1. Adu S V (1957) Report on the detailed soil survey of the Central Agricultural Station, Nyankpala, Ghana Department of Soil and Landuse Survey, Kulnasi
2. Abekoe M K (1989) The role of concretions in phosphorus availability in a typical concretionary soil of northern Ghana. Unpublished M.Phil. Thesis, University of Ghana
3. Acquaye D K, Owusu-Bennoah E, Tiessen H & Abekoe M K (1992) Recent studies on phosphorus in concretionary soils of northern Ghana.In: Tiessen H and Frossard E (eds.) Phosphorus Cycles in Terrestrial and Aquatic Ecosystems. Proceedings: Saskatchewan Institute of Pedology, Saskatoon: 149?156
4. Akinola A, Agboola A A & Ayodele O J (1983) An attempt to evaluate plant phosphorus in Western Nigeria savannah soils under traditional fallow systems. 3rd Intern. Congress on Phosphorus Compounds, Brussels: 216?286
5. Bowman R A & Cole C V (1978) Transformations of organic phosphorus substrates in soils as evaluated by NaHCO3 extraction. Soil Sci. 125: 49?54