CO2 sequestration by Enhanced Weathering of agricultural soils in Norfolk, UK

Enhanced Weathering (EW) of silicate rocks is a carbon dioxide (CO ₂ ) removal (CDR) strategy whereby powdered rock is applied to the land and/or ocean in order to mitigate climate warming through accelerated rates of chemical weathering. Agricultural sites are particularly suited for EW as they host infastructure needed to implement EW, and the nutrients released during weathering facilitate a number of food security co-benefits such as increased crop yields [1].

Here we present results from EW field trials conducted in Norfolk, United Kingdom, with two different crops, namely peas and sugar beet. The field site features sandy, quick- draining soils and shallow carbonate bedrock. For each crop, basalt rock powder was applied to 0.5 ha plots at a rate of 40 tons ha ^-1 yr ^-1 , and an equivalent sized control plot where no rock powder was applied was monitored simultaneously. We use major ion concentrations and radiogenic Sr isotope ratios ( ⁸⁷ Sr/ ⁸⁶ Sr) of the soil water, crop biomass, and soil exchangeable leachates, as well as analyses of the carbonate concentration and the C isotope composition of soil inorganic carbon (d ¹³ C-SIC) in the bulk soil, to quantify the extent of CO ₂ sequestration for each plot. Our results suggest that basalt application in the pea field increased CO ₂ sequestration by as much as 30% as compared to the control field, while basalt application in the sugar beet field produced only small changes in CO ₂ sequestration. Preliminary data also indicate that CO ₂ sequestration in the basalt-treated plots was achieved through both the weathering of basalt as well as increased weathering of the underlying carbonate bedrock. Finally, we examine the potential co-benefits of basalt application, including changes to crop yield and pest resistance, as well as potential pitfalls such as increased concentrations of heavy metals in water, soil, and plant reservoirs.

[1] Beerling et al. (2018), Nature Plants, 4, 138-147.