Soil Solution

(the liquid phase of soil), water with dissolved gases, minerals, and organic matter that reaches the soil after passing through the atmosphere and percolating through the soil horizons. The solution may be in a film, capillary, or gravitational form, depending on the moisture content of the soil. It participates in soil formation, physicochemical and biochemical reactions, the cycle of matter in soil, and plant nutrition. Its composition is determined by soil-forming processes, vegetation, general climatic conditions, the season, weather, and man’s activity, such as the addition of fertilizers.

Soil moisture contains dissolved gases, including oxygen, carbon dioxide, nitrogen, and ammonia; dissolved mineral substances, such as salts of calcium, magnesium, sodium, and potassium and compounds of aluminum, iron, manganese, and silica (as the ion SiO₄^4- and in colloidal form); and dissolved organic matter—fatty organic acids and their salts, humic acids, sugars, and amino acids. The concentration of substances is low (usually not exceeding 0.1 percent) in nonsaline soils but very high in solonchaks and solonetses (as much as several percent and higher). A high content of substances in the soil solution is injurious to plants, making it difficult for water and nutrients to reach them and thus causing physiological dryness.

The reaction of the soil solution varies from one soil group to another. Podzolic, gray-forest, and peat soils and red and yellow earths have an acid pH; sodium carbonate solonetses have an alkaline pH; and ordinary chernozems, and meadow and cinna-monic soils have a neutral or weakly alkaline pH. An excessively acid or alkaline soil solution has an adverse effect on plant growth and development.