Chemical Composition of Organic Carbon in Tropical Soils Under Agricultural Cultivation and Peat-Swamp Forest

Year of Publishing
2024
Organisation
ASEAN
Tags
Language
English
AQM Activity Type
Decision Support
Resource type
Reports, Case Studies & Assessments
Themes
Agriculture
Forests
Regions
Asia and the Pacific
Governance level
All levels
cover
Description
Soil organic carbon (SOC) is important for agricultural production and from an environmental perspective. This research determined the chemical composition of SOC and studied factors related to its distribution for various crops and peat-swamp forests in the tropical region. In total, 21 topsoil samples were collected from areas of paddy rice, sugarcane, cassava, pineapple, oil palm, para rubber, and peat-swamp forest in Thailand. Four groups of SOC chemical composition were investigated (carbonyl C, aromatic C, O-alkyl C, and alkyl C) using solid-state C-13 nuclear magnetic resonance spectroscopy (NMR). The dominant peak of the NMR spectra indicated that SOC originated from a variety of lignin compound units. The results revealed the dominant SOC chemical component was O-alkyl C (36.57-50.90%), followed by alkyl C (22.32-32.60%), aromatic C (16.65-23.41%), and carbonyl C (7.99-10.95%), respectively. Most of the SOC chemical components were derived from plant debris, particularly biodegraded lignin compounds. There were slightly differences between the distributions of the SOC functional groups in each vegetation type, perhaps partially as a result of the specific management activities for each crop, including tillage. Furthermore, alkyl C was related to some soil properties (silt and clay fractions), while O-alkyl C was related to available P in the soil. The hydrophobicity index, aromaticity index, and degree of humification were in the ranges 0.69-1.12, 0.17-0.23, and 0.46-0.92, respectively. These findings provided SOC chemical composition data of several economic crops to further support soil management for crop production and carbon stock preservation in tropical soils.