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Sorghum vulgare Sorghum Pers. - Cereals - Herbaceous crops

Sorghum vulgare Sorghum Pers. - Cereals - Herbaceous crops


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Class: Monocotyledones
Order: Glumiflorae
Family: Graminaceae (Gramineae or Poaceae)
Sub family: Andropogonoideae
Tribe: Andropogonaceae
Sub-tribe: Sorghastreae
Species: Sorghum vulgare Pers.
Synonym: Sorghum bicolor (L.) Moench.

French: sorghum, gros millet; English: kaffir corn; Spanish: milium zaburrum; German: Sorghum Kaffernhirse.

Origin and diffusion

Sorghum was one of the first plants to be cultivated: the current forms are believed to have originated in West Africa several thousand years ago. From Africa, sorghum has spread all over the world: in ancient times in Asia and Europe, more recently in America and Australia.
Sorghum is the fourth most important cereal in the world agricultural economy, after wheat, rice and corn.
In subsistence farming in the Third World, grain is used directly for human nutrition, as these countries cannot afford livestock processing; the yields are very low, of the order 0.5-1 t / ha, both for the primitive cultivation technique and for the adverse environmental conditions: sorghum is grown where the environment is too dry for the otherwise well-liked corn.
In advanced agriculture, the grain is intended for animal feed, in competition with that of corn, of which it has similar nutritional value. In the USA, moreover, a certain part is destined for industrial transformation into ethyl alcohol.
Italy cultivates just 29,000 hectares despite the fact that it could be hoped to extend over much larger areas.

Sorghum - Sorghum vulgare Pers. (Photo L. Pauwels)

Botanical characters

Sorghum (Sorghum bicolor) is a grass belonging to the Andropogoneae tribe (the same to which the sugar cane belongs). Another species of the same genus is the Sorghum halepense, or sorghum of Aleppo or sorghetta, known as a fearsome weed.
Cultivated sorghum is an annual herbaceous plant.
The stalk, 1 to 3 meters high, is formed by a series of knots and internodes filled with marrow which in some forms is rather dry, in others succulent and sugary.
The leaves are linear, lanceolate, inserted alternately at each node of the stem; the flap is hairless with a pruinose surface and at the edges it has a slight indentation easily perceptible to the touch.
The number of leaves is greater the later the variety is: on average 8-10 for the earliest varieties, 18-20 for the later ones. The whole surface of the leaf sheaths and the stem is glaucous due to the presence of a thick waxy bloom. The buds of the basal nodes of the culmo often sprout causing a certain tillering of the plant. The production capacity is maximum in forage sorghum, while it is limited in grain.
The root system is, like that of corn, collated and formed by embryonic and adventitious roots: however, more than corn is expanded in width and depth; moreover, the roots are more robust and fibrous than those of maize and have a greater ability to extract water.
The inflorescence is a terminal raceme commonly called "panicolo" with a normally erect bearing, but in some cases hanging; the panicle is compact or sparse depending on the length and strength of the main axis and side branches. Spikelets always paired two by two are inserted on the side branches of the panicle: one is sessile and fertile, the other is pedunculated and sterile.
The sessile spikelet is formed:
1. by two glumes which at maturity become leathery and shiny;
2. by two glumelle of which the upper very small and the lower paper;
3. from a typically graminaceous bisexual flower, formed by a super ovary, uniovular, with bifurcated stylus and plumed stigma, and by androceous of three stamens.
In some varieties of sorghum the kernels are dressed remaining the adhering glumes, in others they are naked. The glumes can be variously colored: from reddish to brown-purplish.
The grain can be white, yellow, brown, reddish, brown-violet due to the presence of pigments in the cells of the pericarp or spermoderm or both.
The caryopsis have very variable dimensions, weighing from 15 milligrams to 35-40.
The flowering of a panicolo begins about two days after the earing, starting with the apical flowers and proceeding towards the base until completing in 6-10 days. Under normal conditions fertilization is autogamy for about 95%.
Sorghum has the characteristic that the plant remains green when the grain is ripe.
The sorghum plant, when young, contains a highly toxic cyanogenetic glucoside called durrine, which hydrolyzes in the stomach into glucose, p-oxybenzoic aldehyde and hydrogen cyanide. The durrine content is not constant, but varies with the age of the plant: as it approaches maturity it decreases until it disappears; young plants have the highest concentration, so durrine is only a problem for forage sorghum.
The many existing forms of sorghum can be classified according to their destination as follows.
- 1 Broom or broom sorghum (Sorghum vulgare var. Technicum). The main axis of the panicolo is very short and very long and elastic branches are inserted on it, almost to form an umbrella-shaped inflorescence. This inflorescence, deprived of the grain, is used for the manufacture of brooms and brushes. The harvest is done when the grain matures, however to avoid that the weight of this fold deforming the ramifications of the panicle, making it unsuitable for the purpose, it is necessary that at the milky maturation the culms are folded so that the panicles hang down.
- 2 Sugary springs (Sorghum vulgare var. Saccharatum). They are very tall, large-stemmed plants, with large leaves, juicy and sugary stems due to the presence in the marrow of large quantities of sucrose (15-20%). In the last century great hopes were raised about the possibility of growing sorghum for the production of sugar. Except that in sorghum sucrose is always accompanied by significant quantities of invert sugar which inhibits crystallization. Therefore the sugar sorghums are of minimal importance and are used for the preparation of syrups and for the alcohol industry or as a forage crop.
- 3 Forage springs. The sorghum plant, both young and milky or waxy maturation of the grain, lends itself very well to feeding livestock.
- 4 Grain springs. They are grown for their grain which is used for human nutrition in developing countries or for the feeding of livestock in developed countries.

