Gearing up your grassland for silage

Assessing soil structure

• Use the AHDB Soil Assessment Guide or similar Visual Evaluation of Soil Structure.
• Get your spade out and gain your own experience of your soils.
• Dig in spring as soils are drying up.
• Know the textural classification of your soils as this helps interpretation.
• Focus on smell, compaction, rooting depth, colour and counting worms.
• Dig where grass growth is great and where it is disappointing.
• When starting out, dig where you know there is compaction to get ‘your eye in’.
• If you have compaction at the surface it is worth considering spike aeration. This won’t improve yields of silage grass, but it will help to get air in, stimulate earlier growth and improve water infiltration if it turns wet.
• If you have compaction further down (at 10-15cm) consider sward lifting in the coming autumn (not this spring) and this will help with grass yields in 2026. Using a sward lifter in spring is likely to cause as much damage to yields in 2025 as doing any good, as the operation is invasive to grass roots and will cause a drop in yield up to four weeks after doing it.
• Relieving soil compaction can easily return 1-2 tonnes DM/ha from your silage system.

Improving grass leys

• Target lowest performing fields and check soil structure and fertility first.
• The best timing options for reseeding are spring and late summer (April and August for most locations).
• Plan what you want from the crop – grazing/cutting/both.
• Use seed mixtures that are made up from varieties on the recommended list of grasses and clovers – they have the latest genetics for yield, quality and efficiency.
• Focus on intermediate and late perennial ryegrasses and no more than 40% tetraploids (by weight) in the grass mix, as these don’t provide the longevity that the sward needs.
• If ploughing, use the opportunity to fix soil compaction (sward lifters, mole ploughs, ploughing depth).
• If direct drilling, cut/graze really hard first and consider burning-off.
• Always use a roller to get good seed/soil contact, but don’t roll too much!
• If concerned about germination rates, drill in two directions.
• Light graze about 3 to 4 weeks after grass emerges to stimulate tillering.
• Do you need to sow clovers? Modern varieties will grow under inorganic fertiliser nitrogen applications, giving a protein and digestibility advantage to the silage, but if you don’t want to consider managing the sward for clover, then don’t spend money on putting them in the seed mixture. White clover needs a combination of cutting and grazing each season to maintain sufficient cover in the sward to bring the advantages. Red clover needs careful management with higher cutting heights than we use for grass only swards, so that the growing point isn’t removed, and avoiding soil compaction is also important for survival.

Targets and applications

• Soil pH should be 6.5
• Target indices are 2 for P (phosphate), 2+ for K (potash), 2 for Mg (magnesium).
• Consider trace elements but appreciate that most soils in the UK are low.
• Ca (calcium) is worth looking at, but remember it can be leached.
• Ca/Mg balance can indicate risk of soil compaction, but won’t indicate yield potential.
• Have a field-by-field nutrient management plan that matches the use of slurries, manures and bought-in nutrients. Use it and update it.
• Refer to the Fertiliser Manual (RB209) for planning nitrogen rates.
• For correcting soil pH refer to the lime calculator.
• Don’t use limes that contain magnesium (use calcium lime only).
• For correcting P and K refer to the P&K calculator or MANNER NPK or the Farm Crap App.
• K is critical for silage yield and quality. A three-year trial by Teagasc in Ireland adding 320kg/ha potash to soil with a K index of 1 lifted average silage metabolisable energy (ME) from 10.9MJ/kg DM to 11.5MJ/kg DM and yields by at least 2t DM/ha for a three-cut system.
• Apply sulphur with your nitrogen. Almost all soils are now deficient in sulphur and applying 80-120kg SO3/ha, split over the whole silage season will improve yield and protein content.

Using muck and slurries

• Get your muck and slurry analysed for N, P and K (the Fertiliser Manual figures are averages, and you can only plan in detail and reduce brought-in inputs without risk to yield, if you know what your manures contain).
• Incorporate into your nutrient management plan for every field (soil reserves and manures first, then bagged fertiliser to top-up).
• If you are importing manures (e.g. digestate and pig/poultry muck) get them analysed.
• Target low P and K index soils.
• Always follow the code of good agricultural practice when applying manures.
• To maximise the nitrogen availability in your manures:
  ✔ Apply in season as much as possible.
  ✔ Use dribble bars and injectors.
  ✔ Incorporate into soil when you can.
  ✔ Take a little and often approach (no more than 30,000 litres/ha or 2,600 gals/acre of slurry in one application).
• Don’t rely on manures for sulphur inputs – remember that sulphur in manures is generally at low concentrations and is unavailable for plant uptake in the season of application.

Healthy plants have reduced fungal disease and are less likely to have field-formed mycotoxins.

George Fisher