Hardsetting in sandy soils: a review

Hardsetting soils dry with high strength, but soften again upon re-wetting. Affected soil layers can form a transient constraint to root growth, developing and diminishing with fluctuations in soil water. Several studies have explored physical and chemical mechanisms for hardsetting, including the role of certain soil particle arrangements and the presence of cementing agents between sand grains. However, the process is not fully understood and is likely to vary between soils. Traditionally, hardsetting has been aligned with Red-brown earths within the context of Australian agricultural soils; however, this review explores its increasing recognition as a constraint in sandy soils. High strength that restricts root elongation is a common constraint in sandy soils, but the contribution of hardsetting to this problem is largely unknown. Measuring and identifying hardsetting has proven challenging due to the lack of objective standards in quantifying it as a soil property. In-field measurements such as the use of cone penetrometers can provide an indicator of high strength, but only at the present moisture level. Measurements taken from intact or reassembled soils can provide greater value when used to determine how the strength of the soil changes across a range of moisture levels. The management of high-strength agricultural soils that have hardsetting properties may require different approaches to current deep tillage practices, to prevent the natural reconsolidation of hard layers.