The deep sands of Western Australia are often constrained by water repellence, subsoil acidity, subsoil compaction, and inadequate water and nutrient retention. These limitations hinder rooting depth and root density in subsoils, limiting the use of soil moisture from the deeper subsoil and decreasing crop water use efficiency. This study examined the impact of surface-applied nitrogen (N) rates on both above and below ground performance of a triticale crop (Triticum secale) in a re-engineered deep sand profile where subsoil constraints were overcome through soil loosening and incorporating lime and clay to 80 cm depth. A factorial experiment assessed four levels of N fertiliser applied as top dressing (0, 75, 150, and 225 kg N/ha) across three re-engineering treatments: (i) soil loosening alone, (ii) soil loosening with deep incorporated lime, and (iii) loosening with both deep incorporated lime and clay. A triticale crop was grown in 80 cm tall, reconstructed soil columns representing the above treatment combinations. Intact cores extracted from the field in an area of no tillage were used as the paddock control.

Re-engineering significantly increased rooting depth, with maximum root penetration reaching 60–80 cm, compared to 30 cm in the paddock control. In the paddock control with no nitrogen fertiliser, 87% of roots occurred in the top 10 cm, whereas in the re-engineered treatments, only 43–63% of roots were confined to this layer. Grain, biomass and protein yields improved with increasing N rates (P < 0.001), with the highest values occurring at 225 kg N/ha. Soil loosening alone doubled grain yield, while lime incorporation further enhanced productivity by increasing subsoil pH. However, adding clay provided no additional yield benefits.

These findings highlight the potential of soil re-engineering combined with increased N application to enhance crop productivity in water-limited environments and provide insights for the management of sandy soils.