Evaluation of the Effects of Vineyard Floor Management Practices on Soil Microbiology

Final Report for SW02-008

Project Type: Research and Education
Funds awarded in 2002: $27,496.00
Projected End Date: 12/31/2005
Matching Non-Federal Funds: $21,225.00
Region: Western
State: California
Principal Investigator:
Richard Smith
University of California Cooperative Extension
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Project Information

Abstract:

A long-term comparison of various vineyard floor management practices (weed control and cover crops) indicates that weed control treatments had no impact on soil microbial biomass, but had a significant interactive effect with the rye cover crop on mycorrhizal colonization of grapevine roots, presumably due to differential effects on the composition of weed species that also host mycorrhizal fungi. Cover crops increased soil microbial biomass in the row middles, and there is some evidence that they may increase microbial biomass in adjacent vine rows. Cover crops increased soil organic matter and reduced levels of soil nitrate and phosphorus, which can help reduce losses of these nutrients in runoff.

Project Objectives:

Objectives:
1. To examine the changes that occur over multiple years in microbial biomass, abundance and diversity of soil mycorrhizae, and associated nutrient availability in a long-term evaluation of alternative vineyard floor management strategies in comparison with the standard practices utilized on the Central Coast of California.

2. To extend the information developed by this project through University of California Cooperative Extension viticulture program for the Central Coast and through outreach efforts of the Central Coast Vineyard Team. Outreach efforts are to include field days, seminars, and articles in newsletter articles and industry trade journals.

Introduction:

Cover crops and weed management are components of vineyard floor management and are key components to successful wine grape production. Both cover crop and weed control options have to be considered carefully because they have short-term economic and crop production implications; however, they may also have long-term implications for overall soil health and productivity, which also may affect yield and economic profitability.

Weed management is a key component of vineyard floor management. Weeds compete with grape vines for water, soil nutrients, and sometimes sunlight. Weed competition is most severe during the first three years after planting when vine root growth is limited, but heavy stands of annual and perennial weeds can reduce growth and yield in well-established vineyards (Elmore and Donaldson, 1999). Vineyards with dense weed growth often require additional water and fertilizer to maintain production (Lanini and Bendixen, 1992). Weed management decisions and methods used are based on numerous factors, such as economics, scale of production, terrain, soil type, irrigation method, potential for groundwater contamination, permit requirements, and grower philosophy. Weeds in Central Coast vineyards are commonly controlled either chemically or mechanically in a 2- to 4-foot-wide strip in the vine row.

Cover crops are an important component of a comprehensive vineyard floor management system. They can suppress weeds (Elmore et al. 1997), provide habitat for beneficial arthropod populations (Costello and Daane 1998; and Zalom et al. 1992, 1993), can benefit vine growth and productivity (Costello and Daane 1997; Hirschfelt et al. 1993), can cycle nitrogen for crop growth (Christensen 1971, Hirschfelt et al. 1993), and can improve soil structure and prevention of erosion (Gaffney and Van Der Grinten 1991). The impact of cover crops on soil microbiology has been less well studied. Cover crops increase microbial activity in soil (Wyland et al. 1996, Lundquist et al. 1999 and Scow, 1997) in row crops and in the row middles in vineyards (Lüftenegger and Foissner 1989). However, Ingels et al. (2005) showed that microbial biomass was higher in the row middles where the cover crop was growing and not under the vines on the berm.

Arbuscular mycorrhizal (AM) fungi are an important group of beneficial soil microbes that form mutualistic symbioses with grapevines. They benefit grapevines in terms of improved shoot and root growth (Biricolti et al. 1997; Linderman and Davis 2001; Schubert et al. 1988), higher tissue concentrations of P (Biricolti et al. 1997), and the production of a more compact, highly branched root system (Schellenbaum et al. 1991). In the field, AM fungi naturally colonize the roots of grapevines, as demonstrated by studies on indigenous AM fungi in California vineyards (Cheng and Baumgartner 2004; Menge et al. 1983) and in other grape-growing regions (Deal et al. 1972; Nappi et al. 1985; Possingham and Groot-Obbink 1971). On occasions when AM fungi do not naturally colonize the roots of grapevines, such as after soil fumigation, grapevines may suffer severe nutrient deficiencies (Menge et al. 1983). The results of these studies collectively support the hypothesis that grapevines are dependent on mycorrhizal associations for adequate nutrition.

