Depth-specific soil phosphorus dynamics and grain phosphorus recovery in barley–legume cropping systems under contrasting irrigation

Abstract Background and aims Improving phosphorus (P) acquisition under water-limited conditions is critical for sustaining productivity and nutrient acquisition in semi-arid agroecosystems. This study evaluated the effects of deficit irrigation and barley–legume diversification on soil P dynamics, grain P accumulation, and grain phosphorus recovery (GPR) in a semi-arid calcareous soil. Methods A four-year field experiment was conducted in southern Idaho, USA, using two irrigation regimes (100ET and 50ET) and seven barley-based monocropping, intercropping, and rotational systems involving barley ( Hordeum vulgare L.), pea ( Pisum sativum L.), lentil ( Lens culinaris Medik.), and chickpea ( Cicer arietinum L.). Soil available P (Olsen-P) was measured to a depth of 90 cm, and depth-wise depletion was quantified using slope analysis within the 0–60 cm soil profile. Grain total P and GPR were also determined. Results Soil Olsen-P declined significantly with depth and over time, indicating cumulative biological extraction of native soil P in the absence of P fertilization. Depth-wise depletion analysis revealed steeper phosphorus depletion gradients under deficit irrigation, particularly in barley–legume intercropping systems, indicating greater profile-scale phosphorus extraction. Barley–legume systems enhanced phosphorus acquisition relative to monocropped barley, with the strongest responses observed in lentil-based systems. Deficit irrigation increased grain P accumulation and GPR, while barley–lentil intercropping consistently exhibited the highest GPR. Conclusion Cereal–legume diversification improved phosphorus acquisition and grain phosphorus recovery in semi-arid calcareous soils, particularly in lentil-based systems. Deficit irrigation increased profile-scale phosphorus extraction and GPR, highlighting the potential of cereal–legume diversification to enhance phosphorus acquisition under water-limited conditions.