Evaluation of climate change impacts and effectiveness of adaptation options on crop yield in the Southeastern United States

The Environmental Policy Integrated Climate (EPIC) model was used to assess the impacts of climate change and proposed adaptation measures on yields of corn (Zea mays L.) and soybean (Glycine max L.) as well as aggregated yields of C-3 [soybean, alfalfa (Medicago saliva L.), winter wheat (Triticum aestivwn L.)] and C-4 [corn, sorghum (Sorghum bicolor L.), pearl millet (Pennisetum glaucum L.)] crop types from representative farms in ten Southeastern US states. Adaptations included annual biochar applications and irrigation. Historical baseline (1979-2009) and future (2041-2070) climate scenarios were used for simulations with baseline and future CO2 concentrations of 360 ppmv and 500 ppmv, respectively. Four regional climate models (RCMs) nested within global climate models (GCMs) were used to run future simulations. The experiment was analyzed as randomized complete block design with split-plots in time for baseline vs. future comparisons, and as a randomized complete block design with repeated measures for comparisons between future periods within each RCM_GCM model. Compared to historical baseline scenario, increases in future corn yield ranged between 36-83%, but yields decreased by 5-13% towards 2066-2070 due to temperature stress. Future soybean yields decreased by 1-13% due to temperature and moisture stresses. Future aggregated C-4 crops produced higher yields compared to historical C-4 yields. There were no differences between future aggregated and historical C-3 crop yields. Both crop types were negatively affected by progressing climate change impacts towards the end of 2066-2070 simulation period. Reductions in future aggregated C-3 crop yields ranged between 10-22%, and between 6-10% for C-4 crops. We explained lower reductions in C-4 compared to C-3 crops due to a lesser degree of photorespiration, better water use efficiency, and better heat tolerance under conditions of high light intensities and increased temperatures in C-4 crops. Irrigation resulted in increased future corn yields between 29-33%, and 3-38% of aggregated C-4 crop yields, with no effect on soybean or aggregated C-3 crop yields. In some regions, biochar applications caused significant yield reductions of 9.5-20% for corn, 5-7% for aggregated C-3, and 3-5% for aggregated C-4 crops, depending on the model. Yield reductions were ascribed to alterations in plant nutrient availability. It was concluded that under drier weather scenarios, irrigation may be a promising adaptation strategy for agriculture in the Southeastern US.