Vineyard cover crops have been shown to enhance indigenous populations of AM fungi in vineyard soils and grapevine roots (Baumgartner et al. 2005; Cheng and Baumgartner 2005). Vineyard cover crops host AM fungi, with the notable exception of Brassica species (Schreiner and Koide 1993). In California, planting cover crops in between vineyard rows is a common practice during the dormant season, used mainly to reduce soil erosion from winter rains, but also to improve soil fertility and structure (Ingels et al. 1998). Mycorrhizal networks may form in vineyards between grapevines and cover crops, thereby allowing mycorrhizal roots to better utilize nutrients from senescing cover crops, as has been demonstrated in the greenhouse (Cheng and Baumgartner 2004).

There is little known about the effects of weed control practices on AM fungi. Most practices are likely to affect AM fungi indirectly, through their effects on the abundance of mycorrhizal weeds. Possible direct effects of weed control practices on AM fungi are more applicable to practices that involve soil disruption, which would also affect AM fungal propagules in the soil.

One objective of this research was to determine the effects of cover cropping and weed control practices on AM fungi. Our initial study in 2002 and 2003, which was based on seasonal measurements of mycorrhizal colonization, showed that mycorrhizal colonization differed significantly among grapevines in the different weed control treatments, but did not correspond with seasonal changes in total weed frequency (Baumgartner et al. 2005). While total weed frequency might not be a determinant of mycorrhizal colonization in the different weed control treatments, we anticipate that the frequency of certain weed species, and their mycorrhizal status, might be important determinants. In order to address this research question, we focused on annual measurements of mycorrhizal colonization of grapevine roots, instead of seasonal measurements, from 2003 to 2005.

In our initial study, we also found that cover crops had no effect on grapevine mycorrhizal colonization, despite detection of 10-fold higher spore populations in cover cropped middles, compared to bare middles (Baumgartner et al. 2005). Cover crops were mycorrhizal and shared four AM fungal species (Glomus aggregatum, G. etunicatum, G. mosseae, G. scintillans) in common with grapevines, but the lack of close contact between grapevine roots and cover crop roots in the upper soil layer of the vineyard middles may have prevented grapevines from accessing the high spore populations. Therefore, we stopped taking measurements of mycorrhizal colonization and spore populations in the vineyard middles. The results presented here focus on analyses of the annual measurements of mycorrhizal colonization of grapevine roots, collected from 2003 to 2005.

These studies undertook the task of evaluating the impact of cover crops and weed control on microbial biomass and mycorrhizae, and associated impact on crop nutrition. The WSARE funded portion of this study was complemented by funding from the American Vineyard Foundation (AVF) to examine the impact of vineyard floor management practices on crop yield and quality, runoff and water infiltration, weed populations, soil physical properties, and economics. This vineyard floor management was established in the fall of 2000 and evaluations have been conducted over five growing seasons. It has generated a great deal of interest from the growers that are interested in the impact of practices on soil microbiology. At the conclusion of the WSARE funded portion of the trial in 2005 the trial site will continue to be evaluated by other researchers attracted to this project to continue soil microbiological and nutrient cycling evaluations.

Cooperators

Click linked name(s) to expand
  • Kendra Baumgartner
  • Larry Bettiga
  • Louise Jackson

Research

Materials and methods:

The study was established in a drip-irrigated vineyard in the Central Coast grape-growing region of California, USA, in the town of Greenfield (approximately 130 miles southeast of San Francisco, CA). Greenfield has a Mediterranean climate; annual rainfall is low (4 – 8 inches). The vineyard was established in 1996 with Vitis vinifera L. cv. Chardonnay on Teleki 5C (V. berlandieri Planch. x V. riparia Michx.) rootstock. Vine spacing was 8.0 feet between rows and 6 feet within rows. The soil was Elder Loam with gravelly substratum.

Weed control treatments included: 1) standard preemergence (simazine @ 1.8 lb a.i./A + oxyfluorfen @ 1.0 lbs a.i./A) applied in the winter followed by postemergence herbicides (glyphosate @ 2.0% + oxyfluorfen @ 1.0%) applied in the spring and summer as needed with a Patchen® light activated sprayer; 2) postemergence herbicides (glyphosate @ 2.0% + oxyfluorfen @ 1.0%) applied as needed in the spring and summer with a Patchen® light activated sprayer; and 3) cultivation treatment with a Radius Weeder® (Clemens & Co., Wittlich, Germany) cultivator utilized in the spring and summer as needed. The cultivation treatment consisted of a metal bar held perpendicular to the direction of tractor movement. When inserted slightly below the soil surface, it severs weed shoots from their roots. Herbicide applications and cultivations were timed in accordance with grower practices.

