Tillage and nitrogen fertilization influences on grain and soil nitrogen in a spring wheat-fallow system

Spring wheat (Triticum aestivum L.) is generally produced in the northern G reat Plains using tillage and a crop-fallow system. This study evaluated th e influence of tillage system [conventional-till (CT), minimum-till (MT), a nd no-till (NT)] and N fertilizer rate (0, 22, and 45 kg N ha(-1)) on grain N, grain N removal from cropping system, and changes in residual postharve st soil NO3-N during six rotation cycles of a dryland spring wheat-fallow ( SW-F) cropping system. Grain N concentration increased vith increasing N ra te and was higher with CT (33-3 g kg(-1)) than with NT (32.3 g kg-1) at 45 kg ha(-1) N rate. Grain N removal per crop was greater with CT (70 kg N ha (1)) and MT (68 kg N ha(-1)) than with NT (66 kg N ha (1)) and tended to in crease with increasing N rate, but varied with rotation cycle. Total grain N removal in six rotation cycles was in the order: CT > MT > NT. Total grai n N removal by six SW crops was increased by N fertilization, with only 21 and 17% of the applied N removed in the grain for the 22 and 45 kg ha(-1) N rates, respectively. Postharvest soil NO3-N levels in the 150-cm profile v aried with N rate and rotation cycle, with residual NO3-N increasing during consecutive dry crop cycles. In contrast, some leaching of NO3-N below the SW root zone may have occurred during wetter crop cycles. Soil profile NO3 -N levels tended to be greater with CT and MT than with NT. Variation in pr ecipitation during rotation cycles and N fertilization impacted grain N rem oval and residual soil NO3-N levels more than tillage system within this SW -F cropping system.