Submitted to: Proceedings Great Plains Soil Fertility Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/15/2000
Publication Date: 3/5/2000
Citation: Halvorson, A.D., Wienhold, B.J., Reule, C.A. 2000. Long-term tillage and nitrogen fertilization effect on c sequestration. Proceedings Great Plains Soil Fertility Conference. Kansas State Unviersity, Manhattan and Potash and Phosphate Institute, Brookings, SD. 8:16-21. Interpretive Summary: Nitrogen (N) is applied to optimize crop yields and economic returns in the Great Plains. Increases in soil organic carbon (SOC) can have positive effects on soil productivity and quality. The effects of N fertilization on crop residue production and SOC levels under different long-term dryland and irrigated cropping systems were evaluated. Four dryland and one irrigated cropping systems studies that had received N applications to the same plots from 9 up to 30 years were used in this evaluation. Crop residue production increased with increasing rates of N fertilization in all cropping systems. SOC levels increased with increasing N rates for two no-till intensively cropped dryland sites in Colorado and one intensively tilled small grain-sugarbeet irrigated site in Montana. In North Dakota, tillage system and N fertilization rate had no effect on SOC in a spring wheat-fallow system; however, SOC increased with decreasing tillage intensity in the spring wheat-winter wheat-sunflower system with n differences due to N rate. The results indicate that reducing tillage intensity and maintaining an adequate N fertility program for optimum crop yields will enhance SOC levels which will contribute to improved soil productivity and quality.
Technical Abstract: No-till (NT) increases the potential to intensify cropping frequency under dryland conditions in the Great Plains. More frequent cropping requires N input to maintain economical yields. We evaluated the effects of long-term N fertilization on crop residue production and its subsequent effects on soil organic C (SOC) in four dryland cropping systems and one irrigated cropping system. Nitrogen rates had been applied to the same plots from 9 up to 30 years. Cropping systems included two annual cropping systems, one wheat-corn (sorghum)-fallow, one wheat-fallow, and one irrigated sugarbeet- rotation. Crop residue production varied with cropping and tillage system, but increased with increasing N rate in all systems. Increased amounts of crop residue returned to the soil with increasing N rate resulted in increased levels of SOC in the Colorado studies. In North Dakota, SOC was not influenced by N rate or tillage system in a spring wheat-fallow rotation. However, NT resulted in increased SOC levels over that of minimum-till (MT) and conventional-till (CT) systems in spring wheat-winter wheat-sunflower rotation. At the intensively tilled irrigated site in Montana, SOC levels declined from 1953 to 1983, with SOC levels being lowest with the lower N rates. At the highest N rate, 400 lb N/a, SOC was maintained near the initial 1953 SOC level. SOC levels can be enhanced by increasing crop residue production through adequate N fertility.