This study simulates the leaf area index (LAI), above-ground dry matter (ADM) and seed yield of soybean grown in an alfisol soil and humid tropical climate of Nigeria, West Africa. It used the calibration datasets for 2011 and 2012 to validate the field experiment conducted at the Teaching and Research Farms, Obafemi Awolowo University, Ile-Ife, Nigeria from September 2015 to December 2015. The model was evaluated using root-mean-square-error (RMSE), mean bias, (MB) and percentage bias (PMB). Model sensitivity tests were also carried out to assess the potential impacts of higher temperatures on soybean growth and development. There were good agreements between model simulations of the crop parameters and the field measurements. The models effectively replicated the observations of LAI (MB = 0.339 kg ha-1; PMB = 26%; RMSE = 0.611 kg ha-1) and grain yields (MB = 3.28 kg ha-1; PMB = 0.17%; RMSE = 3.28 kg ha-1). Sensitivity tests revealed that additional warming up to 6oC could reduce VPD (~ 2.0%) and LAI (~ 23.5%). However, soybean ADM and grain yield improved with increase in temperatures near the optimal threshold value during the growing period. Further increase in temperatures by ≥ 4oC reducedthe ADM by ~ 23.8% and the grain yield by ~ 1%. The findings suggested that future warmer climate could have significant negative impacts on the growth and development of soybeans in the study area.

Highlights

• There were fairly good agreements between model simulations and field measurements of leaf area index, biomass and seed yield of soybeans
• The simulations replicated the essential hydro-meteorological features of humid tropical region of Nigeria adequately.
• Grain yield and aerial biomass of soybean improved with increase in temperatures by 1 to 4oC in the seasons.
• Temperatures above the optimal threshold value, 30oC reduced the aerial biomass and grain yield.
• In the future, warmer climate could reduce productivity of soybeans in the humid southwest Nigeria.