Adverse impacts of agriculture on soil, water and food quality

Modern agriculture has led to serious declines in soil and water quality as a result of practices which are not sustainable in the long-term. The greatest impact on soil quality has been in terms of soil loss, an irreversible process with 25, 8 and 12% of the crop-, pasture- and rangeland, respectively, in the United States of America (USA) eroding at rates faster than soil loss tolerance levels (National Research Council, 1993). Despite the ravages of erosion being known for a long time, only very small reductions in erosion rates have been recorded in these categories of land over the period 1982 to 1987. This possibly reflects the prediction that crop yields are only likely to decline by 10% over the next 100 years due to soil erosion at current high input levels (Putnam et al., 1988) which indicates that, to be effective in countering erosion, efforts should focus on offsite damage caused to rivers and lakes. In terms of water quality, agriculture has been the source of 64 and 57% of the non-point pollution of rivers and lakes in the US, respectively, with sediment and nutrients accounting for 60 and 81% of the pollution in affected rivers and lakes, respectively (Carey, 1991). Non-point source pollution from soil erosion impairs beneficial uses of water, fish spawning and rearing habitats and increases the cost of municipal water treatment, maintenance of navigational channels, irrigation systems and reservoir storage (Clark et al., 1985). In the USA, soil erosion costs $1.3 billion in lost productivity and $3 billion in off-site economic damage (Ribaudo, 1987).