ABSTRACT
In detecting changes in soil quality, it is imperative to provide quantitative information on the effects of agricultural land uses on soil properties. This study analyzed the comparative effects of mixed tree (Gmelina arborea Roxb. and Tectona grandis L. f.) plantation and cassava crop (Manihot esculenta Crantz) cultivation on soil quality in Odighi, Edo State, Nigeria. The objectives of the study were to evaluate the status of the soil properties under each land use; assess the implications of the different agricultural land uses on the physicochemical and biological properties of soil; determine significant variations in the physicochemical and biological properties of soils among the different land uses; ascertain if any significant relationship exist between the physicochemical and biological properties of soils under each land use; and examine the cause-effect relationship between the physicochemical and biological properties of soils under each land use in the study area. Using the transect sampling design, a 100 m × 100 m sample area was established in all the sites. Three 100 m transects were laid on each sample area and uniformly spaced at intervals of 25 m. Along each transect, three sampling points were mapped out at a distance of 50 m apart and soil samples were collected from each sampling point at constant depth levels of 0 to 15 and 15 to 30 cm. Hence, a total of 54 soil samples were collected for the study. Soil physical (sand, silt, clay, texture, BD and TP), chemical (pH, EA, ECEC, OM, TOC, TN, Avail P, Ca, Na, Mg, K, Fe, Cu, Mn and Zn) and biological (THBC and THFC) properties were analyzed following standard operational procedures, and data obtained were subjected to Analysis of Variance (ANOVA), Pearson Product-Moment Correlation and Multiple Regression statistical techniques. The results indicated significant variations (p < 0.05) in sand, silt, BD, TP, pH, K, Fe, THBC and THFC concentrations in the topsoil (0 to 15 cm depth) acros all the land uses. In the subsoil (15 to 30 cm depth), there were significant variations (p < 0.05) in the concentrations of sand, silt, clay, BD, TP, pH, Na, K and Mn across all the land uses. Significant positive as well as negative relationships at p < 0.01 and p < 0.05 existed between the physicochemical and biological characteristics of soil while cause and effect relationships existed between the soil properties. The study concluded that the agricultural land uses had both positive and negative impacts on the soil properties in the study area and recommended that farmers should periodically fallow their lands to sequester organic matter, stabilize soil aggregates and improve nutrient cycles for sustainable agricultural production.
