Soil organic matter and microbial community structure in set-aside and intensively managed arable soils in NE-Saxony, Germany

The effects of set-aside and intensive management of agricultural soils on soil organic carbon (SOC) and nitrogen (N) mineralisation rates (gross and net rates), microbial biomass (chloroform-fumigation extraction method) and microbial community structure (phospholipid fatty acid analysis, PLFA) were assessed during one growing season (June and September). A former arable soil which has been set-aside as fallow with natural succession vegetation (“fallow land”) was compared to a soil under intensive agricultural management (“intensive”) with site conditions typical of NE-Saxony, Germany. The soil type was a sandy Cambisol. Six years of intensive agricultural management significantly decreased SOC and TN contents as well as pH and increased NO₃-N contents in the topsoil (0-10cm) compared to fallow soil. As indicated by higher gross N mineralisation rates, the potential to deliver N increased during the fallow period. However, the substrate use efficiency of microorganisms and the turnover of the microbial biomass were higher in the intensively managed soil. Independent of management system SOC mineralisation, net N mineralisation, gross NH₄ consumption and gross NO₃ transformation rates increased with increasing water content from June to September. Principal component analysis of PLFA data indicated differences in the microbial community composition between the sites. However, in total the soil microbial community was more stable against land-use changes than against seasonal changes. The PLFA profiles of both sites changed into the same direction from June to September. Only the relative abundances of PLFA marker characteristic of Gram⁻ bacteria and fungi showed a sitextime interaction as did the MBC/MBN ratio and the MBN content. In total, the influence of land-use on most examined parameters of the sandy Cambisol was less pronounced than seasonal changes. Therefore, set-aside and taking set-aside land back into intensive agricultural production seem to be a reasonable management practice for sites on sandy Cambisols in NE-Saxony, Germany.