22 March 1996

Return to normal for soil nitrogen reserves

NITROGEN reserves in soils are back to normal after two low years, says ADAS.

As a result, soils are well supplied with nitrogen and standard book recommendations will suffice on most crops and soils, though malting barleys will need extra care.

Over 100 sites are used each year to assess levels across the main arable areas of the UK, says Brian Chambers at Gleadthorpe. At each site ADAS fieldsmen take 20 cores to a depth of 90cm (35.5in) in autumn and spring.

"Thats a fair representation of cereal rooting depth in most soils," says Mr Chambers. Cores are immediately cooled and then frozen before being delivered to ADAS Wolverhampton for analysis.

Results show heavy and medium soils contain about 93kg/ha (74 units/acre) of soil mineral N after cereals, a little above normal.

Lighter soils contain 62kg/ha (50 units/acre), some 20kg/ha (16 units/acre) more than last year. "Malting barley growers may need to be conservative with nitrogen," he advises.

More care will be needed on higher index soils, whatever the crop. "After rape, we are finding levels up to 109kg/ha. Thats about 30kg/ha more than last year, probably because growers applied more N in response to higher rape prices."

Growers should reduce applications by 25kg/ha (20 units/acre) to allow for the extra residues, and at least that after pulses or potatoes even on light land, he suggests.

N values are consistent across regions, adds Mr Chambers. "Everywhere has been reasonably dry. Large parts of the east have had less than 100mm of drainage, which is extremely low."

&#8226 N levels normal after dry winter.

&#8226 Book recommendations suitable for most crops and soils.

&#8226 Assess malting barley needs with care.

&#8226 Allow for break crop residues.