Prediction of Soil Water Thresholds for Trees in the Semi-Arid Region on the Loess Plateau

Abstract

It is important to obtain the soil water content threshold (θTHR) for agricultural water management. However, the measurement of θTHR is time consuming and needs specialized and expensive equipment. The accuracy of the empirical estimates is often low. Therefore, the development of a simple, rapid, and accurate prediction method for θTHR is the focus of the present study. The value of θTHR is regarded as the soil water content at the capillary break capacity (θCB). A formula based on field capacity (θFC) and soil bulk density (Db) is proposed to calculate θCB, expressed as θCB=θFC−0.21*1−Db/2.65. Six soils from six published studies on the response of tree physiological processes to water deficit were used to calculate θCB using this formula. The calculated θCB values were compared with the measured θTHR. The results showed that the calculated θCB values were nearly equal to the measured θTHR. A highly significant (adj R2 = 0.9826, p < 0.001) linear relationship with a slope of 0.9506 and a y intercept of 0.0072 was found between the calculated θCB and measured θTHR. The formula proposed in this study provides a novel approach for estimating the θTHR of trees in the semi-arid regions on the Loess Plateau.