Measuring vine transpiration using sap flow sensors: Validation/calibration of a new sap flow technique on large grapevines growing in a weighing lysimeter

Weighing lysimeters are the standard for crop evapotranspiration (ETc) measurements. A large weighing lysimeter at the Kearney Agricultural Center has been successfully used since 1987 to measure water use of Thompson Seedless grapevines during vineyard establishment and once the vines were mature. While weighing lysimeters will provide a direct measure of grapevine water use, they are expensive to build and much time is needed to ensure their measurements are accurate. An alternative, allowing the accurate measurement of many vines at one time and highly portable, would be useful in viticulture. One such technique would be the use of sap flow sensors, which have been used to measure transpiration of young and mature grapevines. In this study we further developed and implemented a newly modified sap flow technique capable of precisely measuring both high and low rates of grapevine transpiration. The output of the sensors was then validated against transpiration of vines growing in the weighing lysimeter.

The compensation heat pulse method (CHPM), which has been shown to work well under high flow rate conditions, and the heat ratio method (HRM), shown to work well under low and reverse flow conditions, were used to measure sap flow in this study. These sensors were installed in the trunks of the vines in the lysimeter and on several vines growing outside the lysimeter. Sap flow velocity was converted into water volume per hour by obtaining an estimate of the cross-sectional area of the trunk’s xylem active in the transport of water. In addition, a mini-lysimeter (small grapevines growing in a pot setting on a scale) was also used to make a comparison between water use and sap flow measured with the sensors.

Grapevine water use measured with the weighing lysimeter is minimal during the evening and increases rapidly during the day with a maximum value near solar noon and then decreases as the sun sets in the afternoon. During the 2008 growing season maximum daily water use was in excess of 65 L day-1 (> 17 gallons) with maximum hourly water use of 8 L (~2.1 gallons). The maximum crop coefficient was greater than 1.35, which occurred the end of July. The daily patterns of sap flow velocity measured with the dual CHPM-HMR method mimicked the daily pattern of grapevine water use measured with the weighing lysimeter. Peak values of sap flow velocity converted to liters of water per vine per hour were similar to those measured by the lysimeter. The sap flow sensors responded quickly to changes in grapevine water use brought about by shading the vines for an hour and then removing the shade. The sap flow sensors also demonstrated the decrease in daily water use after irrigation was terminated for a period of 9 days and then showed a rapid increase in water use once irrigation resumed.

The results indicated that water use measured with the weighing lysimeter and with sap flow sensors were highly correlated with one another. The CHPM method was able to measure high flow rates while the HRM method was somewhat better at detecting low flow velocities. Once the cross-sectional area of the xylem active in transporting water has been determined, values of grapevine transpiration will be accurately determined with the two sap flow methods used in this study.

Evaluation of irrigation management based on local crop coefficient measurements

This project continues earlier work in the use of solar panels as shade-measuring devices, for estimating the percentage of the vineyard floor shaded by the vine leaf canopy, which is the same as the amount of direct sunlight intercepted by the leaf canopy. The primary use of the shade area value is to calculate the irrigation crop coefficient, based on a relationship developed by Dr. Larry Williams at the Kearney Ag Center.

In the 2007 work, the method was used to track the evolution of the midday canopy shaded area in an irrigation trial near Paso Robles. Companion readings of other water-related measurements, including leaf water potential, soil moisture, and leaf temperature, were also made throughout the season.

The shaded area values were used to calculate the site-specific crop coefficient throughout the season, and then to express the actual applied irrigation amounts for the different treatments as percentages of the full vine water requirement, e.g the {aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of Full ETc.

Comparisons of the {aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of Full ETc values to leaf water potentials showed some correlation, but not a very strong one. Comparisons with the leaf temperature readings made throughout the season will be done in early 2008.

Further evaluation and testing of the shade-measuring device increased our understanding of the possible degree and types of error associated with using the method. Tests of the effects of the height of the shade source above the solar panel indicated that a relatively small error occurs as the shade height increases, due to reflected light from surrounding objects. Leaf tissue was found to have similar shade-producing effects as opaque cardstock, as far as the response of the solar panel was concerned. Lastly, alterations of the electronic circuit in the device to improve reliability also led to fundamental a change in the device response, meaning that a device-specific calibration will be required.

