Modeling N2O and N2 fluxes from organic fertilization

Background and Objective

Fertilizing agricultural soils with liquid manures affects gaseous N losses to the atmosphere including N₂O, N₂, NH₃ and NO 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 (surface, injected, incorporated) impact N₂O and N₂ fluxes from agricultural soils, how their optimization could mitigate N₂O and NH₃ emissions while maintaining crop yields and how models would have to be improved to find these relevant 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 overall aim of the project is to test and improve the ability of biogeochemical models to predict effects from liquid manure fertilization on N₂O and N₂ fluxes. We will use existing and new data on the basis of conceptual understanding where we target mechanisms that are until now not properly accounted for in the models.

Specific objectives are

• Compile existing data-sets and collect new data-sets suitable to test and calibrate existing and improved models.
• Investigate the effects of fertilization with liquid organic manures under varying pH and using different application techniques on N-transformations, N₂, N₂O and NO fluxes and elucidate the respective control factors.
• Improve and calibrate the nitrification, denitrification and decomposition sub-models for better modelling of liquid organic manure effects.
• Apply and validate the model with existing data sets from field
• Test GHG mitigation strategies based on optimized slurry fertilization using the calibrated and improved models.

Target Group

Scientific community

Approach

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 develop or improve and test empirical and process-based models.

The second part of the work program includes model development, improvement and testing 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 will implement the ability to model gradients due to organic hotspots using algorithms of the “Static Model”. We plan to use this concept and integrate it with other process-based models (DeNi model and/or DNDC). The selected process-based 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.

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.

Our Research Questions

• Are anaerobic processes and N₂ and N₂O emissions enhanced by concentrated distribution of slurry compared to homogeneous distribution?
• Are N₂ and N₂O emissions reduced by factors increasing the initial uptake of degradable volatile solids into the soil matrix?
• Are current biogeochemical models underestimating slurry-induced N₂ and N₂O fluxes due to the lack of routines to take non-homogenous slurry distribution into account?
• Can these shortcomings be solved by implementing additional compartments for slurry fractions?

Results

Laboratory work of the first funding phase is completed (see first publication under "Projektverknüpfungen zu Publikationen, Projektbewirtschaftung und Stellenangeboten", a second publication is under reveiw). Development and application of the models  is ongoing. First findings  have been reported as part of two overwiew papers (both submitted, one already accepted).  A proposal for extending the project for further 3 years was submitted to DFG in due time. The final report of the first funding phase is part of the proposal and is thus not available to the public.