Soils on organic farms are healthier, according to the most comprehensive study yet comparing farming practices. The 21-year study found that although crop yields are 20% lower, organic farming uses less fertilizer and energy than conventional methods and supports greater biodiversity.

Paul Mäder of Switzerland’s Research Institute of Organic Agriculture and his colleagues compared the yield and ecological ramifications of growing potato, winter wheat, and grass/clover crops using four different farming techniques. The two conventional methods they evaluated relied upon synthetic pesticides and either only mineral fertilizers or a combination of mineral and manure fertilizers. The organic techniques used manure fertilizers and naturally derived pesticides.

The researchers found that the organic farming methods used 26-53% less energy per unit of land and that the inputs of nitrogen, phosphorus, and potassium in the organic systems were 34-51% lower. They credit the higher microbial diversity observed in the soil of the organic plots for their more efficient utilization of soil resources. The highest level of microbial diversity was associated with the biodynamic organic farming technique, a less-popular approach which its adherents say uses “special plant, animal, and mineral preparations [to] stimulate and balance vital processes in soil and plants.”

The soils in the organic plots were 10-60% more stable, the scientists found, which implies that they would be less prone to erosion. The organic plants had 40% more roots colonized by the mycorrhizae fungus that help plants take up nutrients than conventionally grown plants, and the organic soils contained 1.3–3.2 times more earthworms.

Because healthy ecosystems are characterized by higher levels of biodiversity, the researchers conclude that the higher level of bioactivity and biodiversity associated with organic farming methods “is likely to provide a positive contribution toward the development of higher food web levels including birds and larger animals.” (Science 2002, 296, 1694-1697)