Solubilization of phosphate rock using Aspergillus niger: Potential for an alternative P-fertilizer

Kim D. Schneider and Peter van Straaten

Abstract
Phosphorus deficiencies are limiting crop production in many agricultural soils worldwide where conventional fertilizers are inaccessible. High costs of conventional phosphate fertilizers prevent smallholder farmers in developing countries from using these types of fertilizers. Chemical fertilizers are also prohibited for use on organic farms.

As an alternative, locally available sources of phosphate rock (PR) are being increasingly recognized for their potential role in soil fertility improvement. In order for applications of PR to be effective, phosphorus must be made plant-available. Recently, there have been advances in the use of organic acid-producing microorganisms to solubilize PR. Four strains of Aspergillus niger, a filamentous fungus known to produce citric acid, were screened for PR solubilization and citric acid production. A. niger ATCC 9142 was selected for further use due to its superior ability to produce citric acid. The solubilization of three different phosphate rocks (2 igneous and 1 sedimentary) was investigated in liquid media. Phosphate solubilized was quantified and compared 1) when PR was added to the A. niger fermentation culture medium at onset, with 2) when it was reacted with the culture supernatant after acid production has occurred.

Preliminary results are promising and show consistent PR solubilization for all rocks.


Source
Organic Agriculture Research Symposium held at the 26th Guelph Organic Conference, University of Guelph, January 2007


Author Locations & Affiliations
Department of Land Resource Science, University of Guelph, Guelph, ON


en français


Posted February 2007