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Guidelines for farmers in nitrate vulnerable zones

Booklet 4: N available from livestock - manure applications

The amount of N available to the crop following the application of manure is dependent upon:

• type of manure

• method of application

• soil type

• month of application

The tables in this section will enable you to calculate how much N is available following applications of livestock manure. These figures can then be used in your Fertiliser and Manure Plan, to adjust the application rate for inorganic N fertiliser.

Available N is released slowly from the organic N content of manure over a period of months to years. Where the crop does not take up this available N, it may be lost through leaching during the following winter, or it can accumulate in soil organic matter and provide further long-term savings in N fertiliser inputs. Assume 10% of the total N content of livestock manure becomes available for the second crop following application and adjust the fertiliser N requirements accordingly.

Using the tables

The information derived from these tables is used as part of the Manure Planning process. Entering the relevant information into Table G will enable you to calculate the amount of N available to crops. The requirement for inorganic N can then be adjusted accordingly.

Step 1: Identify the appropriate manure type from column 1.

Step 2: Read across until you find the appropriate incorporation time and dry matter, then read back to get the Ref. No.

Step 3: Read across to the fourth column to get the Total N (kg/t).

Step 4: Read across to the appropriate 'Time of application' and soil type columns, to get the % of N available in spring.

As an alternative to using the typical values you can use actual values, based on your own analysis. In order to obtain a representative figure it is advisable to take a number of samples.

It should be noted that:

• The values for % N in the tables are estimates for the east of Scotland. Lower values should be used in most years for the wetter west.

• These values assume incorporation by ploughing. Cultivation using discs or tines is likely to be less effective in minimising ammonia losses and intermediate values of nitrogen availability should be used.

• For grass leys that are not being ploughed up, the 'over 6 hours' or 'over 24 hours' categories should be used, as appropriate.

Percentage of total N available* in Spring following application of different manure types (% of total N)

• The yield response to summer application on grass can be variable according to weather conditions. Later applications (July/August) are likely to be less effective.

• Previous manure: assume 10% of the total N content of manures become available for the second crop following application.

Percentage of total N available* in Spring following application of cattle slurry (% of total N)

* The yield response to summer application on grass can be variable according to weather conditions. Later applications (July/August) are likely to be less effective.
* Previous manure: assume 10% of the total N content of manures become available for the second crop following application.

Percentage of total N available* in Spring following application of separated cattle slurries and pig slurry

• The yield response to summer application on grass can be variable according to weather conditions. Later applications (July/August) are likely to be less effective.

• Previous manure: assume 10% of the total N content of manure become available for the second crop following application.

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