Cover crop treatments included: 1) no cover crop (bare ground), 2) Secale cereale L. cv. Merced rye (rye), and 3) X Triticosecale Wittm. ex A. Camus cv.Trios 102 (triticale). Cover crops were planted with a vineyard seed drill in the central 32 inches of the 8.0 feet wide rows just before the start of the rainy season in the winters of 2000-01, 2001-02, 2002-03, 2003-04 and 2004-05. They were mowed in spring to provide frost protection for the vines and they senesced in summer. Before planting new cover crop seed each November, middles were disced to smooth out dried stubble remaining from the previous winter’s cover crop and any weeds that became established during the growing season. Bare ground middles were kept free of weeds with discing during the spring and summer as needed.

Weed control treatments (established in the vine rows) and cover crop treatments (established in the row middles) were arranged in a 3 x 3 split-block design with three replicate blocks, covering a total of 23 vineyard rows (7.0 acres). Each block contained six vine rows and six adjacent middles. Weed control treatments (mainplot treatments) were applied along the entire length of each vine row, which included approximately 300 grapevines. Cover crop treatments (subplot treatments) were applied along one-third of each middle and were continuous across mainplot treatments in each block. Each replicate mainplot x subplot treatment combination included approximately 100 grapevines and covered an area of 0.11 acre. Data were collected from every other vine row and adjacent middle.

Soil microbial biomass: Fourteen microbial biomass evaluations were conducted during this project, eleven of which were conducted with WSARE funding. Evaluations were conducted on the following dates: Nov. 11, 2001; April 15 and August 5, 2002; Jan. 7, April 15, July 1 and Nov. 15, 2003; March 2, June 8, Sept. 7 and Dec. 13, 2004; and March 14, July 7 and Nov. 14, 2005. Soils samples (15 composited from each) were collected from the vine rows of the preemergence and cultivation treatments and the adjacent row middles of the Merced rye cover cropped and bare treatments (only these two treatments were analyzed due to limitations in being able to handle more samples in our lab). A 0.75 inch corer was used to collect soil to a depth of 1 foot in the vine rows; a pick was used to loosen the soil to the depth of 1 foot in the row middles and the loose soil was collected with a trowel. The soil was immediately placed on ice. The samples were transported to the laboratory. On the same day the samples were mixed, weighed and analyzed for soil microbial biomass carbon (MBC). Duplicate 25 g samples from each sample were processed using the fumigation-extraction method (Vance et al., 1987).

Data were analyzed by vine rows or middles by season with a strip-block, repeated measures ANOVA model using the GLM procedure in SAS (SAS System, Version 9.1, SAS Institute, Inc., Cary, NC, USA). In this analysis, between-subject factors were block, weed treatment (main plot factor: Clemens cultivation or standard post-emergence), and cover crop treatment (sub-plot factor: Merced rye or bare ground) and a within-subject factor of year (2001, 2002, 2003, 2004, 2005). The statistical model included the main effects of these factors as well as a subset of necessary and meaningful interactive effects. The same ANOVA model was used over all seasons to evaluate trends in microbial biomass over the five years in the vine rows and the middles. Statistically significant differences in means were separated by Duncan’s LSD or Tukey’s HSD methods.

Mycorrhizae: Grapevine roots were collected on three dates: 16 April 2003, 3 May 2004, 2 June 2005. A shovel was used to collect approximately 8 cm of grapevine root length from every fourth grapevine, giving a composite sample that consisted of roots from a total of 20 grapevines per replicate vine row. Grapevine roots were collected from within 40 cm of the vine trunk, in the upper 30 cm of soil. A subsample of roots was taken from each composite sample and stained using the method of Koske and Gemma (1989). Percent root length colonization of each weighed subsample (0.75 g of fresh roots) was estimated using the grid-line intersect method (Giovannetti and Mosse 1980). Mycorrhizal colonization was expressed as the percentage of intersects where AM fungal structures were present out of the total number of intersects examined (100 intersects) for an average of three grid rearrangements per subsample. Mycorrhizal colonization per 100 intersects was adjusted for percent root length, where root length was estimated from 100 intersect counts (Newman 1966).

Weed species frequency was quantified in replicate vine rows monthly, throughout the growing seasons of 2003, 2004, and 2005. Frequency was measured by placing a 100-foot-long transect line parallel to the vine row and noting the presence or absence of a weed and the weed’s identity every 1 foot. Weed frequency (%) was expressed as the percentage of 100 points along the transect line examined where an individual weed was present. Cover crops were considered weeds when present in vine rows.

