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Guidelines for farmers in nitrate vulnerable zones

Table 9: Winter oilseed rape: N recommendations in kg/ha

On sandy shallow soils, apply half to two-thirds of the N recommendation in the seedbed and the balance at tuber initiation.

Varieties exhibiting vigorous and prolonged haulm growth (indeterminate varieties)
e.g. Maris Piper, Saturna, Cultra - reduce by 10%
Cara (very indeterminate variety) - reduce by 25-30%
Varieties producing small and short-lived canopies (determinate varieties)
e.g. Estima, Maris Peer, Saxon - increase by 10%.

N increases the growth rate and persistence of leaves. The increase in leaf growth can be at the expense of root growth. Only moderate amounts of N are required for 'root' brassicas unless the foliage can be used to provide forage in September/October. The root dry matter % and winter hardiness will be reduced by excess N.

Direct sowing without a cover crop invariably gives the best establishment, especially of clover, and in dry summers, as the plants suffer less competition for moisture, light and nutrients. For further information see SAC Technical Note T31 (revised) on "Grass and clover establishment".

N Requirements for established grass

N requirements for grass take into account Site Class (see Table 3) and N residue group (see Table 4):

These rates should be adjusted to take account of the nitrogen available from organic manure applications, when preparing your Fertiliser and Manure Plan. See Booklet 2, Manure Planning.

These rates should be adjusted to take account of the nitrogen available from organic manure applications, when preparing your Fertiliser and Manure Plan. See Booklet 2, Manure Planning.

Seasonal application of nitrogen fertiliser: grazing

Nitrogen should be applied at regular intervals over the grazing season at a declining rate to match the falling response to nitrogen by the grass.

• Under optimal conditions grass can utilise approximately 2.5kg N/ha/day of growth.

• The first dressing should be about 6 weeks before turnout (maximum rate 100kg N/ha) or at the time of 'T-sum 200'.

• Should 'T-sum 200' occur much earlier than normal, delaying until the first period of mild weather will reduce the risk of nitrogen loss.

• No nitrogen should be applied after mid-August to reduce the risk of winter losses of nitrogen. The response to nitrogen will also be lower after this time.

Seasonal application of nitrogen fertiliser: silage

• Based on a daily uptake of 2.5kg N/ha the optimum rate of nitrogen application for the first cut is 120-140kg.

• N/ha applied 8 weeks before expected date of cutting.

• Higher rates and delayed application increase the risk of nitrate-N in the grass and poor fermentation.

• A split dressing of the optimum nitrogen rate may be beneficial in reducing nitrogen losses, and encouraging earlier growth. The second dressing should be applied at least 4 weeks before cutting.

• If split dressing, apply 40-50kg N/ha 10 weeks before cutting (i.e. about the same time as the grazing application). Apply the remainder 4 weeks later.

Examples of application patterns for a range of annual nitrogen rates are given in Tables 16 and 17 below. These rates should be adjusted to take account of the available nitrogen in organic manure when preparing your Fertiliser and Manure Plan. See Booklet 2, Fertiliser and Manure Planning - Part 2, Manure Planning.

* For a high-clover sward

* For a high-clover sward
** For 1-2 year leys (2 or 3 cut system)

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