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

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

Summary

A long-term comparison of various vineyard floor management practices (weed control and cover crops) indicated no differences in soil microbial biomass in the vine rows, but there was greater microbial biomass in the cover cropped row middles than uncover cropped row middles. Grapevine mycorrhizal colonization was significantly higher in 2004 (25.99%) than in 2003 (8.75%). There were differences in grapevine colonization among weed control treatments. No differences were observed in the nutritional status of the crop due to mycorrhizal colonization. Grower interest in the soil microbiological impacts of vineyard floor practices remains strong.

Objectives/Performance Targets

Objectives:
1). To examine the changes that occur 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. Continue these studies for a minimum of three years to observe long-term impacts

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, articles in newsletters and industry trade journals.

To address the objectives listed above we are examining the impact of various vineyard floor management practices on soil microbiology. We have an assembled group of collaborating researchers, a cooperating grower and the Central Coast Vineyard Team (CCVT), a grower group working on sustainable agriculture. The on-farm research and extension project is being conducted in a vineyard in the Salinas Valley of California. The project receives support from two funding agencies: Western Sustainable Agriculture Research and Education (WSARE) and the American Vineyard Foundation (AVF). WSARE funds supports the objectives listed above on examinations of soil microbial biomass, abundance and diversity of soil mycorrhizae and associated crop and soil nutrition. AVF funds support examinations on weed control, grape yield and quality, water use and runoff, soil physical characteristics, and economic analysis of the vineyard floor management practices. The two funding sources contribute to a comprehensive project that is shedding light on many aspects of the impacts of vineyard floor management practices and allowing us to examine interactions between the components. Both funding agencies are dedicated to outreach and education to the grower community, and through collaboration of the CCVT and the established viticulture program in Monterey County, we are actively reaching out to growers in the Central Coast area of California as well as to other researchers through professional meetings. Although this is the report to Western SARE, we have included currently available results from the AVF-funded portion of the project to make a more complete and comprehensive report.

Accomplishments/Milestones

Western SARE-Funded Portion

A long-term 7-acre research plot was established in 2000. The entire plot is 23 vine rows wide (on 8 foot spacing) by 1,660 feet long (7 acres). The vines are one clone of Chardonnay on Teleki 5C rootstock. The soil type of the site is Elder Loam with gravelly substratum. The main plots are three weed control treatments: 1) standard preemergence (simazine @ 1.8 lb a.i./A + oxyfluorfen @ 1.0 lbs a.i./A) followed by postemergence herbicides (glyphosate @ 2.0% + oxyfluorfen @ 1.0%) applied as needed applied with a Patchen® light activated sprayer; 2) postemergence herbicides (glyphosate @ 2.0% + oxyfluorfen @ 1.0%) applied as needed with a Patchen® light activated sprayer; and 3) cultivation only with a Clemens® cultivator. Each weed control plot is divided into three cover crop subplots: 1) uncover cropped control; 2) Merced rye (a full statured cereal); and 3) Trios 102 triticale (a low growing winter cereal). The treatments are arranged in randomized blocks and replicated three times. Cover crops are planted in the middle 32 inches of the 8-foot-wide vine rows. The cover crops were planted in the winters of 2000-01, 2001-02, 2002-03, and 2003-04, and have just been established for the 2004-05 season.

We have completed four field seasons and trends are beginning to emerge in some aspects of the soil microbiology between treatments, which are discussed below. The interaction with growers on this project has been productive. We had an exceptionally good tailgate meeting on June 2nd this year. The cooperating grower talked about what he has learned from the project, and all of the researchers that are involved in both the WSARE- and AVF-funded portions of this project presented their results. We were encouraged by the growers attending this meeting to continue our soil microbiological investigations and to expand them to include evaluations of the soil microbial communities in the various vineyard floor plots.

The following are the details of the evaluations made on the vineyard floor microbiology and soil and plant nutrition:

Soil Microbial Biomass:

Soil microbial biomass samples have been collected on eleven dates thus far. The 2004 samples were collected on March 2, June 8, September 7 and December 13. All samples were extracted and submitted to the lab at UC, Davis, but the carbon analyses were not available at the time of this writing. The complete 2001 to 2003 results are presented in tables 1 and 2. There was no difference between the soil microbial biomass in the vine row in the standard verses the cultivation weed control treatments (table 1). There was no difference on individual sampling dates in soil microbial biomass in the vine rows adjacent to Merced rye cover crop or uncover cropped row middles, but the mean of all the sampling dates indicates that there is increased microbial biomass in the vine rows next to row middles cover cropped with Merced rye (table 1). It is unclear why this should be the case as there is 12 – 15 inch wheel traffic strip between the row middles and the vine row. In spite of the difficulty in explaining this result at this point, it may be a positive trend for overall soil health in the vine rows, which is the location of the majority of vine roots. There was no difference in soil microbial biomass in the row middles amongst weed control treatments (table 2). However, there was significantly greater soil microbial biomass in the Merced rye cover cropped plots than the uncover cropped row middles on three sampling dates and over all (table 2). It is unclear at this point what the significance of greater microbial biomass in the row middles may have on vines growing in the vine rows, which is also the location of the majority of roots.

