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

Commodities

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

Practices

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

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
industries.

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 farms^2,3.

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
pools⁷.

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
sources.

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.

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