Importance of soil structure, carbon translocation and crop residue quality for carbon storage in cropland soils
Final Report Abstract
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 asymptotic 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 project was to find explanations for the observed relationships by considering soil structure, nitrogen availability, and carbon saturation effects. Controlled short-term incubation experiments, physical and biological fractionation methods and development of soil structural properties will be related to the less controlled, but long-term, findings of the field experiment. Overall, we could show, that the observed non-linear relationship between SOC stocks and C-inputs (Figure 1) can be explained by different qualities of the C-inputs. Root residues mineralize slower than aboveground biomass, thereby inducing longer-lasting priming effects on SOC. The slower mineralization can be explained by the chemistry, and likely also by a higher physical protection within (micro-)aggregates. With increasing rates of C-input, priming increased (leading to faster mineralization of SOC) and the proportion of residues within aggregates decreases (leading to lower physical protection of residues). The balance between physical protection, priming and the ratio of functionally different above- and belowground C inputs is therefore crucial for the soil organic carbon balance in the Puch experiment. Carbon saturation of the mineral fraction or carbon translocation to the subsoil were not important mechanisms. Further experiments are needed to evaluate if the shown mechanisms are generally or only specifically valid.
Publications
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(2017) Decadal nitrogen fertilization decreases mineral-associated and subsoil carbon. Land Degradation & Development
Shahbaz M, Kuzyakov Y, Maqsood S, Weendlad M, Heitkamp F
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(2017) Decrease of soil organic matter stabilization with increasing inputs: mechanisms and controls. Geoderma
Shahbaz M, Kuzyakov Y, Heitkamp F
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(2017) Microbial decomposition of soil organic matter is mediated by quality and quantity of crop residues: mechanisms and thresholds. Biology and Fertility of soils
Shahbaz M, Kuzyakov Y, Sanaullah M, Heitkamp F, Zelenev V, Kumar A, Blagodatskaya E
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(2018) Priming effects induced by glucose and decaying plant residues on SOM decomposition: A three source 13C/14C partitioning study. Soil Biology and Biochemistry
Shahbaz M, Kumar A, Kuzyakov Y, Börjesson G, Blagodatskaya E
