Sugars were measured at 25% using a Refractometer PAL-1 . The C content of sugar was calculated at 42% using the formula of sucrose. Below ground biomass was measured by pneumatically excavating the root system with compressed air applied at 0.7 Mpa for three of the 12 sampling blocks, exposing two vines each in 8 m3 pits. The soil was prewetted prior to excavation to facilitate removal and minimize root damage. A root restricting duripan, common in this soil, provided an effective rooting depth of about 40 cm at this site with only 5–10 fine and small roots able to penetrate below this depth in each plot. Roots were washed, cut into smaller segments and separated into four size classes , oven-dried at 60 °C for 48 h and weighed. Larger roots were left in the oven for 4 days. Stumps were considered part of the root system for this analysis.In vineyard ecosystems, annual C is represented by fruit, leaves and canes, and is either removed from the system and/or incorporated into the soil C pools, square pots for plants which was not considered further. Structures whose tissues remain in the plant were considered perennial C.
Woody biomass volumes were measured and used for perennial C estimates. Cordon and trunk diameters were measured using a digital caliper at four locations per piece and averaged, and lengths were measured with a calibrated tape. Sixty vines were used for the analysis; twelve vines were omitted due to missing values in one or more vine fractions. All statistical estimates were conducted in R.An earth moving machine was used to uproot vines and gather them together to form mounds. Twenty-six mounds consisting of trunks plus cordons and canes were measured across this vineyard block . The mounds represented comparable spatial footprints within the vineyard area . Mound C stocks were estimated using their biomass contribution areas, physical size, density and either a semi-ovoid or hemispherical model.The present study provides results for an assessment of vineyard biomass that is comparable with data from previous studies, as well as estimates of below ground biomass that are more precise than previous reports. While most studies on C sequestration in vineyards have focused on soil C, some have quantified above ground biomass and C stocks. For example, a study of grapevines in California found net primary productivity values between 5.5 and 11 Mg C ha−1 —figures that are comparable to our mean estimate of 12.4 Mg C ha−1 . For pruned biomass, our estimate of 1.1 Mg C ha−1 were comparable to two assessments that estimated 2.5 Mg of pruned biomass ha−1 for both almonds and vineyards. Researchers reported that mature orchard crops in California allocated, on average, one third of their NPP to harvestable biomass, and mature vines allocated 35–50% of that year’s production to grape clusters.
Our estimate of 50% of annual biomass C allocated to harvested clusters represent the fraction of the structures grown during the season . Furthermore, if woody annual increments were considered this proportion would be even lower. Likewise the observed 1.7 Mg ha−1 in fruit represents ~14% of total biomass , which is within 10% of other studies in the region at similar vine densities. More importantly, this study reports the fraction of C that could be recovered from winemaking and returned to the soil for potential long term storage. However, this study is restricted to the agronomic and environmental conditions of the site, and the methodology would require validation and potential adjustment in other locations and conditions. Few studies have conducted a thorough evaluation of belowground vine biomass in vineyards, although Elderfield did estimate that fine roots contributed 20–30% of total NPP and that C was responsible for 45% of that dry matter. More recently, Brunori et al. studied the capability of grapevines to efficiently store C throughout the growing season and found that root systems contributed to between 9 and 26% of the total vine C fixation in a model Vitis vinifera sativa L. cv Merlot/berlandieri rupestris vineyard. The results of our study provide a utilitarian analysis of C storage in mature wine grape vines, including above and below ground fractions and annual vs. perennial allocations. Such information constitutes the basic unit of measurement from which one can then estimate the contribution of wine grapes to C budgets at multiple scales— fruit, plant or vineyard level—and by region, sector, or in mixed crop analyses. Our study builds on earlier research that focused on the basic physiology, development and allocation of biomass in vines.
