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:For the Christian Alternative band, please see Silage


Cattle eating corn (maize) silage


Silage is fermented, high-moisture fodder that can be fed to ruminants (cud-chewing animals like cattle and sheep) or used as a biofuel feedstock for anaerobic digesters. It is fermented and stored in a process called ensilage or silaging, and usually made from grass crops, including corn (maize) or sorghum or other cereals, using the entire green plant (not just the grain). Silage can be made from many field crops, and special terms may be used depending on type (oatlage for oats, haylage for alfalfa – but see below for different UK use of the term haylage).

Silage is made either by placing cut green vegetation in a silo, or by piling it in a large heap covered with plastic sheet, or by wrapping large bales in plastic film.

Making silage

Silage must be made from plant material with a suitable moisture content, about 50% to 60%, depending on the means of storage, the degree of compression, and the amount of water that will be lost in storage. For corn (maize), harvest begins when the whole-plant moisture is at a suitable level. For pasture-type crops, the grass is mowed and allowed to wilt for a day or so until the moisture content drops to a suitable level.

The plant material is collected, chopped into pieces about long and packed. In the early days of mechanized agriculture, stalks were cut and collected manually using a knife and horsedrawn wagon, and fed into a stationary machine called a "silo filler" that would chop the stalks and blow them up a narrow tube to the top of a tower silo. Current technology uses mechanical forage harvesters that collect and chop the plant material, and deposit it in trucks or wagons. These forage harvesters can be either tractor-drawn or self-propelled. Harvesters blow the silage into the wagon via a chute at the rear or side of the machine. Silage may also be emptied into a bagger, which puts the silage into a large plastic bag that is laid out on the ground.

In North America, Australia, North-Western Europe, and frequently in New Zealandmarker, silage is placed in large heaps on the ground and rolled by tractor to push out the air, then wrapped in plastic covers held by recycled tires.

In New Zealand and Northern Europe, the silo or "pit" is often a bunker built into the side of a bank, usually made out of concrete or old wooden railroad ties (railway sleepers). The chopped grass can then be dumped in at the top, to be drawn from the bottom in winter. This requires considerable effort to compress the stack in the silo to cure it properly. Again the pit is covered with plastic sheet and weighed down with tires.

In an alternative method the cut vegetation is baled, making balage (North America) or haylage (UK). The grass or other forage is cut and partly dried until it contains 30–40% moisture (much drier than bulk silage, but too damp to be stored as dry hay). It is then made into large bales which are wrapped tightly in plastic to exclude air. The plastic may wrap the whole of each cylindrical or cuboid bale, or be wrapped around only the curved sides of a cylindrical bale, leaving the ends uncovered. In this case, the bales are placed tightly end to end on the ground, making a long continuous "sausage" of silage, often at the side of a field. Baled silage is handled using a front-loader, either impaling the bale on a spike, or by using a special grab. Holes made by a spike are re-sealed to avoid spoilage.

Fermentation

Silage undergoes anaerobic fermentation, which starts about 48 hours after the silo is filled. In the past, the fermentation was conducted by indigenous microorganisms, but, today, some bulk silage is inoculated with specific microorganisms to speed fermentation or improve the resulting silage. The process converts sugars to acids and exhausts any oxygen present in the crop material. Fermentation is essentially complete after about two weeks. Silage inoculants contain one or more strains of lactic acid bacteria, and the most common is Lactobacillus plantarum. Other bacteria used in inoculants include Lactobacillus buchneri, Enterococcus faecium and Pediococcus species.

Pollution and waste

The fermentation process of silo or pit silage releases liquid. Silo effluent contains nitric acid (HNO3), which is corrosive. It can also contaminate water courses unless collected and treated – the high nutrient content can lead to eutrophication (growth of bacterial or algal blooms).

Plastic sheeting used for sealing pit or baled silage needs proper disposal, and in some areas there are recycling schemes for it.

Storing silage

Silage must be firmly packed to minimize the oxygen content, or it will spoil.Four major stages silage goes through in a silo:
  • Presealing, which, after the first few days after filling a silo, enables some respiration and some dry matter (DM) loss, but stops
  • Fermentation, which occurs over a few weeks; pH drops; there is more DM loss, but hemicelluous is broken down; aerobic respiration stops
  • Infiltration, which enables some oxygen infiltration, allowing for limited microbial respiration; available carbohydrates (CHOs) are lost as heat and gas
  • Emptying, which exposes surface, causing additional loss; rate of loss increases.


Silage underneath plastic sheeting, held down by scrap tires.
Concrete beneath the silage prevents liquor leaching out.


Anaerobic digestion

Anaerobic digesters
Silage is a useful feedstock for anaerobic digestion. Here silage can be fed into anaerobic digesters to produce biogas that, in turn, can be used to generate electricity and heat.

Safety

Silos are hazardous, and deaths occur in the process of filling and maintaining them. There is a risk of injury by machinery or from falls. When a silo is filled, fine dust particles in the air can become explosive because of their large aggregate surface area. Also, fermentation presents respiratory hazards. "Silo gas", consisting primarily of nitrogen dioxide, is released in the early stages of fermentation, and can be lethal. Lack of oxygen inside the silo can cause asphyxiation. Molds that grow when air reaches cured silage can cause toxic organic dust syndrome. Silage bales are heavy, and can fall, roll or overbalance machinery. Silage itself poses no special danger.

Nutrition

The ensiled product retains a much larger proportion of its nutrients than if the crop had been dried and stored as hay or stover. Bulk silage is commonly fed to dairy cattle, while baled silage tends to be used for beef cattle, sheep and horses.

Since silage goes through a fermentation process, energy is used by fermentative bacteria to produce volatile fatty acids (VFA), such as acetate, propionate, lactate, and butyrate, which preserve the forage. The result is that the silage is lower in energy than the original forage, since the fermentative bacteria use some of the carbohydrates to produce VFA. Thus, the ensiling process preserves forages, but does not improve the quality or the nutrient value.

See also



References

  1. www.dictionary.com



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