Application of water budget equation model to farmer's fields of "Tambaguro" soybean

Abstract

A water budget equation model was developed to support farmer's decision for irrigation to his fields in the previous study. This study applied the model to farmer's fields actually, and evaluated a method to estimate model parameter for available water holding capacity (AWHC). Since the estimated volumetric soil moisture content (SMC) was well correspondent with the measured SMC, the model was able to evaluate the fluctuation of water availability in farmer's fields. Rate of available water (Aw) to AWHC (Aw/AWHC) calculated from the model was linearly related to change of instrument reading per day (ΔIR) in the simple soil moisture measuring system developed by Kurose (2006). In order to estimate AWHC, changes of instrument readings (IRs) for 3 periods were necessary for each field. Estimated AWHC varied from 24 to 73mm among investigated fields, and the value made it possible to predict daily change of IR. It is important to enhance reliability on the basis of more data.