By Charlotte Westwood, Veterinary Nutritionist, PGG Wrightson Seeds
For much of NZ pasture silage season has been underway for some time. Making silage is a comprehensive topic, and this article focuses on just one aspect of silage – wilting pasture/lucerne for ensiling.
Getting the dry matter (DM) percentage (%) right through wilting is a key part of a good silage. We’re not talking about direct chop crops like whole crop cereal silage or maize – rather, pasture, lucerne and greenchop cereal silage. So, that’s the green stuff that’s too wet to direct chop.
Why wilt mown feed?
Chasing really good pasture/lucerne silage means mowing when feed quality is high - decent MJME, moderate to high crude protein, moderate NDF and good water-soluble carb levels. At these growth stages the challenge is, mown feed will be way too wet to direct chop/ensile without wilting first. So, we mow and allow water to evaporate off so the end product is drier.
Key reasons to wilt (increase DM%) before ensiling is:
- Get the best silage fermentation we can
- Prevent any effluent (silage juice) run off (loss of DM of which is mostly soluble, good quality nutrients AND an environmental hazard)
How fast should we try to wilt mown feed?
The faster we can wilt our mown greenfeed the better. A bit like using a desiccator to dry down fruit, tomatoes and the like in your kitchen. Slow those dry down times and things end badly! Silage from mown greenchop feeds is no different.
The shorter time that mown feed is lying around the paddock, the less sugars (and energy) are lost from the greenfeed. Though you’ve mown your pasture, it’ll still respire lying around on the ground. Respiration means converting water soluble carbohydrates (sugars) into water and carbon dioxide plus energy (heat) – which is why a windrow of mown pasture warms up. This is also due to bacteria on the surface of the mown greenfeed consuming sugars too. The sugar levels of wilted pasture will almost always be lower than standing non-mown greenfeed. Our aim of a good wilt is to minimise the amount of sugars (and energy) consumed between mowing and picking up the cut forage from the paddock.
The ideal target is no more than 24 hours from mowing til getting the feed under or in plastic.
How long does greenfeed take to wilt down?
There are many things that influence how long it will take to wilt down.
- DM % (water content) of the fresh forage
- DM yield
- Time of day cut
- Presence of dew (or not) or even frost
- If it’s on the ground overnight
- Weather (rain, sunshine, wind, temperature, humidity etc)
- Other factors – chop length (longer chop length wilts more slowly), if the mower chucks mown feed out in wide swaths or narrow etc. And if you’re tedding mown feed to try to dry it out.
Tetraploid ryegrasses contain slightly lower DM% than diploid ryegrasses. Wilt time might be slightly longer for tetraploids, but realistically, all of the above factors are more likely to change wilt time than ryegrass ploidy.
What’s our target DM% for ensiling mown feeds?
For stack or pit pasture silage, our target is somewhere between 30% and 35% DM when it goes into the stack/pit or 35 to 40% DM for bales. Wetter than 30% DM increases risk of effluent ooze from the stack or bulgy ‘pear shaped’ bales. The drier silage gets especially over 40% DM it gets the harder it is to pack the stack well or get really tight bales, time taken to reach final pH (acidity) is longer, so quality will be poorer. And dry stacks tend to heat up again at the face at feed out.
For lucerne stack or pit silage, target is a bit higher than for pasture silage/baleage. For lucerne, target somewhere around 35% DM (stack/pit) and 40% DM (bales). Most of you know that lucerne silage and baleage is harder to make than pasture silage, so we often target a higher DM% going into the bale or under plastic than we do for pasture silage.
Is your cut forage ready to stack or bale?
There are lots of rules of thumbs/ tips and tricks to tell what DM% your cut forage has reached, including microwave oven dry down techniques. Let us know your techniques you use, and/or if you'd like more information about these DM% estimate techniques.
Cut in the morning and get in the stack faster, or mow in the afternoon (more sugars) and risk longer time on the ground?
This argument often comes up:
- Mow earlier in the morning (lower water soluble carbs) but more drying time through the day, so less likely it’ll have to lie around in the paddock for a second night. OR;
- Cut later in the day, less drying time = you may need to leave it out overnight for a second night.
Morning cuts (once dew is off) might be better than cutting later in the day - if you can get the feed in the stack the following day (one night out) or better still, later the same day if a hot, drying Norwest wind is blowing (for us Cantabrians!). The longer mown feed lies around in the paddock (more than 24 hours), you may end up losing more water soluble carbs than what you were trying to chase by cutting in the afternoon when levels of water soluble carbs can be (slightly) higher.
Silage making is often as much an “art” as it is a “science”. We’d love to hear what tips and tricks help you get awesome silage into the stack, pit or bale – sharing with the rest of us would be great, look forward to hearing from you.