Climate Variability and Nitrogen Rate Interactions Affecting Corn Nitrogen Use Efficiency In Alabama.

Nitrogen (N) fertilization is an important practice to increase yield; however, plant–soil interactions to in-season changes in climatic conditions result on site-specific responses of corn to nitrogen rates. The objective of this study was to evaluate the effect of different climatic conditions and N fertilizer rate on N use efficiency (NUE) and yield of Corn. Between 2009 and 2012, a nitrogen field study conducted in North and Central Alabama included multiple rates of nitrogen.  The experiments were completely randomized with five replications. The CERES-Maize model was calibrated and validated with data from the nitrogen field study before modeling simulations were conducted. Results from a seasonal analysis, using 61 years of daily historic weather data, indicated that corn response to N fertilization changed based on the in-season rainfall conditions and soil type (Silt loam in North and Loamy sand in Central AL). When simulations was focused on years with different rainfall amount and distribution for the May-June period, period of side-dress N application and pollination-silking, results showed that corn response to N rates under wet May-June years was higher that dry years at both locations. For corn growing under rainfed conditions in Central AL, grain yield reached a plateau rate of 56 and 112 kg N ha^-1 during a dry and wet May-June years, respectively. For rained conditions of North AL, simulation results showed a higher nitrogen corn yield response. During dry May-June years no N fertilizer was needed to achieve the maximum yield, while in wet May-June years, 56 kg N ha^-1 was sufficient to reach the plateau and no significant yield differences were observed when higher N rates were applied. Data showed that rainfall patterns had a very strong relation to Nitrogen response and it changes based on soil type. Results from this study could be used by corn farmers to support nitrogen management decision under the Alabama conditions.