Mycorrhizae:

Arbuscular mycorrhizal fungi (AMF) are an important group of beneficial soil microbes that form mutualistic symbioses with grapevines. Grapevines respond positively to inoculation with AMF. Greenhouse studies showed that inoculated grapevines have larger shoot and root biomass, greater P concentrations, and more compact, highly branched roots than noninoculated grapevines. Field studies showed that grapevines become severely stunted in fumigated soil because of the absence of AMF propagules. Soil fumigation may also have long-term effects on AMF species diversity after vineyard establishment.

Vineyard floor management, specifically weed control and cover cropping, impact mycorrhizal colonization of grapevine roots. Past analyses of the relationship among weeds and mycorrhizae in a California vineyard showed that seasonal changes in mycorrhizal colonization differed among grapevines in weed control treatments, but did not correspond with seasonal changes in weed frequency (Baumgartner et al 2005 in press). Differences in grapevine colonization among weed control treatments may, instead, be due to differences in mycorrhizal status and/or AMF species composition among dominant weeds.

In 2003 and 2004, we began focusing on mycorrhizal colonization of grapevine roots and weed frequency in the same vineyard. Specific objectives were: 1) to determine if weed control affects AMF species diversity, and 2) to examine the relationship among weed species diversity and AMF species diversity.

Grapevine mycorrhizal colonization was significantly higher in 2004 (25.99%) than in 2003 (8.75%) (Table 3). Despite these differences, similar trends were observed in both years among the weed control treatment-cover crop treatment combinations (Figure 1). Effects of cover crop treatment, weed control treatment, and year on weed frequency were different from those of mycorrhizal colonization (Table 3). Weed frequency was affected by weed control treatment in 2003, but not in 2004 (Table 4).

Even though mycorrhizal colonization of grapevines in the different weed control treatments did not correspond to weed frequency, it is possible that individual weed species affect mycorrhizal colonization. Dominant weed species varied among cover crop treatment  year  weed control treatment combinations (data not shown). In 2005, we will use a multivariate approach to determine if weed control treatments affect weed species frequency. We will use a similar approach to examine AMF species diversity among the different cover crop treatment-weed control treatment combinations.

Soil Fertility and Crop Nutrition:

Leaf blades and on the grape leaf petioles analyses have been conducted at flowering for four growing seasons. Thus far we have not detected any difference in the nutritional status of the vines in any of the vineyard floor treatments (tables 5 and 6).

Soil samples of the vine rows and the row middles have also been collected at flowering over the past four years. In 2004 we observed greater nitrate in the uncover cropped row middles, which has been a consistent observation over the four years of evaluations (table 7). We did not see higher phosphorus in the uncover cropped row middles in 2004 as was observed in the three previous seasons. Higher sodium was observed in the uncover cropped row middles again in 2004, which was consistent with results obtained in 2002 and 2003. 2004 was the first year that we observed significantly higher levels of organic matter and zinc in the cover cropped row middles than in the uncover cropped middles. In the vine rows there was slightly lower potassium in the cultivation treatment than the standard and postemergence treatments (table 8).

American Vineyard Foundation Portion

The AVF funding covers other investigations underway in the vineyard floor management alternative project. Investigations covered by this project include: weed, water use and runoff, crop yield and quality evaluations, as well as economic evaluations. This part of the project complements the soil microbiological and crop nutrition evaluations that are funded by WSARE. It has also greatly assisted in outreach efforts for the project because we are able to provide growers a comprehensive evaluation of short as well as long-term vineyard floor management practices.

