ABSTRACT

Geo-physical and chemical properties were determined in tidewater that floods the mangrove forestland in Ogonokom-Abua, Rivers State, to provide an insight into the characteristics and inherent potential of the soils in agriculture. Three soil units (sites) were identified based on their moisture regimes as non-flooded, partially flooded, and completely flooded. Two composite soil samples each from the three sites representing flat beds and ridges were subjected to laboratory analyses. The data on tidewater revealed high turbidity level of 30 NTU as sediments in suspension and large amount of dissolved solids (23,345.00 mg.L'), particularly sulphate (1,044.09 mg.U') and chloride (1,214.50 mg.L 1) salts as well as an electrical conductivity (salinity) level of 33.4 dS .m. The soils themselves were, thus, exceedingly saline (20.0 — 36.5 dS.m 1) and indicated varying degrees of drawbacks in agriculture including extreme acidity, sodium and aluminium toxicity, low plant nutrient contents, nutrient imbalance and sandy textures besides recurrent waterlogging in flooded units. A new system of soil quality evaluation was developed in which soil properties were rated on a 5-point scoring scale and integrated into Soil Quality Classes. The soils scored 56.84, 49.47 and 43.16% in units (sites) I, II and III, respectively, and generally belonged to Soil Quality Class 3. Soil unit (site) I was classified as fairly fertile (50 — 60%) in sub-class 3(i) requiring large management inputs in agriculture, and units (sites) II and III as marginally fertile (40 — 50%) in sub-class 3(u) with imperatives for enormous soil amendment being only a step away from unproductive soils. Four varieties of the sugarcane crop (NCS-oOl, NCS-002, NCS-005 and "Bida local" labeled as Varieties 1, 2, 3 and 4, respectively) were cultivated with different agricultural management practices to test and validate the soil quality classification system. The trial was a 2 x 2 x 4 factorial experiment in split-split-plot format following a Randomized Complete Block Design (RCBD) and replicated three (3) times to represent the soil units (sites). Unfavourable, un-amended (natural) soil conditions impacted severely on the plants as reflected in poor growth indices. Growth was abruptly truncated in the plants in such characters as stem height (length), internode length, number of green leaves, leaf length and leaf sheath length at the sixth or ninth month after planting (MAP) and these decreased sharply down to maturation at the twelfth month indicating reduced tolerance to soil constraints over time. Within the main experimental treatments, soil limitations notwithstanding, soil units (sites), land preparation methods, and sugarcane varieties showed significant differences in growth parameters of the crop, and trends in certain growth indicators were highly and significantly correlated with time by increasing or decreasing with age of the plants. Soil unit (site) I (non-flooded), ridge planting (in flooded soils), and Varieties 2 and 1 (in that order of preference) displayed dominance in several sugarcane growth parameters tested and are, therefore, recommended for agricultural exploit. Conversely, 1-node and 2-nodes in planting materials produced similar results in all growth parameters of the crop investigated, hence, the 1-node planting material is recommended in order to save "seed pieces" and reduce production costs for the cultivation of the aforementioned sugarcane varieties in the mangrove forest ecosystem in the study area.