Abstract
The moisture content of soil is an important factor in determining the productivity of plants. Many of the climatological models used in estimating plant yields are expressed in terms of a humidity index calculated from weather data, such as precipitation, air temperature and humidity, and solar radiation. The “Chikugo” model developed by the authors is presented as an example of the above. While this kind of model works well for large space and time scales, in order to accurately monitor soil moisture and estimate plant yields for smaller space and time scales, direct evaluation of soil moisture content is necessary. With that in mind, we will present a simple model to estimate soil moisture content on a daily basis from weather data. The model is based on a simple water balance in flat layered soil and is written as:
AW=R-Et-Sp'
where dW is the change in soil moisture content, R is precipitation, Et is evapotranspiration, and Sp is surplus water. The terms Et and Sp are estimated from weather data on the basis of the moisture characteristics of the soil. When the values derived from the model were compared with actual soil moisture measurements, a very good correlation was obtained.
