Biological characteristics and economic importance of maize in modern crop production

Biological characteristics and agrotechnical value of maize

Maize belongs to the group of millet-like cereals (the second group of cereal crops), which also includes rice, millet, sorghum, and foxtail millet. Unlike typical cereals of the first group, these crops are heat-loving, light-loving, require a short day length, and are characterized by high drought resistance (with the exception of rice). They are less demanding of soil fertility than wheat and barley, but under favorable conditions, they are capable of providing maximum yield.

The biological structure of maize has a number of characteristic features. Male inflorescences are represented by panicles, and female ones by ears. The lower flowers of the spikelets are usually reduced and sterile, the grain has no furrow or tuft, and it always germinates with a single embryonic root. The tillering nodes in the plants are formed close to the soil surface.

For an agronomist, maize is valuable as an effective row crop in crop rotation. It helps to clear fields of weeds, improves the soil moisture regime, and contributes to the preservation of its soil fertility. Maize serves as a valuable predecessor for cereals and other crops, and also shows high productivity in stubble, double, mixed, and intercropped sowing.

Economic importance, nutritional value, and global productivity

Maize is a crop of universal use. Its grain at a standard humidity of 14–15% contains 65–70% carbohydrates, 9–12% proteins, and 4–6% lipids. For food purposes, it is used for flour (it is mixed with wheat and rye flour for baking bread, and used to make mamaliga and confectionery products), groats with a yield of up to 64% (including corn semolina), starch, glucose, molasses, alcohol, and beer. From the grain embryos, which contain 30–40% lipids, food-grade oil and vitamin E are obtained. Also, boiled and canned ears and maize grains in the milk ripeness stage are used for food.

As a forage crop, maize occupies a leading place in livestock farming: about 60% of world grain production is spent on feed. It surpasses most crops in the harvesting of feed units per hectare at moderate labor costs. It is not only the grain that goes into feed for livestock, but also silage from green mass, which is rich in carotene, as well as dry leaves, stalks, and cob cobs remaining after harvesting.

• Nutritional value of grain (per 1 kg) — 1.34 feed units
• Digestible protein of grain (per 1 kg) — 78 g
• Nutritional value of stalks (per 1 kg) — 0.37 feed units
• Digestible protein of stalks (per 1 kg) — 20 g
• Yield of feed units per 1 ha — 6280 kg
• Protein harvest per 1 ha — 413 kg

The industrial application of corn is also diverse. Stalks are used to produce paper, building boards, insulation materials, and linoleum. Corn cobs serve as raw material for the production of furfural, which is necessary for oil refining and the manufacture of plastics and synthetic fibers. In medicine, styles and stigmas (corn silk) are used, while activated carbon and anesthetics are derived from the stalks and cobs.

In terms of yield of grain, corn is second only to rice, ranking third in the world in total production after wheat and rice. According to FAO data, the leading positions in corn cultivation are held by the USA (where it accounts for 60% of the country's total grain harvest) and China. Below is the production dynamics of corn by leading producing countries.

Country	Production in 1995, thousand tons	Production in 2000, thousand tons	Production in 2005, thousand tons
USA	225 453	187 969	280 228
China	64 102	112 362	131 145
Brazil	22 018	36 267	34 860
Mexico	14 103	18 353	20 500
Argentina	11 900	11 404	19 500
India	6 644	9 534	14 500
France	12 409	12 740	13 226
Indonesia	4 330	8 246	12 014
South Africa	8 444	4 866	11 996
Italy	6 357	8 454	10 622

Cultivation geography and productivity potential

Global demand for corn is steadily increasing. This forces farms to expand the area under the crop. Yield is heavily influenced by technology: while the global average is about 50 centners/ha, in advanced European farms this level is exceeded twofold or more. The record world grain harvest reached the mark of 232.2 centners/ha.

