Fertility status and management implications of wetland soils for sustainable crop production in Akwa Ibom State, Nigeria

Environment Development and Sustainability 11(2):393-406. DOI: 10.1007/s10668-007-9120-5

ABSTRACT Fertility status of soils of three wetland types in Akwa Ibom State, Nigeria, was investigated. The wetland types are Inland
Valley (IV), Flood Plain (FP) and Mangrove (MG). The soils have silt-clay ratios above 0.15 and 0.25 indicating that they
are of young parent materials with low degree of weathering and possible weatherable minerals for plant nutrition. The pH
of the soils was near neutral (>6.4) when wet but extremely acid (>3.5) when dried indicating that the soils are potential
acid sulphate soils. Organic matter content was high with mean values of 12.59, 6.03 and 3.20% for IV, FP and MG soils, respectively.
Total N (nitrogen) was low except in IV soils where the value was above the 0.30% critical level. The C:N ratios were narrow
with mean of 20.90, 12.17 and 12.12 for IV, FP and MG soils, respectively. The contents of basic cations [Calcium (Ca), Magnesium
(Mg), Potasium (K) and Sodium (Na)] were low while acidic cations [Aluminium (Al) and Hydrogen (H)] were high. The Ca:Mg ratios
were below the optimum range of 3:1 to 4:1 required for most crops. The Mg:K ratios were above 1.2, below which yields of
crops like corn and soybean may be reduced. Effective cation exchange capacity (ECEC) was below the 20cmol/kg. Percent base
saturation was low (<38) indicating that the soils are potentially less fertile. Exchangeable Al and percent Al saturation
were high, above 60% in IV and FP soils. Electrical conductivity was above the critical value of 2dsm−1 while exchangeable sodium percentage was less than 15. Available Phosphorus (P) and low, <10ppm and free Fe2O3/clay ratios were <0.15. Positive correlation existed between silt and ECEC, implying that silt contributed to nutrient status
of the soils. Generally, fertility status of the soil is low and would require maintenance of adequate organic matter, application
of lime and organic and inorganic fertilizers, drainage and irrigation if the land is to be used for intensive/sustainable
crop production.