SUBSTITUTING BAGGED fertilisers with livestock manures and slurries has become a hot topic as artificial fertiliser prices have spiralled.

With slurries, keeping them as dry as possible is essential. The more dilute they become the lower the nutrient value they contain, John Morgan of Creedy Associates told visitors to a Practical Use of Manures workshop in Dorset.

He explained that 1cu m of thick slurry with a dry matter content of 10% contained 4kg of nitrogen. “But a thin, watery slurry with just 2% dry matter contains only 1.5kg/cu m of nitrogen. Reducing the amount of water entering slurry storage can significantly improve its fertiliser value.”

Delegates at the workshop at Denhay Farms 350-cow dairy unit were told that the farm collected nearly twice as much dirty water as it did slurry. “Slurry production totals about 3525cu m a year, but dirty water volume is 5386cu m a year,” said Mr Morgan.

“Dirty water costs about 80p/cu m to dispose of, but has little nutrient value. It only contains 0.3kg/cu m of nitrogen, a trace of phosphate and 0.3kg/cu m of potash. This makes it essential to reduce the amount of dirty water produced and collected on all farms.”

Mr Morgan said assessing whether run off from yards counted as dirty or clean water would be time well spent. Diverting clean water from yards and other areas directly into streams and ditches would reduce the volume of dirty water to be spread and hence cut spreading costs.

“And it needn’t be difficult to do either. With silage clamps you can install two drainage pipes, one leading to the dirty water tank and the other to the clean water disposal system.

“When clamps are in use then run off should be directed down the dirty water pipe by putting a bung in the clean water pipe. But when clamps are empty the bung can be placed in the dirty water pipe and run off sent down the clean water pipe.”

Additionally, extending clamp sheets out over the end of the clamp means run off from the top of the clamp can go into the clean water system, while effluent can enter the slurry system, suggested David Munday, also of Creedy Associates.

jonathan.long@rbi.co.uk