Characterizing Willamette Valley Soil Moisture and Grapevine Response under Drying Seasonal Conditions

A commercial vineyard in the north Willamette Valley was selected for this research based on the availability of three soil classes of interest that contain vineyards of the same age, cultivar and rootstock. The soil types include volcanic soils, sedimentary soils, and marine sediment soils. Soil moisture sensors were purchased in fall 2019 and installed in January 2020 into two monitoring sites within each soil classification. Soil probes were installed to a depth of 18 and 36 inches under-vine and in the middle of the alleyway between rows. Sensors are currently measuring soil volumetric soil moisture and temperature continuously and will be monitored for three growing seasons. The first vineyard measurements began in 2020. Since funding was received four months prior to this reporting, there is no data to report at this time.

Mitigation of Vineyard Greenhouse Gas Production Using Organic Floor Management

Since April 2013, this study has closely monitored the effects of organic floor fertility strategies (leguminous cover crops, grape pomace composted with manure) in concert with soil carbon storage techniques (biochar and grape pomace compost) Gathered annually are a number of soil, vine, and grape metrics at the University of California Oakville Station. Preliminary effects of these treatments on soil greenhouse gas emissions (nitrous oxide, carbon dioxide, and methane), plant available nitrogen (ammonium and nitrate), soil moisture, vine vigor, and berry quality were discerned. Perhaps the most important results acquired thus far are the monthly trends and magnitude of soil nitrous oxide (N2O) emissions and mineral N availability. Nitrous oxide is a GHG with 300 times the global warming potential of carbon dioxide (CO2), therefore causing significant potential carbon offsets, and limited N fertility was found to severely restrict harvest yields during the decade preceding this investigation. Periods of large N2O production were largely initiated by substantial rain events. When cover cropped or compost supplemented soils were amended with biochar, significant reductions in N2O were observed compared to organically fertilized controls during individual rain periods. However, when organic N fertilizer was not present, biochar-only plots emitted significantly more N2O than conventional controls. There was little difference throughout the year in plant available nitrogen as ammonium (NH4-N) among all treatments, yet a striking contrast in plant available nitrogen as nitrate (NO3-N). Yields have been restored to ca 4+ tons per acre and although yields for the non-conventional treatments were significantly higher in 2013, they did not differ from conventionally fertilized plots in 2014. Thus, this study demonstrates that organic ground fertilizations used in concert with biochar amendments can increase NO3-N provisions while maintaining NH4-N and decreasing vineyard scale N2O emissions.

No significant changes in carbon leaving the soil as CO2 or methane (CH4), were detected on an annual basis. In yearly assessments of total carbon, we were able to determine that both biochar and grape pomace compost did appreciably increase soil carbon content compared to conventional controls upon application. However, we found that the effect of these treatments on annual increases in carbon were negligible but the study will need to continue over years to discern long-term effects.

Update of the Paso Robles Soil Salinity Survey

This 2012 project completed the fourth repeat sampling of soils at vineyards in the Paso Robles Groundwater Basin area. These vineyards are irrigated with groundwater of varying quality, leading to the potential for soil salinity levels to increase over time. Elevated soil salinity conditions will in turn lead to degraded soil quality and reduced vine growth and production. The information on soil salinity levels and trends resulting from this study will enable growers to design vineyards and manage the soil and water to ensure long term sustainable production.

The initial sampling was carried out in 2006 at 100 vineyard sites in the area east of Paso Robles; sampling at the same locations was repeated in 2007, 2009 and 2012. The results have shown a clear trend for increasing levels of the soil electrical conductivity and the soil sodium content; these two factors are the primary salinity parameters of concern in the region. Increases in the soil electrical conductivity imposes additional water stress on the vineyards, and higher soil sodium content leads to degraded soil physical quality with important implications for reducing desirable soil drainage and aeration conditions. The average soil electrical conductivity in 2012 was 3.09 dS/m, which is greater than the standard damage threshold value for sensitive vine rootstocks.

The main salinity toxicity component of concern in the area is boron; this was assessed only in 2009 and 2012, and showed a slight increase over this period. The 2012, over 20%of the sites had soil boron levels that exceeded the standard grapevine damage tolerance range of 0.5-0.75 mg/L. There is concern that boron levels in the groundwater may increase as water levels in the aquifer decline and increased mixing of lower-quality water from deeper in the groundwater basin occurs; thus establishing baseline boron levels will help gauge any such changes over time.

