Yield increases during the organic transition: improving soil quality or increasing experience?

Reported increases in crop yields over the first few years of organic farming (especially during the 3-year “transitional” period established in US law) have been attributed to gradual improvements in soil properties, such as the capacity of the soil microbial community to mineralize N or to suppress disease. To test the hypothesis that yield increases with years of organic farming are due to improvements in soil properties, we compared identically managed organic and transitional plots differing only in duration of organic management (>5 versus