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Response to the Letter to the Editor Regarding Our Viewpoint “Sequestering Soil Organic Carbon: A Nitrogen Dilemma”

Response to the Letter to the Editor Regarding Our Viewpoint “Sequestering Soil Organic Carbon: A Nitrogen Dilemma”

We disagree with the statement by Soussana et al. that the 4p1000 goal is already sufficiently spatially diversified because it is related to the local soil organic C (SOC) stock. This implies that soils with a large SOC stock will normally have a larger nitrogen (N) (and phosphorus, P) surplus than those containing less SOC. We fail to see the rationale for their statement in two ways. First, at the global scale, many soils with a large SOC stock will be (extensively) grazed grasslands, which typically have small inputs of N4 and P inputs and small surpluses. In contrast, many intensively managed arable soils, which typically have lower SOC stocks, have large inputs of N and P leading to large surpluses. Second, in general, soils with a low SOC stock (e.g., old arable soils, degraded lands, mine wastes) have greater potential for increasing SOC than soils with high SOC stocks. Focusing C sequestration efforts on these soils would seem advantageous, both for climate change mitigation and for improving soil quality.

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