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Influence of Elemental Sulphur, Oxalic Acid, and Phosphoric Acid as Acidulating Agents on Phosphorous Dissolution from Rock Phosphate

Phosphorous is a limiting mineral element in crop productivity due to its less availability and fixed form in the soil. Due to its agricultural benefit, most farmers seek for alternative method to supply phosphorous in sufficient amount in the farming systems. Although the soluble P is relatively expensive for the peasant farmers, rock phosphate has proved to be quite efficient due to availability among the small scale holders. However, rock phosphate is faced with insolubility challenges hence is not readily available in the soils to promote crop growth.  Therefore, this study sought to establish the influence of various acidulating agents in dissolution of phosphorus in to rock phosphate. The study was carried out in a laboratory environment in Completely Randomized Design consisting of the following treatment: control (bare soil); Mijingu Rock Phosphte (MRP) and soil; MRP, soil and oxalic acid; MRP, soil and phosphoric acid; phosphoric acid and soil; MRP, soil and elemental sulphur and replicated three times. The incubation period was 90 days and the phosphorous dissolution rate was measured at interval of 30 days. The result revealed that the treatments had significant (P≤0.05) influence on the dissolution of the phosphorus from both rock phosphate and soil. Elemental sulphur was superior in increasing the rate of phosphorus dissolution form rock phosphate.  At 30 days, elemental sulphur had elicited release of a total of 37.5 ppm phosphorus while the control had the least, recording 5.37 ppm. A similar trend was observed in both 60 and 90 days. Regression analysis also exhibited positive relationship between the acidulating agents and the phosphorous dissolution rate from the rock phosphate. Therefore, elemental sulphur can be recommended to be used by in agricultural fields to enhanced solubilisation of rock phosphate and enhance supply of phosphorous.