Determining In-Season Nitrogen Requirements for Maize Using Model and Sensor Based Approaches.

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.