Precipitation irregularity and solar radiation play a role in determining short-season soybean yield

Abstract Climate change, resulting from increased atmospheric CO2, will affect temperature and precipitation amount and regularity. Changes in solar radiation have been observed in the recent past. Precipitation irregularity is a measure of rainfall distribution during a growing season (calculated as the standard error of the slope from regression of cumulative precipitation on day of the growing season). We investigated whether precipitation irregularity and solar radiation contributed to soybean yield. Fourteen short-season cultivars, released from 1930 to 1992, were grown from 1993 to 2019 at Ottawa, Canada. Stepwise multiple linear regression was used to investigate the contribution to seed yield of precipitation irregularity and solar radiation, and also previously modeled parameters genetic improvement, annual [CO2], and cumulative precipitation and average minimum temperature during the vegetative, flowering and podding, and seed filling growth stages. While solar radiation and precipitation irregularity did not trend over the years of our study and precipitation irregularity was not related to growing season precipitation, both were significant factors in our model, accounting for 2.5% and 6.5%, respectively, of the seed yield variability. Precipitation during all three stages were similar as they each accounted for 4%–7% of seed yield variability. We observed contrasting temperature effects where higher minimum temperature during vegetative and seed filling reduced yield, while during flowering and podding increased yield. Estimated yield improvement due to elevated [CO2] was 7.8 kg ha−1 ppm−1 and to genetic improvement over time was 7.1 kg ha−1 year−1. Over the extremes of our study we found that precipitation irregularity could cause up to a 30% yield reduction.