Allelopathic effects and weed suppressive ability of cover crops

Field and laboratory experiments were conducted to investigate the weed suppressing effects of cover crops in single and mixed cultivation. Weed densities in the field experiments ranged from 0 to 267 plants/m(2) with Chenopodium album L., Matricaria chamomilla L., Stellaria media (L.) Vill. as predominant weeds. It was found that mustard (Sinapis alba L.), fodder radish (Raphanus sativus var. niger J. Kern) and spring vetch (Vicia sativa L.) supressed weeds by 60% and cover crop mixtures controlled weeds by 66% during the fallow period at three experimental locations in 2013, 2014 and 2015. The biochemical effect of the same cover crops/mixtures on weed growth was analysed in laboratory experiments. Aqueous cover crop extracts were applied on weeds and analysed using LC/MS/MS. Mean germination time, germination rate and root length of weeds were determined. Extracts prolonged the germination time by 54% compared to the control with only water. In all cases, inhibitory effects on germination rate and root length were measured. Weed density in the field was found to be correlated with the root length in the germination tests. Our work reveals that biochemical effects play a major role in weed suppression of cover crops.