14 March 1996

Outdoor sow cuts

REDUCING outdoor sow stocking rates cuts pollution risks from nitrate leaching.

ADAS soil scientist Brian Chambers says control of nitrates in water could be stricter and a study was set up between ADAS Gleadthorpe, Notts, and Cambac Research centre, Berks, to quantify nitrate losses from outdoor pigs.

"The study compared three stocking rates of 25, 18 and 12 sows a hectare on arable stubble, barley undersown with grass and a grass ley," says Dr Chambers.

At 25/ha (10/acre), which is common, N leaching losses were 56kg/ha (45 units/acre). That was cut by 15% to 48kg/ha (38 units/ acre) when stocking was cut to 18/ha (7/acre), and by 85% to 8kg/ ha (6 units/acre) at 12/ha (5/acre).

"In the lightly stocked paddock the sustained grass cover held much of the nitrates. In that paddock nitrate levels in drainage water were consistently below the EU maximum of 11.3mg/litre." &#42