There are numerous, diverse, and increasing demands on agriculture in the twenty-first century. In addition to meeting the demands for the economic production of food, feed, fiber, and fuel, agriculture of the twenty-first century must also address environmental concerns, especially in regard to water quality and the accelerated greenhouse effect. Soil is a biofilter, and a reduction in the thickness of the topsoil layer through erosion has a direct negative effect on the buffering and filtering capacity of the soil and on the emission of greenhouse gases into the atmosphere. Soil erosion preferentially removes soil organic matter because it is light and is concentrated in the surface layer. A large fraction of the C thus displaced by water runoff may be prone to mineralization, leading to its emission into the atmosphere as CO2. It is estimated that globally 1.1 billion tons of C may be emitted annually as CO2 because of displacement by water erosion. In addition, some of the organic matter deposited in depressional sites and aquatic ecosystems may lead to the emission of methane (CH4) and nitrous oxide (N2O). In comparison to CO2, the global warming potential is twenty-one for CH4 and 310 for N2O.
Sustainable agriculture, therefore, is a viable production system based on environmentally benign agricultural practices. The objective of sustainable agriculture is to enhance and sustain production while improving soil fertility, soil tilth, and soil health. While enhancing production, sustainable agriculture must also address environmental issues with regard to water quality and the greenhouse effect. Rather than being the cause, improved agriculture is a solution to certain environmental problems.
Sustainable agriculture implies profitable farming on a continuous basis while preserving the natural resource base. It is not synonymous with low-input, organic, or alternative agriculture. In some cases, low input may sustain profitable and environmentally sound farming. In others, it might not. The addition of organic amendments might enhance soil quality, but may not eliminate the need for the judicious use of fertilizers. Large quantities (10 to 20 ton/hectare/year) of organic manures are needed to supply enough nutrients to produce the desired yields. Therefore, the use of organic manures, although desirable, may not be logistically feasible. In sub-Saharan Africa, low inputs on impoverished soils and low yields have been responsible for low standards of living, severe malnutrition, and widespread problems of soil and environmental degradation. Therefore, the adoption of RMPs is a necessary prerequisite to feeding the earth's expected ten billion inhabitants by the year 2100. Judicious management includes the conversion of marginal agricultural soils to restorative land use and adoption of RMPs. Technological options differ among soils, ecoregions, and social and cultural settings, but the underlying basic principles remain the same. see also Carver, George Washington; Cryptosporidosis; Green Revolution; Integrated Pest Management; Pesticides.
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Raising poultry is big industry on Maryland's Eastern Shore, but there's a problem. The 600 million birds annually create about 800,000 tons of chicken manure. They may soon be creating electricity. Environmentalists, the poultry industry and local officials are enthusiastically studying plans to build a 40-megawatt power plant that would burn chicken manure mixed with wood shavings to generate electricity. Fibrowatt, the British company making the proposal, already operates three poultry-manure-powered generating plants in England and is currently building a plant in Minnesota to be powered by turkey manure.
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