited capacity of harvesting equipment and processing equipment, and the fact that peas are of optimal quality for a very short period, a full range of different varieties, soils and conditions must be used to maximize income and a planned seeding program that includes the full range of available ripeness.
Fields for sowing green peas are selected according to soil type and aspect as they affect the rate of development and maturity of the crop. In the UK and temperate regions, early sowing is preferred, although in the more southern parts of Europe sowing is done in the fall to avoid the high temperatures of the following season and the subsequent effect on moisture availability and quality. On soils with medium to heavy topography, there is usually enough moisture in the sowing layer for the crop until flowering. Until then, precipitation has little or no effect on the crop unless it is excessive and has a negative effect on soil structure.
In Eastern and Northern Europe, the United States and Australasia, combination peas are almost always grown as a spring crop, although in regions with warmer and drier climates special winter-hardy varieties are planted in the fall. Early sowing can make a significant contribution to high yields, but cold, wet soil conditions in early spring are detrimental, so sowing should be done later when soil conditions improve. The quality of combination peas, especially those grown for human consumption, is usually better than peas sown later because weather conditions are usually better at harvest time and therefore there is less seed staining caused by secondary saprophytic fungi that can colonize the pods.
Main article: Leguminous crops of the crop rotation
When placing crops in the crop rotation, the relief and exposure of slopes are taken into account. In arid conditions, it is better to place peas in low places to reduce the impact of moisture deficit. In northern areas, on the contrary, the crops are placed on the elevated terrain for better and faster warming.
Preferably, peas should be sown after well fertilized preceding crops such as cereals (spring and winter) and row crops (sugar beets, potatoes, corn, flax (according to Autko, flax is considered a bad preceding crop). Among vegetable crops, root crops, cucumber, cruciferous crops, and early potatoes are considered the best predecessors.
Peas are bad for permanent crops and repeated sowing due to their susceptibility to root rots and “pea fatigue”. Return it to its original place no earlier than 4-6 years later.
The longer the crop rotation, the less likely the accumulation of soil-borne pests and diseases. Research in the 1970s showed that peas should not be grown in the field more often than every 5 years (Biddle, 1983). Since then, however, it has become more common, especially in Great Britain and Europe, to increase crop rotations to 6 or even 7 years. Diseases caused by a complex of soil fungi have been shown to have a serious effect on yield. This complex usually includes Fusarium solani, Didymella pinodella (syn. Phoma medicaginis var. pinodella) and Aphanomyces euteiches. All of them, once established in the soil, reduce their activity over a long period of time, and after a high level of their content is detected, pea crops may be unprofitable for 10 years or more. Similarly, pests such as the pea cyst nematode (Heterodera gottingiana) can persist as viable cysts in the soil for about 15 years.
Bad predecessors are sunflowers because of the fallen and legumes because of common pests and diseases, corn, cabbage and other crops that leave rough post-harvest residues, as well as after legumes, rapeseed.
In the rotation, the distance between the fields of legumes should be at least 500 m.
Peas are a good preceding crop for winter and spring grain crops, industrial crops.
For the formation of 1 ton of seeds and the corresponding amount of straw peas consume from the soil 45-60 kg of nitrogen, 17-20 kg of phosphorus, 35-40 kg of potassium, 25-30 kg of calcium.
Peas require only a minimum level of fertility. Green peas have a relatively short growing season, but they have a well-developed tap root and a limited number of lateral roots. Combined peas grow for a longer period and therefore may be deficient in some nutrients before maturity. It is less responsive to fertilizer nutrients than most crops. The main nutrients are potassium (K) and phosphorus (P), while nitrogen (N) comes through nitrogen fixation in the roots.
Potassium (K2O) is the most important of the basic elements; its deficiency has a detrimental effect on the crop because it promotes the enzymatic process involved in nitrogen fixation. The optimum level of potassium in the soil is about 200 mg/l, above which there is no further increase in yields. Severe deficiencies cause yellowing and burning around the edges of the leaves, and because potassium is associated with nitrogen fixation, nitrogen deficiencies can also occur, causing chlorosis and stunting in severe cases. Critical potassium concentrations in leaves are below 1.1-1.2% dry matter.
Phosphates (P2O5) have been thought to have little effect on pea growth and yield, but research continues to demonstrate the importance of P in pea nutrition. Phosphate is an essential nutrient for efficient pea root nodule formation, and it is thought that deficiency may reduce the number of root nodules and therefore affect nitrogen fixation efficiency. More recent research has shown that pea response to different soil P values is related to both yield and quality (Morris, 2013). Phosphate deficiency can reduce seedling viability, reduce yield, and lead to premature crop maturity, with an optimum Olsen P value of about 26-45 mg/kg.
Generally, peas are able to grow normally and produce maximum yield due to nitrogen fixation in the root nodules. The presence of nitrate (NO3) in the soil delays nodule formation and thus impairs the nitrogen-fixing activity of the plant. After nodule formation, in the presence of mineral nitrogen, root uptake can supplement or replace symbiotic fixation, and natural fixation ceases when the nitrogen content in the soil is high. Green peas can fix about 200 kg of nitrogen during the growing season, so there is enough nitrogen to sustain growth, with residual nitrogen remaining in the haulm and root system, which then becomes available for the next crop. The nitrogen-fixing bacterium Rhizobium leguminosarum, which is responsible for nodulation in peas, appears to be readily available in soils in Great Britain, Europe, and America. In the absence of a natural population of Rhizobium, seed or soil inoculation is practiced.
In addition to the primary benefit of fixing nitrogen from the atmosphere, the environmental impact is greatly reduced by reducing N2O emissions by legumes in general. N2O measurements taken in field experiments over several years in the UK have shown that N2O emissions are extremely low throughout the growing season, and in the case of green peas, even after they have been removed from the field (R. Sylvester-Bradley, 2014, unpublished). Similar results have been reported by researchers in Europe (Jeuffroy et al., 2013) and Canada.
Peas are responsive to the application of organic fertilizer to preceding crops. Mineral fertilizers are recommended to be applied directly under peas. In general, fertilize pea crops according to the level of essential nutrients in the soil. Fertiliser recommendations vary slightly from country to country.
Pea fertilizer requirements (kg/ha) (Defra, 2010, UK) depending on soil index (ADAS classification):
- index 0 (very low) – N 0 kg/ha, P2O5 100 kg/ha, K2O 100 kg/ha, MgO 100 kg/ha;
- index 1 (low) – N 0 kg/ha, P2O5 70 kg/ha, K2O 70 kg/ha, MgO 50 kg/ha;
- index 2 (medium) – N 0 kg/ha, P2O5 40 kg/ha, K2O 20-40 kg/ha, MgO 0 kg/ha;
- index >2 (high) – N 0 kg/ha, P2O5 0 kg/ha, K2O 0 kg/ha, MgO 0 kg/ha.
Of the calculated nitrogen requirement of peas, only 30% or less is usually applied; the rest is provided by nitrogen fixation. Under favorable conditions, when nitrogen fixation is most productive, the application of nitrogen fertilizers can be abandoned. Phosphorus, on the contrary, apply 1.5 times more of the calculated amount.
On cultivated soils after fertilized predecessors, ie, when the content of available forms of phosphorus and potassium over 15 mg per 100 g of soil, pea yields can be 3 t/ha of grain, even without fertilization.
With a low content of humus (less than 2%), phosphorus and potassium (less than 5-10 mg per 100 g of soil), make full mineral fertilizer. At the same time phosphorus and potassium are made taking into account the planned yield, nitrogen – taking into account the amount of absorbed atmospheric nitrogen.
Phosphorus-potassium fertilizer is made under the main treatment, depending on the security of soils in the amount of P40-80K50-130, nitrogen – under pre-sowing cultivation.
Peas is able to absorb phosphorus from sparingly soluble compounds, so as a phosphorus fertilizer for it can be used phosphate flour in an amount of 300-500 kg/ha.
Good results are obtained by row application of phosphate fertilizers during sowing in the amount of P10-20. In the Non-Black Soil Zone are more effective when applied to the rows of complex granular fertilizers; the rate of phosphorus is the same.
Peas also respond well to the application of microfertilizers, especially molybdenum and boron. The effectiveness of boron and molybdenum fertilizers is related to their influence on the activity of symbiotic microorganisms. These fertilizers are applied when the content of molybdenum and boron in the soil is below 0.3 mg/kg. For this purpose, molybdenum granulated superphosphate can be used, which is applied at sowing in the rows, or make pre-sowing treatment of seeds with microfertilizers. Boric fertilizer is effective on acidic sod-podzolic and gray forest soils after the introduction of lime fertilizers. It is advisable to treat the seeds with one micronutrient and apply the second one to the soil during sowing.
Peas are susceptible to deficiency of some micronutrients, especially manganese (Mn) and sulfur (S). Manganese deficiency occurs mainly in alkaline or organic soils and affects chlorophyll production, leading to intercropping chlorosis. In more mature crops, it also causes a condition known as “bog spotting,” in which the adaxial surface cells of cotyledons become necrotic, which reduces production quality and, in the case of mature crops, can reduce seed germination.
Manganese deficiency most often occurs in soils high in organic matter, it is also aided by high alkalinity, especially if soils have been overwatered; it also occurs more often when plants are under stress, such as during exceptionally dry seasons, very wet seasons and when soil is compacted. Correcting the deficiency and preventing bog spot is accomplished by repeated foliar treatments with manganese sulfate (Knott, 1996).
Sulfur deficiency can occur if peas are grown on very light, free-draining soils. Deficient crops are stunted and pale in color, which in turn adversely affects yields. Although the response to sulfur is not as great as for some crops in the husky family, such as oilseed rape (canola), a preplant application of 25-35 kg SO3/ha of elemental sulfur to the soil can be beneficial where sulfur levels are known to be low (PGRO, 2015).
Peas can grow normally on soils with pH below 5.8, but as long as the effects of manganese deficiency are eliminated.
Magnesium (Mg) deficiency is less common than manganese, especially in the UK. It occurs late in the growing season and is rarely severe enough to require remedial action. Magnesium is an essential element for chlorophyll production, and its deficiency causes intervegetative chlorosis, but unlike manganese deficiency, leaf margins remain green. It does not affect product quality, although there is some evidence that yields can be lost in exceptional circumstances. It is most common in light soils during wet seasons and can be caused in many soils by excessive application of potassium fertilizer.
On soils with a pH below 5.8, soil liming is necessary or the crop will be very stunted and pale, and root nodule formation will be suppressed or absent.
Soils with a pH of less than 5.6 should be limeed. Lime materials are applied under the preceding crop at full hydrolytic acidity. It is better to use dolomite flour as lime material.
It is well known that water deficiency is a major limiting factor for pea plants (Pumphrey et al., 1979). The most critical growth stages of pea plants occur when water deficits coincide with vegetative growth and up to the onset of flowering. Growth decreases and flower and pod size decreases. If water deficit occurs between the beginning of flowering and the last stage of pod development, the number of seeds laid in the pods decreases. Work has shown a positive effect of moderate water deficiency on yield when it occurs shortly before and after flowering (Salter, 1962; Stocker, 1973). Recent studies in the UK compared growth and yield of peas under drought stress with yields on soils maintained at field productivity levels and found that growth, seed yield and seed weight decreased dramatically in drought stressed peas (E. Uber and A.J. Biddle, 2009, unpublished). Therefore, response to irrigation is very important under drought conditions.
The timing of irrigation is critical and should be related to specific growth stages and soil moisture deficits. When most pea varieties are sown, the soil is usually close to field moisture capacity, and irrigation rarely increases yield if done before flowering, although it does increase haulm growth. Irrigation during vegetative growth can reduce pea yields, so it is not used unless the seed is very dry and adequate germination cannot otherwise occur, or when the crop is severely wilted.6
Peas are most responsive to irrigation when the first flowers open. The response to irrigation is thought to be strongest at this stage because the root system stops growing, making the plant more vulnerable to lack of water. The increase in yield with irrigation at this time is often very significant and can be as much as 50% due to more pods contributing to the yield and more peas per pod.
