Abstract
The world needs around 150 Pg of negative carbon emissions to mitigate climate change. Global soils may provide a stable, sizeable reservoir to help achieve this goal by sequestering atmospheric carbon dioxide as soil organic carbon (SOC). In turn, SOC can support healthy soils and provide a multitude of ecosystem benefits. To support SOC sequestration, researchers and policy makers must be able to precisely measure the amount of SOC in a given plot of land. SOC measurement is typically accomplished by taking soil cores selected at random from the plot under study, mixing (compositing) some of them together, and analyzing (assaying) the composited samples in a laboratory. Compositing reduces assay costs, which can be substantial. Taking samples is also costly. Given uncertainties and costs in both sampling and assay along with a desired estimation precision, there is an optimal composite size that will minimize the budget required to achieve that precision. Conversely, given a fixed budget, there is a composite size that minimizes uncertainty. In this paper, we describe and formalize sampling and assay for SOC and derive the optima for three commonly used assay methods: dry combustion in an elemental analyzer, loss-on-ignition, and mid-infrared spectroscopy. We demonstrate the utility of this approach using data from a soil survey conducted in California. We give recommendations for practice and provide software to implement our framework.
Highlights
Climate change is likely to put enormous strain on nature and human societies in the coming decades
Global soils may provide a stable, sizeable reservoir to help achieve this goal by sequestering atmospheric carbon dioxide as soil organic carbon (SOC)
Dividing by μand combining this with the dry combustion in an elemental analyzer (DC-elemental analyzers (EAs)) error, we estimated an error variance for LOI of σδ,LOI = 0.11 in the top soil and σδ,LOI = 0.67 in deep soil
Summary
Climate change is likely to put enormous strain on nature and human societies in the coming decades. It is largely driven by the release of atmospheric carbon. Soils have lost about 50% - 70% of their carbon to the atmosphere. Soil still accounts for the 2nd largest store of carbon on Earth after the ocean, containing about 7.5 times that of the atmosphere [1]. Agriculture is one of the largest contributors to global carbon emissions
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