Wheat is one of the most important crops to humankind as it is a staple of many diets around the world. From the results of studies on fossil wheat kernels found in various countries of the Middle East, it is assumed that the beginning of wheat cultivation can be traced back to a few millennia B.C. In the Fertile Crescent, a geographical area situated between the Mediterranean Sea, Red Sea, and Persian Gulf once known as “Mesopotamia”, the earliest cultivated wheat was emmer wheat. Emmer wheat was first cultivated in 8500 B.C. In Western Europe Wheat spread in the Stone Age (8,000-5,000 B.C.). In the Americas, wheat has a recent history. In the first half of the sixteenth century, it was grown in Mexico, Peru, and Chile. Nowadays, the global trade of wheat is greater than all other crops combined. China produces more wheat than any other country, followed by India, Russia, and the United States.
Wheat is belonging to the grass family. There are many species and subspecies of wheat, but species of agronomic and economic interest are just two: soft wheat (Triticum aestivum) and durum wheat (Triticum durum). Wheat is an annual plant, with an erect stem, with cylindrical section, formed by 5-8 nodes and internodes, depending on the species and variety. The number of leaves per plant varies from 5 to 8, the leaf blade has a linear-lanceolate shape. The importance of the last leaf is noteworthy, a flag leaf in the filling phase of the kernels. Wheat has a fibrous root system, with primary roots and adventitious roots that originate from the basal nodes of the main stem and of the tillers. The inflorescence is an ear, and the pollination is anemophilous. The fruit is a caryopsis with an elliptical, oval shape and an accentuated ventral furrow.
The biological cycle of wheat, as in many other annual plants, coincides with the productive one. The main phenological stages are:
Sowing-emergency: it begins with the germination of the seed and proceeds with the development of the seedling until it emerges from the surface of the soil (emergence). Under optimal conditions, this phase lasts for 10-15 days.
Leaf development and beginning of tillering: after the emergency, development proceeds with the emission of new leaves. At the axilla of each leaf, a bud develops that exactly repeats the structure of the main stem and which, as it develops, gives rise to a tiller. During the tillering phase, the growth of the root system also proceeds, each stem in fact differentiates its own root system.
Tillering-beginning of stem elongation: the emission of the tillers proceeds with a rhythm depending on the temperatures. During tillering, the plants have a bushy appearance. The number of culms per plant present at this time largely exceeds the number that will be brought to maturity. The latter represents the tillering index which in normal cultivation conditions varies from 0,5 to 2.
Stem elongation: in this phase a rapid elongation of the internodes occurs, starting from the basal ones. The internodes gradually reach greater lengths, rapidly bringing the ear upwards. At this stage, the last leaf called the flag leaf is also clearly visible.
Flowering: flowering lasts an average of 4-8 days and after fertilization the development of the caryopsis begins.
Growth and ripening: in this phase the caryopsis first increase in size, accumulate reserve substances (starch and protein substances) and finally quickly lose moisture until the maturation phase, suitable for harvesting.
Wheat is a micro-thermo cereal, different adaptation mechanisms dependent on the reaction to low temperatures and the photoperiod allow it to synchronize the different phases of the production cycle to the most favorable periods of the year for environmental conditions. The ideal temperatures for growth and production are around 18-20 °C (64.4-68 °F). Sensitivity to frost is high in the germination and emergence phases. Cold resistance increases between emergence and the fourth leaf, reaching its maximum in full tillering. Wheat adapts to a wide range of soil conditions. The ideal conditions are in clayey soils, with a good structure and well-endowed with organic substance. Wheat benefits from the alternation with other species, in fact already in the first year of thanks or re-growth, that is, when it returns to the same soil, the reduction in grain yields is marked. Renewal crops, such as corn, tomato, potato, tobacco, sunflower, are good crop precessions for wheat, as this cereal can very well exploit the residual fertility that these crops leave in the soil.
The quantity of nutritional elements needed by the plant varies according to genetic factors and environmental conditions. The higher the product yields, the greater the quantities of nutrients absorbed.
Today it is necessary to optimize fertilization, to make the crop absorb most if not all the elements supplied with the fertilizers, avoiding underdoses that limit production or overdoses that represent an economic loss for the farmer as well as a potential risk from an environmental standpoint.
Among the essential nutrients for the plant, nitrogen is the one that is most frequently found in the soil in insufficient quantities to meet the needs of the wheat. Nitrogen fertilization is therefore of primary importance in the cultivation of this cereal and is almost always necessary to obtain high product yields.
Nitrogen influences the production of wheat in several ways. An abundant availability of the element delays the senescence of the foliar apparatus, resulting in a longer duration of assimilation and increases leaf expansion with a direct effect on the photosynthetic capacity. Furthermore, optimal availability of this element produces greater tillering, lower mortality of the stems and better fertility of the ears. The absorption rate of nitrogen from the soil reaches its maximum during stem elongation and normally decreases until it stops during caryopsis growth and ripening.
The plant also needs to find a good concentration of phosphorus in the soil, especially in the first weeks after sowing, even if the greater share absorbs it during stem elongation. Also, for potassium, the largest amount is absorbed during stem elongation.
The crop also benefits from the application of products with a biostimulant action, based on beneficial microorganisms and vegetable protein hydrolysates. These products are able to stimulate the emergence and root development in the early stages of seedling development, to improve the availability of nutrients in the soil, to increase the yield from a quantitative and qualitative standpoint, to reduce the negative impact of climatic stresses and to increase the nutrient use efficiency (NUE). The application of biostimulants increases the environmental and economic sustainability of the production system.
Ear 1 cm