Available Soil Phosphorus in Coconut Plantations in Boralu and Pallama Soil Series, under different Fertilizer Regimes, in Gampaha District of Sri Lanka

Coconut plantations in the Gampaha District of Sri Lanka are generally under fertilized or not fertilized at all. The available soil phosphorus in the two major coconut growing soils in the district viz. Boralu and Pallama series, under three fertilizer regimes, organic manures, inorganic fertilizers, or no fertilizer, over the preceding five-year period, was determined and mapped. Some 32,400 ha were covered with 30 sampling locations. Leaf P content was also determined at selected sampling locations. Available P in the Boralu and Pallama soils was at a ‘medium' level of sufficiency, with a mean of 16 mg/kg, even in unfertilized coconut plantations. Leaf-P concentration in all the coconut plantations fertilized annually with inorganics, ranging from 0.135 to 0.196%, were higher than the critical leaf-P concentration (0.120%). These findings show that the available phosphorus in the two major soil series in the Gampaha District, were generally sufficient to support a healthy growth of coconut. Key Words: Available phosphorus, Boralu soil series, Coconut, Fertilizer, Pallama soil series. doi: 10.4038/cocos.v18i0.987 COCOS (2007), 1