Utilization of Optical Sensor and Crop Modeling to Assist Nitrogen Fertilization Management in Maize.

Nitrogen fertilizer use efficiency in maize is low, mainly due to asynchrony between nitrogen crop uptake dynamic and soil N availability, moreover when high N rates are applied. The objective of this work was to evaluate different N fertilization strategies by management zones in maize. For each management zone an economical optimum N rate (EONR) was determined by using long- term simulations. Nitrogen fertilization strategies compared EONR at planting against split N fertilization rates (50% EONR at planting, and 50% EONR at planting plus 25, 50, 75, 100 or 125 % of EONR at V12). Sensor based N fertilization rates (SBNR) were calculated using NDVI measurements from a Green Seeker sensor at V12, for each treatment the response index was estimated respect to EONR plots NDVI and attainable yields estimated long-term simulation. Crop growth around flowering and grain yield were determined. Crop growth and NDVI readings at V12 showed similar crop N status between EONR at planting vs 50% of EONR. Response index varied between 1.02 to 1.18%, and estimated maximum N fertilization rate was 30 kg ha^-1. Maize grain yield ranged from 5932 to 10400 kg ha^-1. There were grain yield differences among zones, whereas there were non-significant grain yield differences among treatments. Estimated sensor based yield responses were similar to observed. Additionally, for the evaluated management zones, simulations results showed that in 50% of cases only with 50% EONR + 25% of EONR at V12 allows improve EUN and grain yield respect to the complete EONR applied at planting. In order to refine N fertilization, we are studying how to integrate on season rainfall from planting to time of side-dress N fertilization with rainfall records in different ENSO regimes or stochastic rainfall predictions.