Effects of Soil Pore Size Distribution on Integral Energy of Different Soil Water Ranges

Soil pore size distribution (SPSD) is one of the most important soil physical quality indices which reflect soil inherent characteristics and its management system. The soil water integral energy (EI) is an index that represents the amount of energy needed to uptake a mass unit of soil water by plants. In this research, we studied the effects of SPSD curves location and shape parameters on EI index of different soil water ranges in medium to coarse-textured soilsof Torogh Agricultural and Natural Resources Research and Education Station in Khorasan-Razavi province. Thirty points with different soil textures and organic carbon contents were selected. After conducting required laboratory and field measurements using standard methods, the soil moisture release curve (SMRC) parameters, the SPSD curve parameters, plant available water (PAW) and least limiting water range (LLWR) which were measured in matric heads of 100 and 330 cm for the field capacity, integral water capacity (IWC) and EI of the mentioned soil water ranges were calculated and the relationships between the SPSD curve location and shape parameters and EI values (for PAW100, PAW330, LLWR100, LLWR330 and IWC) were statistically analyzed. The results showed that, in medium to coarse-textured soils, increasing the equivalent pore diameter and reducing the diversity of soil pore sizes along with the tendency of the SPSD curves to be more peaked in the center and more tailed at the two ends compared with lognormal distribution could lead to lower EI and easier uptake of water by plants in different soil water ranges.