Genomic Science Program
U.S. Department of Energy | Office of Science | Biological and Environmental Research Program

Interactions Between Enhanced Rock Weathering and Soil Organic Carbon Cycling in Coordinated, National-Scale Field Trials

Authors:

Noah W. Sokol1* (sokol1@lllnl.gov), Daniel Maxbauer2, Radomir Schmidt3, Anthony O’Geen3, Isabel Montañez3, Alexis Weintraub4, Noah Planavasky4, Eric Slessarev4, Peter Nico5, Jennifer Pett-Ridge1,6

Institutions:

1Lawrence Livermore National Laboratory; 2Carleton College; 3University of California–Davis; 4Yale University; 5Lawrence Berkeley National Laboratory; 6 Life and Environmental Sciences Department, University of California–Merced

Goals

The Terraforming Soil Energy Earthshot Research Center (EERC) will study biological and geological solutions to accelerate scalable, affordable carbon drawdown in the United States’ 166 million hectares of agricultural soils. Research objectives include gene-edited plants and microorganisms that accelerate carbon sequestration, strategies that encourage soil mineral-organic interactions, and models that predict carbon durability in small soil pores as well as regional-scale estimates of locations with opportunities for increased soil carbon removal.

Abstract

If applied at scale on croplands, enhanced rock weathering (ERW) could feasibly remove 0.5 to 2 Pg C of atmospheric carbon dioxide (CO2) each year through amendments of relatively fast reacting crushed alkaline minerals (e.g., crushed basalt rock). However, several critical unknowns limit the scalability of ERW as a carbon drawdown strategy. First, published data remain limited and existing field studies employ different approaches for measuring inorganic carbon (C) removal, making it difficult to compare the net C removal of ERW across agricultural regions. Second, the impacts of ERW on soil organic carbon (SOC) and soil microbial communities are poorly understood. Given the massive size of the SOC reservoir, small SOC gains or losses could either amplify or entirely negate the inorganic C drawdown benefits of ERW. The EERC will address this gap by assessing impacts of field trials across different major agricultural regions within the United States (California, the Midwest, and Southeast) using a standardized set of total C drawdown measurements. Here, the team presents some preliminary data from existing field trials.

At three field trials in the Central Valley of California, the team found that stocks of mineral- associated organic matter (MAOM) were 8 to 16% lower in the surface soil (0 to 10 cm) of plots with crushed basalt amendments versus unamended controls. At the sites where baseline data was available, crushed rock amendments did not lead to net losses of total soil organic matter relative to initial conditions; however, the accrual rate of surface soil MAOM over the two-year period was 60 to 97% lower in plots with crushed rock relative to control plots. At the field trial in Minnesota on a typical corn-soybean rotational field, researchers found increased porewater alkalinity and increased yield in acidic soils treated with steel slag, though minimal effect of basalt on inorganic C removal, SOC, or plant yield. At the Illinois site, after 3 years of basalt application, the group found a signal for elevated or negligible shifts in crop yields, with the largest shifts observed in oats and soy. Using a cation accounting method, which tracks calcium and magnesium concentrations in the silicate phases relative to detrital elements, researchers found evidence for significant amounts of basalt weathering (representing multiple tons of carbon dioxide removal per hectare per year). Despite high basalt application rates and a signal for extensive weathering, the soil pH in the plots stayed near neutral, suggesting limited agronomic risk from the practice in these soils.

In sum, this group found evidence of inorganic C removal at some sites, and contrasting effects on SOC at the sites where it was measured. The next phase of field trials will be to measure the effects of ERW on inorganic C and SOC using a similar experimental design, a standardized sampling protocol, and a common set of C measurements, in order to facilitate more accurate and comparable estimates of net C removal across regions. Researchers will also investigate how co-applying organic amendments with crushed rock may hold promise for optimizing microbial-mediated inorganic and organic C removal.

Funding Information

This research is based upon work of the Lawrence Livermore National Laboratory (LLNL) ‘Terraforming Soil’ Energy Earthshot Research Center (EERC), supported by the U.S. DOE Office of Science, BER program, Basic Energy Sciences (BES) and Advanced Scientific Computing Research (ASCR) programs under Award Number SCW1841 to LLNL, and subcontracts to University of California–Davis; Yale University; Carleton College; and Lawrence Berkeley National Laboratory. Work at LLNL was performed under U.S. DOE Contract DE- AC52-07NA27344. Initial work at the Working Lands Innovation sites was supported by a California Strategic Growth Council grant CCR20007. Field trials in Minnesota are supported by the National Science Foundation (NSF-EAR 2208133).