Previous research has also examined vineyard-level carbon at the landscape level with coarser estimates of the absolute C storage capacity of vines of different ages, as well as the relative contribution of vines and woody biomass in natural vegetation in mixed vineyard-wildland landscapes. The combination of findings from those studies, together with the more precise and complete carbon-by-vine structure assessment provided here, mean that managers now have access to methods and analytical tools that allow precise and detailed C estimates from the individual vine to whole-farm scales. As carbon accounting in vineyard landscapes becomes more sophisticated, widespread and economically relevant, such vineyard-level analyses will become increasingly important for informing management decisions. The greater vine-level measuring precision that this study affords should also translate into improved scaled-up C assessments . In California alone, for example, there are more than 230,000 ha are planted in vines. Given that for many, if not most of those hectares, the exact number of individual vines is known, it is easy to see how improvements in vine-level measuring accuracy can have benefits from the individual farmer to the entire sector. Previous efforts to develop rough allometric woody biomass equations for vines notwithstanding, there is still a need to improve our precision in estimating of how biomass changes with different parameters. Because the present analysis was conducted for 15 year old Cabernet vines, there is now a need for calibrating how vine C varies with age, varietal and training system. There is also uncertainty around the influence of grafting onto rootstock on C accumulation in vines. As mentioned in the methods, the vines in this study were not grafted—an artifact of the root-limiting duripan approximately 50 cm below the soil surface. The site’s location on the flat, valley bottom of a river floodplain also means that its topography, while typical of other vineyard sites per se, created conditions that limit soil depth, drainage and decomposition. As such, the physical conditions examined here may differ significantly from more hilly regions in California, such as Sonoma and Mendocino counties. Similarly, the lack of a surrounding natural vegetation buffer at this site compared to other vineyards may mean that the ecological conditions of the soil communities may or may not have been broadly typical of those found in other vineyard sites. Thus, to the extent that future studies can document the degree to which such parameters influence C accumulation in vines or across sites, large square plant pots they will improve the accuracy and utility of C estimation methods and enable viticulturists to be among the first sectors in agriculture for which accurate C accounting is an industry wide possibility. The current study was also designed to complement a growing body of research focusing on soil-vine interactions . Woody carbon reserves and sugar accumulation play a supportive role in grape quality, the main determinant of crop value in wine grapes. The extent to which biomass production, especially in below ground reservoirs, relates to soil carbon is of immediate interest for those focused on nutrient cycling, plant health and fruit production, as well as for those concerned with C storage. The soil-vine interface may also be the area where management techniques can have the highest impact on C stocks and harvest potential. We expect the below ground estimates of root biomass and C provided here will be helpful in this regard and for developing a more thorough understanding of below ground C stores at the landscape level. For example, Williams et al.estimated this component to be the largest reservoir of C in the vineyard landscape they examined, but they did not include root biomass in their calculations. Others have assumed root systems to be ~30% of vine biomass based on the reported biomass values for roots, trunk, and cordons . With the contribution of this study, the magnitude of the below ground reservoir can now be updated.California’s Mediterranean climate, albeit highly variable with frequent periods of drought and floods, provided the foundation for a diverse and vibrant agricultural industry to grow in response to the availability of low-cost labor and water supplies. Starting in the middle of the 19th century field crops–grains, forages, and cotton–dominated California crop landscapes, if not value of production, for a hundred years.
Toward the beginning of the 20th century, though, California agriculture began its move toward intensive cropping of vegetables and fruits. Railroads helped expand produce markets and low-wage immigrant labor. Later, migrants from the Dust Bowl, and then from Mexico, kept labor costs on fruit and vegetable farms competitive . Importantly, irrigation infrastructure and regulation—particularly water pumping, storage, transport, and rules of use—allowed cultivation of water-intensive summer crops where no rain fell for 6 mo each year. The Great Depression catalyzed massive surface water infrastructure developments such as the Colorado River Project and, in the late 1930s, the Central Valley Project by the US Bureau of Reclamation . Further growth of infrastructure in the postwar era included the State Water Project serving mostly cities and some agricultural lands in central and southern California. Infrastructure development over this period created one of the largest and most engineered irrigated agricultural systems in the world. The water supply network bridged the gap of hundreds of kilometers between the water-rich north—with mountains and heavy precipitation in the winter—and the low-precipitation Mediterranean climate central and south that plays host to most of California agriculture production and population. For nearly two centuries California farms have prospered through technological adoption, innovation investments, and on-farm management improvements. Yet with a changing climate coupled with increased concerns over the environment and sustainability, the landscape of California agriculture is changing. Over the past two decades, noticeably less land and water has been devoted to extensive field crops, as farms shifted to vegetables and tree and vine crops. These specialty crops generally produce higher revenues per unit of land and water . Expectations of higher returns have contributed to more than half of the state’s irrigated agricultural croplands growing fruits, nuts, and vegetables, which comprise roughly 80% of the farm revenue and employment . The degree to which these changes and concerns significantly reduce agriculture’s presence and productivity will depend on how Californians, including its growers and policymakers, respond.The mosaic of agriculture in California is driven by a variety of natural and human-created conditions . California’s terrain, climate, and soil heterogeneity are instrumental to California’s diverse array of agricultural commodities. The irrigated crop footprint alone is nearly 3.8 million hectares . Land in farms spans more than 10 million ha, producing over 400 crop and livestock commodities that annually generate around $50 billion in cash receipts and support 420,000 jobs in 2021 . The food and beverage processing sector, which primarily relies on local crop and animal supplies, supports an additional 250,000 jobs. Agriculture contributes significant shares of the income and employment in areas such as the CV, where labor, capital, irrigation water, management, and downstream sectors in livestock and food processing are closely linked. We briefly describe agriculture in three regions comprising the largest areas of irrigated acreage and commodity value: the CV, the Southern California Region, and the Coastal California. Agriculture in California’s foothills and mountain areas provide nearly 5 million ha of pasture and hay for cattle, along with the winter snow pack that historically stores nearly a third of California’s runoff that supplies CV irrigation as well as urban water use. CV. The nearly 52,000 km2 CV accounts for more than two thirds of California’s irrigated agriculture, encompassing a few major cities and dozens of moderate-sized rural communities. The northern part of the CV contains the Sacramento Valley and the Sacramento River basin, which averages 890 mm/y. of precipitation and is close to the snow pack-heavy northern mountains.