Every reference with a DOI in the deposited reference list resolved to a known
work in Crossref or DataCite at the dated check, and none carried a retraction,
withdrawal, or removal notice.
The 35 references without a DOI — listed, not checked
no DOI — not checkedAnderson JM, Ingram JSI. 1993. Tropical soil biology and fertility. A handbook of methods. 2nd ed. Wallington: CAB International; p. 221.
no DOI — not checkedBray RH, Kurtz LT. 1954. Determination of total, organic and available forms of P in soils. Soil Sci. 59:45–59.
no DOI — not checkedChikezie IA, Eswaran H, Asawalam DO, Ano AO. 2010. Characterization of two benchmark soils of contrasting parent materials in Abia state, southeastern Nigeria. Global J Pure Appl Sci. 16:23–29.
no DOI — not checkedDebella-Gilo M Etzelmuller B Klakegg O. 2007. Digital soil mapping using digital terrain analysis and statistical modeling integrated into GIS: examples from Vestfold County of Norway. In: Bjørke JT Tveite H editors. Proceedings of the 11th Scandinavian Research Conference on Geographical Information Science (ScanGIS’2007); 2007 September 5–7; Ås: ScanGIS; p. 237–253.
no DOI — not checkedEneje RC, Ndu A. 2007. Percent clay, aggregate size distribution and stability with depth along a toposequence formed on coastal plain sands. Online J Earth Sci. 1:108–112.
no DOI — not checkedFakolade OR, Obasi RA. 2012. The geochemical assessment of sub surface coastal plain clastic deposits of eastern Dahomey, basin around Lagos Area, South West, Nigeria. J Sci Technol. 1:301–307.
no DOI — not checkedFaniran A, Areola O. 1978. Essentials of soil study: with special reference to tropical areas. London: Heinemann Educational Books Ltd.
no DOI — not checkedFAO. 2006. Guidelines for soil descriptions. 5th ed. Rome: FAO.
no DOI — not checkedHarter RD. 2007. Acid soils of the tropics. Echo Technical notes 48. North Fort Myers (FL): ECHO Community; p. 11.
no DOI — not checkedIBM. 2011. IBM SPSS statistics for Windows, Version 20.0. Armonk (NY): IBM.
no DOI — not checkedIgwe CA 2001. Free oxide distribution in Niger flood plain soils in relation to their total and available phosphorus. In: Proceedings of Soil Science Society of Nigeria; 2001 November 5–9. Calabar: University of Calabar; p. 196–201.
no DOI — not checkedIUSS Working Group WRB. 2007. World reference base for soil resources 2006. First update 2007. World Soil Resources Report No. 103. Rome: FAO.
no DOI — not checkedMchra OP, Jackson ML. 1960. Iron oxides removal from soils and days. Dithionite-citrate systems buffered with sodium bicarbonate. Clay Clay Min. 7:313–327.
no DOI — not checkedMckeague JA, Day JA. 1966. Ammonium oxalate and DCB extraction of Fe and Al. Can J Soil Sci. 46:3–22.
no DOI — not checkedMonkhouse R. 1966. The geology of eastern Nigeria. Nsukka: Academic Forum Publisher; p. 110.
no DOI — not checkedMontecillo LC. 1983. Total clay and organic matter in relation to soil cation exchange capacity. Phillipp J Crop Sci. 8:41–44.
no DOI — not checkedMoore ID Hutchinson MF. 1991. Spatial extension of hydrologic process modeling. In: International Hydrology and Water Resources Symposium 2–4 October 1991. Perth: The Institution of Engineers; p. 803–808.
no DOI — not checkedObi JC, Ogban PI, Utuk II. 2011. Spatial variability of particle sizes of coastal plain sands soils of southeastern Nigeria. Nig J Trop Agri Food, Environ Extension. 10(2):16–28.
no DOI — not checkedObi JC, Ogunkunle AO, Olatunji OO. 2008. Extractable iron and aluminum distribution in Macrotermitinae nigeriensis infested Guinea Savana Alfisol. Agric J. 3:345–348.
no DOI — not checkedOdu CTI, Babalola O, Udo EJ, Ogunkunle AO, Bakare TA, Adeoye GO. 1986. Laboratory manual for agronomic studies in soil, plant and microbiology. Ibadan: University of Ibadan; p. 83.
no DOI — not checkedOfomata GEK. 1981. Actual and potential erosion in Nigeria and measures for control. In: Udo EJ, Sobulo RA, editors. Acid sands of southeastern Nigeria. Special Publication Monograph No. 1. Ibadan: Soil Science Society of Nigeria; p. 151–165.
no DOI — not checkedOgban PI, Ekerette IO. 2001. Physical and chemical properties of the coastal plain sands soils of southeastern Nigeria. Nig J Soil Environ Res. 2:6–14.
no DOI — not checkedOguike PC, Mbagwu JSC. 2009. Variations in some physical properties and organic matter content of soils of coastal plain sand under different land use types. World J Agric Sci. 5:63–69.
no DOI — not checkedOgunkunle AO. 1993. Variation of some soil properties along two toposequences on quartzite schist and banded gneiss in southern Nigeria. Geoderma. 30:397–402.
no DOI — not checkedOjanuga AG, Lekwa G, Akamigbo FOR. 1981. Survey classification and genesis of acid soils. In: Udo EJ, Sobulo RA, editors. Acid sands of southern Nigeria. Special Publication Monograph No. 1. Ibadan: Soil Science Society of Nigeria; p. 1–20.
no DOI — not checkedOlatunji OO, Ogunkunle AO, Tabi FO. 2007. Influence of parent material and topography on some soil properties in southwestern Nigeria. Nig J Soil Environ Res. 7:1–6.
no DOI — not checkedOsodeke VE. 1995. Phosphorus sorption characteristics of soils of the forest zone of southwestern Nigeria. Nig J Agric Tech. 4:6–11.
no DOI — not checkedOsodeke VE, Nwotiti IL, Nuga BO. 2005. Sesquioxides distribution along a toposequence in Umudike area of southeastern Nigeria. EJEAFChe. 4:1117–1124.
no DOI — not checkedPetters SW Usoro EJ Udo EJ Obot UW Okpon SN. 1989. Physical background soils and landuse and ecological problems. Technical Report of the Task Force on Soils and Landuse Survey Akwa Ibom State. Uyo: Govt. Print Office; 630pp.
no DOI — not checkedSAS Institute. 2011. SAS systems for information delivery for Windows. Version 9.2. Cary (NC): SAS® Institute Inc.
no DOI — not checkedSchwertmann U, Herbillon AJ. 1992. Some aspects of fertility associated with mineralogy of highly weathered tropical soils. In: Lal R, Sachez PA, editors. Myths and science of soils of the tropics. SSS Spec. Publ. 29. Madison (WI): SSSA and ASA; p. 49–59.
no DOI — not checkedSivanesan A, Waller JM. 1987. Nigerian soil: productivity and potential. Lagos: Expansion Today Nigeria Ltd; p. 35.
no DOI — not checkedSoil Survey Staff. 2006. Keys to soil taxonomy. United States Department of Agriculture, Natural Resources Conservation Services. 10th ed. Washington (DC): USDA; p. 331.
no DOI — not checkedSparks DL. 1996. Methods of soil analysis. Part 3, Chemical methods. Soil Science Society of America. Book Series No. 5. Madison (WI): SSSA.
no DOI — not checkedTolk JA. 2003. Soils, permanent wilting points. Encyclopedia of water science. New York (NY): Marcel Dekker.
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