Can a Fall Nitrate Test Improve Wheat Nitrogen Management in the Mid-Atlantic, USA?.

In the Mid-Atlantic USA, farmers have economic and environmental reasons to optimize fertilizer nitrogen (FN) for corn (Zea mays, L.).  During the past decade, average corn yield in Maryland ranged from 4655 to 9749 kg ha^-1.  This wide range is primarily attributable to rainfall which varies annually.  Even with very good corn nitrogen (N) management, the potential for highly variable residual nitrate (NO₃-N) exists across sites and years.  For example, at 13 study sites over 4 years, corn plots that received a moderate 135 kg N ha^-1 had residual NO₃-N levels ranging from 9 to 77 kg ha^-1 in the surface 0.3 m  of soil.  Higher corn FN rates of 202 and 270 kg N ha^-1 produced even higher ranges of residual NO₃-N.  Winter wheat (Triticum aestivum, L.) planted after corn is well suited to utilize residual NO₃-N.   However, many Mid-Atlantic farmers use 20-40 kg ha^-1 FN at wheat planting without consideration of residual soil NO₃-N.  Ignoring residual NO₃-N when planting wheat can result in economic loss for farmers through unnecessary FN applications, as well as environmental concern about NO₃-N leaching into the groundwater during fall-spring recharge.  The most reliable method for measuring residual NO₃-N is a soil test; although awaiting lab results is a limitation during the short period between corn harvest and wheat planting.  This project is examining the potential for adapting the quick NO₃-N test, known as the Pre-sidedress Nitrate Test (PSNT), as an alternative to traditional laboratory-based soil analysis.  In addition, this project is examining wheat response to a range of fall residual NO₃-N levels, with the objective of establishing fall FN recommendations for wheat based on residual NO₃-N levels.  A summary of results from experiments conducted over four years and five sites across Maryland will be presented.