Organic agriculture may be as old as dirt, but that doesn’t mean its impacts are fully understood. A team of scientists in the United States and Canada are doing their part to change that.
Researchers at UC Santa Barbara, University of British Columbia, and University of Colorado Boulder discovered that organic farming significantly affects the amount of pesticide used in neighboring fields. The study, published in Science, found that the impact depends on the density and spacing of organic and conventional fields, and clustering organic fields together could provide the most benefits for all farmers.
“We find that organic cropland generally leads to a decrease in pesticide use on nearby organic fields,” said lead author Ashley Larsen, an ecologist at UCSB’s Bren School of Environmental Science & Management. “In contrast, organic agriculture leads to a small, but significant, increase in pesticide use on nearby conventional fields.” The authors suspect that the different responses reflect different reliance on natural pest control methods, although they admit the mechanisms are difficult to test with their data.
There’s been a push to increase organic production in the U.S., which begs the question of how this will affect pests and pest control for other farms. Most pesticide studies have focused on the field level, Larsen said, comparing metrics like biodiversity, soil health and pesticide use between organic and conventional fields. However, agricultural pests and their predators move beyond field boundaries. So the group sought to understand these interactions between fields, which they call “spillover effects.”
Organic farmers can benefit from a greater abundance or persistence of their pests’ natural enemies, which can be harmed by chemical pesticides in conventional fields. Thus, organic farmers could benefit from clustering together. On the other hand, an influx of insects from organic fields could drive up the use of chemical pesticides in conventional fields, since these fields have smaller, less effective populations of those beneficial species.
Unfortunately, when organic and conventional farms are distributed evenly, both kinds of farmers often lose out. “Clustering organic fields concentrates the pest control benefits to organics and reduces the costs to conventional fields,” Larsen said. And, as the share of organic agriculture increases, the beneficial effect of organic fields on one another starts to dominate.
These pithy conclusions are the culmination of an involved process. The authors faced major challenges even finding usable data. “You have to be able to identify specific fields in a spatial data format, link that spatial data to each field’s pesticide-use rates, and also determine which fields are organic and which are conventional,” Powers explained. This information comes from several sources that can be tough to combine. What’s more, agricultural spatial data and pesticide use aren’t particularly well tracked, especially outside of California.