• Global area sown for grain — more than 142.68 million ha
• US share in the global area structure — about 35%
• Global average grain yield — about 50 centners/ha
• Record world grain yield — 232.2 centners/ha
• Potential grain yield in Belarus — 50–70 centners/ha
• Potential green mass harvest in Belarus — 350–400 centners/ha

In crop production, corn is cultivated both for grain and for silage with green fodder. Differences in climate and cultivation goals determine both the scale of sowing and the average productivity by region. Below are the indicators of crop cultivation in the Russian Federation and the Republic of Belarus for various directions of use.

Region and cultivation goal	Period / year	Sown area	Average yield
Russia (North Caucasian, Lower Volga, Central-Chernozem regions), for grain	—	720 thousand ha	32.5 centners/ha
Russia (except northern regions), for silage and green fodder	Period 5 years	about 3 million ha	170 centners/ha
Belarus (expansion in a number of regions), for grain	2008	100.3 thousand ha (1.3% above plan)	66.7 centners/ha (total harvest — 668.5 thousand tons)
Belarus, for green fodder and silage	2008	over 615.3 thousand ha (97.7% of plan)	235.8 centners/ha (total harvest — 14.5 million tons)

To increase the profitability of livestock farming, farms are increasing corn grain production volumes. The plans of the Belarusian agricultural sector include expanding areas using grain technology to 200 thousand ha, which will allow for the production of at least 1 million tons of domestic grain. In the silage direction, the task is set to bring the average yield of green mass to 300 centners/ha by the end of 2010 with a total harvest of 13–14 million tons.

Hybrid breeding and historical roots of the crop

The development of domestic breeding solves the problem of dependence on imported sowing material. Field trials of the parent forms of the Beliz hybrid in 2004 and the subsequent production of 2.5 thousand tons of hybrid seeds in 2005 proved the possibility of fully meeting internal regional needs. With the commissioning of new seed plants, the annual production volume of processed seeds is planned to be increased to 7.5 thousand tons to fully cover domestic demand.

In the 2005 variety trials, the following hybrids demonstrated high yields:

• standard sweet corn cultivar Parumben-340 — 197 centners/ha;
• Parumben-198MBF1 — 182 centners/ha;
• Lyudmila — 190 centners/ha.

The following domestic hybrids and joint developments are available to agronomists for implementation:

• Belarusian hybrids: Beliz, Polessky 212SV;
• Belarusian-Moldovan hybrids: Bemo 160 MV, Bemo 181SV, Bemo 182SV, Bemo 210SV, Bemo 172SV;
• Belarusian-Ukrainian hybrids: Adonis 180SV, Adonis 224SV, MOS 182SV, MEL 272SV, VAR 330MV.

Maize (Zea mays L.) is an ancient heat-loving crop, the wild ancestors of which have not yet been found. It is assumed that it originated in Mexico or Guatemala as a result of crossing an extinct ancestor of maize with a wild grass called Tripsacum, with teosinte acting as its distant forefather. Archaeological findings of cobs in Mexico City date back to 3,500 BC, and the age of fossilized pollen in Peru and Bolivia is estimated at 5,000–10,000 BC. By the time of the discovery of the New World in 1492, it was already the staple food crop of both Americas.

Before the discovery of America, maize was not grown in the Old World. The first grain samples were brought to Spain by participants of the second expedition to the New World, after which publications in 1511 and 1516 attracted the attention of European botanists to the plant. The scientific name of the genus Zea goes back to the Greek "to live," emphasizing the exceptional importance of this cereal crop. Various versions of the name took root in European languages:

• in Vienna and Berlin — maize;
• in Budapest — kukorica;
• in Warsaw — kukurydza;
• in Bucharest and Sofia — kukuruza (from the Turkish "kokoroz" — a tall-stemmed plant).

Maize quickly spread throughout Europe and the Mediterranean, and by 1496 Portuguese navigators had already brought it to India, China, Guinea, and the island of Java.

A little later, maize spread throughout the territory of the Russian state — in Georgia (17th century), in the North Caucasus, Ukraine, Moldova, then in Central Asia, the Lower Volga region, and more northern areas (for example, in the Oryol, Tula, and Kaluga provinces — 19th century). However, in Russia, maize did not have great economic importance for a long time, and in 1913 only 1.3 million hectares were occupied by its sowings.

