Attributing soybean yield increases from the 1930s to 1990s in Canada to cultivar improvement and climate change

The genotype improvement together with advancing management practices may have contributed to the increasing yield and quality of soybean in the past century. However, very few studies systemically clarified the contributions to soybean yield increases in Canada from genotype improvement and climate change. Quantifying contributions to yield increase from genotype improvement and climate change will provide useful information for developing adaptation strategies for soybean industry to climate change. It is difficult and costly to mimic historical climate for a long-term field experiment. On the other hand, crop models are valuable tools to simulate crop growth with historical climate data. The objectives were to quantify contributions to soybean yield increases from genotype improvement and climate change from 1940s to 1990s in Canada, using an approach combining field experiments and crop modelling. A total of 37 cultivars of maturity group (MG) 00 and 0, released from 1940s to 1990s, were grown in eastern Canada in 1993 and 1994. The CSM-CROPGRO-Soybean model was used to simulate soybean yields under water limited and unlimited conditions and varied CO2 concentration levels. Soybean yield trends from statistical datasets, experiments and simulations were fitted to the linear regression models, respectively. The relative yield change per year was calculated based on the linear regression and the average yield. The results showed that soybean yield increased 1.28% per year in eastern Canada. Genotype improvement led to yield increase 0.5% per year. Soybean yield annually increased 0.7% attributed to climate change, of which 0.29% to the increased CO2 concentration, deducting yield decrease 0.07% caused by increased temperature. Therefore, the soybean yield increases could be attributed to genotype improvement by 40%, climate change in CO2 and temperature by 17%. Rainfall might determine over 30%, and management improvement like weed control and applications of pesticide and herbicide for the rest of yield increase.