Pindan is an indigenous word to described red soils of the Kimberley region of Western Australia. These soils are classified as Arenosols, Tenosols or Kandosols under the Australian Soil Classification (ASC). Pindan typically has a loamy sand or clayey sand topsoil grading to sandy loam or sandy clay loam. Soil hardsetting and subsoil compaction are common soil constraints which costs the national agricultural industry in excess of $850 million / annum. A soil assessment was conducted in January 2025 to investigate poor performance of fodder crops growing on DPIRD’s research site at Skuthorpe, Broome. The site has been under annual and perennial crop rotation since 2020. Previously, it was used for annual horticulture and initially established as a mango orchard. Despite adequate soil moisture and nutrients, annual crop trials (particularly forage sorghum) have been repeatedly compromised by uneven, patchy and poor growth in 2023 and 2024.
To investigate the cause of underperformance, six soil pits were dug; three on forage sorghum, two on sweet sorghum, one on four-year-old perennial Rhodes grass, and one in ‘virgin soil’ under native vegetation. The soil profiles were characterised including soil physical and chemical analysis.
The findings from this investigation, paired with previous testing for biological constraints, found that a combination of biotic and abiotic factors could be causing poor crop performance. The soil pits revealed that soil compaction at around 20-30cm is likely contributing to poor growth, by constraining root growth to the top 20cm of soil. This was confirmed by very high bulk densities at 20-30cm (over 1.8g/cm3), as well as further down the soil profile. The virgin soil under native vegetation, by comparison, was measurably less compacted. Prior testing in 2024 found very high numbers of stubby-root nematodes and the presence of Pythium root rot in the areas growing forage sorghum.