Selecting and Managing Vineyard Cover Crops to Reduce Consumption of Net Basin Water

Selecting and Managing Vineyard Cover Crops to Reduce Consumption of Net Basin Water

Summary

A decline in the Paso Robles Groundwater Basin has increased awareness of water conservation practices in vineyards. Cover crops can improve water infiltration from precipitation while also preventing erosion and building organic matter in soil. However, the cost of those cover crops in terms of water use is not well understood in the Central Coast. This is a two-year study to evaluate the effects of cover crop selections and the management of grass cover crops on soil moisture. Neither the selection of cover crop nor the timing and method of terminating a grass cover crop affected soil moisture in the first year.

Objectives/Performance Targets

List of Objectives
(1) Evaluate five cover crop species for their impact on water infiltration, soil moisture retention, and use of plant available water in the vineyard. November – May, 2015-2016.
(1a) Cover crop species will be compared to a non-cover cropped control in three of five sites using a randomized complete block design with three replicate treatments per block, on a 0.5 acre experimental block per site. A field plot example is provided as a supporting document. (November – May, 2014-2016).
(1b) Soil Moisture will be logged with sensors at two depths in three replicate treatments at one of the sites, and gravimetric soil moisture will be measured at two depths in three replicate treatments at all sites.Soil Moisture will be logged with sensors at two depths in three replicate treatments at one of the sites, and gravimetric soil moisture will be measured at two depths in three replicate treatments at all sites.
(1c) Above ground biomass will be measured for each cover crop. (March)
(1d) Effects of treatments on seasonal vine growth will be measured via
dormant pruning weights of vines in each replicate plot.
(2) Evaluate treatments to suppress and terminate cover crops and their impact on water infiltration, soil moisture retention, use of plant available water in the vineyard. November – May, 2015-2016.
(2a) Treatments to suppress or terminate a cover crop including mowing, chemical mowing (a standard systemic herbicide as a control). A cultivation soil treatment and a non-cropped “fallow” treatment will serve as controls.
(2b) Suppression and termination of the cover crops will be tested at two of five sites, randomized complete block design with three replicate treatments per block, on a 0.5 acre experimental block per site. A field plot example is provided as a supporting document. (November – May, 2014-2016).
(2c) Additional data will be collected according to methods described in Objective 1, b-d.
(3) Perform economic evaluation of vineyard floor management practices and document financial return on investment in terms of potential water savings. May – June, 2016.
(4) Promote and maximize the adoption of beneficial practices by producers from the findings of this cover crop project and extended through a well-established portfolio of outreach mechanisms including tailgate meetings, newsletters, email blast, website, social media, fact sheets, presentations, and trade publications. January 2015 – December 2016.
(5) Measure adoption of water conservation practices identified in this project by survey of the producer audience who participate in tailgate meetings, webinar, and online educational module. April 2016 – April 2017.

Accomplishments/Milestones

This project consists of two experiments. The first experiment measures the effect of five species of cover crop (plus clean cultivation as a control) on soil moisture.

TABLE 1

The second experiment measures the effect of six different techniques and/or timings of cover crop termination on soil moisture.

Each experiment was replicated at three sites on the east side of Paso Robles, California with randomized complete block designs.

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The first round of data collection and processing was conducted in April and May of 2015.

Samples for determining soil moisture and cover crop biomass were collected in late April of 2015 and processed at California Polytechnic State University San Luis Obispo.

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The gravimetric soil moisture contents of the soil samples and the dry matter biomasses of the plant samples were measured and datasets for analysis were created.

Table 2

Table 3

Initial results show that the timing and manner of terminating a cover crop did not affect gravimetric soil moisture. Similarly, the selection of cover crop planted did not affect gravimetric soil moisture.

TABLE 4

TABLE 5

At this point in the experiment, the timing and manner of terminating a cover crop in a vineyard did not significantly affect soil moisture. This is especially interesting given that one of the treatments was clean cultivation. One would expect less soil moisture in plots where a cover crop was grown compared to plots with no surface vegetation in the vineyard middles. This is not the case, suggesting that the presence of a cover crop in a vineyard middle during the winter and spring months did not increase the quantity of water that must be supplied to vines through irrigation.

One factor which could have affected this experiment is the lack of rainfall during the winter of 2014- 2015.

TABLE 6

If more water had been available during the growth of the cover crop, differences between the treatments might have been observed. Additional data must be collected in seasons with higher rainfall to determine if seasonal rainfall is a factor. The winter of 2015-2016 (the second year of this project) is expected to be wetter than normal, thus comparison might be possible at the end of this project.

To assess the effects of the experiments on vine growth, cane count and cane weight data is being collected during the winter of 2015-2016.

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At one of the five sites soil moisture sensors were installed (Decagon EC5) and data logged every 30 minutes (Decagon EmB5) to provide data points from more than a single time point in the year. These data are currently being analyzed to provide information on volumetric soil moisture over time.

At the end of the first year of this project two experiments were successfully executed at five vineyard sites. Data were collected from the first year and the experiments have been prepared and planted for the second year.

A fact sheet describing the experiments and preliminary findings has been created and is posted on the Vineyard team website (www.vineyardteam.org).

• Figure 1. Example of experimental design for the cover crop selection experiment as executed at one project site
• Figure 3. Cover crop selections used in this project.
• Figure 4. Cover crop termination methods and/or timings employed in this project.
• Figure 5. Cover crop biomass samples were collected using three randomized samples per replicate.
• Figure 6. Auguring pilot holes for soil samples.
• Table 4. One-way ANOVA of treatment effects on soil moisture- cover crop termination experiment.
• Table 5. One-way ANOVA of treatment effects on soil moisture- cover crop selection experiment.
• Table 6. Precipitation November 2014 to April 2015 compared to 10-year average for same period.
• Figure 10. Pruning vines.
• W-SARE Fact Sheet
• Table 1. Cover crop comparison treatments and cover crop termination treatments in the two experiments.
• Figure 8. Soil samples for gravimetric moisture content collected at 18 and 36 inch depth.
• Table 3. Mean plant biomass (Dry matter, grams) of cover crops sampled April 2015, cover crop selection experiment.
• Figure 2. Example of experimental design for the cover crop termination experiment as executed at one project site.
• Figure 7. Soil samples being taken at 18” and 36” depths for gravimetric water content analysis.
• Table 2. Mean plant biomass (Dry matter, grams) of cover crops sampled April 2015, Cover crop termination experiment.
• Figure 11. Weighing canes after count.
• Figure 9. Counting canes to measure vine growth.

Impacts and Contributions/Outcomes

If results from the second year of the experiments are consistent with the first, the implications for growers are substantial. Fears regarding the depletion of soil moisture by cover crops would be unfounded. Growers can be confident they are not reducing the soil moisture available to their vines as a result of planting any of a broad range of cover crop species. Similarly, decisions about the timing and method of cover crop termination need not take soil moisture depletion into account within the time ranges tested in this study. Higher rainfall has already been recorded in the second year of this project compared to year one, which will allow comparison of cover crop varieties and cover crop termination practices on volumetric and gravimetric soil moisture in two distinct growing seasons.

Collaborators: