Dissolution of phosphate rocks in Malaysian soils under rubber and their availability to plants
1992
Lau, C. H. | Mahmud bin Abd. Wahab
The dissolution of four phosphate rocks (Christmas Island, North Carolina, Togo and Jordanian) in five soils under rubber was studied. Determination of exchangeable calcium in the soils by BaC 12-triethanolamine at pH 8.1 showed that rapid dissolution of phosphate rocks took place in the initial fourteen days. For the more reactive North Carolina and Jordanian phosphate rocks, higher dissolution was observed. In the least reactive Togo rocks, the dissolution was low even at pH 5.2. In soils with high silt and clay content, the dissolution of phosphate rock is enhanced even though it is made up of coarser materials. Repeated extraction of exchangeable calcium in the soils after the incubation period indicated that about 84% of calcium from the phosphate rock added to the soils was recovered compared with 64% for soluble P by the Bray II procedure. When triple superphosphate was applied, 87%-94% of added calcium was accounted for, in contrast with 25%-31%for Bray II P. Although these results suggest that there is a tendency for the Bray II P to under-estimate the dissolution of phosphate rocks in Malaysian soils, glasshouse experiments with Pueraria javanica as an indicator crop showed that the Bray II P provides a better index for assessing the availability of soil phosphorus.
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