The following are the details of the evaluations made on the vineyard floor weed control, soil physical parameters, runoff, crop yield, and economics:

Weed control:

The impact of the various weed control strategies was evaluated by measuring weed frequency on four dates in 2004. The Clemens cultivator treatment had greater total weed frequency on the spring evaluation dates (tables 9 and 10), but not in the summer evaluations or overall (tables 11, 12 and 13). We have begun to analyze the trends for the three weed control treatments over the past four seasons which indicate that the three weed control strategies have distinct weed communities. There has been an increase in summer annual weeds, in particular common purslane (Portulaca oleracea), in the cultivation treatment. There were low levels of purslane at the trial site prior to the initiation of the trial. However, over the four years that we have conducted the trial, the levels of purslane have increased dramatically in the cultivation treatment. This has influenced the economics of the cultivation treatment because the grower has sent a hand crew to weed out the purslane in the past two years. Likewise, in the post emergent treatment horseweed (Conyza canadensis) has increased. This increase in horseweed may be related to the use of glyphosate and oxyfluorfen, which are both weak on horseweed. As a result the grower has made one application of glufosinate in the past two seasons to bring this weed under control. Nutsedge (Cyperus esculentus) is the most common weed in the preemergence weed control treatment and is generally adequately controlled with postemergent applications of glyphosate. In 2005 we intend to analyze the plant community data in each of the weed control treatments with principle components analysis to better understand the changes in the plant communities in each of the treatments.

Soil physical parameters:

Soil compaction data are not yet available for 2004.

Runoff:

Total precipitation at the field trial was 7.4 inches during the 2002-2003 winter and 7.6 inches during the 2003-2004 winter (Figure 2A and 2B). A majority of the runoff was collected from December 20-23 during the 2002-2003 winter and February 25-26 during the 2003-2004 winter.

The total run-off collected from individual plots during the 2003-2004 rainy season ranged from 15 to 421 gallons or 0.2-7.6 % of a 2 inch rain event in February, and 0.07-2.0% of the cumulative rainfall for the season (Figure 3 A and B). Run-off collected from the bare treatment was significantly higher than in the rye cover crop treatment. Run-off from the triticale treatment was not significantly less than the run-off from the bare treatment. This difference may be due to differences in the percent cover provided by the two cover crops at the time of the 2004 rain event (table 4).

Soil Moisture:

The average soil moisture levels between the vine rows in the 6- to 42-inch layer were significantly different among cover crop treatments during the rainy season. Average soil moisture of the rye and bare treatments was less than in the triticale treatment in early January (Figure 5). The rye treatment had the lowest moisture content during March, presumably because it had the most vegetation and therefore had the highest evapotranspiration rate. The soil moisture levels of all cover crop treatments declined to 18% by late April, after which plots were irrigated (Figure 5).

Average soil moisture levels between the vine rows (middle) in the 6- to 42-inch layer were significantly different among cover crop treatments during the irrigation season. Soil moisture between the vine rows increased the most in the bare treatment after irrigation started, suggesting that more lateral movement of moisture occurred in the bare treatment than in the cover cropped treatments (Figure 6). In contrast, soil moisture levels under the vine rows were high at the start of the irrigation season, declining from 24% to 19% by late September (Figure 7). Differences among cover crop treatments, although statistically significant, were much less under the vine rows than in the middle of the plots.

Crop yield and quality:

No differences in crop yields were observed in 2004 between the weed control treatments (Table 14), as was the case in the previous three years of the trial. For 2004 plots with the rye cover in the middles had significantly higher yields. Although, differences in the quality of the grapes were observed in the first year of the trials little difference in fruit composition has been observed due to weed or cover treatments. It appears that vine growth and grape quality are related to irrigation management practices that in most cases are able to override the impact of the water use by the cover crops.

Economic Evaluation:

Partial budget economic analyses were made for 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. 2004 results were still being analyzed at the time of this report. However, 2002 partial budget analyses show that costs range from a low of $94 per acre for the post-emergence/bare ground treatment combination to a high of $173 per acre for the preemergence/Trios 102 treatment combination (table 15). In 2003 the low was again the post-emergence/bare ground treatment combination at $130 and the high was the cultivation/Trios 102 treatment at $184 (table 15). The post-emergence treatment is economical with regards to herbicides applied per acre. The high cost in 2002 is attributable to the cost of the herbicides and in 2003 the cost of labor to clean up weeds that escaped from the cultivation (i.e. especially around the stems of the vines there the cultivator does not reach).