Irrigation during late flowering or petal fall does not increase yield, having no effect on either the weight or number of pods on the plant or the weight of peas in the pod. There is a slight resumption of root growth during this period, but no increase in haulm weight. Irrigation during petal drop can increase the occurrence of pod rot caused by Botrytis cinerea.
Irrigation during pod filling shows a significant increase in yield. The number of peas in the pod and the average weight of the peas increase.
The response of green peas to irrigation with 25 mm water/ha (Biddle et al., 1988; data summarized by the Institute of Horticultural Research, Welsbourne, UK) at the stage:
- vegetative growth resulted in an increase in aboveground weight of 60%, pea husked weight decreased by 5%;
- onset of flowering resulted in 30% increase in above-ground weight, weight of husked peas – 30%;
- setting of pods had no effect;
- pod emergence did not result in increase in weight of above-ground parts but increased weight of swollen peas by 20%;
- wetting and filling the pods led to an increase in the weight of the above-ground part by 30% and weight of swollen peas by 40%.
Irrigation during vegetative growth and early flowering was found to have little effect on ripening rate, but application of irrigation during pod swelling could delay the harvest date of peas for freezing or canning by about 2 days (HDC, 2012).
Work in the UK and elsewhere shows that the responses of green and combined (dry) peas are very similar and there is insufficient evidence to suggest that irrigation regimes should be different. A review of the physiological effects of water stress and response to water was presented by Lecoeur and Guilioni (2010).
The main tasks of tillage when growing peas are weed control, moisture retention, and leveling. Tillage, in general, is similar to tillage for early spring cereals.
The main treatment includes stubble flaking and plowing. After harvesting of forecrop it is necessary to stubble the soil to a depth of 8-10 cm. Not less than 20 days after husking in case of weeds regrowth it is necessary to plow with plough with skimmer to the depth of the arable horizon.
When clogged root weeds in 2 weeks after the first removal, ie when the foliage rosettes appear, do the second at a depth of 10-12 cm. After plowing with plows with skimmers.
To combat rhizomatous weeds perform discing in perpendicular directions with heavy disc harrows БДТ-7, 0 on 10-12 cm. After the emergence of wheatgrass sprouts, deep plowing is carried out.
In steppe regions, where there is a risk of wind erosion, treatment is carried out in layers: 1-2 stubble loosening at 8-10 cm, then deep loosening with plowshare to a depth of 22-25 cm.
In dry conditions in winter, snow and melt water retention is carried out.
The task of pre-sowing tillage is loosening the seed layer and leveling the surface of the field for subsequent uniform seeding. It includes early spring harrowing, surface leveling with heavy toothed harrows БЗТС-1,0 type, one cultivation on 8-10 cm in aggregate with middle harrows across or diagonally to the direction of the main plowing. At strong compaction of the soil is carried out plowing to a depth of 16-18 cm. When weeds appear, if necessary, carry out additional 1-3 cultivation to a depth of 8-10 cm.
At flat-cutting in autumn, in spring the moisture is closed using needle harrows БИГ-ЗА, for pre-sowing loosening special cultivators are used.
Partly because of size, seed is a significant expense in pea production. Quality seed is very important, especially if sown during the cold season.
A pea seed consists of a seed coat (test tube), two seedpods, and a germinal axis. The seed coat protects the seedpod and germinal axis. There is a rumen, known as the hilum, and a small micropile at the point of detachment from the seedstalk, which allows water to pass through in the early stages of imbibition. Pea seeds must have the ability to germinate and produce a strong, vigorous sprout, often in cool, moist conditions. It is the ability of the seed to exhibit such qualities that is characterized as good seed viability. Green peas often have to be sown very early in the spring, when it can take up to 6 weeks for seedlings to emerge, although at temperatures below 4 °C the germination process is almost non-existent. Seeds with low viability often become infected by soil fungi such as Pythium spp., resulting in no sprouting. Wrinkled green pea seeds are much more susceptible to this problem than round-seeded or marrow-shaped combination pea varieties.
Seed tests have been developed to determine the viability of green pea seeds, and the conductivity test is almost universally accepted as a valid test method (ISTA, 2006). The test is based on the fact that when soaked in water, carbohydrates and inorganic salts are released from the seeds. The more leachates lost, the lower the degree of seed viability and therefore the more likely the seed will not germinate under unfavorable conditions. The test measures the electrolyte content of the water after soaking peas for 24 hours. Interpretation of the test results gives an indication of seed performance under different conditions.
A set of pea seed viability assessments has been developed in the United Kingdom and is now widely used in seed production. Estimates are based on units of electrical conductivity (microsimens) measured in 250 ml of water after 50 pea seeds have been soaked for 24 h. The estimate is derived from the readings divided by the dry weight of the seeds and is expressed in microSiemens (μSm) per gram. The following are the viability scores and their interpretation for use (PGRO, 2014):
- >24.0 μSm/g, high viability, seeds are suitable for early sowing;
- 24.1-29.0 μSm/g, medium viability, some seed loss is possible under unfavorable conditions, but it can be used for later sowing without problems;
- 29.1-43.0 μS/mg, low viability, not suitable for early sowing and may fail in cold wet conditions;
- <43.1 μS/mg, very low viability, not suitable for sowing.
There are several factors that can cause low viability in peas, the most important of which is seed coat integrity. Microscopic cracking of the seed coat during harvesting or seed processing can lead to rapid germination of the seed, which damages the germ cells, releasing excessive amounts of salts and sugars. These damaged areas quickly become infected with soil fungal pathogens, especially Pythium spp. (Matthews, 1971). Commercially, seeds are often treated with a fungicide to protect them from such losses, but seeds with low viability are likely to fail despite such protection.
Seed-borne diseases, especially Ascochyta pisi and Mycosphaerella pinodes, can also negatively affect the emergence of pea seedlings in the field. Again, it is very important to use healthy seed, although some reduction in low levels of seed-borne fungal pathogens can be achieved by applying a systemic fungicide seed treatment.
Compared to wrinkled green pea seeds, combined (dry) pea seeds are usually round or dimpled and are not as susceptible to seed coat damage and are not as susceptible to preharvest mortality due to low seed viability. Although attempts have been made to identify seed lots with a propensity for low seed viability, the amount of filtrates lost during imbibition is not as great, and so the conductivity test has not been found to be relevant for combined pea seeds (Bladon and Biddle, 1991). Seeds are much more robust and can germinate successfully in a wide range of soil conditions. In practice, seed fungicide treatments are used commercially, but in many cases they are not necessary unless control of seed-borne Ascochyta spp.
To stimulate symbiotic nitrogen fixation processes, seed pretreatment with bacterial fertilizers, such as rhizotorfin.
Seeding sequence of green peas is driven by harvesting at the critical stage of maturity, determined within 6 weeks. Two factors in crop production make this possible: the use of early- and late-maturing varieties and controlled seeding from early spring through early summer. The beginning of the harvest season is usually determined by the processor because there are requirements for a production target for the season and optimal daily plant output. Such planning is also necessary for the large-scale chickpea market, where it is important to ensure sufficient labor at harvest.
This information is used by the individual grower or grower cooperative to plan production at each production site. The goal of the seeding program is to ensure that each crop consistently reaches the desired maturity, ensuring a smooth harvesting and processing run, with a product of consistent quality. Seeding intervals are based on the fact that temperature is the main factor affecting growth rate.
Accumulated heat units (AHU) can be defined as the difference between the base temperature for crop growth and the average of the daily maximum and minimum air temperatures. The base temperature is the temperature below which growth does not occur, for peas it is 4.4°C. In the U.K. and in areas with similar growing conditions, it is common to allow 11-12 AHU between each sowing period to allow for a 1-day harvesting difference between crops. Thus, in cool spring conditions, seeding can be done 2-3 weeks apart, while this interval is greatly reduced later in the season. Usually several varieties with different predicted maturity differences are used, so the program uses early varieties, varieties for the main crop and late varieties. These need to be integrated into the AHU program to provide harvest overlap equivalent to the varietal maturity difference (Biddle et al., 1988).
In some areas, a different approach is used, where successive crops of green peas are started as soon as the seed of the previous crop begins to germinate, i.e., when the radicle (stub) emerges from the seedpod and before the plumula emerges. In this method, it is also necessary to use varieties with different maturity dates.
For combined (dry) peas, there is a correlation between sowing date and yield, although soil conditions in early spring have a more important influence on sowing date than early sowing date. Early sowing has consistently contributed significantly to high yields, a fact proven in the 1950s when it was found that yields were reduced by 0.125 t/ha for each week of delay after the beginning of March or the first opportunity to plant in spring (Biddle et al., 1988); however, the exact sowing date must depend on soil and weather conditions.
Autumn sowing is practiced in some countries where it is necessary to establish a crop before high summer temperatures and when drought conditions are likely. In these cases, peas should be planted as late in the fall as possible, when germination and development of early sprouts is slowed to avoid wind damage to the sprouts that have just appeared. Once established, winter-hardy varieties of combination peas can withstand frost for long periods of cold weather.
In temperate climates, peas are usually planted in spring or late fall and early winter if there are no severe frosts. Peas can tolerate light frosts before flowering. In the tropics and subtropics, planting is done at high altitudes and during seasonal periods when temperatures are relatively cool.
For Russian conditions, early sowing dates of composite peas are preferable in all major cultivation zones with the exception of Western Siberia and northern Kazakhstan, where sowing is carried out in the second half of May because of the risk of June drought. As a rule, the optimal sowing dates coincide with the optimal dates for early spring cereal crops.
A 7-12-day delay in sowing peas leads to a 0.2-0.3 t/ha decrease in the Nonchernozem zone and a 0.3-0.5 t/ha decrease in the forest-steppe part of the Black Earth zone.
For sowing peas, the row method with a row spacing of 10-15 cm is used, less often narrow-row and cross-row. These methods reduce the lodging of crops, facilitate harvesting, reduce crop losses and obtain the highest yields.
For hand harvesting peas for the fresh market, peas are grown in rows spaced 75-90 cm apart.
For machine harvesting, seeds are planted in moist soil at a good density to an even depth of about 3-5 cm, with 3-5 cm in a row and 20-30 cm between rows. Usually the planting density is 80-90 plants per m2. At this planting density, tillering is kept to a minimum. In garden peas, the pods that develop on branching stems mature too late to contribute to the marketable yield, especially in machine harvesting; therefore, single-stemmed plants are preferred. Lodging reduces yields because it makes mechanized harvesting difficult. Due to the mutual support of intertwined plants, high density can reduce the tendency to lodging. Determinant and short-stemmed varieties are used to limit lodging. With the exception of home gardens or the production of edible chick peas, indeterminant varieties and trellises are rarely used.
The gap between tillage and sowing for more than 6 hours is not allowed.
For sowing peas, we use row crop planters, such as СПУ-6, АППМ-6, АКПМ-6, Ferabox-300, Lemken, Amazone, С3-3,6, СЗА-3,6, СЗП-3,6. These seeders allow to sow seeds deeper than narrow-row seeders, and are less likely to be clogged in wet soil. For better penetration into the soil of coulters following the tracks of tracks or wheels of the tractor, on the lower links of the rear linkage of the tractor mounted ripper, which consists of a beam and articulated sections of the cultivator КРН-4,2 with chisels. In addition, sowing or medium harrows are installed on the tractor’s hitch to level the soil after the rippers. The speed of the unit should not be more than 5-6 km / h.
In areas where flat tillage is used, СЗС-2,1 seeders are used.
As an alternative, direct seeding in minimally tilled stubble is used in some cases, although this is not currently widely practiced.
Seeding rates and seeding density
Seeding rates are extremely variable due to large differences in seed size between varieties, so the amount of seed sown can vary from 70 to more than 200 kg/ha. Total yields may increase with higher seeding densities, but seed costs may exceed the cost of yield gains.
