Corn Residual Nitrate and its Implications for Fall Nitrogen Management in Winter Wheat
Forrestal, Patrick Joseph
Kratochvil, Robert J
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Corn (Zea mays, L.) production typically requires supplemental nitrogen (N) to optimize yields. In dryland corn production systems, where N is applied during the early to mid-vegetative growth stages, inappropriate N applications or limited moisture during the growing season can result in large disparities between optimum and applied N rates. This leads to variable post-harvest residual nitrate (NO3-N) accumulation, which is susceptible to loss. However, this NO3-N could provide the starter N requirement of the subsequent winter wheat (Triticum aestivum, L.) crop. Accounting for residual NO3-N present at wheat planting is important to avoid compounding N loss potential due to corn residual NO3-N accumulation. The objectives of this study were to 1) examine plant based tools for assessing soil NO3-N; 2) to examine post-harvest residual NO3-N accumulation patterns following corn production; 3) to determine optimum fall starter N rates for winter wheat production; and 4) to identify a soil NO3-N level above which starter N could be forgone without negative agronomic effect. This study found that plant canopy measurements are useful tools for assessing corn N management and for identifying drought sites, which had the greatest NO3-N accumulations. The corn stalk nitrate test was significantly (p<0.001) and positively correlated with soil residual NO3-N (r2=0.41). Greatest soil residual NO3-N accumulation occurred where drought conditions reduced production. The agronomic optimum fall starter N rate for winter wheat in Maryland is 17 to 34 kg N ha-1 where soil NO3-N concentration to 15 cm depth is less than 15 mg kg-1. However, the fall starter N response was highly variable and declined significantly (p<0.01) as fall precipitation after planting increased. The results of this study indicate that residual NO3-N levels at planting should be considered before applying fall starter N to winter wheat.