Contributions of fine mineral particles and active Al/Fe to stabilization of plant material in neutral-to-alkaline soils of Indo-Gangetic Plain

• Published in: Geoderma 2023-12, Vol.440, p.116709, Article 116709
• Main Authors: Zhong, Ruohan, Lyu, Han, Kumari, Monika, Mishra, Ajay Kumar, Jat, M.L., Dahlgren, Randy A., Funakawa, Shinya, Watanabe, Tetsuhiro
• Format: Article
• Language: English
• Subjects: 13C tracing; Clay and silt; Fractionation; Pyrolysis-GC/MS; Soil organic matter; Topsoil and subsoil
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/j.geoderma.2023.116709

Factors controlling organic carbon stabilization are elusive in neutral-to-alkaline soils, thereby hindering the assessment of carbon sequestration potential across vast agricultural regions like the Indo-Gangetic Plain (IGP). This study investigated controls over mineralization and stabilization of added organic matter in tropical neutral-to-alkaline soils with low organic carbon (SOC). Using topsoil and subsoil samples from 12 sites of upper-to-lower IGP, we conducted a one-year incubation with and without adding 13C-labeled maize material. We tracked CO2 release and residual C remaining in soil organic matter fractions (free, occluded particulate (oPOM), and mineral-associated organic matter (MAOM)) and analyzed organic matter molecular compositions in incubated soils using pyrolysis-GC/MS. Our results revealed that 48 ± 7 % of added maize C was mineralized, mostly within the first 70 days. Higher active Al/Fe, notably Al, retarded primary maize mineralization by facilitating aggregation. High SOC content and SOC saturation degree resulted in more maize mineralization. The disappearance of maize-unique compounds (e.g., neophytadiene) revealed substantial degradation of added maize. Regarding SOC composition, maize addition increased the relative abundance of fatty acids and decreased that of N-containing compounds. Most residual maize-derived C was found in stabilized fractions, MAOM (77 ± 15 % of residual maize C) and oPOM (8 ± 4 %). Clay fraction contributed to most maize-derived C stabilization as MAOM (path coefficient (β) = 0.81**). Moreover, the significant correlation (P