Enhanced Weathering and Biomass Incorporation: a Synergistic Pathway Towards Increased Soil Carbon Storage and Credit Revenue in California Orchards

Project Overview

Project Type: Research and Education
Funds awarded in 2024: $349,871.00
Projected End Date: 03/31/2027
Grant Recipient: University of California, Davis
Region: Western
State: California
Principal Investigator:
Elias Marvinney
University of California, Davis
Scott Keenan
Emily Smet
California Association of Resource Conservation Districts


  • Fruits: avocados, olives
  • Nuts: almonds, walnuts


  • Education and Training: technical assistance
  • Farm Business Management: value added, other
  • Natural Resources/Environment: carbon sequestration, soil stabilization
  • Soil Management: organic matter

    Proposal abstract:

    California’s Central Valley represents more than 73% of the US
    agricultural economy in fruit and nut crops1, due to
    its uniquely suitable combination of soils, climate and
    geography. However, this region also suffers from significant air
    quality issues resulting from the interaction of geographic
    factors with intensive land use in close proximity to vulnerable
    communities. This crisis has spurred increased restrictions on
    agricultural burning. Coupled with ongoing closure of bioenergy
    infrastructure, this has reduced biomass management options and
    increased financial strain on many growers, threatening the
    economic sustainability of California’s perennial cropping

    One promising alternative for orchard removal is Whole Orchard
    Recycling (WOR), in which biomass is chipped and returned to
    soil, substantially reducing life cycle pollutant and greenhouse
    gas (GHG) emissions. However, the cost of WOR implementation is
    high, and may even exceed burn permit violation
    fines2, creating a perverse incentive and setting the
    stage for friction between growers, communities, and regulatory
    agencies. Although WOR incentive funding exists, opportunities
    are limited and often unfeasible for smaller farms2,3.

    Prior work has demonstrated that WOR has the potential to return
    up to 2 tons carbon per acre to the soil in organic
    pools4 – a potential source of carbon credit revenue.
    However, this represents only a small fraction of the carbon in
    chipped biomass, with the rest lost during decomposition as
    CO2. Despite recommendations5 for a major
    value increase, carbon credits in California today are worth only
    about $30 per ton6 - insufficient to offset the effort
    and costs of quantification, verification, and carbon market
    access let alone incentivize WOR adoption.

    In pursuit of state-supported healthy soil goals, some growers
    are also investigating enhanced weathering amendment (EWA) - an
    ancient technique using basaltic rock flour as a soil amendment.
    When exposed to water from irrigation or precipitation, this
    material absorbs CO2 to create carbonate minerals
    which enhance soil structure, infiltration, and water holding
    capacity while storing carbon in long-term inorganic

    This project hypothesizes that a synergistic combination of these
    practices will increase soil carbon storage and credit revenue
    potential by enhancing in-soil capture of WOR biomass-derived
    CO2 before loss to the atmosphere, reducing soil
    CO2 emission and accumulating carbon in both inorganic
    and organic pools. Block trials will be conducted in
    collaboration with participating orchard growers as well as
    Carbonaught8, a developer of EWA products and
    associated carbon credit protocols. Soil carbon accumulation
    under various treatments will be quantified and used to model the
    potential for access to carbon credit payment revenue streams for
    growers, based on crop, soils, and spatial relationships with EWA

    In collaboration with the California Association of Resource
    Conservation Districts (CARCD)9, these findings will
    be used to develop a Best Management Practice guidance document
    focused on WOR, EWA and most importantly, procedures for grower
    access to voluntary carbon credit  markets. This material
    will be disseminated to growers through coordination with
    Resource Conservation District technical advisors10,
    Farm Bureau and Cooperative Extension representatives, web
    resources and webinar, and field day events at the trial sites.

    Project objectives from proposal:

    Research Objectives

    1. Quantify soil C in organic and inorganic pools under
      different WOR and EWA application rates
    2. Test hypothesis: Combined WOR + EWA results in higher C
      accumulation than either WOR or EWA alone
    3. Develop life cycle assessment model to account for transport
      and application emissions in calculation of net GHG benefits and
      impacts to ecosystems and communities
    4. Extrapolate findings to hypothetical statewide adoption in
      orchard agroecosystems

    Educational Objectives

    1. Develop carbon market access opportunities for growers
      following ongoing work at UC Davis and by Carbonaught
    2. Develop BMP guidelines for implementation of EWA alone and in
      combination with WOR
    3. Disseminate findings via field day demonstration, cooperative
      extension, industry conference, webinar, and published materials
    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.