Soil Hydrology Overview

This data reflects both the quality of the soil structure, the amount of water available for growth and the ease by which these soils are able to be irrigated. The data indicates how much water is available for vigorous tree and fruit growth, as well as how much water is available for tree maintenance and survival. This data can also be used to better schedule irrigation, and compare irrigation requirements between soils.

All soil layers have relatively low drainable porosity, and a relatively high proportion of tightly held soil moisture. The topsoil consists of four soil horizons a thin A11, over an A12 and A13 which differ in colour and overly a paler stony A2 horizon. Given the A horizons extend to over 70 cm depth, the subsoil or B horizons have very little influence on soil hydrology or moisture availability. The A12 and A13 horizons are the dominant water holding soil layers, both appear to be moderately compact having bulk densities of 1.41 g/cm³ and 1.48 g/cm³ respectively. Furthermore, the drainable porosity in the A11, A12 and A13 horizons range from 3.7 % to 5.2 % whereas the ideal drainable porosity for a topsoil is around 10%. These measures indicate the upper soil profile is compact and lacking in macroporosity.

The A11, A12 and A13 horizons hold decreasing amounts of plant available water (PAWC) with depth at 33.5 %, 28.3 % and 23.7 % respectively. However, as a proportion of the total soil water, these horizons hold a moderate amount of readily available soil water at 11.3 %, 9.3% and 8.6 % respectively, which sums to 36.5 mm readily available soil moisture to a depth of 40 cm. These horizons do however contain a large amount of tightly held soil moisture which sums to 68.1 mm to 40 cm depth which is available for tree function and survival but not rapid growth. The A2 horizon is extremely compact at 1.80 g/cm³, has minimal drainable porosity at 1.3 % and holds only 4.8% readily available soil moisture.