Soil can become acidified as a result of its own physical properties, microbial activity, climate, vegetation, and the addition of acidifying fertilizers. As a result, important nutrients can be lost, and toxicities from aluminum and manganese may occur. Liming, the application to land of material containing calcium, usually chalk or limestone, is often used as a standard measure in order to reduce problems of soil acidity.
Salts introduced in irrigation water, blown inland from oceans, or produced by weathering may accumulate in topsoil and cause toxicity to crops. This is normally controlled by applying more water than the crop can use, so that excess salts are leached downward below the root zone. It is important, however, that the irrigation water does not have high salt content and that drainage is not a problem. The addition of calcium salts, such as calcium sulfate, together with organic manures, is also effective in treating salt-affected soils.
One focus of research in the field of plant nutrition has been the study of the mechanisms plants employ in avoiding or tolerating toxic elements, such as aluminum, manganese, and salts, and accessing scarce nutrients, such as phosphorus, in the soil. Knowing how plants cope with various nutrient stresses will help the effort of breeding crops that are better able to withstand adverse soil nutrient conditions and achieve high yields by making use of their own genetic potential.
See also: Soil and Plant Nutrients
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