New model-based insights for strategic nitrogen recommendations adapted to given soil and climate
Mesbah, M., Pattey, E., Jégo, G., Didier, A., Geng, X., Tremblay, N., Zhang, F. (2018). New model-based insights for strategic nitrogen recommendations adapted to given soil and climate. Agronomy for Sustainable Development, [online] 38(4), http://dx.doi.org/10.1007/s13593-018-0505-7
Plain language summary
Rain-fed corn crops require applications of nitrogen that vary depending on the heat and water supply during the growing season. Climate variation makes it difficult to predict the nitrogen rate required for a given season and soil properties. Crop model predictions were analyzed in order to determine the strategic rates of mineral nitrogen that should be applied for a given region and soil type. The methodology developed, called Identifier NEMO, uses predictions from 50–60 years of daily climate data (by region and soil type) to obtain information on optimum nitrogen levels, nitrogen use efficiency, and recommendations for soil application rates that are based on target yields and that limit the release of reactive nitrogen into the environment. This methodology was applied in a case study of the Mixedwood Plains Ecozone, where over 90% of Canadian corn is produced. Five regions (Windsor, London, Ottawa, St-Hubert, Quebec) and three types of contrasting, dominant soils per region were chosen. Two groups of soil regions were identified based on their level of nitrogen use efficiency. If nitrogen use efficiency was low, higher nitrogen application rates were required. For high levels of efficiency, the recommendations were much lower. Overall, the nitrogen recommendations from the study were 20–40 kg N ha-1 lower than those given by provincial committees. The differences between the two groups of soil regions were due to the mid-range value of the soil water retention capacity, which favoured higher yields for lower nitrogen application recommendations.
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.