- 1Faculty of Agriculture, Tokyo University of Agriculture and Technology, Tokyo, Japan (x.lou@live.cn)
- 2Institute of Agriculture, Tokyo University of Agriculture and Technology, Tokyo, Japan
- 3Graduate School of Agriculture, Kyoto University, Kyoto, Japan
- 4Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, Kyoto, Japan
Enhancing soil organic carbon (SOC) accumulation is vital for improving agricultural productivity, soil health, and climate change mitigation, particularly in alkaline Indian soils with severe SOC deficiency. Amorphous Al (Am-Al) would be the major factor regulating SOC in volcanic and humid regions, and biochar has shown promise in improving SOC accumulation in temperate and tropical regions. Yet, their mechanisms and feasibility as amendments for enhancing SOC accumulation remain underexplored, especially in alkaline soils. This study investigates the effects of Am-Al and rice-husk biochar on the stabilization and mineralization of newly added plant materials in the alkaline Indian cropland soil (Inceptisol, 0-15 cm, pH: 8.8, SOC: 5.2 g kg−1, clay: 21%) through a one-year incubation experiment at 25℃ and 60% of water holding capacity. Treatments included Am-Al (Al(OH)3·mH2O; pH: 7.0, oxalate extractable Al: 58 g kg−1, BET specific surface area (SSABET): 290 m2 g−1; 10 g kg−1 soil) and biochar (formed at 550℃ for 4 hrs; SSABET: 180 m2 g−1; 10 g kg−1 soil) with and without washing (pH 9.2 and 6.9), with combination of plant residues (13C-labeled maize residue; 350 g C kg−1; 34% of 13C; <1 mm powder; 1 g kg−1 soil). The amounts and 13C ratios of respired CO2 and SOC during incubation were measured to quantify the mineralization and remaining added residues. The qualitative changes were monitored using 13C NMR and pyrolysis-GCMS.
Am-Al significantly reduced residue mineralization within the first 14 days, resulting in 27% versus 33% residue-derived CO₂ emissions for soils with and without Am-Al, respectively. Although this retardation diminished after 14 days, the legacy effect resulted in higher residue-derived C after one year, mostly in the <100 μm fraction (>90%). Am-Al preferentially stabilized plant residues directly, as indicated by a higher odd-over-even predominance of n-alkanes, reflecting a stronger plant contribution to lipids than microbial contributions. Minimal qualitative changes in residue decomposition patterns were observed in soils with and without Am-Al, as indicated by similar C functional group compositions. It suggests that stabilization may be primarily driven by adsorption rather than changing decomposition pathways, with some preferential stabilization of carbohydrate C (-C-O-) indicated by its smaller decrease among all functional groups. Biochar-amended soils also showed significant increases in remaining residue-derived C compared to controls. Still, they were lower than Am-Al treatments after one year, with stabilization effects becoming significant only in the later stages of incubation (post-day 168). This delayed effect is likely due to substrate substitution for soil microbes from residue to biochar rather than preferential stabilization. These findings highlight the divergent mechanisms of Am-Al and biochar in enhancing SOC accumulation, with Am-Al offering stronger stabilization from early stages and biochar contributing during later stages. Also, SSA may not be the only primary factor regulating the effectiveness of Am-Al and biochar in influencing SOC stabilization. This research underscores the potential of these amendments for SOC management in alkaline, low-carbon soils.
How to cite: Zhong, R., Lyu, H., Nishiki, A., Seki, M., Sugihara, S., and Watanabe, T.: Divergent impact of amorphous aluminum hydroxide and biochar on enhancing organic carbon accumulation in low-carbon alkaline Indian soil, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15185, https://doi.org/10.5194/egusphere-egu25-15185, 2025.