Temporal Dynamics of Soil Carbon Stocks and Mineralization Rates in Coffea arabica Agroforestry Systems

The increasing demand for agricultural land is driving deforestation, which contributes to rising greenhouse gas emissions—a primary driver of climate change. Agroforestry systems present a valuable alternative approach for mitigating these emissions. This study investigates the influence of various agroforestry systems on key parameters for assessing soil carbon dynamics, including soil carbon stock, microbial biomass carbon (MBC), and microbial respiration (MR) in northern Thailand. The study compared different agroforestry systems: coffee monoculture (CA), coffee intercropped with forest trees (CF), coffee intercropped with persimmon trees (CP), and natural forest (NF) as reference areas. Soil samples were collected from three depths (0–20, 20–40, and 40–60 cm) across three seasons (rainy, cold, and summer). Results showed that soil carbon from land-use changes from NF to coffee agroforestry systems led to a 12.10% increase in CF and an 11.89% decrease in CP. The CA system showed a non-significant 9.06% decrease compared to the natural forest. MBC levels were higher in the agroforestry coffee areas (CF and CP), comparable to those in NF. However, CA exhibited significantly lower MBC (p < 0.05) compared to other treatments. While MBC and MR showed a positive correlation, higher MBC did not necessarily indicate increased microbial activity or significant dissolved organic carbon (DOC) accumulation. Environmental factors, particularly seasonal variations, significantly influenced the results across all three investigations. This study demonstrates that both agroforestry coffee systems (CF and CP) more effectively mitigate deforestation impacts and enhance soil fertility compared to coffee monoculture. For carbon stock enhancement specifically, CF emerged as the optimal choice.