“Some of the most clear-cut examples of desertification are those that have occurred on farmland because the resulting declines in crop yield are relatively straightforward to monitor. Fields on which just a single crop is grown year after year, so-called ‘monocultures’, will slowly become degraded, as studies on cropland in the semi-arid Pampas of Argentina have shown. The long-term cultivation of millet has affected both the chemical and physical properties of soils. The depletion of nutrients means that larger amounts of fertilizers have to be applied to maintain crop yields, while declines in organic matter and soil stability have meant a greater susceptibility to erosion.”