Data were analyzed using the MIXED procedure in SAS (SAS® System, version 8.2, SAS Institute Inc., Cary, NC, USA). A three-way analysis of variance (ANOVA) was used to determine the effects of cover crop (bare ground, rye, triticale), weed control (cultivation, post-emergence, pre-emergence), year (2003, 2004, 2005), and their interactions on grapevine mycorrhizal colonization. Cover crop, year, weed control, and their interactions were treated as fixed effects. Block effects and the interactions of block with cover crop, year, and weed control were treated as random effects. Year was treated as a repeated measure. A log10 transformation was performed on grapevine colonization data to normalize variances; reverse-transformed means are presented. Simulation-based t-tests were used for mean comparisons.

Soil and plant nutrition: Plant and soil tissue samples were collected at flowering on May 30, 2003, May 12, 2004, and May 18, 2005. Twenty whole leaves opposite a fruit cluster were collected from each plot. The petioles were removed from the blades and both tissues were dried at 50 °C for 48 hours. Soil samples were collected as described above for soil microbial biomass. The soil was air dried for two weeks. Tissue and soils were sent to the UC, DANR Analytical Laboratory for analyses (see tables 2 – 12 for list of analyses).

Research results and discussion:

WSARE Funded Portion

This type of research requires time to observe trends in microbial populations over seasons and years. After five complete field seasons, clear trends have emerged with regard to the impacts of the vineyard floor treatments on soil microbiology, which are discussed below. This project evolved since its inception in 2000 as an evaluation of alternative vineyard floor management practices to reduce runoff and leaching of the preemergence herbicide simazine. The growers urged us to include evaluations of the impact of vineyard floor management practices on soil microbiology and we were fortunate in 2002 to obtain funding from WSARE to include these types of evaluations. This project has received a great deal of interest as growers are very interested in sound, science-based evaluation of the impact of cultural practices on soil microbiology. We have cooperated with the Central Coast Vineyard Team (CCVT) to conduct outreach to growers on the Central Coast of California, and this project has also been extended through the University of California Cooperative Extension Viticulture Program. The project will continue after the WSARE funds terminate in 2005. Kerri Steenwerth, a USDA Vineyard Specialist based at UC, Davis, recognized the value of this long-term project and initiated soil microbiological investigations at the site in 2005. We are cooperating with her to maintain the plots so that she can conduct phospholipid fatty acid (PLFA) analysis of the microbial community. In addition, this project spurred the initiation of another study examining planting cover crops on the vine row in order to maximize the benefits of cover crops in the zone where most of the vine roots are located.

The following is a summary of the findings of the impact of vineyard floor management practices on microbiology and soil and plant nutrition:

Mycorrhizae:

