Soil organic carbon, nutrients and relevant enzyme activities in particle-size fractions under conservational versus traditional agricultural management

Micro-scale investigation is helpful for better understanding of the relationships between organic matter, microorganisms and nutrients in soil, and for better interpretation of modifications induced by soil management. The soil particle-size fractions (2000–200, 200–63, 63–2, and 2–0.1 μm), contents of soil organic carbon (SOC), total N (STN), available P (SAP), dissolved organic C (DOC), light fraction organic C (LOC), microbial biomass N (MBN), basal respiration (SBR), and relevant enzyme activities of C, N and P transformations, such as β-glucosidase (β-G), N-acetyl-β-glucosaminidase (N-G), protease, urease and alkaline phosphomonoesterase (APH) were analyzed to study the effects of 8-year-period conservational (no-till with residue retention) (CAM) versus traditional agricultural management (moldboard plowing without residue retention) (TAM) to a Haplic Cambisol soil in the North China Plain (NCP). Our results showed that CAM significantly enlarged the stocks of SOC, DOC, LOC, STN and SAP in the 0–10 cm layer, increased the contents of SOC, STN and SAP in the sand fractions, and promoted all of the enzyme activities in the bulk soil and all of the four particle-size fractions. Our results suggested that CAM increased the nutrient contents in the sand fractions by both enlarging the content of particulate organic matter and enhancing the activities of enzymes involved in nutrient cycling in these fractions. On the contrary, the contents of SOC and nutrients in the silt and clay fractions were relatively resistant to the conversion from CAM to TAM, indicating the limitation of CAM for stable SOC sequestration.