Environmental needs

Sorghum has greater thermal requirements than corn: to germinate and be born with acceptable readiness it requires soil temperatures of 14 ° C, compared to the 12 ° C required for corn.
Sorghum has lower water requirements than corn: it has been called "camel plant" as it is able to withstand water deficiencies with reduced damage. We recall the main morphological and physiological equipment that give the sorghum characters of marked eroticism:
- 1 Strongly cutinized leaves, covered with bloom, with less numerous and smaller stomata than those of corn;
- 2 unit water consumption among the lowest (considered to be around 250);
- 3 deep and expanded roots, capable of extracting water from the soil even when it is strongly retained;
- 4 Protoplasm capable of withstanding irreversible damage relatively high temperatures and rather high dehydration;
- 5 Ability to enter vegetative stasis by slowing down the vital processes in case of water "stress" to resume them with limited damage as soon as more favorable water conditions are restored (in maize, on the other hand, water stress stops growth irreparably).
It is obvious that this dryness has limits: it is still necessary that between the water reserves of the soil and the supply of rain during the life cycle, it is necessary to be able to count on a quantity of water estimated at around 300-350 mm (or 3,000 -3.500 m3 / ha).
In deep soils with good water retention capacity (therefore excluding loose ones) it is sufficient that it rains 120-150 mm in the months from June to August to ensure yields, if not very high, at least satisfactory from a technical and economic point of view.
These conditions are found in several central regions: Emilia Romagna, Tuscany, Marche, Umbria, Lazio and in certain internal parts of Abruzzo, Molise and Campania, also in many of those less favored hilly areas, commonly called "marginal". In the southern regions, which are too arid, sorghum without irrigation cannot be proposed, but it could give excellent productive responses to limited irrigations, having a relief character.
As far as the soil is concerned, sorghum also adapts well to heavy clayey ones with mediocre structure; tolerates a wide range of acidity (from pH 5.5 to 8.5) and high salinity.

Variety

As for maize, an intensive spring-growing cannot fail to resort to hybrid varieties, for their superior qualities of uniformity and vigor and, therefore, of productivity.
Choice of the hybrid. The correct length of the cycle (indicated with the same system as the FAO classes) is fundamental, as only with the types of appropriate earliness can we think of fully exploiting the limited water resources in the best possible way.
In environments where you can count on a certain summer rainfall, the best results are obtained with the class 300-400 hybrids, which enter into vegetative stasis as soon as the water reserves of the soil are exhausted and remain there until the first rains , when vegetative activity resumes. It is to be avoided to cultivate medium-late or late springs, given the serious risks that occur with them not to see the grain ripen.
Among the morphological characters, the low size and a good breeding of the panicolo take on particular importance in terms of mechanization: all the hybrid hybrids are dwarf, that is, they measure 1.3-1.5 m in height instead of 2-3 meters and more than normal types; in addition, to facilitate combine harvesting, it is important that the panicle is supported by a long peduncle, so as to be well spaced from the last leaf; in this way, by appropriately adjusting the cutting height of the cutter bar, panicles can be collected exclusively (or almost) thus avoiding the green parts of the plant.
A reduced tillering power is desirable in the grain types, to avoid delays in the maturation of the secondary panicles.
To be marketable in the EU, the sorghum grain must have a low tannin content, the presence of which lowers the digestibility of the protein. Therefore the hybrids that had been selected for high tannin content in order to make them resistant to bird predation (BR: Bird Resistent hybrids) are being abandoned.

