The short-term fate of urea applied to barley in a humid climate. II. A simple model

Abstract

A simple model describing the transformations, leaching and plant uptake of the nitrogen (N) in urea fertilizer applied to a barley crop is presented. The model considers the root zone as a single compartment and uses daily time steps, and so can be run on a small programmable calculator. It consists of separate submodels for water, fertilizer N and native soil N. Data from a field experiment described in a companion paper were used for parameterization, and the model was then tested on another data set from that experiment. The model successfully predicted the effect, on the leaching and plant uptake of fertilizer N, of a large increase in rainfall plus irrigation from 103 mm to 186 mm in the 35 days following sowing and urea application. As an example of the model's utility, it is used to predict that if 30 mm of drainage occurred within 24 h of fertilizer application, about 33% of the fertilizer N would be leached from the root zone in the silt loam soil studied. However, the same amount of drainage occurring a week after fertilizer application would result only in about 8% of the fertilizer N being leached. The complementary roles that process-oriented field experiments and simple mechanistic models can play in soil fertility research are discussed.