Residual phosphorus and management strategy for grain sorghum on a vertisol

Fertilizer phosphorus (P) use on Vertisols of the semi-arid zone in India i s becoming more common, so it is important that for developing P management strategies the residual value of P is allowed. Little information is avail able on this aspect for crops such as sorghum under rainfed cropping. A fie ld experiment was conducted for three years to study the response of sorghu m to fertilizer P (0, 10, 20, and 40 kg P ha(-1)) in the absence and presen ce 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 rai nfall received during the cropping season (June-September), P applied in th e previous season had strong residual effects. Sorghum yield and P uptake i n treatments in which P was applied at 20 or 40 kg P ha(-1) once in two yea rs was at par with or higher than in treatments in which 10 kg or 20 kg P h a(-1) was added every year. Ninety percent relative grain yield was achieve d at about 20 kg ha(-1) of fresh P and the results presented show that appl ication of 40 kg P ha(-1) once in two years can satisfactorily meet the P r equirement of sorghum on the Vertisol.