Increased yield and CO2 sequestration potential with the C4 cereal Sorghum bicolor cultivated in basaltic rock dust-amended agricultural soil.

Mike E Kelland,Lyla L Taylor,Steven A Banwart,Simon J Kemp,Mark E Hodson,Amy L Lewis,Christopher R Pearce,Sue E Hartley,Rachael H James,Mark R Lomas,Binoy Sarkar,T E Anne Cotton,Jonathan R Leake,Peter W Wade,David J Beerling,M Grace Andrews

doi:10.1111/gcb.15089

Abstract

Land-based enhanced rock weathering (ERW) is a biogeochemical carbon dioxide removal (CDR) strategy aiming to accelerate natural geological processes of carbon sequestration through application of crushed silicate rocks, such as basalt, to croplands and forested landscapes. However, the efficacy of the approach when undertaken with basalt, and its potential co-benefits for agriculture, require experimental and field evaluation. Here we report that amending a UK clay-loam agricultural soil with a high loading (10kg/m2 ) of relatively coarse-grained crushed basalt significantly increased the yield (21±9.4%, SE) of the important C4 cereal Sorghum bicolor under controlled environmental conditions, without accumulation of potentially toxic trace elements in the seeds. Yield increases resulted from the basalt treatment after 120days without P- and K-fertilizer addition. Shoot silicon concentrations also increased significantly (26±5.4%, SE), with potential benefits for crop resistance to biotic and abiotic stress. Elemental budgets indicate substantial release of base cations important for inorganic carbon removal and their accumulation mainly in the soil exchangeable pools. Geochemical reactive transport modelling, constrained by elemental budgets, indicated CO2 sequestration rates of 2-4t CO2 /ha, 1-5years after a single application of basaltic rock dust, including via newly formed soil carbonate minerals whose long-term fate requires assessment through field trials. This represents an approximately fourfold increase in carbon capture compared to control plant-soil systems without basalt. Our results build support for ERW deployment as a CDR technique compatible with spreading basalt powder on acidic loamy soils common across millions of hectares of western European and North American agriculture.

Highlights

Deployment of large-scale carbon dioxide removal (CDR) strategies are required together with drastic phase-down of CO2 emissions from fossil fuels to meet internationally agreed climate targets (UNEP, 2018)
We investigate Enhanced rock weathering (ERW) carbon removal and co-benefits with the C4 crop Sorghum bicolor grown at bench-scale in mildly acidic clay-loam agricultural soil amended with basaltic rock dust
We have shown that amending a slightly acidic clay-loam soil with a high loading of coarse-grained basaltic rock dust substantially increases Sorghum yield without P and K fertilizer usage or adverse trace element uptake into the seed, under experimental conditions

Summary

| INTRODUCTION

Deployment of large-scale carbon dioxide removal (CDR) strategies are required together with drastic phase-down of CO2 emissions from fossil fuels to meet internationally agreed climate targets (UNEP, 2018). Numerical modelling investigations (Köhler et al, 2010; Taylor et al, 2016) have assessed the CDR potential of ERW largely in the context of tropical forests, but the focus is turning towards croplands and soils on which deployment with existing land-spreading technology should be feasible (Beerling et al, 2018; Kantola et al, 2017; Strefler, Amann, Bauer, Kriegler, & Hartmann, 2018). We investigate ERW carbon removal and co-benefits with the C4 crop Sorghum bicolor grown at bench-scale in mildly acidic clay-loam agricultural soil amended with basaltic rock dust. Our experimental approach is a first step towards understanding the potential applicability of ERW with basalt in a temperate-zone agricultural context which will be important for understanding suitability for large-scale deployment of this CDR strategy (Beerling et al, 2018; Haque, Santos, Dutta, Thimmanagari, & Chiang, 2019; Zhang et al, 2018). Over longer multiyear time horizons, we assess dissolution trajectories and resulting CDR using a 1 D reactive transport soil profile geochemical model calibrated to our experimental results, measured basalt mineralogy and particle size distribution

| MATERIALS AND METHODS

| RESULTS AND DISCUSSION

| CONCLUSIONS