Soil management practices can contribute to net carbon neutrality in California

Abstract

Stabilizing climate requires reducing greenhouse gas (GHG) emissions and storing atmospheric carbon dioxide (CO _2 ) in land or ocean systems. Soil management practices can reduce GHG emissions or sequester atmospheric CO _2 into inorganic and organic forms. However, whether soil carbon strategies represent a viable and impactful climate mitigation pathway is uncertain. A specific question concerns the role that land-management practices and soil amendments can play in realizing California’s ambition for carbon neutrality by 2045. Here we examine the carbon flux impacts of soil conservation (i.e., compost, reduced tillage, cover crop) and enhanced silicate rock weathering (EW) practices at different areal extents of implementation in cropland, grassland, and savanna in California under two climate change cases. We show that with implementation areas of 15% or 50% of private cultivated land, grassland, and savanna in California, soil conservation practices alone can contribute $1.4_{0.7}^{2.1}$ % ( $ - 1.8_{ - 0.9}^{ - 2.7}$ Mt CO _2 eq y ^−1 ) and $4.6_{2.3}^{6.9}$ % ( $ - 6.0_{ - 3.0}^{ - 8.9}$ Mt CO _2 eq y ^−1 ) of the additional emissions reduction needed (beyond previous targets) to meet the 2045 net neutrality goal (−129.3 Mt CO _2 eq y ^−1 ), respectively, on an average annual basis, including climate uncertainty. Including EW in these scenarios increases the total contributions of management practices to $4.1_{2.5}^{5.6}$ % ( $ - 5.2_{ - 3.2}^{ - 7.3}$ Mt CO _2 eq y ^−1 ) and $13.5_{8.2}^{18.6}$ % ( $ - 17.5_{ - 10.7}^{ - 24.2}$ Mt CO _2 eq y ^−1 ), respectively, of this reduction. This highlights that the extent of implementation area is a major factor in determining benefits and that EW has the potential to make a real contribution to net reduction targets. Results are similar across climate cases, indicating that contemporary field data can be used to make future projections. With EW there remains mechanistic uncertainties, however, such as rock dissolution rate and environmental controls on weathering products, which require additional field research to improve understanding of the technological efficacy of this approach for California’s 2045 carbon neutrality goal.

Keywords

• emissions reduction
• land use
• soil carbon
• inorganic carbon
• enhanced weathering
• CALAND