What to do in preparation for second cut silage

Date published: 19 May 2020

Chris Breen, a Dairy Adviser at the College of Agriculture, Food and Rural Enterprise said: “The online CAFRE Crop Nutrient Calculator is useful for working out slurry and fertiliser requirements for second cut silage based on soil analysis.

“The fertiliser rate should be 80 - 100 kg N / ha (80 units per acre) allowing for any slurry nitrogen (N) applied (approximately 6 units N in 1000 gallons of slurry in the summer). Include phosphate (P) and potash (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 or 27:6:6 will help to make up the shortfall in P and K. If only the K index is low then a zero P compound such as 26:0:6 should be used.

“At soil index 2 for phosphate and index 1 for potash, typical indices of fields with a history of being cut for silage, slurry has the potential to provide some of the nitrogen and potash and all of the phosphate. An application of 22 cubic metres of dairy cow slurry per hectare (2,000 gallons per acre) and 375 kg (three bags per acre) of a 24:0:13 type fertiliser can meet second cut requirements at these indexes. At a practical level evenly spread slurry improves silage fermentation and minimizes sward damage.

“All silage cuts 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.”

Use of low emission slurry spreading equipment (LESSE)

Chris Breen continued: “Low emission spreading equipment to spread slurry is becoming more common on farms. Such equipment is being encouraged to improve air quality as less of the nitrogen in the slurry is lost as ammonia into the atmosphere.

“Use of a trailing shoe or band spreader rather than the traditional inverted splash plate has many benefits for the farmer which include better nitrogen utilization and produces better grass yields to same fertiliser input – Trailing shoe +24% more grass and by band spreader +16% more grass. It also produces less grass contamination and means that slurry can be spread up to four weeks after cutting and can be spread within 3 metres of a watercourse rather than 10 metres.

“Use of LESSE has now become a legal requirement for farms operating under a nitrates derogation, with all slurry spread after June 15 on such farms needing to be applied using one of the low emission techniques.”

Liming of Grassland

Often not treated as a priority, liming is critical to ensuring good grass growth. Consideration should be given now to lime applications where soil analysis shows a need. The pH for mineral soils should be 6.0 – 6.5.

Applying lime will correct the soil pH, allow nutrients in the soil to become more available and allow nutrients supplied by fertiliser to become more available. Liming will also improve soil structure, encourage earthworms, as well helping to reduce weeds and to keep ryegrass and clover in the swards.

When should liming be carried out?

Chris Breen said: “In the past, on many farms lime was only applied at reseeding. However liming more often is important where soil analysis shows a need.

“The availability of granulated lime has made application easier throughout the grazing season. As ground lime has varying particle sizes it takes the larger particles longer to break down so traditionally ground lime was applied in the autumn to allow breakdown over the winter. “Applying slurry soon after the application of lime is not recommended due to the increased risk of ammonia N volatilisation. Spreading lime one to two weeks after a slurry application doesn’t cause a problem.”

Should ground limestone or granulated lime be used?

This will depend on a number factors: A very low soil pH (5.2) will require high quantities of granulated lime which will be much more expensive than ground lime. Granulated lime can be applied by a fertiliser spreader, without need for employing a contractor. It can also be applied on small areas more easily. Moreover, granulated lime is finer and more quickly available as a neutralizing agent. Ground lime takes time to break down but acts over a longer period.

You can discuss liming and fertiliser recommendations with your local CAFRE Dairy Development Adviser or telephone 0300 200 7843 and ask to be directed to a local adviser.