Available Water Capacity for Australian Areas of Intensive Agriculture of Layer 1 (A-Horizon – Top-Soil)

Surface of predicted Available Soil Water Holding Capacity of layer 1 (A Horizon a Top-soil) surface for the intensive agricultural areas of Australia. Data modelled from area based observations made by soil agencies both State and CSIRO and presented as 0.01 degree grid cells. Available water capacity (AWC) is a measure of the store of water available for plants to use. AWC is presented here as the estimated total for the horizon, measured in millimetres (mm). The amount of water that is held by the soil varies according to a number of soil properties including, soil texture, organic matter content, bulk density and soil structure development. Available water capacity has been calculated as the difference in volumetric water content at 0.1 bar and 15 bar (matric potentials of -10 kPa and -1.5 mPa) for each layer. These represent respectively the field capacity (maximum water content following free drainage) and the permanent wilting point (lower limit of soil moisture available to plants). The final ASRIS polygon attributed surfaces are a mosaic of all of the data obtained from various state and federal agencies. The surfaces have been constructed with the best available soil survey information available at the time. The surfaces also rely on a number of assumptions. One being that an area weighted mean is a good estimate of the soil attributes for that polygon or map-unit. Another assumption made is that the look-up tables provided by McKenzie et al. (2000), state and territories accurately depict the soil attribute values for each soil type. The digital map data is provided in geographical coordinates based on the World Geodetic System 1984 (WGS84) datum. This raster data set has a grid resolution of 0.001 degrees (approximately equivalent to 1.1 km). The data set is a product of the National Land and Water Resources Audit (NLWRA) as a base dataset.

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