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Over the past decades, average global wheat yields have increased by about 250 %, mainly due to the cultivation of high-yielding wheat cultivars. This selection process not only affected aboveground parts of plants, but in some cases also reduced root biomass, with potentially large consequences for the amount of organic carbon (OC) transferred to the soil. To study the effect of wheat breeding for high-yielding cultivars on subsoil OC dynamics, two old and two new wheat cultivars from the Swiss wheat breeding program were grown for one growing season in 1.5 m deep lysimeters and pulse labeled with 13CO2 to quantify the amount of assimilated carbon that was transferred belowground and can potentially be stabilized in the soil. The results show that although the old wheat cultivars with higher root biomass transferred more assimilated carbon belowground compared to more recent cultivars, no significant differences in net rhizodeposition were found between the different cultivars. As a consequence, the long-term effect of wheat cultivar selection on soil organic carbon (SOC) stocks will depend on the amount of root biomass that is stabilized in the soil. Our results suggest that the process of wheat selection for high-yielding cultivars resulted in lower amounts of belowground carbon translocation, with potentially important effects on SOC stocks. Further research is necessary to quantify the long-term importance of this effect. [ABSTRACT FROM AUTHOR]

Over the past decades, average global wheat yields have increased by about 250 %, mainly due to the cultivation of high-yielding wheat cultivars. This selection process not only affected aboveground parts of plants, but in some cases also reduced the root biomass, with potentially large consequences for the amount of organic carbon (OC) transferred to the soil. To study the effect of wheat breeding for high-yielding cultivars on subsoil OC dynamics, two old and two new wheat cultivars from the Swiss wheat breeding program were grown for one growing season in 1.5 m-deep lysimeters and pulse-labelled with 13CO2, to quantify the amount of assimilated carbon that was transferred belowground and potentially stabilized in the soil. The results show that although the old wheat cultivars with higher root biomass transferred more assimilated carbon belowground compared to more recent cultivars, no significant differences in net soil organic carbon (SOC) stabilization were found between the different cultivars. As a consequence, the long-term effect of wheat cultivar selection on SOC stocks will depend on the amount of root biomass that is stabilized in the soil. Our results suggest that the process of wheat selection for high-yielding cultivars resulted in lower amounts of belowground carbon translocation, with potentially important effects on SOC stocks. Further research is necessary to quantify the long-term importance of this effect. [ABSTRACT FROM AUTHOR]

Management of croplands affects the soil organic carbon content in the soil. Thus, changes in the management might increase the SOC content. However, changes in the management go along with a risk of decreased yield. Therefore, these two aspects needs to be analysed together. Emission factors (EF) are an easy approach to calculate the impact of the changes and they are widely applied in different studies. These emission factors are generic and estimated for actual climatic conditions. The values might vary among countries or for changed climatic conditions. Therefore, this study presents computer simulation based calculations for EF in UK on six croplands (all wheat). The EF are calculated by using simulation results of the biogeochemical models LandscapeDNDC and DAYCENT. The considered management practises included changes in fertilizer amounts, residue management and tillage. Additional, fertilizer plots were tested for manure application instead of mineral fertilizer. The results show varying impacts through the different test sites, but with a general trend of highest SOC increases for changes in residue management (residues left on the field) and manure application. The scale of the impacts is different on the different soil types, with higher impacts of residue management on clayey soils and higher tillage effects on sandy soils. An additional analysis of impacts on yield showed that mitigation options resulted in a greater reduction in yield under a future climate than under the current climate. The calculated EF is not in entirely in agreement with IPCC values, especially for some values for manure and residue management that exceed IPCC values for the UK. The results of the study show that the IPCC values need to be adapted for a country specific analysis. Additionally, the EF might change for future climate conditions, which needs to be considered in future estimates. [ABSTRACT FROM AUTHOR]