Murakami, K.; Iizumi, T.

Crop rotation offers multifaceted benefits for climate adaptation and mitigation. As rising temperatures accelerate crop development, it is necessary to adjust the rotation order and sowing dates of crops in a rotation system. Such an adjustment can enhance agricultural productivity at the whole rotation system level even under warmer conditions. Here, we present a computational approach to identify the crop rotation calendar (the order and sowing dates of rotation crops) that maximizes total crop output with available climatic resources. In this study, the rotation order indicates the cyclical sequence of crop species without intercropping, cover crop and fallow. This approach involves two steps: (1) generating crop windows (the timing and length of crop duration from sowing to harvest) and corresponding outputs (production per unit land area per harvest) for the rotation crops using a crop growth model with daily weather inputs; and (2) applying an optimization algorithm to identify a single subset of crop windows of rotation crops that maximizes the total crop output while satisfying agronomic constraints. We applied this method to a four-year, four-crop rotation system in northern Japan, with historical and projected climates from 2000 to 2100. The results revealed that adjusting crop windows would reduce the time to complete all rotation crops in the system (shortened rotation cycle) and enhance the system-level annual productivity [kgDW ha-1 year-1] with time. The increase in this productivity is approximately 0.5 % per year under high warming of the Shared Socioeconomic Pathway 5-8.5. Optimizing the rotation order in addition to the rotation crops sowing dates showed the changes in the most productive rotation orders, demonstrating the dynamic nature of rotation planning under climate change. Our methodology offers a flexible, scalable means of designing cropping system to harness the positive effect of climate change on long-term food security.