Grain legumes

Economic importance

Grain legumes occupy second place after cereals as the main source of food in the world. The term “legumes” refers to the edible seeds of pod-bearing plants.

Grain legumes are cultivated to obtain seeds with a high protein content. According to the method of use, they are divided into food, fodder, industrial and universal crops. Common bean and lentil are characterized by high taste and culinary qualities and are used for human food. Grass pea, chickpea, faba beans, white and yellow lupin are used for the production of compound feeds, although in some countries chickpea and white lupin seeds are eaten. Until recently, soybean was used as an industrial oilseed crop. At present it is used mainly as a fodder and food crop, while retaining its importance as an oilseed raw material. In terms of versatility of use, soybean has no equal among field crops. Pea is also distinguished by universal use; it is used both for food and for animal feed.

According to zootechnical standards, 1 feed unit should contain 110–115 g of digestible protein; the actual content is 96 g, i.e. 83–87% of the norm. Protein deficiency leads to 20–30% overconsumption of feed per unit of livestock product and is one of the obstacles to further increasing animal productivity.

Grain legumes, possessing high fodder value, also improve the assimilation by animals of feeds from other crops with low protein content.

The protein content in the harvest of grain legumes is determined by the variety and region of cultivation, but primarily by the conditions of symbiotic nitrogen fixation, i.e. by the agrochemical parameters of the soil and moisture supply of the plants. On acidic soils poor in nutrients, nitrogen fixation is weakly active or does not occur at all; plants experience nitrogen starvation, and the yield and content of crude protein in green mass and seeds sharply decrease. A lack of moisture on nitrogen-poor soils acts similarly. For these reasons, the protein content of the same crop is 10–15%.

The protein of grain legume seeds is distinguished by its completeness for use as feed. The content of essential amino acids is 1.5–3 times higher than in the protein of cereal crops. Thus, 1 kg of soybean seeds contains 6 times more lysine than 1 kg of wheat.

The seeds of some grain legumes contain a fairly large amount of fat: soybean — 16–27%, chickpea — about 5%, white lupin — up to 10%, which also contributes to higher fodder value.

In nutritional value, 1 kg of grain is equivalent to 1.1–1.4 feed units, and the supply of digestible protein is from 160 to 200 g. The vegetative mass is used for preparing hay, haylage, grass meal and for green fodder. Ensiling the green mass of grain legumes with maize or other crops increases the protein balance of the silage. Mixed crops of legumes and cereal crops make it possible to increase the fodder value of the latter.

The industrial raw-material importance of grain legumes lies in the fact that their seeds are used for making groats and flour, confectionery, canned goods, oils, food and feed concentrates. Vegetable canned goods are produced from unripe seeds and fruits. Soybean seed oil has food and technical importance. The enzyme urease and bean protein are used in medicine. Soybean and grass pea seeds serve as raw material for the production of casein, glue and plastics.

Agronomic importance lies in ensuring a large harvest of plant protein; they deplete soil nitrogen less than non-legume crops. Despite the fact that symbiotically fixed nitrogen is removed with the harvest, more nitrogen remains with the organic residues of grain legumes than with the residues of other crops, so they have proven themselves as good preceding crops in crop rotation. The root system of many legume plants is capable of assimilating nutrients that are difficult for other crops to access, for example, trisubstituted phosphates.

Alkaloid varieties of yellow lupin are cultivated as green manure on sandy soils, and narrow-leaved lupin on loamy soils. In this case, green mass yields of up to 30 t/ha are formed. Some grain legumes are grown as intermediate crops in different zones of the country for green fodder and to increase soil fertility.

Importance of vegetable legume crops

Vegetable legume crops are considered a useful source of nutrients and are recommended by health organizations and nutritionists as a staple food. They are rich sources of vitamins, minerals and carbohydrates in the human diet and a useful source of protein and energy in livestock diets. They represent an important source of protein for vegetarians and have a low glycemic index (Rizkalla et al., 2002). Legumes are an important food product in tropical and subtropical countries, where they are second only to cereals as a source of protein. They are also recognized as a food with significant potential health benefits. They contain complex carbohydrates (dietary fiber, resistant starch and oligosaccharides), protein with a good amino acid profile (high in lysine), important vitamins such as B vitamins, folates and iron, as well as antioxidants and polyphenols.

