Availability of nitrogen supply from cover crops during residual decomposition by soil microorganisms and its utilization by lettuce (Lactuca sativa L.)

•Cover crops promoted the enzymatic β-glucosidase (BG) activity and soil microbial biomass (SMB) at different values and timing.•Sequential peaks of BG activity and SMB under HV may emphasize the role of soil microorganisms on the inorganic N supply. Utilizing inorganic nitrogen (N) derived from cover crop decomposition by subsequent plant cultivation is important. Its correlation with microbial β-glucosidase enzyme (BG) activity and soil microbial biomass (SMB) as well as cover crop types remains poorly known. Hence, we evaluated the effects of rye, hairy vetch (HV), and their mixture (rye+HV) on nitrogen use efficiency (NUE) by lettuce and soil biochemical properties in fields and pots. Lettuce was rotated with cover crops and examined for N content. Soils at 0–10 cm deep were measured for biochemical status. Lettuce NUE was maximum in rye+HV (47.5%) and HV (27.1%); thus, soil inorganic N supplied in decomposition was efficiently used. Meanwhile, rye retained soil inorganic N concentration (lettuce NUE, −2.31%). Compared with control, HV sequentially promoted BG activity and SMB for 8 and 2 times during the N mineralization process, respectively, assuming the roles of soil microorganisms on inorganic N regulation from cover crop residues. Rye and rye+HV increased BG activity and SMB over the control, at particular timing, showing their potential in maintaining those microbial attributes in the decomposition process.