Sandy soils are highly significant to agricultural production in arid and semi-arid regions of southern Australia. High soil strength in a subsurface horizon that develops in these soils through processes of compaction, hardsetting or cementation often severely restricts root growth. Shallow root systems are particularly problematic in these soils insofar as access to already low resources is limited. Hardsetting, a process where horizons become hard and structureless upon drying, may account for some of the inconsistent crop responses observed following deep ripping. However, it is unclear how variation in soil moisture within and between seasons impacts the role of hardsetting in these soils, and the subsequent restrictions to rooting depth and ultimately crop production.
In order to investigate root growth in a hardsetting soil under controlled moisture conditions we constructed columns with a subsurface compacted soil layer that set hard upon drying. Wheat was grown in these columns under variable moisture conditions for 42 days. Root growth was measured non-destructively by x-ray computed tomography in addition to physical properties and Winrhizo scanning analysis. Temporal hardsetting induced by a wet-dry watering cycle did not significantly alter the distribution of roots. Only where dry conditions were maintained did the hardsetting layer provide a physical barrier to roots accessing deeper water, and result in significant growth reductions above and below ground. In-situ root imaging results from a 2025 field trial will be presented to show how this constraint affects crop growth across multiple timepoints.