Cereal crops

In the world

Cereal crops account for about half of all sown areas of world agriculture. At the end of the 20th century, the sown area of cereal crops in the world was about 700 million ha, that is, 70% of the entire sown area; the gross harvest was 2100 million t; the average yield was 3.0 t/ha.

In Russia

For many years, the gross grain harvest in the USSR increased mainly due to expansion of sown areas. In 1940, the sown area under cereal crops was 110.7 million ha, whereas in 1984 it was 119.6 million ha. The increase in sown areas occurred in almost all years from 1940 to 1984, but especially in 1954-1958 during the development of virgin and fallow lands. Sown areas of cereals also expanded as a result of reducing the area of clean fallows.

During the same period, sown areas of winter and spring wheat, primarily high-yielding intensive varieties, barley, rice and grain legumes increased. At the same time, sowings of winter rye, maize, oats, millet and buckwheat somewhat decreased.

From 1940 to 1976-1980, the yield of cereals in the USSR increased from 8.6 to 16.0 dt/ha. Yield increases were noted for all cereal crops except buckwheat.

The gross harvest on average in 1976-1980 and 1986-1990 was 106.0 and 104.3 million t, respectively. In 1992 it was 106.9 million t, with a sown area of 61.9 million ha. However, the reforms begun in Russia in 1991 led to a sharp decline in grain production. On average in 1994-1998, the gross harvest was 70 million t; in 1998, less than 48 million t.

In 2001-2005 in Russia, the sown area of cereal crops was 43.7 million ha; the gross harvest — 78.1 million t; the average yield — 1.9 t/ha.

Root system

The root system is fibrous. During seed germination, primary (embryonic) roots are formed. In bread grains of Group I, the number of primary (embryonic) roots is up to 3-8; for Group II — 1. Embryonic roots function throughout the entire life of the plants; their importance increases under drought conditions.

Secondary (nodal, adventitious) roots are formed 12-18 days after emergence from underground stem nodes. For their rapid growth and development, optimal soil moisture is important; when the topsoil dries out, their growth is greatly slowed or completely stopped. A good yield of cereal crops is possible only with well-developed nodal roots. Secondary roots are of great importance for plants. Thus, when spring wheat develops only with primary roots, the yield is 65% of the yield of plants with developed primary and secondary root systems.

In tall cereal crops such as maize and sorghum, support (aerial) roots may form from stem nodes located close to the soil surface. They contribute to plant resistance to lodging and participate in the supply of nutrients.

The depth of penetration of the root system in cereal crops can reach 150-200 cm, but the bulk (75-90%) is located in the arable soil layer (0-30 cm). In the total mass of dry matter, roots account for about 20-25%. The most powerful root system is characteristic of maize, winter wheat and rye.

The structure of the root system and the nature of its development are determined by the plant species and variety. The most powerful root system is possessed by winter rye, oats and maize. In the roots, not only absorption of water and dissolved nutrients occurs, but also the formation of organic substances, for example, organophosphorus compounds, amino acids, amides, alkaloids.

Stem

The stem of cereal crops is represented by a cylindrical straw, hollow or filled with parenchyma (sorghum, maize). More often it consists of 5-7 internodes separated by special partitions — nodes; in maize and sorghum — 8-16. In long-stemmed maize varieties, the number of internodes can reach 25. Their number corresponds to the number of leaves.

Stem growth is usually called intercalary, since it occurs due to elongation of all internodes. Moreover, each new internode grows faster than the previous one. The upper internode is much longer than the lower one and reaches maximum length during flowering. It has the form of an S-shaped growth curve, in which at the beginning and end of the growing season its rates are slower, and in the middle, in the phases of stem elongation, heading and flowering, they are intensive.

Resistance to lodging depends on the thickness and strength of the internodes. The stem has maximum thickness in the middle part and minimum in the upper part. Its strength depends on the composition of mechanical tissue. It has the ability to form lateral shoots from underground stem nodes.

When secondary roots and lateral shoots form from the underground nodes of the stem, the tillering phase of cereal crops begins.

Leaf

The leaf of cereal crops is linear and consists of a leaf sheath and a leaf blade; at their junction there are a ligule — ligula — a thin colorless film, and auricles, which are systematic characters in identifying cereals of the first group. The ligule fits tightly to the stem and prevents water from penetrating inside the leaf sheath.

