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Environmental concerns arise from many agricultural activities and sources including concentrated livestock production, pesticide and chemical use, deforestation, drainage of wetlands, soil erosion from cropland, and the use of fragile lands. Soil erosion from farmland threatens the productivity of 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 loams are better able to sustain erosion without loss of productivity than are areas where topsoils are shallower. Erosion affects productivity because it removes the surface soils, containing most of the organic matter, plant nutrients, and fine soil particles, which help to retain water and 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 then is 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 immediate economic benefit to the farmer, but such cost-benefit analyses fail to take into account the long-term losses of fertility and water-holding capacity 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 negative effects 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 American farms are also causing excessive erosion, which threatens productivity over the long term. For example, 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 a billion 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 on the soil surface. This residue protects the soil from wind and rain and 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 of beneficial insect and animal species, and in some areas they contaminate water supplies. Surface runoff 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 at least 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 weed control. Even when soil erosion is not excessive, intensive agriculture can impair soil quality by depleting the natural supplies of trace elements and organic matter. In natural ecosystems, soil fertility is maintained by the diverse contributions and recycling of nutrients by a wide range of plant and animal species. When this diversity is replaced by a single species grown year after year, some trace elements are depleted if not replaced by fertilization. The organic content of the soil also diminishes unless crop residues or other organic materials are supplied in sufficient quantities to replace that consumed over time. In the Northeast water supplies are generally plentiful, but are increasingly becoming threatened by contamination. Farming is one potential source of such contamination. Surface runoff carries manure, fertilizers, and pesticides into streams, lakes, and reservoirs, in some cases causing unacceptable levels of bacteria, nutrients, or synthetic organic compounds. Similarly, water percolating downward through farm fields carries with it dissolved chemicals, which can include nitrate fertilizers and soluble pesticides. In sufficient quantities these can contaminate groundwater supplies. Nutrients are lost from agricultural fields through runoff, drainage, or attachment to eroded soil particles. The amounts lost depend on the soil type and organic matter content, the climate, slope of the land, and depth to groundwater, as well as on the amount and.type of fertilizer and irrigation used. The three major nutrients in fertilizers are nitrogen, phosphorus, and potassium. Of these, nitrogen is the most readily lost because of its high solubility in the nitrate form. Leaching of nitrate from agricultural fields can elevate concentrations in underlying groundwater to levels unacceptable for drinking water quality. In the Suffolk County area of Long Island, for example, almost 10 percent of private wells tested for nitrate exceed the 10 mg/l drinking water standard. Phosphorus does not leach as readily as nitrate because it is more tightly bound to soil particles. However, it is carried with eroded soils into surface water bodies, where it may cause excessive growth of aquatic plants. If this process proceeds far enough, lakes and reservoirs become choked with decaying mats of algae, which have offensive odors and can cause fish kills from the resulting lack of dissolved oxygen. Potassium, the third major nutrient in fertilizers, does not cause water quality problems because it is not hazardous in drinking water and is not a limiting nutrient for growth of aquatic plants. It is tightly held by soil particles and so can be removed from fields by erosion, but generally not by leaching. The trend toward intensive crop production in modern farming has led to increased potential for damage by pests and diseases. Predators that would be present in a mixed biological community are not supported by large fields of a single crop; so farmers, instead, rely on chemical measures for crop protection. Use of pesticides on U.S. farms has risen 1O-fold over the past 40 years as agriculture has become more intensive. One drawback to this is that pesticides generally kill not only the pest of concern, but also a wide range of other organisms, including beneficial insects and other pest predators. Once the effect of the pesticide wears off, the pest species is likely to recover more rapidly than its predators because of differences in the available food supply. Previously unimportant species may also become significant crop pests when their natural predators are killed by pesticide applications. Another drawback to the increasing pesticide use is the development of resistance in pest species. The individual pests that survive pesticide applications continue to breed, gradually producing a population with greater tolerance to the chemicals applied. Presticides, therefore, have to be used in ever increasing quantities or replaced with new chemicals to adequately control pest populations. Following World War II, DDT and related chlorinated hydrocarbons were introduced as potent new pesticides and were used throughout the world for protection of agricultural crops, as well as control of mosquitoes, lice, and other human pests. In 1962 Rachel Carson's book Silent Spring brought public attention to the fact that these organic compounds are highly persistent in the environment and accumulate in animal tissues, causing water contamination, fish kills, and decline of some bird populations. DDT was banned for agricultural use in the United States in 1973, and since that time it and similar chlorinated hydrocarbons have been replaced by less persistent, but more acutely toxic, compounds. Because some of these new pesticides are highly soluble in water, they may leach to groundwater underlying farming regions. In Suffolk County at the eastern end of Long Island, for example, 13 different pesticides have been measured at least once in groundwater samples. Twelve percent of the wells tested in Suffolk County have exceeded the drinking water guideline for aldicarb, a highly soluble pesticide used from 1975 to 1979 to control thc Colorado potato beetle. Nationwide sampling for pesticides has been quite limited, but 23 states have reported at least one of 22 pesticides in groundwater. In the past couple of decades, awareness has been growing of the many potential problems caused by the heavy use of chemicals in modern agriculture. This, combined with the rapid rise in the cost of fertilizers and pesticides, has led many farmers to seek ways of reducing their reliance on chemical- intensive methods of farming. A small but growing percentage of farmers are farming with no synthetic chemicals, and many others are reducing their overall chemical use. Agriculture research has begun to focus on ways of maintaining environmental quality while producing acceptable crop yields. One example is integrated pest management, aimed at controlling pests through a combination of methods that minimize undesirable ecological effects. Continuing research and education need to be conducted on farming practices that produce profitable yields while maintaining environmental quality and the long-term productivity of the land. Bibliography: Word Count: 1677
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