Silage pits are structures used on farms, their primary role is for storage and crop preservation. This can include crops such as plants, grass, corn, animal feed, and more. Due to the manner of storing (compacted and without air) a process known as fermentation can occur. 

Here is a more in-depth look at the functions of the silage pit. 

1. Creates an anaerobic environment 

As mentioned previously, silage pits allow for the fermentation process to occur, this is by creating an anaerobic environment. This enabled by creating an oxygen free environment, which is done by:

• Compaction: Forage is chopped and then driven over repeatedly by tractors or heavy machinery to press it tightly and remove as much trapped air as possible.
• Sealing: Once filled, the pit is covered with an airtight plastic sheet, often weighted down with tires or gravel bags to maintain the seal and keep oxygen out.

2. Enables the fermentation process

The anaerobic conditions allow beneficial microorganisms, mainly lactic acid bacteria, to take over. Here is what these bacteria do:

• Lactic acid production: These bacteria consume the plant’s natural sugars (carbohydrates) and convert them into lactic acid.
• Pickling effect: The buildup of lactic acid rapidly lowers the pH. This low pH is what preserves the forage, essentially “pickling” it. The acidity stops the activity of spoilage microorganisms like moulds and yeasts and plant enzymes.

3. Preserves nutritional value

As a result of the fermentation process being successful, the following results are achieved:

• Retain nutrients: It locks in the nutritional value of the crop, including proteins and sugars, minimising the loss that would occur if the crop were left to dry as hay. This preserved, high-quality feed (silage) ensures livestock have a consistent and nutritious food source during times when fresh pasture is scarce, such as in winter or during a drought.

4. Manages silage effluent

During the fermentation process, a byproduct is created. This highly polluting liquid, called silage effluent, is released, especially from high-moisture crops. As a result, this liquid must be collected and disposed of correctly.

A well-designed silage pit has an impermeable floor and drainage channels that collect this effluent. The pit’s design prevents this corrosive liquid from leaching into the ground, which would contaminate water sources like rivers, streams, and wells. The collected effluent is then stored in a tank and must be managed responsibly, often by being diluted and spread onto land as a fertiliser.

Which livestock eat silage (and might use a pit)?

Silage is a primary feed source, especially in winter or dry seasons, for ruminants (Cattle, goats sheep). This is because their digestive system is well-suited to handle large amounts of high-fiber fermented forage.

Silage can also be used as a feed for pigs, although in smaller amounts and sometimes after processing, but it is not a primary or necessary component of their diet.

Are there alternatives that don’t require a silage pit?

Yes. Livestock, even ruminants, can be successfully fed and managed using several alternatives to silage, which means a silage pit is not a universal necessity:

• Hay and haylage: These are very common alternatives. Hay is dried forage, while haylage is partially dried forage with higher moisture content than hay but lower than silage, often stored in wrapped bales (eliminating the need for a pit).
• Pasture/fresh forage: During the growing season, grazing is the most common and often the cheapest feed source.
• Grains and Concentrates: Feeds like barley, maize, and commercial pellets are used to supplement the diet, especially for high-producing animals.
• Root Crops: Fodder beet, turnips, and swedes can be fed to cattle, sheep, and goats.
• Straw: Used as a roughage source, especially for maintaining mature animals, but must be supplemented with higher-quality feed.

Can livestock be harmed by a silage pit?

Yes, livestock face harm from silage pits through two primary dangers:

1. Ingestion & inhalation hazards:
   • Contaminated feed: Moulds and bacteria in spoiled silage can cause illness, abortion, and reduced performance due to mycotoxins and pathogens like Listeria.
   • Toxic gasses: Pits release deadly gases like NO2​ and CO2​ which can escape and cause severe respiratory harm or asphyxiation in nearby animals.
2. Physical & environmental hazards:
   • Accidents: Animals can be injured or killed by the collapse of the silage face or by falling into the pit.
   • Effluent: Highly polluting and corrosive silage liquid can contaminate water sources used by livestock.

How deep should a silage pit be ideally?

The ideal depth of a silage pit (or the height of a bunker silo) is a balance between achieving good feed quality and maintaining safe, efficient management. Instead of thinking of a single magic number for depth, focus on the range dictated by construction and management. For example:

• Bunker wall height: Most commercially manufactured bunker walls range from 8 to 16 feet (2.4 to 4.9 meters) tall. The final height of the silage will be near or slightly above the walls.
• Settled silage height: A common and safe target for the height of settled silage is up to 12 feet (about 3.6 meters). The silage will be packed higher than this during the filling process, then settle down.

What to remember when it comes to silage depth

Your decision on how deep to build should be driven by three core priorities:

1. Feed-out rate (preventing spoilage): This is the most critical management factor. You must remove enough silage from the exposed face every day to prevent aerobic spoilage (heating and moulding).
   • You should aim to remove at least 6 to 12 inches (15 to 30 cm) per day across the entire face.
   • If your pit is very deep, you have to ensure it’s also wide enough to feed enough animals daily to meet that removal rate. A pit that is too deep for a small herd is inefficient because the face will be exposed too long, causing massive waste.
2. Compaction quality: Deeper silage means more weight on the lower layers, which improves density and pushes oxygen out. Better density equals better preservation and lower losses. However, the height must not exceed what your packing machinery can safely and effectively compact in thin layers. 
3. Safety and equipment: The depth/height is ultimately capped by the maximum safe reach of your front-end loader or telehandler. Stacking silage too high creates a significant risk of the silage face collapsing and burying the operator, or the machinery overturning.

Creating a silage pit with interlocking concrete blocks