Do cover crops stabilize wine grape productivity in a variable climate?

Do cover crops stabilize wine grape productivity in a variable climate?

Summary

Commonly reported benefits of under-vine cover crops include reduced vine vegetative growth, herbicide elimination, decreased nutrient runoff, enhanced species diversity, and decreased management costs. Here we consider potential for an additional benefit: stabilization of grapevine responses to variable soil moisture availability in the Northeast. In wet years, grapevines exhibit excessive vegetative growth, which can be mitigated by under-vine cover crops’ competition for resources. In dry years, water stress can threaten grape productivity. This inter-annual variation is anticipated to exacerbate with climate change. While the benefits of under-vine cover crops in wet years are well documented, benefits under dry conditions are more speculative. Cover crops have been shown to shift grapevine root distribution deeper. This may improve stability of production in grapevines when conditions are dry. Our proposal will examine Noiret (Vitis vinifera hybrid) vine response to a grass cover crop (Festuca rubra) and moisture availability in Pennsylvania. Above- and belowground responses will be measured in vegetative growth, depth of resource uptake, root characteristics, and rhizospheric microbiota abundance. With targeted examinations of water uptake by roots and whole-vine response, we will provide inference on whether reductions in productivity with drought are mitigated in grapevines with cover crops. In addition, we will address previously undescribed mechanisms of resource competition, including any impacts on microbiota. We anticipate this project to lead to more informed decisions on how to maximize the multitude of benefits associated with under-vine cover crops in the variable weather conditions of the Northeast. 

Objectives/Performance Targets

1. In comparison to grapevines growing in bare soil:

• (a) Under normal precipitation conditions, do under-vine cover crops limit grapevine resource uptake, vegetative growth and fruit production?
• (b) Under variable soil moisture, do grapevines with under-vine cover crops show deeper roots and more stabilized production?
• (c) Do grapevine roots that compete with roots of under-vine cover crops have shorter lifespans and lower root production in shallow soil?

2. Will rhizospheric microbial communities by grapevine roots, including mycorrhizal fungi, be enhanced with under-vine cover crops?
3. Provide information that will assist growers understanding of how under-vines cover crops can regulate vine growth and productivity under variable water conditions.

The achievement of all of these objectives are still in progress, although steps and deadlines are being met as outlined in the proposal with adjustments due to unforeseen obstacles (fully described in part 3). The inability to construct a rain-out shelter and rely on irrigation manipulation has caused a slight shift in objective 1b from the original proposal. The wording has thus changed to “variable soil moisture” from “restricted rainfall”.

Accomplishments/Milestones

Since the award of the SARE grant my project has steadily moved along, but has encountered a few obstacles that required adjustments. Most time on the project was spent late summer and early fall on troubleshooting rain-out shelter design.  We ran into several unanticipated obstacles when factors such as tractor movement and belowground water flow were attempted to be controlled. Although we were able to find a construction solution, the costs were far beyond the scope of this grant. As a result, in order to examine limited water resource impacts, we will rely on variations in irrigation if a significant dry period in the summer occurs. This also meant needing to move the project from the commercial vineyard of our farmer-cooperator, which did not have irrigation installed, to the PSU research vineyard that does have irrigation installed.

Although losing the context of working directly with a farmer-cooperator, the location change brings several benefits. I will be able to more closely monitor and measure the experimental plots because the research vineyard is less than half the distance as the commercial vineyard and our lab has on-site technical support. The young vines to be studied at the site are at a critical stage of root development and are randomized on two separate rootstocks, which will allow a greater depth of inference into vine responses. Additionally, as a research site owned by the university, there is long-term security in the experimental manipulations in order to guarantee possibilities for long-term study. Lastly, with the aforementioned long-term security it will allow us to construct deeper root boxes in order to have a fuller picture of root function.

Root box design began fall 2016, after planting a cover crop at the site in late September. We dug test holes and marked up a design for a deep root box, to 1 m. The boxes will be constructed this winter and installed early spring. This deeper root box will allow more insightful isotopic water measurements this growing season with applications of water now possible at different depths. In addition to depth of water uptake measurements, this growing season all other outlined in the grant will be collected (baseline climate and soil data, grapevine production, aboveground measures, and belowground measures). Statistical analysis for these measures will be completed next fall and winter and results disseminated in spring, as outlined in the proposal.

Impacts and Contributions/Outcomes

Due to the necessity of changing vineyard sites, the project is still in implementation phase and measures need to be collected before anticipated contributions and outcomes will be fully achieved. Measures will be able to provide important inference into how cover crops mechanistically impact vine growth. We anticipate this inference to be important to addressing risks to cover crop adoption so that growers can fully benefit from the herbicide elimination, decreased leachates, and increased wine quality that has been documented with cover crops. Furthermore, we anticipate that results will provide important inference into the potential additional benefit of resiliency to variable moisture conditions that are anticipated to increase with climate change.

Not specifically related to the granted project, we did analyze impacts of cover crop plantings on harvest and juice characteristics at the commercial vineyard experimental plots originally intended to be the study site of this grant. We were able to directly inform the grower that the cover crop did significantly impact certain desirable juice characteristics. Furthermore, this information will be interesting to compare to later findings at the research vineyard, and will likely be discussed in a blog post in the future.

Collaborators: