Residual phosphorus and management strategy for grain sorghum on a vertisol

Abstract

Fertilizer phosphorus (P) use on Vertisols of the semi‐arid zone in India is becoming more common, so it is important that for developing P management strategies the residual value of P is allowed. Little information is available on this aspect for crops such as sorghum under rainfed cropping. A field experiment was conducted for three years to study the response of sorghum to fertilizer P (0, 10, 20, and 40 kg P ha^‐1) in the absence and presence of P residues from the preceding year on a Vertisol (Typic Pellustert), low in extractable P (0.4 mg kg^‐1 soil Olsen‐P). Despite the variable rainfall received during the cropping season (June‐September), P applied in the previous season had strong residual effects. Sorghum yield and P uptake in treatments in which P was applied at 20 or 40 kg P ha^‐1 once in two years was at par with or higher than in treatments in which 10 kg or 20 kg P ha^‐1 was added every year. Ninety percent relative grain yield was achieved at about 20 kg ha^‐1 of fresh P and the results presented show that application of 40 kg P ha^‐1 once in two years can satisfactorily meet the P requirement of sorghum on the Vertisol.