Before consumption, legumes are harvested, processed and processed in various ways and subjected to several primary and secondary processes, such as cleaning, dehulling, peeling, grinding and crushing. In many developed countries, there is very little growth in interest in using whole legumes and their milled components, especially flour and fractions such as protein, starch and fiber, and in using them in food products. There are new developments in the use of processing technologies, such as extrusion cooking, including these ingredients for the production of special food products such as pasta, baby food, snacks, dry soups and pet food. In addition, research is underway on the use of legume ingredients in pharmaceutical or “nutraceutical” products (Carbonaro, 2011).

Sown areas and cultivation regions

In world agriculture, grain legumes occupy 135–160 million ha, which is approximately 13% of the area sown to cereals. The largest sown areas are in India and China. The gross harvest is 230 million t, or 9 times less than that of cereals. The average yield in the world is 1.5 t/ha.

In the USSR, by 1984, grain legumes occupied 6.7 million ha; in Russia, 1.2–2.0 million ha, with yields in the 1990s of 1.2–1.6 t/ha. The gross harvest was 1.8 million t. The most widespread crop in our country is pea. In terms of sown area, which was 4.95 million ha, and the harvest of pea seeds, the USSR ranked first in the world. A large share of sown areas also fell to soybean and lupin. Common bean, lentil, chickpea, grass pea and faba beans are cultivated on small areas.

In the dry areas of the steppe zone, drought-resistant chickpea and grass pea are sown; on fertile clay and loamy soils of the Baltic region, Polesie, the central part of the forest zone and the Cis-Urals, faba beans are high-yielding; on sandy soils, yellow fodder lupin is grown.

In the Far East, in some regions of the North Caucasus, Ukraine, Moldova and the Lower Volga region, soybean is the most valuable crop.

Taxonomy

The legume family (Fabaceae, formerly Leguminosae) is an extensive and very large botanical family consisting of more than 450 genera and more than 12 thousand species. Many species are important as sources of food for humans and animals.

Legume crops have been cultivated in various parts of the world for more than 6000 years. Wild forms of many modern legumes do not occur, although, according to Vavilov, some legume species appear to be associated with certain identified centers of origin. For example, some species of common bean (Phaseolus sp.) he assigned to the New World (North and South America), and some others identified as Phaseolus to the Old World. However, those species that were assigned to the Old World and previously identified as Phaseolus are now correctly classified in the large and widespread genus Vigna.

The legume family was divided into three main subfamilies: Caesalpinioideae, Mimosoideae and Papilionoideae, but recently Caesalpinioideae was further divided into several genera, including the tribe Cercideae (Group, 2013), which contains a small group of tropical and temperate woody plants with flowers similar to those of Papilionoideae.

The subfamily Mimosoideae includes 82 genera and more than 3200 species. Like Caesalpinioideae, species of Mimosoideae are mainly tropical woody plants, but there are several species from the temperate climate. Woody perennial legumes are widely distributed, and many species of this group have the ability to fix atmospheric nitrogen, so they have colonized many regions of the world with low soil nutrient content. They are also used commercially for timber or various extracts such as gum and dyes.

The subfamily Papilionoideae (or Faboideae) is the largest group of legumes, including about 650 genera and almost 19,000 species (Lewis et al., 2005).

As representatives of the large-seeded legume group of the family Fabaceae, pea and common bean belong to several separate taxonomic groups. Among them, three lineages have a number of groups that contain cultivated plants.

The most economically important group is Phaseoleae, which includes soybean (Glycine max), species of Phaseolus spp. and cowpea (Vigna unguiculata). The second group, Genisteae, contains lupin (Lupinus spp.), of which there are three economically important grain legume species: white lupin (Lupinus albus), narrow-leaved lupin (Lupinus angustifolius) and yellow lupin (Lupinus luteus). The third taxonomic group, Fabeae, contains the so-called cool-season legume crops, which include garden pea (Pisum sativum) and horse or faba beans (botanical name broad bean Vicia faba), as well as lentil (Lens sp.) and grass pea (Lathyrus sp.).

