Process-oriented modelling to mitigate greenhouse gas emission on dairy farms adapting to climate change

Gepubliceerd op
25 september 2014

Modelling exercises within the project AnimalChange indicate net on-farm GHG emissions (neglecting off-farm and indirect emissions) per unit of milk produced are lower for intensive dairy farming, with enteric methane contributing most.

The research project AnimalChange, funded by the EU (under grant agreement number FP7-266018) and the Dutch Ministry of Economic Affairs, delivers estimates of the potential of mitigation options to reduce greenhouse gases (GHG) emissions (i.e. emission of carbon dioxide, methane and nitrous oxide) and indicates the implications of an livestock production systems adapting to future climatic conditions. Cow productivity has a profound effect on intensity of CH4 emission when expressed per unit of milk or per hectare. Effect of stocking density and intensity of the dairy farm management becomes more prominent when comparing farms that are highly different in level of intensity.

Modelling dairy GHG emissions

In collaboration with Teagasc (Ireland), INRA (France) and Aarhus University (Denmark), Wageningen UR Livestock Research used process-oriented models to simulate the effects of mitigation and adaptation options on GHG emission from enteric fermentation in livestock, stored manure and soils. Wageningen UR Livestock Research contributed with a process-based model of enteric fermentation in lactating cows; a world-wide unique IPCC Tier 3 approach in use in the Dutch inventory of GHG emissions since 2005. Simulation results suggest IPPC Tier 2 methodology should be abandoned when aiming to evaluate the effect of case-specific management options on GHG emission. Adoption of Tier 2 methodology is particularly instrumental at the scale for which it originally has been developed, i.e. national surveys and for average farming conditions.

Mitigation measures   

Measures to mitigate enteric CH4 emission are higher N fertilisation of grassland, earlier cutting of grass, exchange of grass silage for maize silage, later cutting of maize crop, inclusion of starch-rich supplements in grass-based diets, and inclusion of protein-rich supplements in maize silage-based diets. Simulated CH4 emissions were generally lower than estimated by IPCC Tier 2 methodology (6.5% of ingested gross energy emitted as CH4, irrespective of farming conditions). Relative to the mitigation potentials simulated, alternative measures of fat and nitrate supplementation of the diet remain highly effective, and can add-on to the mitigation potential if trade-offs on cow health and fibre digestibility are prevented. Also the pasture and soil models show emission factors that strongly differ from IPCC Tier 2 defaults. They further show a large impact of climate scenarios, management options and initial soil and grassland conditions on soil-related emissions.

Farm cases

Studying a selection of well-monitored case farms widely differing in intensity of nutrition and farm management, net on-farm GHG budget per unit of milk produced seem lower with more intensive farming. However, when taking into account off-farm GHG emissions associated to maize silage and concentrates purchased and the higher fossil energy use with the more intensive farm management, GHG emissions per kg of milk produced become more comparable or higher for intensive farming. Milk production achieved per ha always remains higher with intensive farming.