Silo is a storage bin for chopped plants and grains. Silos used on farms allow farmers to supply livestock with nutritious feed all year and to delay the sale of their crops. Silos are also used at grain-handling terminals, where trucks, trains, and ships are filled with grain for shipment to markets.
Farmers use machines to chop up the plants for storage. The chopped material is called silage. Farmers use hay, corn, grain, juicy grasses called sorghums, and other high-moisture crop products for silage. Machines blow the silage in at the top of the silo. Silos are unloaded from the bottom.
If silage is packed properly, all air is forced out. Feed and grains do not spoil in a silo, because molds that cause spoilage cannot survive without air. Chemical changes that occur in the silage called fermentation also help prevent rotting. Acids produced by fermentation help to prevent the growth of molds. If a feed does not have enough starch or sugar for fermentation, farmers may add hydrochloric acid, sulfur dioxide, sodium metabisulfite, or other acids to keep it from spoiling. Molasses or ground grains may be used to make legumes (pea plants) into silage. They contain starches and sugars that help to start fermentation.
Americans learned how to make silos from Europeans in the 1870’s. The first silos were pits covered with boards. Then Fred L. Hatch, an Illinois farmer, built a square, wooden silo above ground in 1873. But its corners made it impossible to pack the feed tightly. In 1882, Franklin H. King, an agricultural scientist in Wisconsin, built a round silo. Round silos resist the pressure of tightly packed feed best. Today, round silos made of stone, brick, clay tile, sheet metal, concrete, or wood blocks are used worldwide. Airtight, fiberglass-lined steel silos are used where farmers use silage all year.
Other types of silos include trench, bunker, and box silos. The trench silo is made by digging a large trench, filling it with silage, and then covering it with a sheet of heavy plastic. The bunker silo is built above ground, and usually has wood or concrete sides. One or both ends may be left open. The box silo also is built above ground with poles and wood siding. Livestock can take feed from these types themselves. A temporary plastic silo can be made by tightly packing silage into a large, round bag. A machine fills the bag, using a spinning ram to force out air.
