Phosphorus fertilizer recommendations for fodder based cereal crops

A field study was carried out to explore the phosphorus adsorption capacity of Rasulpur soil series of Pakistan for determination of P fertilizer doses, internal and external P requirements of the wheat, sorghum fodder and rice crops. Sorption isotherm was constructed in the laboratory and sorption data was fitted into modified Freundlich model and theoretical doses were computed for field application to develop soil solution P levels of 0.01, 0.02, 0.03, 0.04, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.40 and 0.50 mg L^-1 along with a control of native P soil solution. The studies were conducted in permanent layout in randomized complete block design (RCBD) with three replications. Phosphorus was also applied @ 13.65 and 19.65 mg P kg^-1 to subsequent sorghum fodder and rice crops, respectively. All the data were analysed statistically by DMR test and simple regression and correlations were used for computing internal and external P requirements. Maximum wheat grain yield recorded was 3.30 t ha^-1; sorghum fresh fodder yield 38.33 t ha^-1 and rice paddy yield 4.14 t ha^-1. Internal P requirement for wheat determined was 0.236 % at booting stage and 0.343% at harvest, for sorghum fodder, 0.175 % and for rice, 0.179% at booting stage and 0.234 % at harvest. External Olsen P requirement for wheat was 9.91, for sorghum fodder 15.33 and for rice, 10.24 mg kg^-1 Olsen P, respectively.