Evaluating in-Season Nitrogen Application Rate Decision Support Tools for Maize (Zea mays L.).

In maize production, determining appropriate nitrogen (N) rates is a critical part of achieving profitable yields while minimizing. The purpose of this study was to compare N rate recommendations from currently available in-season N rate decision tools with the agronomically optimum N rate (AONR). These in-season decision tools are: 1) the Virginia Corn Algorithm (VCA); 2) the Maize-N computer simulation model; 3) the Nutrient Expert (NE) for Maize computer simulation model; and 4) the yield-goal based standard rate currently recommended in Virginia.  A total of eight field experiments were established in the Virginia coastal plain region in 2013-2014 and each employed a split-plot design with four replications. Main plots were cover crop species, either cereal rye (Secale cereale L.), hairy vetch (Vicia villosa L.) or rye-vetch mix. Subplots were N rates, including either 0 or 45 kg N ha-1 applied at planting in a full factorial with sidedress rates of 0, 45, 90, 135, and 180 kg N ha-1 applied to corn at the V5 stage  as urea ammonium nitrate (UAN). Maize-N and NE systems generally prescribed higher N rates compared to the VCA.