Optimization of rice (Oryza sativa L.) and subsequent soybean (Glycine max L. Merr) cropping calendars under the climate change conditions using dynamical general circulation models (GCMs) and DSSAT crop model

Climate change and the global warming phenomenon is one of the main concerns of human societies. In this study, the impact of climate change on rice, as the main crop in Guilan province, Iran and soybean production as the second crop was investigated. To adapt to the negative impact of climate change in future, optimal crop calendars were indentified for different rice and soybean cultivars using two periods of 2021-2035 and 2036-2050. We used a 12-year phenological dataset of two rice cultivars (Hashemi and Alikazemi) and two years data of two soybean cultivars (Williams and Hobbit). Moreover, we used downscaled meteorological parameters of MarkSimGCM data based on the output of three general circulation models (GCMs) under three different RCP scenarios. Finally, the aforementioned data were used as the inputs of the DSSAT crop model to simulate the genetic coefficients and crop yields of rice and soybeans. The results showed that yield values decreased as compared to the observation period. Rice, cv. Hashemi, yield decreased 31% under the RCP8.5 scenario within 2036-50 period and 23% for cv. Alikazemi as compared to the observation period. Model results indicated that 10 days of acceleration in planting date, in all scenarios and periods, will lead to higher crop yields than the current planting date. For the RCP8.5 scenario of 2036-50 period, changing the planting date reduced the yield by up to 15%. For soybeans unlike the rice, delaying the planting date will increase crop yield. Therefore, on the third planting date (6th of September) for soybeans cv. Williams, up to 24% reduction in seed yield will be mitigated. For cv. Hobbit, on average 28% seed yield increase was estimated as compared to the current planting date. In conclusion, shifiting the planting date for rice to the early days of growing season and delaying the planting date for second crop (soybean) can mitigate crops yield reduction due to climate change.