Inhibitory effects of cover crop mulch on germination and growth of Stellaria media (L.) Vill., Chenopodium album L. and Matricaria chamomilla L.

Cover crops may suppress weeds due to their competitive effects and the release of inhibitory compounds. We examined the inhibitory influence of 11 cover crop mulches on the germination and growth of weed species (Stellaria media (L.) Vill., Chenopodium album L. and Matricaria chamomilla L.) in laboratory, greenhouse and field experiments. In the laboratory, cover crop extracts were tested in germination bioassays at six concentrations (0-500 mg ml−1). The germination rate and root length (i) were measured 10 days after treatment (DAT). Pot experiments were carried out in the greenhouse to investigate the effects of cover crop mulch (ii) incorporated into the soil on weed germination and weed dry mass. Field trials measured the suppressive effects of cover crops and cover crop mixtures on weeds (iii). Correlations were determined between the experiments to quantify the competition and the biochemical effects of cover crops separately. Cover crop extracts at a concentration of 125 mg ml−1 (i) significantly reduced the weed germination rate by 47% and the root length by 32% on average. M. chamomilla showed a lower susceptibility to the extracts of S. alba, R. sativus var. niger and H. annuus compared to C. album and S. media. The mulch-soil mixtures (ii) significantly reduced the germination rate by 50% and the dry mass by 47% on average across all three weed species, while M. chamomilla showed the highest tolerance to the mulches of V. sativa and A. strigosa. The correlation analysis revealed a strong positive correlation between extract toxicity and field weed suppression and, thus, indicated a high impact of the biochemical effects of the tested cover crops on weed suppression, especially for S. media and M. chamomilla.