Fabaceae:

1. Papilionoideae: Genisteae (lupin), Phaseoleae (soybean, vigna, common bean);
2. Fabeae: grass pea, lentil, pea, vetch;
3. Mimosoideae;
4. Caesalpinioideae.

Botanical description

Legumes (Fabaceae) are dicotyledonous annual and perennial plants; most cultivated vegetable and grain legumes are annual.

Seeds

The seeds are of various shapes (from round to flat and angular), sizes and colors. The seed consists of a seed coat and an embryo. At the place where the seed attaches to the fruit, the seed hilum remains; in common bean, there are tubercles of the chalaza and micropyle. The embryo consists of two fleshy cotyledons and the embryonic root and bud enclosed between them, from which the aboveground part of the plant subsequently forms. The cotyledon represents the embryonic leaves, in which the reserves of nutrients used during germination are concentrated.

Biological characteristics

Growth phases (phenological phases)

Growth phases of grain legumes:

• germination;
• emergence;
• stem branching;
• budding;
• flowering;
• pod formation;
• ripening;
• full ripeness.

Intensive cultivation technology

Post-harvest seed processing

After harvesting, the seeds are immediately passed through preliminary cleaning machines of the type OVP-20A, ZAV-10, ZAV-20, K-527. At seed moisture less than 17%, further cleaning and sorting are continued on machines OS-4.5, SM-4, K-523 or on grain cleaning complexes ZAV, KZS with attachments SPL-5 and SP-10.

At moisture more than 17%, after preliminary cleaning they are dried on active ventilation dryers in an aggregate with air heaters of the type VPT-400, VPT-600, TAU-075, TAU-1.5 or shaft dryers. During drying, the following regimes are observed:

• at seed moisture before drying more than 27% — heat carrier temperature 25°C;
• at moisture 21–27% — temperature 28°C;
• at moisture 18–21% — temperature 32°C;
• at moisture less than 18% — temperature 40°C.

The layer height should be no more than 50–70 cm. Air consumption per 1 h is 1000–1500 m³/t of seeds. The drying duration under the indicated regimes is 2–3 days.

Among shaft dryers, SZSH-8, SZSH-16, SZSH-16R, T-662 (GDR), M-819 (Poland) are used.

If the capacity of the drying units is insufficient for the entire batch of wet grain, the excess is placed for temporary storage in floor units or active ventilation bins BV-25, BV-40.

Seeds dried to standard moisture of 13–16% depending on the crop, cleaned and sorted, are stored in dry ventilated rooms with a layer height of no more than 2.5 m or in bags up to 8 rows high and no more than the length of 2 bags wide.

Cultivation for green mass

The maximum yield of green mass of legume crops of high quality at the lowest cost is obtained when cultivating perennial legume grasses in pure stands. However, due to the limited area of such stands for obtaining green mass used for the production of grass meal, haylage and summer animal feeding, annual legume crops are grown. The seeds of field pea, narrow-leaved lupin, common and hairy vetch are almost not used in the feed industry; they are grown mainly for green mass. For green mass, crops of typical grain use are also cultivated — garden pea, faba beans, grass pea, soybean and white lupin.

The agronomic practice of cultivating grain legumes for green mass is mainly similar to the agronomic practice of cultivating them for seeds. Only the seeding rate is increased by 10–15%.

Harvesting for green mass is carried out during the period of full seed filling in the middle pods, when the lower pods begin to yellow or brown, the upper ones finish seed filling, and the plants have not yet shed their leaves. When harvested in the flowering phase, most crops accumulate only 30–40% of the protein from the maximum possible.

When there is a need for early harvesting for green mass on a farm, it is advisable to sow several species of grain legumes with different dates of yield formation. The different onset of flowering and seed filling phases will extend the green mass harvesting period by 40 days with a minimal shortfall in yield.

Mixed crops of grain legumes

In farm practice, the cultivation of cereals for green mass is common, for example, oats, winter rye, maize, sorghum. However, feeds based on cereal crops contain little protein. Thus, the green mass of oats contains 2 times less protein than the green mass of common vetch; the content of digestible protein in the green mass of maize is 2.5 times less than in garden pea, 3 times less than in soybean, and 3.5 times less than in grass pea.

