Rice is one of the oldest food plants, originating in Southeast Asia and a species of swamp, although in its phylogenesis there are different genotypes capable of carrying out the cycle in non-submerged soil with the sole contribution of high atmospheric precipitation. The antiquity of the culture is confirmed by Chinese and Southeast Asian archaeological finds dating back to 6000-7000 BC. In the West, the first news about rice came after Alexander the Great’s expedition to the east, but the commercialization began only with the Arabs who cultivated it in Spain in the 8th century. Rice is one of the most widely consumed grains in the world and a substantial portion of the diet of many Asian countries, where it is grown extensively. Rice is produced in about 120 countries worldwide, but China and India together account for more than 50 percent of both rice production globally.
Rice is a cereal belonging to the grass family and to the Oryza genus. The most widely cultivated species belong to the sativa species, of which three geographical subspecies are distinguished: Indica, to which the subspecies cultivated in India, Southeast Asian countries, and southern China, javanica, limited to the equatorial belt of Indonesia and japonica, to the which are referable the forms cultivated in Japan, Korea, northern China, Egypt, Turkey, Italy, Spain, Portugal, and North America.
Rice is an annual species, cespitose with a fibrous root system consisting of very numerous adventitious roots. The leaves have an elongated lamina, an entire margin, and a rough surface due to the presence of short and stiff hairs on both pages.
The inflorescence is a panicle, and the flowers are hermaphrodites.
The caryopsis, compressed laterally, of a more elongated shape in the spp. Indica and javanica and more rounded in spp. Japonica is anatomically similar to that of wheat and related cereals.
The biological cycle of rice takes place through the phases of:
Germination: in this phase the rice has specific thermal and humidity needs, but it is also particularly sensitive to the amount of oxygen available. As for humidity, germination begins whether the seeds are placed in a fairly humid environment or immersed in water. The germination phase is considered completed when the plant has formed the second-third leaf.
Tillering: tillering begins with the development of a shoot from the axillary bud of the lowest leaf and can continue by other buds of the primary and secondary culm. The development of the tillering shoots is accompanied by that of adventitious roots, which soon exceed in importance those of embryonic origin. The differentiation of the flower apex marks the beginning of the reproductive period and the end of the tillering period.
Stem elongation: this phase is characterized by the elongation of the internodes, the growth of the leaves and the progressive development of the inflorescence. The stem elongation ends with the reaching of the maximum height of the fertile culms of the plant and with the emission of the inflorescences.
Flowering: flowering is gradual starting from the final part of the panicle of the main culm and continuing in the tillering culms according to the order of their formation.
Ripening: in this phase the caryopsis swells and increases its concentration in dry matter.
Nitrogen (N) is undoubtedly the element that can affect the productivity of the crop by acting directly on the growth of the plant, its size, the number of tillering stems, the weight of the grain and its protein content. Nitrogen absorption increases during the tillering phase and reaches its maximum after flowering. During ripening, absorption is significantly reduced, and the element is mainly translocated from the leaves to the grains. Although less evident, the influence of phosphorus (P) on production is very important especially during vegetative development during which it favors the tillering and elongation of the roots. During the reproductive period, it favors the early flowering and therefore the ripening process, especially in cold climate conditions. The absorption of phosphorus is slower than that of nitrogen until the flower beginnings are formed; subsequently the absorption increases until after flowering and is exhausted during ripening. Potassium (K) is an important enzymatic cofactor, its action affects the size and weight of the grains, favors the thickening of cell walls. It is mainly absorbed from tillering to flowering.
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.