Adsorption and Desorption Behaviour of Phosphorus as Influenced by Integrated Phosphorus Management Modules in Pigeonpea-Wheat System

Sustainable phosphorus (P)-management is highly pertinent in the present day agriculture as global Preserve is highly limited. Adsorption-desorption studies help elucidate complex phosphorus chemistry influenced by management practices. The present investigation has been taken up to ascertain the Padsorption-desorption pattern in pigeonpea (PP) (Cajanus cajan (L.) Millsp.)-wheat (W) (Triticum aestivum L.) system under alkaline Fluvisol. Field experiment was conducted for three years (2019-2022) in randomised block design with four replication having six treatments namely: T₁: PP₀-W₀ (subscripts denote the P₂O₅ rate applied to the crop, in kg ha^-1); T₂: PP₆₀- W₆₀; T₃: PP₃₆-W₃₆ + 5 t farmyard manure (FYM) ha^-1 T₄: PP₃₆-W₃₆+ 1 t poultry manure (PM) ha^-1; T₅: PPP₃₆-W₃₆+ 50% wheat residue (WR); T₆: PP₃₆-W₃₆+ 50% WR + phosphate solubilizing bacteria (PSB) at ICAR-IIPR. Experimental findings showed, available P content was highest in PP₃₆-W₃₆ + PM and langmuir adsorption parameters like maximum P adsorption capacity (b) and affinity constant (k) was noted maximum in PP₀-W₀ and the trend of ‘b’ in pigeonpea follows: PP₃₆-W₃₆+ WR > PP₆₀-W₆₀³; PP₃₆-W₃₆+ WR > PP₃₆-W₃₆ + FYM = PP₃₆-W₃₆ +PM. Low maximum P buffering capacity (MPBC) due to reduced P-fixation in plots received PM indirectly refers to the need of lesser P-fertilisers in both the crops. In case of desorption, higher value of ‘a’ in PP₀-W₀ (121.26 and 135 in pigeonpea and wheat respectively) refers to the marginal P-supplying potential as compared to PP₃₆-W₃₆ + PM (67.62 in pigeonpea) and PP₃₆-W₃₆+ FYM (81.54 in pigeonpea). Also, a higher desorption index (DI) in control plots indicates inability of crops to utilise soil P due to high bonding energy. In the end, application of PP₃₆-W₃₆+PM improved P-availability and has higher potential to supply P to crops.