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DIVISION S-8-NUTRIENT MANAGEMENT & SOIL & PLANT ANALYSIS

Comparison of Gross Nitrogen Mineralization Rates by Zero-Order Models

Toyama Agricultural Research Center, Soils and Fertilizer Section, 1124-1 Yoshioka, Toyama, 939-8153, Japan

Corresponding author (shigeru{at}agri.pref.toyama.jp)

Several zero-order models for estimating gross N mineralization rate (M) using ¹⁵N have been proposed. In a comparison of the Ms estimated with some experimentally determined values, different models sometimes gave substantially different results. Although the Ms are estimated by using changes in NH₄–N (NH₄–¹⁴N + NH₄–¹⁵N) and NH₄–¹⁵N, a comprehensive comparison based on model equations is lacking. I compared four zero-order models to clarify the extent of the difference in estimated Ms between models under different conditions of changes in NH₄–N and NH₄–¹⁵N. The ratio of M by one model equation to M by another is expressed by and , where AT is NH₄–N, AL is NH₄–¹⁵N, 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 Ms are. Estimation of M must be done with caution when r 0.2 since model differences increase uncertainties in estimates.

Abbreviations: C, NH₄–N consuming rate • I, gross N immobilization rate • M, gross N mineralization rate