Submitted to: Agronomy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/28/2001
Publication Date: 10/1/2001
Citation: Halvorson, A.D., Wienhold, B.J., Black, A.L. 2001. Tillage and nitrogen fertilization influences on grain and soil nitrogen in a spring wheat-fallow system. Agronomy Journal. 93:1130-1135. Interpretive Summary: A long-term study evaluating the influence of tillage and N fertilization on spring wheat grain yields within a spring wheat-fallow (SW-F) cropping system was recently competed. This study evaluated the influence of tillage system and N fertilizer rate on N removal in the grain and residual spring soil NO3-N within this SW-F system over 12 years. Grain N removal from the system and soil NO3-N levels varied with N rate, year, and cropping sequence. Total N removed in the grain in the SW-F sequence tended to be lowest with no-till (NT)in this spring wheat-fallow system compared with conventional-till (CT) and minimum-till (MT), but no tillage differences in the F-SW sequence. Nitrogen fertilization increased the amount of total grain N removed in six spring wheat crops in the F-SW sequence only. Total grain N removal with 6 crops as a fraction of total fertilizer applied was 21, and 17% for the 22 and 45 kg N ha-1 fertilizer rates, respectively. Soil NO3-N levels were not affected by N rate or tillage system during the initial years (1985-1989), but increased significantly following drought years (1988 and 1989). Soil NO3-N levels varied with year and cropping sequence, increased with increasing N rates after the drought years and tended to be higher with CT and MT than with NT. Soil NO3-N movement below the crop root-zone appears to have occurred in only 1 or 2 years following above average precipitation periods. The results show that dry years and N fertilization impact grain N removal and residual soil NO3-N levels more than tillage system within a spring wheat-f system. Soil testing for residual NO3-N is essential for proper N management within the SW-F cropping system.
Technical Abstract: Spring wheat (Triticum aestivum L.) is generally produced in the northern Great Plains using mechanical tillage and a crop-fallow system. This study evaluated the influence of tillage system [conventional-till (CT), minimum- (MT), and no-till (NT)] and N fertilizer rate (0, 22, and 45 kg N ha-1) on ity of N removed in harvested grain and changes in residual spring soil NO3-N during 12 years in a dryland spring wheat-fallow (SW-F) cropping system. Grain N removal varied with cropping sequence, N rate, and year. For SW-F sequence, yearly grain N removal tended to be greater with CT and MT than with NT, but had no effect in F-SW sequence. Nitrogen fertilization increased the amount of total grain N removed in six spring wheat crops in the F-SW sequence only. Only 21 and 17% of the N applied was removed in the grain for the 22 and 45 kg ha-1 N rates, respectively. Tillage system influenced total grain N removal only in the SW-F sequence, with total grain N removal being greater with CT and MT than with NT. Soil NO3-N levels in the 150 cm profile varied with cropping sequence, N rate, tillage, and year. Total NO3-N levels were similar from year to year prior to drought years. Following drought years, soil NO3-N levels increased significantly in the profile, with some apparent leaching loss of N below the root-zone during and following wetter years. Soil NO3-N levels increased with increasing N rate following drought years. Soil profile NO3- els tended to be greater with CT and MT than with NT. The results show that dry years and N fertilization impact grain N removal and residual soil NO3-N levels more than tillage system within a spring wheat-fallow system.