Statistical equations for estimating field capacity, wilting point and available water capacity of soils from their saturation percentage

Statistical equations were derived for estimating three soil moisture constants, i.e. field capacity (FC), wilting point (WP) and available water capacity (AWC), from soil saturation percentage (SP), which is an easily determinable parameter. The regression equations were evaluated from a data set obtained on 438 soil samples collected from different horizons of 111 profiles of the Indogangetic Plains in northern India, having a wide variation of texture and other physico-chemical properties. The three soil moisture constants were positively correlated with logarithms of SP (r = 0·985 for FC v. In SP, 0·979 for WP v. In SP, and 0·914 for AWC v. In SP). The regression equations were thetested on an independent set of experimental data on 57 samples collected from 14 representative soil profiles of the study area. Values of the three moisture constants of this data set, predicted from the regression equations, were in exceptionally good agreement with the observed values. The mean estimation error (the error of the estimated value relative to the measured value) was only 0·55% for FC, 0·12% for WP and 0·67% for AWC.