Estimating soil water retention in a selected range of soil pores using tension disc infiltrometer data

The hydraulic properties of soil, such as soil moisture characteristic and pore size distribution, are very important for the interpretation of the physical characteristics of soil and the management of agricultural practices. The current standard methods employing pressure chamber, however, are often time-consuming and difficult to carry out. In this study, we proposed a simple approach to estimate the soil moisture retention and soil pore size, with sufficient accuracy, using steady-state infiltration data. First, the tension disc infiltration data was interpreted using Woodingʹs analytical solution to obtain the K(h) function, from which Ks (saturated hydraulic conductivity) was optimized. The Ks value was then used as an initial input data for the Brooks–Corey model fit to obtain the water retention parameters αBC and b, and the soil water retention characteristics within a selected range of soil pores of 9–450 μm were predicted. The proposed approach was tested for three differently textured soils in laboratory test and one undisturbed field soils. The measurement was replicated for three to five times for each soil. The validity of this method was confirmed by showing good linear regression relationship with data sets obtained by standard pressure chamber method, yielding slopes being close to unity and r2 values being >0.86. This observation strongly suggests that the proposed method can be applied for the in situ measurement of water retention and pore size in field soils. The results of this work will enable us to easily determine the temporal changes of hydrodynamic nature of soil using tension disc infiltrometer technique.