Increased soil organic carbon in organically managed croplands: Evidence from on-farm monitoring in Bavaria (Germany)

Organic farming is widely associated with environmental benefits and is commonly assumed to promote soil organic carbon (SOC). However, it remains unclear to what extent organic farming leads to higher SOC contents under practical farming conditions. This study compares SOC contents and their temporal changes in organically and conventionally managed arable soils across Bavaria using data from the Bavarian Soil Organic Matter Monitoring Program. The dataset comprises 198 conventionally and 65 organically managed sites, all representing practical farming conditions, with repeated soil sampling after a ten-year period (initial sampling: 2001/2008; resampling: 2011/2018). SOC at resampling tended to be higher under organic management. A higher proportion of perennial grass-clover leys and other perennial forage crops and a lower share of root crops in organic crop rotations were identified as key drivers of SOC, which are intrinsic to organic agriculture but can be applied in any management system. Across all sites, SOC showed a non-significant decline of 0.74 % (16.19 to 16.07 g kg −1 ), while total nitrogen (Nt) increased significantly by 3.13 % (1.60 to 1.65 g kg −1 ). Organically managed sites exhibited a slight mean increase in SOC (+0.73 %), whereas conventionally managed sites showed a mean decrease (−1.14 %). Temporal SOC changes were further influenced by soil texture, with clay-rich soils showing slightly stronger declines or weaker increases. The increase in Nt, combined with contrasting SOC trends, resulted in a significant narrowing of the C:N-ratio across all sites (10.16 to 9.74; −4.13 %). The decline was stronger under conventional (10.14 to 9.69; −4.44 %) than organic management (10.22 to 9.95; −2.64 %). This shift may enhance SOC mineralization and increase the risk of future SOC losses. These findings highlight that results from experimental systems may not fully translate to practical farming conditions and underline the importance of long-term monitoring to develop effective, practice-oriented management strategies for maintaining or enhancing SOC stocks.