Tropentag, September 16 - 18, 2026, Göttingen "Towards multi-functional agro-ecosystems promoting climate-resilient futures"

Interactive effects of soil restoration strategies on nutrient dynamics in the tropical savannah

¹Technische Universität München, School of Life Sciences, Germany
²Lancaster University, Lancaster Environment Center, United Kingdom
³University of Natural Resources and Life Sciences Vienna (BOKU), Institute of Soil Research, Austria
⁴International Livestock Research Institute (ILRI), Kenya

Abstract

Grassland soil degradation poses major environmental challenges, with nutrient depletion and disruption of microbial communities limiting ecosystem recovery. However, restoration often relies on natural regeneration (i.e, passive restoration), which is often insufficient, and thus active intervention is necessary. We established a full-factorial field experiment to test whether soil inoculum, organic amendments (manure), and physical disturbance (tillage) interact to affect soil nitrogen dynamics and microbial properties in a degraded grassland of Kenya.
The three-way treatment interaction increased NH₄⁺ (p < 0.05), though the soil inoculum alone increased NH₄⁺ even more (p < 0.01). Combining soil inoculum with manure reduced NH₄⁺ (p < 0.05) while increasing microbial biomass nitrogen (MBN) (p < 0.05). Tillage eliminated both effects, resulting in intermediate NH₄⁺ levels, an increase in NO₃^- (p < 0.05), and a reduction in microbial biomass carbon (MBC) (p < 0.01). Manure alone increased MBN, while tillage consistently increased NO₃^- and decreased MBC.
These results suggest three nitrogen dynamics pathways: i) mineralisation (inoculum-enhanced organic matter breakdown), ii) immobilisation (manure + inoculum-driven microbial sequestration), and iii) physical override (tillage-induced disruption of biological processes). Since the inoculation effect depended on whether manure was applied, restoration outcomes are context-dependent, so strategies should target specific goals: tillage for immediate nutrient availability, inoculation for enhanced mineralisation, or inoculum + manure for long-term biological soil development.

Keywords: Grassland restoration, nitrogen dynamics, organic amendments, soil microbes

Contact Address: Habtamu Sibilu, Technische Universität München, School of Life Sciences, Liesel-Beckmann-Str. 4, 85356 Freising, Germany, e-mail: h.sibilutum.de