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

Step 2 Calculate the maximum limit for N applications to the crop type taking account of any relevant adjustments

Complete Table 1 to calculate the maximum limit for N applications to the crop type.

Enter the crop type, harvest year and N max limit (before adjustments) in the spaces provided above the table (see Leaflet 3 for the N max limits). Then complete columns 1 to 9 for each field growing that crop type.

Column 1 Enter the field name/reference.
Column 2 Enter the cropped area of the field (ha).
Column 3 Enter your expected yield.
Column 4
 
Enter +20 if the soil type is ‘shallow’ and the crop type is autumn or early winter sown wheat or winter barley.

Column 5

Enter an appropriate adjustment (see Leaflet 3) to the N max limit if your justifiable expected yield is above the standard yield for the crop type.
Column 6 Enter +40 if a milling wheat variety is being grown.

Column 7

Enter +80 if the current or previous crop has had straw or paper sludge applied to it.
Column 8 For grassland, enter +40 if three or more cuts of grass are taken from the field.

Column 9

Calculate the adjusted N max limit (kgN/ha) for each field. To do this, add the numbers in columns 4 to 8 to the N max limit (before adjustments) that you entered at the top of the table.

Column 10

Calculate the maximum limit for nitrogen applications (kgN) for each field (multiply column 2 by column 9). Add up the values in column 10 for all fields and enter this number in box A at the bottom of column 10 to give the maximum limit for nitrogen  applications to the crop type.

Examples of completed versions of Table 1 are provided overleaf.

Note: You can convert the total limit for N applications given in box A into an average and adjusted N max limit for the crop type by:

Dividing the figure in Box A by the total area of the crop type (i.e. the sum of column 2)

This average and adjusted N max limit could prove useful when planning your applications of nitrogen at the start of the growing season to ensure that you do not breach the N max limit
.

 
Examples of Table 1 completed for an arable and grass crop.

Crop type: Wheat, autumn or early winter sown

Harvest year: 2009

N max limit (before adjustments): 220 N kg/ha

Crop type: Grassland

Harvest year: 2009

N max limit (before adjustments): 330 N kg/ha

Table 1. The adjusted N max limits for each field and for the whole area of the crop type.

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