This project has provided an important evaluation of fundamental soil salinity conditions over a broad region, and has identified important trends of interest to the local grape industry. These types of conditions are not unique to the Paso Robles area; other regions of the Central Coast will also have similar conditions due to the use of marginal quality groundwater for irrigation and the lack of effective natural leaching by rainfall. Prudent vineyard managers will assess water and soil salinity factors prior to planting, will choose appropriate rootstocks for the expected conditions, and will manage soil and water to reduce the potential for salinity levels to increase over time.

Pairing Sensor Technology with Traditional Water Relations Parameters to Determine Mechanistic Differences Among Grapevine Cultivars in Response to Soil Water Deficits and Environmental Factors

A study was conducted over a three year period to evaluate traditional (measurement of leaf water potential (Ψleaf)) and new techniques (sap flow sensors and petiole ‘dendrometer’ sensors) to monitor vine water status in the field.  Seventeen red, wine grape cultivars grafted onto 1103P and grown in a replicated trial at the Kearney Agricultural Research and Extension Center were evaluated to determine the appropriateness of Ψleafas a means to determine vine water status.  Four of the cultivars, Cabernet Sauvignon, Grenache noir, Petite sirah and Syrah, were used to evaluate sap flow sensors to measure grapevine transpiration.  Lastly, petiole ‘dendrometers’ were attached to Cabernet Sauvignon and Thompson Seedless grapevines to compare daily petiole diameter variations with measures of Ψleaf and grapevine water use measured with a weighing lysimeter.

One of the criteria for classification as a grape cultivar being isohydric vs. anisohydric is that midday Ψleafbetween a well-watered and water-stressed plant should be similar or at least not significantly different.  If this were the case, Ψleaf could not be used to assess vine water status.  Based upon the clear differences in Ψleafmeasured mid-morning, midday and mid-afternoon between irrigated and non-irrigated vines across years all the cultivars measured in this study would be classified as anisohydric.  Others have suggested that the Ψleaf of a near-isohydric cultivar will decrease in response to soil water deficits but only to a certain level (~ -1.5 MPa for Grenache) while that of an anisohydric cultivar will continue to decrease (values < -1.5 MPa for Syrah).  Midday Ψleaf of water stressed vines before and after veraison of all cultivars were not significantly different from one another and were more negative than -1.8 MPa as would be expected for an anisohydric cultivar.  Therefore the use of midday Ψleaf would be appropriate for use in an irrigation management program.

The sap flow technique used in this study was able to discern volumetric sap flow and sap flow velocity differences among cultivars differing in canopy size with the exception of one case (Cabernet Sauvignon in 2010).  The technique was also able to differentiate between the two irrigation treatments on a daily and diurnal basis.  These differences in sap flow between treatments were also reflected in grapevine Ψleaf measurements.  Lastly, sap flow volume/velocity varied from one day to the other in response to a reduction in evaporative demand across cultivars and irrigation treatment.  However, the values of daily volumetric sap flow in 2011 for the irrigated vines were less than those estimated from the product of the crop coefficient, derived from the shaded area of each cultivar, and daily ETo.  In addition, the diurnal sap flow velocity across cultivars and irrigation treatments appeared to increase rapidly early in the morning and thereafter leveled off.  They did not follow the diurnal pattern of solar radiation as shown in other research.  Therefore, the sap flow technique as measured under the conditions of this study would not provide a reliable, quantitative measure of grapevine transpiration.  As such, it would also not be a stand-alone technique to assist in an irrigation management program, but has some utility in tracking relative changes in water use associated with stress.

A bend or deflection sensitive transducer was used as a means to monitor vine water status, measuring the diameter of a leaf’s petiole and/or the cluster’s peduncle. Daily maximum and minimum petiole diameters and the daily shrinkage were correlated with vine water status or vine water use.  Petioles started to shrink as soon as water use increased as the sun came up in the morning and continued to shrink until the midday peak of vine transpiration (petiole diameter increased as the sun went down in the afternoon).  The daily petiole diameter contractions remained fairly constant when grapevines were irrigated daily at full ETc or numerous times a week when being deficit irrigated.  When irrigations were terminated, daily max and min petiole diameters decreased and the daily contractions increased.  Monitoring peduncles provided the extra benefit of assessing growth rate of that tissue.  Peduncle diameter growth rate was reflective of irrigation treatment when measurements were taken between veraison and fruit maturity.  Further research is needed for this promising technique to assess vine water status to include measurements taken between berry set and veraison.