Only in the mid-20th century, on the initiative of N. S. Khrushchev, serious attention was paid to the widespread expansion of maize sowings for food and feed purposes. Currently, in the CIS, the main areas of maize sowings for grain are located in Ukraine (predominantly in its southern part), the North Caucasus, Moldova, and Transcaucasia. The maize crop extends to approximately 50° N.

The widespread distribution of maize in world agriculture is due to the following reasons: maize is one of the most productive plants; it has a great ability to adapt to various soil and climatic conditions.

Maize belongs to the Poaceae (or Gramineae) family and has only one species — common maize, or maize (Zea mays L.). Maize is a cultivated plant, and its wild ancestors have not been established.

Maize is an annual, monoecious, diclinous plant. Its female flowers are collected in an inflorescence called a cob, and the male ones in a tassel. second group 185

Fig. 20. Maize: morphological features (a); in the field in July (b); cob in cross-section (c); individual caryopsis (d); maize subspecies (e) — dent (1), flint (2, 4), floury (3), sweet (5), popcorn (6)

The root system is powerful, fibrous, and multi-tiered, with roots reaching a depth of up to 3 m. An anatomical feature of the structure of the maize root system is the presence of air cavities, indicating the high sensitivity of the roots to the presence of oxygen.

The stem is thick, fleshy, succulent, up to 7 cm in diameter. The plant height is usually from 60 cm to 6 m, depending on different soil and climatic conditions.

The male flowers are located in pairs at the top of the plant on the tassel's raceme-like branches; the female ones sit as cobs in the leaf axils on the lateral surfaces of the stem, and the silk is single and very long.

Maize is a cross-pollinating (wind-pollinated) crop. The male and female flowers do not bloom at the same time, which is also an important condition for cross-pollination. The tassel blooms 3–8 days before the styles of the cobs emerge. Warm, humid weather with a light breeze is favorable for pollination. In rainy weather, the pollen is washed away, and excessive dryness kills it. Adverse conditions lead to kernel gaps.

The fruit is a large caryopsis, usually bare and smooth. The grain consists of a hull, endosperm, and embryo. The endosperm contains both mealy and horny parts. The caryopses of maize of different groups and cultivars (hybrids) have different colors — white, cream, yellow, orange, red, and purple. Depending on the cultivar and growing conditions, 200–1000 grains are formed in a cob, with an average cob having 500–600 grains.

Based on the shape, structure, and chemical composition of the caryopses, nine subspecies of maize are distinguished:

• dent (the most common subspecies);
• semi-dent;
• flint;
• floury;
• floury-sugar;
• sweet;
• pop;
• waxy;
• pod.

As a result of long-term selection, humans have created over 10,000 different forms, cultivars, and hybrids of maize, which have various economic purposes: food, feed, and industrial.

Dent maize (indentata) (Fig. 20, d — 1) is the most common subspecies, and is relatively new to cultivation. The grain is large, elongated-prismatic, with a dent on the top, resembling a horse's tooth in shape. The endosperm is vitreous on the sides of the grain, while in the center and at the top it is floury. Cultivars and hybrids belonging to this subspecies are relatively late-maturing.

Flint maize (indurata) (Fig. 20, d — 2, 4) is by origin one of the most ancient subspecies, possessing the widest range on the globe. It is distinguished by cold resistance, lodging resistance, disease resistance, and lower demands on growing conditions; it has both extremely late-maturing and extremely early-maturing forms. The grain is rounded, compressed, smooth, and shiny. The endosperm is vitreous and only in the central part of the grain is it floury. It is a valuable raw material for the production of flour, from which mamaliga, bakery products, and groats are prepared.

Subspecies	Starch, %	Protein, %	Fat, %
Dent	68—76	8—10	about 5
Flint	65—83	8—18	up to 5

Floury maize (amylacea) (Fig. 20, d — 3) has the same grain shape as flint maize. The grain is almost entirely filled with a floury mass. The horny endosperm is absent or represented only by a thin outer layer.

