Impact of land-use diversity on soil biological properties and humic substances under tropical climates
Emmanuel Amoakwah1, Vincent Logah2
1CSIR - Soil Research Institute, Land Evaluation, Ghana
Humic substances are considered to be the most stable and recalcitrant C pool in soil organic matter that have the propensity to contribute to the soil C stock and soil quality. Land use diversity has a significant influence on humic substances, which further affects carbon stratification and stocks, and overall soil quality. The goal of the study was to improve our understanding on how primary forest conversion to other land use types influences soil biological properties and quantitative changes in humic substances in a tropical ecosystem. Geo-referenced composite soils from primary forest, wetlands, cowpea, maize and cassava plantations were collected and analyzed. Soil biological activity, measured as basal respiration rates (BR) efflux, declined significantly between 19.4% – 30.4% upon primary forest conversion to the other land use types. Microbial efficiency measured as metabolic quotient (qR) significantly reduced by 14.5%, 18.8%, and 22.4% upon forest conversion to cowpea, maize and cassava cultivation, respectively. Averaged across depth, forest conversion led to significant decrease in humic acids by 64.9% when forest was converted to cowpea and maize production. Significant reductions of 64.4% and 68.9% in humin concentrations were also recorded in the cowpea and maize agroecosystems, respectively. Among the land-use agroecosystems, the fulvic acid concentrations were high when forest was converted to cowpea (169.2% increase), maize (138.5% increase) and cassava (123.1%) production. Total glucose (Tglucose) concentration significantly declined upon primary forest conversion. Humification index (HI), as one of the indicators of TOC quality decreased significantly upon primary forest conversion to the other landuse types. A significant decline of 29.2%, 38.0% and 58.9% in the HI was observed in the soils used for cowpea, maize and cassava cultivation, relative to the forest. Among the soil properties measured, the specific maintenance respiration rates and fulvic acids contributed most to the variability in TOC stock depletion upon primary forest conversion to other land use types.
Keywords: Basal respiration, degree of humification, fulvic acid, humic acid, humification index, metabolic quotient
Contact Address: Emmanuel Amoakwah, CSIR - Soil Research Institute, Land Evaluation, Academy post office pmb, 00233 Kumasi, Ghana, e-mail: emmaamoakwahyahoo.co.uk