Gabriel Farm Healthy Soils Demonstration Project


The effects of actively aerated compost tea and wood chip-based mulch applications on greenhouse gas emissions, soil carbon sequestration and weed suppression in a Sonoma County pome fruit orchard. 


California Department of Food and Agriculture – Healthy Soils Program Demonstration Project

Cooperating Entities:

  • Gabriel Farm
  • Carbon Cycle Institute
  • San Francisco State University
  • Intuit Ag

Funds Requested:

$249,871.83 (33% of budget is associated with the primary research activity and 23% of budget is associated with procurement of greenhouse gas measurement equipment).

Gabriel Farm:

Established in 2000, Gabriel Farm is a 14-acre family farm located in beautiful Sonoma County. Each year they open their farm to visitors who like to share the farming experience with their family and friends.  Lucy has been farming organically in Sebastopol for the past 25 years and was trained in organic farming at the UC Santa Cruz Center for Agroecology & Sustainable Food Systems (CASFS). In addition to farming, Lucy is also a Licensed Marriage Family Therapist. Torrey is a farmer, math educator and itinerant philosopher. Torrey also serves as a board member for: the Oak Grove Union School District, the Rotary Club of Sebastopol and the Gold Ridge Resource Conservation District. Henry Olson, age 12, is Gabriel Farm's farmer in training.

Gabriel Farm grows 9 acres of Asian Pears, 2 acres of Certified Organic Apples, and various other organic crops including: Persimmons, Raspberries, Pluots, Tomatoes, Pineapple Guavas, Blackberries, Lavender, Pumpkins and Winters Squash.  Their U-Pick program is a membership program because they are a small farm with a limited amount of produce.  They decided to offer the U-Pick experience to their dedicated customers who are interested in supporting local agriculture.


Project Description:

Orchard understories perform a number of ecosystem services and each can impact each other (e.g. water relations and gas exchange), and each ecosystem service is interconnected and impacted by one or more management decisions by the producer.  In organic farming systems, tillage is often utilized in the rows for weed control and suppression.  However, this practice has negative consequences that can include the loss of soil structure, accelerated decomposition of organic matter, reduction of infiltration rates, and increased susceptibility to water and wind erosion. This project will test both the practice of mulching as a weed control, and the practice of inoculating the soil with actively aerated compost tea to improve soil health.

This project will utilize the current practice of tillage in the orchard rows as the Control. Three Treatment scenarios will be established to test against the Control Rows. These are: T1 – Compost Tea Only (tillage), T2 – Mulch Only (no tillage), and T3 – Mulch and Compost Tea (no tillage). Soil sampling and gas exchange sampling will be conducted to measure change in total organic carbon, soil organic matter, bulk density, infiltration rates, CO2, CH4 and N2O flux between the orchard soil and the atmosphere.

While the literature shows that mulching applications can work well to conserve water and suppress weeds in orchard rows, less is known of its effects on carbon sequestration and GHG emissions, especially in the presence of microbial-rich, actively aerated compost tea applications. We hypothesize that woodchip-based mulch for weed suppression, when combined with actively aerated compost tea (T1) will remain effective at controlling weeds, while measurably increasing the soil carbon pool and releasing less CO2, CH4, and N20 to the atmosphere over the life of the project then that of the Compost Tea rows (T1), Mulch Only rows (T2) or the Control rows (C).

Describe the geographic location and possible scale (state or local) at which the project anticipates influencing farmers and ranchers to adopt the demonstrated agricultural management practices.

The project site is located at Gabriel Farm in western Sonoma County near the city of Sebastopol. Historically, this was the central apple production area in northern California. While many acres that were previously dedicated to apples have been converted to vineyard and residential development, there has been a resurgence of local interest in apple production for the table and for cider. This has spread to surrounding areas including historical orchard lands in Mendocino County (Anderson Valley, Ukiah Valley), and Lake County (Kelseyville, Middletown, Lakeport) as well as other apple growing regions in the state, such as the Sierra Nevada foothills.

Gabriel Farm is a known innovator. Their willingness to experiment and test practices, their reputation in the community as an active small family farm, and their central location in the Sonoma County apple region were instrumental in choosing Gabriel Farm for this demonstration project. The issues that Gabriel Farm faces in relation to soil health and orchard floor management are not unique. Weed management and soil health concerns are key issues among orchardists throughout the north coast region and the state.

