Dear Dr.Srinivasa Rao, interesting question. As I understand the threshold values for carbon sequestration may be the saturation levels in different soils under given set of environmental conditions. Soils under forestry for longtime in different environments may have threshold levels of carbon sequestration.
Dr.Srinivasa Rao,the threshold hold values for carbon sequestration in soil may differ in different environments,land uses and managements.Carbon saturation levels in soils under natural forest for long time may be threshhold values for carbon sequestration. Soil organic carbon levels in longterm experments receing fertilizers, manures and irrigation may also give near threshhold values of carbon sequestration.Long term experments under conservation agriculture and well maintained grasslands may also have near threshold level of carbon sequestration in soil.
Thank you very much. I am particularly looking for rainfed dryland ecosystems.
In the last decade or so a number of papers have been published on carbon sequestration under different soil-crop-climatic conditions.It is now time to synthesize the information on broader perspectve incorporating all the component researches.First question is do we have some base line values for soil carbon in different soils,under dominant cropping systems in a particular environment,say rainfed dry land ecosystem? Base line values of carbon may vary under different management levels also.To get the rate of carbon sequestration we need to generate the carbon sequestration (cumulative,stock) for a considerable period or duration under defined condions(soil,crop,environment and management).From this one can compute the seqestration rate (kg/ha/yr).From this one can extrapolate the figure for a decade or more to get potential sequestration or threshold value.But there is risk in extrapolation.Carbon saturation levels in near by forest area may be much different from agricultural area which is a disturbed ecosystem(except conservation agricuture area).Continuous fresh carbon input is a precondition to maintain certain carbon level.Carbon saturation level depends first on climate,then on soil type especially the content of finer paticles,clay and silt ,aggregation (micro and small macro agregates), microbial synthesis of humus,mycorrhizae etc.When soil carbon level is approaching near saturation level in particular enviroment,the proportion of input carbon going into passive/stable/recalsitrant pool will be less and the proportion of active/lablie/particulate carbon will be more( which is subjected to mineralizaton and more CO2 emissions).So the saturation level attainable will be less than the predicted figure from sequestration rate. Getting steady state carbon threshold values in rainfed ecosystem is questionable unless we control as many factors as possible.Using some model(modified model for rainfed system),one can simulate conditions and get predicted threshold values which can be compard with values obtained in long term experiments in raifed areas.Let us further debate the isuue.
The following Dissertation of University of Pennsylvania by Wenting Feng provides a thorough picture of carbon saturation,its determination, factors influencing saturation and related aspects .
Testing the soil carbon saturation theory:Maximal carbon stabilization and soil organic matter stability as a function of organic inputs. 2012
http://repository.upenn.edu/edissertation/507
- Badges
- Science topic
- Similar topics
- Agriculture
- Soil Science
- Soil