Process-based modeling of nitrous oxide emissions from wheat-cropped soils at the sub-regional scale
Résumé
Arable soils are a large source of nitrous oxide (N2O) emissions, making up half of the biogenic emissions worldwide. Estimating their source strength requires methods capable of capturing the spatial and temporal variability of \ony~emissions, along with the effects of crop management. Here, we applied a process-based model, CERES, with geo-referenced input data on soils, weather, and land use to map N2O emissions from wheat-cropped soils in three agriculture intensive regions in France. Emissions were mostly controlled by soil type and local climate conditions, and only to a minor extent by the doses of fertilizer nitrogen applied. As a result, the direct emission factors calculated at the regional level were much smaller (ranging from 0.0005 to 0.0016 kg N2O-N kg N) than the value of 0.01125 kg N2O-N kg N currently recommended in the IPCC Tier 1 methodology. However, regional emissions were highly sensitive to the soil inorganic N content at the beginning of the simulation in late summer. Mitigation measures should therfore target a reduction in the amount of soil inorganic N upon sowing of winter crops, and a decrease of the soil N2O production potential itself. From a general perspective, taking into account the spatial variability of soils and climate thereby appears necessary to improve the accuracy of national inventories, and to tailor mitigation strategies to regional characteristics.