Silage is fodder made from green foliage crops which have been preserved by fermentation to the point of souring. It is fed to cattle, sheep, and other ruminants. The fermentation and storage process is called ensilage, ensiling, or silaging. The exact methods vary, depending on available technology, local tradition, and prevailing climate. Silage is usually made from grass crops including maize, rye, sorghum, or other cereals, using the entire green plant (not just the grain). Specific terms may be used for silage made from particular crops, such as oatlage for oats and haylage for alfalfa (haylage may also refer to high dry-matter silage made from hay).
History Using the same technique as the process for making sauerkraut, green fodder has been preserved for animals in parts of Germany since the start of the 19th century. This practice gained the attention of French agriculturist Auguste Goffart of Sologne, near Orléans. He published a book in 1877 which described the experiences of preserving green crops in silos. Goffart's experience attracted considerable attention. The conditions of dairy farming in the United States suited the ensiling of green maize fodder, and was soon adopted by New England farmers. Francis Morris of Maryland prepared the first silage produced in America in 1876. The favourable results obtained in the US led to the introduction of the system in the United Kingdom, where Thomas Kirby first introduced the process for British dairy herds. Modern silage preserved with acid and prevented from contact with air was invented by Finnish academic and professor of chemistry Artturi Ilmari Virtanen. Virtanen was awarded the 1945 Nobel prize in chemistry "for his research and inventions in agricultural and nutrition chemistry, especially for his fodder preservation method", practically inventing modern silage. Early silos were made of stone or concrete either above or below ground, but it is recognized that air may be sufficiently excluded in a tightly pressed stack, though in this case a few inches of the fodder around the sides is generally useless owing to mildew. In the US, structures were typically constructed of wooden cylinders 35 to 40 feet (11 to 12 m) in depth. In the early days of mechanized agriculture (late 1800s), stalks were cut and collected manually using a knife and horsedrawn wagon, and fed into a stationary machine called a "silo filler" that chopped the stalks and blew them up a narrow tube to the top of a tower silo.
Production
The crops most often used for ensilage are the ordinary grasses, clovers, alfalfa, vetches, oats, rye, and maize. Many crops have ensilaging potential, including potatoes and various weeds, notably spurrey such as Spergula arvensis. Silage must be made from plant material with a suitable moisture content: about 50–60% depending on the means of storage, the degree of compression, and the amount of water that will be lost in storage, but not exceeding 75%. Weather during harvest need not be as fair and dry as when harvesting for drying. For corn, harvest begins when the whole-plant moisture is at a suitable level, ideally a few days before it is ripe. For pasture-type crops, the grass is mown and allowed to wilt for a day or so until the moisture content drops to a suitable level. Ideally the crop is mowed when in full flower, and deposited in the silo on the day of its cutting. After harvesting, crops are shredded to pieces about 15 mm (1⁄2 in) long. The material is spread in uniform layers over the floor of the silo, and closely packed. When the silo is filled or the stack built, a layer of straw or some other dry porous substance may be spread over the surface. In the silo, the pressure of the material, when chaffed, excludes air from all but the top layer; in the case of the stack, extra pressure is applied by weights to prevent excessive heating.
Equipment Forage harvesters 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 chaff into the wagon through a chute at the rear or side of the machine. Chaff 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, northwestern Europe, and New Zealand, it is common for silage to be placed in large heaps on the ground, compacted by tractor to push out the air, then covered with plastic sheets that are held down by used tires or tire ring walls. In New Zealand and Northern Europe, "clamps" made of concrete or old wooden railway ties (sleepers) and built into the side of a bank are sometimes used. 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 formed into bales using a baler, making balage (North America) or silage bales (UK, Australia, New Zealand). 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. The wrapping may be performed by a bale wrapper, while the baled silage is handled using a bale handler or a front-loader, either impaling the bale on a flap, or by using a special grab. The flaps do not hole the bales. In the UK, baled silage is most often made in round bales about 1.2 m × 1.2 m (4 ft × 4 ft), individually wrapped with four to six layers of "bale wrap plastic" (black, white or green 25-micrometre stretch film). The percentage of dry matter can vary from about 20% dry matter upwards. The continuous "sausage" referred to above is made with a special machine that wraps the bales as they are pushed through a rotating hoop, which applies the bale wrap to the outside of the bales (round or square) in a continuous wrap. The machine places the bales on the ground after wrapping by moving forward slowly during the wrapping process.
Haylage
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