The Influence of Deficit and Dryland Irrigation onRoot Distribution, Root Water Relations and Fruit Quality & Yields

The overall goal of this project is to develop a basic understanding of temporal and spatial patterns of root survivorship in the drip irrigation zone, and in dry soils outside the wet-up zone, and to assess how such heterogeneity in available water influences vine performance in a wine grape vineyard. The project is ongoing and is being carried out in an established 11-year-old Merlot vineyard at the UCDavis Research Station in the Oakville Region of Napa Valley and the vines have been subjected to deficit and dryland irrigation treatments for four years. The response is being assessed for two rootstocks (Vitis berlandieri x V. rupestris cv 1103P and V. riparia x V. rupestris cv 101-14 Mgt) that are popular in upland (1103P) and valley (101-14) sites in the North Coast and other regions. The project has been a collaborative effort between U.C. Davis (D.R. Smart) and the Pennsylvania State University (D.M. Eissenstat). During the first three years following the initiation of the study, we have achieved a better understanding of root growth and survival through pursuit of several objectives. These objectives and the insights they are providing are of great value to wine grape, table grape and raisin grape growers. In this investigation, for example, we have documented that water can be transported, through flow eversal, throughout woody tissues of the vine by moving it axially across the high resistance transport pathways of stems. These findings provide tremendous insight into water transport processes that may be of fundamental importance for other high priority research issues in California viticulture like berry shrivel, where one hypothesis is that reversal of water flow leads to loss of berry turgor. Our results concerning root survival are providing further insights into the role root system health, or sustainability, plays in yield decline under deficit irrigation. The two rootstocks have had diametrically opposite responses to irrigation deprivation. We have found that rootstock 101-14 has diminished capacity for roots to absorb nitrogen (N), and is not very responsive to N fertigation treatments (15 to 40 kg N ha-1). One major consequence of this difference results in lower yeast assimilable nitrogen contents in musts of 101-14, and this N deficiency has had a strong influence on fermentations and wine quality. We have documented that phylloxera plays a major role in the longevity of fine roots of the two rootstocks, even though they are known for good phylloxera resistance. The project is supporting efforts in other laboratories to understand how phylloxera feeding influences root health and the general longevity of these rootstocks. The project has produced no less than five peer-reviewed publications, each breaking new ground in viticulture and the information concerning rootstock behavior under the irrigation deprivation treatments is brought regularly to the organizations such as the Clear Lake Winegrowers Association, the North Coast Viticulture Technical Group, the Sonoma County Viticulture Tech group as well as the regular meetings of the American Society of Enology & Viticulture.

The Evaluation of Continuous Thermistor-based Leaf Temperature Measurements and an Indicator of Vine Water Status in Irrigated Winegrapes

Significant differences in leaf temperature relative to ambient air temperature were discernable for winegrapes under four different levels of irrigation stress. Greater differences in canopy temperature were discernable in the morning as compared to the afternoon, when no significant differences were seen. The method employed uses inexpensive thermistors (temperature sensors), which are placed in direct contact with the underside of leaves; each thermistor is read automatically every 15 minutes with a datalogger, allowing measurements to be taken over the summer season with minimal effort. The equipment has been deployed for two summers with no failures.

The influence of deficit and dryland irrigation on root distribution, root water relations and fruit quality and yield decline

This research focuses on the influence deficit and dryland irrigation on root proliferation, temporal and spatial patterns of water and nutrient availability, fruit quality, and yield loss. The overall goal of this project is to develop a basic understanding of temporal and spatial patterns of root survivorship in the drip irrigation zone, and in dry soils outside the wet-up zone, and to assess how such heterogeneity in available water influences vine performance in a wine grape vineyard. The project is ongoing and is being carried out in an established 11-year-old Merlot vineyard at the UCDavis Research Station in the Oakville Region of Napa Valley and the vines have been subjected to deficit and dryland irrigation treatments for four years. The response is being assessed for two rootstocks (Vitis berlandieri x V. rupestris cv 1103P and V. riparia x V. rupestris cv 101-14 Mgt) that are popular in upland (1103P) and valley (101-14) sites in the North Coast and other regions. The project has been a collaborative effort between U.C. Davis (D.R. Smart) and the Pennsylvania State University (D.M. Eissenstat).

