Improving barley (Hordeum vulgare L.) yield through deeper root architecture impacted by nitrogen management in a re-engineered Kurosol

Context Subsoil acidity and compaction are major constraints to crop productivity on duplex (Kurosol) soils in southern Australia and globally, restricting root growth, limiting access to water and nutrients, and reducing nitrogen (N) use efficiency. Conventional amelioration practices, such as surface liming and shallow tillage, often fail to remove these interacting constraints at depth, resulting in persistent yield gaps under water-limited conditions. Aims This study investigated how soil re-engineering, particularly deep lime incorporation, interacts with N fertilisation to influence barley (Hordeum vulgare L.) root system architecture, soil properties, water use and crop performance in an acidic Kurosol. Methods A semi-controlled reconstructed soil column experiment was conducted using 80-cm-deep re-engineered soil profiles using a Kurosol in Western Australia. Re-engineering treatments comprised soil loosening with or without lime incorporation to depth, combined with four surface-applied N rates (0–225 kg N ha−1) applied in split applications. Root traits, soil chemical properties, residual soil volumetric water content (VWC), shoot biomass, grain yield and protein yield were measured at crop maturity. Analysis of variance, Pearson correlations and regression analyses were used to quantify relationships between root traits, soil properties and crop performance. Key results Deep lime incorporation substantially increased subsoil pH (0.01 M CaCl2) and reduced extractable aluminium to near-undetectable levels throughout the soil profile. This chemical amelioration enabled a deeper and more uniform vertical distribution of the root system compared with the loosening-only treatment, thereby enhancing the capacity of plants to forage for subsoil water and nutrients. Lime incorporation increased total root surface area by 1.5-fold and volumetric root length density by 1.9-fold relative to soil loosening alone. Grain yield and shoot biomass responded linearly to increasing N rates only in limed soils, whereas responses plateaued at moderate N rates in unlimed soils, demonstrating that N fertiliser efficiency was constrained by subsoil acidity. Root surface area was the strongest predictor of grain yield and biomass (R2 > 0.8), outperforming root length-based metrics. Residual soil VWC at harvest was strongly and negatively correlated with root traits and yield, indicating enhanced subsoil water extraction under terminal moisture stress. Liming also increased subsoil organic carbon and altered residual nutrient distributions, highlighting broader soil quality benefits. Conclusions The combined alleviation of subsoil acidity and compaction fundamentally altered root system architecture, unlocked subsoil resource use and enhanced barley responsiveness to N fertilisation in a Kurosol. Implications These findings demonstrate that effective management of duplex soils requires integrated soil re-engineering and nutrient strategies. While the column approach provided mechanistic insight, field-scale validation is required to assess persistence, rainfall interactions and the economic feasibility of deep liming combined with optimised N management in water-limited farming systems.