19 July 2002

SUSTAINABLE FARMING: 8

NITROGEN FROM MANURES

A little forward planning is all it takes to make better use of manure applications to supply nitrogen to crops, advises ADAS soil scientist Paddy Johnson.

Abiding by the rules for the newly expanded nitrate vulnerable zones will not be difficult, although growers must remember that the loading limit for arable land will be reduced from 250kg/ha N to 170kg/ha N in Dec 2002, says Mr Johnson.

The first action is to calculate whether there is enough land available to comply with NVZ requirements. "Work out the amount of N secreted by livestock and calculate the area available for manure spreading."

Standard figures are available for guidance, so once production has been calculated it is a case of comparing it with the limit. The rules set a limit for organic manure loadings of 250kg/ha of total N on grassland and 210kg/ha of total N on arable land.

"These limits include manure deposited by animals at pasture and they apply annually, from December to December in the following year," he adds.

No more than 250kg/ha can be applied to any one field. "Thats about 43t/ha of manure," says Mr Johnson.

Growers on sandy or shallow soils (less than 40cm deep) have to respect timing restrictions with slurries, poultry manures and liquid digested sewage.