Cultivation technique

Place in the rotation

Grain sorghum could without serious inconveniences (except for infestations of striga in tropical countries) succeed itself, but it is normally considered a renewal plant that follows and precedes a winter cereal.
Sorghum is not frequent in repeated cultivation, given that in arid environments where sorghum is taken into consideration, the safest and most profitable crops are winter cereals, to which sorghum alternates to avoid the inconveniences of the thanks.
After sorghum the fertility of the soil is lower than after maize and other renewal plants, so much so that the subsequent cereal, generally wheat, tends to produce less. The main cause of the lower production potential of wheat after sorghum is the lower availability of nitrogen, caused by a greater biological immobilization of this element.
Grain sorghum does not lend itself to being made in the second crop, but only in the main crop.

Soil preparation

Since the sorghum is a dry crop plant, it is necessary to try to promote the deepening and to create the most abundant water reserves in the soil: this is done through deep tillage done promptly, that is, before the start of the rainy season, as plowing or, better yet , as a two-layer process.
Any possible inter-crop cultivation should be excluded as it would decrease water supplies and make it difficult or impossible to prepare the seedbed with the perfection that sorghum requires.
The smallness of the seed, the delicacy of the seedlings and the late sowing date require extremely accurate preparation of the soil for sowing.
In clay soils it is necessary that the soil is prepared very promptly, during the autumn and winter, with energetic harrows and grubbers, so that when sowing it is already well leveled and administered, so as not to require that the intervention of harrows light that move only a very superficial layer. Only in this way, leaving atmospheric agents the task of perfecting the shredding of the surface soil and avoiding to re-mix the layers, can we hope to put the seeds, in conditions conducive to germination and emergence: soil managed so as to adhere well to seeds, moist already at the small depth (20-30 mm) to which the seeds are to be put, structured so as to prevent the formation of a crust.
Perfect soil preparation is the most delicate point of the crop.

Variety choice

The hybrids of sorghum that experience has shown to be the most suitable and reliable in Italy are those which are neither too early nor too late, but medium-early cycle of the earliness classes 300 or 400, corresponding to 105-110 conventional days.

Composting

Since it is a dry crop, the mineral one must be limited, the more the scarce the water availability. In the absence of manure, the most advisable doses are as follows: 40-60 Kg / ha of P2O5 to be given pre-sowing; 80-100 kg / ha of nitrogen to be sown as urea. Given the clayey nature of the land on which sorghum can be grown, the usefulness of potassium fertilization is uncertain.

Sowing and weeding

The sowing time is determined by the minimum temperature for germination, which in the case of sorghum is higher than that of corn: 14 ° C instead of 12 ° C; this obliges to sow 10-15 days after corn, that is from late April (in the South) to mid-May in the Center.
Since sorghum is grown in arid environments, it is imperative to sow it as quickly as possible, bearing in mind that any delay in sowing will have a negative impact on production.
With the medium-early hybrids, which are the most cultivated, the sowing is done in rows approx. 0.40-0.50 m, using the wheat sowing machine or the precision sowing machine of the beet adjusted to sow a quantity of seed sufficient to ensure a population of 15-30 plants per m2. providing for an inevitable share of bankruptcies (of the order of 40-50%), the use of 10-15 Kg / ha of seed should be envisaged.
The yield of the sorghum less than the corn depends on the number of plants per m2 thanks to the ability that the sorghum has to gather and thus self-regulate its density.
The sowing depth is very important: if excessive it makes the emergence of the seedlings problematic, if insufficient it exposes the seeds to dangers or to desiccation or predation by birds. The ideal depth is 20-30 mm (maximum 40) in soil that is possibly well firmed by a pre-seed rolling.
The chemical weeding of sorghum has considerable limitations in the very low number of active ingredients whose use is allowed on this species.
The control of sorghum weeds could usefully be done with mechanical weeding which, in a non-irrigated crop such as sorghum, would also achieve other advantages, in addition to the control of weeds: better aeration of the rhizosphere and water economy especially in the clayey lands prone to cracking.

