Environmental sustainability
See also: Overgrazing; Overfishing
The environmental sustainabiltiy of agriculture consists of three components: agricultural production, demand for agricultural products and food policy. (Pimentel et al., 2000) There are several gauges of environmental sustainability including the Input and Output Rules advanced by Daly, Cobb and Goodman (Daly and Cobb, 1994) and the Serafian Rule. (El Serafy, 1993) The Output Rule states that waste emissions of an action should be kept within the assimilative capacity of the local environment without unacceptable degradation of future waste absorptive capacity or othe ecosystem services. The Input Rule for renewables states that harvesting rates of renewables must be within regenerative capacity of the natural system. For non-renewables the Input Rule says that depletion rates should be under the historical rate at which renewable substitutes were developed according to the Serafian Quasi-sustainablity Rule. The key parameters of agricultural production that impact sustainability are (a) intensiveness of fossil fuel use; (b) application of excessive chemicals to the soil; (c) overharvesting that leaves insufficient residual plant material; (d) intensive water use; and (e) excessive compaction or erosion of topsoils.
Specific sustainablity practices are found in the application of polycultural cultivation; steady state fishery production; use of grazing practices that minimize erosion and are compatible with native plant survival; rotational cropping and grazing practices that allow sustaining of carbon, nitrogen and other geochemical cycles