Modeling for Changes in the Surface Water Phosphorus Concentration in Paddy Fields

Abstract

A mathematical model including conditions of irrigation flow rate, irrigation water quality and fertilizing as operating variable was built for estimating the phosphorus outflow from paddy fields. This model consists of balance equations and rate equations such as adsorption, desorption, bioturbation and other relevant rate processes.
Six experiments using lysimeters under various conditions of paddy fields were carried out to estimate structure and verify validity of this model.
The model simulated the phosphorus concentration in surface water under various conditions with enough accuracy, reflecting the annual changes and the effect of fertilizing. High stability of the model was checked by a sensitivity analysis. Phenomena inside of experimental paddy fields were estimated to be described well. This model will be applied to actual paddy fields after verification tests have been carried out in large-scale fields.