The objective of this study was to evaluate soil moisture condition and the water saving effect of subsurface irrigation in the Shimajiri Mahji soil field. Okinawa is located in the southern islands of Japan and has a subtropical climate. Recently, there has been an increase in the demand for irrigation water in this area, and with high rates of moisture evaporation from the soil and challenges in storing water for agriculture, the shortage of irrigation water is a serious problem in Okinawa. Shimajiri Mahji soil is a specific soil type that is distributed over 40% of the cultivable area in Okinawa. Water retention in Shimajiri Mahji soil is relatively high, however, water loss by soil evaporation is high due to high temperatures and large isolation. To solve this problem, subsurface irrigation was introduced in Okinawa, however, it is difficult to evaluate water movement from the soil surface and maintain proper soil moisture conditions for crop growth. Here, a two-dimensional simulation model describing soil moisture and heat transfers was developed. To evaluate vapor and liquid water movement separately, equations concerning soil moisture and heat transfers were implemented. To obtain input data and verify the accuracy of the simulation model, an experiment by slit was conducted in a glasshouse. Soil moisture, soil temperature, distribution of solar radiation on the soil surface, temperature, and humidity in the glasshouse were measured. Soil water retentivity and hydraulic conductivity of the Shimajiri Mahji soil were also evaluated. In the experiment, the volumetric water content remained relatively high around the root zone after subsurface irrigation. The moisture at the soil surface was very low and nearly constant. The trend predicted by the model fitted the simulated volumetric moisture content with the experimental measurements, confirming the accuracy of this model. The temporal and spatial changes of soil moisture content were evaluated using the model, and the movement of soil moisture during subsurface irrigation was visualized. By using this model, the amount of soil evaporation, transpiration, and evapotranspiration with surface and subsurface irrigation were calculated, and the water saving effect of subsurface irrigation was evaluated. The simulation results indicated that soil evaporation can be reduced by 60% through subsurface irrigation instead of surface irrigation. Thus, subsurface irrigation is effective in reducing water loss due to soil evaporation, and the method outlined here enables quantification of the water saving effect of subsurface irrigation.
|Number of pages||6|
|Journal||Journal of Food, Agriculture and Environment|
|Publication status||Published - Jul 1 2015|
All Science Journal Classification (ASJC) codes
- Food Science
- Agricultural and Biological Sciences (miscellaneous)
- Environmental Science(all)