At the base of the leaf sheath, linear auricles, or horns — auricula — are formed on both sides, embracing the stem. The structure of the ligule and auricles in most cereal plants differs in the early phases of growth. For example, the ligule in wheat, rye and barley is short, often with cilia; in barley — very large, without cilia, semilunar; in rye — short without cilia, falling off early; oats have no auricles.

The number of leaves and their sizes differ among different cereal crops and varieties.

Inflorescence

The inflorescence of cereal crops is represented by two types:

• compound spike (wheat, rye, triticale and barley);
• panicle (oats, millet, sorghum and rice).

Unlike other crops, two inflorescences are formed on one maize plant — in the upper part of the stem a panicle with male flowers, while in the leaf axils — ears with female flowers.

Flower

The flower of cereal crops has two flower scales — the lower (outer) and the upper (inner). The outer flower scale in awned forms has an awn. The upper one is thinner and flat. Between the flower scales are the ovary with an anatropous ovule and two plumose stigmas, and three stamens (six in rice). At the base of the flower scales are two thin films — lodicules, which, swelling during flowering, cause the flower to open.

In wheat, the flowers are broad, multi-veined, with a longitudinal keel; in rye — very narrow, single-veined; in barley — narrow, almost linear; in oats — broad, with many convex longitudinal veins.

Fruit

Longitudinal section of a wheat grain:

1 — brush; 2 — endosperm; 3-5 — fruit coats; 6 — seed coat; 7 — aleurone layer; 8 — scutellum; 9 — plumule; 10 — embryonic stem; 11 — radicle.

The fruit is represented by a one-seeded caryopsis, usually called a grain. It contains a single seed covered by a seed coat, formed from two integuments of the ovule, and a pericarp formed from the ovary. The caryopsis consists of the embryo, endosperm and the seed and fruit coats fused with them.

In hulled bread grains, the caryopsis is covered by flower scales, which may fuse with it, as in barley, or only tightly enclose it, as in oats, millet, sorghum, rice. The embryo accounts for 2-12% of grain mass. The embryo consists of the embryonic root and stem, plumule and scutellum, which represents modified cotyledons.

The grain of naked wheat and rye is easily separated from the scales. The flower scales of millet, foxtail millet and rice tightly enclose the caryopsis; in hulled barley they may fuse with the caryopsis.

The endosperm makes up 70-85% of grain mass. Its tissues consist of parenchyma cells filled with starch grains, between which protein substance is located. The peripheral part of the endosperm, called the aleurone layer, does not contain starch; it consists of large cells filled with soluble protein substance. The aleurone layer contains enzymes and biologically active substances that regulate the process of grain germination.

The embryo is located at the base of the caryopsis on the convex side. It consists of the scutellum, connecting it with the endosperm, the plumule covered with rudimentary leaves, the primary stem and root. The embryo accounts for 1.5-2.5% of caryopsis mass in wheat, rye and barley, 2-3.5% in oats, 10-14% in maize.

The fruit and seed coats account for 5-7% of the total grain mass.

Proteins

Simple proteins are usually called proteins; complex ones — proteids. Simple proteins are represented by groups of albumins (water-soluble), globulins (salt-soluble), glutelins (soluble in acids and alkalis), prolamins, or gliadins (soluble in 70-80% ethanol). The last two groups are of greatest value, with an optimal ratio for baking of about 1:1.

The highest amount of protein is characteristic of durum wheat varieties. Protein content in grain for all cereals increases when they are grown from north to south and from west to east. Grain quality is influenced by climate dryness and nitrogen content in soil. For example, protein content in spring wheat grain grown in the Northwestern regions of the country is 12.6%, whereas in areas of Northern Kazakhstan — 17.3% (long-term data of the Central Chemical Laboratory of the State Commission for Variety Testing).

Protein content in grain is influenced by applied agricultural practices: for example, application of organic and mineral fertilizers, placement after the best preceding crops. Wheat grain harvested at the wax ripeness stage contains more protein than that harvested at full ripeness. Protein quality depends on amino acid composition, primarily valine, lysine, tryptophan.

Gluten

Flour quality is characterized by gluten content, which is a clot of water-insoluble protein (gluten) substances remaining after washing dough free of starch, fiber and other substances. Gluten contains a little fat, starch and ash elements. The highest-quality gluten is located in the center of the grain; its quality sharply decreases when grain germinates or is damaged by frost or pests.

