Dissolution of phosphate rock in the rhizosphere of upland rice soils

Abstract

The availability of nutrients is high in the rhizosphere of plants. However, the information on level of phosphorus (H₂PO^‐ ₄) and calcium (Ca²⁺) following the dissolution of phosphate rock (PR) material in the rhizosphere is still lacking. The release of phosphorus (H₂PO^‐ ₄) and calcium (Ca²⁺) from 0 and 500 mg P/kg soil of Hamrewein phosphate rock (HPR) and gafsa phosphate rock (GPR) added to Bungor (Typic Paleudult), Sedu (Typic Sulfaquept), and Tin tailing soils packed in seven‐compartment each of 5‐mm thickness rhizobox and sown with upland rice (Buntar variety) was determined by using either 0.5M NaOH‐extractable P (δP) or 0.5M NaHCO₃‐extractable P (δP_b) and 0.5M BaCl₂/TEA‐extractable Ca (δCa). The amounts of δCa and δpH_w increased within the rhizosphere having the highest value in the central compartment. In contrast, δP and δP_b decreased within the rhizosphere having the lowest value in the central compartment. Sedu soil gave the highest value of δP_b (135.4 mg P/kg soil), δP (230.5 mg P/kg soil), and ACa (2283.1 mg Ca/kg soil) whereas, Tin tailing soil gave the lowest value δP_b (2.5 mg P/kg soil), AP (19.8 mg/P kg soil), and δCa (47.9 mg Ca/kg soil). This was attributed to a much lower pH of Sedu soil compared to Tin tailing soil. All parameters measured gave a much higher value in GPR‐ than that of HPR‐treated soils. The dissolution of PR materials was higher in the rhizobox compared to a closed‐incubation system. This indicates that the rhizosphere of upland rice promotes the dissolution of PR materials, and consequently, increases the amounts of H₂PO^‐ ₄ and Ca²⁺ in the rhizosphere.