Importance of soil structure, carbon translocation and crop residue quality for carbon storage in cropland soils

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Cropland soils may be a sink or source for atmospheric CO2. In general, it is assumed that C-input into soil and soil organic carbon (SOC) levels are linearly related. This gives rise to environmental concerns regarding the removal of crop residue. In recent years it has been shown that residue incorporation increases SOC levels only to small extents. In the well designed and documented long-term experiment of Puch, Germany, an observed quadratic relationship contradicted the predicted (Rothamsted Carbon model 26-3) relationship of C-input (range of 1-5 Mg C ha-1 year-1) and SOC changes. The purpose of the proposed project is to find explanations for the observed relationships by considering soil structure, nitrogen availability, and carbon saturation effects. Controlled short-term incubation experiments, physical, biological and chemical fractionation methods and development of soil structural properties will be related to the less controlled, but long-term, findings of the field experiment. Explaining the deviations between prediction and observation in this case study will be an important step in designing a climate friendly and economically sound agriculture while sustaining physical, biological and chemical soil fertility.