Although our soils have been formed over long periods of time, some of them are being destroyed, within a span of only a few years, due to the misdeeds of mankind. Many of our once-fertile soils have already been converted to agriculturally-unfit alkaline or saline lands or marshlands. More than 25 million hectares of such barren lands are now estimated to be distributed throughout the world.
Soil constitutes a biogeochemical shell around land and shallow waters. It is a product of the interactions of living matter with rocks. It profoundly affects the growth of living organisms (especially plants) and is in turn influenced by the activities of the latter. Recent increases in the pace of industrialization, urbanization and other activities of civilized man have had a tremendous impact not only on the soils but also on other components of die biosphere.
Unplanned destruction of forests and forest litter has brought about serious changes both in land and water. The washing-off of fine soil particles from deforested areas has caused considerable soil erosion.
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There has also been a great increase in run-off, pollution, turbidity and mineralization in rivers and extensive silting in water reservoirs, all resulting from the untoward consequences of increased erosion.
Some erosion of soil results from the deforestation that is quite prevalent in the Himalayas. Erosion in the Himalayan ranges is caused both by natural climatic influences ranging from tropical to arctic, and by man-made causes.
Forest cover greatly reduces erosion of the soil so that it keeps pace with the rate of new soil formation. The increasing population pressure is fast denuding the Himalayas of their forests. Bare, unprotected soil cannot store large quantities of water.
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The soils are compacted by heavy rain and then washed away. Consequently, the rivers are flooded during rainy season, springs dry up during the dry season in some localities, rivers meander in the plains at the foothills and large amounts of gravel and sedimentary material tend to accumulate.
Modern agricultural practices seek to counter the above processes of soil destruction by advocating increased use and application of chemical fertilizers, but this is an ecologically dangerous practice.
What is really needed is an entire series of preventive and remedial measures such as recourse to contour and strip farming, a network of forest plantations in clumps and rows, a regular sowing of grass in crop rotations, the preferential use of organic, rather than inorganic, manures, etc. (Kovda, 1972). The use of organic manure is especially desirable since it tends to preserve the quality of soils and also their humus content.
In recent years, soil scientists have been greatly concerned with the Problem of safeguarding soils from exogenous chemical substances, mineral fertilizers, pesticides, etc. Heavy doses of the wrong kind of inorganic fertilizer have often resulted in creating excessive acidity or alkalinity in the soil, and the indiscriminate use of pesticides and fungicides has caused adverse effects on soils in addition to their well-known effects on the activities of soil microbes, flora and fauna. Various kinds of air pollutants and noxious gases also have a harmful effect on soils (Kovda, 1972).
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The soil should be regarded as a living community of microorganisms, algae, fungi, protozoa and metazoa. It contains many inorganic and organic substances which are products of weathering and decay of organic matter. Microbes normally oxidize these substances to inorganic oxides, but some organic compounds reaching oxygen-deficient ground water may remain incompletely oxidized and add to pollution. Chemical pollution of soils results from contamination of the soil with various chemicals.
Several countries of Africa lying along the south of the Sahara desert are now suffering the severe effects of prolonged drought caused by rain failure or inadequacy during the past few years. The desert has also been found to advance southwards by several kilometers each year.
Local inhabitant’s plant millet in tiny plots of topsoil fenced in with straw matting to avoid the sand; they water the wilting shoots by bringing cupfuls of the precious and scarce water, often from long distances. Despite such frugality, however, the resource could be better managed.
The current practice, which leads to resource squandering and wastage, is to set bush fires to drive out and exterminate desert rats. Such practices result in considerable impoverishment of the top soil. Another similar practice is the chop down the scarce tree wealth for firewood and to let cattle eat up Acacia branches.
Acacia and other similar plants are, however, very useful since they help check the advance of desert by breaking the winds, by humus formation, by binding soil by means of deep penetrating roots, and by trapping the scarce rainwater. If only excessive destruction of grazing of trees could be controlled, and many more trees or bushes planted, much of the land could be successfully conserved and reclaimed in due course of time.