Mineralogy and pedogenesis in a soil chronosequence on a floodplain, eastern Nigeria

Studies on soils of the floodplain of lower Niger river are scanty although this floodplain forms a very important agricultural resource base in Nigeria. The objective of this study is to provide comprehensive information on the characteristics of the soils with respect to their mineralogy and the effect of seasonal flooding on their properties. Five soil profiles located on a depositional sequence were studied. The soils are deep, poorly drained and fine to medium textured. Mottling and periodic waterlogging are prominent morphological properties and pedogenetic process. The dominant clay mineral is kaolinite, comprising more than 40% of the total clay minerals in the clay fractions. Other clay minerals are the interlayered vermiculites (IV) and smectite. Quartz and feldspars are also prominent in the fine-earth fraction. The prominence of gibbsite and kaolinite is postulated to originate from a direct transformation of feldspars from the up river with younger parent material. The occurrence of lepidocrocite, hematite and ferrihydrite is attributed to the high moisture regimes which favour the formation of lepidocrocite which, under favourable weathering conditions, give rise to hematite and ferrihydrites. The annual cyclic flooding and drying plays a significant role in the weathering, transportation and eventual redistribution processes of the minerals. Results obtained from this study will provide information on agrotechnology transfer. Agro-Science Vol. 6 (2) 2007: pp. 1-15