Efficiency of a novel biodegradable pyrolysis liquid-amended mulch in weed control

Agrochemicals and plastics represent a burden on natural ecosystems and there is an urgent need to introduce alternative plant protection measures that have fewer negative impacts on the environment. Replacement of plastic mulches and synthetic pesticides with their biodegradable alternatives offers a way to decrease chemical residues. Pyrolysis liquids (PL) have been suggested as easily degradable and residue-free herbicides for agriculture. We tested the efficiency of PL (1%-10% of volume) containing peat mulch (PLM) in weed control under glasshouse and field conditions. We also estimated the length of the withdrawal period needed between PLM spreading and sowing/planting for crops and examined the light permeability and effects of PLM on soil temperature. In the glasshouse, the mulch amended with 5%-10% PL inhibited weed germination entirely. In the agricultural field, the number of weeds remained 44%-60% lower under PLM than under the control mulch. In a study performed in a city park, weed cover around the base of trees remained 64%-85% lower under PLM than without a mulch. However, a 7-21 d withdrawal period, depending on crop plant species, is needed to avoid injuring the crops. PLM inhibited sunlight effectively and the effects on soil heat sum across the growing season remained small. The weed-inhibiting effect of PLM is probably a result of both the PL compounds and the solid cover, formed by the sticky PL and peat fibres, which acts as a mechanical barrier. We conclude that the PLM is a promising alternative to plastic mulches.