Managing Cover Crops to Control Weeds, Conserve Soil Moisture, and Enhance Growth of Establishing Vines in Oregon's Willamette Valley

Cover crop biomass management is being evaluated in a 3-year trial to determine impacts on vine nutrition, water conservation, and reduced herbicide and fertilizer inputs in new vineyards.  A winter annual cover crop of crimson clover and cereal rye was planted in a newly established commercial vineyard (2008). Cover was mown in spring and biomass distributed in four treatments compared to a non-cover treatment. In-row treatments of 0, 1X and 3X biomass mulch rates were compared to biomass incorporations into the alleyway and a non-cover cropped treatment.  Each treatment was replicated five times with 20 vines per replicate.  In season one (2009), leaf area per vine tended to be higher in mulched treatments than non-mulched, with no differences observed in shoot lengths.  SPAD readings indicating leaf chlorophyll content were higher in mulched treatments than non-mulched treatments by mid-season. Leaf blade and petiole %C, %N, and C:N ratio at véraison were not different between treatments, though a trend was noted in leaf blade %N.  Leaf blade and petiole macro- and micronutrient analyses by ICP will be performed in March 2010.  Soil nitrate and ammonia analyses will be performed in February 2010.  Vines were not water stressed throughout the season. Leaf and shoot biomass in destructively harvested grapevines was four-fold greater in the 3X mulch treatment.  Fine root biomass of commercial vines was significantly higher in the 3X mulch treatment.  Volumetric soil moisture at 0-23 cm was greater in mulched than non-mulched treatments.  In-row soil compaction was lowest in mulched treatments. In-row weed suppression was highest in mulched treatments with nearly 100% suppression of broadleaf and grass species.  Preliminary data indicate that winter annual cover crops may not compete with young vines and may be managed to enhance growth in non-irrigated vineyards.