Effect of Slow-Release Phosphorus Components in Calcined and Acidulated Phosphate Rock Significantly Correlated with Ground-Water Levels in Lowland Rice Cultivation in Centre West Burkina Faso

Low phosphorus (P) soils in sub-Saharan Africa (SSA) is a major constraint for rice production. This study employed two methods, calcination and partial acidulation, to determine low-grade phosphate of rocks and evaluate the fertilization effects of calcinated and partially acidulated phosphate rocks (CPR and PAPR, respectively). A field experiment was conducted involving four farmers' fields with different ground-water levels (GWLs) during 2019 and 2020 in the Centre West region of Burkina Faso. CPR, PAPR, and single superphosphate (SSP) were applied at the rates of 0, 7.6, 15.3, and 30.5 kg P ha(-1), with the SSP mainly consisting of the water-soluble P fraction (WP), PAPR of the WP, the alkaline ammonium citrate-soluble P fraction (SP), CPR of the SP, and a 2% citric acid-soluble P fraction. The average grain yield (mean & PLUSMN; standard deviation Mg ha(-1)) in P application at 0, 7.6, 15.3, and 30.5 kg P ha(-1) was 1.64 & PLUSMN; 0.59, 2.87 & PLUSMN; 0.94, 3.33 & PLUSMN; 1.06, and 3.95 & PLUSMN; 1.18, respectively, which confirms the significant increase expected by P fertilization. On the contrary, significant positive relationships between GWL and grain yield were found in CPR and PAPR treatments at a low P application rate, but not in SSP treatments. These results suggest a positive effect of slow-release P in fields with high GWL. Therefore, GWL should be considered when selecting P fertilizer types to maximize the fertilization effect. Both CPR and PAPR can replace conventional high-cost P fertilizer. These findings contribute significantly to the efficient use of local P resources and addressing food shortages in SSA.