Forms of phosphorus under long term fertilization to sorghum-wheat sequence on vertisols and their relationship with yield

The present investigation (2000–2001) was carried out during 13 cyde of Long Term Fertilizer Experiment started since 1988. There were 14 treatments replicated 4 times in RBD, comprised of NPK levels with and without FYM. Sulphur and Zinc. The results of the present study revealed that all the fractions of P evaluated (Sal. P, A1-P, Fe-P, Ca-P, R-S-P, Occl-P, IO-P and D-p) showed an appreciable P built up under 150% NPK and 100% NPK + 10 t FYM ha⁻¹. The relative abundance of native P fractions in soil followed the order Ca-P > A1-P > R-S-P > Fe-P > Ocol-P > Saloid P. Results revealed that, there was significant increase in organic carbon, total N and available P to the extent of 76%, 25% and 80% respectively, than at the start of the experiment because of long term manuring and fertilization. Highest yield of grain and fodder/straw of sorghum and wheat were found in a plot receiving 100% NPK + 10 t FYM ha⁻¹ followed by 150% NPK. Available P showed highly significant correlation with total P. Similarly IO-P, O-P, total P, Available P, Sal-P are highly significantly correlated with yield of crops.