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

Commodities

• Fruits: olives
• Nuts: almonds, walnuts

Practices

• Education and Training: technical assistance
• Farm Business Management: value added
• 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