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 that there is greater soil microbial biomass in the cover cropped vine row middles over those that were uncover cropped. There were higher spore populations of mycorrhizae in the cover cropped row middles versus the bare row middles in the spring, but this did not affect mycorrhizal colonization of grape roots. Mycorrhizal colonization of grape roots was higher in the cultivation and postemergence weed control treatments than in the preemergence weed control treatment. Treatments with higher levels of mycorrhizal colonization did not have higher nutrient content or yield.

Objectives/Performance Targets

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, and articles in newsletter articles and industry trade journals.

In order to address the objectives listed above we are engaging in a project in which a group of collaborating researchers, a cooperating grower and grower group, the Central Coast Vineyard Team (CCVT), are conducting an on-farm research and extension project in a vineyard in the Salinas Valley of California. The project receives support from two funding agencies: American Vineyard Foundation (AVF) and Western Sustainable Agriculture Research and Education (WSARE). The overall goal of the project is to examine the long-term impacts of vineyard floor practices such as cover cropping and weed control on soil microbiology and physical parameters, plant nutrition, weed control, soil water, runoff, and crop yield. AVF support (which was originally funded by the California Department of Pesticide Regulation Reduced Risk Pest Management Program) addresses the impact of alternative vineyard floor management practices on weed control, grape yield and quality, soil physical characteristics, runoff, as well as the economics of the various alternative practices. WSARE supports the impact of the vineyard floor practices on microbial biomass, abundance and diversity of soil mycorrhizae, and associated nutrient availability. While the funding sources are separate, understanding the multiple components of this system are relevant to understanding the project as a whole, therefore we will mention some of the results from the AVF funded portion of the project in this report. In addition, included are outreach efforts and publications by the researchers this year.

Accomplishments/Milestones

Accomplishments/Milestones
WSARE Funded Portion

The establishment of a long-term research plot of this size (7 acres total) is significant resource. The plot is 23 vine rows wide (8 foot spacing) by 1660 feet long. The plot is planted to one clone of the cultivar Chardonnay on Teleki 5C rootstock. The soil type of the trial site is Elder Loam with gravelly substratum. The main plots are three weed control treatments (1- standard preemergence followed by postemergence herbicides, 2) all postemergence herbicide, and 3) all Clemens cultivator) weed control and within each weed control treatment the plots are divided into three cover crop subplots (1-bare control, 2-Merced rye, and 3) Trios 102 triticale). 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 have been planted in the winters of 2000-01, 2001-02, 2002-03 and have just been established for the 2003-04 season.

This project is entering the fourth year. We have now accumulated sufficient data on the impact of the vineyard floor practices to make preliminary observations on the impacts of these practices on the soil microbiology and plant nutrition. Significantly greater microbial biomass was observed in cover cropped than the uncover cropped row middles, but no differences have been observed among the weed control treatments. There have been significant differences in mycorrhizae observed among the weed control treatments. For instance, lower mycorrhizal colonization was observed in the preemergence herbicide treatment and higher mycorrhizal colonization was observed in the Clemens cultivation and postemergence herbicide treatments. This observation will be repeated this coming season, but it could be due to direct impact of the preemergence herbicide on mycorrhizal colonization. Cover crops had no effect on mycorrhizal colonization of vine roots. The greater levels of mycorrhizal colonization on some weed treatments did not affect the nutritional status of the plants.

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

Microbial Biomass:

Samples for soil microbial biomass have been collected on seven dates (one in 2001, two in 2002 and four in 2003) the last three sampling dates from 2003 have not yet been analyzed due to personnel changes at the Jackson lab. Table 1 shows the microbial biomass of the vine rows by cover crop treatment and the microbial biomass of the row middles by weed treatment. For the last two evaluation dates, microbial biomass has been significantly greater in cover cropped row middles than in uncover cropped row middles. There are no other significant trends.

