An impact of agroforestry-based coffee cultivation and nitrogen fertilization on soil carbon dynamics and microbial metabolic activity: a controlled incubation study

Land use changes significantly impact soil carbon dynamics, as the soil microenvironment beneath different canopy structures and the distinct root properties of various plant species influence soil respiration rates and microbial communities. In northern Thailand, substantial forest areas have been converted to agricultural land, necessitating a comprehensive understanding of the resulting effects on soil carbon processes. This study aims to quantify soil CO<sub>2</sub> emissions and dissolved organic carbon (DOC) concentrations across diverse coffee cultivation systems under nitrogen-fertilized and unfertilized conditions. The research was conducted at the Arabica coffee plantation within the Nhong Hoi Highland Agricultural Research Station, Chiang Mai province, Thailand. Four land use types were investigated: (1) Forest, (2) coffee monoculture, (3) coffee grown with forest, (4) coffee grown with horticulture (persimmon). The study examined the effects of nitrogen fertilization on soil microbial respiration and carbon mineralization dynamics. Soil samples were collected from the topsoil layer (0–20 cm) and subjected to laboratory incubation experiments. Destructive sampling was performed at days 1, 4, 7, 14, 21, 35, and 65 post-incubations for DOC and CO<sub>2</sub> emission analyses through microbial respiration. The highest soil carbon emission (0.1261 mg C g<sup>-1</sup> soil<sup>-1</sup>) was observed in unfertilized coffee-forest integration systems, followed by nitrogen-fertilized coffee-forest integration (0.1085 mg C g<sup>-1</sup> soil<sup>-1</sup>). Nitrogen fertilization in natural forest soils significantly increased DOC concentrations (<i>p</i> < 0.05), while unfertilized natural forest soils showed no significant difference. For cumulative CO<sub>2</sub> emissions, unfertilized coffee-forest integration systems exhibited the highest cumulative CO<sub>2</sub> emissions (10.3 mg kg<sup>-1</sup>), while unfertilized natural forest soils demonstrated the lowest (4 mg kg<sup>-1</sup>). These findings suggest that coffee cultivation integrated with forest or horticultural species may offer a promising approach for Arabica coffee production, potentially enhancing biodiversity, soil conservation, and carbon sequestration compared to monoculture systems. The study underscores the complex interactions between land use practices, nitrogen fertilization, and soil carbon dynamics in highland agroecosystems. Further research is warranted to elucidate the long-term effects of these integrated cultivation systems on soil health, ecosystem services, and climate change mitigation potential in highland tropical environments.