In-season decision support tools for estimating sidedress nitrogen rates for corn in the Mid-Atlantic Coastal Plain

In corn (Zea mays L.) production, determining appropriate nitrogen (N) rates is a critical part of achieving profitable yields, while minimizing negative environmental effects. Many tools to assist in the determination of optimum corn sidedress N rates exist, however, those that are low cost, that can be used in real time and that do not require extensive scouting or sampling may be preferred. This study compared the rates prescribed by four in-season N rate recommendation approaches: (1) the Virginia Corn Algorithm (VCA); (2) the Maize-N simulation model; (3) the Nutrient Expert for Maize (NE-Maize) model; and (4) the standard yield goal-based approach used in Virginia for N rate prescription, nitrogen use efficiency (NUE), and corn performance. The VCA uses canopy reflectance from pre-existing high and low N areas to determine potential response to additional N fertilizer. Maize-N generates recommendations based on crop and soil-specific input parameters as well as long-term and current season weather data. The NE-Maize model requires input of site and crop specific data, as well as the history of inputs and crop rotation and generates recommendations based on previous result from studies conducted in similar environments. The purpose of this study was to compare N rate recommendations from these various systems for performance and utility in the mid-Atlantic region. A total of seven field trials were conducted from 2012 to 2014 in Virginia each with four replications in a randomized complete block design. Treatments evaluated included a complete factorial of four different pre-plant rates (0, 45, 90, and 134 kg ha⁻¹) with the three different simulation model-prescribed rates and the yield-goal approach applied at sidedress. There were no differences in corn grain yield between the different systems or pre-plant N rate application at any location. Corn grain and stover N uptake were infrequently affected by treatment, but generally increased with increasing N rate applied, when a difference existed. Partial factor productivity (PFP) of N generally declined with increasing pre-plant N rate for all in-season N recommendation systems. The PFP for the in-season N rate recommendations generated from the VCA approach was greatest in four of seven instances with a mean of 68 kg grain kg N⁻¹. Additionally, based on our results the Maize-N model, 56 kg grain kg N⁻¹, also shows promise in this environment. While additional research is needed to validate these findings, producers should consider the use of sidedress N rate decision support tools to increase efficiency of N fertilizer.