Models4Pastures : Nitrous oxide from agriculture

Nitrous oxide is one of the four most important greenhouse gases. It is produced, among other ways, in soils and released from there to the atmosphere. Little is known about the spatial and temporal differences in nitrous oxide emissions from varying pasture systems. The modelling of grazed systems is difficult due to the animals’ selective grazing and the displacement of nutrients (i.e. nitrogen) to relatively small patches of dung and urine. A comprehensive analysis of both, available in-situ measured N2O flux data and a thorough comparison of simulation models remains lacking. Nevertheless, such comparisons are essential in order to improve the assessment of potential mitigation options of nitrous oxide emissions.

The primary aim was to test good-bet strategies to mitigate nitrous oxide from pastures experimentally in Switzerland as well as with several biogeochemical process models for temperate pastures across the globe.

A secondary aim was to improve the models to better simulate multi-species grasslands, which is a big challenge for the majority of available models.

The experimental data in Switzerland showed, that N2O emissions can be reduced by approx. 50% when replacing organic fertilizer input with biological nitrogen fixation of legumes. Simultaneously, the different pathway of nitrogen provisioning with legume intercropping to the pasture system did not affect productivity. Moreover, another analysis in Central Europe showed that, management, particularly fertilization, is the major driver of N2O emissions followed by environmental conditions.

Ensemble modelling (many models simulate the same treatment) of a range of mitigation options revealed that the results for N2O emission and yield prediction differ considerably and specific improvements to reliably simulate mitigation options in pasture systems are necessary. Also, not only reducing N inputs into grazed systems leads to reduced N2O emissions, a combined reduction of animal numbers further helps to reduce negative environmental impacts such as greenhouse gas emissions.

Continuous measurements of N2O exchange provides invaluable data and ongoing measurements need to be maintained. Experimental setups in order to quantify N2O emissions in-situ need to be expanded to more treatments as well as across climatic gradients and different intensities of agricultural production systems.

Future experimental research must include biogeochemical process models from the very beginning in order to improve the models by being able to simulate multi-species grasslands as well as resembling more (all) ecosystem processes.

The project has shown that N2O emissions can be significantly reduced when adjusting nitrogen inputs in pastures systems from fertilizer amendments to biological nitrogen fixation via legume intercropping. Subsequent follow-on effects, i.e. co-benefits for animal feeding (better digestibility, reduced methane emissions from enteric fermentation), long-term stability of these findings as well as other usage for the still produced organic fertilizer at farm-scale need to be investigated. Finally, less fertilizer inputs (organic and inorganic) will not only reduce negative environmental effects but can furthermore optimise cost-efficiency while maintaining yields.

Robust models for assessing the effectiveness of technologies and managements to reduce N2O emissions from grazed pastures (Models4Pastures)