The high yielding varieties (HYVs) of rice and wheat diffused in the developing countries require high energy inputs in the form of water, chemical fertilizers and crop protection chemicals. Out of these, the crop protection chemicals bring radical change in the chemical properties of Soil and thus transform the environment.
Crop protection chemicals are compounds that are artificially produced on a large scale to improve the efficiency of crop by eliminating competition from weeds.
Chemicals are also used in apple, mango and orange orchards to protect the fruits from insects and pests. There are various groups of pesticides that are designated according to target species.
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The Indian Council of Medical Research (ICMR) conducted a survey and revealed the existence of excessive residues of DDT and other pesticides in bovine milk, lead, copper, zinc; cadmium and arsenic were also detected in rice, wheat, maize, mustard, cotton, sesame and fruits. It is because of the contaminated feed to animals and spraying of crops fodder and orchards. The contamination of food with chemicals is a major public health problem in India.
The crop protection chemicals undoubtedly enhance agricultural production, and bring substantial environmental changes. The use of organ chlorine such as DDT has had profound effects on wildlife. Herbicides to control broad leaved weeds have altered the balance of weed populations so that in solving one problem, others are created. In order to overcome the new problems, new plant protection chemicals are required which bring more changes in the environment and thus the vicious circle continues.
Soil is a complex mixture of rock particles, organic material, living organism, air and water. Under natural conditions soil is constantly being formed by the physical and chemical decomposition of rock material and by the decay of organic matter. It is simultaneously being eroded, for soil erosion is as natural a process as soil formation. Soil erosion is a worldwide phenomenon. The rate of soil erosion in a given region is influenced by
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(i) Rainfall erosivity,
(ii) Volume of run off,
(iii) Wind strength,
(iv) Relief,
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(v) Slope angle,
(vi) Slope length,
(vii) Slope shortening (terrace, ridges),
(viii) Length of wind fetch, and
(ix) Shelter belts.
The rate of soil erosion also depends on the pressure of population on arable land, cropping patterns, fallowing, crop rotation, land management, use of fertilizers and tillage practices.
According to one estimate, 75,000 million tonnes of productive soil is eroded annually. In India, the problem of soil erosion is quite serious as annually about 6,000 million tonnes of soil is being eroded annually.
In Turkey, about 75 per cent of the arable land is affected by soil erosion (Mannion, op. cit.: 193). In China and India, about 60 per cent of their cultivated land is affected by wind and water erosion
Soil erosion not only affects the areas from which soil is removed but also affects the environment where it is deposited.
Such deposits if take place in lakes and ponds, destroy the aquatic ecosystems by adding more nutrients, notably nitrogen and phosphorous.
It is, therefore, necessary to adopt remedial measures to combat soil erosion and to protect the neighboring agro-ecosystems.