Biomass carbon sequestration potential of fallow periods following shifting cultivation in Quara district, North Western Lowland of Ethiopia

Abstract

Increasing food demand in Ethiopia has intensified shifting cultivation, shortening fallow periods and potentially reducing carbon storage. However, biomass carbon stock variation across fallow-age categories in Ethiopia’s shifting cultivation systems remains poorly understood. This study estimates biomass carbon stocks across six fallow periods (2–4 [F1], 5–7 [F2], 8–10 [F3], 11–13 [F4], 14–16 [F5], and 17–20 years [F6]) in Quara district, Northwest Ethiopia. The study site was purposively selected. Vegetation data were collected from 54 randomly laid quadrats (20 × 20 m²) along fallow gradients. Biomass carbon was estimated using species-specific allometric equations. Differences in mean biomass carbon stocks across fallow periods were analyzed with one-way ANOVA. The findings showed that fallow length significantly affects carbon sequestration potential, with longer fallow periods exhibiting greater biomass carbon accumulation. The highest carbon stocks were consistently observed in the oldest fallow period (F6: 17–20 years), with 34.16 ± 6.65 Mg ha⁻¹ for above-ground biomass (AGB), 8.88 ± 1.73 Mg ha⁻¹ for below-ground biomass (BGB), 16.40 ± 3.19 Mg ha⁻¹ for above-ground carbon (AGC), and 4.26 ± 0.83 Mg ha⁻¹ for below-ground carbon (BGC). In contrast, the youngest fallow (F1: 2–4 years) showed significantly lower values across all parameters, with only 15.67 ± 9.14 Mg ha⁻¹ AGB, 4.07 ± 2.38 Mg ha⁻¹ BGB, 7.52 ± 4.39 Mg ha⁻¹ AGC, and 1.95 ± 1.14 Mg ha⁻¹ BGC. Older fallows (F6) accumulated 75.8 Mg ha⁻¹ carbon dioxide equivalent (CO₂e) compared to 34.8 Mg ha⁻¹ in younger fallows (F1). Peak sequestration rate occurred during F3-F4 (4.03 Mg ha⁻¹ TBC, 14.77 Mg ha⁻¹ CO₂e), indicating optimal carbon capture, while the lowest rate (0.51 Mg ha⁻¹ TBC, 1.86 Mg ha⁻¹ CO₂e) in F4-F5 suggested ecological constraints. Cumulative sequestration rate across F1-F6 reached 11.18 Mg ha⁻¹ TBC (41.02 Mg ha⁻¹ CO₂e), highlighting fallow lands carbon storage potential. Results demonstrate that extended fallow periods enhance biomass carbon stocks, supporting their integration into REDD + and carbon credit programs, especially in rotational agriculture systems. Future studies should examine species-specific carbon contributions.