Submitted to: American Chemical Society Abstracts
Publication Type: Abstract only
Publication Acceptance Date: 4/20/2000
Publication Date: 8/24/2000
Citation: Halvorson, A.D. 2000. Nitrogen fertilization, tillage, and cropping system influences on soil organic carbon. American Chemical Society Abstracts. Interpretive Summary:
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. Established N 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-wheat rotation. Crop residue production varied with cropping and tillage system, but increased with increasing N rate in all systems. The increased amount of crop residue returned to the soil with increasing N rate resulted in increased levels of SOC in the NT dryland studies in Colorado. In North Dakota, SOC was not influenced by N fertilization or tillage system in a spring wheat-fallow rotation. However, NT resulted in increased SOC levels over that of the minimum-till (MT) and conventional-till (CT) systems in a spring wheat-winter wheat-sunf rotation after 12 years. 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 in 1983. At the highest N rate (448 kg N/ha) SOC was maintained near the initial 1953 SOC level. The increase in SOC with N fertilization contributes toward improved soil quality and productivity. Soil organic carbon levels can be enhanced by increasing crop yields and residue production through adequate N fertility.