During the first three years following the initiation of the study, we have achieved a better understanding of root growth and survival through pursuit of several objectives. These objectives and the insights they are providing are of great value to wine grape, table grape and raisin grape growers. In this investigation, for example, we have documented that water can be transported, through flow reversal, throughout woody tissues of the vine by moving it axially across the high resistance transport pathways of stems. These findings provide tremendous insight into water transport processes that may be of fundamental importance for other high priority research issues in California viticulture like berry shrivel, where one hypothesis is that reversal of water flow leads to loss of berry turgor.

Our results concerning root survival are providing further insights into the role root system health, or sustainability, plays in yield decline under deficit irrigation. The two rootstocks have had diametrically opposite responses to irrigation deprivation. We have found that rootstock 101-14 has diminished capacity for roots to absorb nitrogen (N), and is not very responsive to N fertigation treatments (15 to 40 kg N ha-1). One major consequence of this difference results in lower yeast assimilable nitrogen contents in musts of 101-14, and this N deficiency has had a strong influence on fermentations and wine quality. We have documented that phylloxera plays a major role in the longevity of fine roots of the two rootstocks, even though they are known for good phylloxera resistance. The project is supporting efforts in other laboratories to understand how phylloxera feeding influences root health and the general longevity of these rootstocks.

The project has produced no less than five peer-reviewed publications, each breaking new ground in viticulture and the information concerning rootstock behavior under the irrigation deprivation treatments is brought regularly to the organizations such as the Clear Lake Winegrowers Association, the North Coast Viticulture Technical Group, the Sonoma County Viticulture Tech group as well as the regular meetings of the American Society of Enology & Viticulture.

Comparison of Irrigation Management Strategies to Optimize Wine Grape Productivity and Fruit Composition

A study was continued in a Cabernet Sauvignon vineyard at the J. Lohr Winery near Paso Robles during 2005. Treatments included three irrigation strategies: sustained deficit irrigation (SuDI – where vines are irrigated at some fraction of vineyard water use throughout the season), regulated deficit irrigation (RDI ? where vines are deficit irrigated as some time during the growing season [in this study between set and veraison or veraison and harvest]) and depletion of soil moisture (an irrigation event takes place once every two weeks). Applied water amounts at various fractions (0.375, 0.56, 0.75 and 1.12) of estimated ETc were included in each of the irrigation strategies, with the exception of the soil water depletion treatment. The PRD irrigation technique was not used in 2005 in this portion of the trial as it was not shown to differ from the SuDI technique in 2002 and 2003. However, a separate study comparing the following three irrigation treatments 1.12, 0.56 SuDI and 0.56 PRD was continued in 2005.

Vine water status was monitored throughout the growing season. The results indicated that the leaf water potential of vines irrigated a specific fraction of estimated ETc were similar regardless of irrigation management technique. For example, if the vines were irrigated at 0.375 times ETc, midday leaf water potential was similar regardless if sustained deficit irrigation (SuDI) or regulated deficit irrigation (RDI) was being used at the time the measurements were being made.

Berry size of vines deficit irrigated (0.375 and 0.56 of ETc) between berry set and veraison and then irrigated at greater applied water amounts thereafter (1.12 ETc), was greater than those of vines deficit irrigated throughout the growing season and those deficit irrigated between veraison and harvest. However, berry size of vines that were deficit irrigated between veraison and harvest were larger that those of vines deficit irrigated season long. Berry size of vines irrigated only once every two weeks was not significantly different than those on vines irrigated at the 0.357 ETc amount using SuDI.

As applied water increased yield increased. Yields of vines irrigated at 0.375 and 0.56 of ETc using SuDI, were 70 and 83{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23}, respectively, that of vines irrigated at 1.12 of estimated ETc. Deficit irrigating vines between veraison and harvest reduced yields approximately 23{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} when compared to the 1.12 treatment. Small lot wines were made at J. Lohr winery of all the irrigation treatments used in 2005. They have not been analyzed as of the date this report was written.

