The Irish Grassland Association held two farm walks last week on the topic of ‘Making good quality silage’, which saw strong crowds of 200 to 300 farmers attending each event. The main speakers at each event were Padraig O’Kiely and Tim Keady, with B&T adviser David Colbourne and Austin Callaghan speaking at the Cavan and Mayo event respectively.

Sward type

Padraig O’Kiely, Teagasc, Grange focused on the role of soil fertility, sward type, fertilizer application and grazing out dead grass from the sward to increase silage quality.

He stressed to farmers on the day that sward composition will affect grass silage quality, saying that where swards consist of a high proportion of perennial ryegrass, grass growth rates and digestibility will be higher than older swards. In addition, they can have twice as much sugar content as swards containing old pasture.

Grazing before closing

The importance of grazing swards tight before closing for silage was also highlighted. Table 1 shows the effect of pre-grazing management on silage quality.

O’Kiely said that the dead butt of grass at the base of a heavy overwintered sward would have a very low digestibility of 40 to 50 DMD, which is similar to that of straw.

The study, which was conducted at Grange, showed that where there was an accumulation of dead herbage at the base of the sward, silage quality was 6% DMD lower than swards that were grazed bare to 5cm in either spring or autumn. However, he noted that by grazing out these swards, silage yield would be slightly lower by 1.4t to 2t DM/ha than where the swards are not grazed out.

Soil fertility

The importance of maintaining good soil fertility was highlighted by local Teagasc B&T adviser Austin Callaghan. He said that to maximise silage yield, farmers should target a maximum nitrogen application of 100 units/acre. He highlighted the value of slurry saying that spreading it in spring under ideal conditions could see up to 10 units of nitrogen being available per 1,000 gallons of slurry.

Grass uses approximately two units of nitrogen per acre per day or 14 units per acre per week, so a field that is dressed with 100 units/acre will have all the nitrogen used in 50 days, or slightly over seven weeks.

He put particular emphasis on phosphate, saying that over 60% of Irish grassland soils are now in index one and two, and this is a worrying trend. The ideal P index is three and it can take four to six years of compound fertilizer use to increase soil fertility by one unit.

He said that at soil P index one, grass silage yields can be reduced by 7t to 8t/ha. He said that soil sampling is vital and should not be looked at as an extra cost. A soil analysis costs €25 and will suffice for up to 10 acres of land. Over five years, it equates to a 50c/acre per year cost.

Lime

Austin finalised his talk on what he called the most important point — lime. He said that even with the correct soil P and K levels, fertilizers will not work efficiently if the pH of the soil is too acidic. The optimum pH for grassland is 6.2 to 6.7, or 5.2 to 5.6 for peat soils.

However, many Irish soils have a pH of much below this. In order to improve the nitrogen and other nutrients from the soil, lime should be applied to hit these targets.

Attaining high levels of animal performance

Tim Keady of Teagasc, Athenry, spoke about the importance of making good quality silage and the effects of this on animal performance.

He said that the largest crop grown in Ireland is grass silage. Approximately 22 million tonnes are harvested annually in a 40:60 split between round bales and clamp. Silage analysed over the winter was, on average, 4% lower than last year and varied from 52DMD to 82DMD.

Keady said that the lower range of results under ad-lib feeding would not be sufficient to maintain animal liveweight, while the upper end would be sufficient to have cows producing 23kg to 24kg of milk or have finishing cattle gaining 1.2kg liveweight per day.

Table 2 shows the mean, minimum and maximum of all silage samples tested in 2012. Keady outlined that the variation in silage quality had a huge effect on potential animal growth rates and that farmers should be focused on maximising gain from silage by striving to make the best quality silage possible.

Increase quality

He stressed that as you increase silage quality, feed inputs can be decreased which can reduce the wintering cost of cattle. He outlined that a 5 DMD increase in silage quality in the diet of a lactating dairy cow would result in the ability to reduce supplementation levels by 2.75kg concentrates per day or 85kg per month.

The same five-unit increase in the silage quality when fed to finishing cattle would allow for a decrease of 1.8kg concentrates per head per day, or 270kg over the 150-day finishing period. In addition, the effect of delaying the silage harvest by one week was also outlined. Each week of a delay in silage harvesting results in a 3.3 DMD drop in silage digestibility.

Keady said that this would require an additional 1.8kg concentrate per head per day to a dairy cow, 1.2kg per day to a beef animal and 0.23kg per day to a finishing lamb to sustain animal performance at the same level as if the silage was cut a week earlier.

He also said that once grass is cut, it should be lifted before 36 hours on the ground. If left longer than 36 hours, then the DMD will reduce by 0.5 to 2 DMD per 24 hours.

Make sure you have good silage

Higher digestibility silage can be made using a perennial ryegrass sward.

Grazing the sward to between 4cm and 5cm in early spring or the previous autumn can increase silage digestibility by approximately 7 DMD.

Grass should be predominantly in the leafy stage at harvest — removing surplus grass as baled silage is an excellent example of this.

Ryegrass swards contain higher levels of sugar in the grass than older swards and, for that reason, they are much easier to preserve.

Where slurry is applied in spring, it should be applied to low covers to avoid carryover of surface contamination.

A maximum of 125kg N/ha (100 units N/acre) should be applied to a first cut silage sward and should be cut at least seven weeks after the application.

Silage should be made in dry, sunny weather.

Do not mow the crop until the dew has evaporated.

The wider the windrow the better the wilt. Tedding is ideal.

Tips on making good silage

  • Grass should be wilted for one day to make firm bales that will maintain their shape and avoid air entering the bale.
  • Ensure that at least four layers of wrap are placed on each bale.
  • Under Irish conditions, the colour of the wrap does not directly affect quality.
  • Avoid excessive transportation of wrapped bales as damage to the plastic seal may occur.
  • Move wrapped bales to storage immediately to avoid sagging and bird damage.
  • Handle wrapped bales gently.
  • Protect wrapped bales from damage and repair damage when it occurs.

    • Q&A

    Can slurry and fertilizer be applied at the same time?

    Austin Callaghan:

    To maximise uptake of nitrogen, leave five to seven days between slurry and nitrogen application.

    What is the maximum lime application per acre?

    Austin: The maximum application rate would be 3t/acre. However, a ‘little and often’ approach would be more beneficial.

    What are the ideal conditions for spreading slurry?

    Austin: The ideal conditions to spread slurry are in the spring on an overcast day with a little mist and little to no wind.

    Is wilting about drying off the dew off the grass or drying the moisture out of the grass?

    Tim Keady: For pit silage, the optimum DM should be 22% to 24%. A standing crop will allow the dew to dry more quickly, once cut. Ideally, it should be tedded to allow to wilt quickly. This will both allow dew to dry and decrease the internal moisture content of the grass.

    Are silage additives any use?

    Tim: There are many different types of additives such as acids, molasses and inoculants. Studies have shown that acids and molasses will increase the fermentation, resulting in improved intakes and cattle performance.