For agricultural production to be sustained over time, the capacity of the environment to provide critical levels of support needs to be maintained. The environment performs several functions in relation to agriculture. Natural resources, such as water, soils, solar energy, forests, and minerals are all inputs to agriculture. The environment also serves the critical function of absorbing and dissipating the wastes generated by agricultural production. Sustainable agricultural practices explicitly recognize the need for linkages between agricultural production, ecosystems, and rural communities. The need to evaluate agricultural practices in terms of their overall sustainability is increasingly important. Sustainable agricultural systems are thought of as integrated systems of plant and animal production which over the long run continue to satisfy human food and fiber needs, maintain and improve environmental quality and the natural resource base, and enhance the quality of life for farmers and society as a whole (US Congress 1990).