Biological Indicators of Soil Condition on the Kabanyolo Experimental Field, Uganda

Soil biological activity is an integral characteristic reflecting the state of soil fertility, biodiversity, and the activity of soil processes carried out by soil organisms. In Africa, studies of soil biological properties are few compared to the agrochemical research. In this paper, we present an assessment of multiple biochemical and microbiological properties of soil from an agricultural field located in the African tropical savanna. We determined basal respiration, substrate-induced respiration, C of microbial biomass, the potential activity of denitrification, nitrogen fixation activity, and estimated prokaryotic components in the soil microbial complex by quantitative PCR. Basal respiration of soils ranged from 0.77 ± 0.04 to 1.90 ± 0.23 μg C-CO₂·g⁻¹·h⁻¹, and substrate-induced respiration ranged from 3.31 ± 0.17 to 7.84 ± 1.04 μg C-CO₂·g⁻¹·h⁻¹. The C reserves of microbial biomass averaged 403.7 ± 121.6 μg C·g⁻¹ of soil. The N₂O emission from the upper layer on average amounted to 2.79 ng N-N₂O·g⁻¹·day⁻¹, and the potential denitrification activity reached 745 ± 98 ng N-N₂O·g⁻¹·h⁻¹. The number of copies of bacterial genes varied from (0.19 ± 0.02) × 10⁸ to (3.52 ± 0.8) × 10⁸ copies·g⁻¹, and of archaea—from (0.10 ± 0.01) × 10⁷ to (0.29 ± 0.01) × 10⁷ copies·g⁻¹ of soil. These results were in good agreement with the studies in other seasonally wet tropical regions: the biological activity was relatively low. The difference between biological indicators of the experimental field and the reference profile were insignificant except for nitrogen loss, which was higher in the ploughed field. Biological indicators strongly varied in space; we explained their heterogeneity by non-uniform management practices in the course of agrochemical field experiments in the past. The use of organic fertilisers may cause the release of climatically active gases due to intensive microbial respiration and denitrification, but the intensity of emission would strongly depend on the cultivation and management method.