Sandy-surfaced soils dominate Western Australian (WA) landscapes, including the most productive agricultural areas. Their properties, such as non-wetting, low fertility and rapid drainage, impact agriculture established after land clearing.
We conservatively define sandy soils as having sand texture (i.e. > 75% sand and < 12% clay) to 30cm or more. For simplicity we refer to three basic sandy soil ‘types’: sandy earths (sands grading to loams or clays), sandy duplex (sand over clay) and deep sands (> 80cm). Stony and ironstone gravel soils are typically also sandy, but have not been included in the area estimate.
Sandy soils cover approximately 32% (800,000 sqkm) of the state and 67% (127,000 sqkm) of the wheatbelt, dominated by rainfed grain production. Differences in soil properties between sandy soil types are important. Sandy soils originate from various parent materials under differing climate, ecological and biogeochemical conditions. For example, well-sorted sediments tend to develop into more readily compacted sandy soils, while poorly sorted sediments are more resistant to compaction, reflecting the energy of the deposition environment. Deep colored sands are more productive than deeply weathered pale or bleached sands. Sandy earths tend to be more fertile than deep sands, with more clay at depth holding water. In duplex soils, rain water will perch on the clay subsoil which can boost or constrain productivity, depending on the season and length of waterlogging. Duplex subsoil horizons may be sodic and/or alkaline and/or saline, requiring different management approaches. Ironstone gravels in sands affect rooting conditions, nutrients and plant available water, effects that are often, but not always, negative for production.
Today’s soils reflect past and present conditions, as products of WA’s geologic history and biological evolution. Understanding the distribution of diverse sandy soils improves targeting of research and sustainable agricultural management to boost productivity.