The content of wet gluten varies in wheat from 16 to 50%, rye — from 3.1 to 9.5%, barley — from 2 to 19%.

The quality and yield of gluten depend on external conditions. Thus, in dry and hot weather the gluten content is higher, whereas damage to grain by the harmful turtle bug leads to a sharp decrease in content. Quality gluten can stretch in length without breaking and resists stretching.

Wheat gluten is the most valuable, and wheat bread is distinguished by increased porosity and digestibility. Rye gluten is less elastic and extensible.

Carbohydrates

Among carbohydrates, the greatest amount is starch, 80% of which by mass of all carbohydrates is contained in the endosperm. The rest is sugar, contained mainly in the embryo (about 1.5% of grain mass). Carbohydrates are concentrated in the central part of the caryopsis.

Depending on the nature of starch grains and their location in endosperm cells, grain is divided into mealy and vitreous. In the endosperm of mealy grain, the spaces between large starch grains are filled with small ones with thin protein layers. In vitreous grain, small starch grains are almost absent; protein layers are thicker and fill all spaces between large grains.

Starch content in grain increases when crops are moved from east to west and from south to north, that is, in the opposite direction compared to the change in protein content.

Fiber is a high-molecular polysaccharide contained in cell walls, grain coats and scales of hulled crops. Fiber content in small grains is higher than in large ones.

Fats

Fat content in grain varies from 2 to 6%. The content of fats and lipids is extremely uneven in grain; they are mainly concentrated in embryos: in wheat about 14%, rye and barley — 13.4%, millet — 20%, oats — up to 26%, maize — up to 40%.

High fat content in flour leads to its rancidity.

Ash substances

In hulled cereal crops, ash is mainly contained in the hulls; in naked ones — in the pericarp. During complex milling, most of the ash is separated with bran.

Ash substances are represented by compounds of phosphorus (up to 50% of the total mass of ash substances), calcium (up to 2.8%), potassium (up to 30%), sulfur, silicon, magnesium (up to 12%), etc. Their greatest amount occurs in the coat and scales.

Enzymes and vitamins

Grain also contains enzymes involved in life processes, for example, amylase (breaks down poly- and disaccharides), protease, maltase, cytase, diastase, lipase (breaks down fats), peroxidase.

Grain contains vitamins: B₁, B₂, B₆, PP, E, A.

Water

Water participating in physiological processes is present in grain in the form of:

• chemically bound, that is, part of molecules of substances in certain ratios; this water is characterized by constancy and inertness;
• physicochemically bound water, enters the grain in various ratios; may be in the form of adsorption-bound, osmotically absorbed or structural water;
• mechanically bound, or free, water; its amount can vary greatly; easily lost upon drying.

Nutrient removal with harvest

Nutrient removal with harvest of major nutrients by the cereal crop harvest, in % of biological:

• nitrogen 75;
• phosphorus (P₂O₅) — 79;
• potassium (K₂O) — 64.

Germination

The embryo absorbs water faster than the endosperm, which leads to uneven swelling of the grain and rupture of the coat. Larger grain with a dense coat, high protein and fat content requires more time for swelling.

The rate of water absorption depends on temperature, concentration of soil solution, structure and size of grain. The optimal temperature during swelling for cereals is 10-21°C. Vitreous or large grain absorbs water more slowly than mealy or small grain. For this reason, the more uniform the seed material, the more uniform the emergence. Hulled grains swell more slowly than naked ones.

In swollen grain, under the action of enzymes, hydrolysis of reserve nutrients of the endosperm occurs. Special enzymes cytase and amylase break down starch and hemicellulose of the endosperm into simple carbohydrates dextrin and maltose. The enzyme invertase converts sugars into glucose and fructose, which are used by the germinating plant for respiration and cell growth. The enzyme protease breaks down proteins to amino acids and ammonia; lipase breaks down fats to fatty acids and glycerol.

During grain germination, reserve nutrients are broken down with the formation of compounds from which plant organs are formed. D. N. Pryanishnikov established that endosperm proteins upon enzymatic breakdown form amino acids and small amounts of asparagine and glutamine. These substances react with carbohydrate breakdown products, thereby serving for the formation of new proteins in the growing embryo.

