Assessing the Impact of N Fertilizer on Soybean Yield and Quality Using a Modeling Approach

Abstract

HighlightsSimulating the effect of high N fertilizer rates with the CSM-CROPGRO-Soybean model for Brazil.Simulated and observed plant tissue N accumulation increased with an increase in N fertilizer rates.N use efficiency decreased with N fertilization on soybeans under long-term scenarios.Both model simulations and observations indicate only a small response in crop yield to high N fertilization.Abstract. Soybean [Glycine max (L.)] is one of the main sources of food protein in the world. To achieve a high yield and grain protein concentration, soybean requires a large amount of nitrogen (N). Many studies have evaluated N fertilization in soybean, with the hypothesis that symbiotic N fixation may not be sufficient to supply N for high-yielding soybean. This study aimed to evaluate the performance of the CSM-CROPGRO-Soybean model with field data to determine the impact of N fertilizer on soybean and explore long-term scenarios. The experiments consisted of a combination of available water management and N fertilizer levels over eight crop seasons. After calibration and evaluation, the CSM-CROPGRO-Soybean model was used to explore the soil and plant N balance. We also applied the model to explore different N fertilization rates in long-term scenarios. The results showed that the model was able to simulate soybean growth with a very good agreement for all sites (D-statistic ranging from 0.63 to 0.99). The observed and simulated crop yield gains from N fertilization were small and not proportional to the amount of N fertilizer applied. The model underestimated the effect of N fertilizer on grain protein concentration increment, but there was a consistent trend towards an increase in protein concentration observed in measured data. Simulations of soil inorganic N balance suggested very high losses of N by volatilization for urea-N fertilization treatments. The long-term scenarios showed that using N rates above 600 kg ha-1 is potentially inappropriate, and a higher crop N use efficiency was obtained with no N fertilizer. Keywords: Ammonia volatilization, Crop yield, Crop N use efficiency, CROPGRO-Soybean model, Grain protein concentration, Nitrogen balance.