Assessing Yield Stability in Long-Term Trials.

Adapting to climate change is a new imperative for agriculture.  Adaptation requires not just shifts in planting dates, cultivars, or species to match new weather norms, but new cropping and management systems that are more resilient to increasing year-to-year variation in weather.  Yield stability is a key measure of resilience.  Here we use stability analysis (Guertal et al., 1994; Raun et al., 1993) to assess the yield stability of different cropping systems treatments in two long-term trials.  In each case, the yield for each treatment was regressed on the annual mean yield of all treatments combined, designated the “environment mean yield,” which reflects the overall growing conditions for each year including temperature, rainfall, pest pressure, and effectiveness of pest and crop management.  Regressing treatment yields on the environment mean yield allows one to evaluate the relative response of treatments over the range of growing conditions that occurred.  Stability analysis applied to results from a 17-year cropping systems study in Maine demonstrated that soil quality improvement resulting from repeated additions of manure to a potato-barley rotation increased potato yield stability compared with a nonamended fertilizer-based treatment.  Yields in the amended system were less influenced by adverse growing conditions, particularly rainfall.  Total and U.S. no. 1 yields in the poorest-yielding year were 63 and 59% of maximum yields, respectively, in the amended system, compared with 45 and 46% in the nonameneded system.  Results from the Long-term Ecological Research site in Michigan also will be presented.