Evaluation of the Effects of Vineyard Floor Management Practices on Soil Microbiology
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 the cultivation treatment had higher infection with mycorrhizae presumably due to the presence of more weeds that stimulated mycorrhizal associations. 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.
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.
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 Progam. 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:
Grapevine mycorrhizal colonization varied significantly from year to year (P < 0.0001; Table 1). Colonization increased significantly in each successive year of the study; 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 cover crop treatments; hence the weed control treatment x cover crop treatment interaction (P = 0.0394; Table 1). Similar trends were observed in all years among the weed control treatment-cover crop treatment combinations (Figure 1). Mycorrhizal colonization was higher for grapevines in rows adjacent to rye, relative to those adjacent to triticale or to bare ground. This was the case for cultivated vine rows and for vine rows treated with post-emergence herbicides. In contrast, grapevines in vine rows treated with post-emergence herbicides 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. Abiotic factors, such as soil moisture, may also be a determinant of mycorrhizal colonization of grapevines. Now that all the data for the study have been collected, we plan to examine the relationships among weed frequency, soil nutrition, vine nutrition, mycorrhizal colonization, and soil moisture. Soil Microbial Biomass: Evaluations of soil microbial biomass of the vine rows and row middles have been conducted over five growing seasons. Preemergence herbicides did not lower microbial biomass in the fall and winter (Figure 2). There was higher microbial biomass in the cultivation treatment in the vine row in the spring and summer 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 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. In 2005 nitrate-N was lower in the cultivation treatment in vine row (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 2003 chloride was lower in the row middles adjacent to the standard weed control treatment and sodium, calcium and magnesium were higher in the row middles adjacent to the cultivation treatment (Table 9). The mechanism for this to occur is unclear and this trend was 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 trios cover crop treatment. The biggest impacts on soil nutrient levels were in the cover crop treatment in the vine rows. 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 the level of benefit that increased organic matter in the row middles have on overall vine health.
Impacts and Contributions/Outcomes
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.
USDA Pathologist/Sustainable Vineyard Specialist
Dept. of Plant Pathology, University of California
Davis, CA 95616
Office Phone: 5307547461
University of California Cooperative Extension
Salinas, CA 93901
Office Phone: 8317597361
Associate Professor/Cooperative Extension Speciali
University of California
Dept. of Land, Air and Water Resources
Davis, CA 95616
Office Phone: 5307549116