Understanding soil quality and resilience: effects of perturbations and natural variations on nitrous oxide emission, water retention and structure

Lead Research Organisation: Rothamsted Research
Department Name: Unlisted


This project will promote and improve the understanding and predictability of soil quality and resilience, and assist with the minimisation of nitrous oxide (N2O) production. Grassland and arable soils with similar clay contents, but variable organic carbon content and age of ley, will be studied at 7 cm core and 50 cm precision lysimeter scale. The samples will be studied at typical ambient density, or after fast or slow compaction. A hierarchical approach will be taken to the properties of the samples, ranging from void structure through quasi-static and dynamic fluid properties, to structure-mediated chemical and biological processes. The void structure of the soil samples will be measured by X-ray computed tomography, and water retention curves will be measured with the help of a novel gravity drainage cell. The dispersion and breakthrough of conservative (bromide) tracer and nitrate will be measured using a new precision lysimeter and rainfall simulator. Nitrous oxide emissions will be measured under conditions which are structure mediated but neither carbon-nor nitrogen-limited. Dominance of denitrification over nitrification will be checked by measurement of isotope and isotopomer ratios. The results will be interpreted by a new multi-scale pore model of soil structure. Two hypothetical structures of soil will be generated, with micropores which act hydrologically parallel to macro-pores, or which act in series with the macropores. Inputs to the model will be the macro-pore size distribution from X-ray CT scans, and the full range water retention curves. Outputs will be conservative tracer breakthrough characteristics, nitrate dispersion characteristics, and rate of N2O production. We aim to obtain outputs sufficiently aligned with experiment that they can not only explain the properties of the sample set, but also predict the properties of other soils and conditions, thus allowing the fundamental advances to inform policy on land management.


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