Water Relations Factors Relating to Syrah Disorder on the Central Coast

The 2005 research on Syrah Disorder on the Central Coast continued to look at the effects of environmental variables on symptom expression; in particular, water stress and salinity stress were analyzed in more detail. Work also continued to investigate a potential common virus in affected plantings.

The applied irrigation treatments and salinity treatments led to measurable differences in leaf water potential, stomatal conductance, and berry weight, but did not lead to notable differences in leaf symptoms at the two principal research sites. However, both of the experimental blocks as a whole displayed very different symptom expression in 2005 as compared to 2004; one block had very delayed and reduced symptoms as compared to 2004, while the other block had much more severe symptoms. This suggests that environmental influences on a larger scale (such as winter rainfall amounts, crop load, etc.) do play some role in symptom expression. Continued virus testing has not yet identified a common pathogen that could explain the symptoms, which in many instances resembles leafroll virus.

Cultural Practices for Integrating Arthropod Pest management with Improvements in Grape and Wine Quality

Research has shown leafhoppers (Erythroneura spp.) to be sensitive to vine water stress: Leafhopper adults lay fewer eggs on grape leaves and leafhopper nymphs have higher mortality. In our previous studies we have found second generation leafhopper nymphs to be dramatically lower under a mid-season deficit irrigation regime. In addition, vine water stress, either just prior to harvest, or more recently, mid-season, has been used to improve the color and flavor of wine. The aim of our study is to use one vineyard cultural practice, i.e., timely deficit irrigation, to achieve several goals: 1) Decrease density of leafhoppers 2) Improve quality of winegrapes and 3) Make more efficient use of water. We set up an experiment in a Paso Robles vineyard to compare two deficit irrigation treatments to the grower?s standard irrigation practice, which was to irrigate as close to the full evapotranspirative needs of the vineyard as possible (i.e., 1.0 ETc). One of our treatments was to reduce that to 50{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} (i.e., 0.5 ETc) between berry set and veraison and the other was to reduce that to 25{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} (i.e., 0.25 ETc) between berry set and veraison. The actual deficit irrigation period was between June 6 and August 20. Leafhopper numbers early in the season were quite high, and a communication error with the spray crew did not protect our study site from being treated with an insecticide, and we therefore lost the leafhopper data for the 2001 season. We estimated vine water stress by taking measurements of leaf water potential every week. Water stress did not show up until 4 weeks after the deficit irrigation treatments were initiated, and for the next six weeks, water stress was about 5{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} higher under the deficit irrigation treatments, but there was no stress difference between 0.5 ETc and 0.25 ETc. We also made weekly measurements of stomatal conductance, which is a measure of the leaf gas (CO2 and water) exchange rate (measured in mol m-2 s-1). Stomatal conductance was about 40{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} higher in the 1.0 ETc treatment than the deficit treatments for the entire period measured, but again, there was no difference between 0.5 ETc and 0.25 ETc. At harvest, we took berry samples and analyzed them for sugar (°Brix), size (berry weight) and color (skin extraction), and we took yield samples in each treatment. Yield was about 25{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} lower in the deficit irrigation treatments compared to 1.0 ETo, and again, there was no difference between the 0.5 ETc and 0.25 ETc.treatments. Neither °Brix nor berry weight differed among any of the treatments. Color intensity of the skin extraction was highest in 0.50 ETc, and significantly different from 1.0 ETc, but not 0.25 ETc In winter we took pruning weights as a measure of vine vigor. Compared to 1.0 ETc, vigor declined by about 30{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} in the 0.25 ETc treatment, but no significant difference was detected in the 0.50 ETc treatment.

