1 March 2002

Take account of maize crops higher demand

NITROGEN requirements of maize are much higher than values published in DEFRAs RB209 guide and producers should take this into account when calculating artificial nitrogen fertiliser applications which comply with NVZ legislation.

"In Kingshay studies we have worked out maize nitrogen requirements by determining nitrogen content of mature plants top to toe," says Kingshay technical director James Hague.

According to Kingshay studies, nitrogen requirements of crops yielding 35t/ha fresh weight (14t/acre) are 180kg/ha (96 units/acre) ranging to 260kg (208 units/acre) for yields of 50t/ha (20t/acre). "This compares with a maximum crop requirement of only 120kg/ha in RB209. At this level, crops will not attain maximum yield."

Kingshay recommendations should be acceptable to those enforcing NVZ rules as they are based on true crop requirements, says Mr Hague.

Calculating permitted fertiliser applications depends on knowing the amount of nitrogen applied via slurry, he says.

Maize at Colin and Martyn Burnells farm typically yields 42t/ha (16.8t/acre) so nitrogen requirement is 220kg/ha (176 units/acre), says Mr Hague.

"Using the maximum permitted level of nitrogen from organic manure – 250kg/ha slurry, with a nitrogen content of 3kg/t, can be applied at 83t/ha – about 15 loads a hectare for the Burnells. But only 35% of nitrogen from slurry is available to growing crops at that point in the season, so this level of slurry will contribute just 88kg/ha."

As well as organic manure nitrogen contribution, nitrogen supplied from soil mineralisation processes also needs to be taken into account.

"Soil which has received muck applications at the maximum level and has previously been cropped with grass will have high fertility levels, supplying up to 60kg/ha a season to maize."

"Adding together manure and soil nitrogen contributions for the Burnells maize land gives a total of 148kg/ha. Subtracting this from the 220kg/ha crop requirement leaves 72kg/ha which can be applied as artificial fertiliser. This could be applied as a combination as seed-bed, starter fertiliser or top dressing," advises Mr Hague.

For silage fields, grass nitrogen requirement for three cuts is 280kg/ha (224 units/acre), he says. "For slurry applied at 56t/ha to high fertility soil, nitrogen fertiliser requirements are 110kg/ha for one cut, a further 70kg/ha for second cut and an extra 50kg/ha for third cut."

In addition to calculating fertiliser needs, all fertiliser and slurry applications must be recorded as well as stocking rates, to comply with NVZ rules, he adds. &#42

&#8226 Maize higher than RB209.

&#8226 Work out slurry contribution.

&#8226 Calculate soil nitrogen level.

Kingshay studies determined the nitrogen content of plants from "top to toe", says James Hague.