Temporal and Spatial Patterns of Water and Nutrient Availability, and the Physiological Capacity of Root Nutrient Acquisition in Dry Soils Under Deficit Irrigation

The overall goal of this project is to develop an understanding of the impact of deficit irrigation and fertilization timing on Vitis root demography, physiological processes and vine performance in terms of yield and quality indices. The project is long-term and will require at least two more growing seasons to completion. There are five interdependent objectives we are working towards within this framework. Objective 1 examines the limits, in time and space, of soil moisture when drip irrigation is employed in a vineyard with deep (³ 2m) clay loam soils: We conducted deuterium oxide labeling experiments in 2002 and found that the presence of grapevine roots had a major influence on the extent of the drip irrigation wet-up zone as a consequence of root water absorption. These experiments will help us delimit the extent of the wet-up zone. We installed a TDR system to acquire spatial and temporal soil moisture data from the drip zone and route it to a web site where it is archived for analytical purposes. Objective 2 studies the timing and spatial distribution of root proliferation (seasonal patterns of proliferation and duration of physiologically active lifetime) under deficit irrigation. We installed 120 transparent minirhizotron observation tubes and acquired nearly a full seasons data set consisting of more than 170,000 digital images using fiber optics. Our preliminary results indicate that deficit irrigation results in greater summertime root mortality. The ultimate impact of such mortality on vine performance will need to be assessed during a further two growing seasons. Objective 3 examines the temporal and spatial distribution of nitrogen, potassium and phosphorous in the wet-up zone and in dry soils. We deferred these investigations to 2003 in lieu of the extensive labor required to install the observation tubes needed for the success of this project. Our root imaging has become the most ambitious currently in progress [1], and has required our close collaboration with Bartz Technologies Inc. to modify and develop software that is allowing us to acquire, archive and process images more rapidly than was previously feasible. Under Objective 4 we are examining the contribution of roots that proliferate into dry soil zones on the water and nutrient economy of the vine. In 2002 we monitored stem water potentials and took seasonal leaf and petiole samples that show substantial changes in leaf N content during the growing season. The interactions among irrigation practice (factor 1, deficit or not), timing of nitrogen and potassium fertilizer application (factor 2, early spring or autumn) and type of rootstock (factor 3, vigorous or not) on fruit yield and quality are being investigated under Objective 5. Our preliminary results indicate minor yield and quality differences for the three irrigation treatments. The fertilization treatments will not take effect until the upcoming growing season.