Characterization and dissolution properties of phytolith occluded phosphorus in rice straw

- Phosphorus (P) can be trapped inside silicaceous phytoliths.
- In kinetic experiments we found a correlation between soluble silicon (Si) and P.
- It suggests that P release might be controlled by the dissolution of phytolith.
- Treatment temperature affects phytolith dissolution by changing removal rate of occluded carbon and modifying phytolith surface.
- Pretreatment of the rice straw at 500-700 °C is optimal to provide available P and Si.

Silicon (Si) is assimilated from soil by rice and is deposited in shoots in inter- and intracellularly, resulting in the formation of silicaceous structures, namely phytoliths. During the precipitation of Si, elements present in xylem/phloem sap, including phosphorus (P), can also be occluded in the phytolith. We examined the release of Si and P from the rice straw derived phytolith to elaborate the desilification mechanism, and the potential effects of phytolith as a nutrient ammendment. Data from batch heating experiments revealed that P trapped in the phytolith structure could be released accompanying with the dissolution of the phytolith. The highest values of soluble Si and P were found in the range of 500-700 °C. The chemical composition, X-ray diffraction, infrared spectra and specific surface area (SSA) data suggested that the presence of occluded organic carbon at <500 °C and crystallization of silica at >700 °C were the main reasons for lower dissolution rates of phytolith and decreasing P release. With respect to practices of burning rice straw, it can be recommended that treatment temperature needs to be taken into account to maximize P release for crops.

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