Impacts of Intensive Farming on Soil and Water Resources Damage to Soil. Soil erosion from farmland threatens the productivityof agricultural fields and causes a number of problems elsewhere in the environment. An average of 10 times as much soil erodes from American agricultural fields as is replaced by natural soil formation processes. Because it takes up to 300 years for 1 inch of agricultural topsoil to form, soil that is lost is essentially irreplaceable. The consequences for long-term crop yields have not been adequately quantified. The amount of erosion varies considerably from one field to another, depending on soil type, slope of the field, drainage patterns,and crop management practices; and the effects of the erosion vary also. Areas with deep organic loamsare better able to sustain erosion without loss of productivity than are areas where topsoils are shallower. Erosion affects productivity becauseit removes the surface soils, containing most of the organic matter, plant nutrients, and fine soilparticles, which help to retain waterand nutrients in the root zone where they are available to plants. The subsoils that remain tend to be less fertile, less absorbent, and less able to retain pesticides, fertilizers, and other plant nutrients. Why thenis erosion allowed to continue at excessive levels on many U.S. farms? Often the short-term costs of implementing erosion control measures far exceed the immediateeconomic benefit to the farmer, butsuch cost-benefit analyses fail to take into account the long-term losses of fertility and water-holdingcapacity of the soil. Up to a certain point, increased fertilization and irrigation will compensate for the lower soil fertility. Long-term loss of farmland productivity and damage to the environment from eroded sediments, therefore, often are overlooked in the need for short-term economic gains. Over the past 50 years, the negativeeffects of soil erosion on farm productivity have been masked by improved technology and increasing use of fertilizers and pesticides. Ironically, many of these measures used to increase the short-term productivity of Americanfarms are also causing excessive erosion, which threatens productivity over the long term. Forexample, diminished use of cover crops leaves soils unprotected from wind and rain during much of the year, and increased mechanization has led to use of larger fields without windbreaks or drainage contours.The effects of erosion are also felt elsewhere in the environment. A recent study estimated the off-site cost of cropland erosion in the United States to be in the range of abillion dollars per year (Clark, Haverkamp, and Chapman 1985). Eroded soil clogs streams, rivers, lakes, and reservoirs, resulting in increased flooding, decreased reservoir capacity, and destruction of habitats for many species of fish and other aquatic life. The eroded soils contain nutrients and other chemicals that are beneficial on farm fields, but can impair water quality when carried away by erosion. As a result, drinking water supplies may contain nitrate or organic chemicals in concentrations that exceed public health standards,or surface waters may become clogged with excessive plant growth from the added nutrients. In recent years American farmers have increasingly adopted conservation tillage as a method of cutting soil and water losses by leaving a protective crop residue onthe soil surface. This residue protects the soil from wind and rainand can greatly reduce cropland erosion. One drawback to conservation tillage, however, is that weed control is accomplished using chemical herbicides rather than physical cultivation. These chemicals reduce the populations ofbeneficial insect and animal species,and in some areas they contaminate water supplies. Surfacerunoff carries herbicides to streams and lakes, and groundwater can become contaminated by percolation of water and dissolved chemicals downward through the soil. Eight different herbicides have been detected in groundwater in atleast 18 states, and others have been found in more limited ranges. Methods need to be developed for combining the soil- saving aspects of conservation tillage with less chemically intensive means of weedcontrol.
Posted on: Wed, 19 Jun 2013 04:53:50 +0000
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