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New model makes it easier to predict GHG emissions in different livestock grazing systems

Research Digest

Predicting the nitrous oxide (N2O), ammonia, methane and carbon dioxide emissions generated by different livestock systems will become easier following the development of a model, by researchers at Rothamsted Research and the Bristol Veterinary School.

The computer model simulates the intricate workings of a livestock farm, accurately mimicking grass growth, the amount of beef and lamb it produces, and the greenhouse gas emissions of its animals. It will enable complex systems to be analysed without the need for realworld experiments.

Measurement of greenhouse gas emissions in livestock production is challenging. Emerging agri-tech to support the transition to net zero is to be discussed at an Agri-TechE event to be held at Rothamsted Research, Harpenden.   

Lead author Dr Lianhai Wu said: “Our computer model accurately predicts animal and grass growth, greenhouse gas emissions, as well as nutrient and water cycling by taking into account the effects of factors such as livestock breed, climate, soil types and feed quality and quantity.

“The model could potentially integrate economic, environmental and social factors as well to provide decision makers with the ability to forecast, interpret and respond to potential threats or opportunities for UK livestock farmers.”

Ruminant livestock can make an important contribution to global food security by converting feed that is unsuitable for human consumption into high value food protein, however overuse of bought in feed and intensive production may create adverse environmental impacts.

Predict GHG emissions from livestock systems

The extended SPACSYS model enables estimates of ruminent growth under different feeding regimes. Intake of herbage (plants other than grass) and concentrates and the energy they contain was simulated in the component. Animal growth was validated by using liveweight data from over 200 finishing beef cattle and 900 lambs collected from the North Wyke Farm Platform (NWFP) in southwest England, UK, between 2011 and 2018.

Agriculture is the major source of NH3 emissions to the atmosphere, primarily deriving from livestock. The study provided insights into nitrogen cycles on a permanent pasture grazing system. It showed that 13% of the nitrogen applied as manure and deposited as excreta during grazing was lost to the air via ammonia volatilisation.

Of the inorganic nitrogen applied as Ammonium Nitrate at 190 to 260 kg ha−1, 37–61% was removed from the fields either as silage or animal intake. However, 15–26% was lost through surface runoff or drainage and 1.14% was emitted to the atmosphere as N2O.

Supplied by Rothamsted Research

Novel whole system model

It is novel to link animal, plant, soil and atmosphere together into a whole system model. By doing so it is possible to quantitatively investigate the dynamics of animal and grass production and nutrient fate, and their interactions under varied environmental conditions.

Through this study, the configuration for a permanent pasture grazing system has been validated. Researchers observe that the extended model has the potential to investigate the responses of the system on and consequences for a range of agronomic management and grazing strategies.
L. Wu, P. Harris, T.H. Misselbrook, M.R.F. Lee, Simulating grazing beef and sheep systems, Agricultural Systems, Volume 195, 2022,103307,ISSN 0308-521X.