Soil health management outweighs edaphic properties in explaining soil organic matter across working organic farms

Rebuilding soil organic carbon (SOC) on agricultural lands plays a pivotal role in mitigating climate change and improving soil function, yet its accumulation is constrained by both management practices and inherent soil properties. Scientists and farm advisors recommend that farmers plant cover crops, reduce tillage, and add organic amendments to increase SOC, yet the effectiveness of practices intended to improve soil health may be limited by underlying edaphic controls such as mineralogy, texture, and pH. Given that SOC consists of two distinct fractions – particulate organic matter (POM) and mineral-associated organic matter (MAOM) – which differ in their stability and response to management, a critical question emerges: How do soil health practices compare to edaphic factors in influencing carbon fractions and overall stocks? Despite extensive research in controlled field settings, real-world farming contexts remain less understood, limiting our ability to predict SOC gains across diverse soil conditions. Here, we evaluate how in-season and recent (< 5 years) implementation of soil health management systems on working farms relates to SOC fractions and stocks across 28 organic fields growing leafy greens in the Central Coast of California. Continuous living cover was associated with higher free particulate organic matter (fPOM; +3.16 Mg C ha −1 between representative high- and low-cover sites, 95 % CI: 0.82–5.92), with weaker, borderline associations with MAOM carbon concentration ( p =0.07–0.11 depending on model specification) and total carbon stock ( p =0.068). Reduced tillage showed a similar pattern, with a clear association with fPOM (+1.58 Mg C ha −1 , 95 % CI: 0.39–2.93) and a weaker association with MAOM ( p =0.07–0.09). Crop diversity was associated with higher occluded POM (+1.35 Mg C ha −1 , 95 % CI: 0.11–2.53). We found no association between organic amendments and any measured carbon pool. On average, management variables explain 3.7 times more variance than edaphic variables across carbon fractions, while edaphic variables explained roughly 2.1 times more variance for total carbon stock. These findings suggest soil health management is most clearly linked to particulate carbon accumulation, with more tentative evidence for mineral-associated carbon and total stock, across a wide range of edaphic conditions on working organic farms. We studied how soil-building practices like cover cropping, reduced tillage, and crop diversity affect soil carbon on farms in California. We find that maintaining living plants throughout the year and reducing tillage can boost multiple forms of soil carbon with distinct functions and longevity. While soil type matters, how the land is managed often had a greater effect. This suggests that improving farming practices can meaningfully increase carbon in the soil and draw down atmospheric carbon.