ARCHIVE: Nitrate Vulnerable Zones (NVZs) - Guidance for Farmers. The N max limit (Leaflet 7 - PB12736g)

2. Calculating your compliance

The Regulations set out the factors you must take into account when calculating your compliance with the N max limit.

You can adjust the N max limits that apply to the crops grown on your farm to take account of local information relating to the field or crop (e.g. higher than standard yields, grain quality targets, shallow soil type). The notes to Table 5, Leaflet 3 describe the permitted adjustments.

When determining the amount of nitrogen available for crop uptake from applications of livestock manure, YOU MUST:

  • First establish the total amount of nitrogen in the manure using the standard values in Table 7, Leaflet 3 or by sampling and analysis; and
  • Then calculate the amount of crop available nitrogen using the minimum percentages provided in Table 8, Leaflet 3.

It is recommended that you take account of the N max limits when planning your use of nitrogen (see Leaflet 6). If you only do the calculation after harvest you may find that you have already exceeded the limit.

To help with your calculation, you can use the step-by-step guide at the back of this Leaflet (Annex 1) or the PLANET software. The Environment Agency will accept either as a valid record of your calculation.

Important points to note when calculating compliance with the N max limit:

  • If your field records demonstrate that the nitrogen application rate to each field growing a particular crop type is lower than the N max limit for that crop type, then you can be confident that you have complied with the N max limit and do not need to complete the full calculation described in Annex 1.
  • The N max limit only applies to nitrogen from applications of manufactured nitrogen fertiliser and the crop available nitrogen from applications of livestock manure. You do not need to allow for the nitrogen from:
    • livestock manure that is directly deposited by grazing animals;
    • applications of other types of organic manure that are not from livestock (e.g. sewage sludge, compost); or
    • applications of other types of nitrogen-containing materials (e.g. dredging from ditches).
  • You should include any crops grown on land (in an NVZ) which is rented by you and is under your control during the growing season of the crop.
  • If you want to adjust the N max limit for a crop on the basis that you expect to achieve a higher than standard yield, you should have written evidence from at least two previous crops to show that this is a realistic estimate of the likely crop yield.
  • The percentages for calculating crop available nitrogen in slurry and poultry manure (provided in Table 8, Leaflet 3) will increase from 1 January 2012. This is when applications of these types of livestock manure must shift to times of the year when more nitrogen will be supplied to the crop (as this is the latest date from which the closed periods for organic manures (Leaflet 8) will apply).
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