Mycorrhizae:

Weed control had a significant effect on mycorrhizal colonization of grapevines. Grapevines in rows treated with preemergence herbicides had significantly lower mycorrhizal colonization than that of cultivated rows (Table 2, Figure 1) when averaged over three evaluation dates. Vine rows that received the standard weed control treatment had the lowest mycorrhizal colonization and the lowest weed frequency. Vine rows that received the Clemens treatment had the highest mycorrhizal colonization of grapevine roots and the highest weed frequency. In contrast, the trend between mycorrhizal colonization of grapevines and weed frequency was not observed in the postemergent treatment. Vine rows that received the postemergent treatment had high mycorrhizal colonization of grapevine roots, but low weed frequency.

Since mycorrhizal colonization of grapevine roots corresponded with weed frequency in two of three weed control treatments, the weed control treatment correlation with mycorrhizal colonization may be a function of weed suppression. The weed control effect on mycorrhizal colonization of grapevine roots may, instead, be a function of direct effects of herbicides on grapevine growth. Low mycorrhizal colonization of grapevine roots in the standard weed control treatment, compared to the Clemens and postemergent treatments, may be attributable to direct effects of the herbicides used in this treatment (glyphosate, oxyfluorfen, and simazine) on grapevines.

We anticipated we would find low mycorrhizal colonization in the Clemens treatment, based on past reports of the negative effects of soil cultivation on mycorrhizal colonization. High mycorrhizal colonization in the Clemens treatment (Table 2, Figure 1) may be due not only to high weed frequency but also location of weeds with respect to grapevine trunks. This treatment was done with the Radius Weeder®, which is mounted on an articulating arm that pulls the metal bar out of the soil before it contacts the grapevine trunk, leaving weeds at the base of the grapevine trunk (where grapevine roots are more concentrated and where we collected them from) untouched.

Neither cover crop had an effect on colonization of grapevine roots (Table 2), despite higher spore populations in spring in cover cropped middles compared to bare middles. The cover crops were mycorrhizal and shared four AM fungal species, Glomus aggregatum, G. etunicatum, G. mosseae, and G. scintillans, in common with the grapevines (Table 3). However, we found no contact between grapevine roots and cover crop roots. Even though the cover crop roots were colonized by some of the same AM fungal species as the grapevines, it appears that lack of overlap between their root systems in the vineyard we studied prevented grapevine roots from accessing AM fungal propagules in the middles.

There was a significant effect of season on mycorrhizal colonization of grapevine roots and spore populations. Low mycorrhizal colonization of grapevine roots in spring, which coincided with early bloom, may be due to slow internal fungal growth relative to root growth. Seasonal changes in mycorrhizal colonization of grapevine roots did not correspond to seasonal changes in AM fungal spore populations in vine row soil, suggesting that spores may not be the primary means of colonization of grapevine roots.

Soil Fertility and Crop Nutrition:

Analyses have been conducted for three years on the grape leaf blades and on the grape leaf petioles. The data from the petiole analyses is listed in Table 4; the leaf blade analyses were not available for this report. There are no major differences of note in the petiole tissue analyses from 2003. The previous two years also show no major differences between treatments in grape tissue analyses.

Data from the soil analyses for 2003 are shown in Tables 5 and 6. The row middles in the uncover cropped treatment had higher nitrate (N03-N) and phosphorus (P). This trend is consistent with the data from years one and two, however these previous years showed higher levels of these nutrients in the soil of both the vine rows and the row middles. Higher sodium (Na) in the uncover cropped row middles was also observed in 2003, which is consistent with data from year two. Data from year three also suggest that there is higher sodium (Na) in vine rows that were under the Clemens weed control treatments.

American Vineyard Foundation Portion

Cover crop treatments have been successfully applied for four successive years and weed control treatments for three years thus far. The Clemens cultivator, which is an organically acceptable weed control option, has provided adequate weed control, but it has the following challenges: It has a higher cost than the preemergence and the postemergence weed control strategies. It also, leaves weeds around the trunk of the vines, which have been removed by one hand weeding for the past two seasons at substantial additional cost. One concern over the use of the Clemens cultivator was adverse impact on soil physical parameters; however, we did not observe a negative trend in the soil penetrometer readings taken in 2003. No differences in yield have been observed in the three years and the observed impact of cover crops that was made in year one appears to be related to irrigation management practices that in most cases are able to override the impact of the water use by the cover crops.

