Faba bean as green manure for field weed control in maize

Summary Field observations on crop rotations with maize in temperate areas suggest that faba bean ( Vicia faba ) could exert some weed control when used as a green manure. To test this hypothesis, two glasshouse pot experiments and two field experiments were conducted on the weeding effects over time of faba bean incorporated into the soil. In the pots, faba bean concentrations of 1% and 2% of soil dry weight reduced the germination, root and shoot elongation and aerial biomass of Echinochloa crus galli and Amaranthus retroflexus by ca. 70% when the seeds were sown at the time of faba bean incorporation. These inhibitory effects declined with the delay in sowing. From ca. 21 days after incorporation, fertilising effects became evident in both the maize and the two weeds. In the two field experiments, on land with a history of maize growing in which faba bean biomasses of 6700 and 12 100 kg ha −1 were soil‐incorporated, residue‐mediated reductions of the density and biomass of naturally occurring dominant dicotyledon ( A. retroflexus , Chenopodium album and Solanum nigrum ) and monocotyledon weeds ( Digitaria sanguinalis and Cyperus rotundus ) were observed. At emergence, mean differences with respect to control plots ranged from −14.8% to −69.8% for density and from −46.9 to −78.5% for biomass. Impacts were visible at the flowering time, and still statistically significant for some dicotyledons, leading to mean differences of total weed biomass up to −67.2% compared with control plots. Our results indicate that faba bean has potential as green manure for weed control in maize cropping systems.