Minjingu phosphate rock availability in low-pH highly weathered soil as affected by added salts

Abstract

Concentrations and identity of ions in the soil solution may affect soil phosphorus (P) reactions and P availability. In this study, the magnitude of these reactions was evaluated following the application of Minjingu phosphate rock (MPR) combined with chloride and carbonate salts of Na and Ca within an incubation experiment. Twenty-one days later NaOH-P and HCl-P were determined. This investigation was undertaken with the aim of identifying the role of Ca-ion activity in the liquid phase on the solubilization of MPR and formation of insoluble Ca-P phases.The increase in pH was higher with Na 2 CO 3 than with CaCO 3 , while both CaCl 2 and NaCl resulted in slight decreases in pH. The dissolution of MPR was higher overall when MPR was applied singularly than for the combined application of the phosphate rock with salts of calcium or sodium after 60 days of incubation. Dissolution of MPR decreased as levels of CaCO 3 or CaCl 2 increased but the decrease was more pronounced in CaCO 3 -treated than in CaCl 2 -treated soils.Ca-ion activity in the liquid phase is the main factor responsible for the insolubilization of MPR and the formation of insoluble Ca-P phases (HCl P). The formation of Ca-P solid phases increased with the concentration of Ca-ions, and was governed by the pH and nature of the accompanying anion. For soils with low levels of exchangeable cations and where liming is a recommended intervention measure, Ca from lime will form insoluble P phases and reduce the dissolution of PR and P availability to plants.

Solubilization of Bayóvar Natural Phosphate Rock under the Drain Effect of Calcium and Phosphorus at Two Levels of Acidity

“…In addition, these authors observed a higher increase of P concentration in the soil solution when using a mixed resin (cationic and anionic), compared to the anionic resin, indicating the high effectiveness of Ca-sink in the equilibrium displacement. Similarly, [13] observed an increase of 39% to 65% of P in solution when using mixed resin instead of anionic. Finally, one can think about P-sink behavior leading to the development of non-labile forms [10], thus disfavoring the plant, such as soil-sink promoted by Fe and Al oxyhydroxides.…”

“…Thus, a less significant NP solubilization should occur in tropical dystrophic soils, with a low effective CEC (condition for lower Ca-drain effectiveness), than in those less weathered ones, with a high effective S. V. Novais et al Open Journal of Soil Science CEC, a condition for greater Ca-sink condition [13]. [5] observed higher P solubilization (solution-P) when the soil pH, initially alkaline, was reduced to 6.5 and then to 5.5.…”