Nationally Coordinated Research to Predict Manure Nitrogen Availability.

Approximately 46,000 Mg of manure-derived N is produced each day in the U.S.  This represents not only a significant source of N for crop production, but also a potentially harmful contaminant.  Management practices must be developed that optimize recycling of this N to plants, while protecting the environment.  A team of USDA-ARS scientists is conducting nationally coordinated research to develop predictions of manure N availability to protect water quality and improve farm solvency.  Experimental design and research protocols were developed and used in common across all participating locations.  Laboratory incubations were conducted at each location with a minimum of 3 soils, 3 temperatures, 2 wetting/drying regimes, and 2 manure treatments.  A soil from the central U.S. (Catlin silt loam, fine-silty, mixed, superactive, mesic Oxyaquic Arguidoll) was used as an internal reference across all locations.  Soil N mineralization rate from the Catlin silt loam averaged 0.0216 mg N/kg soil/degree day, and did not differ across five of the six locations, indicating that data compilation and comparison across locations are valid for the methods employed.  In general, soil water fluctuation between 30 and 60 % water-filled pore space did not effect N mineralization.  Soil temperature did impact manure N mineralization, but this could be accounted for by expressing N mineralization relationships versus “Degree Days”.  The most dramatic influence on N mineralization appeared related to the soils themselves.  These relationships must be further understood before accurate predictions of manure N mineralization can be developed or generalized across soils.