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

Authors:

P Loganathan ,

Coconut Research Institute, Lunuwila, LK
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PMN Dayaratne,

Coconut Research Institute, Lunuwila, LK
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RT Shanmuganathan

Coconut Research Institute, Lunuwila, LK
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Abstract

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 NH4 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 NH4 OAc-P were significant (P < 0.05) and with Al-P and Ca-P were close to significant.

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  

How to Cite: Loganathan, P., Dayaratne, P. & Shanmuganathan, R., (2009). Evaluation of the phosphorus status of some coconut growing soils of Sri Lanka. COCOS. 2, pp.29–43. DOI: http://doi.org/10.4038/cocos.v2i0.813
Published on 16 Jul 2009.
Peer Reviewed

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