Assessment of Yield with Altered Soybean Traits Under Climate Change in Southern Brazil: Performance of the Crop Model and Genotype Trait

Abstract:

Water deficit is the main factor responsible for soybean yield gap in Southern Brazil and tends to increase under climate change scenarios. Alternatives need be identified in order to create options to reduce the yield gap. One alternative is the selection of soybean cultivars with traits associated to drought tolerance. Thus, the aim of this study, via use of crop models, is to evaluate genetic traits that can help to improve soybean yield under climate change scenarios in Southern Brazil by improving the crop tolerance to water deficit. For this, the CSM-CROPGRO-Soybean model was used to simulate soybean yield in Southern Brazil and evaluate yield with altered genetic traits. The first step was to calibrate the model for a Brazilian soybean cultivar, using results from irrigated and rainfed experiments conducted in different sowing dates and locations in Southern Brazil. The CSM-CROPGRO-Soybean estimated a mean yield of 3551 (SD = 1439) kg ha^-1, while the mean observed yield was 3313 (SD = 1105) kg ha^-1. The mean error was 238 kg ha^-1 (7.2%), mean error absolute was 765 kg ha^-1 (23%) and modeling efficiency was 0.27, with a good relationship between observed and simulated yield (Figure 1). The model was able to estimate soybean yield for different levels of soil water available during the crop season. The next steps of the project are to manipulate the coefficients related with rooting depth extension, early stomata closure at high soil water contents, transpiration limited to a maximum rate, and N₂ fixation drought tolerance in the model in order to identify their impact on yield under current and future climate scenarios in all soybean production regions in Southern Brazil. The soybean yield from different changed traits will be evaluated in order to define guidelines for breeding programs, allowing the saving of resources and time in the new cultivars development process, focused on adaptation to climate change.