Impact of Voluntary Sustainability Standards on the Chemical Quality of Coffee Farm Soils in Southern Colombia

Coffee farming in Colombia is influenced by various voluntary sustainability standards that require measures to preserve and improve soil quality. This study evaluated the impact of nine certification schemes on soil chemical quality in 320 coffee farms in southern Colombia using Propensity Score Matching. Soil samples from each farm were analyzed for 17 chemical parameters. Principal component analysis (PCA) identified a minimum data set (MDS) of five key indicators—Base Saturation, organic matter (OM), Ca2++Mg2+/K+, Al3+ Saturation, and phosphorus (P)—which were used to calculate a soil quality index (SQI). All certification schemes showed similar SQI values, classified as moderate (Category III), with no statistically significant differences between certified farms and their matched non-certified counterparts. Among the schemes evaluated, triple certification (RAS-FLO-UTZ) showed the highest positive treatment effect, followed by organic certification, though neither reached statistical significance. The findings suggest that certification status alone does not reliably predict soil chemical quality differences, and that farm-level characteristics and management practices may be stronger determinants of soil quality than certification.