Cereal root growth in a sandy soil with a hardsetting subsurface horizon was restricted only under dry conditions

Background and aims High soil strength that develops in sandy soils through compaction and hardsetting processes can severely restrict root growth, reducing access to limited resources. 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. Methods To investigate root growth in hardsetting soil under controlled moisture conditions, soil columns were constructed with a subsurface compacted soil layer that hardset upon drying. A ripping treatment was applied to this soil in half of the pots, and wheat ( Triticum aestivum cv. Scepter) was grown in these soil columns under three contrasting watering regimes for 42 days. Soil strength was measured with a lab-based penetrometer prior to dismantling the soil columns to assess root distribution. Results The compacted soil layer hardset at a water content close to wilting point. Only where dry conditions were maintained did the compacted layer provide a physical barrier to root growth accessing deeper soil water. In these soils, ripping resulted in a significant increase in deep root growth and a 39% increase in shoot biomass. Temporal hardsetting, induced by a wet-dry watering cycle did not significantly alter the distribution of roots. Conclusions Hardsetting restricts root access to deeper water only under prolonged dry conditions, indicating that its field impact is strongly moderated by moisture dynamics. This interaction likely explains variable crop responses to deep ripping in sandy, hardsetting soils.