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Fertiliser for First Cut Silage

March 25, 2022

“Farmers preparing nutrient management programmes for first cut silage should assess herd forage requirements for the upcoming winter and use the DAERA online crop nutrient calculator to assess fertiliser requirements,” writes College of Agriculture, Food and Rural Enterprise (CAFRE) Dairy Technologists Aidan Cushnahan and Robert Patterson.  Reducing fertiliser applications below recommended levels may reduce costs in the short term but may also result in significant reductions in grass yields, which will have to be supplemented with the purchase of more expensive alternatives.

With most farmers having applied slurry to their silage swards, thoughts now turn to fertiliser applications. The increase in fertiliser price and concerns about product availability has caused many producers to question the most appropriate course of action. The following steps should be taken to optimise the use of this resource.

Carry out a fodder budget to assess the amount of silage required for your herd.  The figures quoted in Table 1 can be used to achieve this.  Remember to allow 10 – 15 % extra for field and in silo losses.

Winter Fodder Budget Worksheet

Remove all non-productive livestock from your herd as soon as possible. Carrying out a critical review by identifying the livestock that are not contributing to your business and removing them earlier rather than later, will reduce the herd’s demand for silage.  For example, six “problem” dairy cows can consume up to 50 t fresh silage over a six month period. Removing these animals now could be equally as beneficial to fodder supplies over the year as removing significantly more animals next winter.

Use the DAERA Online Crop Nutrient Management Calculator to match the nitrogen (N) supply according to requirements for first cut silage (120 kg N/ ha). This will allow you to accurately account for slurry already applied and estimate how much additional N is required and whether there is the need for extra phosphorus (P) and potassium (K). The calculator can be found at

Remember that optimal grass growth responses to fertiliser N are obtained in the period leading to and around cutting grass for first cut silage.  Therefore where possible try to match the amount of fertiliser applied to crop requirements.

Ensure your spinner is calibrated appropriately for the product being applied and consider the benefits of split applications when applying fertiliser for first cut silage, to minimise the risk of losses.

If you are planning to reduce fertiliser inputs for first cut silage it is important to note that any savings in fertiliser may be offset by later having to source more expensive alternatives to address potential reductions in grass dry matter (DM) yield. 

For example, in a recent scenario generated for a 100 dairy herd plus followers at a stocking rate of 2.0 CE/ ha, it was estimated that reducing applications of CAN by 20 kg N/ ha per cut over a 3 cut silage system, could reduce the amount of fertiliser applied by 7.4 t leading to a saving of around £6,500.  However, the reduction in yield may result in a reduction of around 200 t silage (60 t DM) to the resulting fodder stocks on the farm than in previous years.  Replacing this with purchased silage at £40/ t could result in a cost of £8,000.  Alternatively replacing the deficit with concentrate at £400/ t could cost around £27,000.

The impact of this scenario will vary according to a range of factors, including stocking rate, the productivity of your silage swards, the cost of alternatives and what existing stocks of silage you have on your farm.  Nevertheless it is still vital that you follow the steps outlined in this article if you are considering this course of action.

In summary, dairy farmers planning fertiliser applications for first cut silage should assess their winter fodder requirements and use the crop nutrient calculator programme to accurately determine the amount of fertiliser to be applied.  Farmers considering reducing applications for first cut silage should critically review the full impact of this option before adopting it.  Discuss the options that best meet the needs of your farm with your local CAFRE Dairy Adviser.

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