Modelling the Impact of Liquid Organic Fertilization and associated Application Techniques on N2O and N2 Emissions from Agricultural Soils

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Fertilizing arable soils with liquid manures affects gaseous N losses to the atmosphere including NO, N2O and N2 as well as nitrate leaching. These emissions impair nitrogen use efficiency of crops and contribute to the greenhouse effect and stratospheric ozone destruction and pollution of aquatic resources. Their extent depends on the complex interaction between manure application techniques and properties of manures and soil. Whereas the type of manure effects on N transformations including gaseous fluxes is known, their prediction is still poor because previous investigations mostly excluded N2 flux quantification and current models do not consider the process dynamics arising from the spatial dispersion of manure components within the soil. Our proposal addresses the general question, how liquid manure fertilization and its application mode impact N2O and N2 fluxes from agricultural soils, how their optimization could mitigate emission while maintaining crop yields and how models would have to be improved to find answers. We will address this by targeted experiments to quantify N2, N2O and NO fluxes as well as gross rates of mineralization and nitrification of soil-manure systems under controlled conditions and using results to evaluate and improve models. The first part of the work program includes laboratory experiments to compare the effect of different techniques of liquid manure application in combination with soil and manure properties on N2O and N2 emissions. This will be a basis to test and improve empirical and process based models. Furthermore, we will use data from micro-lysimeter experiments and field experiments from cooperating projects to test the models. The second part of the work program includes model testing and improvement based on the experimental data. We will first test and calibrate an existing conceptual "Static Model" that takes into account spatial distribution of manure components. This is to evaluate the potential usefulness of its conceptual approach for implementation into mechanistic numerical models. For the latter we plan to use the models CoupModel and DNDC. These models could simulate the effects of slurry application techniques dynamically by their ability to predict the interaction of respiration, diffusion, mineralization, pH and their impact on nitrification and denitrification over time. Both models are designed to model bulk soil conditions and transport only in relation to soil-atmosphere gradients. We will implement the ability to model gradients due to organic hotspots using algorithms of the "Static Model".The last part of the work program will evaluate manure effects in arable agriculture and potential greenhouse gas mitigation options using improved models. Simulations will be designed for testing assumptions of realistic environmental conditions in order to predict manure effects on N2 and N2O fluxes in various soil and climate conditions and in dependence of manure properties.