Livestock farmers are familiar with the fertiliser value of manures and slurries, but despite this the storage and use of this resource is often not optimised and the management of manures to maximise their nutrient potential is not always seen as a priority.
A tonne of slurry from a housed dairy cow can contain up to 2.6 kg of nitrogen, 1 kg of phosphate and 3 kg of potash. At current prices, this values the nutrients produced by an average cow at around £130 per head per year, before additional elements such as sulphur and magnesium are accounted for. It therefore makes sense to do everything possible to maintain this resource in its optimum condition.
When storing and applying manures and slurries there are a number of factors to consider; a balance needs to be struck between techniques which result in the greatest amount of available nitrogen being made available to the plant, and complying with environmental best practice and NVZ restrictions.
If constructing or upgrading storage facilities, it is also important to consider their location on the farm. While putting the lagoon or tank next to the yard may seem the most obvious choice, the distance between here and the fields on which material will be applied should be considered. With increasing fuel costs, the relative costs of storage and transport need to be carefully assessed.Consideration also needs to be given to application equipment. Where the main unit is located near the centre of the holding umbilical systems may be suitable, while application machinery should be designed to minimise loses via injection or trailing shoes.Storage must be designed, not only to provide sufficient capacity, but to minimise dilution of the slurry by rain or clean water. Clean water entering the slurry system increases the volume of material to be stored, transported and applied, increasing the associated energy and fuel costs.
For example, a typical 12 cu m slurry tanker full of concentrated slurry has a fertiliser value around £625. Diluting this slurry not only means the fertiliser value in each load is reduced, but increases the number of loads which need to be spread, increasing operation costs. It also increases the overall storage capacity required to be compliant with any NVZ regulations and environmental best practice which affects the initial capital cost. Some estimates for a 20 m diameter storage tank suggest that 100 cm of annual rainfall could require an extra 26 loads just because of the extra volume of the added water.
While in some cases it may be appropriate to opt for large scale engineering solutions, such as the construction of a new store, in some cases simple improvements can be made by covering lagoons and tanks, redirecting clean water away from the slurry facilities or modifying existing application equipment.
Oliver McEntyre, Barclays National Agricultural Specialist, said: "Given the value of manures and slurries, and the increasing costs of energy and synthetic fertilisers, farmers need to ensure they are making the most of the resources they have. It is essential to view slurry as a key input rather than a waste product that must be dealt with.
"It is important to take stock and to see whether facilities which were suitable when they were designed still meet the needs of a business and legislation which may have changed. Any costs associated with improving or upgrading manure storage and application should be seen in the context of maximising the value of the slurry or manure."
One farm which has recently taken practical steps to preserve the value of his slurry is WTJ Blewett of St Dennis, Cornwall. The farm, which is surrounded by extensive china clay mining, comprises a mixture of owned and rented land with 300 dairy cattle and 200 beef finishers.
Mr Blewett has recently completed the construction of a new 5,600 cu. m. slurry store, giving him the capacity to store 600 tanker loads of material. By working closely with the Environment Agency and his landlord throughout the project he has a state of the art storage facility which not only represents environmental best practice, but which also helps to maintain the fertiliser value of his slurry.
Mr Blewett said "Barclays assisted with the project by increasing our overdraft facility to ensure we had sufficient working capital for the duration of construction. This has enabled us to create sufficient storage capacity for our future requirements in even the most challenging weather conditions."