Effects of groundcover management practices in a Fraser fir (Abies fraseri)-cover crop intercropping system on soil microbial biomass and community catabolic diversity
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Soil microbial biomass carbon (SMB-C) and nitrogen (SMB-N) as well as microbial community-level physiological profiling (CLPP) were investigated in an intercropping system involving Fraser fir, two leguminous (Dutch white clover and alfalfa) and a non-leguminous (perennial rye grass) cover crops. For each cover crop, two competition-management practices, banding and no banding, were evaluated. Conventionally-managed plots were used as controls. Soil microbial biomass was assessed at the 0-15, 15-30 and 30-35 cm soil depths and CLPP at the 0-15 cm soil depth. Cover cropping had limited early effects on soil organic carbon. However, significant increase of total soil nitrogen at the surface soil layer was observed. The leguminous cover crops with banding yielded higher SMB-C and SMB-N than the non legume. SMB-C and SMB-N significantly decreased with soil depth. Plots managed with bands averaged 559 mg SMB-C kg-1 dry soil, and plots without bands averaged 536 mg C kg-1 dry soil. For SMB-N, plots managed with bands averaged 83 mg N kg-1 dry soil, while plots without bands averaged 79 mg N kg-1 dry soil. Leguminous cover crops significantly improved microbial community diversity compared to the controls. Multivariate analysis showed that the microbial communities in plots with cover crops had a catabolic potential that differed from that of control, with the communities from the leguminous cover crops with bandings exhibiting the strongest dissimilarity. These results suggest that cover cropping with proper management can provide a good environment for microbial development and be an alternative approach to sustainable tree production.