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

Abstract

A model was developed to simulate biosolids mineralisation, nitrate leaching and nitrate uptake by plants. This functional model considers only the end product of a simplified treatment of the processes that occur without taking into account their rates. It is specifically structured for the use as a practical decision support tool for Sydney Water Corporation and other biosolids users for the beneficial application of biosolids on agricultural lands without nitrate accretion to groundwater. The model uses fundamental principles and the relevant concepts from available models to estimate movement 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 another, biosolids were applied to a winter wheat crop. In both cases, nitrate movement in soil was monitored by soil sampling. In a third experiment, bromide ion was used as a surrogate for nitrate to trace vertical solute movement under simulated rainfall. In all 3 experiments, the agreement of model predictions of nitrogen movement based on the distribution pattern and the position of the peak concentrations of nitrogen, with measured values was sufficient to support the validity of the model for nitrate movement in soil after biosolids application. The model is simple with easily available inputs and is of sufficient accuracy as a decision support tool in the management of biosolids application.