ABSTRACT
Available water capacity (AWC) is defined as the amount of water (cm3 water/100 cm3 soil) retained in the soil between “field capacity” (FC) and the “permanent wilting point” (PWP). FC and PWP are defined as the volumetric fraction of water in the soil at soil water potentials of 10 to 33 kPa and 1500 kPa, respectively. One of the paradigms of soil science is that AWC is positively related to soil organic matter (SOM) because SOM raises FC more than PWP. SOM enhances soil water retention because of its hydrophilic nature and its positive influence on soil structure. It improves soil structure by enhancing aggregate formation, thereby increasing porosity in the range of pore sizes that retain plant-available water, and enhancing infiltration and water retention throughout the rooting zone. Understanding the sensitivity of AWC to SOM is important for assessments of how environmental changes that influence SOM content could affect AWC and sustainability of agricultural productivity.
