Untangling belowground response of grapevines to cover crop competition

Abstract

Context and purpose of the study ‐ Cover crops are planted in vineyards for multiple benefits including soil conservation, weed management, regulation of grapevine vegetative growth, and improved fruit quality. In humid climates where inter‐row cover crops are standard management, we evaluated under‐ vine cover crops for beneficial reductions in vegetative growth. Several factors affect the impact of under‐vine cover crops on vine growth and productivity, including seasonal resource availability, vine age, and rootstock. To better understand these factors, we examined belowground processes that might clarify mechanisms of resource competition between grapevines and cover crops.

Material and methods ‐ Field examinations of mature vinifera and young inter‐specific hybrid grapevines grafted on two rootstocks varying in vigor, Riparia (Vitis riparia) and 101‐14 Mgt (Vitis riparia x Vitis rupestris), were conducted at three humid, eastern US vineyards. Both destructive (soil coring) and non‐destructive (minirhizotron technique) methods were used for root observations and analysis.

Results ‐ Roots of young and mature vines coped with under‐vine cover crop competition by avoiding shallow soil regions mainly colonized by cover crops roots, suggesting complementary use of water and nutrients. In mature vines, cover crop competition also induced shorter lifespan of grapevine roots, but did not affect root morphological traits, such as specific root length, diameter, mycorrhizal fungal colonization, and root branching. In contrast, young grapevine root systems responded to competition by increasing specific root length and decreasing absorptive root diameter, regardless of the rootstock. Although rootstocks displayed a similar belowground response, young vines grafted on the low‐vigor rootstock exhibited less growth reduction during the first year suggesting that tolerance of cover crop competition may be rootstock dependent. Overall, young grapevines growing with cover crops tended to have greater reductions in growth compared to mature vines, suggesting that vines acclimate to competition over multiple years.