Abstract
Soil quality variation in the tropical rainforest zone of Akamkpa upon conversion from the natural vegetation to other landuse types (natural forest, reforested lands, cultivated upland soils, swamps, soils around quarry sites, built-up areas and fallow lands) was evaluated with a view to ascertain the changes in physical, chemical and biological characteristics of the soils and determine to what extent these changes affects soil quality degradation rates and vulnerability potential. Surface soil samples were collected from four points in each landuse type at the depth of 0-15cm and mixed to obtain a composite sample for routine laboratory analysis of selected soil quality parameters. The soils were generally sandy loam to clay loam on the surface and lateritic clay at the subsurface. Bulk density varied from 1.12-1.48mgcm3, soil porosity was higher in cultivated soil (78.83%) and lower in the swamps (25.22%) water holding capacity was highest in swamps (72.9%) and lowest in the built-up areas (33.6%). Aggregate stability index was lower in the cultivated soils (0.44) and higher in the natural forest (0.69). pH value varied from 4.2-6.0, organic carbon levels were higher in the natural forest (9.84gkg) and lowest in built-up areas (4.16gkg-1). Total nitrogen varied from 0.42-0.72gkg, the value was lowest in built-up areas and highest in the natural forest soils. C:N ratio varied from 8.63-13.12. these values were lowest in cultivated soils than natural forest and reforested soils. Available P was highest in fallow lands and lowest in built-up areas. Exchangeable bases show variability across landuse types with calclium, potassium, ECEC higher in natural forest soils. Al3+, SAR, Fe, Mn, Cu and S higher were in soils around quarry mines than any other landuse type. Reforested lands, cultivated uplands and fallow lands showed a slight variability in the selected chemical parameters. The biological properties were highly correlated with soil quality status in response to landuse change types. Total microbial biomass was higher in reforested lands and lowest in built-up areas, while active microbial biomas was higher in fallow lands. Higher rates of qCO2:T for the cultivated soils, qCO2:A rates was higher for fallow lands. Resuts revealed that built-up areas and soils around quarry mines has a significantly ower SDR/VP than any other landuse type. Percentage soil quality rating was higher in the fallow land (88.0%), forested lands and reforested lands (83.3%), cultivated uplands (66.0%) swamps (56%), soils around quarry mines (44%) and built-up areas (33%). The findings suggest that the soils under fallow are slightly capable to resist degradation. Management practices such as planting leguminous crops, increased fallow period, organic manuring, planting of fast growing vegetative species and returning crop residues to the soil as a way of building up used carbon stocks.
Highlights
Landuse changes especially cultivation of deforested land may rapidly diminish soil quality, as ecologically sensitive components of the tropical rainforest ecosystem are not able to buffer the effects of agricultural practices and other landuse changes [28]
The sand content was highest in soils around quarry mines and cultivated uplands, the soils around quarry mines areas and swamps recorded the highest silt content while highest clay content was recorded in swamps and fallow lands
The silt-clay ratio of the soils was low (0.42-0.59) indicating the advanced stage of weathering of parent materials from which the soils are developed the lower silt and slightly lower clay in other landuse types is probably due to the factor of toposequence as most of the natural forests and swamps are located at the two ends of land height (Upper slope and lower-slope), preferential removal of silt by accelerated water erosion during high precipitation months [10,32,36,38]
Summary
Landuse changes especially cultivation of deforested land may rapidly diminish soil quality, as ecologically sensitive components of the tropical rainforest ecosystem are not able to buffer the effects of agricultural practices and other landuse changes [28]. Studies carried out by [22,35,40] reported a positive correlation between landuse changes and loss of soil quality especially chemical properties and soil aggregate stability which is considered a soil quality indicator that provides information on the soils ability to function as a basic component of the ecosystem. This study has not been investigated and reported in this area, assessment of soil properties upon conversion of natural forests for varying landuses is of great importance to food security and detecting early changes in soil quality.
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