How to expand your slurry storage to meet new NVZ regulations

Years of under-investment, rapid herd expansion and new environmental legislation means many farmers are facing costly changes to their slurry infrastructure. But with so many options to choose from, how can you maximise your return on investment?

The cheapest, and most effective place to start is by examining your clean and dirty water management, says the England Catchment Sensitive Farming Delivery Initiative. Established to reduce diffuse pollution in targeted river catchments, it has held a series of meetings with farmers to offer practical advice on how to manage and use slurry and dirty water more effectively.

At a recent meeting near Taunton, Somerset, CSF Officer Roy Hayes said proposed new environmental regulations could require dairy farmers in Nitrate Vulnerable Zone areas to have 22 weeks’ slurry storage – more than double the current average. “That is likely to cost the average dairy farm £40,000. But by separating clean and dirty water, producers can massively reduce the amount of storage required.”

By making better use of existing storage, farmers can cut their long-term expenditure significantly, says ADAS consultant Stephen Bell. “If you’re going to have to spend money, you need to make sure you’re spending it as wisely and efficiently as possible.”

A dairy herd with 100 cows produces around 5.8cu m of slurry every day over the winter, says Mr Bell. But assuming an annual rainfall of 865mm, every square metre of concrete yard or roof will produce 865 litres of runoff a year. “That’s an awful lot of water that has to be dealt with.”

Under the NVZ proposals, which could be extended to cover 70% of England’s farmland, any water which enters the slurry system will have to be stored over a winter closed period of between 12 and 16 weeks, and allowed for in the 22-week storage calculation. This includes parlour washings, rainwater and silage effluent, as well as the slurry itself.

So by preventing that water from entering the slurry store, farmers can dramatically cut their storage requirement, reducing both capital expenditure and slurry handling costs, says Mr Bell. “Have a look around your farm and think about where the water goes – consider roof water, yard slopes and dairy washings, and separate the clean and dirty water areas, sources, and destinations.”

Options range from fixing broken gutters – costing pence – to concreting yards and installing kerbs to intercept runoff, or covering open areas at a likely cost of £35-£45/m2.

But every farm is different, and slurry handling systems have to suit individual farm types, he adds. Those with existing tin tanks can easily install another ring to enlarge capacity, or add a roof to prevent rainwater adding to the slurry volume.

New tin tanks or concrete stores can be built for about £30-£40/cu m, but are not suitable for straw or sand bedding as the slurry needs to be a well mixed liquid that is easy to pump.

Earth bank lagoons can offer the cheapest option for some, at £10-£25/cu m, although they are very inefficient in terms of space, says Mr Bell. “And that price is only if you have a 70% clay soil – if you need a liner that cost doubles.”

Separator systems can reduce slurry volumes by 10-30%, producing solid manure which can then be stored on fields and spread throughout the closed period. Mechanical separators reduce slurry by 20-30%, compared with about 10% with weeping walls, but cost significantly more at £20,000-£30,000. Both are suitable for straw-bed systems, not sand.

The separated liquid must then be stored – although water which is only slightly dirty containing less than 30% available nitrogen as a percentage of the total nitrogen content, may potentially fall outside the rules.

A popular choice for farmers building new units is underground storage with slatted floors. “This is very efficient as no rainfall enters the store,” says Mr Bell. However, it is more expensive to install, costing more than double the other systems.

Other alternatives include composting manure, creating reed beds, or installing an anaerobic digester – the financial benefits of which need to be examined carefully, he adds.

Anyone considering erecting new storage, or substantially altering or enlarging existing systems, must also consider planning permission and Environment Agency regulations. “If you’re going to spend many thousands of pounds on a store it’s a good idea to have a chat with the EA before you start, to make sure you’re going to meet their requirements.”

Case Study

James and Mary Read keep 150 dairy cows at Pyrland Farm, Taunton, Somerset, and need to make some dramatic changes to comply with the proposed NVZ regulations.

“We have a lot of open concrete yard and old traditional buildings with poor guttering,” says Mr Read. “We scrape all the slurry into the pit which holds enough for three weeks in dry conditions – if it rains it’s less than a week.”

He plans to replace the existing wooden cubicles with a steel frame shed to cover much of the collecting yards, taking the rainwater away to a soak-away. “That will reduce the amount of slurry we produce considerably.” He will install enough cubicles to house 200 cows, with an underground slurry store and slatted floor, to prevent any rainwater entering the store.

With 1800cu m of storage, he expects the project to cost about £150,000 – equivalent to around £83/cu m. “These new rules are going to force us to spend a huge amount of money for no financial gain.”

The value of manures

Soaring fertiliser prices are making many farmers reassess the value of their slurry and manure – and they can save as much as £80/ha (£32/acre) by doing so. A typical manure or slurry contains enough Phosphate and Potash to eliminate the need for any other fertiliser on maize crops or grassland, says Roy Hayes, Somerset Catchment Sensitive Farming officer. Applied at the right time – early spring is best – it will also almost halve the inorganic nitrogen requirement.

Using a conditioner like Milbury Systems‘ Aeromixer can also improve the uniformity of slurry, with reduced odour and nutrient emissions, enabling consistent nutrient application across the field.

“With high fertiliser prices, farmers need to be making better use of slurries and manures,” he says. “This means calculating the nutrient content of your muck, carefully targeting crop nutrient requirements, and applying the slurry or manure at the optimum time using the best technique available.”

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