Decline in the quality of soils by the action of man and nature is called soil pollution. The main factors of soil pollution include excessive erosion, greater use of chemical fertilizers, pesticides, insecticides and herbicides, urban and industrial wastes, forest fires, water logging, leaching and drought etc. Studies have shown that soil pollution is increasing at a faster rate both in rural and urban areas of India.
The increasing use of chemical fertilizers and biocides particularly after Green Revolution, the use of untreated industrial water in irrigation, over irrigation, deforestation, defective land use practices etc. have led to the degradation of soils in many parts of the country. The consumption of chemical fertilizers has more than tripled from 5.5 million tons in 1980-81 to 18.07 million tons in 1999-2000. Punjab, Haryana, Andhra Pradesh and Tamil Nadu have higher per hectare consumption of chemical fertilizers. Excessive use of fertilizers has led to the degradation of soils in many parts of these states.
Similarly the annual production of various types of biocides in India has increased from 2,350 tons in 1955 to 149,795 tons in 1983. Some important biocides used in the country include malathions, chlorinated hydrocarbons (D.D.T., dieldrin, aldrin, endrin, lindane etc.) arsenic containing pesticides and sodium flour acetates etc. Biocides reach the food chain in toxic forms and enter the bodies of animals and human beings.
Use of pesticides has increased the incidence of physical deformities in the children of tea estates workers in Darjeeling area (Down to Earth, 31. 10.2000, p. 26). Similar studies have shown neural tube defect in new born babies in Punjab, Haryana, and Rajasthan and northern states where use of pesticides is increasing in agriculture.
Falty disposal of industrial and urban wastes and use of urban sewage for irrigation badly affect the physical and chemical properties of the soils. Kumra, in his study of Kanpur city, has found that excessive use of chemical fertilizers and improper disposal of industrial wastes have increased the alkalinity of soils in the fringe area of the city.
Here the concentration of nitrogen in the soils varies from 40-640 pounds/acre, phosphorus from 0.03 to 0.085 percent, soluble salts from 0.03 to 0.27 percent and soil pH from 7.32 to 10.1. Minining activities also cause irreparable damage to nearby soils. Coal dust spreads over the agricultural fields of the mining areas. Numerous mica chips are seen scattered over the agricultural fields in Kodarma mica belt of Jharkhand. Magnesite dusts mixed with soils increases pH value of the soils. Soils near copper mining and smelting near Khetri, Dariba, Ghatsila, Rakha etc. are so polluted that no plant growth becomes possible.