back 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.Contamination of WaterIn 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.FertilizersNutrie...
