Thursday, November 16, 2006 - 9:15 AM

Excess N in Soil-Crop Systems: Assessment and Integration with N Recommendations.

David R. Huggins, USDA ARS-Pullman, 215 Johnson Hall, Pullman, WA 99164, Doug Beegle, Pennsylvania State Univ, 116 Ag Sci & Ind Bldg, University Park, PA 16802, Kevin Bronson, Texas A&M Univ, Ag Exp Station, Route 3, Box 219, Lubbock, TX 79403, Ardell Halvorson, USDA-ARS, 2150 Center Ave, Bldg D, Ft. Collins, CO 80526, John J. Meisinger, Bldg 163F Room 6, BARC-East, 10300 Baltimore Ave, Beltsville, MD 20705-2350, and James Schepers, 113 Keim Hall, Univ of Nebraska, Lincoln, NE 68583-0915.

Nitrogen management has traditionally focused on evaluating crop N requirements using N response functions coupled with plant and soil testing to diagnose N deficiencies and fertilizer needs. Estimated N use efficiencies are implicit in many of these approaches, but measures of inefficient N use, including surplus N and N losses, are often not explicitly utilized in N management programs.  Excess N can be defined as available soil N that exceeds current crop requirements and has a high risk of loss to environmentally adverse pathways during the course of a crop sequence or rotation.  Assessment of N surpluses and losses has been the focus of many recent studies through measures of soil properties (e.g. residual nitrate, pre-sidedress nitrate), crop characteristics (e.g. stalk nitrate, petiole nitrate), and crop performance (e.g. N recovery, N inputs versus outputs).  Our objectives are to review current methods of assessing excess N in cropping systems and to explore their application in evaluating N management practices and in formulating revised N recommendations.  Developing methods to identify and evaluate practices or conditions contributing to excess N will be an increasingly important part of N management as adverse environmental and economic  impacts of surplus N increase.