Soil Liming

the application of lime and other calcium fertilizers to the soil to eliminate excess acidity, harmful for many agricultural crops; a means of chemically improving acid soils. Soil liming is based on replacing ions of hydrogen and aluminum with ions of calcium and magnesium in the absorption complex of the soil. As a result of the neutralization of soil acidity and the increase in calcium content during liming, the vitality of useful microorganisms (for example, nodule bacteria and microorganisms that mineralize organic remains and humus) is stengthened, the soil is enriched with nutrient elements accessible to plants, and the physical properties of the soil are improved (structure, water permeability). Soil liming increases the effectiveness of organic and mineral fertilizers.

Soil liming is used extensively on podzolic, soddy-podzolic, and certain peat soils and less often on gray forest soils and red soils. Podzolic soils with a pH in salt extract of less than 4.5 require liming for all crops, and those with a pH of 4.5–5.0 must be limed for all crops except lupine. Where the pH is 5.1–5.5 lime must be applied for all crops that are highly sensitive to acidity (beets, cabbage, onions, garlic, clover, alfalfa, and currants), for crops requiring a weakly acid and close to neutral reaction (rutabagas, turnips, vetch, beans, corn, wheat, barley, cucumbers, apples, and cherries), and for crops able to withstand moderate acidity but producing higher yields where large doses of lime are applied (oats, rye, timothy, and buckwheat). In podzolic soils with a pH of 5.6–6.0, liming is required only for beets and alfalfa, and where the pH is more than 6.0 the soil need not be limed. The dosage of lime fertilizers depends on the degree of soil acidity and on its texture and should be sufficient to support a weakly acid soil reaction for 10–12 years, which will ensure normal conditions for the growth and development of most agricultural crops (see Table 1).

The dosage of lime fertilizers can be reduced when they are not placed deep in the soil and are used together with organic and mineral fertilizers. Lime fertilizers are usually applied once per crop rotation. In some cases, for example, if the crops in the rotation differ greatly in their need for liming, it is advisable to apply the full dose in parts (in stages). Lime fertilizers can be spread over fields in the spring, summer, and fall; on level areas lime can be applied on frozen soil and light snow. The effectiveness of soil liming depends to a large extent on the evenness of the fertilizer’s distribution over the surface and on its thorough working into the soil. Liming produces a significant gain in yield. Average gains for the USSR (in centners per hectare) are as follows: ear grain crops (grain) 0.5–4, legumes (grain) 1–3, feed beets 30–60, potatoes 5–15, flax (straw) 1-3, clover (hay) 7–15, cabbage 30–70, and carrots 15–45. In order to lime soils on a planned basis special soil studies and field tests are made, and cartograms of soil acidity and liming are compiled.