Modeling soil moisture effects on net nitrogen mineralization in loamy wetland soils

Nutrient dynamics in wetland ecosystems are largely controlled by soil moisture content. Therefore, the influence of soil moisture content on N mineralization should be explicitly taken into account in hydro-ecological models. The aim of this research was to establish relationships between N mineralization and soil moisture content in loamy to silty textured soils of floodplain wetlands in central Belgium. Large undisturbed soil cores were taken, incubated for 3 months under various moisture contents, and zero order and first order N mineralization rates were calculated. We used the percentage water-filled pore space (WFPS) as an expression of soil moisture because it is a better index for aeration dependent biological processes than volumetric moisture content or water retention. The relationship between the N mineralization rate and %WFPS was described by a Gaussian model. The optimum WFPS for N mineralization ranged between 57% and 78%, with a mean of 65% ± 6% WFPS. Expected annual net N mineralization rates at field temperature (9.7°C) and at optimal moisture content varied between 30 and 186 kg N ha-1 (0–15 cm depth) year-1, with a mean of 110 ± 42 kg N ha-1 (0–15 cm) year-1. The mean N turnover rate amounted to 2.3 ± 1.1 g N 100 g-1 N year-1. Multiple linear regressions between N mineralization and general soil parameters showed that soil structure has an overriding impact on N mineralization in wetland ecosystems.