Site-Specific Analysis of Maize Yield Response to Nitrogen in Argentina.

Site-specific nitrogen (N) management can contribute to maximize N use efficiency, increasing production profits and reducing environmental impacts. Today’s challenge is to identify management zones (MZ) with different probability and magnitude of yield response to N, contemplating seasonal and spatial variability. The objective of this on-going research is to determine the economic optimum nitrogen rate (EONR) for maize (Zea mays L.) and its temporal stability at contrasting MZ based on elevation, apparent soil electrical conductivity (ECa), and image analysis. Ten N rate trials were conducted in several MZ at two farms in Nueve de Julio, Buenos Aires, Argentina during the 2012/13 season. Treatments were seven N rates (0, 25, 50, 100, 150, 200, and 250 kg ha^-1) applied as broadcasted urea in a randomized complete block design with three replications. High amount of precipitation during the spring produced significant N losses (some of the N response curves were linear) and reduced productivity differences across MZ. Maize yield and EONR varied from 8732 to 15620 and from 130 to 281 kg ha^-1, respectively across MZ. There was no significant relationship between maize yield at the EONR and the EONR. However, the EONR tended to decrease as the elevation of the MZ increased and the ECa decreased (the EONR was 60 kg N ha^-1 lower at the highest hill with the lowest ECa with respect to the lowest laying area having the highest ECa). Differences in maize yield and EONR are expected to be greater in drier years as forecasted for 2013/2014. Yield response to N at different MZ will be evaluated during several years to estimate the seasonal stability of the EONR. This information is important to provide local producers with science-based site-specific N recommendations for variable rate N application.