Submitted to: Nebraska Agricultural Experiment Station Bulletin
Publication Type: Experiment Station
Publication Acceptance Date: July 22, 2010
Publication Date: November 15, 2010
Citation: Varvel, G.E. 2010. Long-term Cropping Systems Study. Nebraska Agricultural Experiment Station Bulletin. September/October 2010. 14(5):2. Available: http://ardc.unl.edu/2010SeptemberOctoberExtendedVisions.pdf Technical Abstract: This long-term study has been conducted on the Agronomy Farm at ARDC since the early 1970’s. In the beginning, the objectives were mainly related to crop production as affected by different cropping systems. The cropping systems included in the study are Continuous Corn, Soybean, and Sorghum; 2-year Corn-Soybean and Sorghum-Soybean rotations; and 4-year Oat+Clover-Sorghum-Soybean-Corn and Soybean-Sorghum-Oat+Clover-Corn rotations. In 1983, three nitrogen fertilizer levels were included for each of the crops. Yields results from the past 25 years have shown a slight benefit from rotation for corn and soybean, but grain sorghum has yielded just as well in monoculture as in rotation when sufficient N fertilizer was applied. In later years, questions have emerged about the long-term effects of these cropping systems on soil quality, nitrogen fertilizer and precipitation use efficiency, and greenhouse gas emissions. A major factor in soil quality, carbon sequestration (organic matter) has been measured at several points in time over the past 20+ years. Soil carbon levels have generally been maintained at levels measured in 1984 in continuous corn and sorghum with sufficient N fertilizer for optimum yields and in the 4-year cropping systems at all N fertilizer levels. Soil carbon levels have declined in the continuous soybean, corn-soybean, and sorghum-soybean cropping systems regardless of N fertilizer application level. In 2007, the study was converted to no-till. Grain yield, carbon sequestration, greenhouse gas emissions, and other related factors will continue to be evaluated.