Sorghum

Economic importance

Sorghum, as an agricultural crop, is of interest for arid regions. Under these conditions, its yield exceeds that of maize and spring barley. According to data from variety-testing plots of the North Caucasus over many years of observations, the grain yield of sorghum was 29.3 dt/ha, maize — 25 dt/ha, spring barley — 19.8 dt/ha.

Sorghum has several directions of use: grain for animal feed, raw material for the production of compound feeds, the starch and alcohol industry, and groats. In many regions of Africa, India, East and Central Asia, it serves as the main bread plant.

In the world, sorghum as a food plant ranks fifth, after wheat, rice, maize, and barley.

The green mass of sorghum is used for livestock feed or silage, which in quality is slightly inferior to maize silage. When stems are mown before they become coarse, good-quality hay is obtained. After mowing, sorghum can regrow and be used for green fodder or as pasture.

A fodder feature of sorghum is that its leaves and stems remain succulent when the grain is fully ripe.

100 kg of grain equals 119 feed units, green mass — 23.5 feed units, silage — 22 feed units, hay — 49.2 feed units. The grain contains up to 15% protein rich in lysine; the stems of sweet varieties contain 10–15% sugars, and the juice 24%, which are used to make syrups.

Panicles of broom sorghum are used to make brooms and brushes. Sorghum can be used as a barrier crop for snow retention, creating strips of tall-stemmed plants that protect crops from wind erosion. Cultivation in stubble and aftergrass sowings is of interest.

History of the crop

The place of origin of sorghum is considered to be equatorial Africa. The crop was known 3,000 years BCE in India and China, and 2,500 years BCE in Central Asia.

Sorghum was brought to Russia in the 17th century.

Cultivation areas and yield

Sorghum is distributed in many countries of the world. In India, the sown area is 16 million ha, in the USA — 5.7 million ha, in Africa — 15.4 million ha. Large sown areas exist in the countries of the Middle East, China, Romania, Bulgaria, Hungary, Italy, Australia, South America, and Japan. In total, by 1980 the world sown area of sorghum was 47.7 million ha, or 7% of the sown area of cereal crops; the average yield was 14.2 dt/ha. The gross grain harvest was 75 million t, or 4% of the total grain harvest.

During the USSR period, the sown area under sorghum was about 150 thousand ha, mainly in Central Asia, southern Ukraine, Moldova, the North Caucasus, Transcaucasia, the Lower Volga region, and Kazakhstan. The average yield was about 15 dt/ha.

In Russia, there are no statistical data on sorghum. The sown area is estimated at 20–30 thousand ha (25 thousand ha in 1997), gross grain harvest 25–35 thousand t, with average yields of 1.2–1.4 t/ha of grain and 20–30 t/ha of green mass. The main sown areas are concentrated in the dry steppe of the Southern Federal District (North Caucasus and Lower Volga region).

In the steppe zone, sorghum is capable of giving stable grain yields of 2.5–3 t/ha and green mass yields of 20–30 t/ha.

At state variety-testing plots, grain yield varied from 25 to 50 dt/ha, green mass for silage from 20 to 30 t/ha, and under irrigation 80–100 t/ha. In 1982, high yields were obtained in Rostov Oblast (kolkhoz “Put’ Lenina”) — 21.2 dt/ha on 700 ha, in Zernogradsky District (kolkhoz “Litunova”) — 24.8 dt/ha on 200 ha.

The use of hybrid sorghum seeds, which exhibit high heterosis in the first generation, is becoming widespread.

In arid regions, highly productive hybrids give higher yields than maize. According to the Genichesk Experimental Station of the VNII of Maize, the grain sorghum hybrid Stepnoy 5 averaged 52.4 dt/ha of grain over 8 years, which is 28.8 dt/ha higher than the maize yield. At the Rybnitsa state variety-testing plot in Moldova, over 5 years the average yield of this hybrid was 78.1 dt/ha, and of the maize hybrid VIR 42 — 60.2 dt/ha.

Botanical description

The genus sorghum (Sorghum Moench (Pers.)) in Russia is represented by cultivated species:

• common sorghum (Sorghum vulgare¹⁾ Pers.) — cultivated for fodder, industrial, and food purposes;
• durra — Sorghum cernum¹⁾ Host. — with a curved inflorescence;
• gaoliang — Sorghum chinense Jakuchev;
• Sudan grass — Sorghum sudanense Pers., cultivated as a fodder plant.