Irrigation

In climatic environments with very high spring-summer aridity (southern Italy) not even sorghum can satisfactorily produce in dry crops.
In these cases, a very interesting spring growing is possible if there are water supplies that have no better use. It is a question of providing a limited irrigation aid when the sorghum cultivation passes the most critical phase that goes from the barrel to the milky maturation. In this period, contributions of the order of 150-200 mm allow to reach productions of the order of 8 t / ha of dry grain and more. Sorghum goes very deep to draw water and therefore can be irrigated so as to wet 1 m of thickness; in addition, the need for timeliness is much less felt than in maize, given that for irrigation the irrigation intervention limit is lower than in maize and that sorghum can enter retirement.

Collection and use

Sorghum ripening goes through the same phases described for other cereals: milky ripening, waxy ripening, physiological ripening. Almost never, given the time of harvest, the grain is dry enough not to require drying.
It should be remembered that sorghum, unlike maize, keeps the leaves and stems completely green even when the grain is ripe.
Sorghum grain is harvested with the same wheat combine harvesters, adjusting the cutting height so high that only panicos are collected if possible; for this reason, types with a good panicle exemption from the last leaf are preferable.
The grain yields achievable with sorghum are variable according to the seasonal trend: in very favorable conditions of soil and summer rainfall they can reach 8-9 t / ha of grain; average yields of 6 t / ha are to be considered good.
By comparing it with the dry crop of maize, of which sorghum should be the substitute, it can be said that in unfavorable environments and vintages the sorghum far exceeds maize.
It should be noted that to date, a little wrongly and a little rightly, sorghum has not met with great sympathy with Italian farmers, for the following main reasons:
- 1 Difficulty in having regular births;
- 2 Excessive maturation delay;
- 3 Difficulty of drying due to the concomitance with that of corn;
- 4 Predation by birds during granigion;
- 5 poor fertility conditions for subsequent wheat;
- 6 Difficulty in placing the product;
- 7 Low selling price (compared to the corn of which it has similar nutritional value).
None of these difficulties is insurmountable with a better knowledge of the cultivation technique and many of them would be destined to decrease until they disappear as the cultivation of sorghum spread.

Adversity and pests

The adversities that can damage the sorghum are not many and serious in Italy where the crop is not widespread. On the other hand, there are many that are found in the aragogenic plaques.
- 1 Meteorological adversity. The low temperatures at the beginning of the vegetation are to be feared, also because they can accentuate the attacks of aphids on young seedlings. The lodging is not to be feared in the grain varieties, which are very low and robust, while it is a serious problem for certain forage springs of great development and for which the lodging represents a very serious obstacle to mechanical harvesting.
- 2 Cryptogamic adversity. They are not very worrying, at least as long as the crop is not very extensive. We remember the rot of the seedlings (Fusarium, Pythium), which are prevented by tanning the seeds and avoiding too early sowing; the stem rot (Fusarium, Macrophomina phaseali, Rhizoctonia solani), the maize mosaic retardant.
- 3 Parasitic adversity. The first danger is represented by the terrestrial insects (elateridi and agrostidi) against which the disinfestation must be done when sowing.
Aphids (Aphis maidis) can be very harmful when attacking young plants. The fight is not easy when the insects are on the underside of the leaves.
During vegetation damage can be caused by the pyramids (Ostrinia nubilalis, Sesamia cretica) which undermine the stem.
In the southern regions or in the event of late sowing, serious damage is caused by two diptera, the cecidomy (Contarinia sorghicola), whose larvae consume the ovaries or the caryopsis just formed, and the atherigona (Atherigona soccata), which causes the destruction of the vegetative apex of the stems in the rising phase, causing their stunting and stimulating the emission of tillering buds.
- 1 Birds. Different birds, mostly passeraceous, are a scourge for sorghum, at least as long as cultivation is done on limited surfaces. They rest on the panicles consuming the grains in formation, from the milky ripening onwards.
- 2 Parasitic plants. In tropical spring regions a scourge is represented by a parasitic plant, the Striga, which parasitizes the roots of sorghum with its austori.
In Italian arboriculture the only treatments to be systematically foreseen are tanning and geodisinfestation.


Video: Sorghum: Growing and Harvesting (May 2022).