Silage '17: getting quality right in bales

One of the biggest changes in Irish agriculture over the last 10 years has been the way in which making round bale silage has become a key feature of good grassland management. Prior to this, round bales were the preserve of smaller farmers or farmers who did not have a suitable concrete base in which to make pit silage.

But, today, most farmers in the country make round bales of silage either as main cuts, or strategically during the main growing season. It is this strategic use of bale silage that has evolved over the years into a key grassland management tool.

In the past, it was more common to close off fields for first- and second-cut silage with the rest of the farm grazed. If grass covers got strong, paddocks were topped after grazing to improve quality. If grass covers decreased, topping was stopped and extra supplement was fed.

The cost per kilo of grass dry matter is lower than for pit silage and bales suit smaller crops better than pit silage

What we see on farms today is that bale silage has replaced topping as a way of improving grass quality. Surplus grass is identified and cut and baled almost straight away, usually at much lighter covers than main-crop silage. Making bales facilitates this form of silage because the farmer is charged per bale, not per acre as per pit silage, so the cost per kilo of grass dry matter is lower than for pit silage and bales suit smaller crops better than pit silage.

The good grassland managers have stopped topping fields and will instead prioritise paddocks that need mechanical correction for bale silage. With topping, the cut grass is let go to waste and subsequent grass growth is reduced by around 5%. This is because topping inevitably cuts off some regrowth since grazing and it takes the grass plant longer and uses more energy for a second regrowth to appear.

Quality

Most dairy farmers now talk about having a number of high-quality bales to be fed out to the herd in the spring and autumn and at times of the year when grass growth decreases such as a summer drought. Some farmers talk about having between two and three quality bales available per cow. A lot depends on stocking rate and soil type.

When we talk about silage, we can break it up into two distinct categories; good-quality silage for milking cows or fattening cattle and then lower quality silage suitable only for dry cow feed. The type of grass that goes into each bale is very different.

Having the correct pre-mowing yield is important for quality

The high-quality bales should be cut from grass swards with covers of between 1,500kg and 2,500kg DM/ha. Any covers higher than this will probably fall into the dry cow silage category as the percentage of stem relative to leaf increases and the DMD will drop.

So having the correct pre-mowing yield is important for quality. Two things to watch out for when cutting grass for silage are the sugar levels and the nitrate levels. Sugars are converted to acids in the fermentation process. Sugar levels are highest in the afternoon. The target is above 3% sugar and this can be tested by a refractometer. Some very leafy swards can have low sugar levels so it can be hard to get a good fermentation on really leafy grass.

High nitrate levels in grass inhibit buffering so it reduces the drop in pH necessary for fermentation. High nitrate levels can be a particular issue when taking out surplus paddocks for silage as the fertiliser may have been applied recently for grazing and not with cutting for silage in mind. Nitrates can be checked by test strips and the target is to have nitrates below 800ppm.

The optimum dry matter for bale silage is between 20% and 35%

However, achieving a good wilt will help to reduce the effect of high nitrate levels. The other, and important, benefit of wilting is to reduce the dry matter of the grass. The optimum dry matter for bale silage is between 20% and 35%. This can be achieved by leaving 3m rows of silage for 24 hours after cutting. Teagasc research says grass in 6m rows will need to be left for 48 hours to get the same wilt while tedded grass will get too dry if left for longer than 24 hours.

Another target for high-quality fermented bale silage is to have the pH level less than four. The target for DMD is to have it greater than 75%. In terms of energy the target is to have metabolisable energy at 11 to 12 MJ/kgDM and a UFL of 0.9 to 0.95. In terms of crude protein, high-quality bale silage should be testing in excess of 18% protein. The range in high-quality silage is usually 18% to 25% protein.

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