Combined (dry) peas
The optimal seeding rate of pea seeds for small- and medium-seeded varieties in the arid zone, for example, in the Volga region, Kazakhstan, Kyrgyzstan, is 0.8-0.9 million/ha of germinated seeds. In the steppe areas, for example, in the Urals and Siberia – 1 million/ha. In the zone of sufficient moisture: the north-west of the European part, Central Black Earth and Non-Black Earth zone, the Volga-Vyatka region, Polesie and steppe forests of Ukraine, Belarus, the Baltic countries seeding rate is 1-1.3 million/ha of germinated seeds. In the case of harrowing crops rate is increased to 1.4 million/ha of germinating seeds.
Depending on the early maturity of varieties, we recommend seeding rates, mln.pcs./ha:
- early varieties – 1.3-1.4;
- medium early – 1.1-1.2;
- medium – 1.0
- late – 0.8-0.9.
For coarse-grained varieties, the seeding rate is 0.8-0.9 mln/ha of germinated seeds.
Weighted seeding rates are: for small-seeded varieties – 150-250 kg/ha, large-seeded – 240-300 kg/ha.
The response to increased plant density may be due to differences in growth characteristics of varieties rather than seed size; however, changes in plant spacing can affect growth habitus, and when populations decrease, pea stems are encouraged to develop side branches that can produce enough pods to make a positive contribution to yield, so the optimal density for combination peas is lower than that for green peas.
In the United Kingdom, the optimal planting density for large-seeded varieties is 65 plants/m2, whereas for round-seeded white or large-seeded blue varieties the optimal density is 70 plants/m2 (PGRO, 2015). Since most commercial combination peas are harvested mechanically, there is no need to plant wide rows unless intercropping techniques are used.
Green (vining) peas
Seeds make up the largest single cost of growing this crop, so much work has been done to maximize production efficiency by determining the optimum plant density for maximum profit. When plant density is increased, yields increase rapidly at first and then more slowly until a point is reached at which there is no further increase in yield. As the population increases beyond this point, yields gradually decline, and the value of any yield increase obtained by increasing plant density by increasing the seeding rate must be weighed against the cost of additional seed (King, 1967). The development and introduction of aphila varieties can also affect the optimum plant density required, but little experimental work has been done with sufficiently reliable results to determine specific optimum requirements for different varieties or types. In the UK and Europe, the most effective plant density is around 100 plants/m2 (PGRO, 2015). Although most pea varieties are planted in rows 10-15 cm apart, there is an advantage to using more precise plant spacing to ensure that individual plants grow evenly. Work carried out with semi-precision seeders in the United Kingdom showed that there was significant uniformity of maturity at harvest, probably due to the reduced tendency of the stems to branch, with more precise seed placement; in addition, precision seeding delayed the harvest date by about 2 days without affecting yields (Smith, 2007).
Large-scale commercial pea production is done with effective herbicides and without the row spacing restrictions that were previously determined by the need for intercropping. The advantages of tighter row spacing in providing a more uniform plant distribution across the field are increased competitiveness of peas against weeds and uniform crop maturity. However, the availability of older herbicides is becoming increasingly limited as awareness of the possible negative environmental effects of persistent active ingredients in soil-applied herbicides grows. Currently, a row spacing of about 20 cm or less is commonly used. As the availability of selective herbicides has become increasingly limited, the recent use of mechanical weed control with shallow-depth spring cultivators or self-guided inter-row cultivators could have a significant impact on production.
When growing chick peas, different growing systems can determine seeding methods, row spacing, plant spacing, and required densities. When growing pod peas without support, sowing can be done as for green peas, with narrow row spacing and a target plant density of 100 plants/m2. Some systems require multiple harvesting and access to the crop by hand. Peas can be sown in beds typically 1 m wide so that they can be approached by foot. For early planting or fall planting of peas, the rows can be protected with a fleece and narrow beds can be used. For crops with support, the rows are wide enough to allow access between trellises or wire supports. The distance between the plants remains about 2.5 cm.
The sowing depth of peas, as a crop with larger seeds, is greater than that of cereals. The depth is determined by soil and meteorological conditions. For the Black Earth zone it is 6-8 cm, in arid areas – 8-10 cm.
Peas are well tolerant of deep embedding, which allows sowing in dry conditions, where the top soil quickly dries out, to deeper layers.
In cool and wet spring, the depth is reduced to 5-7 cm, in heavy soils of northern areas – to 4-5 cm.
Depending on soil structure, the depth of sowing is recommended: on light soils – 7-8 cm; on medium soils – 5-6 cm; on heavy soils – 3-4 cm. If there is a lack of moisture, the seed embedding depth should be increased by 1 cm.
Small-seeded varieties and with early sowing, the depth is reduced by 1-2 cm.
There is almost no significant difference between the recommended sowing depth of green and combination peas: in general, for green peas the sowing depth is usually about 5 cm with subsequent rolling of the soil, for combination peas – 4-5 cm, with early sowing a little shallower, and late – a little deeper if soil moisture is low.
Pea crop care includes weed, disease and pest control.
After sowing in dry weather, the soil is rolled with the use of ring-spiked rollers ЗККШ-6. The method is effective in most cases, except for wet and heavy clay soils.
To control weeds carry out preemergence and postemergence harrowing which allows to reduce by 60-80% weed infestation of crops by annual weeds. Pre-emergent harrowing is done 4-5 days after sowing when weeds reach the white threads phase. Harrowing on the shoots is carried out in the phase of 2-5 leaves of pea plants before the formation of tendrils and mass growth of weeds. Harrowing is carried out in the daytime only across the rows or diagonally by harrows with retracted tines at a speed not exceeding 6 km/h.
Light harrows or reticulated harrows such as ЗБП-0,6А and БСО-4А are used for harrowing on light soils, medium and heavy – medium tooth harrows, for example, БЗСС-1.0.
With a lack of moisture, low air temperature is recommended foliar feeding liquid complex fertilizers.
Preparations against diseases
Fusarium root rot – Phytosporin-M (titer not less than 2 billion living cells and spores in 1 g of Bacillus subtilis, strain 26D), pre-sowing treatment of seeds.
Rust and powdery mildew – Alto (400 g/l, ciproconazole), spraying during vegetation.
Ascochytosis, rust, powdery mildew, chocolate leaf spot – Rex Duo (310 g/l thiophanamethyl + 187 g/l epoxiconazole), spraying during vegetation.
Pea competitiveness is enhanced when plants that give good ground cover are evenly distributed in narrow rows. Although this is not sufficient for complete weed suppression, it increases the effectiveness of any weed control measures that may be needed.
Not only do weeds reduce yields, but they can also seriously affect crop handling and quality of harvested peas (Knott and Halila, 1988). Harvesting of peas by self-propelled vines can be severely hampered by weeds such as Polygonum (Polygonum) and Stellaria spp. in Europe. Dense weed populations also slow the viner’s throughput, and pea husking efficiency is greatly reduced because the bulk of the weeds pass through the drum, increasing harvest time and compromising pea quality.
For combined (dry) peas, weed growth slows the natural drying of the crop and increases the time it is exposed to weather and disease, thereby reducing quality and profit. Weeds also slow down harvesting speed and create difficulties. Chemical desiccation may be required to eliminate weeds, which increases production costs (Knott, 2002).
When growing peas, contamination of produce by weed residue creates problems for the processor. Seed heads of field thistle (Cirsium arvense) and common poppy (Papaver rhoeas) as well as chamomile (Matricaria) and Tripleurospermum spp., berries of black nightshade (Solanum nigrum), white bryonia (Bryonia dioica) and potatoes from the previous crop are all extremely difficult to separate from production. Although plants are able to remove contaminants of a different color from peas, contaminants of the same color and specific gravity as peas remain. If contamination levels are high when the peas arrive at the factory, a certain percentage may not be removed by conventional cleaning operations. Given the limited manual sorting capabilities of most factories, the only solution is to cull produce from the contaminated area.
In addition to contamination, some weeds can spoil produce. For example, dogwood (Anthemis cotula) and the berries of black nightshade, brionia, and cranberry are toxic to some degree, and while it is unlikely that enough of them would be present in a sample to create a serious danger to the consumer, the risk does exist.
Some weeds are carriers of crop pathogens and their presence increases the risk of disease in the crop; for example, some cruciferous weeds are carriers of white mold (Sclerotinia sclerotiorum).
Cereal weeds in particular are a frequent cause of yield loss in peas due to direct competition. Some annual weeds, such as wild oats (Avena fatua) or black grass (Alopecurus myosuroides), can produce large seed stocks that can remain viable for many years; in addition, repeated use of certain herbicides in crop rotations has caused populations of some species to develop resistance. Perennial weeds such as couch grass (Elymus repens) and others are difficult to control because they emerge and grow at the same time as peas, and there are very few selective graminicides available or safe for the crop. In some situations peas can also be competitors of cultivated cereals such as barley.
Cultural control tools
Many weed problems can be reduced by stubble cleaning associated with effective plowing done in the fall. Stubble cleaning is a cheap and effective way to control perennial weeds, but it must be done in dry weather. Early light tillage of wet soil after the previous grain harvest promotes germination of cereal seeds or oilseed rape as well as germination of annual grasses such as bromegrass (Anisantha sterilis), but the decline in blackgrass and oats is greatest where stubble is undisturbed and there is bird predation.
The timing of sowing can also affect weed populations, and later sowing can allow time for a seed sodding approach. In this case, the cultivated land is seeded with germinating weeds and then tilled again just before seeding, disturbing the roots of the weed seedlings and allowing them to dry out (Davies and Welsh, 2002).
Only light spring cultivation is usually required to create a suitable seedbed, but cultivation has limited effect where overwintering weeds are well established. In peas, the use of narrow row spacing has eliminated the need for intercropping, but the use of toothed weeders such as the Einbock weeder, which sweeps through the topsoil, can be effective in removing small weed seedlings without unnecessary damage to pea plants. Time is of the essence, and work has shown that such weeding can be effective at certain stages of weed and crop growth. Early experiments have shown that some control of shallow-rooted annual weeds can be achieved by using weeding in the early stages of growth, from the second to fifth vegetative node. This treatment is more effective on lighter soil types and should be done when the surface is dry. Weeding can be done along or across the rows without causing significant damage to the crop. Later passes can be done along the rows, but this can cause damage to the pea crop, especially when it begins to bloom. Serious damage will occur if passes are made across the rows at later growth stages (PGRO, 2015a).
Biofumigants have been used for many years, and considerable research is continuing on the use of these techniques on annual crops. The technique is based on applying fresh, mulched plant material to the soil that releases several substances that can suppress soil-borne pests or diseases, and in some cases it is claimed to suppress weeds as well. Plants of the genus Cabbage (Brassica) are particularly active sulfur accumulators and synthesize significant amounts of sulfur-rich glucosinolates. Damaged leaves secrete myrosinase enzymes that break down glucosinolates into several products, including isothiocyanates (which are very toxic). Work has shown that these products are active against some soil-borne diseases and pests, but there are claims that weed suppression can also be achieved.
Growing a Brassica cover crop for use as a biofumigant involves establishing a fall crop, usually mustard, particularly brown mustard (Caliente) (Brassica juncea), although other members of the crucifer family (Cruciferae) can also be used.
While the use of such cover crops has several advantages in farming, such as providing a source of nutrients for newly developing crops, helping to improve soil structure by adding organic matter, and having some effect in suppressing pests such as nematodes, there is little reliable information that this technique can become a sustainable weed suppressant in pea and bean crops. It has been suggested that crucifers may have allelopathic effects on weeds, and reports from Europe and North America also suggest that crucifers may be used for integrated weed control (Tollsten and Bergstrom, 1988; Turk et al., 2005). However, there is no reliable evidence of weed reduction in the growing crop (Haramoto and Gallandt, 2005a,b). Similarly, there are reports of suppression of A. myosuroides with a cover crop of mustard preceding spring sowing of horde beans (Jim Scrimshaw), but the effect was not repeated on beans from year to year, although other work on winter cereals has shown significant suppression. This may be due in part to a lack of glucosinolate stability in the soil during weed germination, or other factors may be involved.
Well-proven pre-emergent herbicides for controlling most annual weeds in the UK are based on mixtures or tank mixtures of active ingredients with pendimethalin. These include clomazone, which is particularly useful for controlling the clementine (Galium aparine), linuron, a general purpose residual herbicide, and imazamox, which is also useful for oilseed rape as a litter and also for some suppression of potatoes left over from the previous crop.
The only post-emergent materials used are based on a tank mixture of bentazone, which is effective against broadleaf weeds, and MCPB, which again is effective against small seedlings of oilseed rape as well as thistles. Cereal weeds such as oatmeal can be controlled with postemergence graminicides such as fluazifop-p-butyl, cycloxidime, quizalofop-p-ethyl, or teproxidime, and preemergence application of triallate is useful against oatmeal (PGRO, 2016).
The selectivity of contact herbicides in foliar applications depends in part on the differential retention of the herbicide by the crop and weeds. Pea leaves are covered with a large amount of epicuticular wax that repels aerosol droplets. The leaf wax of maria white (Chenopodium album), for example, is not as water-repellent and is damaged by greater retention of contact herbicide. Other post-emergent herbicides have a contact effect on peas, and if the amount of wax on the leaves is low or it is damaged by wind, hail, frost, flying sand particles or mechanical damage of some kind, the effectiveness of the waxy cuticle is reduced and serious burns can occur.
If post-emergence preparations are planned, the amount of wax on the leaves can be checked before spraying by taking a sample of the plant and dipping it in a container with a 1% solution of methyl violet dye. The plant is then taken out and the excess dye is carefully shaken off. The amount of dye retained indicates areas where the waxy cuticle is damaged or incomplete. This level is evaluated and the decision to apply herbicide is made when a satisfactory level of dye-repelling tissue is reached. In some cases, it may take several days for the wax to build up before spraying is safe, especially after a period of poor weather conditions.
For peas, the main post-emergent herbicide currently used in Europe is bentazon, sometimes mixed with the phenoxybutyral pesticide MCPB, and it is important that wax levels be high when using such a mixture.
The selectivity of translocated herbicides depends on the pea’s resistance and the susceptibility of the weed to the herbicide. Peas may have a mechanism to break down the herbicide to a non-toxic derivative, or conversely, a susceptible weed may metabolize the toxic derivative through a biochemical process that peas do not possess. An example is the non-toxic MCPB, which is converted to the toxic phenoxyacetic MCPA by b-oxidation in susceptible broadleaf weeds, whereas legumes lack this metabolic process. The selective use of bentazone may be due to differential retention and uptake as well as the ability to metabolize bentazone.
In controlling weeds in pea crops, herbicides are used:
- Prometrin (selectin, gezagard-50) – soil-acting herbicide, spray the soil before sowing under harrowing, effective against dicotyledonous annual weeds, doses on light soils – 1-1.5 kg/ha a.s., on boggy rich in organic matter – 2-2.5 kg/ha a.s.;
- sodium trichloroacetate (TCA) – similar to prometrin, also effective against wheatgrass at the doses of 4.5-12.6 kg/ha a.s.;
- 2М-4XM (Sys-67, MB) – used for vegetative weeds, in the phase of three leaves of the culture, the dose – 2-3 kg/ha per hectare, harrowing on sprouts in this case is not carried out;
- Bazagran – used when growing peas for grain, contact herbicide against annual dicotyledonous weeds, used in the phase of 3-6 leaves of peas at a dose of 1.5-1.9 l/ha;
- Agritox – is used when growing peas for grain against annual dicotyledonous weeds, spraying in the phase of 3-5 true leaves of peas;
- Fusilad Super – against annual and perennial cereal weeds, spraying at the phase of 4-5 leaves in peas;
- Fusilad Forte – against annual and perennial cereal weeds, spraying of crops in the phase of 2-4 leaves of weeds, regardless of the phase of the culture vegetation;
- Pivot – used when growing peas for grain against annual and perennial cereal weeds, spraying the soil after sowing or in the phase of 3-6 leaves of peas.
Harvesting green peas
Pea varieties continue to improve through careful selection. At first, peas were pale in color and susceptible to bad weather and disease. Modern varieties are very disease resistant, high yielding, and generally have improved palatability. Plant architecture has been modified in many varieties by reducing plant height, reducing vegetative growth by changing the shape of the leaves or replacing the leaves with tendrils and strengthening the stems. A number of varieties are available that provide a 6-8 week harvesting period, allowing for a continuous supply of fresh product to the plant for freezing or canning.
The optimal time to harvest is when the pods are well filled and the seeds are still soft and immature. As the seeds mature, their firmness increases, the seed coat thickens and becomes tough, and the sugars are converted to starch. Peas ripen quickly at high temperatures and are at their optimum quality for only a day or two. Therefore, it is important to choose the right varieties and planting dates to predict harvesting periods and to achieve high yields and quality. Varieties with different ripening dates are grown to extend production.
In domestic practice, peas are harvested when 70-75% of beans have reached technical ripeness. Control over the ripeness of the crops begins a week before the expected harvesting date. Sampling is conducted every 2-3 days from different parts of the field and from different heights of crops. In practice, ripeness can be checked with a textometer, a tenterometer, and a finometer.
Ripening is accompanied by rapid changes in chemical composition, which affect the taste and texture of peas. There is a loss of moisture and a change in the proportions of sugar, starch, cellulose, hemicellulose, and pectin, which generally increases the total amount of dry matter. As maturity increases, sugar is converted to starch, so measuring the amount of alcohol insoluble solids (AIS) can be used as an indicator of maturity: the total percentage of AIS increases as maturity increases, and this correlates with the quality assessment that can be made by organoleptic methods. Such a laboratory process is time-consuming.
Harvest control is now based on accurate measurement of maturity. Since pea seed development occurs rapidly over a short period, it is important to equate yield with an identifiable state of seed development; maturity in this sense means edible quality. Edible quality is usually determined objectively by means of a tenderometer. The first Martin Pea Tenderometer was invented in the early 1950s and even today derivatives of the original tenderometer provide farmers and mills with a reliable and practical means of assessing optimum harvest time because it measures the physical properties of pea quality in a reproducible way.
The tenderometer measures the resistance of a sample of peas to crushing pressure, that is, relative hardness, by slicing the peas in a closed chamber and measuring the shearing resistance; the greater the resistance, the less tender the peas are. Tenderometer readings, adjusted for temperature, correlate well with edible quality, determined by sweetness, tenderness, and starchiness.
Typically, the instrument has an upper grid of thin metal plates, which can be driven by a motor through a second grid mounted on the same shaft. A sample of peas is placed in the space between the grids, and when the instrument is driven, the peas are first compressed, then crushed, and finally squeezed through the lower grid. The force used is measured by the instrument and displayed as a scale of 0-200 units, which is then corrected for temperature fluctuations. The units are not easy to determine because they have been developed over many years of cross-checking instruments and fresh peas of varying degrees of maturity.
Harvest ripeness on a tenterometer is determined in TE units (1 TE = 70 g/cm2), guided by a scale:
- < 70 TE – crop not mature;
- 100-110 TE – suitable for freezing;
- 110-120 TE for canning.
Because of the negative correlation between maturity and yield, the price paid to farmers for better and less mature peas is usually adjusted upward.
When determining ripeness on a Finometer, the hardness of the peas at the beginning of harvest should be 29-30°, and 56° at the end (the appearance of a reticulated pattern on the bean flaps).
The operation of harvesting peas is highly mechanized. Typically, peas are picked from fields that are nearing harvest, and small samples are taken by hand or with a small pea harvesting machine to obtain a tenderometer reading. Readings can be taken daily 2-3 days before harvest to determine optimum maturity.
String peas are harvested by hand to minimize damage to the pods. The pods are separated from the stems in the field and packed into boxes before being transported to the farm or to the packinghouse for packing. The optimum time to harvest chickpeas can also be determined using a tenderizer, but generally on a larger scale an estimate of the percentage of peas in the pods is used. When harvest time arrives, the pods are usually harvested in a single full harvest by pulling the plant at ground level and hanging it up by its roots so that the pods are better visible.
In most cases to produce fresh produce for the market, several harvests are done by hand as the pods develop. Although this is a labor-intensive process, manual harvesting minimizes physical damage and helps preserve quality longer. When marketed, the peas are stored in their pods and are not peeled until they are ready for cooking and consumption. When peas are removed from their pods, their post-harvest life is greatly shortened.
Sugar pea varieties with pods and crunchy peas are not harvested by machine. Hand-harvesting is sometimes done daily to avoid over-ripening of the pods. The proper harvest stage is when the pods reach full size, but before the seeds appear. Peas have slightly more developed seeds, but not yet ripe. Harvesting indeterminate, edible pea pods can go on for many weeks, and frequent harvesting promotes additional blooms.
Harvesting is now mechanized on a large scale. By the 1950s, many farms had stationary wineries owned by farmers and factories. Their use was based on the fact that peas were cut in the field, loaded into a trailer and transported to the farm. The peas were then hand-fed to the elevators to the stationary viners, where the peas were threshed, washed, and cooled before being transported to the plant. The next step was the introduction of trailed viners, which picked up the cut crop in the field and vinified the peas on site, unloading the vinified peas into a trailer before transporting them to the plant.
Since then, self-propelled pea harvesters have been the primary form of harvesting, and peas are delivered to the plant within 2 hours of harvesting. Modern comprehensive pea harvesters combine harvesting, threshing, and cleaning operations. The pods are separated from the stalks and conveyed by conveyors to the threshing drum, where the peas are threshed from the pods; the peas fall through a series of screens, which are kept clean by rotating brushes located along the length of the drum. The peas and some of the waste leave the machine through a further waste removal process, after which the waste is discharged into the field. The peas are stored in a hopper before being unloaded into a trailer and taken out of the field, usually directly to the plant.
In some cases, whips are harvested by machine or by hand and taken to a stationary viner, where the peas are separated from the pods. In order for the harvesting equipment to work efficiently, the plants must have a determinate habitus, short stiff stems, and the pods must be concentrated close to the top of the plant. Harvesters work more efficiently when plants have sparse foliage; this is an advantage of leafless varieties.
Using a single mechanical harvest may cause some peas to be overripe and others to be unripe. This applies more to processing than fresh use. Peas of different maturity levels of the same variety are usually separated by size. Since peas of different maturity have different specific gravities, they can also be separated by flotation using brine of different concentrations.
Harvesting dry peas
Many pea varieties are characterized by strong lodging, low bean attachment on the stalks, uneven and prolonged ripening, bean bursting, shattering of seeds, their damage during threshing. For these reasons, the two-phase harvesting method is preferable. Premature harvesting results in wrinkled seeds, reduces yields, and increases the time and energy required for subsequent drying.
Harvesting peas in fields is delayed as long as possible to allow late pods to ripen. Delayed harvesting can lead to seed shattering.
During the two-phase harvesting, mow in windrows when 60-75% of beans are dark (white, yellow), seeds are 30-40% moist (in fully dried condition, moisture content is less than 15%), and the seeds are fully formed and hardened. During this period, the beans of the upper tier are pale green in color, while the stems and leaves are yellow. Mowing is carried out by the harvesters type ЖБР-4,2 at a speed of 5 km/h, or by mowers КС-2,1, equipped with a device ПБА-4 or ПБ-2,1 at a speed of 6-7 km/h.
Mowing direction is transverse to lodging, for short-stemmed varieties – towards the direction of lodging. Threshing is usually carried out after 3-4 days in good weather when the peas, passing through the cutterbar, are not damaged, the moisture content of the seeds at this 16-19 (25)%. When moisture content is less than 15%, strong crushing and losses from shattering are noted, and when moisture content is over 20%, damage to the seed germ is observed. Peas harvested at this slightly higher moisture content usually retain their color even after drying. Peas for animal feed can be harvested at lower moisture levels, thereby reducing the need for artificial drying.
For the selection of windrows combine harvesters are equipped with conveyor copy pickers ППТ-3, ППТ-3А. To prevent re-entry of the grain into the drum fully open the louvers of the grid and increase blowing.
The method of direct combine is used on poorly lodged crops of short-stemmed and not shrinking varieties. Typically, this method peas are harvested in the Volga region, Eastern Siberia, the steppe regions of Ukraine, where, provided the fields are clean of weeds and uniform maturation, one-phase method often has an advantage. Harvesting begins when the seeds reach full ripeness. Combine harvesters are equipped with spring-loaded stalk lifters for this method of harvesting. The threshing units are adjusted in the same way as for swath pick-up.
The direct harvester method is also used in case of high production volumes.
Combine harvesting of peas has several features, including reducing the speed of the threshing drum and the installation of appropriate screens to prevent the peas together with the straw.
Table. Operating modes of threshing machines
|Rotation frequency, rpm|
|Gaps between reel whips and deck strips, mm|
|in the middle part|
A combination of the two harvesting methods is possible, with direct harvesting carried out on clean fields at full ripeness and grain moisture of 16-19%.
Both methods are suitable for harvesting moustached pea varieties.
The time between threshing and processing should not exceed 1.5 hours, as the products may begin to spoil. This requirement limits the distance from the place of cultivation to the place of processing, which should be no more than 50 km.
Seeds coming to threshing floor cleaned and dried to a moisture content of 12-14%.
For long-term storage, peas must be dried to 14% moisture content. Drying can be done artificially, but the seeds are relatively large and moisture extraction from the center can be a slow process compared to drying grain crops. They also have low airflow resistance, and there is very little lateral air movement when drying in bulk. Ideally, the temperature of the blowing air should be around 43°C, otherwise seed coat damage can occur. If the crop is intended to be used as seed, high temperatures and drying too quickly can have a negative effect on germination.
Pea haulm is useful as animal feed, so it is often harvested and pressed immediately after harvesting. The nutritional value of straw is similar to barley straw, but it has a little more protein and less fiber.
Mixed crops of peas and oats also use double threshing, which threshes mature beans at a reduced frequency of drum rotation to 400-500 revolutions per minute. The remaining unripe beans are dried in windrows for 3-4 days and subjected to a second threshing process.
Selection work is aimed at developing varieties that are more resistant to lodging and shattering.
The crop is harvested when fully ripe, but in some cases, ripening may be uneven or there may be weeds that delay ripening. In this case, chemical desiccation may be used for harvesting.
Desiccation involves applying chemicals to prevent further growth of the crop and weeds, followed by direct harvesting when the peas are sufficiently dry. Desiccation can lead to lodging of the crop, and if applied too early, there is a risk of stem failure due to insufficient lignification. Other effects include shriveled seeds; if peas are left in the field longer than the optimal time for harvesting, pod shattering can occur when peas spill out of the pods and cannot be harvested by the combine. The crop is usually harvested with a combine harvester without prior mowing. It is preferable to harvest when the peas pass without damage when the dry matter reaches 75%.
Reglon Super, spraying 7-10 days before harvesting.
Harvesting string peas
String peas are harvested as whole pods and harvested by hand to minimize damage. The peas are separated from the stems in the field and packed in boxes before being transported to the farm or packinghouse.
Three types of fresh peas come to market, including standard garden peas or English peas, whose pods are picked by hand to peel, sugar or snow peas, which are picked when the seeds develop but before the pod is wiry. Garden or English peas are usually grown on a large scale in fields without additional support for the stems, much like the stalked pea, while the other two types can be grown in beds or in trays. It depends on the variety chosen whether they will be grown on a bed or require support in the form of a wire or trellis system. Plants grown on beds are usually harvested at the same time, while crops grown on wire or trellis systems are harvested over a period of time, allowing for multiple harvest dates. Some crops are planted in the fall and protected by a fleece cover, which is removed the following spring when the danger of frost has passed. This system allows for an early harvest. Growing these crops requires a lot of manual labor, but the end product can be more expensive.
Storage and post-processing
Post-processing of green peas
The factories are usually located within 3 hours of delivery, but if that is not possible, the green peas can be chilled at the farm to 4°C before transportation using ice water. Top quality peas are delivered and frozen within 120-150 minutes.
Upon arrival at the factory, the green peas are sampled to determine the tenderometric index and level of foreign impurities, which may include pods, stems, insects or shellfish, stones, etc. Peas that do not meet quality standards may be rejected by the factory and returned to the farm.
The peas are poured into storage bins, from where they are transported by elevators to the remaining cleaning stages. These include blowing with compressed air and washing in tanks designed to remove light debris and stones for later removal. The clean peas are then either frozen or canned.
There are two types of commercial processes for freezing: vibrating table systems and belt systems. In vibrating table freezers, chilled air is supplied through holes in the floor of the platform, and the angle of the holes allows the peas to be moved in a wave-like pattern to the freezer outlets. Some freezers also vibrate to keep peas fast frozen individually. In a belt freezer, peas are frozen on a mesh belt through which cold air is driven as the belt passes through the freezer. At this stage, the frozen peas can be optically sorted or screened on vibratory sifters to remove any defects (PGRO, 2015).
The canning operation takes place immediately after peeling and blanching. The peas are steamed to prevent spoilage by microorganisms and then placed in jars where a brine solution, which may contain sugar, salt, and water, is added. The jars are sealed and pressure cooked in an oven for 20 minutes at 121°C. The jars are then refrigerated before being labeled and packaged.
Frozen peas are usually grown under contract with a processor and delivered in the agreed tonnage on a daily schedule throughout the processing season, which can be up to 6-8 weeks. In the UK, reliable supplies to the factories are provided by growers who are usually organized into cooperatives that share drilling, agronomic, and harvesting equipment. Each cooperative or group of producers organizes seed deliveries, drilling and agronomy schedules, and a common set of harvesters and transport allows peas to be delivered to the factory on a regular schedule 24 hours a day, 7 days a week.
To deliver the volumes needed, growers in the U.K. and some other countries have formed pea cooperatives that can jointly own all the growing and harvesting equipment, organize a seed-sowing program to ensure continuity of supply, and work as a single group in harvesting and transporting to the mills. There are currently about 12 pea cooperatives in the U.K., supplying 130,000 tons of peas to eight freezing plants and one cannery during the season.
The peas are typically sold by the processor to retailers and caterers, who in turn supply them to caterers and allied industries. Payments to cooperatives or farmer groups are based on risk-sharing, where farmers receive a fixed payment per ton of frozen product regardless of the variety or time of harvest. Payments are usually negotiated between processors and growers at the beginning of each season. The demand for frozen product varies throughout the year, and frozen peas can be stored in the freezer for many months. Sometimes there are transient inventories when demand is low or yields are high in a particular year, and this affects the contracted acreage for the following year.
Storing green peas
Temperature is a major factor in the conversion of sugar to starch, so it is important that harvested garden peas not be exposed to high temperatures. As little as 3 hours at ambient temperature can result in a significant loss of quality. Rapid, preferably wet refrigeration is necessary to preserve quality. Harvested pods or peeled peas should be cooled as quickly as possible to 0 °C to limit sugar conversion as well as fiber development.
Peas retain a higher quality when unpeeled than when peeled because of less drying. The high CO2 content inside the pod provides a minimally controlled atmosphere. Peeled peas are processed the same day, often a few hours after harvesting. The quality of fresh garden pea pods and edible pod peas can remain in relatively good condition for 1-2 weeks when stored at 0°C and 90% relative humidity. Dry field peas, due to their low moisture content, do not give much trouble in the post-harvest period and during storage.
Post-processing of string peas
The pods are packed into field crates and transported to the packing house on the farm. The crates are quickly moved to a cooler to remove field heat and reduce dehydration. Usually the cooled storage units on the farm are set at 8-10°C. This is especially important if the peas are grown in warm areas. The boxes are transported to the main packing house, where the product is inspected by quality control inspectors and then moved to cool further to 5-8°C, awaiting final packing.
Product uniformity, such as pod length, average number of seeds per pod and pod shape are the main criteria, but also the presence of thread along the pod seam is undesirable for the chard and pea market. The pods should be clean, without stains or physical damage. Color is also important for edible types of pods. The pods should be completely turgid and clean. The stem and calyxes should be green, and the flowers should not be attached to the pods, as this can lead to spots of rot and fungal infestation. The product is not stored in high humidity, as this promotes fungal diseases and rotting.
The pods are then packed in small trays for retail sale and covered with film to allow air movement. Distribution to supermarkets is usually by refrigerated transport at 7-10°C. At retail, most produce is displayed in refrigerated cabinets at about 15°C. Edible chick peas are perishable and cannot retain good quality for more than 2 weeks. Wilting, yellowing of the pods, loss of tenderness, development of starchiness, and rotting are likely to increase after storage for more than 7 days; longer storage of edible peas is usually at 1-3°C to slow the rate of respiration.
Post-processing of combined (dry) peas
After harvesting, dry peas can be stored on the farm or delivered to elevators for long-term storage. Foreign impurities must be removed before use. Many grain traders or cooperative grain elevator companies have large-scale equipment to process dry peas before they are shipped to food processors, packers, or animal feed plants. The peas are first passed through sieves to remove soil, stones or large foreign particles. These are usually gravity separation sieves placed at a slight angle, and the peas are vibrated over the sieves so that non-large seeds and light debris are moved to the upper edges of the sieves and removed. The next operation is to pass the peas through a bank of electronic color sorters. The peas are passed through a beam of light calibrated to activate the compressed air jet when the reflectivity of the peas is out of specification, i.e., lighter or darker due to bleaching or spotting. After activation, the air jet throws the defective peas aside, into a nearby collection bin. Each sorter bank can typically handle about 12 tons per hour.
The next cleaning step may be required if the peas have been damaged by insects such as pea moth (Cydia nigricana) larvae or pea bruchids (Bruchus pisorum), which leave holes in the seeds. This process involves passing the crop through a horizontal cylindrical drum lined with fine needles. As the peas pass through the drum, the damaged peas hit the needles and are then peeled off onto a waste conveyor belt. The needle drum or pin drum can operate in a group of drums to speed up throughput.
Finally, the peas are packaged in bulk bags or small paper bags before being shipped to the shipper or processor.
Peas for animal feed can be milled and pelleted, or green peas can be micronized to produce flaked peas. In micronization, the peas are run under a high-temperature heater, then rolled and allowed to cool. This process is believed to make peas more easily digestible. The micronized product can also be used as an ingredient in pet food.
Marrowfat peas for human consumption can be sent for further processing. In the United Kingdom and some European countries, marrowfat peas are canned as “processed peas”. For this purpose, the dried product is soaked in water for 18 hours, then drained and steamed blanched. The blanched peas are placed in brine jars before being sealed and boiled for 21 minutes at 121°C before being cooled, labeled and shipped to the distribution warehouse.
Peas can also be sold whole and dry for home consumption in small bags. A larger market exists for de-hulled peas, which are then soaked, boiled and eaten as “mushy peas,” a delicacy common in Britain and Australasia as an accompaniment to fish and potatoes.
A number of pea processing processes also include its use as a snack, where peas are deep-fried and flavored. Pea flour is used in the baking industry, and varieties with yellow seeds are preferred for this purpose. Pea flour is useful in some cookie and dough recipes, and because it is gluten-free, pea flour is suitable for the coeliac diet.
Peas are grown either under contract with a trader or sold at the open market. In Europe, peas are often grown by farmers who are members of a grain cooperative, and the peas are stored in bulk until delivered to the end consumer. The quality of peas is very important, especially for the human consumption market, and prices on the open market are not fixed in the same way as for grain, which can be sold forward at a known price. Prices can be volatile depending on demand. Production in other countries may compete for the same markets, and prices reflect supply and quality. Production of high quality marrow peas in the U.K. can be affected by adverse weather at harvest time, and high quality peas can demand high premium prices. Overproduction of pulses in Canada, for example, could also lead to lower animal feed prices.
Resource-saving intensive technology
Resource-saving intensive technology
Resource-saving intensive technology of peas cultivation allows to get the yield up to 3-4 t/ha. It provides for the placement of crops on the best well-fertilized predecessors. Tillage system should provide maximum field clearing of weeds and leveling of the soil surface.
Fertilizer rates are calculated for the planned yield, taking into account the content of phosphorus and potassium in the soil. Under the predecessor make organic fertilizers. Applied phosphate fertilizer in the rows during planting. If there is a deficit of trace elements in the soil, apply microfertilizers, especially molybdenum and boron.
Seed pre-sowing treatment includes treatment with rhizotorfin or similar preparations, and, if necessary, with microfertilizers.
The sowing dates are the earliest in all zones, except for Western Siberia, where sowing is carried out in the second half of May.
Sowing care primarily involves the control of weeds, diseases and pests. Pre-emergence (4-5 days after sowing) and post-emergence (in the phase of 3-5 leaves of the crop) harrowing is carried out.
Marsh spot (hollow heart) is a physiological disorder that occurs in crops deficient in manganese; high soil pH can limit manganese availability.
- Agrotis segetum, A. exclamationis;
- Noctua pronuba;
- Acyrthosiphon pisum;
- Macrosiphum pisi;
- Heliothes spp.;
- Liriomyza huidobrensis, другие виды Liriomyza spp.;
- Phytomyza spp.;
- Agromyza spp.;
- Contarinia pisi;
- Cydia nigricana;
- Sitona lineatus;
- Bruchus pisorum;
- Thrips angusticeps;
- Kakothrips pisivorus, K. robustus;
- Pratylendrus spp.;
- Heterodera spp.;
- Meloidogyne spp.
Stem weevils (Sitona spp.)
Stem weevils (Sitona spp.) have been particularly dangerous pests of vegetable peas during emergence of seedlings in recent years. Infestation of pea crops in Belarusian farms of Grodno and Brest Regions amounts to 5-15%; the weevils occupy 3 and more beetles per m2. Weevils also damage beans, lupine, and other crops of the legume family.
In Belarus, two species cause damage: striped weevil weevil (Sitona lineatus) and bristle-veined weevil (Sitona crinitus). Plants are damaged by both adult beetles and larvae. Damage appears in the form of semicircular holes on leaf margins, cotyledons, and leaf laminae. Adult beetles and larvae also damage the growing point. Mass outbreaks of Nodule Weevil weevils cause severe crop thinning.
Weevils overwinter under plant debris, usually in the fields of perennial grasses. In late April or early May, the beetles crawl out of their wintering places and harm perennial leguminous grasses. When temperature rises above 15°C, the beetles migrate to peas and other annual legumes. In the middle of May, females lay eggs on the soil surface, from which very mobile larvae hatch in 7-10 days. These eggs damage leaves of young plants and can also feed on bacterial nodules on their roots. Larval development lasts about a month, after which they pupate in small cradles. One generation develops per year.
Pea weevil (Sitona lineatus)
Pea, or bean, or striped tuberous weevil (Sitona lineatus).
The pea weevil most often affects peas and beans. This pest is present in most temperate areas of the world where beans are grown, although damage is often greatest in Europe. Leaves of seedlings and young plants affected by the weevil have characteristic feeding damage in the form of semicircular notches on the edges of the leaflets. The damage can be slight or severe, and severe damage can stunt growth, especially during periods of stunted growth at low temperatures. In severe cases, pea and bean yields can be reduced by about 25%, but crops often grow after low levels of damage; however, larvae that develop from eggs laid during feeding feed on underground root nodules. This can reduce nitrogen availability to plants and lead to nitrogen deficiency.
In spring, adult weevils that have migrated from fields where they overwintered begin feeding on newly emerged seedlings, mating and laying eggs at the base of plants. Then the eggs are washed away by rain, and in a few days the larvae hatch from them, making their way to the nitrogen-fixing nodules on the roots. After pupation, the newly emerged adults feed on green tissues and then return to their overwintering sites.
Control of this pest is very difficult because the adults are active during the day when temperatures are relatively high, but when seedlings are very small. The insects prefer lumpy dry soil, so pest control with insecticide spraying is often ineffective. To maximize the effect of pest control, the pest must be controlled during the feeding period, but before the adult lays eggs. In the UK, a monitoring system has been developed to help determine the timing of spraying and estimate the possible level of damage based on insect numbers. It uses a bait containing a synthesized combination of insect aggregation pheromone and legume leaf volatiles. The bait is placed in a funnel trap placed in the fields during sowing. Spraying can be done if a threshold catch has been recorded in the trap (Biddle et al., 1996).
S. lineatus is also the host of the pathogenic fungus Beauvaria bassiana (Steenberg and Ravn, 1996; Maurer et al., 1997), whose spores germinate on the insect surface and penetrate the cuticle after germination. The fungal hyphae then penetrate the body tissues, and eventually the insect dies. The use of aggregation pheromone as an attractant to attract insects to bait containing B. bassiana spores is currently being studied (Bruce, 2016).
Pea aphid (Acyrthosiphon pisum)
Of all pea pests, the pea aphid (Acyrthosiphon pisum), the Pea aphid, is the most common and most harmful pest, both as a direct feeder and as a vector of viruses that reduce yield and plant quality. It is common in many temperate countries, including North and South America, Europe, South Australia, Tasmania and New Zealand. It lives on a wide range of legumes, including peas, clover, vetch, sainfoin, horse bean, and broom. In years of mass aphid reproduction, yields are reduced by as much as 15-20%.
Vegetable pea crops suffer most from aphids during the phase of the beginning of mass formation of buds. Larvae of first instars harm young plants and shoots by sucking their sap. Sap feeding leads to deformation of infected parts, their desiccation and death. Buds infested by phytophage usually do not open. Pods are underdeveloped and produce fewer grains. Infested peas are stunted, the tops become chlorotic, the leaves shriveled, and the aphid’s release of honeydew promotes colonization by secondary molds such as Cladosporium spp. or Botrytis cinerea. Aphids carry pea enation mosaic virus (PEMV), pea apical yellowing virus (PTYV) and pea seed-borne mosaic virus (PSbMV), all of which are detrimental to yield and quality.
Although other aphid species occur on peas, A. pisum is the most common and harmful. Most crops become infested at some time during the growing season. Winged migrants move onto crops in early summer, and colonies quickly develop around growth points and under leaves. Reproduction and colony growth are determined by crop condition and temperature. If temperatures exceed 23°C, aphid reproduction slows (Morgan et al., 2001). Colonies also develop on pods, and feeding continues until pod maturity, when a winged generation emerges and migrates to wintering hosts such as clover and alfalfa, where it lays eggs. The adults are able to survive the mild winter and infest peas early the following year. At this stage, peas are particularly susceptible to viral infection, and viruses such as pea top yellowing virus can be a serious threat.
Eggs overwinter. The founding females that hatch from eggs in the spring, after feeding on perennial legumes, reproduce in several generations. By early June, the breeding females emerge and migrate to the pea crop, where numerous aphid colonies emerge after breeding.
There are various estimates of the economically significant size of populations infesting peas (Biddle et al., 1994). In Europe and other countries, it is common to treat peas as soon as an infestation is detected. In the United Kingdom, it has been shown that significant increases in combined pea yields can be obtained by using aphid control until four pod nodes form on the plants, after which the economic benefit is not achieved.
The overhanging flies (Syrphidae) are important predators of pea aphids, but sometimes infestation of peas with larvae and pupae of overhanging flies has resulted in rejection of crops destined for freezing (PGRO, 1970). The main parasites and predators of aphids include adult beetles and larvae of coccinellids, larvae of common lacewings, and gallicas, which in some years can reduce the number of phytophage to below the economic threshold of harm.
For compound peas, yield loss remains a major problem. Although aphids have not developed resistance to the commonly used aphid pyrimicarb, there are concerns that repeated applications of a single active ingredient will lead to the development of resistance.
Pea seed beetle (Bruchus pisorum)
Pea seed beetle (Bruchus pisorum L.) is common in the United States, Australia, and many warm European countries, but not in Great Britain and Scandinavia.
Peas grown for dry harvest and destined for premium food markets or for seed have oval holes left by emerging adults. High populations of bruchids can develop locally, and once they have settled in an area, infestation levels may be too high for pea processors to clean and sort. Where mechanical cleaning is available, such cleaning incurs penalties for the grower. Damaged seeds may germinate, but small seeds may die from pre-emergence mortality in the field, and damaged pea seeds are considered undesirable to the end user. The presence of live beetles in seed batches can result in a seed batch being classified as uncertified and having to be fumigated.
Adult beetles leave their overwintering site in early summer when maximum temperatures reach 20°C. They fly to flowering crops, feeding on buds and pollen. In the phase when bean leaves begin to form, females lay eggs on their surface, and in 6-10 days larvae hatch from them. After hatching, the larvae penetrate through the bean wall into the developing seed, where they feed on the cotyledons until maturation. The entire larval development cycle takes place inside the bean. Only one larva usually feeds in one grain, and its development cycle lasts 20-23 days. After the seed matures, the larvae pupate and emerge from the seed as adults, cutting their way out, leaving a characteristic round or oval hole. At the end of summer, the newly emerged beetles leave for wintering. The beetles may overwinter in pea grains in storages or in the field in crumbled grains.
Control in the field is difficult because the beetles feed under the pea canopy and are not often exposed to insecticides. Early flowering varieties can avoid damage if the flight of adults from their overwintering sites is delayed by cool temperatures. Work is currently underway to characterize pea resistance based on work done in Australia on Pisum fulvum, but transgenic pea varieties are not currently commercially practiced.
Work in Chile has identified a possible method of biological control using the parasite Uscan senex (Pintureau et al., 1999), and other parasitoids have also been described, but no commercial development has taken place.
Pea midge (Contarinia pisi)
The pea midge (Contarinia pisi Winn.) is common in the northern temperate regions of Europe, Scandinavia, and Great Britain. Peas are most severely affected because pea varieties were bred to produce short flowering periods to allow for more uniform ripening, and this results in most of the flower buds being attacked by the midge larvae. Older pea varieties and most combination pea varieties are more indeterminant, have longer flowering periods and suffer less damage.
Damage to the crop occurs due to larval feeding inside the flower bud, resulting in deformation of the bud and the appearance of a “nettle head” caused by shortening of the flower stems. Damaged buds do not produce pods and fall off. Crops are susceptible to damage when they have reached the closed bud stage, where midges (if present) lay eggs on the outside of the bud, allowing larvae access to the developing bud, where they feed at the base of the flower. Yield losses can be as high as 50% if the larvae damage more flower buds on the apex shoot.
The harmful phase of development is the whitish, spindle-shaped, 2-3 mm long, legless larvae. Usually develops in two generations, with larvae of the first generation feeding inside flowers and those of the second generation inside beans. One pod sometimes contains several dozens of larvae.
Adult midges emerge from the soil of last year’s pea crop in late spring and mate before females start migrating to the crops of the new season. Male midges stay in the field for a short time, after which they die. Females migrate to nearby crops, where they lay eggs in flower buds. After feeding, the larvae drop into the soil, where they migrate through soil cracks and hibernate in the form of cocoons. In late spring, the larvae emerge from the cocoons and pupate, then emerge in early summer.
Because the midge has a very short flight radius, cultural control can be accomplished by growing peas away from previously infested areas. This may require moving production plots for 1-2 years to break the cycle, but this method has been successful in Sweden (Jonsson, 1988). Chemical control is done by spraying insecticides as soon as midges appear on crops, but better results can be achieved by installing a monitoring system, which is a pheromone-based sticky trap that detects early migrating midges (Hillbur et al., 2001; PGRO, 2015).
Pea moth (Cydia nigricana)
The pea moth (Cydia nigricana, syn. Laspeyresia nigricana Steph.), or the pea moth or pea leafminer, is especially troublesome in areas with intensive production of compound peas, as well as in those where green or chick peas are grown nearby, allowing large populations of the pest to develop. It is common throughout Europe in the temperate belt, and some localized populations are found in some western U.S. states, southern Canada, and Japan. The damage increases in hot and dry years.
