Faba Bean Organs Differed in Their Effects on Maize Seed Germination Rate and Soil Microbial Activities as well as Their Decomposition Patterns in a Regosol Soil

This study was purposely designed to evaluate the potential of faba bean ( Vicia faba ) residues as green manure in a maize-faba bean rotation system. Seed germination test and pot experiments were conducted to measure the effects of aqueous extract on maize seed germination and the effects of residues on crop growth and soil microbial activities. Litterbag experiment was conducted to analyze the decomposition patterns of faba bean residues during maize growing season in a regosol soil. The faba bean was separated into roots, stems, leaves, aboveground parts, and whole plants. Seed germination and the lengths of radicle and plumule were lower than those of the control, particularly with 1% aqueous extract concentrations. Aboveground biomass of maize at heading stages was negatively reduced by whole plant, aboveground part, and stem, whereas positively increased by leaf. Faba bean residues varied in their influences on the contents of soil microbial nitrogen and carbon as well as enzyme activities, mainly attributing to their differences in nutrient quality and allelophathy. Faba bean residues showed a quick decomposition rate during the first 5 weeks and slightly decomposed thereafter. The amount of nitrogen (N) released into soil ranged from 3.74 kg N ha −1 in root to 34.67 kg N ha −1 from leaf in the first 5 weeks. Compared with other plant parts, there were more remaining residues in root and stem residues. These results suggest that different management strategies should be taken to balance their negative and positive effects when using faba bean residues as green manure.