The beginning of germination occurs with the growth of embryonic roots, and then the stem. Elevated temperature slows germination, and upon reaching a certain limit — stops growth. Extreme temperatures above 30-35°C are destructive, and below 1-2°C lead to cessation of germination.

Uniformity of germination is negatively affected by lack of air and excess moisture. As seedlings develop, oxygen demand increases. For this reason, deep seed placement is undesirable, especially on heavy soils, as is the formation of a soil crust. Increased salt concentration slows germination.

Emergence

In the first days of life of cereal crops, intensive development of primary (embryonic) roots occurs. Then the stem begins to develop. In naked varieties, the stem appears near the scutellum; in hulled ones — under the flower scale and emerges from the upper end of the grain.

The optimal temperature for emergence and initial growth at usual sowing dates for bread grains of Group I is 6-12°C, Group II — 15-22°C. The minimum germination temperature for Group I is 1-2°C, Group II — 8-10°C. Physiological optima are: for Group I — 20°C, Group II — 25-27°C.

Emergence appears on the soil surface in the form of awls — stem shoots covered with a transparent leaf — the coleoptile. The coleoptile protects the stem and first leaf from mechanical damage during emergence from the soil. As soon as the leaf reaches normal size, the coleoptile dies.

The first leaf completes growth 6-11 days after emergence. Then, about a week after the first leaf unfolds, the second appears in its axil, and then at the same intervals — the third and fourth. At the same time, the root system develops. By the formation of the 3rd-4th leaf, embryonic roots branch well and penetrate to a depth of 30-35 cm. In the tillering phase they reach 40-50 cm; during stem formation — 60-90 cm. Growth is promoted by good soil moisture.

Emergence depends on many factors: characteristics of the crop, moisture, temperature, granulometric composition and soil density, sowing depth and seed germination energy. Warm and wet weather favors rapid emergence (after 4-6 days), whereas a sharp cold snap inhibits this process.

Tillering

In the tillering phase, adventitious (nodal) roots form from underground stem nodes, then lateral shoots appear. More often they form from the uppermost one, called the tillering node and located at a depth of 1-3 cm from the soil surface. The tillering node is a complex formation consisting of close nodes, from which secondary (adventitious) roots and stems (lateral shoots) form. Deeper placement of the tillering node increases plant resistance to lodging and opposition to unfavorable conditions.

Tillering consists in the fact that the bud located at the base of the first leaf enlarges, pushes it aside and forms a lateral shoot. Then in the axils of the lower leaves of lateral shoots, new buds form that can form lateral shoots of the second, third, etc. orders. At the same time, secondary roots form. Unlike embryonic roots, which form from the grain and penetrate to a greater depth, secondary roots form from the tillering node and are located mainly in the surface layer.

Good development of secondary roots is favored by sufficient soil moisture and availability of nutrients, primarily phosphorus. When the top layer dries out, secondary stems and roots do not form. In such conditions, only the main stem and primary root system are formed, which sharply reduces yield.

The first underground node forms on the 5th-7th day after emergence for most bread grains of Group I, or simultaneously with them — in bread grains of Group II and oats.

Light influences the depth of the tillering node. Lack of light leads to its shallow placement. Depth is also influenced by sowing depth, variety, soil type and temperature. Thus, at lower temperature the tillering node deepens; durum wheat varieties also form the tillering node deeper than soft wheat. Deeper placement of the tillering node in winter crops protects them from unfavorable conditions in the winter-spring period.

In cereal plants, the tillering node is a very important organ, since the formation of aboveground mass and root system, drought resistance, winter hardiness, etc. depend on its normal development. Even partial damage can lead to delayed plant growth, and death — to complete loss.

Total tillering (tillering energy) is the number of stems (shoots) developing from one plant. In field conditions, winter crops form 5-8 stems, spring crops — 2-3; under favorable conditions their number can reach 5-10 or more.

Productive tillering is the number of stems per plant that produce grain. When lateral shoots form late, grain does not have time to form and ripen on them. Shoots with unripe grain are usually called late tillers (podgon), and non-heading ones — undersowing (podsed). The higher the productive tillering, the more grain per plant, but the greatest yield per unit area is obtained with slight tillering and optimal stem density.

Under optimal soil and climatic conditions, maximum yield of cereal crops is achieved with total tillering of 5-8 shoots and productive tillering of 2-3. In winter cereals, productive stems are usually 3-6; in barley and oats — 2-3; in spring wheat — 1, sometimes 2; in maize — 1; in rice, millet and sorghum — 2-5. Large spikes and grains form on productive stems.