PDF: Cultural Practices for Integrating Arthropod Pest management with Improvements in Grape and Wine Quality

Effect of Irrigation Frequency on Productivity of Thompson Seedless Grapevines Grown in the San Joaquin Valley Using Drip Irrigation

The last of a four-year study to investigate the effects of irrigation frequency on Thompson Seedless productivity was concluded in 2001. The irrigation frequency treatments included: a.) The application of water whenever the vines in a weighing lysimeter used 2mm (2.11 gallons) of water, b.) The application of water once a day (the amount being equivalent to the day’s use of water by the lysimeter), c.) The application of water every three days (the amount being equivalent to three days use of water by the lysimeter) and d.) The application of water once a week (the amount being equal to seven days use of water by the lysimeter). In addition to the frequency treatments, water was applied in three different amounts: 60, 80 and 100{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of lysimeter vine water use. Lastly, three different trellis treatments were included. The trellis treatments consisted of a single wire, a 0.6 m (2 ft) crossarm and a 1.2 m (4 ft) crossarm. Vine density in the vineyard was 1318 vines per hectare (533 vines per acre).Irrigation of the vines in the lysimeter and the rest of the vineyard commenced on May 29th. Vine water use between budbreak and harvest was 4599 liters (1217 gallons). The water use between budbreak and harvest was equivalent to 609 mm (approximately 24 inches). Applied water between budbreak and harvest was 3915 liters (1035 gallons) or 518 mm (20.4 inches) of water. The amount of water applied to the 60, 80 and 100{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of ET irrigation amounts was 58, 76 and 100{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of actual vine water use (measured with the weighing lysimeter). There were significant effects of irrigation amounts, frequencies and trellis type on berry weight and soluble solids in 1999 and 2000, but no significant interactions. There were no significant effects of irrigation amounts or frequency on final yield in either 1999 or 2000. The results in those two years at the three irrigation amounts were similar to those obtained in previous studies in this vineyard when irrigations commenced prior to bloom, as done in 1999 and 2000. During the 2001-growing season, irrigations were delayed purposely to see how this could affect the results. There were significant irrigation amount by irrigation frequency effects on berry weight, soluble solids and yields in 2001. The delay in starting irrigations resulted in smaller berries for all treatments compared to data from 2000. In general, vines irrigated at the higher frequencies and/or irrigation amounts at 100{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of ETc had the largest berries and highest yields in 2001. These results illustrate that deficit irrigation management practices for Thompson Seedless grapevines can maintain productivity similar to that of fully irrigated vines, if the irrigations are commenced prior to bloom under the conditions of this study.

Effect of Partial Rootzone Drying on Vine Water Relation, Vegetative Growth, Mineral Nutrition, Yield Components, Fruit Composition, and Wine Quality in Sauvignon Blanc Grapevines

Partial rootzone drying (PRD) is an irrigation technique designed to keep part of the rootzone dry and the rest of the rootzone well-watered, in comparison with conventional drip irrigation (CDI) with the entire rootzone irrigated. The objective of this research was to investigate the feasibility and effect of PRD on vine water relation, vegetative growth, mineral nutrition, yield components, fruit composition, wine chemistry, and wine sensory characteristics in mature Sauvignon blanc grapevines (Vitis vinifera L.) grown in the San Joaquin Valley of California. Vineyard water use and canopy microclimate were also evaluated. This study was conducted in a 15-acre bilateral cordon trained mature Sauvignon blanc/Freedom vineyard on Hanford Sandy Loam in the California State University, Fresno Agricultural Laboratory. Treatment factors included irrigation method (PRD and CDI) and irrigation rate (0.4 or 0.8 evapotranspiration, ETc), resulting in 4 treatments, CDI-0.4, CDI-0.8, PRD-0.4, and PRD-0.8. Partial stomatal closure due to reduced irrigation rate resulted in a decrease in stomatal conductance (g), transpiration rate (E), and vine vegetative growth, and in turn, an improvement in water use efficiency. Yield, fruit composition and wine chemistry were not significantly affected by either irrigation method or irrigation rate. Three years? field experiments demonstrated that reducing irrigation rate offers a way for producing a vine with a better balance between vegetative and reproductive development, reducing vine water use controlling vine vigor and canopy density, while maintaining crop yield when compared to standard vineyard irrigation practices. Most of the observed PRD-0.4 effect on vine performance and vine physiology was the result of the reduced irrigation rate rather than keeping part of the rootzone dry and the rest of the rootzone well watered.

PDF: Effect of Partial Rootzone Drying on Vine Water Relation, Vegetative Growth, Mineral Nutrition, Yield Components, Fruit Composition, and Wine Quality in Sauvignon Blanc Grapevines