Towards Resilient and Sustainable Grape Production in the North Central Region with Renewable Mulching Systems

1. Evaluation of the efficacy and horticultural and environmental benefits of different types of renewable biomass mulch

Soil Moisture: A time-domain reflectometer (TDR) soil moisture meter (Spectrum Technologies, Inc., Aurora, IL) was used to measure soil moisture at approximately 2” depth increments in July 2020. The soil moisture meter probes were inserted in the soil under the mulch covers as well as de-hilled soil approximately 6” from the graft unions. The probes were capable of recording soil moisture content at 1.5”, 3”, 4.8” and 8” below the ground level. At least three observations of soil moisture at each depth were recorded for each treatment-replicate. Results suggest that the soil moisture increased with soil depth from 15’s% at 1.5” to high 50’s% at 7”. Unlike 2020, all treatments had similar moisture content at each soil depth (Figure 3).

Figure 3. Soil volumetric water content at different soil depth for different mulch treatments on Regent at the Wooster Research Unit 2.

Infiltration: Soil infiltration rate (unsaturated hydraulic conductivity) was measured in 2020 and 2021. The mini-disk infiltrometer was placed on the soil under the mulch covers and de-hilled soil, approximately 6” from the graft unions, and the amount of water infiltrated was recorded with respect to time for each treatment (Zhang, R. (1997). The suction on the mini-disk infiltrometer was adjusted according to the rate of infiltration. The cumulative infiltration was plotted against the square root of time and a hydraulic conductivity (K) value was determined taking into consideration the respective parameters for the soil type from Van Genuchten tables (Dane et al., 2002; Dohnal et al., 2010). The soil type was classified as silt loam for the experimental site. Even though the trend of soil infiltration increased with mulches, the hydraulic conductivity was not significant among the mulch treatments. (Figure 4).

Figure 4. Hydraulic conductivity for different mulch treatments on Regent grown at the Wooster Research Unit 2

Soil Compaction: Surface and subsurface hardness was measured at 2” intervals of depth when the soil was at field capacity (approximately 48 hours following a soaking rain event) using a FieldScout field penetrometer (Spectrum Technologies, Inc., Aurora, IL). The soil compaction field penetrometer probe was inserted in the soil under the mulch covers as well as de-hilled soil approximately 6” from the graft unions in order to record the soil hardness at a certain depth. The probe was capable of recording soil compaction at 2” depth intervals. One observation of soil compaction was made for each treatment replicate up to 10” depth. Preliminary analysis suggests that soil compaction increased with soil depth but was not different among mulch treatments at each depth Figure 5).

Figure 5. Soil compaction of different mulch treatments at different soil depths on Regent grown at the Wooster Research Unit 2.

Mulching Impact on Weeds and Grapevine Physiology

Weed Infestation: Weed cover percentage was estimated in the 3-ft wide vine rows between the first and last vine of each treatment replicate which included two panels of 24 ft each based on the amount of area that was under weed cover. Weed biomass was harvested in eight 1/4 m² quadrats centered in each row for each treatment replicate around vines 1, 2, 3 and 4 in each panel in order to measure ‘around-vine’ weed biomass. Weed biomass was also harvested in eight 1/4 m² quadrats centered in each row and placed in between vines 1-2, 2-3, 3-4 and 4-5 in each of the two panels for each treatment replicate in order to measure ‘inter-vine’ weed biomass. The weed biomass harvested was classified into grasses and broadleaves and each weed species was identified noting the dominant species for each treatment. Weed biomass was determined by measuring the dry weight of the harvested weeds after oven drying them at 140 °F for 48 hours. The weed cover and weed biomass for different mulch and soil treatments are summarized in Table 7. The mulch treatments were significant for the percentage weed cover. All mulches significantly reduced the percentage weed cover compared to the Soil Hill treatment at the 0.05 level. Wheat straw had the least weed cover followed by miscanthus and corn stover (Figure 6). It is concluded that application of mulch significantly reduced the overall weed growth. The reduction in the amount of herbicides applied and their manifestation into reduced costs will be detailed and a herbicide management plan specific to the mulch treatments will be established while conducting the techno-economic analysis for the mulching practice.

Figure 6. Weed cover of different mulch treatments on Regent grown the Wooster Research Unit.

Yield: Vine yield was measured at harvest time. The yield components consisted of collecting and recording cluster count per vine, crop weight per vine, and 100-berry weight for each treatment-replicate. The Regent variety was harvested in September 2021 and the yield components data were collected for all individual observations of each treatment-replicate at RU2. There was no significant difference in any of the yield components measured (Table 1). It is concluded that mulch has no negative impact on yield of Regent.

Table 1. Effect of mulching on the 2021 yield components of Regent grown at RU2

Fruit Quality: Fruit quality was determined by crushing 100 berry samples and measuring juice sugars, pH and acidity. The 100 berry samples were collected from each treatment replicate at the time of harvest. There was no significant difference in any of the fruit quality parameters measured (Table 2). It is concluded that mulch has no negative impact on fruit quality of Regent.

Table 2. Effect of mulching on the 2021 fruit quality of Regent variety grown at RU2

Scion Rooting: Vine health was assessed by evaluating scion rooting per vine in late summer. Scion rooting readily occurs if soil is left over the graft union. Scion rooting defeats the purpose of the rootstock and the vine size may gradually decline. With the mulching practice, since the mulches were of different types and particle sizes and were kept in place without removal around the graft unions, scion rooting per vine was evaluated at all the experimental sites. Scion rooting was evaluated in the fall of 2021 by recording the number of scion roots per vine which were over 1.5” in length. The number of scion roots of length greater than 1.5” for each treatment were recorded. Miscanthus mulch produced the most roots per vine followed by wheat straw (Figure 7). The significantly high number of scion roots produced by Miscanthus mulch treatment can be attributed to its particle size. Miscanthus mulch treatment applied at RU2 was fine and had particle size less than 1/4” compared to other mulch treatments which had a particle size of over 1”. The smaller particle size would pack the mulch around the graft union and provide a local environment similar to if the graft unions were kept hilled with soil and thus the increase in the scion rooting numbers for the Miscanthus mulch at RU2 was expected. This is not a desirable outcome as scion rooting may lead to phylloxera infection.  Nonetheless, scion rooting can easily be reduced by increasing the mulch particle size (e.g. particle size of 1”). 

