Carbon Sequestration at Troon Vineyard in Oregon’s Applegate Valley
By Garett Long, M.S. Soils and Biogeochemistry, UC Davis, Troon Vineyard Director of Agriculture
As a soil scientist and farmer, I have spent more than a decade trying to better understand the dynamic relationships between soil health, land stewardship, climate change, and ecological resilience. Splitting my time between the farm and the laboratory, I’ve dug more meter-deep soil pits than most people my age. I’ve set up long-term soil health monitoring programs on farms and ranches up and down the West Coast. I’ve helped establish multiple Biodynamic farms and vineyards in California and Oregon, and I’ve witnessed firsthand the numerous and varied impacts of climate change on our working lands, as well as the solutions to help mitigate its worsening effects.
There exists a common misconception that nature is an exceptionally harsh place where organisms are battling it out, eating and parasitizing each other, and competing for limited resources. Cooperation, on the other hand, is much more prevalent ecologically and involves organisms symbiotically working together to achieve a common goal, such as mutual defense or resource acquisition. Today, ecologists recognize that both competition and cooperation are important drivers of ecological communities and evolutionary processes and that the balance between these processes are largely impacted by how we steward the land as farmers.
Healthy soils not only provide a fertile and supportive environment for plants and vines to grow, but they’re also teeming with diverse animal, insect, and microbial life. In fact, there are more organisms in a handful of healthy soil than there are humans who’ve ever lived on Earth.
Plants intentionally secrete on average 50% of the carbohydrates they produce through photosynthesis through their roots, feeding soil microbes. These tiny symbiotic life partners utilize these sugary root exudates to fuel the decomposition of rocks, which in turn releases mineral nutrients that plants happily soak up. The exchange is balanced and mutually beneficial.
Earthworms and burrowing animals also play an important role as they eat, poop, and bury vegetation, moving through the soil and creating pathways for water to infiltrate. Worm castings, manure, and plant matter are all colonized by microbes, which convert these “wastes” into stable soil organic matter (SOM). These organisms build soil structure, which improves – amazingly – water’s ability to both infiltrate and be retained in the soil. Many view earthworms as beneficial, and gophers and voles as detrimental, yet they all convey similar benefits to soil structure.
Healthy soils also support microbially-mediated nutrient cycling, which can reduce, or even eliminate the need for fertilization. Fewer inputs and tractor passes mean cost savings for the farmer and less compaction in the vineyard.
Importantly, healthy soils are better able to resist and recover from environmental stresses, such as drought, flooding, and disease, which are influenced largely by the quantity of greenhouse gasses in Earth’s atmosphere.
The reality is our carbon cycle is out of balance. Plants are the master mediators of carbon. By planting cover crops and perennial plants such as trees and grapevines, farmers are able to leverage this capability of living plants to sequester carbon in the soil of agricultural lands. In addition to the sugary root exudates that plants secrete, they also store C in their tissues, such as roots, leaves, and stems.
At Troon Vineyard, we use a mix of more than 30 species of both annual and perennial cover crops in the vineyard. In the alleys, we plant a mix of vigorous grasses such as fescues, rye and triticale, and legumes, which double as forage for our sheep and chickens when we graze our dormant vineyards. Undervine, we use a low-growing mix of wildflowers, subterranean and balansa clovers, and perennial forbs. Burnett (Sanguisorba sp.) and poppies (Papaver sp.) do particularly well growing under vine in the granitic soils of the Applegate Valley of southern Oregon (USDA Hardiness Zone 8).
Choosing the right cover crop mix for your specific site deserves its own article entirely, but a few main principles apply.
Diversity - you may not see every species you plant in the first year. Some “pioneer” species help build soil conditions that will help other plants thrive in the future. Some seeds can lie dormant for years.
Mimic nature - the most productive and resilient ecosystems on Earth are polycultures, which feature plants with different root architectures, light and water needs, seasonality, etc. Establishing a diverse mix of plant life aboveground will lead to a more diverse microbial population belowground, making the whole system more resilient to disease and pest outbreaks.
Plant flowers - flowers not only bring color and beauty to your vineyards, but also attract beneficial insects. Providing a mix of flowering plants that bloom throughout the year ensures a constant supply of pollen and nectar, which support both pollinators and beneficial predators.
Many people instinctively believe that cover crops will compete for limited resources such as water and nutrients, but this reality is short-lived. While a one to three-year-old grapevine may be stunted by dense bunchgrasses with similarly shallow root systems, vines quickly extend their taproots several feet below ground where the soil buffers both temperature swings and moisture availability. The negative influence of competition is typically overcome within the first three years following establishment.
Cover crop management will also have a potentially huge impact on vine and soil health. In southern Oregon, hard spring frosts are common through mid-April and possibly even in May. Mature cover crops prevent air circulation and will trap cold air among the vines; they should be mowed just prior to the first hard freeze in spring. Cover crops can also be managed by grazing livestock. Rotational grazing provides a lens through which sheep, followed by chickens, can be viewed as “biological lawn mowers” that do not require diesel or operators. Rather, they provide an additional revenue stream for farmers in the form of eggs, meat, wool, and dairy products, while also fertilizing the vineyard with their manure. Grazing should be managed to leave at least 30-50% of the total plant biomass for adequate regrowth and to achieve the maximum benefits of both cover cropping and animal integration.
A dense canopy of cover crops, or even standing dry matter, keeps the soil shaded and shielded from harsh winds and sunlight. By protecting the soil from evaporation and UV light, microbes have an ideal environment to continue mobilizing nutrients throughout the growing season. Well-fed microbes support more vigorous plants that require less fertilization and irrigation and sequester more carbon. Cover crops act like armor for the soil, and should not be disturbed.
Soil disturbance, such as discing, weed knifing, or other forms of tillage disrupts soil structure and creates conditions in which soil organic matter is consumed by microbes and converted into CO2 via respiration. Fungi are particularly susceptible to tillage and may require several seasons to reestablish following disturbance. The vast majority of fungi are not pathogenic, and in fact are critical partners in turning the readily available glucose-laden root exudates into stable soil organic matter. Mycorrhizal fungi are particularly important symbiotic organisms, as they are masterful at scavenging water, phosphorus, and other soil nutrients, effectively expanding a plant’s root zone 10-100x.
Sequestering carbon and building soil organic matter requires a multi-prong approach that involves leveraging several principles. However, farmers should experiment with any number of new practices, introducing regenerative practices at a comfortable pace. To review, these principles of soil health may be applied independently, or simultaneously for added benefits:
Cover cropping feeds and protects the soil, provides forage for livestock and habitat for beneficial insects, prevents evaporation, and keeps weedy species from taking over.
Keep a living root in the ground in order to pump C into the soil throughout the entire year.
Apply compost to feed soil life and introduce diverse microorganisms. By incorporating grape pomace into your compost piles, you’ll be reintroducing beneficial yeasts back into the vineyard.
Biodiversity imparts resilience by breaking cycles of pest and disease, and creating a polyculture in which plants, animals, and microbes all mutually benefit.
Reduce soil disturbance to maintain soil structure and prevent soil C from being returned to the atmosphere via microbial respiration.
Livestock integration provides cover crop management (mowing) and fertilization (manure), as well as additional revenue streams.
On any farm or vineyard, anywhere on the planet, utilizing these key principles of soil health can tip the balance in favor of cooperation over competition, and sequester massive amounts of CO2 on working lands. These principles collectively contribute to healthier soils, which support healthy plants, animals, communities, and ultimately planetary health.