Slurry and fertiliser applications for late spring

Date published: 02 April 2020

Advice from CAFRE Dairying advisers

Advice from CAFRE Dairying advisers
You should aim to have slurry and fertiliser applied by April 8.

With the exceptionally wet weather during February and early March, slurry and fertiliser applications have been delayed. On many farms, especially in the west, ground conditions have just recently improved enough for slurry and fertiliser spreading. Use soil testing results to choose suitable fertilisers ensuring good soil fertility and grass growth. Research has shown that low fertility soil, with phosphate index 1 or below, equates to a severe loss in grass growth over 12 months of more than 2t DM/ha.

Use Soil Analysis Results

Soil analysis is a reliable and cost-effective method of measuring the existing status of phosphate (P) and potash (K). The results provide a sound basis for planning this year’s fertiliser programme. The Nitrates Action Programme prohibits the use of P fertiliser unless soil analysis shows that the level of soil P is inadequate for the need of the next crop. On most dairy farms P levels are adequate, especially on land that regularly receives slurry. Talk on the phone or email to your local CAFRE Dairy Adviser who can help with explaining the results and discussing what type and amount of fertiliser to use.

Slurry Spreading

Dairy cow slurry is a valuable source of nutrients for grass growth and should be taken into account before deciding on the type of fertiliser and amount of fertiliser to apply.  On land with soil indices of 2 or above for P and K, slurry applied at 33,000 litres/hectare (3,000 gallons/acre) in spring will supply approximately 34kg nitrogen (N) / hectare (27 units/acre), 41kg P / hectare (32 units/acre) and 96 kg K / hectare (77 units/acre).  At this stage of the spring no more than 3,000 gallons per acre should be applied.

Methods of applying slurry like the trailing shoe or band spreading reduce the loss of nitrogen to the atmosphere compared to the conventional splash plate.  Research at AFBI, Hillsborough has demonstrated that spreading slurry using a trailing shoe machine increases the utilisation of slurry nitrogen by up to 25 per cent compared to a conventional inverted splash plate. Slurry is best applied to silage fields where it can make a major contribution to the high K requirement of the silage crop.  When applying slurry it is important not to apply to waterlogged land, within 10 metres of a watercourse or 20 metres from a lake in order to maximise the value of the slurry and minimise the risk of pollution. If using low emission spreading with band spreader or trailing shoe then the 10 metres rule is reduced to three metres.

It is also important to highlight that dairy farmers who have a derogation must apply at least 50 per cent of total slurry before June 15 and then after that date, they must apply slurry by low emission spreading techniques.

Fertiliser for Silage

Aim to have all fertiliser and slurry applied by April 8, or at least five weeks ahead of cutting date and make allowance for any slurry applied earlier in the year. It is best, if at all possible at this late stage, to allow a week between spreading slurry and fertiliser to reduce N losses. The fertiliser rate should be a total of 100 - 120 kg N / ha (100 units per acre) allowing for any slurry N applied (Nine units N in 1,000 gallons of slurry).  Include P and K depending on soil analysis. If your soil analysis has shown low indices for P and K (1 or below) a compound fertiliser such as 27:4:4 will help to make up the shortfall in P and K. If the P index is above 1 then a zero P compound must be used.

All silage fields should receive sulphur (S) each year at 30 - 40 kg/ha (24 – 32 units per acre). Research has shown that there are yield responses to additional S in most soils especially on sandy soils and where high N levels - over 100 kg N/ha (80 units/acre) are used.

Fertiliser for Grazing

On many dairy farms grazing fields have adequate levels of P and K because most of these nutrients removed by grazed grass are returned to the soil in the dung and urine.  Consequently there is scope for using mainly a straight N fertiliser at a lower cost than a compound fertiliser, without compromising grass output. Further applications of N should be applied after each grazing depending on grass supply and weather conditions.

Rolling of silage ground

Silage fields should be checked now and only roll where necessary as it will set back growth. Minimise rolling where possible to the perimeter of fields or areas that have been damaged last autumn.


It is important to make optimum use of slurry and apply the correct amount and type of fertiliser in order to reduce costs and minimise the risk of pollution:

  • Spread slurry and fertiliser (or top up) this week weather permitting.
  • Use soil analysis results and allow for slurry nutrients.
  • Use fertiliser containing at least five per cent S.
  • Use a zero P fertiliser for silage fields when suitable.
  • Apply mainly straight N fertiliser on grazing fields.
  • Consider rolling but only if damage has been done last Autumn.

Feel free to discuss with your local CAFRE Dairying Adviser who is available to assist over the phone and by email.

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