Nitrogen balance needed

1 March 2002

Nitrogen balance needed

NVZ is the latest acronym

to plague dairy producers,

with most likely to be

affected in one way or

another. Marianne Curtis

visited one Devon dairy

producer and his adviser to

find out what regulations

will mean in practice

ABOUT 20% of dairy herds could fall outside proposed Nitrogen Vulnerable Zone rules because they have insufficient land.

But many others may be harbouring unnecessary fears about the legislation, says James Hague, technical director of the Kingshay Farming Trust.

"Most NVZ rules represent good practice, which many farms would follow anyway." But producers can expect to have to balance nitrogen inputs and outputs more carefully.

The first stage in assessing what impact NVZ legislation may have on a unit is to calculate nitrogen production from organic manures. This has already been carried out at East Hilltown Farm, Chulmleigh, Devon, run by Colin Burnell and his son, Martyn.

The unit carries 135 dairy cows weighing 600kg, 30 heifers of 12-24 months and 30 more of 6-12 months. Categorising stock is important to work out nitrogen production a year, says Mr Hague (see table).

"Multiply stock numbers by the amount of nitrogen excreted by that class of stock a head a year and total the resulting figures. For East Hilltown Farm, this total is 16,080kg."

Nitrogen levels permitted on the farms grass and arable land should be calculated next. The Burnells unit has 28.3ha (70 acres) of maize, 16.1ha (40 acres) wheat and 72.8ha (180 acres) grassland. Maize is categorised as arable land.

"Total nitrogen allowed a hectare is 210kg for arable land and 250kg for grassland. It is lower for arable land because there are periods when there is no crop in the ground, so mineralised nitrogen could be leached, unlike grass which takes up nitrogen mineralised in soil all year round."

Permitted N levels for arable land are likely to fall further, to 170kg/ha (136 units/acre), in four years time, but grassland levels should remain the same, he adds.

Multiplying arable and grassland areas by current allowances gives a total of 27,524kg of N from organic manure permitted on the Burnells land. Subtracting the farms organic manure N production total of 16,080kg shows it is 11,444kg below the nitrogen threshold. It could, therefore, carry an extra 108 cows, before contravening NVZ rules, calculates Mr Hague.

Acquiring extra rented land over the past 4-5 years has ensured the Burnells have stayed within nitrogen limits, but this may not be a solution for everyone, says Mr Hague. "Producers could end up renting land for silly money to comply with NVZ legislation, but there are other options."

One is to reduce cow numbers. This may seem drastic, but many herds carry inefficient cows which drag down margins, agree Mr Hague and Colin Burnell. "Losing our 10 lowest performing cows would boost profit by £8000 a year," says Mr Burnell.

Cutting stock numbers increases feeding and cubicle space – beneficial for production – and can extend heifer longevity by reducing stress. There is also less likelihood of running out of forage, which is also a disaster for profit, says Mr Hague.

"With each cows maintenance requirement equivalent to 4670 litres of milk a year, worth about £840, keeping extra unproductive cows is wasting feed and money which could be used to boost yields of more efficient ones," he says.

Another option for producers with insufficient land who grow maize is to return maize land to grass, with its higher N input allowance, says Mr Hague. "Or consider paying arable farmers to grow maize on contract." Exporting manure to arable producers below N limits could also offer a solution, he adds.

Extra slurry storage capacity will be required on many dairy farms to enable them to comply with proposed NVZ rules.

James Hague (left) and Martin and Colin Burnell have worked out NVZ implications for East Hilltown Farm.

Stock type N excreted

(kg a head

a year)

Dairy cows (600kg) 106

Dairy cows (550kg) 96


finisher (2yrs+) 58


finisher(12-14mths) 47


finisher(6-12mths) 12

Calves kept for six months 7

For other classes of stock, consult the DEFRA guide Manure Planning in NVZs.

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