Organic (不使用化肥的) farmers produce food with least help from pesticides (杀虫剂), but in limiting the use of chemicals on their own land, they may be unknowingly causing an increase in pesticide use over their neighbour's fence (栅栏).
Ashley Larsen at the University of California and her colleagues looked into land-use and pesticide data across 14,000 fields in Kern County, California. The researchers found that when organic farmland is surrounded by conventional (传统的) agriculture, neighbouring farmers seem to increase their pesticide use, with a 10% rise in organic cropland being linked to a 0.3% increase in total pesticide use on conventional fields. Most of this is driven by greater use of pesticides, the researchers found.
This may be because more insects tend to live on organic land and spill over into neighbouring fields, causing conventional farmers there to increase pesticide use, according to Larsen. The effect appears strongest when neighbouring fields are within 2.5 kilometres of the organic "focal field".
However, the researchers noted that the presence of organic farmland is linked to a reduction in pesticide use on neighbouring organic fields, with a 10% increase in the area of nearby organic cropland being related to a 3% decrease in total pesticide use on organic focal fields. This may be because the larger area of organic farmland allows for a bigger and more stable (稳定的) community of beneficial insects.
When organic agriculture makes up a high rate of farmland—perhaps 20% or more—net pesticide use decreases no matter where the organic fields are sited, say the researchers. But when small areas of organic farmland—like in Kern County, where about 5.5% of agricultural land is organic—evenly spread through the landscape, net pesticide use may in fact be higher than when no organic farming is present.
However, this impact can be softened by bunching up organic farmland. Larsen said, "It might be worth considering how to encourage the concentration of new organic fields to basically take full advantage of its pest control benefits and limit the costs of being organic to conventional growers.