Mycorrhizal colonization of grapevine roots increased significantly from 2003 to 2005, a finding that was consistent in all treatments and experimental blocks (P < 0.0001; Table 1). Mycorrhizal colonization was 8.75%, 25.98%, and 49.52% for 2003, 2004, and 2005, respectively. The effects of the three weed control treatments on mycorrhizal colonization of grapevine roots were not consistent among the three cover crop treatments; hence the significant weed control treatment x cover crop treatment interaction (P = 0.0394; Table 1). However, they were consistent over time and in all three experimental blocks. Mycorrhizal colonization was higher among grapevines in rows adjacent to rye, relative to those adjacent to triticale or to bare ground (Figure 1). This was the case for cultivated vine rows and for vine rows in the pre-emergence treatment. In contrast, grapevines in the post-emergence treatment had the lowest mycorrhizal colonization when they were adjacent to rye. Weed frequencies that were measured within a few weeks of our collections of grapevine roots did not correspond to the trends we found in mycorrhizal colonization (data not shown). Weed frequencies varied significantly among weed control treatments in 2003, but not in 2004 or 2005; hence the significant weed control treatment x year interaction (P < 0.0001; Table 1). It is possible that the weed species composition &/or the relative abundance of certain weed species in the post-emergence x rye treatment combination is associated with the low mycorrhizal colonization of grapevines in this treatment. Weed species may vary in their mycorrhizal status and, thus, the presence of certain weed species in the vine row may affect mycorrhizal colonization of grapevine roots more than others. Now that all weed frequency measurements have been taken, we plan to determine if there is a relationship between weed species composition in the vine rows and mycorrhizal colonization of grapevine roots. It is possible that the absence of certain weed species from the post-emergence x rye treatment may explain our findings of low mycorrhizal colonization. Abiotic factors, such as soil moisture and soil mineral status, may also be a determinant of mycorrhizal colonization of grapevines. Soil Microbial Biomass: Evaluations of soil microbial biomass of the vine rows and row middles have been conducted over five growing seasons. In the vine rows, preemergence herbicides did not lower microbial biomass in the fall and winter (Figure 2), while in the spring and summer, microbial biomass was higher in the cultivation treatment when adjacent to rye cover crop. Microbial biomass was higher in the spring, summer and winter in the rye cover crop treatment than in the bare row middles (Figure 3). Microbial biomass varied from year to year in both the vine rows and row middles (Figures 4 and 5). These results confirm earlier observations by Ingels et al (2005) that higher microbial biomass is found in the cover cropped than in bare row middles. There was evidence of higher microbial biomass in the spring and summer in the vine rows in the cultivation treatment. It is not clear why this occurred, but the spring and summer are the most active time of year for cultivation. In addition, it is when the cover crop is actively growing and reaches maximum biomass. It is unclear if the increase in microbial biomass is from cover crop root activity or from leaf tissue sloughing over onto the berm. This may be the first evidence that cover crops grown in the row middles may have an impact on soil microbiology on the berms. Soil Fertility and Crop Nutrition: Tissue Analyses: Extensive grape leaf blades and petioles tissue nutrient analyses were conducted from 2003 to 2005. Weed treatments impacts: Weed treatments did not affect leaf blade or petiole tissue nutrient levels in 2004 and 2005 (Tables 2-6). Cover crop treatment impacts: Cover crops had slight impacts on the nutritional status of the crop. In 2005 boron, phosphate and total P were higher in the leaf blade tissue (Table 2) and in 2003 ammonium was higher in the petiole tissue in the bare treatment (Table 6). In 2005 zinc petiole tissue levels were lower in the bare treatment (Table 4). Soil Analyses: Weed treatments impacts: Weed treatments had slight impacts on the nutrient levels in the soil and effects varied among years, for nutrients, and between vine rows and middles. In the vine rows, in 2005, nitrate-N was lower in the cultivation treatment (Table 7), whereas zinc was lower in the cultivation treatment in both 2005 and 2003 (Tables 7 and 9); potassium was lower in the cultivation treatment in 2004 (Table 8), but was higher in 2003 (Table 9). In the row middles, in 2003, chloride was lower when adjacent to the standard weed control treatment, and sodium, calcium and magnesium were higher when adjacent to the cultivation treatment (Table 9). The mechanism for these effects is unclear and these trends in the row middles were not observed in later evaluations in 2004 and 2005. Cover crop treatment impacts: Cover crop treatments had limited impacts on soil nutrient analyses in adjacent vine rows. In 2005 zinc was lower in the vine row adjacent to the bare row middle treatment (Table 7) and in 2003 phosphorus and potassium were higher in the bare treatment (Table 9); also in 2003 the cation exchange capacity was higher in the vine row adjacent to the triticale cover crop treatment. The biggest impacts on soil nutrient levels were from the cover crop treatment in the row middles. In 2005 organic matter, chloride, and zinc were lower in the bare row middle treatment, while phosphorus, sodium, boron, and pH were higher in this treatment (Table 10). In 2004 sodium and nitrate were higher in the bare treatment while organic matter was lower (Table 11). In 2003 nitrate and sodium and boron were higher in the bare treatment while chloride, phosphorus, and organic matter were lower (Table 12). Interesting trends were observed over the three years of evaluations in the row middles. Nitrate, phosphorus and sodium were generally higher in the bare treatment (Figures 6, 7 and 8). Organic matter levels were higher in the cover crop treatments than the bare treatment each year (Figure 9). Weed control treatments did not impact the nutrition of the crop, but did have impacts on soil nutrition that are difficult to explain. Most of the observed difference occurred in the cultivation treatment, and it is probable that soil disturbance and/or loosening and aerating the soil impacted nutrient availability. Cover crops had significant impacts on key nutrients. For instance, cover crops generally had lower levels of nitrate and consistently lower levels of phosphorus. This would be beneficial in reducing loss of these nutrients in runoff and sediment loss during winter storms. Both cover crops consistently had higher organic matter levels than the bare fallow treatment. It is clear from the many benefits of organic matter provide the soil that this is a beneficial trend; however, it is unclear what benefit that increased organic matter in the row middles has on overall vine health. Highlights of the American Vineyard Foundation Portion Funding from the AVF formed an integral and complementary component to the WSARE-funded portion of this project. The AVF funding provided for investigations on the impacts of the vineyard floor management treatments on weed control, water use and runoff, crop yield and quality evaluations, soil physical properties, as well as economic evaluations. These investigations have greatly enriched the analyses and comparisons that we were able to make of the soil microbiological evaluations. In addition, it also greatly assisted outreach efforts for the project because we are able to provide growers a comprehensive evaluation of short-term and long-term impacts of vineyard floor management practices. The following are highlights from the AVF work with specific reference to how they interact with the WSARE funded soil microbiological evaluations: Weed control: Weed frequency was measured 4 to 5 times in the spring and summer. Evaluation of data over five years indicates that distinct weed communities developed in each weed control treatment. There were low levels of purslane (Portulaca oleracea) and shepherds purse (Capsella bursa pastoris) prior to the initiation of the trial; however over five years, purslane and shepherds purse increased dramatically and were the dominant summer and winter weeds in the cultivation treatment, respectively. Likewise in the postemergence treatment horseweed (Conyza canadensis) increased over the years and became the most common weed. This increase in horseweed may be related to the use of the glyphosate and oxyfluorfen combination, which provides limited control of this weed. As a result, the grower applied glufosinate in each of the past three seasons to bring this weed under control. Nutsedge (Cyperus esculentus) was the most dominant weed in the preemergence weed control treatment, because it is tolerant of the preemergence herbicides; however it became under partial control with postemergent applications of glyphosate. Weeds species tolerant of each of the weed control treatments became dominant over the four years of the trial. The presence of weeds may have affected the level of soil mycorrhizae and microbial biomass in some treatments. Soil physical parameters: There were no differences in penetrometer evaluations between weed control treatments in 2003. However, in 2004 the cultivation treatment had greater soil resistance from 4 to 18 inches than the standard weed control treatment. This result illustrates a potential drawback of cultivation as a weed management technique in vineyards. Runoff: The winters of 2003-04 and 2004-05 provided sufficient rainfall to allow measurements of the impact of the vineyard floor management practices on runoff. The cover crops significantly reduced runoff from the plots. This was surprising given that the cover crop strip is only 32 inches wide out of the total 8 foot wide spacing from vine row to vine row. The cover crops also reduced sediment and nutrient loss in the waters. Soil Moisture: Weed treatments had few impacts on soil moisture measurements. Cover crop impacted soil moisture levels. Merced rye had the lowest soil moisture in the spring until April when irrigations were initiated. The cover crop treatments were drier at the onset of irrigations and lateral movement of irrigation water to the row middles was highest in the bare treatment due to higher initial soil moisture levels. Crop yield and quality: No differences in crop yields were observed in any year of the trial between the weed control and cover crop treatments. Differences in the quality of the grapes were observed in the first year of the trial, however, no difference in fruit composition was observed due to weed or cover treatments in subsequent years. It appears that vine growth and grape quality are related to irrigation management practices and in most cases, override the impact of the water use by the cover crops. Economic Evaluation: Partial budget economic analyses were made for each year from 2002 to 2005 of each vineyard floor management practice, which include estimated costs for equipment use, fuel, lube and repairs, labor (machine and field), material inputs, and interest on operating capital. Partial budgets for the postemergence, cultivation and preemergence treatments are shown in table 13 to 15 and are discussed in the section on economic analysis below.

