Modern agriculture implies the application of large amounts of potent chemicals and pesticides onto the land. Some are applied directly to the soil, others to foliage, but most of the pesticide residues reach the top three inches of soil where the majority of soil fauna are found. Many of the soil fauna and micro-organisms that are essential in the processes of soil formation and maintenance of soil fertility, are killed on contact with these pesticides. The main soil contaminants are arsenic and the chlorinated hydro-carbon insecticides such as DDT, dieldrin and BHC, along with their toxic by-products. Many organic phosphates, when abundant, reduce plant growth.
DDT has been found in agricultural soils at rates up to 10-100 lbs per acre.