17 January 1996

Best to delay

for maximum slurry benefits

By Emma Penny

PRODUCERS running short of slurry storage could apply it now the thaw has come, but benefits will be greater from February application.

Thats according to Peter Dampney, Cambridge-based ADAS soil scientist. "It is still too early to gain maximum benefit from slurry application. However, if you are running out of storage, it can be applied if soils are completely thawed."

But where land is still frozen application should be delayed, warns Genus pollution consultant Paul Henman.

"Even though frost makes application easier, its a high pollution risk. Slurry applied during frosty weather will freeze. When temperatures rise, the slurry will thaw first, will not be able to soak into the frozen ground, and is likely to cause pollution as run-off."

According to Mr Dampney, application on top of snow or before heavy rain can also lead to run-off, particularly on steeper slopes.

"Where ground conditions are less than ideal, aim to apply slurry to better drained fields on the farm, and avoid those with steep slopes which are most likely to suffer from run-off. Also, ensure spreading is not within 10m of open watercourses."

Applying slurry in mid-January will also mean less benefit from the nitrogen in slurry, says Mr Dampney.

"Typical dairy slurry is 6% dry matter, which will supply about 5.5 units/1000gal applied in January. But that will rise to 8 units/1000gal in February or March. Pig slurry typically supplies twice as much."

Despite the lower nutrient supply, applying slurry between now and the end of January will minimise contamination risks on silage land, says Mr Henman.

"If slurry is particularly thick, it should be applied to silage land before the end of January to minimise potential contamination with clostridial bugs. However, thinner, watery slurry can be applied later because it will soak into the ground more quickly."

Producers choosing to apply slurry just now should avoid high application rates, warns Mr Dampney.

"Spreading slurry thinly reduces the potential of contaminating grass silage and improves efficiency of nitrogen use. The Code of Good Agricultural Practice limits applications of manures to 250kg total nitrogen/ha. The contribution from slurry should be considered when planning later fertiliser applications," he says.n