Laura Thompson, University of Nebraska-Lincoln, Falls City, NE, Richard B. Ferguson, Department of Agronomy and Horticulture, University of Nebraska, Lincoln, NE, David W. Franzen, North Dakota State University, Fargo, ND and Newell R Kitchen, USDA-ARS, Columbia, MO
Nitrogen (N), an essential element, is often limiting to plant growth. There is great value in determining the optimum quantity and timing of N application to meet crop needs while minimizing losses. Applying a portion of the total N during the growing season allows for adjustments which can be responsive to actual field conditions which result in varying N needs. Two methods of determining in-season N needs were evaluated, a model and handheld sensor. The Maize-N model was developed to estimate the economically optimum N fertilizer rates for maize by taking into account soil properties, indigenous soil N supply, local climatic conditions and yield potential, crop rotation, tillage and fertilizer formulation, application method and timing. The active crop canopy sensor is responsive to canopy N status during the growing season and when used with high N reference plots, can be used to determine in-season N application rates. Four replications of randomized complete blocks were conducted at each of 6 sites over a 3-state region including Missouri, Nebraska and North Dakota. The model and sensor based approaches were evaluated for yield, nitrogen partial factor productivity, and agronomic efficiency. For all sites, in-season N application rates for model-based treatments exceeded that of sensor-based treatments. Additionally, sensor-based treatments had higher nitrogen use efficiency as seen by partial factor productivity. In a year with high mineralization for Nebraska sites, sensor based application produced higher partial factor productivity of N since the sensor application method required less N and yields were similar between model and sensor based treatments, indicating that in 2012, the sensor-based approach was more responsive to in-season growing conditions.