Simple Method for Estimating the Amount of Water Stored in the Cultivation Layer of Converted Paddy Fields Using an Agro-meteorological Database

Abstract

Irrigation scheduling in converted paddy fields is very important to avoid wet and dry stress. The objective of this study was to develop a simple method for estimating the amount of water stored in the cultivation layer of converted paddy fields using an agro-meteorological database. A bucket model with two parameters, maximum and minimum water storage depths, was employed for estimation. Two parameters were specified based on the soil water measurement in fields and compared with soil water characteristic curves. The simple method was applied for three converted paddy fields. It was found that the estimated amount of water stored in the cultivation layer is in excellent agreement with the measured data in comparison to both field capacity and permanent wilting point specified as the two parameters. Moreover, a different method of soil water measurement (two kinds of capacitance sensor and two installations of the sensors) to specify the two parameters hardly affects the estimated results. Thus, we proposed the water storage ratio which is calculated from the amount of water stored in the cultivation layer, as an indicator for irrigation scheduling.