Nutrient Distribution Patterns in Deficit Irrigated Wine Grape Using Bromide as a Tracer.

Irrigated wine grape (Vitis vinifera L.) production frequently involves applying nitrogen (N) based fertilizers through a drip irrigation system.  However, to attain high quality grapes for making premium wines, water application volumes are frequently low and only a small volume of soil is wetted.  This has the potential to create zones of different water and nutrient availability and violates the assumption of uniformity for soil sample collection.  We used bromide as a tracer, mimicking NO₃-N, to evaluate the distribution in the soil volume below drip emitters in deficit irrigated wine grape.  Soil samples were collected in a radial pattern, by depth, after the irrigation where Br was applied and several irrigation events during the growing season.  Soil moisture was determined on the sample prior to extracting and analyzing the samples for Br.  In addition, leaf tissue samples were collected and analyzed for the movement of Br into the plant. In general, during the growing season soil moisture was restricted to a narrow volume under the emitter.  Br deposition and movement followed the soil moisture patterns, although Br was not persistent in the root zone.  This information can be used to develop recommendations for soil sample collection that reflect the plant root zone.