See more from this Session: Professional Soils and Crops Oral Presentations
Wednesday, June 29, 2011: 9:05 AM
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 growing season moisture can result in 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 this residual NO3-N at wheat planting is important to avoid compounding the N loss potential. The objectives of this study were to 1) examine plant based tools for assessing soil NO3-N; 2) examine post-harvest residual NO3-N accumulation patterns following corn; 3) determine optimum fall starter N rates for winter wheat; and 4) identify a sufficiency soil NO3-N level above which no starter N would be needed. We 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 optimum fall starter N rate for winter wheat is 17 to 34 kg N ha-1 where soil NO3-N concentration is less than 15 mg kg-1. However, the fall starter N response was highly variable and declined significantly (p=0.0017) as fall precipitation after planting increased. Wheat yield response to fall starter N declined significantly (p=0.0056) as residual soil NO3-N increased. Our results determined that residual NO3-N levels at planting should be considered before applying fall starter N.