Response of Soil Microbial Biomass and Activity to Cover Crop Incorporation Methods

Cover crop management in vineyards under a semiarid Mediterranean environment needs strategies that enhance soil C and N status and microbial functioning without increasing disturbance. This study compared cover crops biomass incorporation (harrowing, HR; rotary tillage; RT) and non-incorporation (NI, residues left on the topsoil) into the soil in a 12-year Grecanico dorato vineyard. Traditional vineyard soil management (continuously tilled for weeds control) was also used as a control. Soil samples from 0 to 20 and 20 to 40 cm were analyzed for total organic carbon (TOC), total nitrogen (TN), microbial biomass carbon (MBC) and nitrogen (MBN), and enzyme activities. NI and HR raised TOC and TN in the topsoil versus TR, with NI frequently maintaining advantages at depth. NI also maximized MBC/MBN and reduced the metabolic quotient (qCO2), indicating improved microbial C-use efficiency; RT showed intermediate chemistry but depressed subsoil MBC and altered MBC/MBN. Enzyme profiles reflected contrasting mechanisms: RT boosted β-glucosidase in the topsoil, TR peaked for urease and arylsulfatase but alongside lower biomass and higher specific enzyme activities, while NI supported greater overall functioning via larger biomass and lower per-C enzyme demand. The calculated geometric mean enzyme (GMea) index emphasized transient TR flush versus steadier conservation functioning. Strong vertical stratification occurred for all indices, yet NI transmitted some benefits to 20–40 cm. We conclude that residue retention or moderate incorporation promotes larger, more efficient microbial population and more balanced nutrient cycling, whereas repeated rotary tillage risks subsoil inefficiencies. In semi-arid Mediterranean vineyards, low-disturbance cover-crop incorporation (HR) or, preferably, residue retention at the topsoil (NI) offer a simple, scalable route to sustain soil quality and long-term fertility.