Research conclusions:

This project has provided a comprehensive, long-term evaluation of the impact of various vineyard floor management practices on soil microbiology and other aspects vineyards that are of critical importance to crop production and compliance with water quality concerns. Through the various outreach efforts, we have presented growers with information with which they can assess their operations and make decisions on vineyard floor management options based on their impact on soil health parameters. After the WSARE project is completed we will continue to maintain the treatments in order to enable USDA Vineyard Specialist Kerri Steenwerth, based at UC, Davis, to further investigate the impact of the vineyard floor pactices on other aspects of soil microbiology and nutrient cycling. In addition, the WSARE project spawned a separate follow-up long-term study at a different vineyard in which we will examine the impact of cover crops planted in the vine row. The purpose of this study is to try to bring some of the benefits to the soil that we observed in the row middles where the cover crops are traditionally grown to the vine rows where the majority of the vine roots are located. The growers enthusiastically support both of these ideas in order to see if there are ways to maximize the benefits of cover crops on the soils closer to the area where the vine roots are found.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Six presentations were made to grower groups in 2005 and 16 grower meetings were held over the course of the WSARE project (see list below). The grower meetings ranged from a successful tailgate meeting with the CCVT in 2004, meetings with local vineyard groups, and a large group at the 2005 Sustainable Agriculture Expo. Members of the team made presentations at three professional society meeting since 2003 and published five articles including one in the journal Mycorrhiza. The outreach activities for this project will continue after the conclusion of the WSARE funding. In 2006 Larry Bettiga plans to feature presentation from this project at the Central Coast Wine Grape Seminar in Salinas. He decided this based on feedback that he obtained at the Sustainable Ag Expo in November, 2005 where participants were eager to hear more results of the trials, but time did not allow in his presentation, so he invited participants to come to his meeting in February.

