Nitrogen Mineralization Kinetics in Soil During Long-term Aerobic Laboratory Incubations: A Case Study

Literature data describing curves of cumulative net N mineralization characterized by an initial lag-phase and obtained by long-term (26 weeks) aerobic laboratory incubations were fitted to different regression models by means of nonlinear regression analysis. The model offering the most appropriate description of the data were selected on the basis of the residual sum of squares left unexplained by the regression. The models employed and compared to the classical first-order model were a mixed-order, one-component model: a mixed/first-order, two-component model: and a simplified special case of the previous, mixed/linear, two-component model: where Nₘ and N₀ are the amount of mineralizable N present in the soil at time t and time 0; Nₐ and Nᵣ are the amounts of mineralizable N initially present in the available and resistant fractions, respectively; tᵢ equals length of incubation; rate constants h₁ and h₂ belong to the mixed-order model; k is a first-order rate constant; and C denotes the slope of the linear tail following the pattern described by the mixed-order expression. Data from three soils, unamended or amended with manure, were best described by the mixed/first-order or, alternatively, the mixed/linear model. The fit was significantly better than that offered by the classical first-order, one-component model. The prediction of potentially mineralizable nitrogen (N₀) varied between 108 and 240 mg N kg⁻¹ soil in an unamended soil, depending on the choice of model The authors were supported by grants from the Swedish Council for Planning and Coord. of Res., the Swedish Council for Forestry and Agric. Res., the Swedish Natl. Sci. Res. Council, and the Swedish Environ. Protection Board to the project “Ecology of Arable Land. The Role of Organisms in Nitrogen Cycling.”