Phosphate fixation capacity of Thai acid soils using 32P isotope techniques

Five acid soil samples from benchmark sites in Thailand were collected: Rangsit soil, two samples (Sulfic Tropaquepts or acid sulfate soils), Pakchong soil (Oxic Paleustults) Warin soil (Oxic Paleustults), Mae Taeng soil (Typic Paleustults). The soil P status was characterized in the laboratory by the 32P isotope exchange technique using treatments with and without P addition. In another experiment, the P-fixing capacity of the same soils was examined. They were incubated for 30 days with two Thai phosphate rocks Lamphun PR and RP and Ratchaburi PR, and TSP was used as a standard fertilizer. All of them were added at a rate of 50 mg P kg-1 . The soils can be ranked according to their P- fixing capacity as follows: Rangsit series (acid sulfate soil) > Mae Tang series (Typic Paleustult) > Pakchong series (Oxic Paleustult) > Warin series (Oxic Paleustult). The P availability from TSP decreased after 30 days incubation with the soils. PR from Ratchaburi was more effective than Lamphun PR. (author)