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United States Department of Agriculture

Agricultural Research Service

Title: Soybean Nitrogen Contribution to Corn and Sorghum in Western Corn Belt Rotations

Authors
item Varvel, Gary
item Wilhelm, Wallace

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 1, 2003
Publication Date: May 1, 2003
Citation: VARVEL, G.E., WILHELM, W.W. 2003. SOYBEAN NITROGEN CONTRIBUTION TO CORN AND SORGHUM IN WESTERN CORN BELT ROTATIONS. AGRONOMY JOURNAL 95:1220-1225.

Interpretive Summary: The beneficial effects of crop rotation have long been known, but their use in the U.S. has ebbed and flowed over the years. Changes in farm programs promoting greater crop diversity have resulted in greater use of crop rotations. For crop rotations that include a legume such as soybean, N availability is usually identified as being largely responsible for most of the beneficial effects. Our objective was to utilize yield response data from two long-term studies to determine the amount of N supplied by soybean for corn and sorghum in 2-year rotations. The experiments were located in eastern Nebraska (Mead) (rainfed) and central Nebraska (Shelton)(irrigated). Continuous corn and soybean-corn cropping systems were present in both experiments, while continuous sorghum and soybean-sorghum cropping systems were present at Mead only. There were three N fertilizer rates for the study at Mead and five N fertilizer rates for the study at Shelton. Nitrogen fertilizer replacement values estimated using graphical and regression techniques indicated that corn in a two-year rotation with soybean obtained approximately 65 to 70 kg N ha-1 while sorghum obtained approximately 80 kg N ha-1 in a soybean-sorghum rotation. This amount of N, available to corn and sorghum in 2-year rotations that include soybean, must be considered by farmers when recommendations are formulated to reduce excessive fertilizer N applications and also provides additional encouragement for use of crop rotations.

Technical Abstract: Crop rotation and its beneficial agronomic effects have long been known, but their use in the U.S. has ebbed and flowed. Recently, farm policies promoting greater crop diversity have resulted in greater use of crop rotations. In crop rotations with legumes, N availability is usually identified as responsible for most of the beneficial effects. Our objective was to utilize yield response data from two long-term studies to determine the amount of N supplied by soybean [(Glycine max. (L.) Merr.)] for the following nonlegume crop in 2-year rotations. The experiments were located in eastern Nebraska (Mead) (rainfed) and central Nebraska (Shelton)(irrigated). Continuous corn (Zea mays L.) and soybean-corn cropping systems were present in both experiments, while continuous sorghum [Sorghum bicolor (L.) Moench] and soybean-sorghum cropping systems were present at Mead only. There were three N fertilizer rates for the study at Mead and five N fertilizer rates for the study at Shelton. Nitrogen fertilizer replacement values were estimated using graphical and regression techniques. Results from both techniques indicated that corn in a two-year rotation with soybean obtained approximately 65 to 70 kg N ha-1 while sorghum obtained approximately 80 kg N ha-1 in a soybean-sorghum rotation. This amount of N, available to corn and sorghum in 2-year rotations that include soybean, must be considered by farmers when recommendations are formulated to reduce excessive fertilizer N applications.

Last Modified: 4/17/2014
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