Comparative Solubility Study of Four Phosphatic Fertilizers in Different Solvents and the Effect of Soil

P K Ghosal,T Chakraborty

doi:10.5923/j.re.20120204.07

P K Ghosal, T Chakraborty

Open Access

https://doi.org/10.5923/j.re.20120204.07

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Abstract

Phosphate rocks (PRs) are suitable for direct application as a possible alternative to more expensive soluble phosphate fertilizers in agricultural fields. But the ability of the PRs to release phosphates in the plant available forms depends on the particle size and chemical and mineralogical characteristics of the PRs as well as the properties of the soil in which they are applied. So an experiment was conducted with four sources of phosphatic fertilizers namely Triple super phosphate (TSP â 21.75%P)), Partially acidulated phosphate rock (PAPR â 12.97%P)), Morocco rock phosphate (MORP â 14.87%P)) and Mussoorie rock phosphate (MRP â 8.12%P) whose solubility were tested in six different extractants namely 2% Citric acid, 0.002N Hydrochloric acid, N-Ammonium citrate, Bray-2P extractant, Olsensâs extractant and Morganâs reagent under seven periods of incubation (1, 2, 3, 7, 10, 15 and 30 days), with and without soil. The results revealed that release of P were increased on addition of soil irrespective of fertilizers or extractants used. TSP released maximum P (3.05% - 3.27% with soil, 2.11% - 2.22% without soil) by the 7th day of incubation. The partially acidulated source was found to release P, higher than rock phosphates but lower than TSP, for the initial periods of incubation (1-3 days) (1.31%-1.34% with soil, 0.46% without soil) with an increase in the later periods (7th day onward) (1.27%-1.92% with soil, 0.55%-0.66% without soil). The PRs released maximum P after the 7th day of incubation. Among the different solvents, maximum release of phosphorus was observed by 2% citric acid followed by Bray 2P and Olsenâs extractants.

Highlights

Phosphate rocks (PRs) are suitable for direct application to agricultural fields under certain conditions[1] due to their fairly open, loosely consolidated aggregates of micro -crystals with relatively large surface areas
The data on P- solubility revealed that among P sources, the water soluble and partially soluble sources released almost double the amount of P, with soil than that without soil, for all the extractants (Figures 1,2). This can be explained due to the fact that in the treatments with soil, the readily available P, reacts with the Fe and Al ions in the acid soil thereby forming iron and aluminium phosphate complex as intermediate products which are extracted by the extractants along with the fertilizers
The solubility of P may influence PR dissolution products since the P released from PRs is effectively removed from solution by iron and aluminium oxides, creating a gradient for further dissolution of the PR[13]

Summary

Introduction

Phosphate rocks (PRs) are suitable for direct application to agricultural fields under certain conditions[1] due to their fairly open, loosely consolidated aggregates of micro -crystals with relatively large surface areas. Direct application of phosphate rock to soil as a possible alternative to the more expensive soluble phosphate fertilizers in tropical cropping system has received considerable attention in recent years[2]. The solubility of PR reflects the chemical and mineralogical characteristics of the specific P minerals. Occurring PRs differs widely in their mineralogy and their chemical reactivity or solubility is a measure of the PR’s ability to release phosphorus (P) for plant uptake. Gholizadeh et al[4] reported that to avoid time, trouble and cost of doing field trials for determining the reactivity of PRs, solubility of these in citric acid could be a criterion for predicting their reactivity

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