Nitrogen Rates

Introduction In most crop rotations that include corn, nitrogen (N) applied to the corn phase is a proven and profitable practice. Corn in some rotations requires little to no N input, with first-year corn following established alfalfa as an example. Corn in other rotations requires substantial N input to meet plant requirements, with continuous corn (CC) typically requiring the greatest input. Other rotations or corn phases will be intermediate in N application requirement. With corn in the two most common crop sequences in the Corn Belt, corn following soybean (SC) and CC, if N is not applied yield will suffer. If N is not applied on an on-going basis, over time corn yield will often average around 50-60 bu/acre in CC and 100-110 bu/acre in SC, or less. The soil system typically cannot supply the full corn plant N requirement. On average the yield with no N applied is around 70% in a SC rotation and 55% in CC of the yield obtained at an economic optimum rate. Therefore, supplemental N is needed to reach economic yield potential. Research has been on-going for over 50 years measuring corn response to N application. Guidelines for suggested N rates based on that research have been derived using economic principles to determine economic optimum N rate (EONR) rather than maximum yield. Therefore, recommendations are guided by economic return to N application through corn yield increase. The expectation by many is that simply applying N at economic optimum rates will "solve" the issue of nitrate movement from fields in subsurface drainage. However, nitrate losses occur in corn production systems even when no N is applied, and N application at optimum rates increases loss. To date determination of EONR has not been modified to account for environmental costs resulting from increased nitrate loss to water systems when N is applied, largely due to lack of such cost information and societal decisions on where to partition those costs.
Date Issued
2005 (year uncertain)
Number of Pages
Rights Holder
Minnesota Water Research Digital Library
Rights Management
Public Domain