Effect of olive vegetation water and compost extracts on seed germination of four weed species

Weed management has historically been recognized as one of the main challenges in crop production systems, especially in organic farming settings. Innovative and environment-friendly weed management tools are much needed to overcome weed herbicide resistance and minimize agricultural footprint and energy use. The objective of this study was to test the effect of four dilution levels of olive vegetation water (OVW) and three pomace/compost extracts on seed germination of redroot pigweed (Amaranthus retroflexus L.), little mallow (Malva parviflora L.), common purslane (Portulaca oleracea L.), and common sowthistle (Sonchus oleraceus L.). In the first experiment, four dilutions (100 %, 75 %, 50 %, or 25 %) of OVW and a tap water control treatment were prepared. In the second experiment, extracts were prepared from raw olive pomace, olive/dairy manure mix compost or dairy manure-based compost. For each treatment and species, 100 seeds were divided into 10 Petri dishes. A 2 mL solution from each of the treatments above was applied to each Petri dish and incubated in a growth chamber for 24 days. Redroot pigweed was the most sensitive to OVW treatments, with germination rate dropping from 30 % in the control treatment to 1-4 % for all OVW levels on day 8 after application. In common sowthistle, full strength OVW (OVW100) caused a germination delay of 4 days compared to the control. In little mallow, OVW100 decreased germination rate throughout the duration of the experiment, while OVW75 slightly increased the germination rate after 12 days of application, apparently overcoming seed dormancy. For common purslane, the three higher OVW concentrations decreased germination rate during the first six days. Compost extracts had little effect on weed seed germination, with some of them initially depressing germination in some species or tending to accelerate little mallow germination in the second half of the incubation period. Overall, this study shows that OVW can be used to control weeds or otherwise stimulate their germination so that they can be controlled using other means before planting. This material could possibly be used to deplete the soil weed seed bank.