15 October 2019
Investing in infrastructure to prevent rainwater entering slurry stores will reduce the slurry storage capacity needed on Welsh farms and the cost of spreading it on the land.
Farmers attending a joint Farming Connect and AHDB Dairy event at Gelli Aur College Farm, Llandeilo, were told that rainwater falling onto the roof of a typical 100-cow cubicle shed produces 1200m3 of slurry per year if allowed to drain on a dirty yard.
“Once in the slurry system it has to be stored and spread,’’ said AHDB’s Environment and Buildings Senior Manager, David Ball.
“There are measures you can take to reduce the storage capacity you need by diverting rainwater away from dirty areas, if you don’t have to store it you don’t have to spread it.’’
Mr Ball urged farmers to give this priority. “With new rules planned for 2020, the storage capacity on many farms will have to increase but there are actions you can take to reduce how much capacity you will need,’’ he said.
Ammonia emissions needed to be considered also, he advised, as legislation will almost certainly be put in place to control these.
Covering slurry stores can reduce nitrogen losses in the form of ammonia by between 60-80%, as well as keeping rainwater out of the slurry, said Mr Ball.
A cubic metre of cattle slurry typically contains 2.6kg of nitrogen (N) but, at best, only 50% of this is readily available. By carefully planning time of spreading, application rates, matching crop requirements and manure analysis, more of the nutrient content can be utilised for crop growth, said Mr Ball.
“If it is not used or retained in the soil it is lost, and that means applying it when the plant is going to utilise it.’’
Nitrogen in the slurry produced by a 200-cow herd totals 22 tonnes per year – the equivalent of 58 tonnes of ammonium nitrate; financially, at an ammonium nitrate price of £292/tonne, that nitrogen is worth £16,936 a year, or £85/cow, without taking into account the phosphate and potash (P and K) values. This value can only be captured by careful manure management.
Mr Ball urged farmers to test their slurries to establish their nutrient values. “The best place to sample is out in the field, as it is being spread. If the store has been well agitated this sample will be representative of the store contents and what the crop is receiving.
“Although it is already on the field at this point you will build up a picture over several samples of what you are working with.’’
Mr Ball recommended sending samples to a laboratory for testing as a full report on the values is provided.
At typical values, the total N, P and K in slurry is worth £3.98/m3 or £119.10/ha for a typical 30m3/ha application, he said. “That is a lot of nutrients that you don’t have to import onto the farm, think about trying to utilise as much of that £3.98 as possible.’’
On the same basis, the N, P and K value in farmyard manure is £10.94/t or £218.80/ha for a typical 20t/ha application.
“You shouldn’t be dismissing that, it is a good way of making savings on your fertiliser bill,’’ advised Mr Ball.
Splash plate application, which can lead to 80% of the readily available N content of slurry being lost in the environment, is likely to be banned, he predicted.
“That loss is equivalent to £50/ha for an application rate of 30m3 so there are financial benefits in using band spreaders or injection when applying slurry,’’ he insisted.