Coping with cover crop competition in mature grapevines

Cover crops limit canopy growth in fruit crops to varying magnitudes but mechanisms are poorly understood. Root responses of mature grapevines to understory grass were evaluated in a temperate, humid region of USA. We hypothesized that mature grapevines competing with understory grass would show deeper root distribution with deeper use of soil water but only modest reductions in nitrogen and phosphorus uptake. Root responses assessed included vertical distribution of absorptive root length, mycorrhizal fungal colonization and total vine root length. Extractable soil nitrogen and phosphorous, soil moisture, grapevine nutrient status, and grapevine depth of water uptake were also assessed. In response to cover crop, the well-established grapevines maintained canopy growth, had modest (17 %) reductions in fruit biomass production and exhibited little evidence of restricted uptake of water and nitrogen, despite marked shifts toward deeper grapevine root distribution and a 63 % decreased overall absorptive root length. Mycorrhizal colonization of the grapevines was unaffected by presence of a cover crop. Cover crop competition affected grapevine access to phosphorus more than water or nitrogen. These results illustrate that grapevine root systems are capable of acclimating to understory grass competition, but specific resource limitations are strongly context dependent.