Keywords: perennial grasses, water consumption, surface runoff, water balance calculation, mathematical modeling

// Мелиорация.– 2022. – №2(100) – P 49–60

The calculation of the elements of water balance of the soil under perennial grasses was carried out according to the data obtained at the experimental site of the irrigation complex «Tushkovo» (Belarusian State Agricultural Academy) with a soil surface slope varying within 0.023‒0.027. The smallest error was obtained when calculating the water consumption of perennial grasses according to the maximum air temperatures and biothermal coefficients established on the basis of the physical principle «balance of cause-andeffect interactions in a closed physical system», independent of the method of grass stand use (green mass, haylage, hay, pasture). The analysis showed that with given indicators of surface slopes, surface runoff should be taken into account only at the top of the slope and at a distance along the slope of up to approximately 50 m. In areas located down the slope, surface runoff, as a consumable element of the water balance, can be neglected when cultivating perennial grasses. This limitation is explained by the fact that during rain (or irrigation), about the same amount of water inflowing from the higher part of the slope additionally infiltrates into the soil, as it decreases with surface runoff down the slope.