At Somis in 2018, we observed 3.5 more volunteer raspberry shoots in post rows with mulch compared with other treatments or untreated plots . Unlike weeds, raspberry shoots were able to penetrate mulch and establish, likely benefiting from the greater soil moisture content under it . These results show that weed barrier fabric, mulch and barley can effectively reduce weed control costs in raspberry tunnel post rows, but greater volunteer raspberry shoot management may be required if mulch is used.To estimate the costs of the barley cover crop, we obtained machine use and labor hours for seeding, raking and mowing from cost studies for raspberry production . Cover crop treatment at 500 pounds per acre costs $29.42 for the treatment area minus the weed control benefit of about $18.60, resulting in the net cost approximates of $10.83 for the treatment, or $59.55 per acre per tunnel period . The amount of weed block fabric required for the experimental plot area was 0.22 roll, priced at $349.31 per roll. Ninetymetal pins were used to pin the 1,800–square foot fabric area at a cost of $0.12 per pin. The labor needed for spreading and pinning the fabric in the experiment plot was 1 hour at $15 per hour. Assuming the fabric serves two tunnel periods, raspberries in pots only half of the cost of the fabric material is applied to one tunnel period. Fabric also provides 100% weed control in post rows.

Therefore, the cost of fabric treatment per tunnel period is $29.66 for the treatment area, or $163 per acre for one tunnel period. The volume of applied yard waste mulch should be sufficient to cover the entire post row with a 2- to 3-inch thick layer. Ninety cubic feet of mulch, priced at $0.56 per cubic foot , was applied to the 1,800–square foot treatment area. Delivery and spreading on flat ground with a front end loader and spreader costs $270 per acre. In cases where smaller equipment is used, it would take more labor — at least a day for two people to spread an acre, as it is a slow process and depends on how well the mulch spreads out in the field. In terms of weed control, mulch controlled 70% of the weeds in post row areas. Mulch treatment cost is one of the highest at $35.07 for the treatment area, or $192 per acre per tunnel period. The PAM product was applied at 2 pounds per acre and was priced at $4.00 per pound. PAM was applied six times per tunnel period; hence, the total PAM cost for this treatment is $1.98 for the treatment area. The labor cost for applying PAM was calculated at 250 minutes per acre per time at a wage of $15 per hour. Therefore, the PAM treatment cost became $34.96 per post row, or $192.27 per acre. The costs of the treatments in this study were very low: 0.7% to 2.4% of the total cultural costs of raspberry production . This suggests that little investment in soil and runoff management can be cost-effective over time for sustainable plasticulture crop production.During this trial, California was experiencing the drought of 2011– 2019, and these treatments were used in periods when lower runoff and sediment movement would have been expected. However, we observed similar treatment efficacy during low and high rainfall events in these trials, which suggests the treatments were resilient during wet periods.

The four treatments in the study all reduced runoff flows and sediment transport compared with the untreated rows. However, additional work on runoff flow rates and the effect of infiltration on soluble nitrogen forms is needed to more fully quantify the treatment effects with respect to nitrogen balance in these systems. Our treatment cost analysis serves as a template for tunnel users to assess the feasibility of inputs and costs in their production systems, which may be different from those in this study. During the project we conducted several outreach events for growers and field workers where we displayed the treatments and discussed the in-progress results. At the end of the project, we developed bilingual guidelines for runoff management to facilitate treatment adoptions.These resources enable tunnel users to select best management practices to protect their fields from soil and nutrient losses and to comply with runoff regulations aimed at protecting the environment.Global warming trends due to climate change are likely to continue at the current rate, leading to temperature increases of 1.5–4.5◦C between 2030 and 2052 . Furthermore, changes in precipitation patterns, frequencies of heatwaves, droughts, and a general increase in evapotranspiration rates are also expected . These changes would in turn, affect soil moisture, ground water table, storage of water in reservoirs, and the salinization of shallow aquifers .The effects of climate change are leading to an increasingly negative water balance during the grapevine growing season . The effects have been an advance of grapevine phenology, diminution of yield and a lack of cultivar trait expression at the farm gate . Different approaches have been used in recent years to cope with these effects, such as the use of drought-tolerant rootstocks, clones and/or varieties, improved training systems or increased row spaces, and irrigation applications .

