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Models for Predicting Potentially Mineralizable Nitrogen and Decomposition Rate Constants¹

ABSTRACT

Two equations, a single exponential: N_t = N_o (1 – e^-kt) and a double exponential: N_t = N_o S (1 – e^-kt) + N_o (1 – S)(1 – e^-kt), were used to compare mineralization potentials of soils, where N_t is the N mineralized in time (t), N_o is the potentially mineralizable N, and S and (1 – S) are the fractions of the labile and recalcitrant organic N compounds decomposing at specific rates h and k, respectively. Data were obtained from the published and unpublished incubation studies of Stanford and Smith (MD), Smith et al. (WA), Deans et al. (MN), El-Haris et al. (US), and Griffin and Laine (CT). The double exponential equation provided the "best fit" of the N mineralization-time (N_t/t) curve as determined by the estimated mean square error (MSE). With long-term (>84 d) incubations, N_t/t curves for the double exponential equation resulted in an avg MSE of 6 compared with the single exponential equation (avg MSE of 79) for CT, MN, and MD data sets (n = 20). For short-term (84 d) incubations, N_t/t curves were better estimated by the double exponential (avg MSE = 4, n = 21) than by the single exponential (avg MSE = 12, n = 13) for WA, US, and MN data.

¹ Contribution from the Dep. of Soil Science, Univ. of Minnesota and the Soil and Water Management Research Unit, Northern States Area, USDA-ARS, St. Paul, MN 55108. Minnesota Agr. Exp. Stn., Scientific Journal Series Paper no. 14130.

² Graduate Student, Professor of Soil Microbiology, Research Chemist, USDA-ARS, and Professor; Dep. of Soil Science, respectively.

Received for publication September 18, 1984.