Figure 7. Scion rooting of different mulch treatments on Regent grown the Wooster Research Unit.

2. Developing a Mechanized Prototype for Mulch Delivery

Based on feedback from growers at the focus group meeting in February 2020, our engineering team has developed a general blueprint of a mechanized mulching equipment prototype that comprise of: (i) frame to hold the baled biomass and shredder; (ii) baled biomass shredder; (iii) controlled rate bale feeder for shredder; and (iv) mulch discharge device. After a thorough research, we found that there are some equipment in the market that already possess multiple features needed in the prototype.  So, rather than re-invenit the wheel and to minimize cost and maximize efficiency, we purchased an equipment with the above features and that could deliver large size bales. Our plan is to retrofit this equipment and add the missing features to come up with a new prototype that satisfies the needs of grape growers (based on their input). It is our objective to complete these modifications and have the prototype ready this summer-fall (pending on pandemic situation) to test in the field.

 3. Engaging Local Growers with Project Execution

We have used three-prong approach to engage growers with our project.

1. Focus group: Feb 2020, discussion of project execution and sought input on prototype. We invited about a dozen of growers that own/manage small, medium, and large vineyards. Two cooperating growers who were involved since proposal write-up were also invited to participate at this focus group. We presented the project objectives and sought input on the mulching prototype. We received significant feedback that we used in our next step.

2. Stakeholder baseline survey: Grower’s willingness to adopt mulching was assessed via a researcher developed questionnaire in a pre-post test approach. In 2020, Grape growers and/or vineyard owner in the North-Eastern Region were surveyed to learn more about their perceptions of using mulching as a method of winter protection. The online survey yielded 88 responses.

 Demographics: Respondents represented Canada, Connecticut, Maryland, Michigan*, New Jersey, New York, Ohio*, Pennsylvania, and Virginia (*denotes majority of respondents). Most respondents have been growing grapes commercially for 4-10 years (33.7%; mean of 11-15 years); growing on greater than 15 acres (34%; mean 6 -10 acres); growing grafter vinifera grapevines on more than 15 acres (28%; mean 6 -10 acres).

Winter Protection Practices: When asked about winter protection practices, 22 percent claimed they are using hilling up soil to protect graft unions, closely followed by no practices (18%). The majority of respondents are losing less than $250 per acre from cold damage; average loss is about $501-$1000 per acre. The majority of respondents (87%) have heard of using mulching as a winter protection method and about 69 percent knew of the practice of using wheat straw.

Adoption of New Technologies: Respondents were asked a series of questions to understand their perceptions of using mulching for winter protection. The researcher used Rogers’ Diffusion of Innovation theory to build the questions to gauge their perceptions of the technological practice of mulching.

Relative advantage: A potential adopter should perceive that adopting the practice or technology will be more beneficial to them than what they are currently doing. Data indicates that respondents have a neutral perception of the relative advantage of this particular practice. As a practitioner, this may indicate that there should be more information given to grape growers to be able to influence their perceptions of this practice.

Compatibility: Potential adopters must determine if the technology compatible with their current practices. In this case, respondents were mostly neutral in their perception of compatibility.

Complexity: It is important to consider how complex it is perceived by the potential adopter. Data indicate respondents need more information on how to implement mulching to raise their comfort levels with this practice.

Observability: A potential adopter is more likely to implement the practice if they can see the see the results themselves. Results indicate that respondents have not seen visible results from this practice. There is opportunity here to showcase the effects on mulching for winter protection to potential adopters.

Trialability: When seeking to adopt a new practice/technology, potential adopters often would like to try it out with very little risk to them or their operations. This trial opportunity is key to influencing adoption. Data showed respondents ‘neither disagreed/agreed’ with statements about trialability. Potential adopters of the technology should have the opportunity to try the technology out without significant investment/little risk to them.

Affordability: Data indicated that perhaps they do not know how much it costs or perhaps this relates to their perception of the relative advantage of this practice. If they do not see it as neither affordable nor unaffordable, they might not see how it would be a more beneficial practice that what they are currently doing to protect their vines during winter.

Barriers/challenges: Key themes from responses were: time; cost; availability of material; cost vs. benefit; and labor & energy. Overall, the barriers to this practice may be attributed to lack of proper information on costs, labor, etc. The answers indicate that they have formed a slightly negative perception of using mulching as a practice for winter protection – they do not see the relative advantage over what they are doing. Answers to the questions are below.

Overall, it seems that respondents have a neutral perception of this practice. However, their description of barriers and challenges show that they believe the practice to be costly, time and labor intensive, and does not present a sufficient advantage either over another practice they are using or over not doing anything at all for winter protection. To increase adoption of this practice, it is suggested that researcher and practitioners provide more information about the practice, demonstrate the results and advantages to the growers, and allow them to try it out.

3. On-Farm Trials: Three cooperating growers hosted our mulch trials in commercial setting. Actually, the results presented in this report were collected from a commercial vineyard in Geneva, Ohio. It is our plan to continue the project at these commercial vineyards and repeat the trial during the 2020-2021 season.

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