Comparison of Gross Nitrogen Mineralization Rates by Zero‐Order Models

Several zero‐order models for estimating gross N mineralization rate ( M ) using 15 N have been proposed. In a comparison of the M s estimated with some experimentally determined values, different models sometimes gave substantially different results. Although the M s are estimated by using changes in NH 4 –N (NH 4 – 14 N + NH 4 – 15 N) and NH 4 – 15 N, a comprehensive comparison based on model equations is lacking. I compared four zero‐order models to clarify the extent of the difference in estimated M s between models under different conditions of changes in NH 4 –N and NH 4 – 15 N. The ratio of M by one model equation to M by another is expressed byR = (AT 2AT 1)andr = (AL 2AL 1), where AT is NH 4 –N, AL is NH 4 – 15 N, and the subscripts 1 and 2 denote the initial and final values, respectively. Ranges of R and r are R > 0 and 0 < r < 1, respectively, and R > r The farther r is from 1, the more different the estimated M s are. Estimation of M must be done with caution when r ≤ 0.2 since model differences increase uncertainties in estimates.