The dynamics of development of tillering shoots and nodal roots differ among cereal crops (V. N. Stepanova). For example, in winter and spring rye and oats, tillering and rooting occur simultaneously during the formation of the 3rd-4th leaf. In barley, winter and spring wheat, tillering shoots form at the stage of the third leaf, whereas rooting occurs with the appearance of 4-5 leaves. In millet, tillering occurs during the appearance of the 5th-6th leaf, maize — 6th-7th, sorghum — 7th-8th leaf. Nodal roots in these crops form with the appearance of 3-4 leaves. Earlier appearance of the root system compared with the beginning of tillering determines the ability of crops to better tolerate moisture deficit (except maize) in the first and subsequent periods.

All future parts of the plant are located in the tillering node; at the same time, reserves of nutrients are concentrated in it. Death of the tillering node in all cases leads to plant death.

The beginning of tillering in individual crops is noted at different times, for example, bread grains of Group I — with the formation of 3-4 leaves, bread grains of Group II — in the phase of 5-8 leaves.

The size of the harvest is determined primarily by the power of the root system and aboveground part. According to studies by A. L. Kursanov et al., conducted using the radioactive isotope method, roots, in addition to supplying plants with water and mineral substances, are capable of synthesizing amino acids and nucleoproteins.

Tillering energy and tillering depend on factors such as water-air, thermal, nutrient and light regimes, plant species and variety, seed quality, sowing date, seeding rate, etc. Tillering of cereal crops of the first group can proceed at a temperature of about 5°C, but tillering energy is weak. The optimal temperature for tillering is 10-15°C. Higher temperatures lead to a shortening of the tillering phase, resulting in fewer shoots.

In winter crops, if optimal dates and conditions are observed, tillering occurs in autumn.

The productive significance of the tillering phase is ambiguous. Thus, according to P. N. Konstantinov, A. I. Nosatovsky, P. P. Lukyanenko et al., the tillering phase is undesirable, primarily in arid regions. They believe that much water and nutrients are consumed for the formation of secondary stems, which causes poor nutrition of the main stem, and the grain yield of secondary stems is insufficient to compensate for the shortfall in grain from the main stem. Therefore, they call 1-2-stem plants the optimal type of spring crops for arid regions. The opposite point of view was held by V. R. Williams, V. E. Pisarev, S. A. Muravyov et al. They believed that due to good tillering, a large leaf mass develops, which contributes to the production of more organic substances for grain formation. Under favorable conditions, lateral stems can produce 30-50% of the grain yield. However, under conditions of sufficient moisture, strong tillering can lead to negative results.

Dense sowings are more prone to lodging, photosynthesis conditions and grain filling worsen, and harvesting losses increase. More often, the average number of productive stems per 1 m² is 350-400, providing a yield of 2-3 t/ha. In individual cases, an increase to 700-800 per 1 m² is possible.

Stem elongation

In the tillering phase, the stem (culm) begins to form in cereal crops. The internodes, initially appearing as transverse scars at the base of the embryonic spike or panicle, elongate. The beginning of stem elongation is considered the moment when a stem node can be felt inside the leaf sheath of the main stem at a height of 5 cm from the soil surface.

Sometimes the stem elongation phase is mistakenly taken to be simple elongation of the leaf sheath, for example, this often happens in autumn in overgrown winter crops. First the lower internode elongates, then the second, third, etc., with each new one outstripping the previous in growth. Such formation of the stem (culm) is usually called intercalary.

Heading (ear emergence)

The spike (panicle) and spikelets are laid down in the tillering phase. The heading phase is considered to have begun when one third to one half of the spike (panicle) emerges from the sheath of the upper (flag) leaf of the main stem. The formation of panicles in maize — tassels — occurs earlier compared to the female inflorescences — ears.

Further differentiation of the spike (panicle) begins at temperatures above +15°C. At the stage from stem elongation to heading (ear emergence), cereal crops have increased requirements for light, heat, soil moisture and nutrients, since this period is accompanied by intensive growth and formation of the spike (panicle).

The ratio of nutrients strongly influences the size of the spike. Excess nitrogen during this period delays the formation of the cone for several days and leads to the formation of a large number of spikelets. Excess phosphorus leads to accelerated formation of spikelets and a decrease in their number.

