What It Takes to Model Soybean Phenology for Wide Range of Maturity Group.

Correct simulation of soybean phenology is critical to soybean growth and yield simulation. The current version of SoySim (http://soysim.unl.edu/) was tested and validated for maturity group up to 4. We now attempt to expand to maturity group 8 for the phenology simulation using field observations that cover a wide range of soybean maturity and sowing dates. Because soybean phenology is sensitive to not only temperature but also photoperiod, it becomes critical to understand how each factor and their interaction quantitatively control soybean development. We found that crop development is better simulated using the most limiting factor between temperature and photoperiod instead of the product of the two. We also suspect that threshold values of the two factors for soybean development may be different at different stages of the crop development. The revised SoySim model was tested using datasets independent of model revisions.