Abstract
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.
Highlights
Most of the soils in tropical Africa are strongly weathered and, are poor in major nutrients [1]
Basal respiration and substrate-induced respiration of soils, the C reserves of microbial biomass, the N2O emission from the upper layer of soil, and the potential denitrification activity were similar to the few results reported for other tropical regions of the world, including sub-Saharan Africa
The use of organic fertilisers may have a negative effect on the carbon footprint of tropical agriculture
Summary
Most of the soils in tropical Africa are strongly weathered and, are poor in major nutrients [1]. In Uganda, major nutrients such as N, P, and K, vital for crop production, have been depleted, resulting in unprecedented soil fertility decrease. Various cultural practices, including the use of cover and rotational crops, composts, tillage systems, and others, have been promoted as management options for enhancing soil quality and fertility [6]. Applying these practices allowed for an increase in the abundance and diversity of total soil microbes, the population of beneficial organisms, and decreasing crop pests [6]
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