a physicochemical property of soil functionally related to the concentration of H+ and OH- ions in the solid and liquid parts of the soil. If H+ ions are predominant, the soil reaction is acid; if OH- ions are predominant, it is alkaline. If the concentrations are equal, the soil reaction is neutral. The pH of soils in the USSR varies from 4 to 8.2.
The soil reaction plays an important part in the migration of products of weathering. The migration capacity of Fe, Mn, Sr, and Cu compounds increases in an acid medium, while that of Si and Al compounds increases in an alkaline medium. The soil reaction greatly affects the metabolic level of plants. Because many plants are harmed by a high concentration of [H+] and [Al3+] ions when the soil reaction is acid, acid soils must be treated with lime. Such strongly alkaline soils as solonetz soils and sodium carbonate solonchak soils, which have a high concentration of [OH-] ions and lack structure, are also unfavorable for plant growth and development.
The application of gypsum combined with organic fertilizers neutralizes an alkaline soil reaction and improves the soil’s agronomic properties. Indicators used to determine the soil reaction quantitatively include the pH of a soil suspension in water or a KC1 solution and titratable acidity or alkalinity.
REFERENCESSerdobol’skii, I. P. “Metody opredeleniia pH i okislitel’no-vosstanovitel’nogo potentsiala pri agrokhimicheskikh issledovaniiakh.” In Agrokhimicheskie metody issledovaniia pochv. Moscow, 1960.
Rode, A. A., and V. N. Smirnov. Pochvovedenie, 2nd ed. Moscow, 1972.
Kovda, V. A. Osnovy ucheniia opochvakh, book 2. Moscow, 1973.
IU. A. POLIAKOV