Get a nutritional value from slurry

With sky high nitrogen costs it is now more important than ever to fully exploit the potential savings from spreading muck carefully.

At the same time following good practice will also help with cross-compliance obligations and possibly even earn Environmental Stewardship points.

Slurry from a 200 cow dairy herd contains nutrients equivalent to saving £2000 a year on ammonium nitrate alone and nearly £4000 including phosphate and potash.

Rather than looking at manure management as a problem, farmers should consider the positive benefits that can be achieved from retaining the nutrients, says John Laws from the Institute of Grassland and Environmental Research, North Wyke, Devon.

“Spreading slurry at a rate and time to match crop requirements not only prevents pollution, but also ensures the crop exploits its nutrient value,” he explains.

The first, and possibly most important, step is to prepare a Manure Management Plan, which can be obtained from DEFRA or downloaded from the internet.

This guide helps you to ensure your muck spreading meets the Codes of Good Practice and identifies areas of the farm with greatest pollution risks.

It will also help protect you if anything does go wrong.

While completing this plan it will become clear that one of the best ways to manage slurry most effectively is to minimise the total volume.

It is now a requirement in some areas to have at least four months’ storage, and this volume can be calculated quite easily.

For example a Holstein cross dairy cow produces about 64 litres of undiluted slurry a day.

Adding the parlour washings and run-off from yards this could easily double to 130 litres a day per cow.

This would mean for 100 cows over a 180 day period, total storage needed would be 2340cu m (520,000gal).

“One of the simplest ways to reduce the volume is to divert ‘clean’ water from roofs away to a separate storage area.

This can then be reused, saving not only the extra cost of storage, but also water bills as well,” he adds.

Mr Laws says the dirty water should also be stored and dealt with separately, which is often more cost effective than adding additional slurry storage.

When it comes to spreading, applying the material at the correct time and in amounts that match the crop requirements will not only fulfil Good Agricultural and Environmental Conditions (GAEC), but help crops exploit the full nutrient potential in the slurry.

“The GAEC aims are to reduce pollution from emissions and to groundwater,” says Mr Laws.

He argues that there is 3kg of nitrogen in every cubic metre (1t) of dairy cow slurry.

About half the N is immediately available to the crop whereas the other half becomes available after mineralization in the soil.

This can only be used if there is an actively growing crop present.

And this is where the timing of applications is critical.

“Applying slurry when the crops are not growing wastes nutrients, it also means it cannot be used and will simply wash through the soil into the nearest ditch or river causing pollution,” he says.

There is also the cross-compliance consideration of ensuring the appropriate amounts of nutrients are applied to crops, which means farmers should take account of the fertiliser value of muck when calculating the total application rate.

Help is offered in the format of a DEFRA-funded, ADAS MANNER decision making software, which simple to use and freely available.

This removes the guesswork from estimating the value of N in the slurry and allows users to avoid costly over-application by calculating exactly how much bagged fertiliser is required.

“Applying slurry in the spring will reduce leaching risks as well as ensuring the crop makes the best use of the nutrients,” adds Mr Laws.

“But studies show the majority is still applied between August and January.

This is mainly because many farmers are concerned that spreading any later will adversely affect grazing or silage quality.”

Collaborative IGER and ADAS research proves this is not the case.

“Even conventional surface broadcasting at sensible rates, just six weeks prior to cutting will not affect silage quality.

Using shallow injection or trailing shoe equipment just two weeks before harvest still results in good quality silage being made,” he adds.

Contamination of grazing grass is also an issue.

But IGER research also shows that slurry banding techniques – such as trailing shoe – significantly reduces grass contamination.

There is no affect on grazing between untreated plots and those treated by shallow injection and trailing shoe methods, just five weeks after application.

But moving away from conventional splash-plate type broadcasting to the other methods will greatly reduce ammonia emissions – between 30% to 80% – and help retain valuable nutrients.

Shallow injectors work best in short swards, while trailing shoes offer greater flexibility by also producing good results in longer material.