Lowering the crude protein content of diets can substantially reduce ammonia emissions from dairy cow manures.
This is one of the findings of a major four-year project currently underway at Northern Ireland’s Agri-Food and Biosciences Institute (AFBI).
Ammonia is produced when faeces (which contains the enzyme urease) and urine (which contains urea) mix, with this process taking place on the floors of livestock houses, during slurry storage and at field spreading.
The ammonia gas produced enters the atmosphere and may be deposited locally on sensitive habitats, where the nitrogen within ammonia can cause nutrient enrichment of soil and water and lead to biodiversity loss.
Both livestock production and sensitive habitats have a significant presence in Northern Ireland and, as such, ammonia emissions present a key challenge for the livestock industry in order to support the health of sensitive habitats.
Lowering crude protein
AFBI is partnering with John Thompsons and Sons Ltd., and Trouw Nutrition Ltd., in developing the new project. Department of Agriculture, Environment and Rural Affairs ( DAERA) funding is also available.
In one of the studies within this project, dairy cows were offered diets containing either 14%, 15.5% or 17% crude protein on a dry matter (DM) basis, with the concentrates offered with each treatment formulated using different raw material inclusion levels.
During this study samples of faeces and urine produced from cows on each diet were collected and subsequently mixed and incubated in a temperature-controlled environment.
Ammonia produced from the different manures was then measured over a four-week period using a photo-acoustic gas monitor.
The work has confirmed that reducing dietary crude protein levels from 17% to 14% reduced ammonia emissions by an average of 64%, with emissions from the 15.5% crude protein diet intermediate in nature.
Bigger picture
In addition, the AFBI work clearly demonstrates that ammonia production was highest during the days after the faeces and urine were produced, and gradually decrease over time.
The background document produced by DAERA as part of Northern Ireland’s recent ammonia consultation contextualises the current AFBI work extremely well.
It specifically points out that action on this matter is required urgently, in order to achieve better outcomes for nature, and for public health.
In other words, addressing this challenge is essential to see agriculture thrive while at the same time protecting our environment.
The greater the extent and speed of action to lower ammonia emissions and reduce ammonia concentrations, the greater opportunity there will be to support sustainable farm development.
Northern Ireland has 394 sites of high nature conservation value designated for their protection.
Almost 250 of these are sensitive to the impacts of ammonia and nitrogen. The vast majority of designated sites are currently experiencing ammonia concentrations and nitrogen deposition above the critical levels and loads at which damage to plants may occur.
As a consequence, sustained and tangible reductions in ammonia are required to protect nature, to meet Northern Ireland’s legal obligations and to ensure a sustainable agri-food sector.
Ammonia targets
DAERA has set two 2030 ammonia targets. These are 1) to reduce total agricultural ammonia emissions by at least 30% from 2020 levels and 2) to reduce ammonia levels at internationally designated sites by 40% by 2030.
There are two pillars to the envisaged ammonia abatement strategy that has been proposed by DAERA. Pillar 1 comprises ambitious and verifiable ammonia reduction programme with Pillar 2 centred on conservation actions to protect and restore nature.
The establishment of a stakeholder group, representing primary agriculture, the agri-food supply chain and the environmental sector, has been proposed to advise on implementation of the finally agreed measures.
The steps that can be taken on farm to reduce ammonia production and emission levels are multi-faceted.
The uptake of verifiable ammonia reduction technology in livestock housing will be encouraged. There will also be a requirement to spread all slurry using low emission slurry spreading (LESS) equipment by 2026.
Trials have shown that nitrogen excretion levels in cows’ urine can more than double if dietary protein levels are boosted from 14% to 19%.
This process, in itself, puts an additional energy demand and increases the metabolic stress on the cow.
The fact that urea is a very volatile chemical means that a high proportion of it is lost to the atmosphere when slurry is spread on land.
Urea is also very water soluble. As a consequence, it can add to the pollution threat posed by slurry.
Typically, the nitrogen efficiency of dairy cow diets will be in the region of 22% to 32%.
Reducing emissions
Developing verifiable systems to encourage implementation of longer grazing seasons has significant potential for the future.
The need to reduce ammonia emissions from fertiliser will include a consultation on the potential introduction of a prohibition on the use of urea fertiliser without an inhibitor in 2024.
Establishing systems to implement and verify crude protein reductions in livestock diets can play a key role in reducing farm ammonia production levels, as will the identification and selection of genetic traits that maximise nutrient use efficiency.
In addition, supporting protein crop establishment is already available, courtesy of a pilot scheme.
And, finally steps will be taken to encourage the development and implementation of emerging technologies for ammonia reduction.
Livestock diets
It is universally agreed that reducing crude protein in livestock diets has a significant influence on ammonia emissions.
Reducing the amount of nitrogen in animal feed reduces the amount in excreta, leading to less of the nutrient being available for ammonia generation.
Scientific research shows that ammonia emissions are reduced by 8-10% for every 1% fall in crude protein in pig diets.
Ammonia reductions of up to 35% are thought to be possible in poultry diets.
Across the livestock sectors, including cattle, it is envisaged that reducing crude protein in all livestock diets can achieve an industry wide reduction in ammonia of around 9%.
Trials have shown that nitrogen excretion levels in cows’ urine can more than double if dietary protein levels are boosted from 14% to 19%.
This process, in itself, puts an additional energy demand and increases the metabolic stress on the cow.
Typically, the nitrogen efficiency of dairy cow diets in Northern Ireland will be in the region of 22% to 32%.
