Frank Mickan, Pasture and Fodder Conservation Specialist, Agriculture Victoria
One of the key strategies to making quality silage is cutting it early. However, in Tasmania, early in the season, it can be hard to find two fine days in a row in order to cut and wilt to the desired dry matter. But consider this – cutting early with some rain damage will result in a silage of better quality than that cut later. When pasture is starting to go reproductive, digestibility is dropping about 3–5 percentage units per 7–10 days, and protein dropping 1–3 units.
The aim is to put chopped stack silage in at about 30–35% dry matter content (DM) versus 40–50% DM for baled silage. If this is not done, the silage will undergo a less desirable fermentation, be of lower quality and be less palatable.
The longer a mown crop is on the ground, and/or the more rain that falls on it, the greater the losses of dry matter and quality (energy and protein). This is caused by plant respiration, microbial and bacterial caused losses, leaching losses and some possible leaf shatter.
Let’s look at some scenarios of wet weather and some possible actions to consider.
Short periods of drying weather
Try to beg, borrow or steal a tedder, tedder rake and/or mow with a mower conditioner – all of which will substantially speed up the rate of wilting and possibly beat the rain.The more widely spread and thinner the windrow, the quicker the wilting. Ted 2–3 times if the weather suits. Definitely spread (ted) straight after mowing! Respread after most of the dew has lifted the next morning by whatever sun there is, as it amounts to about 1.00 to 2.5 tonnes/ha of water.
For those farmers who have access to a mower conditioner, leave the swathe boards as wide as possible to produce the thinner, wider, and quicker drying windrows. The tyned types of conditioners are more suited for pastures than the roller types, although the latter are still most suitable for thicker stemmed crops such as summer forages and cereals.
Crop has been cut and rain is threatening
If rain is threatening by late on day 2 or during day 3 after mowing, and the desired amount of wilting had not been achieved, “Go for it!” You’ll never reliably predict the amount or duration of the approaching rain, so if you wait, Murphy’s Law says “It will pour rain.” Forage which is ensiled too wet after laying on the ground for days on end will, at best, have very poor fermentation due to lack of sugars for the ensiling bacteria to convert to acid, which “pickles” the grass to become silage. At worst, the material may not be much better than compost – the probable outcome if it does pour! There will be some effluent produced which must not enter waterways.
Rain has started during harvesting
a) Forage harvesting: Stop harvesting if mud is being carried onto the stack, as this will result in a very poor quality fermentation in the silage. If you are fortunate enough to have a heavily wilted crop, a small amount of rain will not be too detrimental. If water is obviously oozing out of the material being rolled in the stack, it is advisable to stop harvesting. A plastic cover should be placed over the stack and well weighted to preserve the good quality that has so far been ensiled. If there is likely to be a lot of rain over several days, strongly consider completely sealing that stack. The remaining crop, now to be a very poor quality material due to the weather, should be stored in a separate stack/pit from the original, better quality stack.
b) Baling: Stop when the material continually wraps around the lower rollers or when the extra weight of the bales causes undue stress on the baler and/or wrapper. Wet and heavy bales are difficult to wrap and/or move around with small tractors. Heavy rain may affect the seal between the plastic layers, so, if possible, cart the bales to a covered area (eg. tarped area), and wrap the bales out of the rain. Wrapping bales which were baled before rain arrived and have subsequently become wet will lose minimal quality.
Mown swath receiving a lot of rain
Swear a lot and then be comforted (slightly) by the fact that this heavy rain will result in a lot of good quality regrowth.
Mown pasture laying on the ground and receiving several days’ rain will continue to decrease in quantity, quality and palatability. At the same time, the number of undesirable bacteria, moulds, fungi and yeasts in the windrows will be building up at an ever increasing rate. If possible, it may be advantageous to spread the wet material after 3-4 days on the ground, especially before it begins to become slimy and yellow, then black underneath! Do this even if drying weather is some way off. This operation may, when the grass is finally ensiled, prevent or reduce an undesirable fermentation.
When the weather clears and the top of the swath or windrow is dry of loose water, spread the material with a tedder. If the grass was well wilted before the rain dropped, it will redry reasonably quickly.
Material has been on the ground for a week. Do I still make silage or hay?
Early season grass will be initially high in energy (sugars) which is what the silage-making bacteria love and need. If a mown crop is on the ground for a week, the amount of fermentable substrate will be substantially reduced, therefore reducing the likelihood of a desirable fermentation.
However, this problem is worse with later-cut material. If there is little chance of making it as hay (and the wet ground will generally dictate this) then the only options are to:
There are several additives which may aid the fermentation process. For slightly over-wet forage which is still high in sugars, fermentation-stimulating bacterial inoculants are suitable, as is a product containing sulphur compounds + amylase. If forage has been on the ground for many days, it is probably very low in sugars. Buffered acid salts are the best bet, albeit expensive due to the high application needed. Effectiveness will depend on the degree of wilting, how much and how well the additive is incorporated, etc. so there are no guarantees on this working well, or getting all your money back. Do not pick up mud/cow manure inoculating with bad bacteria.