Root Growth and Development of Nematode Communities in a Young Merlot Grape (Vitis vinifera) Vineyard: Influences of Irrigation and Organic Amendments.

The use of drip irrigation and organic soil amendments or mulches can be used to reduce vineyard water consumption. The effects of these water-conserving practices on root growth and soil organisms that may have feedback effects on belowground productivity are, however, not well understood. In 2011, a Merlot grape (Vitis vinifera) vineyard was established to assess the effects of a factorial combination of irrigation practices (drip emitters vs microsprinklers), nutrient sources (compost vs mineral fertilizer applied via fertigation at 40 kg N/ha/year) and mulch (+/- bark mulch) on an array of system responses including root growth, soil nematode communities and soil carbon. Minirhizotron access tubes were installed in each plot in spring of 2012 and root images were collected to a depth of 75 cm biweekly through the 2013 season. Soil samples taken to 30 cm at the end of the 2012 and 2013 growing seasons were analyzed for nematode community structure and soil carbon (total organic C, POX-C, water-extractable C). Root length and volume were affected by nutrient source and mulch at intermediate depths, with the lowest values under mulch and greatest values under either fertilizer or compost treatments. Irrigation did not affect root growth at any depth in 2013. In contrast, population densities of plant-pathogenic ring nematodes (Mesocriconema xenoplax) and root-lesion nematodes (Pratylenchus penetrans), both of which can affect grapevine root growth, were affected by irrigation but not nutrient source or mulch. Ring nematode population densities were larger under drip than microsprinkler irrigation whereas root-lesion population densities were larger under microsprinkler than drip irrigation. Compost and mulch treatments increased soil carbon and the abundance of free-living nematodes. Reasons for the lack of correlation between root growth and populations of plant-pathogenic nematodes will be discussed in light of the early phase in establishment of the vineyard and nematode populations.