Effects of living mulch on young vine growth and soil in a semi-arid vineyard

Although the use of under-trellis plants as weed control (living mulch) in vineyards has been gaining popularity, its effects on soil quality and especially soil biology have not been well studied. Due to functional trait differences, plants may differ in how they compete with vines, and may also change abiotic and biotic soil properties. A living mulch trial was established in the semi-arid Okanagan valley of British Columbia comparing vine growth as well as soil abiotic and biotic outcomes for four living mulch treatments: buffalo grass (Bouteloua dactyloides), Chewing's fescue (Festuca rubra ssp. commutata), birdsfoot trefoil (Lotus corniculatus), and shepherd's purse (Capsella bursa-pastoris) with two industry standards: herbicide and cultivation. After two seasons, strong vine growth responses were seen that depended on living mulch identity, e.g., reduction in leaf N status with grasses, reduction in leaf water potential with the legume, birdsfoot trefoil. These effects were related to plant-induced changes to soil C:N ratio and soil moisture. Although treatments did not change abundance of the measured fungal guilds in bulk soil, abundance of arbuscular mycorrhizal fungi in vine roots was lowest with birdsfoot trefoil as living mulch. This study may help growers to select living mulch species appropriate for the soil conditions and resource availability of their site.