Use of Soil and Litter Arthropods as Biological Indicators of Soil Quality in Southern Rwanda

Abstract - Nsengimana Venuste (2018). Use of soil and litter arthropods as
biological indicators of soil quality in Southern Rwanda. University of Liège,
Gembloux Agro Biotech. Pages: 121, tables: 13, figures: 3
To assess soil quality under different land uses by the use of soil and litter
arthropods as biological indicators, a research was conducted in the Arboretum of
Ruhande and the Rubona agricultural research station in southern Rwanda. Soil and
litter arthropods were collected by pitfall sampling technique and identified to the
family level. Ants (Hymenoptera: Formicidae) were identified to species level. Soil
cores were collected and analysed for soil organic carbon, total nitrogen, available
phosphorus, pH, aggregate stability, cation exchange capacity, electrical conductivity,
silt, and clay and sand soil textures. C:N ratios were calculated from the mass of
carbon to the mass of nitrogen. Higher levels of total nitrogen, soil organic carbon,
and clay and silt soil texture were found in native and exotic tree species. Higher
levels of cation exchange capacity, pH, and electrical conductivity were found in
native tree species and banana plantations, while higher levels of available
phosphorus, aggregate stability and sand soil texture were found in coffee and banana
plantations. The analysis of the abundance of collected soil and litter arthropods
indicated higher abundance of the most of identified families in native and exotic tree
species than in the varieties of coffee and banana plantations. Families of
Scolopendridae, Trombiculidae, Eosentomidae, Formicidae and Staphylinidae
showed strong correlation with soil physicochemical properties. Formicidae highly
occurred in all land uses and discriminated between clay, sand, aggregate stability,
pH, available phosphorus, electrical conductivity and cation exchange capacity. The
ecological functions of identified families contribute to the soil quality through
predation, decomposition, bioturbation and phytophagous that increase soil organic
matter and facilitate water retention and soil aeration. The taxonomy of ants to species
level indicated 30 species belonging to 14 genera, and four subfamilies, the
Formicinae, Dorylinae, Myrmicinae and Ponerinae. These species correlated with soil
properties in different ways, but their ecological functions that contribute to soil
quality are not yet well documented. We recommend further studies to be replicated
in other land uses and ecological zones of Rwanda, to include the impact of climate
variability, altitudinal variation, functional diversity, metal and soil microbiology and
the taxonomy of the entire community composition of collected soil and litter
arthropods to species level in order to generalize these findings.
Key words:
Community composition, Doryllinae, Formicinae, Myrmicinae, Ponerinae, land use,
physicochemical parameters