Plant Physiology - Musienko M. M. 2001

Water regime of plants
Physiological principles of irrigation

For the Water balance of a given region, The ratio of precipitation to evaporation is far more critical than the absolute amount of rainfall. If annual precipitation exceeds evaporation, the region is classified as humid; if the reverse is true, it is arid.

Water scarcity affects one-third of the Earth's land surface. More than half of this area is extremely arid, receiving less than 250 mm of annual rainfall while experiencing evaporation rates of up to 800 mm. Artificial irrigation is the most radical means of combating drought in such agricultural zones. It establishes optimal moisture conditions within the active soil layer, promotes The Development of a rich microflora, and enhances the Mineralization of organic matter, thereby significantly increasing crop productivity.

Irrigated agriculture relies on a scientifically sound and rational irrigation regime, integrated with a mineral Nutrition system tailored to specific crops within a particular soil and climatic zone. Frequently, due to miscalculations in irrigation rates, water percolates into deep, salt-rich soil layers, dissolving salts and causing them to rise toward the arable horizon, leading to soil salinization. As a result, vast areas of fertile land are taken out of agricultural production.

Insufficient watering also has detrimental consequences. Under irrigated conditions, plants develop a large leaf area, transpire intensively, and acquire Anatomical Features characteristic of hydrophytes. Prolonged intervals between waterings are particularly destructive to plant physiological activity and productivity.

Therefore, irrigation timing and rates must be scientifically grounded, making the physiological Diagnosis of plant water supply an urgent priority for irrigated agriculture. The irrigation rate (M) is calculated using the equation:

where M_p is the irrigation rate, m³/ha; H is the calculated soil layer depth, m; a is the bulk density of the soil, g/cm³; B_pw is the field capacity, % of dry soil mass; and B_f is the actual soil moisture content prior to irrigation, % of dry soil mass. However, the most reliable results in determining irrigation timing are achieved by assessing the physiological state of the plant itself. The arsenal of physiological control Methods includes A wide variety of indicators: leaf water absorption capacity, concentration, osmotic pressure and suction force of Cell sap, permeability and viscosity of the Cytoplasm, water-retaining capacity

and water deficit of plant Tissues, stomatal apparatus status, electrolyte leakage and electrical resistance of tissues, water potential value, growth response, and several others.

Under production conditions, a widely used method involves measuring leaf suction force, which correlates with water regime parameters that do not yet cause Metabolic Disorders. For example, the leaf suction force of spring wheat is 0.81–0.91 MPa during the tillering-to-jointing phase, 1.0–1.1 MPa during heading, and 1.11–1.21 MPa during grain filling.

Artificial irrigation creates a unique microclimate that fosters optimal plant development. This factor must be taken into account when applying low-rate irrigation using sprinkler systems.

Thus, the physiological diagnosis of plant water supply, the establishment of a rational irrigation regime, and the optimization of mineral nutrition across various soil and climatic zones must form the foundation of artificial irrigation.