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

Step 3 Calculate the crop available nitrogen supplied from all livestock manure applications to the crop type

Complete Table 2 for each field growing the crop type and receiving one or more applications of livestock manure.

Column 1

Enter the field name/reference receiving the application of livestock manure. If the same field receives more than one application of livestock manure, use one row per application.

Column 2 Enter the cropped area of the field (ha).
Column 3 Enter the type of livestock manure applied (the different types are described in Table 7 in Leaflet 3).
Column 4 Enter the application rate of the manure (t/ha or m³/ha).
Column 5 Calculate the total quantity of manure applied to the field (multiply column 2 by column 4) and enter in column 5. Note: If you already know the total quantity of manure applied, you can enter this directly into column 5 and do not need to enter information in columns 2 or 4.
Column 6 Enter the total nitrogen content of the manure. This must be based on either standard values for the manure type (see Table 7, Leaflet 3) or on the results of sampling and analysis.
Column 7 Enter the percentage of the manure total nitrogen content that is assumed to be available for crop uptake (see Table 8, Leaflet 3 for the standard values that must be used).
Column 8 Multiply column 5 by column 6, then multiply by the percentage value in column 7 to calculate the quantity of crop available nitrogen. Add up the values in column 8 for all applications of livestock manure to the crop type for all fields and enter this number in box B at the bottom of the column.

Note: When multiplying using percentages you should first divide the percentage figure by 100 (e.g. 20% / 100 = 0.2).

Example

A grass field of 8 ha receives an application of 35m³/ha of dairy slurry in late September. Therefore, the total amount of slurry applied is 35 m³/ha x 8 ha = 280 m³.

The total nitrogen content of this manure type is 3 kg N/m³ (from the standard values in Table 7, Leaflet 3). Therefore, the total amount of N applied to the field is 280 m³ x 3 kg N/m³ = 840 kg N.

You must assume that 20% of this nitrogen is available for crop uptake (see Table 8, Leaflet 3). Therefore, the total amount of crop available N applied to the field is 840 kg N x 0.2 = 168 kg N.

Table 2. The crop available nitrogen from livestock manure applications

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