Implementing this demonstration project at Gabriel Farm will enable these practices to reach a broad audience of growers and landowners. While Gabriel Farm is on the small side of agricultural producers at the state level, small orchards are the norm in the north coast region. Within the Gold Ridge Resource Conservation District, there are at least 386 individual parcels totaling more than 3,200 acres dedicated or partially dedicated to apples. These parcels range in size from 1 to 130 acres, with an average parcel size of 8.5 acres. Gabriel Farm is within an hour drive from the Ukiah Valley in Mendocino County, and 1.5 hours from Kelseyville in Lake County, allowing workshops held at Gabriel Farm to be easily reached by other orchardists in the north coast region.

The project will report on the impacts that mulching for weed control both in the presence and absence of actively aerated compost tea has on soil health and GHG emissions. In addition to this information collected for the Healthy Soils Demonstration Project, the producer also plans to collect data from each treatment and control row on brix, fruit pressure, fruit size, and harvest tons. Depending on project outcomes, dissemination of project results through workshops, RCD newsblasts, social media and other forms of outreach may have a significant local impact on managing orchard floor practices for soil health.

Outreach Design

As the overall goal of the project is to increase adoption of climate beneficial practices among orchardists and other farmers in northern California, the recipients will host four on-farm field days to present the project and its practices to other farmers. The field days will discuss planning, implementation and measured project results. They will provide a forum to evaluate practice impacts on soil health, carbon footprints and GHG emissions, while allowing for hands-on learning, farmer to farmer communication, and mentoring. Presenters will include Gold Ridge RCD, Gabriel Farm, Carbon Cycle Institute (CCI), and San Francisco State University (SFSU).

Gabriel Farm will lead outreach efforts by promoting the project and field days through multiple partner organizations (CAFF/Farmer’s Guild, Harmony Farm Supply, Sonoma RCD, CalCAN, Santa Rosa Junior College, Sonoma State University, California Apple Commission, Sonoma County Farm Bureau, Sonoma County Wine Growers, Sonoma County Farm Trails, UC Cooperative Extension) and engage in direct outreach to fellow producers. In addition, Gabriel Farm will promote the project through its website, social media accounts, and will provide updates and narratives of the progress and results of the healthy soils practices. Gold Ridge RCD will provide outreach to promote the project and field days through email blasts, website and social media updates, and blog posts.  The RCD will also release project results through the North Coast Soil Health Hub and through the RCD Project Tracker  We will also share project results through our network with the broader California Association of RCDs.

Gabriel Farm will also promote the HSP Demo Project to the thousands of Bay Area residents it hosts for apple picking and other farm-activities. This group will receive email blasts containing project updates, healthy soils findings and project results. Interpretive signage at the farm that will also be installed to describe the project.

Project results will be disseminated by Gold Ridge RCD, Gabriel Farm, CCI and SFSU. Gold Ridge RCD will share project results locally, through newsletters, email blasts, social media and on its website. The RCD will also release project results through the North Coast Soil Health Hub and through the California Association of RCDs. Gabriel Farm owner, Torrey Olson will present the project at Eco-Farm and the CA Small Farm Conference. CCI will share reports and results from the project through email blasts to carbon farming partners and provide links to project documents on their website. Project sampling methodologies and results will be presented at professional conferences by SFSU Dept. of Geography & Environment faculty and graduate students, who will also seek publishing of project methods and results in peer reviewed journals. Two students will receive training in soil health and GHG emissions assessment and it is anticipated that at least one Master’s thesis will be generated from the project. In addition, students from two classes will be directly impacted; Geog602 Field Methods through a fieldtrip to the orchard for a hands-on class on soil measurement techniques and sampling designs, and Geog314 Bioclimatology, through analysis and discussion of the soil carbon cycle and GHG emissions.

The RCD will maintain an internal database to track project field day attendees, and others who have expressed interest in the project. Eventbrite (, an online event registration platform will also be utilized to track demonstration field day registrants. Field Day attendees will be surveyed immediately following the events, and again three months afterward utilizing a web-based survey. The survey will identify interest in the implementation of climate beneficial farming practices, and potential barriers to adopting such practices for agricultural producers in northern California. The goal of the survey is to assess the attendees’ level of collaboration through indicators such as referrals.

The field days, online information, and one-on-one technical assistance will help create a cadre of producers who can serve as mentors for late adopters. Project proponents will work closely with producer associations and local agricultural organizations to document value-added benefits from adopting climate beneficial practices. Opportunities for marketing and cost-savings will be identified and presented to stakeholders and producers.

For more information contact William Hart - William (at) - (707) 823-5244
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