The Power is Wilting

In the seventies and early eighties, direct cutting of silage was often championed as the best way of preserving the feed value of forage crops. Since then, most British farmers have moved to a wilting system and higher dry matter silage, so what are we trying to achieve with wilting.

The standing crop just prior to cutting has the maximum energy and protein levels. As soon as you cut the grass, the sugar levels begin to fall. So why do sugar levels fall in cut grass?

Despite being cut off in its prime, the plant is still living and as the cells continue to respire they use the sugars stored in the plant as their energy supply. Not only is the grass still alive, but so are the micro-organisms on the plant. The bacteria will continue to use the plant as a food source and they too tuck into the crop’s sugar store.

So why don’t we clamp the silage straight away?

The problem with low dry matter silage is the effluent. As the sugars within the crop are water soluble, the precious energy inside the silage will be disappearing out of the clamp in the flow of effluent. Wilting the grass will reduce the water levels and concentrate the sugars, hopefully locking them inside the clamp.

The other problem with low DM silage is that the chances of achieving a good lactic fermentation are lower. Undesirable clostridia bacteria are more prevalent in low DM silage. 

The more time the crop sits on the ground, the lower the sugar levels will be once it hits the clamp (due to respiration) so the length of wilt has to be a balancing act. A 36hr wilt can result in 6% of the valuable sugars being lost. This begs the obvious question – how long should I wilt my silage?

Wilting needs to be tailored to hit the target dry matter percentage. The current guideline targets 28-32% dry matter as the ideal. The lower end for first ley leafy Italian ryegrasses and the higher for older pasture with more traditional grass species. These figures will maximise the total amount of ME (Metabolizable Energy) preserved from the standing crop through to the ration in front of the cow or inside AD tank.

 So how do I hit the 28-32% dry matter target?

The first thing to do is take a dry matter reading of the standing crop. This will enable you to plan the wilting process. In drought years, late cut crops can often be standing at the target DM and no wilting will be required. Wetter crops should be spread across the entire field area as soon after mowing as possible. Tedding or spinning out the grass will help speed the drying process but the weather conditions are the biggest influencing factors. As the saying goes, “make hay while the sun shines”, read silage for hay.

Does tedding grass increase leaf losses?

If the crop is still below the target dry matter, then leaf losses will be minimal. In drier crops (such as hay) then tedding will increase leaf shatter and leaf losses so unnecessary tedding should be avoided. Rowing up or swathing needs to be done just in front of the forager to maximise the wilting period.

So how long should I wilt my silage?

Assuming wilting is required, the length of wilt depends on the DM of the standing crop, the weather conditions and the time of mowing. Ideally the crop should not wilt for more than 24 hrs but this depends on the time of mowing. So what is the optimum time for mowing silage?

Tradition says you should mow grass in the afternoon, after the sun has been shining on it. This theory is that the plant respires using up sugars all day and night, but it only produces sugars from photosynthesis during daylight hours. Therefore the sugars levels are the highest in the grass in late afternoon.

Cutting crops in the afternoon will mean the crop is going to need around 24hrs of wilting, so is it possible to reduce this? Well if the sun has been shining for a few days, and a good day is forecast, mowing grass in the morning as soon as the dew has lifted can see the silage made in a day. This will reduce the time the crop sits on the ground and will produce the lowest losses of ME for any silage process.

 The “one day” silage process needs the right weather and for the machinery to all run like clockwork but it’s definitely something to aim for.

 If you need further information or help on how to wilt your silage, or for any of the other aspects of silage making covered in this series – contact Jeremy Nash @ jeremynash1@btinternet.com