Soil Moisture Condition and Evapotranspiration in a Maize Field under the Summer Condition of High Temperature and Low Rainfall

Abstract

In the summer of 1994, drought injury in crops occurred due to high temperatures and low rainfall throughout Japan. In this study, the authors examined the characteristics of soil moisture condition and evapotranspiration to determine the water balance in a maize field during the drought.
The results are summarized as follows:
1) The total amount of soil moisture in the soil layer to a depth of 1.0m below surface throughout the growing season was less than the Depletion for Optimum Growth point (DOG). And soil moisture was reduced even at a depth of 2.0m, primarily because of the rapid development of the maize root system and water uptake.
2) Characteristics of the energy balance in the maize field during the growing season under the drought conditions in this study were different from results reported by others for other crops, for example the intensity of latent heat flux approximated net radiation flux, and sensible heat flux was nearly or less than zero.
3) Dry matter production, Total Digestible Nutrients and some other components were less in 1994 than 1995, when those values were comparable to values during a normal year, despite the similarities between the two years in the weather conditions for the growth of maize. This difference may be due to the difference in total amount of soil moisture below the soil surface to a depth of 1.0m at the conclusion of Baiu, the rainy season. In 1995, the soil moisture content was higher than DOG because of the high rainfall during Baiu.
4) On the bases of the above findings, the authors propose a simple irrigation method. When rainfall is insufficient at the end of the rainy season, fields are irrigated only once as soon as possible to attain the field capacity in the soil layer to a depth of 1.0m below surface.