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Modelling nitrogen mineralization from biosolids Rowell, Douglas Murray

Abstract

Decomposition and net nitrogen mineralization from four biosolids, wheat straw, paper fines and Douglas-fir foliar litter were described and modelled. The initial chemical composition of these materials was characterized in terms of organic matter, carbon, nitrogen, proximate fraction analysis and solid-state ¹³C nuclear magnetic resonance spectroscopy. Patterns of decomposition and net nitrogen mineralization over time were described in three incubation trials, one in the greenhouse and two in the field. Patterns were modelled based on the initial chemical characterization. Rates of decomposition were strongly related to the lignocellulose index and the carbon to organic matter ratio. The decomposition model extrapolated well to two field sites when site-specific correction factors were applied. Net nitrogen mineralization was most effectively predicted by initial organic nitrogen concentration and the phenolic content of the materials. While the mineralization models extrapolated less well to the field sites, the variables employed in the greenhouse model were relevant in the field and would be a useful starting point for further modelling of field nitrogen mineralization. Among biosolids there was a strong correlation between organic N concentration and NMR indices of protein, supporting other studies which have found positive correlations between protein content, organic N content and N mineralization in biosolids. Protein indices as described by NMR appear to be of quantitative value and may prove useful in predicting N mineralization from biosolids.

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