Berry weight at veraison was a linear function of mean midday Ψleaf measured between the initiation of irrigation and veraison across cultivars.  The change in berry weight between veraison and September 9 was also a linear function of mean midday Ψleaf when measured between those two times across cutivars.  There was a significant interaction between cultivar and irrigation treatment on yield.  Vines with the highest yields that were not stressed between May and veraison or irrigated at 50%of estimated ETc during that time period did not always have the greatest yield when stressed between May and veraison.  These results indicate that cultivars may respond differently to the imposition of water stress at various times during the growing season.  Tempranillo had the greatest water use efficiency (water used per ton of fruit produced) of all cultivars while Freisa and Malbec the least across irrigation treatments.  It is interesting to point out that Tempranillo was least affected by the irrigation treatments imposed in this study during 2012.  These results indicate that wine grape growers may be able to choose cultivars that are inherently more water use efficient.

Evaluation of Soil Salinity Conditions in Central Coast Vineyards

This project evaluated the distribution of soil salinity parameters at mature commercial vineyards representative of the Central Coast. Soil cores were taken at one-foot increments to a depth of eight feet, at locations in the vine row, the wheel track area, and the row middle. The resulting data was presented as cross-sectional contour diagrams which show clearly how soil chemistry has been altered over time at the test vineyards. Of particular interest to growers is the fate of salts in the deeper rootzone, and the success of their salinity management programs to maintain the rootzone in good condition. The results demonstrate the extreme variability that occurs with the distribution of salinity conditions in a given soil, due to the soil physical characteristics, the quality of the irrigation water, and the use of management tools such as leaching and amendments. At the most salt-affected site, the changes in soil chemistry and accumulation of salts in the rootzone are very visible with this analysis, and do much to explain the vineyard symptoms at this site. Other test sites which represented more moderate salinity levels had varying patterns of salinity distribution, influenced to some predictable degree by the general drainage characteristics of the soil and the use of additional sprinkler irrigation. The results of this study should serve to encourage growers in the region to occasionally conduct deep soil sampling to inform themselves as to the condition of this important but often overlooked soil fraction.

Determination of the Vineyard Irrigation Crop Coefficients within the Paso Robles Groundwater Basin ‘Area of Concern’

This project evaluated the irrigation crop coefficient at 84 vineyards east of Paso Robles, which lie within a region previously designated as a groundwater ?Area of Concern? due to declining groundwater levels. The mid-summer measurements, taken during the peak irrigation water use period, indicated an average crop coefficient of 0.53, with a range from 0.27 to 1.03. The significant degree of variability indicates the wide disparity in theoretical irrigation water requirements for vineyards in the area, and supports the practical observations that ?not one size fits all? with respect to vineyard water requirements. The survey results, while of value in and of themselves, will be used primarily in conjunction with the results on an ongoing UCCE vineyard water use survey, to add value to those measurements. Comparing the volumes of water used between vineyards is not a fair assessment of how efficiently water is managed, because it does not take into account the different water requirements for different vineyards. By having site-specific crop coefficient values in addition to the measured irrigation use data, it is then possible to compare water use as the percentage of ETc applied, which is a more robust comparison between different locations.

Viticulture extension seminars in San Luis Obispo and Santa Barbara Counties

This project organized extension seminars on the Central Coast to bring the most current research-based information to the area vineyard industry. At the March 10 Vineyard Soil Salinity Conference near Templeton, speakers from the UCCE, USDA-ARS, and the winegrape industry covered all aspects of salinity and its management in vineyards. Attendance at this meeting was very positive, with 180 registrants; this was a strong indicator of the importance of this issue to the local industry. The Grape Vine Health Workshop Buellton which was scheduled to be held on February 12 in Buellton did not receive similar interest by clientele, and was cancelled due to the low number of registrants.

Key to the success of the Vineyard Soil Salinity Conference was the large degree of cooperation on behalf of Matt Heil of Constellation Wines, U.S. and Chris Cocchiaro of Wild Horse Winery. Their support of providing the meeting venue as well as lunch for the audience significantly lowered the cost of the event.