Note. ¹⁾ At present, the species common sorghum (Sorghum vulgare) and durra (Sorghum cernum) are combined into one species, sorghum bicolor (Sorghum bicolor).

Common sorghum is most widespread in Russia.

Among wild sorghum species, Johnson grass is widespread in southern Russia — weed plant.

Subspecies

Depending on panicle shape, sorghum is divided into:

• spreading, or paniculate, (effusum Korn), with a loose panicle and long branches;
• compact (contractum Korn) with a compressed, short, very dense panicle, erect or curved stem tip;
• club-shaped (compactum).

Club-shaped sorghum is of main importance in cultivation.

Biological features

Vegetation

Like all millet-like cereals, it initially grows slowly and does not tolerate weed infestation of fields.

Growth phases:

• emergence in mid-season sorghum appears 10–15 days after sowing;
• third leaf;
• tillering phase — 25–30 days after sowing;
• stem elongation — 40–50 days after sowing;
• panicle emergence — 55–65 days after emergence;
• flowering — 5–6 days after panicle emergence;
• milk ripeness of grain;
• wax ripeness of grain;
• full ripeness of grain.

The growing season for varieties of different earliness is 90–160 days.

Crop rotation

Sorghum tolerates repeated sowings well, so it can be grown on permanent plots if there are no cases of bacteriosis. In experiments of the VNII of Maize, sorghum yield when grown on a permanent plot for 10 years did not decrease and averaged 26.9 dt/ha; in a crop rotation link (occupied fallow — winter crops — winter crops — sorghum) it was 24.9 dt/ha.

In crop rotation, sorghum is placed after grain legumes, winter crops, maize, and other row crops. For example, in the steppe of Kabardino-Balkaria, sorghum grain yield after peas was 52.8 dt/ha, after winter wheat 49.5 dt/ha, and silage mass 44.6 and 38.5 t/ha, respectively.

Sorghum is a row crop, so it serves as a good predecessor for spring crops.

Fertilizer

Sorghum is responsive to fertilizer when grown for grain and silage. Fertilizer effectiveness increases under irrigation. Like other cereal plants, sorghum responds most strongly to nitrogen, then phosphorus fertilizers.

Thus, in the steppe zone of Kabardino-Balkaria, various types of fertilizers against an irrigation background gave the following results.

The greatest response to fertilizers is obtained from applying a complete mineral fertilizer, as well as the combined use of organic and mineral fertilizers.

Row fertilizer

Row application of fertilizers at sowing at a rate of N₁₀P₁₀, 4–5 cm to the side of the row and 2–3 cm deeper than the seed placement, is also effective.

Soil treatment

Autumn soil tillage for sorghum consists of stubble disking to a depth of 7–8 cm and deep autumn plowing to a depth of 25–27 cm. Such treatment reduces field weed infestation by 37–50% and increases moisture reserves by 25%. According to the Poltava Agricultural Experimental Station, such treatment increases green mass yield by 22–25%. According to the Volgograd Agricultural Experimental Station, grain yield increases from 19.8 dt/ha to 25.1 dt/ha compared with plowing to a depth of 18–20 cm.

In early spring, harrowing is carried out, then 2–3 pre-sowing cultivations: the first to a depth of 10–12 cm, subsequent ones to 5–6 cm. Under insufficient moisture, after the first cultivation the soil is rolled to provoke weed germination and destroy them with the subsequent pre-sowing cultivation. In a very dry spring, rolling is also carried out before sowing.

Sowing

Mixed sowings

Sorghum is used in mixed sowings, primarily with grain legumes — soybean, grass pea, beans, vetch, etc., in alternating rows. Yield increases by 15–20% compared with sorghum alone, and the fodder quality of the mixture is higher.

The legume crop is sown in separate rows between sorghum rows or in a cross direction at 50–80 kg/ha.

Mixed sowings of maize for silage and sorghum are also used, which increases green mass yield by 3–5 t/ha and lengthens the silage period by 10–15 days. According to the Erastov Experimental Station (Dnipropetrovsk Oblast, Ukraine), sowing maize alone gave 13.5 t/ha of green mass; a combined sowing of two rows of maize and one row of sorghum gave 16.0 t/ha.