Starch	72—83 %
Protein	7—12 %
Fat	5 %

The grain is a valuable raw material for the starch-syrup, alcohol-distilling, and oil-extraction industries.

Sweet maize (saccharata) (Fig. 20, d — 5) emerged as a mutant of dent and flint cultivars. It is considered relatively young in cultivation. It has a large, wrinkled grain consisting of a translucent vitreous endosperm with a characteristic luster on the fracture. In the endosperm of sweet cultivars, besides various forms of starch, water-soluble dextrin and protein are contained.

Biological features of subspecies and climatic requirements

• Seed germination temperature — 8–10 °С
• Frosts dangerous for seedlings — down to -2...-3 °С
• Optimal soil moisture — 75–80% of field water capacity
• Nitrogen application rate per hectare — 90–120 kg active ingredient
• Manure application rate on loams — 35–40 t/ha

Several subspecies of maize are used in production, each having its own biological and economic features. Sweet maize is grown as a vegetable crop for the canning industry, harvesting the grain in the milk ripeness phase. Pop maize is an ancient subspecies with a small horny endosperm, the grain of which pops when heated; it is used for the production of groats and flakes. Waxy maize is cultivated in the USA and European countries for obtaining dextrin, while pod maize, due to strongly developed glumes, has no economic significance.

Maize subspecies	Protein, %	Carbohydrates / Starch, %	Dextrin, %	Fat, %
Sweet (vegetable)	18—20	64 (carbohydrates)	32	8—9
Pop (rice and pearl)	10—14	62—72 (starch)	—	—

Maize is extremely light-demanding and is classified as a short-day plant. The most rapid flowering occurs during an 8–9 hour photoperiod, while an increase in the photoperiod beyond 12–14 hours extends the growing season. The crops vitally require intense sunlight, especially during the early stages of development. Depending on the hybrid's maturity group growing season lasts from 75 to 180 days or more.

Hybrid maturity group	Sum of active temperatures, °С
Early-maturing	2100—2400
Medium- and late-maturing	2600—3000

Maize is a heat-loving crop, sensitive to frosts. Seeds begin to germinate at a soil temperature of 8–10 °C at the sowing depth, and uniform seedlings appear at 10–12 °C in 15–20 days. A temperature drop to 10 °C completely stops plant growth, and frosts down to -2...-3 °C damage seedlings. Until the formation of reproductive organs begins, the crop can withstand air temperatures up to 25 °C without harm.

Maize consumes a large volume of water, although its developed root system and leaf pubescence help it partially absorb moisture from the air. For seed swelling and germination, a volume of water equal to 60% of its mass is required. Favorable conditions for active growth occur when soil moisture is at 75–80% of field water capacity. The crops effectively utilize rainfall in the second half of summer.

To obtain high yields, the crop should be placed on clean, loose, and breathable soils with a deep humus horizon and a neutral or slightly acidic reaction. Chernozems, dark chestnut, dark gray loams, sandy loams, and floodplain soils are suitable. Plant development proceeds through strictly defined phases, the duration of which depends on the weather, the hybrid, and agricultural techniques.

• Beginning and full emergence of seedlings.
• Beginning and full emergence of panicles.
• Beginning and full emergence of ears (silk appearance).
• Milk and milk-waxy stage of grain.
• Waxy ripeness.
• Full ripeness.

Place in crop rotation, tillage, and fertilizer system

Corn is characterized by high plasticity and can tolerate repeated sowing in the same field for 3–5 years without a sharp decrease in yield. The best predecessors for it are row crops, grain legumes, annual, and perennial legume grasses. It is also placed after the second group of cereal crops, where manure was applied. Corn itself is an excellent predecessor for almost all crops in the crop rotation.

Tillage system. The tillage system is built taking into account the weediness of the field, the predecessor, and the particle size distribution of the soil. It includes two main stages: deep primary tillage and thorough pre-sowing preparation. All technological operations are performed in a strict sequence.

