Status of phosphorus in Thai soils and P evaluation using EDTA-NaF extraction method
2003
Phairat Phimsirikul | Matoh, Toru
Although the available P extracted by Bray II method in tropical soil is low, most of tropical plants can grow well. The objective of this study was to study P status and to evaluate the available P extracted by EDTA-NaF method. Top soil and sub soil of 10 dominant soil series in Thailand were analyzed for some chemical properties and characterization of the forms of phosphorus using EDTA-NaF extraction and successive phosphorus extraction by the modified Sekiya method. The soil total P concentration was 38-1137 mg P2O5/kg. The available Bray I-P was very low to high (1-76 mg P2O5/kg) and it approximated 0.17-12 percent of the total P. Iron and aluminum phosphate were the main fraction of inorganic P in acid soil, whereas Ca phosphates were the main fraction of inorganic P in acid soil, whereas Ca phosphates were in calcareous soils. Organic P content accounted for 33-67 percent and most of them were bound with Fe and Al in acid soils and Ca in calcareous soils. P extracted by EDTA-NaF reagent was obviously larger than that of Bray II reagent. The EDTA-NaF extracted P [high molecular weight organic P (HMWP)+inorganic P (EDTA ext P sub(i)] was 7-46 percent and 1-6 percent of total P in acid soils and clacareous soils respectively. The EDTA ext P sub(i) tended to be larger than HMWP except in Tk soil. The total amount of extracted P correlated well with Al-P sub(i) and Fe-P sub(i) which were the main fraction of inorganic P. It also correlated with HMWP, but HMWP did not correlate with organic P determine by ignition method and Ca-P sub(o), Fe-P sub(o) and Al-P sub(o). The EDTA-NaF method may be suitable for P evaluation in the soils which have high amounts of Fe-P sub(i), Al-P sub(i) and organic P widely distributed in Thailand.
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