Cereals

Cereals are cultivated as the main sources of our and reared animals' (goats, sheep, cows, horses, hens, etc.) foods in most countries of the world. They include wheat, oats, barley, etc. They require proper fields, fertilizers, water, sunlight, warm days, cool nights, humidity, proper pesticides, herbicides, etc; and above all necessary expertise and experiences for their growth as crops. Fields are ploughed to sow their seeds and to mix manures with fertilizers and soils. Some chemical fertilzers may also be added during irrigation when crops are growing. Ordinary wheat takes about hundred days to become harvestable. Barley requires less time but more care than wheat does. Their grains are seperated from chaffs by threshers or combined harvesters. Barley chaffs are more suitable for cattle, goats, sheep, horses, etc than wheat chaffs. Their grains are purified from impurities and then milled to produce flours.

Wheat (Triticum aestivum L.) is grown in most regions of the globe due to its importance as a food source, and its enormous genetic variability in phenological response to photoperiod and temperature including vernalization. ^[1] Argentina is one of the countries with the largest wheat-growing area with more than 5 million has. spread all over the country.

Most of the Argentinean wheat is produced in the Pampean region. This region has a temperate humid climate without a dry season but with a warm summer. Precipitation is higher in summer than in winter. The rainfall distribution is close to monsoonal in the north-west of the Pampas and it tends to an isohigrous pattern at the southeast of Buenos Aires. The temperature regime for the region shows that June and July are the coldest months and January is the hottest. Mean monthly temperatures rarely fall below 7ºC and the frost-free period ranges between 180 and 260 days. Temperature indices decrease in the North-South direction, but thermal amplitude also increases from east to west; the frequency and intensity of frost increase westward.

It has an annual rainfall of approximately 600-1000 mm and a mean temperature of 15-17 º C depending on the region, with some differences between the east and the west. Soils in the region are mainly mollisol including argiudolls, hapludolls and haplustolls developed on a deep mass of Pampean loess.^[2] Wheat crops are sown from the second half of May to the first half of August. Varieties are classified as long or short season. Long season varieties have higher requirements of photoperiod or days with low temperatures, although their requirements in vernalization are not as high as in winter varieties cultivated in other countries. Short season varieties have in general low requirements in photoperiod or days with low temperatures, and are similar to some spring varieties. Risk of frost damage at flowering is the main climatic factor determining optimum sowing dates for particular varieties in the various regions. Optimum seeding rates for long-season varieties may vary between 200 to 250 established plants per m2, while short-season varieties tend to be sown with seeding rates between 250 to 350 established plants per m2.^[3]

During grain production, plant species are rotated following different patterns depending on the region but the most common cropping system tends to be the double-cropped full-season-wheat and soybean [Glycine max L. (Merr.)]. The doubled-crop system is usually stable and financially convenient, since the wheat crop provides a financial return during summer and the soybean during autumn and winter.

The grain production region has experienced severe tillage changes in the past twenty years, mostly due to the increased interest in maintaining soils covered with plant residues. This has led to implement zero tillage systems to restore soil structure in large areas cultivated with double-crop sequences such as wheat/soybean; corn (Zea mays L.) - wheat/soybean; or wheat monoculture. Zero tillage is also desirable because of its positive effect on soil organic matter, for maintaining soil humidity and to prevent soil erosion.^[4] Zero tillage can reduce costs by decreasing fuel consumption required to produce a crop. However, in the wheat/soybean system under zero tillage, as in wheat following wheat, the inoculum of necrotrophic fungi usually survives until the next wheat season. Therefore, the use of fungicides is essential to decrease the severity of necrotrophic diseases. On the other hand, nitrogen (N) fertilization is necessary to achieve high yield and grain quality. Even in high soil fertility conditions, N uptake is important because it is positively correlated to grain protein content.^[5] However, N availability may also enhance the development of some foliar diseases caused by fungi. Fungicides are usually applied on foliage to control diseases but they are also used for seed treatments to prevent seed decay (since soil fungicide applications are not a common practice in Argentina).

1. ↑ "Slafer GA, Rawson HM (1994) Sensivity of wheat phasic development to major environmental factors: A re-examination of some assumptions made by physiologists and modellers. Australian Journal of Plant Physiology. 21: 393-426.">
2. ↑ Campos M (2008) Variedades y modelos generales de producción en el movimiento CREA. In: Satorre E, editor. Producción de Trigo. CREA. pp. 73-118.
3. ↑ Satorre E, Slafer GA (1999) Wheat production systems of the pampas. In: Satorre E, Slafer GA, editors. Wheat: ecology and physiology of yield determination. Food Product Press. pp. 333-348.
4. ↑ Trigo E, Cap E, Malach V, Villarreal F (2009) The case of zero-tillage technology in Argentina. International Food Policy Research Institute, Discussion Paper. 40 p.
5. ↑ Stone PJ, Savin R (1999) Grain quality and its physiological determinants. In: Satorre E, Slafer GA, editors. Wheat: ecology and physiology of yield determination. Food Product Press. pp. 85-119.