Presentations
Grower Meetings
Sustainable viticulture in California, Unified Wine and Grape Symposium, Sacramento, January 28, 2003 (attendance 500) – Larry Bettiga

Vineyard floor managementp project update, Central Coast Wine grape Seminar. Salinas, CA February 18, 2003 (attendance 60) – Richard Smith

Update on vineyard floor management project, Central Coast Vineyard Team Board Meeting, Soledad, March 11, 2003 (attendance 20) – Larry Bettiga

Long-term impact of vineyard floor management practices on wine grape production, quality and sustainability, Integrated Grape Production Workgroup Meeting, UC Davis, April 29, 2003 (attendance 30) – Larry Bettiga

Grapevine root pathogens versus beneficial root-inhabitants. Mendocino College 2003 Pest Management Seminar. Mendocino College and Lake County Winegrape Commission. Ukiah, CA. November 7, 2003 (attendance 500) – Kendra Baumgartner,

Vineyard floor management alternatives field day and demonstration, Central Coast Vineyard Team Field Day. Greenfield, CA, June 2, 2004 (attendance 29) – Included presentations and discussions by the grower Jason Smith and cooperating researchers on their areas of involvement in the WSARE/AVF funded project: Kendra Baumgartner, Larry Bettiga, Michael Cahn, Laura Tourte and Richard Smith.

Grapevine root pathogens and beneficial root fungi. Current Issues in Vineyard Health. University of California Extension, University of California, Davis. Davis, CA. November 16, 2004 (attendance 200) – Kendra Baumgartner.

Code of Sustainable Winegrowing IPM Workshop. Saratoga, November 18, 2004. “In Vineyard Discussion of vineyard floor management alternatives research” (attendance 34) – Larry Bettiga.

Vineyard floor management alternatives for weed control and their impact on soil microbiology. At the Salinas Valley Weed School. Salinas, CA, November 18, 2004. (attendance 67) – Richard Smith.

Vineyard floor management alternatives for weed control and their impact on soil microbiology and economics. At the University of California Weed Workgroup. Davis, CA, November 16, 2004 (attendance 34) – Richard Smith.

Disease control in California vineyards: shifting the focus from pesticide reliance to sustainable strategies. E & J Gallo Winery, Modesto, CA. February 17, 2005. (attendance 30) – Kendra Baumgartner.
Central Coast Vineyard Team/Paso Robles Vintner and Growers Association Field Day ‘Effect of Spring Rains on Disease and Weed Management Practices in Vineyards,” Paso Robles, CA, June 2, 2005 (attendance 50) – Larry Bettiga
Stewardship for Small Vineyards/ Santa Clara Valley Water District, “Water Quality Impacts of Vineyard Practices,” Gilroy, September 28, 2005 (attendance 40) – Larry Bettiga.

Post-harvest management of vineyards including cover crops, weed control and soil management. Viticulture Association of the Santa Cruz Mountains, Aptos, CA. October 19, 2005 (attendance 41) – Richard Smith.

Evaluation of the long-term impact of vineyard floor management practices, project results. Sustainable Ag Expo, Paso Robles, CA. November 16, 2005. (attendance 250) – Larry Bettiga.

Sustainable disease control for winegrapes – field applications of our research. Napa Sustainable Winegrowing Group. Napa, CA. December 1, 2005. (attendance 30) – Kendra Baumgartner.

Professional Meetings
Arbuscular mycorrhizal fungi in California vineyards. Association of Applied IPM Ecologists. San Luis Obispo, February 4, 2003 (attendance 45) – Kendra Baumgartner

Effects of vineyard floor management practices on mycorrhizal fungi in a Central Coast, California vineyard. American Society for Enology and Viticulture. Reno, NV. June 20, 2003 (attendance 500) – Kendra Baumgartner,

Association of weed species with vineyard floor management practices in California. 2005 American Society for Enology and Viticulture meeting. Seattle, WA. June 22, 2005 (attendance 85) – Richard Smith.

Publications
Bettiga, L., K. Baumgartner, M. Cahn, L. Jackson, R. Smith, and L. Tourte. 2003 Summary of the long-term experiment on the impact of vineyard floor management practices. Proceeding of the Central Coast Winegrape Seminar, UCCE Monterey County Publication.

