Site-Specific Variable Nitrogen Rate Model in Corn.

Global nitrogen use efficiency (NUE) was estimated in 33% for cereals. Uniform N applications are considered as standard N practice, but is not accounting for the potential spatial variability encountered at the field-scale. A site-specific variable rate N model was developed with the goal of improving NUE, minimizing cost and increasing farmers' profits. The objective of this research project was to evaluate the model developed (including a topographic component, CTI index) in four trials performed during 2010 and 2013 in Cordoba, Argentina. A total of twelve combinations were resulted from the implementation of six N strips (six fertilizer N rates = 0, 40, 80, 160, 320, and variable N rate – kg N ha_-1) and two management zones (low vs. high production). The model implemented was highly influenced by the weather pattern; yield prediction did include both the variable N rate component and the topographic factor: wet year (Yield= 8848 +25.04N -0.06N² +37.69CTI -0.49CTIN), Normal year (Yield=6617+15.95N-0.025N²+47.89CTI-0.63CTIN) or dry year (Yield=5406 +3.18N -0.02N² +21.45CTI +0.27CTIN). For the harvesting procedure, mechanized harvesting was facilitated via use of yield monitor and GPS equipment. After harvest, fertilizer N rates by management zones were optimized for each trial. The variable N rate model postulated before planting and the post-mortem (after harvest) analysis had 88% fit.