In a recent paper by Pimentel and colleagues,“Environmental, Energetic, and Economic Comparisons of Organic and Conventional Farming Systems” (BioScience 55: 573–582), two claims made by the authors warrant closer examination.
The authors cite data from the Rodale Institute's 22-year Farming Systems Trial (FST) showing individual crop yields were “similar to those of conventional systems.” However, they presented no data on total system yields.
I was able to glean wheat yield data from another paper on Rodale's FST for the years 1986–1995, during which they averaged just less than 49 bushels per acre (Hanson et al. 1997). At these yields and assuming a weight of 60 lbs per bushel, the organic wheat would yield an average of 3,302 kg/ha of grain per crop. Combined with the corn and soy yields, this gives an average of 11,906 kg/ha of total grain produced per 3-year rotation. After 15 years, the organic legume rotation would provide 59,530 kg of grain, whereas the conventional rotation would yield 74,253 kg over the same period. Thus, the conventional system yields 25% more grain than the organic system over time. Even with organic wheat yields of 65 bushels per acre, the organic system would produce 20% less grain than the conventional system.
Most disturbing, however, were statements that the “environmental benefits of…less soil erosion…were consistently greater in the organic systems than in the conventional systems” and “crop rotations and cover cropping typical of organic agriculture reduce soil erosion.” Nowhere in the paper were any data provided from the FST or any other source to substantiate these claims. In fact, ongoing work by USDA-ARS researchers has demonstrated the opposite: soil erosion potential (as measured by soil properties) is essentially equal between organic and traditional nonorganic farming systems, but both are significantly more susceptible to erosion than a nonorganic, no-till farming system (Green et al. 2005).