Evaluating the impact of land use change on soil C sequestration, mineralization, and fractionation using stable isotope techniques

Land use significantly influences soil organic carbon (SOC) sequestration and mineralization, impacting its quality and stability. This study compared agroforest, cropland, forest, and grassland sites to evaluate how land use affects soil properties and SOC dynamics. Isotope composition (delta sup 13 and delta sup 15 N) was also used to trace the origin and fate of soil organic matter (SOM). Results showed significant differences in soil properties among land use types. Cropland displayed higher compaction, pH, and phosphorus, while forests and agroforests showed lower compaction and greater porosity. Grassland exhibited higher water-holding capacities, particularly in the upper soil layers. Nutrient concentrations decreased with depth across all sites. Significant differences in SOC and total N (TN) stocks were observed, with agroforests and grasslands demonstrating higher SOC in topsoil compared to forests. Croplands consistently held the lowest SOC and TN stocks. Cropland soils also exhibited faster C mineralization rates, suggesting accelerated organic matter turnover. Isotopic compositions of SOC and vegetation varied by land use and soil depth, reflecting complex biogeochemical interactions. The distribution and concentration of humic substances were also found to be dependent on land use. They exhibited a decreasing concentration with depth and a higher degree of humification in lower soil layers, indicating greater stability and recalcitrance of SOC. Land use has a profound impact on both the quantity and quality of SOC. Croplands contain more easily decomposable SOM, whereas grasslands store a greater proportion of stable C pool, especially within surface soils. Moreover, isotope analysis revealed how vegetation and historical land use shaped SOC characteristics. The study revealed strong correlations between soil properties and C pool dynamics, highlighting the critical role of land use in soil fertility, C sequestration, and overall ecosystem health. These findings highlight the crucial role of land-use decisions in maintaining soil health and promoting C sequestration, which is a key strategy for effectively mitigating climate change. Thus, sustainable management practices, including reduced tillage, cover crops, and organic amendments, are recommended to combat SOC losses often associated with intensive agriculture. The study also emphasizes the crucial importance of managing surface soil effectively, as the impact of land use on soil properties is particularly evident in the top 40 cm of soil.