Mixed sowings of maize, soybean, and sorghum for silage also give good results.

Crop care

After sowing, the soil is rolled with toothed or ring rollers. If a soil crust forms or weeds appear, pre-emergence and post-emergence harrowing (at the 3–4 leaf stage) across the rows is carried out. Harrowing gives good results with dense sowings and well-rooted plants; otherwise, rotary hoes of the MV-2.1 type are used.

When 6–7 leaves have formed, a third harrowing can be carried out, which makes it possible to destroy up to 70% of weeds.

As the soil compacts and weeds grow, 2–3 inter-row cultivations are performed.

To control weeds, spraying with herbicides of the 2,4-D group or others is carried out at the 3–6 leaf stage. The preparation propazine is used after sowing before emergence at 3–6 kg/ha.

In sorghum sowings, the herbicide Agritox (500 g/l) is used against annual dicotyledons; spraying at the tillering phase before stem elongation.

Harvesting

Grain sorghum is practically not prone to shattering, so it can be harvested at full grain ripeness with combines at reduced drum speed — up to 500–600 rpm. When grain moisture is more than 20%, two-phase harvesting is used with the SM-2.6 sorghum harvester or a modified grain combine.

Sweet sorghum is harvested at the end of the wax ripeness phase at a low cut.

Panicles of broom sorghum are usually cut by hand at the beginning of full grain ripeness, but the panicle branches should remain green. The stems are then mown with harvesting machines, for example mowers or headers, and can be used for silage. Grain is removed from the panicles by combing them on special combs.

For silage, sorghum is harvested at the end of milk ripeness — beginning of wax ripeness of grain, before the lower leaves dry and fall.

For green fodder and hay, it is mown before the stem becomes coarse, no later than the beginning of panicle emergence. Afterwards sorghum regrows, giving aftermath, but in it, as well as in young plants, toxic hydrocyanic acid can accumulate due to hydrolysis of the glucoside dhurrin. Its content can vary from 0.003 to 0.31%; a content above 0.1% is considered toxic. With plant age, hydrocyanic acid content sharply decreases and sugar increases. In cut mass after 2 h of wilting, hydrocyanic acid is destroyed.

Progressive cultivation technologies

Technology of sorghum seed production in Rostov Oblast (specialized state farm “Manychsky”). Yield 16–20 dt/ha (1979–1982), sown area up to 2 thousand ha. At the same time, the cost of 100 kg of sorghum seeds in 1982 was 484 rubles, net profit from seed sales was 634 thousand rubles.

Predecessor — grain legumes, maize for silage, winter wheat. Soil treatment included stubble disking to a depth of 5–7 cm following harvest of the predecessor, repeated after weed regrowth. Plowing to a depth of 27–30 cm with application of 60 kg/ha nitrogen and 90 kg/ha phosphorus.

In spring, cultivation was carried out. Seed preparation included air-thermal treatment for 4–5 days and treatment with a film-forming preparation. The sowing method was wide-row with 70 cm row spacing. Seeding rate for early-ripening varieties was 300–400 thousand/ha of viable seeds, for late-ripening varieties 150–180 thousand/ha.

Care consisted of pre-emergence harrowing 4–5 days after sowing, then cultivation with KRN-4.2: the first after emergence, the second simultaneously with top dressing with liquid mineral fertilizers, the third hilling. At the 3–4 leaf stage, treatment was carried out with the herbicide amine salt of 2,4-D at a dose of 0.6–0.8 kg/ha a.i.

Harvesting was carried out in one phase with a converted Niva combine. When grain moisture was more than 20%, harvesting was two-phase: cutting was done with a ZhVN-6 header, threshing with a combine with a GGPPT-3.0 pickup.

Sorghum sowings for seeds of silage varieties were harvested in two phases with a sorghum harvester.

Groups and varieties

According to economic purpose, E. S. Yakushevsky proposed dividing sorghum into: grain, sweet, broom, and grass.

All sorghum species cross easily; the first generation of hybrids is distinguished by high productivity as a result of heterosis. Sorghum–Sudan grass hybrids (Tryokhukosny, Intensivny, Sochnolistny) and hybrids of durra with broom sorghum are of important economic significance.

List of sources

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