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Process Oriented Biogeochemistry Models

Outline. What are included in Biogeochemistry Models?Soil C, N, and P cycling modelsSoil carbon model descriptionSoil nitrogen cycling modelsSoil phosphorus modelsConclusions. Data Sets Used to Test and Parameterize Soil Carbon Models. Total soil carbon from long-term experimentsAgricultural e

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Process Oriented Biogeochemistry Models

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    1. Process Oriented Biogeochemistry Models

    2. Outline What are included in Biogeochemistry Models? Soil C, N, and P cycling models Soil carbon model description Soil nitrogen cycling models Soil phosphorus models Conclusions

    3. Data Sets Used to Test and Parameterize Soil Carbon Models Total soil carbon from long-term experiments Agricultural experiments Grassland and forest experiments Spatial patterns in soil carbon for undisturbed ecosystems Soil texture has more impact than climate on soil carbon levels More carbon with clay soils Less carbon for sandy soils

    4. Data Sets Used to Test and Parameterize Soil Carbon Models C14 dating of soil fractions Turnover of SOM fractions range from <1 year to >5000 years – 0-20 cm depth turnover =200-400 years Labeled C14 and ?C13 addition experiments – adding of labled C14 and ?C13 plant material to the soil in the lab and field

    5. Data Sets Used to Test and Parameterize Soil Carbon Models Long term laboratory incubations of the soil – CO2 loss decreases exponentially with time Physical and chemical soil fractionation experiments – attempts to measure SOM fractions used in models and relate SOM fractions to soil fertility

    6. What do these experiments indicate? Clear evidence for fractions of SOM that have different turnover times (<1 to >5000 years) There are no robust soil fractionation techniques that measure the pools used in SOM models Soil texture has a large impact on stabilization of carbon in the soil Inversely proportional to sand content Proportional to clay content Total soil carbon levels is the best index of soil fertility and used extensively to test models

    10. Model Comparisons of Soil Carbon Models Smith et al. 1997 – Geoderma 81: 152-225 Nine model comparison Use long-term soil carbon data sets from seven experimental sites

    11. Model Comparisons of Soil Carbon Models Moorhead et al. 1999 – Global Biogeochemical Cycles 13: 575-590 Four model comparison Use litter decay data from LIDET Biomass and nitrogen data

    13. Soil Carbon Model Conclusions Most models use 5 to 7 pools to describe soil carbon dynamics Current biogeochemistry match observed soil carbon data quite well We can not currently measure the different carbon pools used in SOM models Extensive data exists to parameterize and test SOM models Impact of soil texture, climate and management on total soil C

    17. N Model Comparison Frolking et al. – Nutrient Cycling in Agroecosystems 52: 77-105 Four model comparison Daycent, DNDC, ExpertN, CASA-NASA Compare soil NO3, NH4, N-Min, T, H2O, and N2O at four sites

    19. N Model Comparison Results Most models results compared well to observed data Difficulty in simulating large N2O fluxes during winter thaw events Annual N2O fluxes are simulated well but daily fluxes are not well simulated Big differences in modeled Nox, NH3, and N2 gas fluxes

    21. Phosphorus Model Comparisons Lewis and McGechan. 2002. – Biosystems Engineering 82: 359-380 Compared four P cycling models Daycent, ANIMO, GLEAMS, EPIC

    22. Phosphorus Model Comparisons Gijsman et al. 1996. – Journal of Agronomy 88: 894-903.

    23. Overall Biogeochemistry Model Conclusions There are many soil C, N, and P cycling models available for simulating Soil C, N and P dynamics and N trace gas fluxes It is difficult to evaluate which of these models is the “best biogeochemistry model” Model comparisons are needed where all of the important output vaiables are observed: Inorganic and organic soil C, N, and P N trace gas fluxes (N2O, NH3, Nox, and N) Soil NO3, NH4, and soil NO3 leaching

    24. Overall Biogeochemistry Model Conclusions Good soil water and temperature and plant production models are needed to drive soil biogeochemistry model Key inputs soil for Biogeochemistry models: Soil water and temperature Plant demand for N and P uptake Vertical and horizontal water flow Dead plant material inputs (C, N, and P) Fert. and atmospheric inputs of N and P

    27. N Model Conclusions It is unclear which of the current N cycling models is the “BEST” It is very difficult to evaluate N cycling submodel performance since there are many important output variables: Soil NO3, NH4, and organic N N gas fluxes – NH4, N2O, Nox, and N2 Soil NO3 leaching

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