Flowering

Flowering — fertilization. In all cereal crops except winter rye, flowering begins soon after heading (ear emergence). Barley flowers before full heading, rye — 8-10 days after.

Flowering of cereals is divided into self-pollinating, for example, in barley, wheat, oats, millet, rice, and cross-pollinating — in rye, maize, sorghum. In self-pollinating plants, anthers mature while the flower is still closed, so pollen usually lands on the stigma of the same flower even before it opens. The most strict self-pollinator is barley, in which pollination occurs during heading and even earlier (closed flowering).

A spike, as a rule, flowers for 3-4 days, a panicle — 6-7 days.

At the onset of the flowering phase, development of the stem, leaves and spike stops. The greatest increase in fresh mass is noted in the heading phase, whereas dry mass — during the wax ripeness of grain.

Flowering reacts quickly to unfavorable weather conditions, for example, a sharp rise or fall in temperature, drought, rains and strong winds. In this case, incomplete pollination occurs, leading to partial grain setting in spikes, panicles, ears, the so-called "through-grain" (gaps in grain set).

Ripening

Ripening — the development of the ovary and the formation of the grain begins after flowering and fertilization. Early sowing dates, increased stand density, application of phosphorus-potassium fertilizers, and warm, clear, dry weather promote accelerated ripening. Conversely, in wet weather or under irrigation, and in thinned crops, the ripening process proceeds slowly.

High temperature and atmospheric and soil drought during the filling period lead to “scalding” or “capture” of the grain: filling is reduced, the grain becomes shriveled and wrinkled, which sharply reduces the yield and its quality. Very rainy and warm weather leads to “run-off” of the grain due to starch hydrolysis and leaching of soluble substances by water.

Normal ripening of cereal crops requires a certain sum of active temperatures. If harvesting is greatly delayed in rainy weather, this can lead to sprouting of grain in the ears on the root and in windrows. In the north of the European part of Russia and in Siberia, in rainy and cold weather, harvesting is often delayed, which can lead to damage of unripe grain by frosts and a sharp decrease in the yield of “frost-damaged” grain and its quality.

N. N. Kuleshov proposes dividing the grain formation process into three stages:

• formation (initiation and formation);
• filling;
• ripening.

Seed initiation — the period from grain initiation to the establishment of final length. The seed can produce a weak sprout. The mass of 1000 seeds equals 1 g. The duration of initiation is 7–9 days or more.

Formation — the period from grain initiation to the establishment of final length. The seeds have a high content of free water and a low content of dry matter. The mass of 1000 grains is 8–12 g.

Filling — the period from the beginning of starch accumulation in the endosperm until its cessation. Moisture content decreases to 37–40%, duration — 20–25 days.

The filling period is divided into four stages:

• Watery state phase — beginning of endosperm cell formation. Dry matter constitutes 2–3% of its maximum amount; phase duration — 6 days.
• Pre-milk phase — grain contents are of watery consistency with a milky tint. Dry matter content — 10%. Phase duration — 6–7 days.
• Milk phase — grain contains a milk-like white liquid. Dry matter accumulated — 50% of mature grain mass. Phase duration — 7–15 days.
• Dough phase — the endosperm acquires dough consistency; dry matter accumulated — 85–90%; phase duration — 4–5 days.

Grain ripening begins with the cessation of the influx of plastic substances. Grain moisture decreases to 8–12% and it becomes suitable for technical use, but seed development is not yet complete.

The filling period is sometimes called the milk ripeness phase, when plants are still green, the stem and leaves begin to yellow in the lower part, the lowest leaves die off, and grain moisture ranges from 60 to 40%.

The ripening period is divided into two phases:

• Wax ripeness phase — the endosperm is waxy, elastic, easily cut with a fingernail, seed coats yellow. Moisture decreases to 30% (22–40%). Phase duration — 3–6 days; embryo growth and accumulation of plastic substances cease. Plants are yellow, except for the 2–3 upper nodes of the stem and part of the inflorescence.
• Hard ripeness phase — the endosperm is hard, mealy or vitreous on fracture, the seed coat is dense and leathery, coloration is typical, moisture 8–22% (depending on the zone). Phase duration — 3–5 days.

In the hard ripeness phase, complex biochemical processes occur, after which the seed acquires the property of germinability. Because of this last stage, two further periods are distinguished: post-harvest maturation and full ripeness.

