A Field Evaluation of Mycorrhizal Inoculants on Grapevine Growth and Nutrient Uptake: Final Report

This final BIOAg report summarizes a short-term field experiment at Washington State University Tri-Cities testing whether arbuscular mycorrhizal fungi (AMF) and phosphorus (P) fertilizer affect growth and nutrient uptake in Vitis vinifera ‘Merlot’ (clone 4), including self-rooted and 1103P rootstock-grafted vines. Vines were grown from August 2020 to September 2021 in a randomized complete block design with four treatments: AMF, P, AMF+P, and an unamended control (resident soil microbiota present in all plots).

COVID-related planting delays and a harsh winter caused high mortality, leaving only enough grafted vines for statistical analysis. In grafted vines, P fertilizer increased soil and foliar P, and AMF+P produced the highest foliar P at harvest. AMF-treated vines had the highest leaf chlorophyll. Treatments affected root biomass and root AMF colonization (P-only plots had the lowest colonization), but there were no detectable effects on height, aboveground biomass, survival, or most other foliar nutrients. Results suggest responses to AMF and P can be variable; growers may benefit from small-scale trials before broad vineyard adoption.