Damage is caused by larvae feeding inside the pods on developing seeds. Damaged peas have irregularly shaped holes or circular holes of varying sizes, and the pods contain a webbed rind. Thus, the produce is spoiled and the damaged seeds are not likely to germinate. In combination peas, damaged seeds have to be removed with an expensive cleaning operation, but in green or pod peas, the crop is likely to be rejected by the processor or retailer.
The pea moth overwinters in the adult caterpillar stage in the soil inside a cocoon, usually in last year’s pea fields. Moth flight from hibernation depends on the temperature of the upper soil layer (in Belarus, it is between 12 and 18°C). The beginning of moth flight coincides with mass flowering of vegetable peas and with the beginning of bean formation. Females begin laying eggs on days 3-8 after flowering, spreading them to the upper and lower sides of apical leaves and, to a lesser extent, to leaflets, petals, and beans. Fertility of moths is from 50 to 300 eggs. Hatching occurs in about 10 days, and the larvae find and penetrate the developing pods and begin feeding on the seeds and their entire developmental cycle takes place inside the bean. After maturation, the larvae leave the pods and fall into the soil, where they bury themselves in the ground and then form a wintering cocoon.
In Belarus, the pea moth develops in one generation.
Since moth populations accumulate in places where peas have grown to maturity, any peas growing in that place the following year are susceptible to infestation.
Chemical treatments are the only effective means of control, but spraying should be done at the time the larvae hatch from their eggs and before they burrow into the developing pods. An effective monitoring system has been developed in the UK and is used commercially to determine when moth activity occurs and to predict the optimum time for spraying.
The monitoring system is based on the use of a synthetic analogue of the sex attractant of female pea moths in sticky traps that are placed on the pea crop just before flowering. By tracking male moth trap catches and daily temperatures, the user of the system determines when the threshold catch was recorded and can calculate the correct spray date (Biddle et al., 1983).
The pea gall nematode (Heterodera gottingiana) is a soil-dwelling pest that can affect peas, fodder beans, vetch (Vicia sativa), lupine (Lupinus spp.) and sweet peas (Lathyrus oderatus). The pest has been recorded in Europe, Russia and the USA, and there are also reports of its occurrence in Japan, China and the Middle East.
Peas are most severely affected; forage beans may also be infested, but serious symptoms or consequences are rare. Infestation occurs in isolated patches of soil where the nematodes multiply and form cysts that remain viable in the soil for years or until the host crop is grown. Affected peas become stunted and pale, and root nodules are absent. Roots affected by the nematode contain swollen bodies of female nematodes that later emerge from the root tissue and dry out, forming numerous lemon-shaped, brown cysts. Plants eventually wither, die and produce no productive pods. Yield loss may be complete in infested areas of the field; and plants may mature prematurely in neighboring areas where they show less symptoms. Forage beans are most often unaffected by infestation, although affected areas in an infested crop may sometimes remain stunted.
Once cysts are formed, their viability can last as long as 20 years, and the only remedy is to avoid growing the host legume in the field for at least that period of time. Cysts can also be transferred to other fields in the soil on implements, and it is believed that the pest has been introduced to other areas by planting imported bulb crops that were grown in old pea-infested fields.
In practice, chemical means of control are not used. Fields with past infestations are not planted with peas or fodder beans (V. faba) for at least 20 years. Soil sampling and extraction of cysts can be carried out, but often small infested areas may be missed during sampling.
When growing vegetable peas for seed, varietal sweeps are carried out:
- first – in the phase of 4-6 pea leaves. Plants with anthocyanin coloring in the axils of leaves, sick, advanced and retarded in growth and development are removed;
- the second – at the beginning of flowering. Plants with anthocyanin coloring in leaf axils, sick, advanced and retarded in growth and development, with colored flowers are removed;
- third – in the phase of the end of flowering – beginning of bean formation. Plants with anthocyanin coloring in leaf axils, sick, advanced and retarded in growth and development are removed;
- Fourth is the phase of 2-4 beans in the biological ripeness. Plants differing in bean shape and maturity are removed.
Approbation of seed crops is carried out in the phase of maturity of the lower beans in most plants.
Peas are harvested for seed at 18-21% moisture content by direct combining. During threshing and subsequent processing of seeds, special attention is paid to the inadmissibility of mixing of seeds of different varieties and reproductions. For this purpose, harvesting of one variety begins with higher reproductions with subsequent transition to harvesting of lower reproductions (e.g.: nursery breeding super elite). When transitioning to another variety, other harvesters and seed-cleaning machines are used or they are thoroughly cleaned from the seeds of the previous variety.
There should be no time gap between harvesting, cleaning and drying to obtain quality seeds. Therefore, immediately after receipt of the crop from the field, pre-cleaning is carried out, and when the moisture content of the seeds is higher than standard – and drying. Processing of pea grains intended for seed purposes is carried out depending on the moisture content before drying at the following temperature regimes:
- at moisture content of 27% and above, the permissible temperature of the coolant is 25 °C;
- at 21-27% moisture content – 28 °C;
- at 18-21% – 32 °C;
- up to 18% – 40 °C.
When large volumes of pea seeds are produced it is advisable to use grain-cleaning complexes (ЗАВ-20, ЗАВ-40) in combination with recirculation dryers.
Pea seeds, dried to a moisture content of 13-15%, cleaned and sorted, stored in dry rooms equipped with ventilation systems. Storage facilities form a specific complex of storehouse fauna, represented by over 20 species of invertebrates belonging to 8 orders, among which mites, cereal moths (Bruchidae), barn moth (Nemapogon granella) and cereal moth (Sitotroga cerealella) prevail.
To prevent seed damage during storage, a number of agrotechnical and organizational measures are carried out:
- Cleaning and repair of storage facilities (there should be no rough, uneven places, cracks and splits inside the granaries).
- Equipping windows with nets to prevent birds from entering the storage, doors must be tightly closed.
- Do not allow storage in the storage room of seeds with waste from seed cleaning.
- The humidity of grain should be maintained no higher than 14%.
The method of mass catching butterflies on pheromone traps is used to protect seeds from scale pests.
Thermal disinfestation – freezing by opening windows in winter cold period – is used for grain pest control.
Within P. sativum, there is considerable genetic variation among species grown in Europe. A related species, Pisum abyssinicum, does not appear to be separated by any genetic barriers, but produces fine-grained and very starchy pea seeds. These are old African mountain species, and because of the ancient use of varieties based on local ecotypes, there was much material of interest to Mendel. His differences between tall and dwarf plants, round and wrinkled seeds, and yellow and green color still underlie the description of all pea species produced commercially.
Although Mendel’s work with peas was instrumental in defining the foundations of genetics, as early as the 16th century many cases of pea varieties produced by natural selection from natural variations were recorded. But it was not until the mid-18th century that the first known crossing of selected lines to produce varieties was made. This gave Mendel a wide range of pea varieties to work with. He focused on such parameters as pod color and characteristics, presence of thread or parchment in the pod, seed shape and color, as well as on breeding and developing varieties with long internodes, producing tall varieties, and varieties with short internodes and reduced internode length, producing a fasciated group of flowers at the top of the plant.
Thanks to recent improvements in the study of pea genomics, methods such as marker-assisted selection (MAS), which identifies a specific location in the plant’s DNA sequence to identify specific markers, tend to underlie all traits. These include disease resistance, plant architecture, seed quality and other traits. Such methods will increase the efficiency with which breeders can select plants with the desired combination of genes throughout the process of variety development.
Wet growing conditions can increase the length of shoots and determinancy. Botanical determinacy can be achieved by breeding for apical determinacy, in which the flowers and subsequent pods are clustered close together. Such a variety may be more suitable for a single mechanized harvesting operation. Recently, modern pea varieties have been further developed to produce a stiffer stem that holds the plant in a more upright position and “afila” varieties that have leaflets turned into tendrils. The tendrils in afila varieties tend to intertwine with each other and provide mutual support.
Such morphological changes have greatly improved the agronomic characteristics of peas, allowing them to be grown in a wide range of geographic areas and used in large-scale harvesting operations.
Older, less determinate varieties are suitable for small-scale and horticultural production, where harvesting is done by hand and multiple harvests from the same set of plants can be harvested to extend the productivity cycle.
Between 1968 and 1984, the agronomic potential of a number of genetic traits controlling foliar characteristics was studied at the John Innes Centre in the UK, primarily in a number of independent spontaneous mutations from Argentina, Russia and Finland, where examples of peas with tendrils (afila gene) replacing leaflets created significant new commercial innovations in both vines and combination peas. This trait could help in providing mutual support for the plants, since the tendrils could intertwine with each other and the risk of lodging in the crop could be reduced. It was also expected to reduce the risk of disease in wet conditions and provide more uniform ripening. The afila (af) mutation in peas has been widely used since the early 1970s after the suggestion that additional tendrils might contribute to the stability of the combined crop (Snoad, 1974). The completely “leafless” pea was one of the original ideotypes for the dry pea breeding program at the John Innes Institute and has since been widely used by private breeders. The first “leafless” variety was bred in Great Britain in 1978 as the “Philby” variety. The leafless ideotype has tendrils consisting of substituted leaves and stems arranged on stems. This “leafless” ideotype was capable of producing enough photosynthate to not restrict the development of the shell, i.e. seeds, at normal agronomic plant abundance. However, when grown at low planting densities, this ideotype was found to be limited, limiting total plant biomass and thus potential yield (Hedley and Ambrose, 1981).
The solution was to retain the afila allele but return to using wild-type seedpods. Increased photosynthetic area solved the problem of the completely leafless form, and the “half leafless” model has been adopted by most of the pea-growing world as the parent material for the past 30 years to create many commercially successful varieties for fresh market, home and garden, freezing and canning, and combination dry peas.
Stiffness of the above-ground stems is of great agronomic importance for commercial pea production because this trait allows the crop to remain upright (especially during periods of inclement weather and before harvest), reduces disease risk, and greatly facilitates mechanized harvesting. Pea stems inherently remain weak at the base, and breeders continue to improve this trait now that genetic variation has been identified for this trait (Zhang et al., 2006).
Disease resistance is also a major goal of plant breeding. Peas are susceptible to several major fungal pathogens that are commonly found in many major growing regions and, in particular, where peas have been cultivated for many years. The fungi tend to evolve rapidly and develop strains that overcome some of the characteristics of resistance. In the case of pea powdery mildew (Erysiphe pisi), resistance has been found to be due to three genes that have been introduced into many modern cultivars. Today, the original resistance gene identified in 1975 is still well conserved, and there are fully or partially resistant varieties that are widely used.
Bacterial infestation of peas (Pseudomonas syringae pv. pisi) is known to exist in several racial forms. Most varieties developed in Europe are completely resistant to race 2, but not to race 5.
Wilt diseases caused by soil root fungi such as Fusarium oxysporum can result from accumulation of the pathogen in the soil after pea cultivation for a long period. F. oxysporum occurs in several races, with races 1 and 2 being the most common in Europe, while several other races (4, 5, and 6) are common in the United States. Resistance has developed to these races, which also appears to be fairly reliable (Porter et al., 2014). As for the other pathogens, varieties have been selected from germplasm showing varying degrees of resistance. In the case of pea downy mildew (Peronospora viciae), several races and pathotypes have been identified (Stegmark, 1994), and no fully resistant varieties could be developed, although a good level of resistance to the prevailing races in some regions is now being achieved. Recently, resistance to other diseases, such as pea enation mosaic virus and seed-borne pea mosaic virus, has been developed.
Very light and sandy soils are unable to retain sufficient moisture during dry seasons, and pea yields are greatly reduced by drought. Although the afila trait is thought to help reduce the effects of drought stress, even between afila varieties there are indications of varietal differences in drought tolerance (E. Uber and A. Biddle, 2011, unpublished). Often crops under drought stress become more susceptible to diseases affecting the root and vascular system, particularly fusarium wilt (F. oxysporum pv. pisi). A multi-partner EU research project is currently underway to develop crops with improved resistance to drought and Fusarium wilt (ABSTRESS, 2013).