Influence of Soil Type and Changes in Soil Solution Chemistry During the Growing Season on Vine Growth Parameters and Grape and Wine Quality

The soils situated in the four vineyard blocks have been found to differ significantly in chemical and physical properties. The soils in Blocks 56 and 57 were classified as related Alfisols. The soils in Block 57 had a loam/sandy loam topsoil and a clayey subsoil with an abrupt textural change. These soils were characterized as fine, smectitic, thermic Typic Palexeralfs. The swales in Block 56 contained shallower, less developed Alfisols characterized as fine-loamy, mixed, superactive, thermic Typic Haploxeralfs. These soils had a strong argillic horizon but coarse fragments were also present. The soils in Block 53 were classified as Vertisols; these were fine, smectitic, thermic Haploxererts. These soils were characterized by greater than 30%clay content and a tendency to “shrink/swell” behavior. On the upper part of the topography, the soils in Block 52 were characterized as Mollisols; these were fine-loamy, mixed, superactive, thermic Calcic Haploxerolls. These soils, found primarily on knolls in the landscape, had calcareous seams, laminar lime concretions and an angular blocky structure in the subsoil.

Soil chemistry analyses revealed several striking differences between sites. Notably, the Mollisols and Vertisols had low K+ availability throughout the profiles. Potassium levels were higher in the Alfisols, but only in the superficial horizons. Soil extract Nitrogen and Phosphorous were also comparatively low in the Mollisols. Electrical conductivity, on the other hand, was particularly high in the Ca-rich Mollisols and increased with depth.

The Alfisol (Palexeralf) in Block 57-5 and the Mollisol in Block 52-3 gave contrasting results in terms of vine, fruit and juice characteristics. Vines grown in the Palexeralf had the following characteristics: average to high vine diameters; the highest fruit yield per vine in terms of weight and cluster number of any vines studied; the highest cluster weight of any vines studied. Finally, juice from these vines had the highest °Brix and lowest total acidity of any in the study. In contrast, vines grown in the Mollisol had the lowest vine diameters of any in the study; they also had the highest root density at depth, the lowest fruit yield per vine (in weight), and the lowest berry cluster weights of any in the study. Juice from these vines had the lowest °Brix of any in the study and among the highest total acidity values. Juice properties were surprisingly consistent over two years of study. Blinded sensory analysis of berries from Year 1 revealed an apparent clustering of sensory characteristics along with soil type, and additional sensory analyses are in progress.

Vines grown on the two other soils, the Vertisol in Block 53 and the Haploxeralf in Block 56, showed intermediate characteristics. Vines grown in Block 53 had above average vine diameters, an even root distribution throughout the profile, and average fruit yield. Juice from these grapes had low °Brix and the second highest Total Acidity of any in the study. Vines grown in Block 56 had average vine diameters, high root density near the soil surface, below average fruit yield per vine, and average berry cluster weights. Juice from this site had the second highest °Brix and the second lowest Total Acidity.

Thus, in this study comparing Cabernet Sauvignon grapes of a single clone, on its own roots, grown in four distinct soil types within a single vineyard, vines grown on contrasting soil types had different growth characteristics which were reflected in differences in fruit yield and juice characteristics. Although analysis of data from Year 2 is ongoing, preliminary findings suggest that many of the trends observed in Year 1 are indeed consistent from year to year.

A third year of sampling and analysis will be essential in order to confirm (or refute) these apparent trends. A major emphasis of our work in Year 3 will be to use statistical tools (i.e., multivariate analysis) to determine the extent to which differences in soil physical and/or chemical properties are related to differences in plant growth characteristics, and to grape and wine sensory and/or chemical properties.

Rootstock Tolerance to Soil Salinity: Impact of Salinity on Popular Grape Rootstocks Grown in Contrasting Soil Types

The major goal of this study is to define the tolerance of particular winegrape rootstocks for saline irrigation conditions. This project addresses a problem of major importance for irrigated vineyards in California. The rootstocks and soil types in this study have been specifically selected for their relevance to the California winegrape industry. The soil types in the study area are extensive in the central and southern Coast Ranges, an area of rapid vineyard expansion. During the first year, we accomplished two major goals:

