Estimating Mineralizable Nitrogen from Organic Materials.

An incubation study was conducted to estimate potentially mineralizable N (PMN) from 42 different organic materials (24 commercially available fertilizers, 10 poultry litters, and 8 composts). Materials were added to soil at a rate estimated to supply 75 mg plant available N kg^-1 soil and N mineralization was measured over 100 d at 30^oC. PMN measured for the composts averaged -3.5% of the total N applied. In contrast, net N mineralization was observed for the majority of poultry litters and commercial fertilizers, where PMN averaged 17.0% of the total N applied for poultry litters and 30.8% for commercially available organic fertilizers. The use of near infrared reflectance spectroscopy allowed for rapid estimates of the initial organic N of the material (r2=0.97) and rate constant of mineralization (r2=0.92) when net N mineralized was fit to first-order kinetics.