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

Weed control:

The impact of the various weed control strategies was evaluated by measuring weed frequency on four dates in 2003 (see Tables 7-11). The Clemens cultivator treatment had higher weeds for most evaluation dates. The notable exception to this trend is the second evaluation in May, when weeds were counted immediately after the monthly cultivation and weed populations were lower in comparison to the other treatments. In general, this trend has been the same over the last three years.

Also as seen in previous years, the postemergence treatment had higher weed populations near the middle of the year which indicates that the postemergence program needs to be more aggressive in controlling early season weeds, especially where marestail (Conyza canadensis) is present. Marestail was brought under good control by the use of Rely (glufosinate) after the third evaluation date.

Plots with cover crops in the row middles had higher populations of weeds in the vine row berms on the first three evaluation dates, but not for the later weed counts.

Soil physical parameters: Soil compaction was measured once in 2003 (Figure 3). While very few differences were detected with these measurements, one interesting finding was that cover cropped soils were significantly more compacted at deeper depths (8-12 cm) than uncover cropped soils. This may be because the cover crops take up more water and dry up the soil in the subsurface layers.

Runoff: No runoff events occurred in 2003.

Economic evaluation: Economic analyses have been performed for each alternative 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. Results from partial budget analyses show that costs range from a low of $87 per acre for the post-emergence/bare ground treatment combination to a high of $150 per acre for the Clemens cultivation/Trios 102 treatment combination.

Crop yield and quality:

No differences in crop yield were observed this year (table 12), as was the case in the previous two years of the trial. However, differences in the quality of the grapes were observed in the first year of the trials. 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.

Outreach

A total of seven presentations were made that discussed the results from this project to the CCVT, local growers, and growers in other parts of the state. A good mix of audiences were reached from the board members of the CCVT to large statewide audiences. Grower interest in detailed soil microbiological impacts of vineyard floor management practices is high. In addition, three publications were submitted or published this year.

Presentations:

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

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

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

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

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 Baumgarder,

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 30) – Kendra Baumgarder,

Publications
Bettiga, L., K. Baumgartner, M. Cahn, L. Jackson, R. Smith, and L. Tourte. Summary of the long-term experiment on the impact of vineyard floor management practices. Proceeding of the Central Coast Winegrape Seminar (in press).

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

Baumgartner, K., Smith, R.F., and L. Bettiga. In Review. Weed control practices and cover crop management affect mycorrhizal colonization of grapevine roots and arbuscular mycorrhizal fungal spore populations in a California vineyard. Mycorrhiza (submitted July 25, 2003).

Impacts and Contributions/Outcomes

Impact and Contributions/Outcomes

This project is starting to mature as it enters its fourth year. All of the observations on soil microbiology must still be considered preliminary at this point, but it will be interesting to see if the trends that we have observed thus far continue into subsequent years. Growers are interested in research based information that sheds light on processes that occur in the soil. Currently, there are many questions that growers have about the impact of their management practices on soil and crop production. Soil microbiology is probably the most difficult aspect area for growers to gain reliable information. This long-term trial has the potential to provide information that helps growers to make informed decisions about their use of alternative vineyard floor management practices.

Key trends that have been noted over the past three years include higher nutrient levels found in uncover cropped soils which suggests that using cover crops conserves nutrients and limits the potential for leaching. We also have seen a trend of greater microbial biomass in cover cropped soils. While this is no surprise, it is important data for growers seeking factual information about cover crops, as microbial biomass can be an important indicator of soil health. As we continue to analyze and take this data, we will be looking for possible differences in microbial biomass between soils treated with herbicides and those that have been cultivated.

In addition, data on the mycorrhizal colonization of the vines from the past year has been very interesting. The low colonization rates of the standard weed control treatment may be an important piece of data that calls for the careful consideration of alternative weed control practices. Data from the coming year may help us sort out the effects of weed treatment and weed growth on the colonization rates.

Collaborators: