Archived from the original on 2013-08-28. ↑ Marcellina Ulunma Okehie-Offoha (1996). Ethnic & cultural diversity in Nigeria. Trenton, N.J.: Africa World Press. ↑ Michigan State University Extension Bulletin E-896: N-P-K Fertilizers Archived 2015-12-24 at the Wayback Machine. ↑ Hall, William L; Robarge, Wayne P; Meeting, American Chemical Society (2004).