Identifying Optimum Nitrogen Fertilizer Rate for Rainfed Corn Under Variable Climate Using the STICS Crop Model: A Case Study in Eastern Canada.

Effective management of nitrogen (N) fertilizer is important for sustainable crop production. While application of N increases crop productivity, it may cause environmental contaminations due to the release of reactive N, particularly for high demand N crops such as corn. Hence, it is highly important to identify an optimum level of N rate that accounts for both environmental and economic factors. However, identifying the optimum N rate is challenging as it is affected by climate, soil properties and other factors. In this study, we use a newly developed methodology to identify an ecophysiological optimum level of N fertilizer based on nitrogen use efficiency (NUE). We illustrate the performance of this methodology for rainfed corn using the STICS crop model adapted for corn in eastern Canada, using 48 to 61 years of climate data, and contrasting soils for 5 regions along the Mixedwood Plains ecozone (42.3^oN 83^oW–46.8^oN 71^oW), where more than 90% of Canadian corn is produced. The results reveal that available water capacity affect the optimum N rates. Soils with higher available water capacity require less N compared to soil with lower available water capacity. The results also indicate that optimum NUEs vary by soil and climate. Depending on the soil texture and region of application, N rates are optimum when 1 kg of additional N results in 10 to 17 kg increase in dry yield (i.e., an NUE of 10 to 17 kg dry yield kg^-1 N). The optimum N rates also vary by the expected yield for the region and soil. For example, to achieve a dry yield of 8 t ha^-1 (9.2 t ha^-1 at 15% moisture), the recommended N values are in the range of 79 to 154 kg ha^-1, which are less than current provincial recommendations in Ontario and Quebec (120-170 kg ha^-1).