About

Process-​based models are needed to test possible mitigation options through developing greater understanding of their efficacy and likely flow-​on effects such as changed input needs and productivity. Few grassland model comparison studies have been published although this is regarded as an essential step in developing robust tools for assessing potential mitigation options.

Models4Pastures tests, improves, and then uses simulation models to provide robust assessments of the impact of N₂O mitigation options in grassland systems across a large geographic and climatic range. Our models and assessments take into account the effects of the mitigation option, and its follow-​on consequences (e.g. changes in grazing intensity) for other gases to understand the net ecosystem effect, food production and variability of production, and the effects on the ability of the soil to sustain production. This work is done in the company of current and proposed FACCE-​JPI projects and other international activities. The Swiss contribution is centered on an experiment with increased legume cover compared to a control area within the footprint of an eddy-​covariance flux tower at Chamau.

Results

The experimental data in Switzerland showed, that N₂O emissions can be reduced by approximately 50% when replacing organic fertiliser input with biological nitrogen fixation of legumes. 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 fertiliser at farm-scale need to be investigated.

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 fertilisation, is the major driver of N₂O emissions followed by environmental conditions. Less fertiliser inputs (organic and inorganic) will not only reduce negative environmental effects but can furthermore optimise cost-efficiency while maintaining yields.

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. In addition, 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.