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Slurry and Fertiliser for SilageFollowing on from the growing problems associated with 2018, great care and attention must be paid to your silage programme. Your most important crop for Winter 2019 is your first cut silage in terms of quantity and quality. You may also need to build your silage wedge back up.

When choosing a suitable fertiliser programme, it is important to first consider your cutting date as this will determine the quality of your first cut silage. Aim to have first cut silage quality at 70% DM or above as this will greatly reduce the supplementation of expensive concentrates next winter. Remember the simple rule to follow is that a grass plant will utilise 2 units of Nitrogen (N) per day in good growing conditions, so if aiming to cut in 35 days, do not apply any more than 70 units of N to the silage crop.

For higher quality cuts of silage over 70% DMD, it is best to aim for a cutting date between 25th of May and early June before heading out date when the sward will go stemmy, resulting in lower quality.

Most farmers will be using slurry in addition to chemical fertiliser as a source of NPK for their silage crop, but it is important to remember the great variability in the nutrient content of slurry on the farm.

Soil Phosphorus (P) & Potassium (K) fertility levels have declined across the country for some time now, and this is inhibited by the over estimation of the nutrient value of slurry. This could be especially seen on intensive farms where they were running an almost closed PK system by not importing enough P’s & K’s.Slurry and Fertiliser for Silage

Slurry quality can vary greatly depending on concentrates fed and its dry matter. Remember, your cattle slurry came from your own farm and its nutrient value will reflect the nutrient status of your soil. A good practice may be taking a representative sample and do a DM and nutrient test. In the absence of a full analysis you should use a hydrometer to determine DM. Pure undiluted cattle slurry will be 7% DM and 1000gls will equal approximately a bag of 5-5-30 when used at this time of year. The ratio of P/K of 1/6 is perfect for recycling back onto silage ground. Use of trailing shoe and injection may increase the N by another 3 units.

DM % can vary by dilution of the slurry tank from milk parlour run off, leaking water bowls and the addition of water to decrease the viscosity for ease of application through umbilical cords, dribble bar and trailing shoe methods. If the slurry is 50% diluted, then its nutrient content will be only half of the above value.

Choose a fertiliser for your silage carefully to match your offtakes and your most recent soil test results. Sulphur (S) is also important and general advice is 20 kg/ha per cut. Choose a High K fertiliser as K plays a key role in the formation of starch, sugar and development of amino acids which are the building blocks of proteins. Where adequate K is not applied N is not used efficiently resulting in N losses.


Maximum recommendations for silage crop based on DM yield 5t/ha for 1st cut and 3t/ha for 2nd & 3rd cut. Make the necessary deductions for early fertiliser application for grazing and also slurry applied.


Nitrogen (N)

Grass cutting regime Nitrogen requirement ( kg/ha)
First cut 125
Second & third cuts 100


Phosphorus (P)

P index 1 2 3 4
First cut 40 kg/ha 30 kg/ha 20 kg/ha 0 kg/ha
Second and third cut 10 10 10 0


Potassium (K)

K index 1 2 3 4
First cut 185 Kg/ha 155 kg/ha 125 kg/ha 0 kg/ha
Second and third cut each 75 75 75 0

Source: Teagasc Green Book


Traditionally low P&K compounds such as 24-2.5-10+S were used as a cover all silage compound, however these low P&K products are not suitable on all farms. Recent soil test results across the country have indicated 60% of grassland soils fall into Index 1 & 2 for Phosphorus. Farmers in association with their advisor should choose a suitable compound as per their soil test results, and in low P &K  situations, High P & K compounds such as 12-8-20+S or 13-6-20+S could be used and then apply straight Nitrogen or SuperCAN CCF to bring up the crops N requirements.

Slurry and Fertiliser for Silage

For more information on fertiliser application for silage, please contact us

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