One need only look to the practices of monoculture and Concentrated Animal Feeding Operations to find examples of degrading agricultural practices. Any time the population of any organism exceeds the natural carrying capacity of a given ecosystem, some damage occurs. It can be a depletion of nutrients, erosion, pollution from waste,or competition with native species. Large-scale livestock operations have been directly linked to the increase of greenhouse gases, the spread of e. coli outbreaks, and possibly a reduction in the effectiveness of antibiotics. Poor agricultural practices have led to massive losses of topsoil in the American Midwest, contributed to the large "dead zone" in the gulf of Mexico, and the over-use of huge amounts of petrochemical fertilizers and pesticides. The best practices include maximizing diversity, using free-range grazing and natural diets, not over-stocking the land that is in use. Research Joel Salatin at Polyface Farm for some excellent ideas on how to raise livestock in a humane manner that is healthy and profitable.

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www.ted.com/talks/michael_pollan_gives_a_plant_s_eye_view.html