Extending the evaluation of the SoySim model to soybean cultivars with high maturation groups

SoySim is a dynamic process-based model for soybean that requires fewer genotype-specific parameters compared to other soybean models such as the CROPGRO-Soybean model. The SoySim model was originally developed and evaluated using cultivars with maturity group (MG) ratings from 0.8 to 4.2 in temperate climate and mid latitudes. The objective of this study was to evaluate the SoySim model for simulating growth, development and yield of soybean cultivars with MG greater than 4.2 grown in the subtropics of Southern Brazil. The range of maturity groups used in this study was from 4.8 to 8.2, including indeterminate and semi-determinate soybean cultivars. Data for model evaluation were from well-managed twelve field experiments across the Rio Grande do Sul State, including on-farm experiments, during five growing seasons (2010/2011-2014/2015), with sowing dates before, during and after the recommended period, and yield ranging from 1.5 to 5.9 Mg ha−1. The errors in the prediction of final node number, R-stages, LAI and seed yield were high mainly for soybean cultivars with maturation group greater than 6, indicating weaknesses of the model in simulating growth and development of cultivars in environment outside the range where the model was calibrated. We conclude that there is a need to review parameters and relationships in the SoySim model to better describe the effect of environment factors, such as temperature and photoperiod, on growth and development of soybean cultivars with maturity group greater than 6, typically used in the tropics and subtropics.