Farm Horizons, November 2007
The rise and fall of silos
By Jennifer Gallus
Minnesota’s agricultural landscape wouldn’t be the same without towering silos old and new. Many of the oldest silos in our area often stand alone, outlasting the barn that once accompanied the round structure.
There were only 91 silos in the US in 1882, according to the US Department of Agriculture. By 1895, there were more than 50,000 silos across the country, and by 1903, there were an estimated 300,000 to 500,000 silos dotting the landscape.
Silos first appeared in the state in the late 1880s, with a construction boom from 1910 to 1925, according to the Minnesota Historic Farms Study.
In 1927, that state had roughly 36,000 silos, which translates into one silo for every five farms.
Silos in Minnesota were extremely important in the storage and preservation of green feeds throughout the winter months. Without the availability of year-round, high-quality green feeds, the state’s dairy industry wouldn’t have successfully evolved the way it did.
The rise in Minnesota’s dairy industry and the rise in the number of dairy farms with silos went hand-in-hand. “Dairy cattle only gave milk from spring to fall when they were fed on green pastures. Limited to this schedule, farmers (in the northern climates) were unable to participate in higher-priced markets for milk. The silo transformed dairy farming by allowing animals to be fed green fodder year-round, which encouraged cows to give milk through the winter,” according to the Minnesota Historic Farms Study.
In 1911, CR Barnes, of the University of Minnesota, wrote, “The owner of a dairy herd of more than 10 or a dozen cows, who has failed to erect a silo, is now to be regarded as ‘behind the age.’” In 1931, RM Washburn, of the University of Minnesota, wrote, “No dairy or general livestock farm is properly equipped for economical production until a silo of some sort is provided,” according to the study.
A high nutritional value of feeds such as chopped corn stalks, grasses, legumes, sorghum, and field corn can be maintained while ensiled. Silage not exposed to air, approximately six inches or deeper within the silo, ferments until all the air in the silage is used up. The silage then stabilizes and the nutritional value is preserved. Silage in the top four inches, exposed to air, will spoil so it was common practice to remove two to four inches of silage per day to keep ahead of spoilage.
Before automatic silage unloaders were invented, silage was unloaded from the top surface layer down. The farmer would climb up the side of the silo, step onto the top layer of silage, and pitch the surface two to four inches down the chute. This labor-intensive practice was alleviated by the invention of automatic unloaders in the late 1940s. However, the unloaders weren’t widely used until the 1950s and 1960s.
In the 1870s, silos were horizontal, and called pit silos. They were built of wood or stone, were dug fully or partially into the ground, and lined with materials such as straw or stones. The first vertical silos, built in the 1880s, were square and were made of wood or stone. However, the square shape created problems with the structure bowing outwards, and allowed air pockets in the corners.
“This caused silage to rot despite attempts to make the silos taller so the heavy silage would settle into the pockets. Subsequent octagonal and round forms worked better, and square silos were rarely built after 1900,” according to the Minnesota Historic Farms Study.
In the 1890s, FH King of Wisconsin’s state agricultural experiment station developed the first successful round vertical silo. It was made of two layers of horizontally placed wood boards. Wooden silos were prone to deterioration, so silos began to be constructed from brick and concrete. By the early 1900s, silos were constructed of reinforced concrete, structural clay tile, cement staves, and galvanized metal.
The cement stave silo was introduced to the state in 1905 and was the most common silo type built in Minnesota. Cement staves are masonry units that hook together with interlocking edges, with mortar applied between the joints. The staves are reinforced by either flat or round metal bands or rods, and reinforce the silo against outward pressure. The inside of the silo was sealed by a thin layer of concrete.
“Cement stave silos were promoted as being permanent, durable, and resistant to fire. They were cheaper than silos of brick and clay tile, and no special masonry skills were needed. They were more durable than concrete block silos and did not need forms used in monolithic concrete,” according to the Minnesota Historic Farms Study.
Patterns located at the tops of silos were unique to the company that built the structure.
Today, cement stave silos are rarely erected, although the cement staves are still being manufactured, according to Bob Schueler of Hanson Silo Company, based in Lake Lillian.
“People are looking for faster feeding. They’re moving towards bunker or flat storage rather than tower,” Schueler said.
Plastic bales of silage are easier to work with, and faster to access. The trend towards flat storage began about 20 years ago, but has picked up momentum in the last decade.
What will happen when silos are no longer built, and the remaining silos decay? Will we someday have a farm landscape void of these traditional farm icons?