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Updating nitrogen and phosphorus credits from manure to maximize fertilizer use efficiency in row crops

Study author(s): Melissa L. Wilson, University of Minnesota, Department of Soil, Water, and Climate
Years of study: 2018-2021
Location(s): n/a

Important: for the complete report, including all tables and figures, please download using the links to the right.

Background Info

Our goal is to verify and/or update N and P credit recommendations from manure so that farmers are able to make better decisions when purchasing and applying commercial fertilizers in the following years.


  • Estimate N and P mineralization from a variety of manures and soil types.
  • Determine the best calculation for plant available N (PAN) and plant available P (PAP).

Key Findings

The main goal of this project is to determine if the University of Minnesota’s current recommendations for manure N and P credits are still applicable. Our data showed that we may need to make adjustments to beef bedded pack and possibly dairy manure, but the last year of the experiment is needed to round out our dataset. In the end, if we are able to provide better recommendations for manure use, then farmers will be able to better maximize their commercial fertilizer purchases, increasing profitability.

Grain yields over the years at each site are shown within the charts in the annual report attached above. Though it was aimed to apply the manure at the same available N rate in the first year, the dairy and beef manure resulted in lower yields than expected at both sites. In the second and third year after application, the manured plots did not receive additional N or P and the yields were significantly decreased, though tended to be slightly better than the no N control plots. Based on this, we do not expect to see a nutrient credit in the fourth year after application.

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