You should expand a silage pit when your current capacity is consistently and noticeably insufficient to meet your livestock’s annual feed requirements, especially if you are having to compromise safety, silage quality, or compliance to fit your crop.

Why you should expand a silage pit

• The most critical reason is a projected or actual annual deficit in your winter feed supply. You should be performing a regular fodder budget (calculating the total silage required for your stock for the housing period and comparing it to what your pit can safely hold).
• A suckling cow might require around 35 kg/head/day of fresh silage, and a milking cow requires more (upwards of 1.75 tonnes of dry matter for a 180-day winter). If your current pit volume cannot store enough for the necessary housing period, you need more capacity.
• If you are constantly tempted to pile the silage too high above the walls, you risk structural failure (collapse of walls), poor consolidation at the shoulders, and significant safety hazards for machinery operators (risk of slipping or overturning).
• The finished silage should generally slope back at no more than 45 degrees from the top of the retaining walls. If you exceed this, the pit is too small for the volume of grass being ensiled.
• Overfilled clamps can lead to poor consolidation, resulting in greater aerobic spoilage and wastage at the top and shoulders. Expanding allows for safe filling heights and better consolidation.
• If you find yourself making an excessive amount of round bales as a temporary overflow solution, and your feeding system is better suited to pit silage (like a complete diet mix), a permanent expansion is likely needed.
• If the area around the pit is too congested, making it difficult for machinery to operate quickly and safely, especially during the rolling and compacting process, more space is needed.

When is the best time to expand a silage pit?

The ideal time to plan and execute a silage pit expansion or new build is when the pit is empty, well in advance of the next silage season. Here is why:

• Inspection time: When the slab is empty, you can thoroughly inspect and repair the existing base, channels, and walls, which is also the perfect time to assess how a new extension would integrate.
• Planning for future growth: The advice is often to “build it twice as big as you want,” as farms tend to outgrow their storage. If you project a need for more stock or higher crop yields in the next 5-10 years, it’s cost-effective to build the extra capacity now.
• Regulatory compliance: Be aware that substantially enlarging or modifying a pit (often defined as a 25% or more increase) may cause it to lose exemption from current regulations, requiring you to notify the relevant environmental agency and bring the entire structure up to modern standards (e.g., impermeable floor, perimeter effluent channels, and sufficient effluent tank capacity).

Can you expand an existing silage pit without rebuilding?

In most cases, yes. It depends upon the silage pit being made from a flexible wall system or a fixed one (as well as other factors). Here are the differences:

• Fixed systems (Cast-in-situ / Poured walls): These are built to a specific size and height. They are the strongest and most durable, but they are the hardest and most costly to expand once complete.
• Modular systems (Interlocking blocks, L-walls): These are built from individual, repeatable units. They offer the best flexibility and ease of expansion (you simply add more units in length) or even moving the entire pit location, provided you extend the foundation first.

Essentially, a silage pit can be extended without rebuilding if:

• You have the budget
• There is ample space
• You are using a modular system for walls. (Fixed systems are possible, just more complicated).
• You are also able to extend the foundations.

Can you use interlocking concrete blocks for a silage pit?