Measurement of Water Flow in Young Grapevines Using the Stem Heat Balance Method

Abstract

There are numerous published discussions on the water use and water requirements of grapes (Vitis vinifera, L.), but data on the actual water use of individual plants in an undisturbed field environment are not available. We assessed the applicability of the stem heat balance method, using commercially available gauges, to determine the daily and seasonal water use of three-year-old Chardonnay plants in New Deal, TX. We first evaluated the gauges in the field by simultaneously measuring the hourly and daily water use of a potted three-year-old Cabernet Sauvignon plant gravimetrically and with a stem flow gauge. Second, we measured, over a period of 100 days between anthesis and harvest, starting on 17 May 1990, the daily sap flow of five Chardonnay plants in a vineyard that was irrigated by flooding. Our results show that the stem flow gauges were accurate within 5% to 10% of the daily value of transpiration as measured gravimetrically. The mean cumulative sap flow of the plants in the field over the entire measurement period was 461 ± 44 kg/plant or 124 ± 12 mm on an area basis. When the total sap flow for each plant was normalized by its leaf area, the variability among plants was greatly reduced. The mean cumulative evapotranspiration (ET) over the 100-day period was measured as 528 ± 13 mm, implying that soil evaporation was 77% of ET. We conclude: (1) that the stem heat balance method is capable of accurately measuring the daily water use of grape plants in the field; (2) that for our experimental conditions, the water use by the grape plants was low compared to the total water loss from the field, to the water use of other field crops in the same area, and to the calculated potential ET of 870 mm.