Silage

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, sorghum or other cereals, using the entire green plant (not just the grain). Specific terms may be used for silage made from particular crops: oatlage for oats, haylage for alfalfa (haylage may also refer to high dry matter silage made from hay).

Using the same technique as the process for making sauerkraut, green fodder was preserved for animals in parts of Germany since the start of the 19th century. This 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.

The modern silage preserved with acid and by preventing 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.

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% to 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.