1. Primary tillage. Stubble breaking and subsequent ploughing to the depth of the arable layer are carried out to destroy weeds and ensure high-quality incorporation of crop residues and fertilizers.
2. Pre-sowing preparation. Includes early harrowing of autumn-ploughed fields and one or two cultivations with mandatory levelling of the field surface to preserve soil moisture and stabilize temperature conditions.
3. Sowing and compaction. Sowing is carried out to the specified depth with mandatory soil compaction before and after the seeder passes to create optimal contact between the seed and soil moisture.

Organic fertilizers are applied before autumn ploughing. The application rate depends on the soil texture: 35–40 t/ha is applied on cultivated loamy soils, and the rate is increased to 40–50 t/ha on sandy loam soils. On permanent maize cultivation plots, it is recommended to apply 100–120 t/ha of organic fertilizers once every 3–4 years.

Mineral nitrogen is applied at a dose of 90–120 kg of active ingredient per hectare. The method and timing of application depend on the mechanical properties of the soil in a specific field. On light soils, the dose is split: one-third of the nitrogen is applied before pre-sowing cultivation, and the remaining two-thirds during inter-row loosening. On cohesive soils, the full rate of nitrogen fertilizers is applied during pre-sowing cultivation.

To obtain uniform emergence and a high crop yield, it is important to observe fertilizer dosages and use high-quality seed material. Phosphorus fertilizers are applied in split doses: 60—90 kg a.i./ha before sowing and another 10—15 kg/ha a.i. directly at the time of sowing. Potash fertilizers in the volume of 90—120 kg a.i. are applied under ploughing on cohesive soils or under spring cultivation if the soils are light. Maize is sown using seeds of hybrids not lower than the first generation, which have undergone seed treatment and encrustation at specialized plants.

• Soil temperature for sowing — 8—10 °C
• Sowing period — 10—12 days
• Inter-row spacing — 70 cm
• Sowing depth on light soils — 5—6 cm
• Sowing depth on cohesive soils — 3—5 cm

Sowing begins after the soil has warmed up at the seed placement depth. Sowing dates depend on the region of cultivation:

• northern zone of Belarus: May 1—10;
• central zone: April 25 — May 10;
• southern zone: April 25 — May 5.

Sowing is carried out using a wide-row, precision method. Optimal plant population density is selected based on the intended use and the type of hybrid:

Purpose	Hybrid type	Density, thousand/ha
Grain	Early-maturing	80—90
Grain	Mid-maturing	70—80
Silage	Mid-early	110—120
Silage	Mid-maturing	100—110
Silage	Mid-late	90—100

To destroy weed seedlings, harrowing to a depth of 1—2 cm is used. It is important to adhere to the optimal timing for operations during the growing season:

1. The first pre-emergence harrowing is carried out 4—6 days after sowing.
2. Repeated pre-emergence harrowing is performed 4—6 days after the first treatment.
3. The third pre-emergence harrowing is done if maize emergence is delayed.
4. Post-emergence harrowing is carried out in the 3—6 leaf stage of the crop.

Once the rows are clearly visible, inter-row cultivation begins. To protect crops from weeds during the critical development period of maize, herbicides such as Primextra Gold TZV or Clariss are used.

Harvesting timelines and technologies

Maize harvesting is usually carried out in September. Timelines and technological methods depend on the intended use of the harvest — for silage or for dry grain.

For silage, maize is harvested in the milk-wax or wax ripeness stage of the grain, which lasts about 10 days. During this period, the leaves and stems are still green and contain about 70 % water, while grain humidity is 35—55 %.

To increase protein content, maize is sown together with legumes: soybeans, beans, or lablab.

Maize for grain is harvested upon reaching full maturity. By this time, the plants turn yellow, the ear husks dry out, and the grain hardens and acquires a characteristic shine. To accelerate grain drying in the field, you can manually open the yellowed husks or spray the crops with a 15% solution of ammonium sulfate (NH4)2SO4.

Harvesting for grain is carried out in two ways:

• in cobs — work begins at a grain moisture of 40%;
• as grain — work starts at a moisture level of no more than 32%.

With either method, the leaf-stem mass is collected simultaneously with the grain portion. To avoid quality losses, the entire volume of harvesting work must be completed within 15 days.