Field evaluation of models of denitrification linked to nitrate leaching for aggregated soil

Abstract

Dynamic simulation models of the nitrogen cycle are an important aid for predicting the effect of land management on nitrate concentration in ground and surface waters. These models often neglect, or treat in a highly empirical way, the process of denitrification. The solute leaching model SLIM, suitable for use in aggregated soil, was linked to two alternative denitrification submodels ('simple structure' and 'aggregate assembly' treatments). The linked models can be used in dynamic simulation of the fate of nitrate in soil. The models were calibrated using water release and soil respiration data from two field sites (a clay loam and a sandy loam). The fate of Br-and 99 atom percentage "NO; tracers on drained plots was measured at these sites. Both models predicted less denitrification from plots receiving small inputs of fresh organic residue than was actually lost; both did better where residue inputs were large. The 'aggregate assembly' model predicted short-term losses immediately after incorporation of residues more successfully than did the 'simple structured' model. The simulated dynamics of denitrification during the autumn and winter in the two models were also very different. Overall N balances were better predicted in the clay loam than the sandy loam. Possible reasons for discrepancies between model output and real data include immobilization (especially when large inputs of residues were incorporated), denitrification in the subsoil, and an inadequate description of the way in which degradation of organic matter depends on temperature.

Simplified denitrification models: Overview and properties

“…The soil structural models consider gaseous diffusion of gases into and out of aggregates. The distribution of aggregates is considered and denitrification occurs only in the anoxic parts of aggregates; examples can be found in, e.g., Arah and Smith (1989), Grant (1991), and Vinten et al (1996). Simplified process models are easier to use and do not consider microbial processes or gaseous diffusion.…”

Modeling nitrate-nitrogen removal process in first-flush reactor for stormwater treatment

“…2c and 2d are based on classic models for microbial growth and nitrogen removal by denitrifying bacteria through mobile-immobile phase solute exchange in porous media, presented by Molz et al [20], Widdowson et al [21], and Hantush and Mariño [18]. While it is generally assumed that the denitrification occurs only in immobile biomass, there are evidences showing that denitrification occurs from both mobile and immobile nitrate pools [22]. Therefore, Eq.…”

Nitrogen and sulphur management: challenges for organic sources in temperate agricultural systems

“…Losses exacerbated by the addition of plant residues have been identified in some studies. For example, on a clay loam soil in Scotland where plots were ploughed and sown to grass in July with an addition of 64 kg N ha 21 as Ca(NO 3 ) 2 , about 18 kg N ha 21 were denitrified from the plots without residues, and twice that amount from those with residues (Vinten et al 1996). There is other evidence that N-rich crop residues may stimulate rapid denitrification and associated nitrous oxide emissions, even in coarse-textured soil.…”