Digital soil mapping of the Fitzroy, Darwin and Mitchell catchments. A technical report to the Australian Government from the CSIRO Northern Australia Water Resource Assessment, part of the National Water Infrastructure Development Fund: water resource assessments

Publication Date

8-7-2018

Publisher

CSIRO

ISBN

978-1-4863-1056-2 (paperback); ISBN 978-1-4863-1057-9 (PDF)

Abstract

The Northern Australia Water Resource Assessment (NAWRA) seeks to support decision making for sustainable regional development, by clarifying the scale and nature of the opportunities for agriculture and other users of water resources in three study areas in northern Australia: the Fitzroy in WA; the Wildman, Adelaide, Mary and Finniss in the NT (the Darwin catchments); and the Mitchell in Qld. Together these represent 197,000 km2, predominantly used for extensive livestock grazing. A fundamental input to the assessment of water resource development, principally for agricultural purposes, is an understanding of the soil and landscape resources available. Specifically, an understanding of the suitability of soils for a wide range of crops, planting seasons and irrigation management is vital. The NAWRA Land Suitability Activity ultimately produced a set of maps and data for 126 crop x season x irrigation type combinations for all three areas at a spatial resolution of 90m. It also produced land suitability maps and data for aquaculture. This is reported in the companion report Thomas et al (2018b). This report details the Digital Soil Mapping (DSM) conducted by the NAWRA Land Suitability Activity and used as input for the land suitability framework. The objective of the work described in this report was to produce digital soil attribute and Soil Generic Group (SGG) maps using a DSM approach from which land suitability maps and data could be derived. Three major tasks were completed. First, new soils data were collected using a statistically robust field sampling strategy. Second, digital soil attribute and Soil Generic Group maps for the Assessment areas were produced. Third, the reliability of the maps produced was evaluated following field validation and model testing. A novel approach was taken for the determination of spatially explicit, quantitative, reliability of the final maps. While not directly applicable to the land suitability framework, a set of common SGGs was derived for the three Assessment areas. These aligned with the Australian Soil Classification and were intended to aid communication of the soil groups found in the catchments as part of the broader NAWRA reporting. Data from nearly 60,000 existing sites in the three jurisdictions, north of latitude 20º S, were combined with data collected from a total of 736 new sites as part of this study. Environmental covariates chosen to represent soil formation processes were used to determine a stratified random survey design for the collection of new data using CLHS and to predict 18 soil attributes. Soil and landscape variables/factors were determined in the field, through chemical and physical laboratory analyses (386 samples) and through Mid-Infrared Spectroscopy (2,500 samples). Soil attributes and SGGs were modelled using a Random Forest approach. Typically, the attributes modelled with the highest accuracy, as determined by validation trip field data, were rockiness, microrelief and surface salinity. The work presented here represents substantial improvement on the existing soil attribute, SGG and land suitability information for the three Assessment areas, particularly in the Fitzroy and the Mitchell catchments.

Number of Pages

120

Keywords

Northern Australia Water Resource Assessment, NAWRA

Disciplines

Natural Resources Management and Policy | Water Resource Management

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