A Regional Investigation of In-season Nitrogen Requirement for Maize Using Model and Sensor-based Recommendation Approaches

N management for corn (Zea mays L.) can be improved by applying a portion of the total required N in-season, allowing for adjustments which are responsive to actual field conditions. This study was conducted to evaluate two approaches for determining in-season N rates: Maize-N model and active crop canopy sensor. The effects of corn hybrid and planting population on recommendations with these two approaches were considered. In a 2-yr study, a total of twelve sites were evaluated over a 3-state region, including sites in Missouri, Nebraska, and North Dakota. Over all site-years combined, in-season N recommendations were generally lower when using the sensor-based approach than the model-based approach. This resulted in observed trends of higher partial factor productivity of N (PFPN) and agronomic efficiency (AE) for the sensorbased treatments than the model-based treatments. Overall, yield was better protected by using the model-based approach than the sensor-based approach. For two Nebraska sites in 2012 where high levels of N mineralization were present, the sensor approach appropriately reduced N application, resulting in no decrease in yield and increased profitability when compared with the non-N-limiting reference. This indicates that specific conditions will increase the environmental and economic benefit of the sensorbased approach. Significant population differences in normalized difference red edge (NDRE) reflectance were observed. Using a reference strip of differing plant population than the target crop resulted in N recommendations different from those obtained using a reference strip and target crop of the same population. It is advised that the non-N-