Although winegrowers still prioritize canopy and soil management and changes in harvest date and wine making techniques over water management , use of irrigation in vineyards is inevitable in historically non-irrigated areas due to the warming trends . Furthermore, many of the viticulture areas of the world rely on irrigation for consistent production , such as California, where irrigation is required to overcome the dry and warm summers. Thus, irrigated agriculture in California is the largest consumer of fresh water, which accounted for about 50% of the total water supplied to the state in 2011–2015 . However, water resources, particularly groundwater, have reached a critical state due to extended drought periods, and overuse by irrigated agriculture . In fact, Alam et al. recently reported that increases in water demand and decreases in surface water supply caused by a warming climate might negatively affect groundwater storage, especially in regions like the San Joaquin Valley of California, where groundwater reserve is already stressed. Therefore, evidence support the necessity of finding sustainable practices in vineyard production systems for longtime exploitation of natural resources, such as water and soil. It was suggested as an indicator of the total water used for grape production to promote sustainable and efficient use of water in viticulture . WF is the sum of three components; the green WF or water from precipitation, the blue WF or irrigation water sourced from surface or groundwater resources, and the gray WF that is the amount of fresh water required to assimilate pollutants to meet specific water quality standards . The agriculture sector accounted for 92% of the total WF . The WF of irrigated crops recently came under scrutiny due to socioeconomic concerns and the need to reduce it . Intrinsic water use efficiency is the ratio of moles of CO2 assimilated and moles of water transpired by the plant . It is an indicator of how efficient the grapevine is, blueberries in containers growing utilizing water to produce photosynthates. Deficit irrigation strategies were developed to reduce the amount of water applied to the grapevine, substantially reducing the WF and increasing the iWUE. The other aim in applying water deficits was to maintain or improve grape berry composition . Deficit irrigation methods apply a predetermined fraction of the crop evapotranspiration , during a portion of the growing season . A large and growing body of literature investigated how these strategies, including various timing, duration, and severity, affected grapevine physiology and consequently, berry composition regarding sugar and anthocyanin accumulation and the subsequent chemical composition in wines . Nevertheless, the WF of these strategies at a local scale in warm climates has not been addressed thoroughly. Arbuscular mycorrhizal fungi are soil-borne fungi that establish mutualistic relationships with terrestrial plants including grapevines, being key components of the viticulture production systems . The symbiosis of grapevines with AMF may be affected by stress factors related to climate change . In addition, previous studies demonstrated that management practices strongly shaped bacterial and fungal communities in vineyard soils , which may modulate grapevine responses to environmental stresses. Under controlled conditions, the association of grapevines with AMF enhanced berry quality when potted grapevines were subjected to deficit irrigation and elevated temperature , whereas berry flavonoid metabolism was upregulated in AMF-inoculated grapevines in vineyards . Previous work indicated that different replacements of the ETc affected grapevine physiology , leading to a different carbon allocation between source and sink organs . This study also demonstrated that replacing 50% of the ETc was sufficient to sustain the grapevine performance through the enhancement of sugar transport that could slow down the detrimental effect of water deficits on yield .

Based on the above-mentioned literature, it was hypothesized that water deficits may increase grapevine iWUE, promoting the balance between vegetative and reproductive growth and improving berry composition in a hot climate and deficit irrigation strategies may exert a different pressure on water resources and AMF associated with grapevines. Therefore, the aim of this study was to evaluate three applied water amounts based on different fractions of the ETc for maintaining berry quality without compromising yield and minimizing their environmental impact concerning total WF and AMF colonization rates. This work covered the effect of irrigation strategies on different interrelated elements of vineyard production systems such as the soil water storage or the AMF abundance together with the productive characteristics in terms of yield and quality, advancing in the knowledge of a more sustainable water management.The experiment was conducted on Cabernet Sauvignon on 110R rootstock during two consecutive seasons in Oakville, CA . Grapevines were planted in 2011 with a spacing of 2.4 by 2.0 m with a row orientation of North West-South East. The grapevines were trained to a bilateral cordon on avertically shoot positioned trellis with a cordon height 96 cm above vineyard floor and pruned to 30 spurs and one bud per spur. The experiment was designed as a randomized complete block with a one-way arrangement of the following fractions of ETc replacement treatments: 25% ETc, 50% ETc, and 100% ETc. Each treatment was replicated six times with five grapevines in each treatment replicate. The three middle vines within the treatment replicate were used for data collection and the two on distal ends were treated as buffer plants. Plants were irrigated weekly with two drip emitters per vine. Other cultural practices were standard for the area and conducted before treatment application.Intraradical AMF colonization was measured after harvest of each season where root samples from the three middle grapevines per treatment replicate were collected at a depth of 15 and 20 cm away from the vine trunk. Root samples were cleaned, cleared, and stained according to methods described in Koske and Gemma . Fifty root segments per replicate were examined under the microscope to determine intraradical AMF colonization as previously described in Torres et al. . Briefly, the extension of mycorrhizal colonization was determined by estimating its product in width and length according to a scale range between 0 and 10, where 0 is the complete absence of fungal structures. Then, the incidence of mycorrhizal colonization was estimated by dividing the number of root segments with the presence of fungal structures and the total observed segments. The intensity of the colonization was calculated as the product between the extension and incidence, and the result was expressed as a percentage of colonization.Berry mass was affected by the applied water treatments during berry ripening in both seasons where it was the highest with the 100% ETc treatment. We did not measure any treatment differences in TSS, pH, or TA in 2019 . In the 2020 growing season, 100% ETc treatment resulted in a lower TSS but higher must pH at harvest, compared with other treatments.In 2019, the 100% ETc decreased berry anthocyanin and flavonol contents from DAF 78 to harvest . In 2020, berry anthocyanin and flavonol contents were not affected by treatments except at prevéraison where 100% ETc decreased berry skin flavonol . At véraison in 2020, the 25% ETc had a significantly lower content of anthocyanins compared with other treatments. Malvidin derivatives were the most abundant anthocyanins found in the Cabernet Sauvignon berry skins, ranging from 74 to 78% and 65 to 74% in 2019 and 2020 growing seasons, respectively .