Muck-spreading, the agricultural practice of spraying fields with liquid manure, will effectively be banned under government plans to reduce air pollution.

Animal manure is a key source of ammonia, a powerful pollutant that, combined with other chemicals in the air, form fine particles that can lodge deep in the lungs, harming human health.

The government announced a new air pollution strategy on Monday that will include a new focus on emissions of ammonia, along with measures to reduce pollution from wood-burning stoves and other fuels. Critics said the plans were inadequate to the scale of the problem and were not legally binding, unlike the EU rules they will replace.

Ammonia emissions, more than four fifths of which come from agriculture, are on the rise. Ways of reducing them on farms require changes to widespread practices: instead of spraying fields with slurry – a method known as “splash plate” – farmers can use more modern methods that create less diffusion, targeting manure to the areas where it is needed.

Slurry can be distributed into narrow, evenly spaced rows or injected into the soil, where its fertilising impact is most effective and its exposure to the air much less.

A Defra spokesperson said: “From 2025 we will require farmers to spread slurry and digestate using only low-emission spreading equipment, such as trailing shoe, trailing hose or injection. Spreading of organic manure, such as slurry, provides crop nutrients and can replace the use of inorganic fertilisers. Use of slurry in this way is a good example of resource use efficiency, provided best practice is used. We will require and support farmers to make investments in the farm infrastructure and equipment that will reduce emissions from this source.”

Prof Mark Sutton, environmental physicist at the Centre for Ecology and Hydrology, said slurry spraying in its current form “probably should be banned”.

“This is the most significant document on controlling ammonia emissions that the government has ever produced,” he said. “It proposes a suite of regulations, permitting and financial support mechanisms which, if adopted, would substantially reduce UK ammonia emissions with major expected benefits for both vulnerable ecosystems and human health.”

He added: “It has often felt like ammonia was the forgotten pollutant, the Cinderella of air pollution policy. [The new strategy] indicates that this is about to change.”

Farmers have been promised support by the government to help them change their practices, and if necessary their equipment, but it is not clear how much money they might receive. The government could include low-emissions practices in its plans to reward farmers for their conservation practices after Brexit. The new agriculture bill, currently passing through parliament, proposes a system of environmental land management contracts that are set out to accommodate ammonia reduction as one of the public goods for which farmers will receive public money and that will replace current EU subsidies.

The National Farmers’ Union said farmers would need “considerable financial support” to make the changes needed and would struggle to meet the government’s proposed timetable. Guy Smith, the NFU deputy president, said more detail was needed on how intensive farms, which will fall under stricter rules, should be defined. He also challenged ministers to explain how the proposed changes could be put in place without raising costs, which would “put the UK beef and dairy sectors at a competitive disadvantage with the rest of the world”.

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Liz Bowles, head of farming at the Soil Association, said intensive livestock production methods should be a key focus because emission rates increase at higher densities. Mega farms are on the rise in the UK: a Guardian investigation found close to 800 intensive farms spread across the country. Their emissions are not quantified by the government.

However, Bowles noted that all forms of farming, if poorly managed, could give rise to ammonia pollution, and she stressed the importance of better storage of animal manures, as well as better methods of using slurry on the soil. She said using trees to capture emissions and provide more effective ventilation systems for livestock housing could also help.

“Ammonia can be very harmful to the lungs, particularly for those already vulnerable, and can also have a detrimental impact on biodiversity as wildlife is also affected. We recognise that changes in farming practice are necessary and this will involve both government regulation and support,” Bowles said.

Tim Farron, the Liberal Democrat environment spokesman, said the government should do more to help: “Farming has an important part to play in helping reduce emissions, whether that’s through restoring carbon sinks or cutting the use of air polluting fertilisers. [We] support the reduction of ammonia in agriculture, but the Conservatives are failing to give farmers the tools to work in tune with nature. We would reward farmers, rather than simply trying to force farmers to change their behaviour.”

The government’s air pollution strategy met with a mixed response, as civil society groups, scientists and health organisations broadly welcomed the intention to reduce air pollution, but many questioned some of the policies and complained about the lack of a detailed timetable and legally binding commitments.

Michael Gove, secretary of state for the environment, attempted to shift the focus away from diesel cars, which are the leading source of nitrogen oxides in urban areas and a key source of particulate emissions. He said: “While air pollution may conjure images of traffic jams and exhaust fumes, transport is only one part of the story, and the new strategy sets out the important role all of us can play in reducing emissions and cleaning up our air to protect our health.”

Several organisations questioned this approach. Greg Archer, a director at the campaigning group Transport & Environment, said: “This new strategy once again fails to tackle the UK’s biggest source of air pollution, the 7m dirty diesel cars on the UK’s roads. The government needs to use new regulations to force carmakers to clean up the dirty diesels on the road or ban them from city centres.”

Tim Mitchell, cabinet member for environment at Westminster council – one of the most air polluted areas in the country – added: “Air quality is the number one concern for our residents. The government’s new strategy is welcome, but we need more details on how and when new measures will be introduced. With 9.9 million drivers in the capital, road transport contributes to more than half of the most deadly emissions. While we’d be ready to take on more responsibilities and powers, we need more resources from government.”