In Situ Acidulation of Rock Phosphate

ABSTRACT

This study was undertaken to study the impact of adding <75 μm elemental sulfur (ES) on P availability from a range of <250 μm ground rock phosphates (RP) namely; Minjingu (Mi) from Tanzania, Khouribga from Morocco (Mo) and Duchess (D) from Australia. Italian ryegrass (Lolium multiflorum, Thumpa tetraploid) grown in a glasshouse was used as the test crop and tops were harvested 5 times over 27 weeks. Co-granulating RP and 10.7% ES yielded 30–70% more ryegrass tops than RP alone, with the greatest effect with Mi. Fertilizer P recovery in the tops from the RP was 5.2% with D and 6.5% and 7.8% from Mi and Mo, respectively. ES addition increased this by 51% from Mo, 98% from D and 194% from Mi. Co-granulation of RP with ES has been shown to be an effective means of releasing plant available P to crops from RP with minimal fertilizer processing.

KEYWORDS:

• Elemental sulfur
• isotopes
• phosphorus
• soil

Acknowledgments

We acknowledge the support of the Australian Government through the Australia Awards Scholarship offered by the Australia Agency for International Development (AusAID) and the University of New England for financially and materially facilitating this study. The support of the Government of Tanzania, through the Prime Minister’s Office, Regional Administration and Local Government Authority (TAMISEMI) and Human Resource Office (Utumishi) for their permission to undertake the study is also acknowledged. The technical assistance provided by Mrs Leanne Lisle for chemical analysis and Mr Michael Faint for glasshouse assistance made the study possible.