Effect of Long-Term Drip Irrigation of Fruit Orchard on the Transformation of Properties of Chernozems

The impact of long-term drip irrigation of apple plantations with low-saline water on the transformation of typical chernozems (Haplic Chernozems) on the Kuban Lowland (Western Ciscaucasia) was studied. The studies were performed in plantations of winter ripening apple tree (Malus domestica) on rootstock M9 (clone T337). The transformation of soil properties of the irrigated chernozem was studied from the first year after the orchard planting until the marketable fruiting (from the first to the fifth growing years). A pronounced seasonal dynamics of changes in the content of soluble salts in soils under the fruit plantations was revealed: an increase in the salt concentration in the local moistening zone during regular drip irrigation and salt moving into deeper soil layers in the winter–spring period. The concentration of soluble salts was the highest in the surface soil layer at the boundary of the moistening area in young apple plantations and within the entire area of soil moistening in fruit-bearing plantations (EC₁ : ₅ = 0.371–0.458 dS/m). After five years of drip irrigation, a decrease in Ca²⁺ concentration to 11.8 cmol(+)/kg and an increase in Mg²⁺ to 24.8 cmol(+)/kg and in Na⁺ to 2.5 cmol(+)/kg were detected in the upper (0–30 cm) soil layer under droppers. Regular drip irrigation caused a significant local increase in soil solonetzisity directly under the droppers even in the first year of drip irrigation: the content of exchangeable sodium increased to 9.0%. Longer irrigation resulted in a gradual increase in the soil volume subjected to solonetzization (alkalization); however, the content of exchangeable sodium remained relatively stable: 6.1–6.7%. Despite the negative changes in soil properties, a significant suppression of the growth of the active part of the root system of apple trees in the local moistening zone was not revealed.