Linking seasonal fractional vegetation cover dynamics with soil organic carbon stock and microbial indicators in tropical agroecosystems

Reliable indicators ofearly soil biological change remain limited intropical agroecosystems, where soil organic carbon (SOC) stocks may respond more slowly than microbial processes. Weevaluated whether seasonal vegetation dynamics derived from Sentinel-2 fractional vegetation cover (FVC) are associated with spatial variation inSOC stock and microbial indicators inJembrana, Bali, Indonesia. Wemapped seasonal FVC from 2019 to2024 and derived site-level metrics ofmean cover and temporal variability (standard deviation, anomaly, coefficient ofvariation, and atemporal stability index). InJuly 2023, wesampled topsoil (0–30cm) at12 sites representing contrasting land uses and topographic settings. Wecalculated SOC stock from organic carbon concentration, bulk density, and sampling depth, and measured basal respiration and culturable microbial density (colony-forming units, CFU). Vegetation cover peaked consistently during the wet season (December toFebruary), and mean site FVC ranged from 0.31 to0.99. Mean FVC showed positive but non-significant associations with culturable microbial density (Spearman’s ρ = 0.48, P= 0.114) and basal respiration (ρ = 0.29, P= 0.361), whereas higher vegetation variability metrics tended tocoincide with lower culturable microbial density (ρ = –0.43 to–0.51, P= 0.090 to0.163). SOC stock showed near-zero coefficients and nostatistical evidence ofassociation with vegetation metrics (ρ = 0.09, P= 0.781) ormicrobial indicators (ρ = 0.01, P=0.975). Principal component analysis ofFVC traits explained 99.65% ofthe variance and separated sites along agradient from stable, high cover tomore variable, lower cover. Overall, FVC stability metrics captured spatial differences that were directionally consistent with microbial indicators, but associations were not statistically significant inthis dataset (n =12). Larger, replicated studies with repeated soil sampling are required toevaluate whether seasonal FVC metrics have robust predictive utility for SOC stock and soil biological indicators.