Tillage in farmland plays an important role not only as a soil management tool for improving the plant root environment, but also as a factor that impacts the hydrological cycle and the energy balance in a region. This is because tillage affects soil moisture and soil temperature greatly in the unsaturated soil zone near the surface, which acts as an interface between the subsurface and the low atmosphere boundary.
In this study, field experiments were conducted under natural weather conditions using two columns of a volcanic ash (andosol) soil to estimate the effects of tillage on soil temperature, pressure head, and evaporation in the unsaturated soil zone. The experimental results were compared with simulated pressure head and soil temperature values in the unsaturated soil zone. A one-dimensional model for simultaneous heat and water transport, based on the theory proposed by P. C. D. Milly in 1982 and 1984, was used. The governing equations were solved by the Galerkin finite element method. The simulated soil temperatures were in good agreement with the measured soil temperatures at most of the soil depths for both columns. After tillage, however, the simulated soil temperatures of the tilled column were higher than those of the untilled column for depths of 4, 9, and 14 cm in the daytime. The simulated pressure head values were in agreement with the measured values up to the tillage in the tilled column. After the tillage treatment for the tilled column and 60 h of elapsed time for the untilled column, the simulated pressure head values were in poorer agreement with the measured ones. After the tillage, however, the simulated pressure head values were greater for the tilled column than for the untilled column for depths of 5, 10, and 25 cm. This reflects the same results as with the measured pressure head results.