The ensiling of forage cereal crops for silage is called whole-crop silage (WCS) or may be referred to as green chop silage, fermented whole-crop or small grains silage.
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The dry matter (DM) range recommended for WCS is 33 per cent to 50 per cent DM, depending on stage of growth and type of equipment used for harvesting.
Cereal crops which have been affected by frost or unfavourable weather conditions resulting in unsatisfactory grain yields can also be ensiled.
Mowing
The stage of growth of the crop at harvest will determine whether it is mown and wilted before harvesting or direct cut and ensiled as a ‘standing’ crop.
However, the height of cutting can have some implications on the stored product.
Cutting height is usually 7cm to 10cm above ground level. Cutting higher will result in a slight increase in nutritive value but reduced yields accordingly.
If mown and wilted the higher cutting height will also tend to keep the mown swath higher off the ground thereby allowing more airflow under the crop and a slightly faster wilting rate. It will also reduce the risk of soil contamination from other equipment operations such as raking.
However, cutting at greater heights will leave behind increased levels of stubble which creates a problem of removal in the future and preparation for the next forage.
Harvesting at flag leaf or boot to early ear emergence stage (18 to 22 per cent DM) will require the crop to be wilted to reach the desired DM content before harvesting, and particularly so for cereal and legume mixtures.
Types of mowers
Roller-type mower: Mowing with a roller-type mower conditioner is recommended to crimp or crack the stems, which will encourage quicker wilting. Wilting rate will be increased by 20 to 40 per cent compared to mowing only.
The amount of increase will depend on: crop yield; weather conditions; effectiveness of conditioning; and width and ‘fluffiness’ of conditioned windrows
Tyned-type mower: Tyned-type mower conditioners will also increase the rate of wilting through mainly an abrading (bruising) action on the leaves and stems plus some crimping.
Brush-type mower: A brush-type mower conditioner will abrade the waxy layers on most surfaces of the plant, which increases the wilting rate.
Conditioners
The aggressiveness of conditioning can be altered on all machines via equipment settings. Drier material — especially if the stems are hollow — are more effectively conditioned by the roller-type machines.
Super conditioners, often used for export oaten hay, have a much more aggressive crimping and abrading action and result in faster drying than even roller conditioners.
Conditioner-only machines will also achieve the desired effects, but will require the extra pass as soon as possible after mowing.
The conditioned stems will allow a more reliable and easier picking up by harvester and baler pick-ups and subsequent feeding into the respective cutting or roller mechanisms.
High-yielding crops will be relatively slow to wilt even if conditioned.
In all cases, leaving the windrow as wide and thin as possible (less dense), and in a ‘fluffy’ state, will increase the wilting rate substantially.
Tedders
Tedders, which spread the mown crop after mowing, will also increase wilting rate, but may not be so effective on high-yielding crops and may fatigue the equipment.
If a tedder is used in a heavy crop, re-tedding half to one day later may be necessary to even out the wilting throughout the windrow. Be wary of creating clumps with repeated teddings in heavy crops.
Another disadvantage with cereal crops, apart from the extra pass required to do the job, is that the tedder must be set up to avoid the tynes picking up soil while operating.
Leaves may dry much quicker than the stems if a tedder is used in crops at later growth stages (grain formation). However, a tedder is very beneficial to re-spread a crop that has been weather-affected.
Forage harvesters
Whole-crop cereals should ideally be harvested using a precision chopping forage harvester to ensure a short chop length (20 to 50mm actual length).
This ensures the material can be well compacted in the stack or pit, minimising the amount of air trapped and thereby reducing losses (nutritive value and DM), due to continued plant and microbial respiration during the early phases of fermentation.
Most other forage harvesting machines, such as self-loading wagons, cut the material to varying lengths, often over 200mm, making adequate compaction very difficult.
The drier the crop DM content at harvest, the shorter the chop length required. Chopping the material short also ensures a thorough mixing of the high nutritive heads with the much lower nutritive stems and leaves.
Increased density also reduces the rate of aerobic spoilage at stack opening, a common although not an insurmountable problem with cereal silages. Less wastage also occurs as animals cannot easily select the heads and leave the stems when fed.
Forage cereals being direct harvested at the later growth stage is increasingly being carried out with forage harvesters that have a cutter bar instead of the typical rotary disc mowers to reduce grain loss. Grain loss from the gaps in the housing of the chopping and feeding mechanisms can be minimised by fitting blanking plates.
