Mean yield gap explains differences in yield stability between organic and conventional systems
Over recent decades, numerous studies have compared agricultural productivity across different management systems and environments, with increasing attention to the stability of crop yields. Yield stability is a key component of agroecosystem resilience under global change, yet it remains unclear whether some cropping systems are more stable than others. The debate over organic farming is particularly heated, as some evidence indicates that organic systems are less stable, while other evidence suggests the opposite. Here, we develop a conceptual and statistical framework for comparing crop yield stability across agricultural systems that explicitly accounts for a parametric function relating inter-annual yield standard deviation to mean yield value. Using a new global dataset of long-term field experiments spanning multiple crop species and environments, we show that the fitted functions relating yield standard deviation and mean yield value obtained for organic and conventional cropping systems share several important similarities. For both systems, the yield coefficient of variation (CV) significantly decreases with mean yield, and most of the difference in yield stability between conventional and organic systems is explained by differences in mean productivity. As a consequence, the CV of the two systems becomes similar as the difference in average efficiency narrows. Our framework reconciles apparently conflicting results in the literature and provides a more robust basis for comparing stability across cropping systems.