1. Bray RM, Kutz LT (1945) Determination of total, organic and available forms of phosphorus in soils. Soil Sci 59:39–45
2. Celi L, Lamacchia S, Barbeis E (2000) Interaction of inositol phosphate with calcite. Nutr Cycl Agroecosys 57:271–277
3. Chien SH, Black CA (1976) Free energy of formation of carbonate apatites in some phosphate rocks. Soil Sci Soc Am J 40:234–239
4. Elhaji E (2003) Researh on Gafsa (Tunisia) phosphate rock and its potential for direct application. In: Rajan SSS, Chien SH (eds) Direct application of phosphate rock and related appropriate technology: latest developments and practical experiences. Proc Int Meeting, Kuala Lumpur, 16–20 July 2001. Musle Shoals, USA, IFDC, pp 200–213
5. Gikonyo EW (2006) Dynamics of current and residual phosphorus in acid tropical soils. PhD Thesis. University Putra Malaysia, Serdang, Selangor, Malaysia