When growing grain legumes in mixed crops with cereal crops, the amount of protein in the green mass increases, and the assimilability and digestibility of cereal protein improve. Thus, the green mass of oats contains 7.8% digestible protein, while in a mixture of oats and vetch it is 1.6 times more. Adding soybean to maize crops increases the content of digestible protein by 2.3 times.

The protein content of legume-cereal mixtures is determined by the ratio of the components. Thus, if in a vetch-oat mixture the share of vetch is 55–60% and oats 40–45% by mass, the content of digestible protein in the mixture reaches 14%; if vetch is only 20–30% in the mixture, the protein content in the mixture is no more than 9%.

Plant protection system

Pests and pea diseases and common bean diseases can reduce yield, spoil quality, threaten the reliability of production and disrupt the capacity of packing and processing enterprises. Very rarely do dramatic losses occur caused by disease infection on an epidemic scale or an unusually strong infestation by a certain pest. Both are often related to climatic conditions. There are less serious losses, for example, when spots of diseased plants appear, or when pest infestation is not very strong, and there are subtle and often unnoticed losses that may be the result of the gradual accumulation of a pest or a soil-borne pathogen, but gradually reducing viability and profitability.

Control methods currently increasingly rely on management and preventive measures rather than a direct treatment approach when symptoms or pests appear. Relying on synthetic pesticides is not recommended, and increasing attention is paid to forecasting, prediction and monitoring as a means of ensuring an avoidance strategy or a managed approach by determining the optimal time for pesticide application and justifying their use. In many countries producing crop processing products, much attention is paid to the need to trace the crop from field to factory, where each input — agronomic, plant nutrition and pesticide application — is recorded by the producer, and these records remain available for verification for some time after harvest.

An assurance scheme known as Red Tractor has operated in the UK for several years as a voluntary standard set by the food industry, and a similar scheme is used in Europe (GLOBALG.A.P.). Both schemes include crop protocols that are standardized in agreement with retailers, food processors and traders to ensure transparency and food safety for the consumer.

In previous decades, many broad-spectrum pesticides were introduced, which were later found to have negative effects on the environment and non-target organisms. The fate of these old pesticides in soil or water is associated with the accumulation of residues that require many years to decompose.

Recent legislation has led to the withdrawal from production of many active ingredients posing a risk to the environment or the operator, and the introduction of new-generation pesticides is now possible only after strict tests conducted by manufacturers. Even then, new research can often find unexpected problems that may be related to the pesticide or its by-products.

At present, pesticides are used less and less, especially in Europe and increasingly in other countries, since pressure from retail requires crop producers for human consumption to guarantee quality, implying full transparency and justification of all measures, including pesticide application on the crop.

Thus, the management of pest and disease control has moved to an integrated approach using any practical methods of forecasting, prediction or monitoring before deciding whether or not to apply pesticides. This includes all aspects of farm management, starting with the use of healthy seeds, field selection, variety and crop rotation, frequent crop monitoring using monitoring systems if available, and a detailed understanding of the crop and the biology of the pest or pathogen.

Vigna and common bean (Vicia spp. and Phaseolus spp.) can be affected by a wide range of pests and diseases, and since these crops are grown in many regions of the world. More complete lists, together with illustrations of pests and their damage, as well as disease symptoms, can be found in a number of publications (Allen and Lennie, 1985; Kraft and Pfleger, 2001; Schwartz et al., 2005; Biddle and Cattlin, 2007).

Since all the described crop species are legumes, they can be hosts of the same organism even with minor differences in races or strains, especially in the case of fungal pathogens, and therefore, where common features exist, they are identified. In each case, symptoms, impact on yield, biology of the pest or disease, monitoring methods and determination of economic thresholds for justifying treatment are described.

References

1. Kolomeichenko V. V. (2007). Crop Production/Textbook. Moscow: Agrobusinesscenter.
2. Vavilov P. P., Gritsenko V. V., Kuznetsov V. S. et al. (1986). Crop Production. Ed. Vavilov P. P. 5th ed., revised and enlarged. Moscow: Agropromizdat.
3. Niklyaev V. S. (2000). Fundamentals of Agricultural Production Technology. Agriculture and Crop Production. Moscow: Bylina.