Tractors are a familiar sight in the fields, but the ploughing they do may pollute nearby lakes and rivers. Reducing ploughing can help to clean up neighbouring waters, a new study from the agricultural state of Ohio suggests 1 . This is mainly because of farmers' rapid adoption of a technique called conservation tillage, says Lynn Forster from Ohio State University. These crop residues anchor the soil, making it more resistant to water or wind erosion.
Excess nutrients allow weeds and algae to bloom, choking out native aquatic species.
Although erosion is only a moderate problem in Ohio, it is the major cause of agricultural land degradation around the world, especially in Asia, says Eric Craswell, director of the International Board for Soil Research and Management in Bangkok, Thailand. Brazilian farmers have also cut back on erosion by adopting minimum tillage, Craswell explains, and researchers are working with other tropical farmers to implement this technique and to plant hedgerows and grass strips to try to reduce erosion. Ohio farms in the two river watersheds occupy about half of all American and Canadian cropland draining into Lake Erie, one of the world's largest freshwater lakes and one that has historically suffered from rural and urban pollution. But conservation tillage should be combined with other practices that minimize the use of chemicals, warns Rattan Lal, a soil scientist also from Ohio State University. Because ploughing controls weeds, farmers who plough less rely more heavily on herbicides for weed control.