Soil acidity

Map of soil acidity. Brown - acidic soil. Blue is alkaline.

Soil acidity ^[1] - the ability of the soil to exhibit the properties of acids.

The presence of hydrogen ions (H-ions) in the soil solution, as well as the exchange of hydrogen and aluminum ions in the soil absorption complex with incomplete neutralization gives the soil an acid reaction.

A number of indicators are used to characterize soil acidity :

• Actual acidity is the pH of the soil solution (in practice, the pH of an aqueous extract is measured at a ratio of soil: water = 1: 2.5 for mineral soils and 1:25 for peat). At pH 7, the reaction of the soil solution is neutral, below 7 it is acidic, and above it is alkaline. Podzolic soils of the forest zone have a predominantly acidic reaction (pH water 4.5–5.5), podzols and peat bogs strongly acidic (pH water 3.5–4.5).
• Potential soil acidity is the acidity of the solid part of the soil, it is expressed in mEq per 100 g of dry soil. The potential acidity parameters also take into account the influence of PPK cations, which can acidify the soil solution ( H ⁺ and Al ³⁺ ).
• The exchange acidity of the soil is caused by the exchange cations of hydrogen and aluminum, which pass into the solution from the soil absorbing complex when interacting with neutral salts. In humus-rich horizons, it is mainly due to H-ions, and in low humus minerals, it is due to Al-ions. The exchange acidity of podzolic soils of the forest zone is 3.5–5, or 0.5–6 mEq per 100 g of dry soil, and gray and brown forest soils are significantly lower.
• Hydrolytic acidity - pH of the extract with a solution of hydrolytically alkaline CH ₃ COONa (allows for more complete displacement of H ⁺ from PPC). It is determined by H-ions passing into the solution upon interaction with the soil of hydrolytically alkaline salts, and includes less mobile H-ions, not displaced by neutral salts. In podzolic soils, hydrolytic acidity is 1-10 mEq per 100 g of dry soil. The magnitude of hydrolytic acidity can also be judged by the saturation of the soil with bases.

The increased acidity of the soil negatively affects the growth of most cultivated plants by reducing the availability of a number of macro- and microelements, and vice versa, increasing the solubility of toxic compounds of manganese , aluminum , iron , boron , etc., as well as deterioration of physical properties. To reduce acidity resort to liming ^[2] .

Soil acidification (the term synonymous with Acidification of the soil is inadmissible) ^[1] - a change in the acid-base properties of the soil caused by the natural soil-forming process, the entry of pollutants, the introduction of physiologically acidic fertilizers and other types of anthropogenic effects.