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Soil landscapes as sources and sinks for greenhouse gases


Project code: ZALF-265
Contract period: 01.01.2006 - 31.12.2022
Purpose of research: Applied research

Soil landscapes constitute significant sources and sinks for greenhouse gases (CO2, N2O, CH4). Their natural functionality is influenced in manifold ways by land use and land management, respectively. Direct interferences in the water balance, for example by drainage practices, are known to modify the redox environment. It is likely to speed up the decay of the humus body resulting in a stronger CO2 emission and providing initial products for denitrification. Indirect interferences, e.g. land-use induced lateral sediment transports into wetlands (edges), will increase the availability of substrates for methanogenes. Parts of soil landscapes, originally having been greenhouse gas sinks, have thus become sources of continental relevance. In view of the societal demand for climate protection now the question has arosen to what extent and by what kind of changes in land use or management these sources of greenhouse gas emissions could be (re)converted into sinks. Although controls of the source function are widely known (e.g. ground-water levels, substrate quality), their regionalisation, i.e. the extrapolation to larger areas, currently still implies major uncertainties. Furthermore, the mechanisms of C sequestration in soil landscapes have not yet been adequately clarified. There is a prime demand for research designed to identify sensitive areas (where could a sink function be realised in the landscape, if at all?), to clarify the chemical bonding forms in soils (interaction between land use and pedogenesis), as well as to develop indicators being both dependable and easy to establish, for the quantitative estimation of emission reductions (new pools for C turnover models?). Finally, the impacts of the measures proposed for emission reduction on the respective landscape’s water budget, as well as on landscape functions, for example on agricultural production, must be taken into due account. Project Objectives Proceeding from the existing knowledge gaps, the project objectives can be defined as follows: · Elaboration of a set of methods for the regional assessment of C sequestration potentials in soil landscapes following land use change, · Elucidation of the mechanisms governing C sequestration in soils as a function of the combined effect of land use and pedogenesis, · Development of a regional model by means of which the impact of land use changes on nitrous oxide and methane emissions can be depicted site-specific. The respective research activities will be guided by the following hypotheses: · The farther away soil landscapes are from their natural quasi-equilibrium state, the higher is their C sequestration potential under changed land use. The sequestration potential has been found to increase in the following order: modified arable land management (direct sowing, rotation fallow, energy plants) < land conversions (arable land to permanent fallow, grassland or forest) < restoration of the original water state changed by amelioration measures (rewetting of drained bogs or non-drained hollow forms), · Reactive mineral surfaces determine the degree of long-term C sequestration in soils. The quantity of reactive mineral surfaces is, in turn, a function of pedogenesis under different land use (records), · In the glacial landscapes of the North-East German Lowland there is a continentally significant potential for emission reduction.

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