Comparison of Three Commonly Used Concepts in Explaining Soil Water Availability for Plants (CPAW, EI and Mh0) and Their Feasibility as an Indicator of Soil Management

The complexity of the concept of soil water availability has led to the emergence of a variety of methods to estimate it, which have always been changing, refining, and replacing. Among those, the conventional method of plant available water (CPAW=FC-PWP) due to convenient measurement has received more attention. In theory, however, the methods of Integral Energy (EI) and Kirchhoff Potential (Mh0) have been considered due to the interference of soil properties and plant ability for water uptake. In this  study, the available water was calculated with CPAW, E I and Mh0 concepts in a wide range of soils (72 samples) with various physical properties and results were compared. Also, different upper limits were tested to determine the water availability and the new field capacity moisture coefficient was used as the upper limit of the concept of water availability. Despite the weak correlation between EI and Mh0, the trend of their variations in different soils is somewhat similar, indicating their similarity in the estimation of available water for plants. In contrast, the lack of a clear relationship between EI and Mh0 with CPAW confirmed their lack of correlation in explaining water availability of the plant. The convenience of using CPAW makes it even more preferable to study the variability of soils in terms of hydraulic properties. On the other hand, the use of EI and Mh0 results will be useful for explaining the available water content but still needs to be modified in terms of determining threshold limits.