The color of peas, especially for freezing, should be bright and uniformly green. In some seasons, a proportion of pale or “light” peas may be present during excessive growing season. Some varieties are more susceptible to this than others, although in general, aphyllous varieties are less susceptible to such problems. The loss or retention of green color of vining and marrowfat pea seeds is an economically significant quality parameter. Work is being done to identify seedling green color markers that may be more resistant to chlorophyll loss or discoloration. Lines with stable green color have been identified and used to create recombinant inbred lines with corresponding maps to identify genetic loci involved in seed color stability (Domoney et al., 2009).
Taste is generally mild and characteristic of peas, and varieties should have no extraneous flavors or bitterness. Sweetness was determined using marker technology (Domoney, 2011). Biochemical changes in seed composition during ripening are determined and quantified. This not only allows specific stages of pea development to be associated with compounds and groups of compounds, but also indicates considerable variation between varieties in the relative amounts of compounds that likely affect quality. The same is true for the content of a group of compounds known as saponins, which are often associated with bitterness characteristics in foods. Differences in saponin content between developmental stages and varieties are likely relevant to quality, and this information is used by breeders to breed lines of peas with these desirable characteristics.
Most new varieties of peas have been obtained by traditional crossbreeding and selection. There have been some developments in genetic manipulation to produce lines with specific insect resistance from Phaseolus by a group from Australia, but this material has never been commercialized, and commercial genetically modified pea varieties are not currently used. New variations are created in non-genetically modified ways through induced mutation programs, and some developments from this method have been commercialized, such as in the production of super-sweet pea lines and herbicide resistance.
Green (vining) pea varieties
Green peas can be divided into sweet and starchy varieties. Sweet varieties have grains with complex starch and seeds that are deeply wrinkled when dry. They are used for canning and freezing in Great Britain, other European and Scandinavian countries, the United States, Canada, Australia, and New Zealand. Starchy peas have simple starchy grains, the dry seed is smooth and spherical, and are grown mostly for canning in southern Europe. The technological properties of the two species are quite different. In addition to being less sweet, smooth-seeded peas have a floury consistency, and the canned product may contain herbs and spices.
Most varieties of peas used commercially are white-flowered. Breeding white-flowered varieties is facilitated by the fact that peas are self-pollinating and therefore not at risk of cross-pollination from insects, etc.
Green peas in practice are grouped according to the time elapsed from sowing to ripening. A difference of 16 days is observed between the earliest and the latest varieties with wrinkled seeds, which are in the “first early” and “main crop” groups, respectively. Between these two extreme groups are the “second earliest” and “early main harvest” groups.
The varieties are then described according to their agronomic characteristics. Harvest dates are called relative maturity, or days earlier or days later compared to a standard variety. Extreme early maturity can be a characteristic useful for production, although yield is often sacrificed for early maturity. Extreme lateness may only be useful for the fresh market sector because processors cannot extend the processing season at the plant because it may conflict with optimal harvest times for other vegetables.
Pea size can vary from season to season, but usually the seed size of a particular variety is within the average range. In Europe, seed size is determined by diameter, with large peas >10.2 mm, medium peas >8.75-10.2 mm, small peas >7.5-8.7 mm, and very small peas (also known as petits pois) <7.5 mm.
Almost all commercial varieties have a relatively determinate habit, i.e., flowering and haulm usually terminate, which ensures relatively uniform ripening. Many commercial varieties in Europe are semi-deciduous, although a number of common deciduous varieties are also grown. Semi-deciduous varieties are not always preferred by growers in countries with drier climates, such as the United States, because there is a perception that these varieties are more susceptible to drought. Sooner maturity and haulm length are often related, as sooner maturity can be achieved by flowering at the lower node. Therefore, it is sometimes the case that early cultivars can be too short and late cultivars can be too long. The length of the haulm is also affected by soil type, area, and season, but this is not such a problem with full pea harvesters (viners). Very tall varieties are often more prone to lodging, even though they have aphylla property. Lodged crops are more susceptible to fungal attack when wet conditions are possible. In addition, lodged crops are difficult to harvest by hand for the fresh market.
Disease susceptibility is an important characteristic of pea varieties because they can seriously affect pod and pea quality. Resistance to powdery mildew (Erysiphe pisi), fusarium wilt race 1 (Fusarium oxysporum f. sp. pisi), and relative resistance to pea downy mildew (Peronospora viciae) are examples of some resistance traits available.
Varieties grown for large-scale commercial freezing or canning are usually determined by the processor, often in consultation with growers. Ideally, all varieties in a harvest program should yield peas of the same size and color, unless a proportion of other varieties are required for a particular purpose, so that if two varieties are to be processed together, the resulting product will be acceptable. Most processing plants run peas for 6 to 8 weeks. Several varieties, each in their respective maturity groups, are required to achieve the required season length. Controlling the timing of sowing is also necessary to ensure the required harvest period, and this area will be discussed later.
Most pea breeders around the world participate in variety trials in various areas of pea-producing countries. These trials are often conducted by the breeders themselves or they allow their varieties to be evaluated and compared with others in independent trials funded by growers, processors, government agencies or universities. Each trial provides data on field qualities, and in some cases evaluates the quality of pea processing after harvest. An example in the UK is the variety trials conducted by the Processor and Producer Research Organization (PGRO, 2014).
Currently, there are a large number of varieties available for use as harvested or fresh market peas. Of particular importance are variety characteristics such as ripening time to harvest (this is a relatively stable characteristic), pea size profile (again a very stable characteristic), haulm length and disease resistance. Environmental factors influence crop growth and, in particular, haulm length and yield. Therefore, the value of the data obtained from variety trials must be considered depending on the geographical area or soil type of the intended crop. Nevertheless, such data are useful because they are often accompanied by data from a well-established variety for comparison.
Many varieties of green peas are traditionally deciduous. In addition, most are susceptible to powdery mildew, which is a concern in temperate areas where peas are grown for long periods of time. Current control of it relies on the use of fungicide seed treatments. Powdery mildew affects crops late in the season and is of concern only for those varieties that are planted late. The main feature of petits pois varieties is that most of the production is in the category of small (>7.5-8.7 mm) and very small (<7.5 mm) seeds. Most commercially available varieties grown in Europe have very similar maturity dates, and there are fewer opportunities for a fully integrated sowing and harvesting program.
In most production systems, peas are harvested by hand, and in some cases peas are picked several times before the crop reaches maturity. This is especially true for varieties grown as chard, where peas are grown in beds and can be supported on wire or trellises. Multiple harvesting may also be the preferred method in much smaller production systems. With the exception of chard and sugar snap peas, there has been very little selection of varieties for the fresh market, and generally either older varieties or specific varieties selected from the broader range of peas currently available are used. There are specific criteria for fresh peas that focus on pod characteristics. Length, color, size and number of peas in the pod are basic characteristics that can vary depending on the requirements of the retailer. In addition, haulm length, disease resistance, and time of harvest are important factors. Early-ripening varieties tend to have shorter haulm lengths and lower yields than late-ripening varieties. Resistance to powdery mildew is an advantage for late-season crops because the disease is favored by warm, dry daytime temperatures and high humidity at night, conditions more typical of late summer. Examples of early, main and late varieties used for hand picking in the fresh market are Early Onward, Feltham First, Elvas, Onward, Kelvedon Wonder, Hurst Greenshaft and Ambassador.
Pea pods, which lack more than minimal wall fibers and produce virtually no filaments when the pods are young, contribute to the formation of mangut types, which generally fall into two categories: those harvested as flat pods before the peas grow in size, known as snow peas; and those harvested as plump pods, where seeds develop inside the pod, known as sugar snap peas. Both types favor stringless pods, which have virtually no parchment inside the pod and no membranous filament running along the apex of the pod from base to tip (McGee and Baggett, 1992). Pod color also varies, and there are a number of chard varieties with green, yellow, or purple pods.
Early in pea breeding in France, a high-growing variety with flat pods was discovered and commercialized in the U.S. to produce a number of pea varieties such as Sugar Ray, Sugar Bon and Sugar Mel, while yellow-flowered varieties such as Golden Sweet and purple-flowered Shiraz are already available. Varieties with flat pods include Oregon Sugar Pod and Snowbird.
In the 1940s, it was discovered that there was an easily extractable arabinoxylan, tragacanth gum, a form of soluble dietary fiber that is present in the walls of pea pods and was thought to give a smooth texture in the mouth when eating sugar snap peas. This led to breeding studies that attempted to develop a shorter pea with high pod density, but whose fresh pods could be harvested mechanically at a suitable harvest time. The Cygnet variety was registered but never effectively developed.
Varieties of dry (combination) peas
Combined peas are harvested dry to be used either for human consumption or to make food for animals, fish, or pets. In the United Kingdom, the varieties of peas harvested in dry form consist mainly of white, blue, and green marrowfruit peas. Most of them are now of the semi-leaf ideotype. In many countries the varieties are mostly white-flowered, but a small number of colored varieties are grown for specialized markets. In the tropics, however, many varieties with colored flowers are produced for human consumption in the local market and are also grown in the United States and Canada for export to the Indian subcontinent and Africa. Colored varieties produce a light brown skin color, often with darker pigmentation. These varieties are usually round and smooth-skinned.
Combined peas are usually classified by flower color and seed type. Seed size depends on growing conditions, but a small number of small-seeded varieties are grown. Of the white-flowered varieties, the marrowfoots are blue-green, large, dimpled and toothed. Varieties in this group are important for human consumption and are used for sale in dry packets, exported for use as a pea snack or canned as large “processed peas.” They are suitable for a wide range of soil types, but are relatively late maturing and less suitable for northern temperate climates. They are also susceptible to preharvest discoloration and require care during harvest to maintain quality. Most marrowfruit is grown in the United Kingdom.
White peas have a white/yellow seed coat and are usually round in shape. Although it is mainly used for animal feed, some varieties of peas are used in canning, as pea meal, or in prepared foods. White-flowered pea varieties are usually the highest yielding and are suitable for a variety of soil types. They are widely grown in Europe, the United States, and Canada.
Blue peas are so named because of the blue-green color of the seeds and green cotyledons. The seeds are usually round and smooth-skinned. They are used for canning as well as micronization in pet food production. Most varieties have a short straw length, stand well in the field until harvest and have good disease resistance. Yields are usually high, but blue peas have the potential for early maturity.
Straw strength is important for successful mechanized harvesting, and resistance to pea diseases caused by powdery mildew reduces the need for chemical seed treatments.
Seeds of colored varieties can be dimpled and indented or smooth and round. The produce is used in specialized markets or for human consumption. Most of the flowering varieties are grown in tropical countries, where peas are used as the main source of protein in dhal or falafel dishes. Older varieties are common leafy types and are indeterminant; they are used as silage for whole crops.
Most varieties in northern countries are sown in the spring, but in countries where rainfall is scarce or temperatures are too high during the summer months, some varieties have been bred for fall sowing. However, peas sown under winter can be susceptible to frost damage and disease. Successful varieties have a long growing season to withstand cold conditions and ideally should be grown in areas where temperatures remain low to prevent excessive vegetative growth (Eteve, 1985).
Experience growing winter peas in continental Europe has shown their susceptibility to diseases under mild winter conditions, especially Mycosphaerella pinodes, which causes severe leaf spot and pod spot. In addition, a seed-borne pathogen that causes bacterial damage to peas can be a problem when late frost damages leaf tissue early in flowering. An approach has been taken to develop varieties with a later flowering date to avoid the risk of frost damage (Eteve et al., 1999). In Europe, the variety Lucy bred by INRA France has had some success, and the experience of growing winter peas and durum wheat in a mixture has also had some success in France.
Autumn peas with colored inflorescences (dun or Austrian winter peas) are sometimes grown in the United States, especially where water supplies are limited during the summer months. Autumn peas are also often grown as a forage crop or green fertilizer in these areas.
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