Evaluation of the phosphorus status of some coconut growing soils of Sri Lanka

The phosphorus status of 58 soil samples representing 15 soil series and four soil Orders (Ultisol, Entisol, Alfisol and Oxisol) in the major coconut-growing regions of Sri Lanka was evaluated by determining the available P extracted by the methods of Olsen, Bray and Kurtz No. 1, Bray & Kurtz No. 2 and NH 4 OAc (pH 4.81 and the various P forms. Total P in the soils ranged from 37 to 338 mg/kg with organic P and active P constituting only about 20 and 50% of the total P respectively. In general the sandy soils of the Entisols and Oxisols had lower tota| and organic P but higher active and available P than the rest. The relative abundance of the various inorganic P forms was generally in the decreasing order of inactive P. Fe-P, Al-P and Ca-P. Al-P and Ca-P were positively correlated with percentage sand and negatively correlated with percentage silt and percentage clay whereas total P and organic P had the opposite trend. Available P extracted by the four methods was very low in almost all soils except some of the sandy soils (Entisols) which had marginal to moderate P concents. They are positively correlated with Al-P, Ca-P, percentage sand and negatively correlated with percentages of silt, clay and organic carbon. Phosphorus concentrations (0.074-0.116%) In the 14th leaf of coconut at the soil sites were all lower than the critical leaf-P concentration (0.120%). Leaf -P correlations with Bray & Kurtz No. 2-P and NH 4 OAc-P were significant (P The study revealed that the coconut-growing soils of Sri Lanka were deficient in total as well as the active and available forms of P except perhaps some of the sandy soils of the Entisol. This was confirmed by coconut leaf P analysis. COCOS, (1984) 2 29-43 doi: 10.4038/cocos.v2i0.813