CRONOSOJA: a daily time-step hierarchical model predicting soybean development across maturity groups in the Southern Cone

Abstract

The phenology of 34 soybean varieties covering a broad range of maturity groups (2.2-6.8) was evaluated in a series of 43 field experiments located in Argentina, Uruguay, and Paraguay. The sowing dates ranged from middle October to end of January (spring and summer months in the Southern hemisphere) and the site latitudes ranged from -24.9 to -35.6, providing a wide range of thermo-photoperiodic conditions during the growing season. Soybean genotypes exhibited wide variation in the days from sowing to specific developmental stages, mostly associated with photoperiod sensitivity. Based on the observed data, daily time-step models were developed and tested, first for each genotype, and then across maturity groups. The final model was made available at http://cronosoja.agro.uba.ar/. We identified base temperatures specific for developmental stages and an extra parameter for calculating the photoperiod multiplier after R1 (flowering) stage. Also, a critical photoperiod length for each maturity group was derived. Model selection showed that the determinants of phenology across maturity groups were mainly affecting early reproductive stages. The model's ability to predict phenology was more robust for early than for late stages of development, especially for sites with lower growing-season temperatures. Therefore, further research is needed to improve the model predictions at low temperatures. Overall this study provides valuable information on the relationship between soybean phenology and environmental factors, which could help to improve the accuracy of simulation models predicting soybean growth and yield in different regions.