Relationships of priming effects with organic amendment composition and soil microbial properties

Soil organic carbon (SOC) sequestration through the application of organic amendments (OAs) is considered an important strategy to offset anthropogenic Cv93.0O₂ emissions while simultaneously enhancing soil quality and food security. The efficiency of SOC sequestration, however, depends on the priming effect which is influenced by interactions of OA composition with soil microbial response variables (MRVs). Yet, there remain large uncertainties surrounding the mechanisms and relationships defining these interactions, hampering the identification of OAs most effective for SOC sequestration and hindering the inclusion of OA dynamics in soil carbon models. In this study therefore, we performed an integrated assessment of these interactions for a cropland soil amended with wood chips, waterway residues, and isotopically enriched road-verge grasses, compost, and bokashi. Changes in 11 microbial properties and priming effects (for isotopically labelled OAs) were monitored for 150 days and related to 22 characterizations of OA composition. We demonstrate that i) hot water extractable to total carbon ratios of OAs are superior predictors of priming effects, ii) dissolvable to hot-water extractable carbon ratios are most closely related to variation in MRV expressions, and iii) priming effects correlate significantly with changes in several MRVs. Findings advocate for the adoption of energetic principles in modelling and predicting microbially-mediated soil carbon dynamics and suggest that application of OAs with high hot water to total carbon concentrations – potentially achievable by composting, but not fermenting, OAs prior to application – can allow for more efficient SOC sequestration.