QUANTIFICATION OF SOIL ORGANIC CARBON AND MICROBIAL BIOMASS CARBON AND NITROGEN AT THE DEMETER AND ECOLAND CERTIFIED FARM, SONNENHOF, WOLPERTSHAUSEN (GERMANY)

Abstract

This study quantifies soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) in a biodynamic Demeter and Ecoland-certified farm located in Sonnenhof, Wolpertshausen (Germany). Soil samples were collected from six crop fields at three depth intervals (0–10, 10–20, and 20–30 cm) under different crop rotations: mustard–spelt wheat–alfalfa, lentils + camelina–coriander–alfalfa, mustard–spelt wheat–coriander, coriander–lentils + camelina–oriental mustard, mustard–coriander–oriental mustard, and alfalfa–alfalfa–spelt wheat.
The results revealed a clear depth-dependent decline of SOC, TN, MBC, and MBN across all sites, with the highest concentrations recorded in surface layers. Among rotations, the alfalfa-based system (Rheinsberg Acker) showed the greatest enrichment in SOC (2.11%), TN (0.22%), MBC (346.52 mg Cmic kg⁻¹), and MBN (58.65 mg Nmic kg⁻¹), demonstrating the critical role of perennial legumes in carbon sequestration and nitrogen accumulation through biological nitrogen fixation and root biomass input. In contrast, mustard–coriander rotations exhibited the lowest values, emphasizing the limited contribution of short-cycle crops to soil fertility.
These findings underscore the importance of diversified crop rotations, particularly those incorporating legumes, in enhancing soil carbon pools, supporting microbial activity, and promoting sustainable agricultural systems aligned with climate change mitigation objectives.