New model-based insights for strategic nitrogen recommendations adapted to given soil and climate

Abstract

Managing nitrogen (N) fertilizer applied in agricultural fields is important for increasing crop productivity while limiting the environmental contamination caused by release of reactive N, especially for crops with high N demand (e.g., corn, Zea mays L.). However, for given soil properties, the optimum amount of N applied depends on climatic conditions. The central question to N management is then what should be the recommended N rate for given soil and climate that would minimize the release of reactive N while maintaining the crop productivity. To address this central challenge of N management, we used a recently developed model-based methodology (called “Identifying NEMO”), which was proved to be effective in identifying ecophysiological optimum N rate and optimum nitrogen use efficiency (NUEopt). We performed modeling for dominant soils and various agroclimatic conditions in five regions along the Mixedwood Plains ecozone, where more than 90% of Canadian corn production takes place. Here, we analyzed for the first time the effect of soil and climate on ecophysiological optimum N rate in an ecozone where there exists a significant agroclimatic gradient. Our results indicated that there were some commonalities among all soils and regions, which we could classify them into two groups with NUEopt ranging from 10 to 17 kg dry yield kg−1 N. For cases with low NUEopt, the recommended N for an expected dry yield of 8 t ha−1 varied from 115 to 199 kg ha−1, whereas they were much lower (79–154 kg ha−1) for cases with high NUEopt. These recommendations were 20–40 kg ha−1 lower than provincial recommendations. Moreover, we found that the different behavior of the two groups was due to soil textures and soils available water holding capacity. For most locations, soils with intermediate available water holding capacity (i.e., 12–15%v) had relatively higher expected yield and lower recommended N.