Irrigation amplifies the benefits of rotational diversity on crop yields and their stability under climatic extremes

The increasing frequency and intensity of hot and dry extremes under climate change are expected to reduce crop yields and their stability. Irrigation and diverse crop rotations have separately been shown to buffer against the negative impacts of such extremes, potentially leading to higher and more stable yields compared with rainfed cropping and monoculture. Yet, their joint effects remain unquantified across a broad range of pedoclimatic conditions and field management practices. Using the newly developed USDA crop sequence boundary data and remotely sensed estimates of annual irrigation occurrence, we quantified the combined effects of crop diversity, prevalence of irrigation, and dry-spell length and temperature on county-level corn and soybean yields in the USA from 2008 to 2023. We also assessed how these factors jointly influence yield stability, defined as low interannual yield variability and measured via the yield standard deviation over the same period. Initial results show that, where rainfed agriculture was more prevalent, corn and soybean yields and their stability were higher with more diversity in rotated crops independently of dry-spell length and temperature. Conversely, under widespread irrigation, more stable corn and soybean yields were generally associated with higher rotational diversity under long or warm dry spells. Under the same conditions, soybean, but not corn, yields were higher with more diverse rotations. Under both longer and warmer dry spells, corn and soybean yields increased with diversity and even more so under higher irrigation prevalence, suggesting that the capacity of rotational diversity to mitigate yield losses under adverse climatic conditions is amplified by irrigation.