Baumgartner, K. 2003. Why and how – Encouraging beneficial AM fungi in vineyard soil. Practical Winery and Vineyard, January/February:57-60.

Bettiga, L. R. Smith, M. Cahn and L. Tourte. 2004. Vineyard floor management practices. Update for Winegrape Growers (Central Coast Vineyard Team Newsletter).Summer, 2004.

Baumgartner, K., R.F. Smith, and L. Bettiga. 2005. Weed control practices and cover crop management affect mycorrhizal colonization of grapevine roots and arbuscular mycorrhizal fungal spore populations in a California vineyard. Mycorrhiza 15:111-119.

Smith, R.F., L. Bettiga and T. Bensen. 2005. Association of weed species with vineyard floor management practices in California. Proceeding of the American Society for Enology and Viticulture Meeting, Seattle, WA, page 8.

Cheng, X. and K. Baumgartner. 2005. Overlap of grapevine and cover-crop roots enhances interactions among grapevines, cover crops, and arbuscular mycorrhizal fungi. Pages 171-174 In Soil Environment and Vine Mineral Nutrition: Symposium Proceedings and Related Papers. 29-30 June 2004, San Diego, CA, P. Christensen, D. R. Smart (eds.). American Society of Enology and Viticulture, Davis, CA.

Project Outcomes

Project outcomes:

Weed control and cover crop operations, timing of operations, type of equipment used, number of passes with equipment and chemicals used were documented and analyzed from 2002 to 2005. We met with the growers each year to discuss the operations that we had documented and discussed the associated costs with them to assure accuracy of our estimates. The postemergence and preemergence treatments were generally the least expensive weed control treatments, and the costs tended to fluctuate to some extent based on weed pressure caused by rainfall patterns and amounts. For instance, the spring of 2005 was wet and it prolonged the period of weed growth and resulted in the most expensive weed control year of the four that were evaluated. The cost of cultivation in 2002 and 2003 was comparable to the chemical treatments; however in 2004 and 2005 the increase in weed pressure of common purslane necessitated the use of supplemental hand labor and the costs of cultivation increased dramatically. In summary, the cultivation treatment developed a problematic weed population that drove the costs to high levels. The postemergence treatments maintained good weed control and used small amounts of chemicals. The chemical weed control treatments did not affect soil microbiology in these studies.

Merced rye cover crop increased production costs by $20-30.00 and Trios 102 triticale by $25-35.00. However, this may not be an annual expense as growers usually manage their cover crops to set seed, reducing the need to reseed each year. These increased costs of cover crops do not appear to dampen the interest in the use of cover crops. They have so many beneficial effects in the vineyard (i.e. nutrient cycling and erosion control) and this study indicated that they clearly have beneficial impacts on soil microbiology and nutrient cycling.

Farmer Adoption

This project has attracted a great deal of attention from growers. It is a unique project that has provided a scientific, long-term evaluation of the impact of vineyard floor management practices on common vineyard floor practices. We know that the cooperating grower has modified some of his weed control practices based on the information that we have generated through this project. We are unable to say at this point if this project has influenced other growers, but given the interest in this project and the questions that we receive following presentations, it is clear that this project is stimulating growers to think about their operations and ways to improve health and the long-term productivity of their vineyards.

Recommendations:

Areas needing additional study

Kerri Steenwerth, USDA Vineyard Specialist based at UC, Davis, is interested to follow up on the plot that we have maintained over the past five years and conduct a study in 2006 that will address the following four objectives: 1) quantify annual CO2 and N2O emissions in response to weed and soil management practices and fertigation, 2) determine the impact of vineyard floor management practices on soil C and N transformations associated with CO2 and N2O emissions, 3) create a budget of NO3 leaching below the grapevine root zone in different weed management practices and in fertigated and unfertigated zones, and 4) describe the effect of the vineyard floor management practices and weed control treatments on soil microbial communities and their associated functions in different seasons. Her research will provide much needed information on 1) effects of management practices on soil C and N transformations associated with CO2 and N2O emissions from a perennial agroecosystem, 2) impacts of soil management and fertigation practices on NO3 leaching, which will help vineyard growers comply with water quality regulations, and 3) potential atmospheric impacts of California vineyard management practices on via N2O and CO2 emissions.

In addition, we feel that based on the findings of this WSARE project there is a need to examine the use of cover crops in the vine row to bring the benefits that cover crops provide to the zone of the vineyard floor where the majority of the roots are found. We are currently initiating a study to address this exact issue.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.