Phosphorus management in rice: A review

Phosphorus is available in low to medium quantity (11 to 22 kg P ha⁻¹) in Indian soils. However, phosphorus is less commonly defichint for rice than upland crops because of its increased concentration in soil solution under flooded condition. Phosphorus exists mainly as Fe-P in rice soils. Submergence increases P availability through reduction of Fe-P, dissolution of occuluded-P, hydrolysis of Fe-P and AI-P, increased mineralisation of organic P, solubilisation of Ca-P (in calcareous soil) and diffusion of P. In single super phosphate (SSP) and diammonium phosphate (DAP) treated soils, the applied P converted mainly to AI-P and Fe-P and while in Mussorrie rock phosphate (MRP) treated soils, applied P remained mainly as Ca-P. Rice plants seemed to utilize P released from Ca-P in black, red, laterite and alluvial soils and in low level laterite as Fe-P. The response of rice to applied P was observed upto 60 and 90 kg P₂O₅ ha⁻¹, but the higher rates showed no beneficial effect. P availability to rice did not differ significantly among different kinds of fertilisers, except on very acidic or very alkaline soils. The use of an alternative source of P like MRP has also been effective in certain situations but not in all. Application of MRP in combination with SSP in 50:50 ratio along with green manure found to be economical rather than application of SSP alone. Efficiency of phosphatic fertilisers was more when applied along with organic manures and phosphobacteria. Split application of phosphorus (basal and top dressing at tillering) was beneficial for Rabi (winter) rice. Foliar spray of DAP 2% at boot leaf, 50% flowering and milky stage increased the rice grain yield during Kharif (rainy) season. It is necessary to apply higher doses of P fertilisers during cooler months of the Rabi season. Nursery manuring with DAP @2 kg per cent (40 m⁻²) of nursery was good especially when the age of the seedlings was limited to 25 days. Residual effect was more when P was applied through MRP than SSP. The magnitude of residual effect depends on the rate and kind of fertilizer used, the cropping and management system followed and to a greater extend on the type of soil.