During post-harvest maturation, synthesis of high-molecular-weight protein compounds is completed, free fatty acids are transformed into fats, carbohydrate molecules become larger, and respiration stops. At the beginning of this phase, seed germinability is low; by the end, it is normal. Duration depends on crop characteristics and external conditions and ranges from several days to several months.

Full ripeness occurs when seeds are ready to begin a new plant life cycle; germinability reaches its maximum. At this stage, plants are yellow, leaves die off, grain is hard and decreases in size.

Harvesting is carried out at the wax ripeness stage by separate combining, and at the full ripeness stage by direct combining.

In a number of regions, for example Northern Kazakhstan, Siberia, etc., ripening of cereal crops is delayed in some years, plants are damaged by frosts, producing frost-damaged grain and leading to reduced yield and worsened quality. Therefore, in these regions two-phase harvesting is used — in the first half of the wax ripeness phase. While in windrows, grain is less damaged by frosts, and plastic substances continue to enter it as long as stems and leaves contain water.

In the Southeast of Russia, premature grain ripening occurs because of dry winds (sukhoveys), as a result of which growth and accumulation of plastic substances stop earlier. Grain becomes wrinkled and shriveled; milling and baking properties deteriorate. Shriveled grain leads to reduced yield. The main means of combating dry winds are expansion of protective field shelterbelts, accumulation of moisture in the soil, use of early-maturing varieties, and harvesting in compressed timeframes.

Fertilization

Row fertilization accelerates growth of the secondary root system of cereal crops, which often determines yield formation. Thus, mineral fertilizers, especially phosphorus fertilizers, increase resistance of cereal crops to root rots and brown rust.

The effect of top dressing is determined by the use of a complex of agronomic practices. Thus, under irrigation of cereal crops, top dressing is a technique for increasing yield and improving grain quality. Of greatest practical importance is late top dressing for increasing grain protein content and improving other quality indicators of wheat.

Soil density

For cereal spike crops, the optimal soil density is 1100–1300 kg/m³.

Sowing

Cereal crops are usually sown by the row method. Row spacing is 15 cm. In areas subject to wind erosion, inter-row width is 22.8 cm. Reducing inter-row width of cereal crops to 7.5 cm allows seeds to be distributed more evenly over the field area.

For their sowing, ordinary row seeders are used, for example, SZ3-6, SZT-3.6, SZS-2.1 and others.

Cereal crops sown from north to south showed a yield 0.2–0.3 t/ha higher than those sown from east to west, owing to better illumination in the morning and evening hours and mutual shading at midday.

Lodging

Lodging of cereals can be caused by unfavorable conditions. The causes of lodging were established at the end of the last century by K. A. Timiryazev. He considered the main cause to be elongation of stem cells due to insufficient illumination, making their walls thinner. Lack of light is caused by strong tillering and excessive vegetative mass. The lower weakened internodes cannot support the weight of the above-ground mass, resulting in lodging of plants. If this occurs early enough, straightening of the straw is possible through growth of leaf nodes; whereas if lodging occurs after earing, no changes in the crop occur.

The risk of lodging of cereals increases under irrigation, which is associated with strong development of vegetative organs, increased moisture of the topsoil, and shallow occurrence of the tillering node.

To prevent lodging, sowing depth is increased, so that the tillering node is located deeper, and potassium and phosphorus fertilizers are applied, which accelerate development of stems and the root system. Phosphorus-potassium fertilizers are applied before tillering. In contrast, early application of nitrogen fertilizers leads to enhanced tillering, delays development, and reduces resistance to lodging.

To make plants resistant to lodging, narrow-row and cross sowing methods are used, with rows arranged from north to south.

The most important measure for preventing lodging is the use of resistant varieties. Also, to prevent this phenomenon, treatment of crops in the tillering phase with a plant growth regulator — tur (chlormequat chloride), which prevents excessive growth and lodging of plants. Late spring and weak plant development sharply reduce the effectiveness of the preparation.

To prevent lodging of cereal crops, special preparations — retardants — are used. They dissolve well in water and easily penetrate plants. Under their action, lower internodes become shorter and thicker, and plant height decreases by 15–25 cm, which increases resistance to lodging. In addition, these preparations increase resistance to drought and root rot diseases by stimulating root system growth.