Outreach:

Central Coast Vineyard Team Tail Gate Meeting:

The highlight of the year was the tailgate session with the CCVT. At this meeting all of the researchers involved with this project presented their results, and in addition, Jason Smith the grower gave his impressions of the project and what he was learning. We had a good number of key growers at the meeting and a good discussion ensued regarding various aspects of the project. One area that growers want further information on is soil microbiology. Growers welcomed the soil microbiological analyses that were presented, but they wanted to know more specifics about the types of organisms and shifts of microbiological communities. After the meeting we discussed this issue and expressed interest that perhaps we could bring another researcher onto the project to address this exact issue. As a result, we are now collaborating with Kerri Steenwerth, USDA Vineyard Weed Specialist at UC, Davis. She has extensive background in soil microbiology and we are currently planning to work with her to conduct phospholipid fatty acid (PLFA) profiles to describe the microbial community composition in the 2005 season. These evaluations are a new development in the evolution of this project which will allow us to delve further into the area of soil microbiology which is an area of interest to the cooperating grower and to other growers in the CCVT.

Other outreach activities

A total of 6 presentations were made by all members of the team working on the WSARE-funded portion of this project (see list below). Presentations ranged from grower meetings and newsletter articles to presentations to other researchers through UC meeting and professional meetings. We have obtained feedback from these presentations. In particular we have picked up good suggestions for aspects of the research that we can conduct in the final stages of the project to answer questions that would be of interest to growers and the scientific community.

Presentations:

Grower Meetings:

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.

Meetings with Professional Colleagues:

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.

Publications:

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

Baumgartner, K., Smith, R.F., and L. Bettiga. 2005 in press. Weed control practices and cover crop management affect mycorrhizal colonization of grapevine roots and arbuscular mycorrhizal fungal spore populations in a California vineyard. Mycorrhiza 14(6).

Impacts and Contributions/Outcomes

We have completed four growing cycles in this project (two with funding provided by WSARE). We are beginning to see trends emerge with regard to the soil microbiology. Growers are interested in the impacts on soil microbiology that we are observing. Interestingly, while they appreciate the observations that we have made thus far, they want more. Kerri Steenwerth, USDA Vineyard Weed Specialist at UC, Davis, is willing to join our project and conduct phospholipid fatty acid (PLFA) profiles to describe the microbial community composition in the various vineyard floor management plots. Her evaluations will be conducted over the 2005 season (the final season of the WSARE-funded project), but we are looking for opportunities to keep this project going and conduct the PLFA analyses in the 2006 season as well.

The evaluations of the impacts of vineyard floor management practices on the soil microbiology project has evolved over the last four years. It was originally funded in 2000 by the State of California Pest Management Alternatives Program to explore alternatives to the use of simazine for weed control, as well as reducing runoff from vineyards. Because we had good commitment from the grower and a well set up plot, growers encouraged us to expand the project and include other research. Specifically growers requested that we explore the soil microbiological implications of the various vineyard floor management practices. That led us to seek WSARE funding, which we were fortunate to receive. Now we are four years into the project and the growers are again pushing us to expand and deepen the level of research. This has been an excellent example of grower-driven research, and we have been fortunate for the most part to be able to meet their requests. Kerri Steenwerth’s work will not be covered by WSARE funding, but WSARE provides us the resources to conduct the studies summarized in this report, which also enables us to expand the scope of the studies and maintain the dialog with growers. It has provided a framework in which a number of other researchers have been able to plug in and contribute. In addition, the AVF also found this project worthwhile and have funded the non-soil microbiological aspects of the project in 2004 with the possibility of continuing in 2005.

At this point this project is providing a comprehensive examination of vineyard floor management practices. This exploration is providing growers with data that are helping them to make decisions on the impacts of vineyard management that range from water use and runoff, weeds, soil microbiology to what the different practices cost. In addition, we have been conducting this project long enough now to begin to see trends in the impacts of the vineyard floor management practices on various aspects of the vineyard. For instance, we are observing changes in the weed population in the vineyard in the cultivation treatment, but we are also able to see how this affects the economics. More subtly, there may be a connection with the weed population and soil mycorrhizae. This is just one example where this type of comprehensive project has allowed us an opportunity to explore a number of production factors and see how they interact with one another over time. We are excited to see if further trends emerge in soil microbiology in the 2005 growing season. In growing systems such as this vineyard some trends take a while to develop and we feel fortunate to have the opportunity with the support of WSARE to undertake these long-term evaluations.

Now that we are entering the final year of the WSARE-funded portion of this trial, we are starting to discuss follow-up research. Based on our experience of vineyard floor management practices we are discussing ways to improve the levels of soil microbiological activity in the vine row. One concept is to look at ways to grow cover crop in the vine row without competing with the vines. One idea is to look at short-term, winter-grown cover crops, which may be able to increase the level of soil microbiology and reduce soil erosion. This concept will be a dramatic change from the way that vineyards are currently managed, and it would be interesting to explore this type of concept in the way that we have evaluated the practices covered in this study.

Collaborators: