The Effect of Temperature on Nitrogen Mineralization in Calcareous Soils Receiving Applications of Dairy Manure.

Dairy manure is commonly applied to crops in Southern Idaho as a source of plant available N.  Researchers have shown that cumulative heat units, or growing degree days (GDD), can be used to predict N release from crop residues and manures.  The majority of N mineralization estimation efforts have been focused on immediate manure applications, as opposed to older or repeated manure applications. The goal of this study was to evaluate the GDD concept for predicting N mineralization receiving annual fall applications of dairy manure. Dairy manure was fall-applied in 2012, 2013, and 2014 to a Portneuf silt loam in Kimberly, Idaho at rates of 866, 1173, and 1103 kg N^-1 ha, respectively. Control soils not receiving manure or fertilizer applications were also included as a treatment. Nitrogen mineralization was monitored in 2013, 2014, and 2015 using the buried bag method.  Buried bags were implemented immediately after spring planting and were collected on a bi-weekly or monthly basis and analyzed for or NH₄N and NO₃N until harvest. Soil temperature was measured at a depth of 10 cm.  Net N mineralized measured throughout the growing season for all 3 yrs was fit to GDD to create a predictive tool for both soil organic matter and manure N mineralization.  The GDD concept may prove to be a simple tool to better estimate plant available N for producers.