  1. Vineyard site selection, soil sampling and soil characterization.
    The two selected vineyard sites are underlain by contrasting soils. Site 1 contains soil profiles in the Arbuckle series, classified as fine-loamy, mixed thermic Typic Haploxeralfs. These soils contain a thick argillic (clay) horizon and have moderately slow to slow permeability. Site 2 contains soils of the Hanford series, with parent material rich in coarse sand and gravel. These soils are classified as coarse-loamy, mixed, non-acid, thermic Typic Xerorthents. They are coarse textured, welldrained soils with little to low runoff and moderately rapid permeability. These two distinct soil types should provide good contrast for the irrigation studies proposed in this project. Soil chemical analysis is currently underway and will lead to a soil map of the area.
  2. Grafting and planting of 10 rootstocks and own-rooted controls at each of the two vineyard sites.
    During the first year of this project, ten different rootstocks were grafted with Cabernet Sauvignon scion and planted at the two designated vineyard sites. A total of 352 vines were planted at each site. Eighty-eight vines (8 replicates of each rootstock plus ownrooted controls) were planted in each of four rows; the four rows will each be subjected to different saline irrigation conditions beginning in Year 2. The rootstocks were selected based upon their popularity and known hardiness in salt-affected soils; for comparison, a few rootstocks with expected intermediate and low salt tolerance were also included. The final list of rootstocks included 101-14 Mgt, 110R (Richter), 1103 P (Paulsen), 140R (Ruggeri), 1616C (Couderc), Harmony, Freedom, Ramsey (Salt Creek), Schwartzmann, and St. George. Ownrooted Cabernet Sauvignon vines (clone 7) were used as a control. The plants are currently being monitored for growth characteristics but were too small for tissue sampling and analysis to be carried out during Year 1.

Having accomplished these two important goals during Year 1, we hope to proceed during Year 2 to begin the irrigation studies, along with detailed soil water sampling and plant tissue sampling. This project benefits from excellent cooperation with an industry collaborator, who also supplies field labor and some technical support.

Aquaporin-regulated response of grapevine roots to salinity

Soil salinization is an emerging problem in California vineyards. Research is needed to more fully understand the physiological response of grapevine roots to salt stress in order to develop cultural strategies that improve in-field management and to facilitate breeding of tolerance. Upon exposure to salinity, roots often exhibit a rapid decrease of water uptake capacity caused by inhibition of water-channel proteins called aquaporins. Aquaporins are found throughout fine root cellular membranes and can control the efficiency of water extraction from the soil. Prevention and/or alleviation of salinity-induced aquaporin inhibition have been demonstrated for some plants using calcium supplements in experimental conditions. Such a mechanism may contribute to the success of gypsum (i.e. calcium sulfate) applications used to lessen the detrimental effects of vineyard salinity. In the original grant, we proposed to address the following short-intermediate term goals:

  1. To quantify aquaporin response to salinity and the ameliorative effects of calcium in a suite of grapevine rootstocks using both hydraulic physiology and molecular probes under hydroponic and soil growth conditions;
  2. To investigate the role that aquaporins play in grapevine rootstock physiological responses to other abiotic factors (i.e. drought, anoxia, nutrient status) and their contribution to vine vigor. We are on target to achieve these goals over a two year funding period. The awarded monies only became available in October 2008 through a Research Support Agreement (RSA) between USDA-ARS and UCDavis. This delayed the initiation of hydroponic studies and molecular analyses to address the first goal listed above. In the mean time, we initiated studies to address the second goal listed above. The current RSA expires 31 September 2009, and an additional year of funding would be used for a 2nd RSA (01 Oct 2009-31 Sept 2010) that would allow completion of all short-intermediate term objectives.

Our results from summer 2008 indicate that aquaporins play an integral role in water uptake across numerous Vitis rootstocks and respond rapidly to nutrient supplements. Aquaporin activity measured with chemical inhibitors was consistently high among several rootstocks, and responded rapidly to calcium nitrate for 110R. We documented significantly higher inherent aquaporin expression in high vigor and drought resistant rootstocks (1103P and 110R) compared to those with low vigor and drought intolerance ratings (420A and 101-14). These inherent differences may explain the known variation in vigor among these rootstocks, likely play a role in divergent patterns of drought tolerance, and represent potential target genes for breeding similar traits.

Since the start of the RSA in October 2008, we optimized methods to quantify aquaporin gene expression for a range of rootstocks subjected to salt stress in an ebb and flow system. Expression analysis in four rootstocks that vary in salt tolerance (Ramsey, Riparia, French Colombard, Thompson seedless) revealed that aquaporins are highly and variably responsive to salt stress among the rootstocks. Preliminary results are reported here. Fine roots for ten additional rootstocks (3309C, 5BB, 420A, 101-14, 110R, 039-16, 1103P, SO4, 140R, Schwarzman) under salt stress have been sampled, and these samples are currently being analyzed.