Making the most of ‘free’ nitrogen

Useful fertiliser savings are on offer to cereal and oilseed rape growers, thanks to a run of drier than average winters.

And sampling for soil mineral nitrogen could be especially valuable this spring, according to ADAS.

Changing circumstances, not least higher nitrogen prices, are making N dressing decisions harder, says senior research soil scientist Peter Dampney.

“But getting them right is increasingly important.”

Growers in NVZs, which now cover much of the country, must follow an Action Programme to avoid jeopardising single payments, he warns.

A key requirement for Environment Agency compliance is that the amount of fertiliser N used on each field must not exceed crop need, taking account of uptake and soil nitrogen supply from organic matter, crop residues and applied manures.

Winter rainfall to the end of January shows that 2005/06 was drier than average in most areas.

So with less than normal leaching there is likely to be more N available from the soil than usual.

The previous two winters were also drier than average.

“Many autumn-sown crops established well due to mild weather and will need little or no early spring nitrogen,” says Mr Dampney.

“And unless there is above-average rainfall from now until the end of March, cuts in the N rate for main spring/summer applications should be considered.”

Low winter rainfall will have most impact:

  • On medium and heavy land after crops such as oilseed rape, pulses, potatoes, brassicas and grassland

  • Where frequent applications of organic manures, such as farmyard manure and slurry, have been applied in recent years

  • Where organic manures have been applied since last autumn