Grain loss may be slightly higher in pre-mown crops due to the rotary disc action of the mower and, particularly if raked before harvesting, DM yield and nutritive value will also be slightly lower.
If the crop is harvested after the soft dough stage, the grain will be hardening as it matures. Forage harvesters — which are fitted with specific rollers for cracking grain — often referred to as ‘primary processing’, will be essential.
Balers
Harvesting WCS using balers is not recommended as dense compaction is often not achieved and vermin damage to the bales in storage can be a serious problem.
If whole-crop cereals are harvested with round and square balers the material needs to be wilted to slightly higher DM contents to ensure a lactic acid fermentation occurs.
Balers with chopping mechanisms are highly recommended to aid compaction. The fermentation process and animal intakes of WCS will also benefit from the chopping.
Once past the ideal stage for harvesting, cereal stems become more lignified (stiffer) and the stems are hollow (contain more air internally). These drier stems will allow increased air to be trapped within and between the stems in the bale. In this situation a chopping baler, with all knives in operation, is highly recommended.
An alternative is to bale at the moister end of the DM range recommended for baling. Baling with some dew on the material will also be useful if DM levels are above those recommended.
Baling at a slower forward speed will also allow most balers to produce a denser bale.
Baling material that’s too dry, or not tightly compacted, results in large volumes of air trapped in the bale, reducing nutritive value and increasing risk of puncture by stalks.
Feedback from some machinery operators indicate that if a mower only is used for the later growth stages of the crop, particularly when baling, the baler should travel in the opposite direction to the mower. The heads of the crop are picked up first, which results in much less trouble in the picking up and feeding in of the forage into the machine.
However, one piece of research has indicated that friction from the rolling mechanisms in some balers induces heavier grain loss than that from forage harvesters.
Applying net-wrap instead of twine will also reduce the amount of air trapped between the plastic and the bale as the twine, especially in slightly loose bales, will pull into the bale. This allows air to travel around the twine once plastic is applied, possibly becoming mouldy, particularly if holed.
Applying net-wrap will also minimise straw stalks protruding from the bales which can puncture the stretch-wrap plastic seal, allowing air to enter.
Silage additives
Most silage additives (usually inoculants) will improve the fermentation process and reduce losses in WCS.
A common problem in WCS is the onset of spoilage and subsequent heating after opening the stack. There are products specifically designed to minimise aerobic deterioration by moulds and yeasts in forage cereals.
All additives are applied during harvest and most require thorough mixing with the forage to be effective. The products are available as liquid or granular form and usually applied behind the pick-up or into the forage harvester chute.
Many inoculants will become ineffective if mixed with treated town water or water becomes too warm before application. Carefully follow the manufacturer's instructions and suggested application rates to ensure the effectiveness of the products.
Weather-affected crops
Forage cereals can be affected by frost, drought, wind (lodging) and shortage of rain at critical grain-filling stages, resulting in crops which may not be harvested economically as a grain crop, but may be ensiled.
A feed analysis of any weather-affected crop is recommended to ascertain its quality for ration formulations.
Lodging: Lodging occurs when portions of the crop fall over due to strong wind, and occasionally in very high-yielding crops and varieties with weak stems.
The lodged plants will then begin to deteriorate in nutritive value, and the grain may even begin to sprout if advanced enough in its formation (hard dough stage).
Harvest the crop within days before its nutritive value deteriorates too much and mould and deleterious bacteria build-up occurs. Travelling in the opposite direction to the lodged plants will ensure less difficulty in the harvest operation and minimal losses.
Crops lodged for some period of time can be a problem as the plants start decaying, making them difficult to harvest and adversely affecting the fermentation process.
Drought-stressed crops: Drought-stressed cereal crops can often be successfully harvested as silage as a salvage operation. Management of these crops for silage is the same as for the usual ensiling operations.
Crops will probably not be at the optimum growth stage for cutting and may need an early decision to cut before the crop quality deteriorates. The material may be drier than ideal, necessitating very short chop, dense compaction and sealed airtight.
Hay-making may be the best option for these crops.
Frost-affected crops: Frosts at the pre-heading to flowering stage of wheat (and most cereals) can affect the plant’s ability to reach a successful grain formation. This has implications for quality of forage cereals harvested after this stage.
Frosts generally do not affect most cereals too severely up to this stage, so should still be of high quality and could be ensiled successfully, if harvested and stored correctly.
– From Agriculture Victoria