Simplified functional model for estimating nitrogen mineralisation and leaching in biosolids-amended soils

A model was developed to simulate biosolids mineralisation, nitrate leachin g and nitrate uptake by plants. This functional model considers only the en d product of a simplified treatment of the processes that occur without tak ing into account their rates. It is specifically structured for the use as a practical decision support tool for Sydney Water Corporation and other bi osolids users for the beneficial application of biosolids on agricultural l ands without nitrate accretion to groundwater. The model uses fundamental p rinciples and the relevant concepts from available models to estimate movem ent of nitrate down the soil profile. The model output was compared against data from 3 independent experiments. In 1 experiment, biosolids were used in a sheep-grazing trial and in anothe r, biosolids were applied to a winter wheat crop. In both cases, nitrate mo vement in soil was monitored by soil sampling. In a third experiment, bromi de ion was used as a surrogate for nitrate to trace vertical solute movemen t under simulated rainfall. In all 3 experiments, the agreement of model pr edictions of nitrogen movement based on the distribution pattern and the po sition of the peak concentrations of nitrogen, with measured values was suf ficient to support the validity of the model for nitrate movement in soil a fter biosolids application. The model is simple with easily available input s and is of sufficient accuracy as a decision support tool in the managemen t of biosolids application.