Influence of indigenous tree presence on soil macrofauna and soil organic matter dynamics in tropical agricultural landscapes

Abstract Trees in farmlands contribute to soil organic matter levels through leaf litter additions and root turnover. Trees also play important roles in the improvement of nutrient cycling and a more efficient utilization of existing soil nutrients as well as those externally applied. Soil macrofauna distribution is influenced by spatial variability of organic resources as they are influenced by land use and climate. There is limited information available on the effect of trees on the spatial distribution of soil macrofauna activity in agricultural landscapes. This study was therefore undertaken to understand the influence of indigenous trees, land use and soil moisture on soil macrofauna as related to changes in soil physical and chemical properties. The soil macrofauna study was conducted at the Kiberashi Sentinel Site, Tanzania (AfSIS), following the LDSF nested sampling design across a total area of 100 square kilometers. A total of six-hundred and forty (640) monoliths (25 x 25 x 10 cm) were collected, soil macrofauna separated by hand sorting, and soil samples prepared for spectroscopic analyses. Organisms were not identified to species and only the main taxa were considered. In the laboratory, organisms were separated into seven broad groups (earthworms, termites, ants, beetles, millipedes, centipedes and “other invertebrates”). Density and biomass of each of these groups were determined in each of the soil monoliths. Mid-Infrared (MIR) Spectroscopic analyses and soil textural analysis were used to characterize monolith soils inhabited by soil macrofauna. Earthworms, centipedes, millipedes and beetles showed significant clustering, while termites and ants did not. Moisture conditions influenced the distribution of earthworms and beetes. Soil total C, pH, available P, clay content and exchangeable bases explained close to 80% of the variation in soil properties. High abundance of beetles and lower abundance of earthworms and centipedes were found in soils of higher pH, while higher C soils had lower abundance of beetles and termites. Higher abundance of termites was found in soils with high clay content.