Be sure to take soil type into account when assessing nitrogen needs this season, urges Kemira.

The firm’s January soil sampling from more than 150 sites for its GrowHow N-Min service shows that on average residual N values are about 10kg/ha up on last year.

Adding the amount likely to become available from mineralisation means the natural crop N supply could overall be 20-30kg/ha more N than in 2005.

But there are considerable differences between soil types, warns Kemira agronomist Allison Grundy.

“The silty soils are generally lower, with silty clays and silty loams both containing just 20kg compared with 30-35kg in 2005.”

Levels in lighter, sandier land are much as last year at 40-45kg/ha.

The biggest differences have been measured in heavier clays and clay loams contain about 40kg/ha of N or twice what they did in 2005, weather being the key driver, says Miss Grundy.

“This year we had relatively warm weather up to Christmas which allowed crops to make use of nitrogen for longer.”

Since then low temperatures and light rain have combined to reduce leaching, even in lighter sandy soils.

Clays have higher N content and are inherently better at holding onto it, she notes.

The main aim of the firm’s sampling is to calibrate its N-Min model by measuring the relationship between the amounts of N in the top 30cm and between 30 and 60cm.

“We have proved over the years that this relationship, once measured for the season, is very consistent and gives reliable results,” says Miss Grundy.

“It means farmers using the N-Min service do not need to provide deep core samples, making the whole process much simpler and reducing the chances of sampling error.”

For details of this year’s samples plus those for the previous five years visit www.kemira-growhow.co.uk

andrew.blake@rbi.co.uk