Agronomic Evaluation of Calcined Crandallite from Three Brazilian Phosphate Deposits

Abstract

Samples from the weathering mantle containing crandallite of three Brazilian phosphate deposits, Tapira, Catalão, and Juquiá, were characterized, calcined, and agronomically evaluated. The calcination process increased total phosphorus (P) and neutral ammonium citrate soluble (NAC) P contents of all samples. The NAC solubility of original Tapira, Catalão, and Juquiá was about 5% of total P, whereas for calcined samples it was 54, 16, and 53%, respectively. In a greenhouse study, rates of P were applied at 0, 10, 20, 40, 80, and 120 mg P kg⁻¹ from the calcined materials and MCP (monocalcium phosphate) to an Ultisol cropped with upland and flooded rice for 65 days. The results showed that the calcined P samples increased dry‐matter yield and P uptake with increasing rates of P applied for both crops. Tapira and Juquiá were more effective for flooded than for upland rice. The calculated values of relative agronomic effectiveness of Tapira, Catalão, and Juquiá with respect to MCP were 57, 48, and 53% in dry‐matter yield for upland rice and 64, 50, and 69% for flooded rice, respectively.

Keywords:

• Calcination
• crandallite
• fertilizer
• flooded rice
• phosphorus
• upland rice

Acknowledgments

The first author expresses his gratitude to FAPESP for the scholarship that made this work possible and to Socal S/A Mineração, Copebrás Ltda, and Bunge Fertilizantes for providing the samples. He also thanks Viviane C. Ferrari for her help and comments.