A FUNCTION DESCRIBING NITROGEN AVAILABILITY FROM ORGANIC SOURCES

A simple first-order mathematical function is presented to describe net
nitrogen (N) immobilization and mineralization from organic materials spread on or incorporated into horticultural soils.
To facilitate the representation of
immobilization, kinetics are determined by a conveniently measured carbon dioxide (CO₂-C) evolution rate.
Other parameters include a substrate conversion efficiency, the C:N ratio of microbial decomposers, and the initial C and N contents of the materials.
The model was parameterized using a previously reported incuba-tion study of uncomposted lawn trimming materials (Sullivan et al., 2004). To avoid
overfitting, parameters are lumped between the different treatments whenever
reasonable.
All parameters were lumped except for two labile/recalcitrant partition factors, one for C and one for N. Results for each of eight lawn trimming materials represented evolving C very well (r²=0.99). Nitrogen immobilization and release fits were reasonable (r²</i =0.71), predicting immobilization and mineralization appropriately.
Parameterization options based on proximate carbon analysis were also introduced.