PROTECTION OF THE SOIL AGAINST POLLUTION
The most widespread substances polluting the soil from the atmosphere are nitric and sulfur oxides. They enter the soil together with precipitation, raise soil acidity and significantly lower fertility.
Higher concentrations of heavy metals in the soil around industrial enterprises deplete the local flora, with the more sensitive species disappearing.
It is a difficult problem to restore the fertility of soil polluted by heavy metals. The main measure, and a cardinal solution to the problem is to improve technology so that waste is not released into the environment. Sometimes various chemical substances are introduced into the soil to neutralize the effect of soil pollutants, and so on.
The soil may be polluted when fertilizer and pesticides are incorrectly used, and also by the waste of livestock breeding complexes.
Until recent times, animal wastes were utilized as a valuable economic source of nutrients for crop
production. Since World War II, commercial fertilizers have become the preferred source for supplementing nutrients in the soil because of their relatively low cost, ease of handling, ease of storing and ready availability. It is imperative that ways are found to utilize agricultural wastes to improve soils and provide added fertility for plant growth.
Soils vary greatly in their physical and chemical properties and are classified according to these properties.
An understanding of these properties provides information needed to determine the suitability of soils for land disposal of wastes. The engineer may find the advice of a soil scientist valuable when attempting to locate soils for waste disposal.
The chemical conditions existing in soils determine the reaction of soil, which may be acid, neutral or alkaline. This reaction in turn determines the availability or solubility of certain elements as well as the response of microorganisms and higher plants.
There is a natural tendency for soils to become acid in humid climates where sufficient rainfall occurs to leach bases from the surface layers. Hydrogen and aluminium become dominant in the exchange complex and the soil is acid in reaction. When soil colloids are dominated by calcium and magnesium on their adsorptive surfaces, the soil is neutral or alkaline in reaction. This condition occurs in limed soils or low rainfall areas.
The soil chemical properties determine the capacity of the soil to break down the complex waste materials added in varying amounts. These properties are also influenced by the application of wastes.
In the past several years, interest in land disposal of domestic wastewaters has increased. This increase arises from a widespread desire to conserve water by recycling. Also, it is thought that land disposal of wastewater would minimize water pollution problems attributed to the presence of large amounts of chemical constituents that can cause significant water quality deterioration in waterbased disposal systems. Additional interest in land disposal has been created by the possibility that nutrients present in domestic wastewaters, such as nitrogen and phosphorus, can be recycled to the land where they could then serve as fertilizer for terrestrial plants. Land application of domestic wastewaters is potentially an ecologically sound practice; however, a number of potential problems associated with such a practice could result in environmental degradation.