Soil, water and climate decide the type of crop grown in a locality. The basis of agriculture is soil and all crops for human food and animal feed depend upon it. But human activities have led to soil pollution and erosion including degradation. This is probably the major cause of unsustainable agriculture production. In order to preserve the fertility and the productivity of the soil, control measures are to be taken to improving the health of all living beings.
Causes of Soil pollution
Soil pollution is caused by the presence of man-made chemicals or other alteration in the natural soil environment. There are many ways of soil pollution which include seepage from a landfill, discharge of industrial waste into the soil, percolation of contaminated water into the soil, rupture of underground storage tanks, excess application of pesticides, herbicides or fertilizer, and solid waste seepage. The most common chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead and other heavy metals. This occurrence of this phenomenon is correlated with the degree of industrialization and intensities of chemical usage. A soil pollutant is any factor which deteriorates the quality, texture and mineral content of the soil or which disturbs the biological balance of the organisms in the soil.
Effects of soil Contamination
Metal ions enter the soil solution from these various forms of combination in different rates they may either remain in solution or pass into the drainage water or be taken up by plants growing on the soil or be retained by the soil in sparingly soluble or insoluble forms. The fate of heavy metals in soil will be controlled by physical and biological processes acting within the soil.The organic matter of these soil have great affinity to heavy metals cations which form stable complexes thereby leading to reduced nutrient content .
Pesticides which are not decomposed rapidly may exert harmful effects to micro-organisms, as a result of which plant growth may be affected. Accumulation is residues of pesticides in higher concentrations in soil and movement into water streams may also lead to their entry into foods and create health hazards. Mercury, cadmium and arsenic are common constituents of pesticides and all these heavy metals are toxic
The over use of NPK fertilizers reduce quantity of vegetables and crops grown on soil over the years. It also reduces the protein content of wheat, maize, grams, etc., grown on that soil. The carbohydrate quality of such crops also gets degraded .Excess potassium content in soil decreases Vitamin C and carotene content in vegetables and fruits. The vegetables and fruits grown on over fertilized soil are more prone to attacks by insects and disease.
How the soil contamination is man-made?
Pollution in soil is associated with indiscriminate use of fertilizers, indiscriminate use of pesticides, insecticides and herbicides, dumping of large quantities of solid waste, deforestation and soil erosion.Fertilizers contaminate the soil with impurities, which come from the raw materials used for their manufacture. Mixed fertilizers often contain ammonium nitrate (NH4NO3), phosphorus as P2O5, and potassium as K2O. For instance, As, Pb and Cd present in traces in rock phosphate mineral get transferred to super phosphate fertilizer. Since the metals are not degradable, their accumulation in the soil above their toxic levels due to excessive use of phosphate fertilizers becomes an indestructible poison for crops. Soil erosion occurs when the weathered soil particles are dislodged and carried away by wind or water. Deforestation, agricultural development, temperature extremes, precipitation including acid rain, and human activities contribute to this erosion. Humans speed up this process by construction, mining, cutting of timber, over cropping and overgrazing. It results in floods and cause soil erosion. Forests and grasslands are an excellent binding material that keeps the soil intact and healthy. They support many habitats and ecosystems, which provide innumerable feeding pathways or food chains to all species. Their loss would threaten food chains and the survival of many species.
Control of soil pollution
A major method of checking this pesticidal pollution is to increase the organic matter content of the sol and choose such pesticides which are non-persistent and leave no harmful residue.Thermal methods, chemical methods and microbial treatment methods are used for treatment of soil. In agriculture reducing chemical fertilisers and pesticides, reducing and reusing and recycling of organic wastes are general practices in reducing soil pollution.
Organic farming provides long term solution to soil contamination. Organic food contributes to better health through reduced pesticide exposure for all and increased nutritional quality. In order to understand the importance of eating organic food from the perspective of toxic pesticide contamination, we need to look at the whole picture—from the farmworkers who do the valuable work of growing food, to the waterways from which we drink, the air we breathe, and the food we eat. Organic food can feed us and keep us healthy without producing the toxic effects of chemical agriculture.
Integrated plant nutrient management (IPNM) and integrated pest management (IPM) and integrated crop and water management are three proven technologies that can provide a solution to soil contamination.Recently precision agriculture has come up which can avoid blanket use of chemicals in the soil and resort to exact use of chemicals as per actual requirement.
- Bidyadhar Maharana , Consultant, Agriculture & NRM