Effect of Phosphocompost on Rice–Wheat System in a Non–calcareous Typic Haplustept

Utilization of rock phosphate through phosphocompost in rice-wheat system was investigated in a field experiment. Application of phosphorus (P) in the form of phosphocompost and inorganic fertilizers at various doses was repeated for five rice-wheat cycles on a coarse loam noncalcarous Typic Haplustept. Higher grain yield (7.41 t ha⁻¹) of rice was obtained in the treatment receiving half of the recommended level of inorganic P in combination with 2 tonnes (t) of phosphocompost ha⁻¹ (N120P13V2). Maximum wheat grain yield of 5.41 t ha⁻¹ was obtained in treatment receiving recommended dose of fertilizers along with 2 t phosphocompost ha⁻¹ (N₁₂₀P₂₆V₂). The relative yield of rice and wheat was 110 and 104%, respectively in the treatment receiving 2 t ha⁻¹ of phosphocompost to each rice and wheat along with inorganic fertilizers (N₁₂₀P₂₆V₂). The addition of 2 tonnes of phosphocompost each to rice and wheat saved 13 kg P₂O₅ ha⁻¹ in wheat and 60 kg N ha⁻¹ in rice. Each cycle of rice-wheat removed 20.2 kg and 42 kg P ha⁻¹ (average of five crop cycles) in control and N₁₂₀P₂₆V₂ treatments, respectively. Each tonne of rice and wheat grain removed 3.19 to 3.25 and 3.36 to 3.50 kg P, respectively. Phosphorus uptake, recovery efficiency, physiological efficiency, agronomic efficiency and recovery of P from compost were higher in rice than in wheat. The Olsen-P and other fractions of P in the soil increased over control in treatments where phosphocompost was added. Olsen-P determined after five cycles correlated positively with total P addition (r = 0.867^***) and different fractions i.e. saloid-P (r= 0.970^***), Fe-P (r = 0.937^***), Al-P (r = 0.964^***) and Ca-P (r = 0.702^*). Activity of the alkaline phosphatase enzyme increased with phosphocompost incorporation.