Managing slurry nutrients: Are you making the most of the brown stuff?

The amount of livestock manure applied in the UK each year would fill all the lanes of the M1, plus the central reservation and hard shoulder from Leeds to London, to a depth of 10m.

However, producers and growers need to be sure of the nutrient content to help them reduce bagged fertiliser, according to a leading industry expert.

Black gold

Speaking at an Agriculture and Horticulture Development Board (AHDB) monitor farm group, John Williams, ADAS principal soil scientist, said around 90 million tonnes of livestock manure is applied in the UK each year but questioned whether farmers were making the most of it.

AHDB Dairy knowledge exchange manager Bryan Nicolson added: “Our data tells us that muck is worth £9.20/t and a cubic metre of slurry has a value of £3.20 in NPK alone. These products have real financial value for the farm – but only if they are stored and used correctly.

“This event aims to make sure farmers have the tools they need to ensure they are getting the most out of their muck and slurry, for example through using AHDB’s Slurry Wizard which allows them to calculate their volume of slurry and storage capacity.”

‘Less bagged fertiliser’

Newark farmer John Miller – who runs one of the ADHB monitor farms – is one of many who are now working to use less bagged fertiliser on his farm by taking advantage of organic manure available.

He said: “We’ve always known that organic manure is a good resource. It’s about applying it effectively and taking account of the nutrients in it so you can reduce the amount of inorganic fertiliser you put on.”

ADHB’s top tips for managing slurry nutrients:

  • Understand what the crop needs, using the ‘AHDB Nutrient Management Guide’;
  • Sample soil to find out what’s in it and what it’s deficient in;
  • Measure the nutrient content of manures. Section two of the Nutrient Management Guide gives a good start to this;
  • Top up with bagged fertiliser, if necessary.

Williams said: “It’s absolutely crucial to understand the nutrient content of manures before you apply them.”

But sampling needs to be done carefully to get a true representation of what’s in the manure. For example, lagoons should be stirred to homogenise the slurry before spreading with samples taken periodically during store emptying to make sure the analysis provides a good measure of the slurry nutrient content.

‘Rocket fuel’

Not all manures are the same and manures with a lot of readily-available nitrogen (N) should be handled carefully.

John Williams said: “Digestate is like rocket fuel – handle it with care. Digestate nutrient content reflects the feedstock used in the anaerobic digestion process.

“Food-based digestate can contain around 7kg of total N/m³ (approximately 6 kg/m³ readily available N) and 25m³/ha would supply 175kg N per hectare – so matching application rates to crop demand is vital.

“Testing the digestate is the best way of knowing the nutrient content, which is essential to make best use of the nutrients.”

Changes

As a result of the meeting, John Miller is considering whether he can apply organic manure in the crop rather than before it, to make better use of the nutrients available.

He said: “The cost of buying equipment to spread the manures in crop is fairly prohibitive for me, so I’d probably be looking at getting a contractor to apply it.

“Perhaps the saving we make in reducing bagged fertiliser would pay for the contractor. And in the long term the increased soil organic matter will hopefully stand us in good stead.

“Bulky organic manures such as farmyard manure, compost and biosolids cake are good for building up soil organic matter. Organic matter does help to build soil resilience by improving important soil properties including available water capacity and soil stability.”

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