A silage bunker can be filled on schedule and still contain loosely packed forage along the walls, under deep piles of freshly delivered crop, or in sections that received too few tractor passes. Those areas hold more air and are more likely to deteriorate during storage and feedout.
Good silage packing comes from matching the delivery rate to the available packing weight, spreading forage in thin layers, covering the working surface with repeated passes, and keeping machinery on a safe, stable route. A practical packing plan starts before the first trailer arrives and continues through density checks and final covering.
This guide follows the filling crew from the first forage delivery through final covering, with practical checks for tractor weight, working routes and packing density. For problems that develop during storage and feedout, see How to Prevent Silage Heating and Dry Matter Loss.
1. What Does Good Silage Compaction Look Like?
Packing squeezes forage particles closer together, reduces the volume of air-filled spaces and helps fermentation move toward low-oxygen conditions. It also makes the stored material less permeable to air when the bunker is opened later.
Three factors have a particularly strong influence on the result:
- Forage condition. Crop type, dry matter content, particle length and kernel processing affect how readily material can be compacted.
- Packing work. Tractor weight, time spent packing, layer thickness and the number and distribution of passes determine how much pressure reaches the forage.
- Bunker geometry. Wall height, available width, ramp slope and the space allocated to delivery vehicles determine how safely and consistently packing can be performed.
A useful benchmark for bunker and pile silage is at least 15 lb of dry matter per cubic foot (approximately 240 kg DM/m³). University of Vermont Extension identifies 18 lb DM/ft³ (about 288 kg DM/m³) or higher as a stronger density goal in Steps for Silage Storage Success. These figures provide reference points for density sampling and reviewing the finished bunker.
2. Check the Bunker and Harvest Plan Before Filling
Before assigning machinery, establish the usable bunker dimensions and the peak hourly delivery rate. The crew needs enough space and packing time to handle forage arriving during the busiest part of the harvest.
Record the following before harvest starts:
| Planning input | Why the crew needs it |
|---|---|
| Usable bunker width, length and wall height | Determines the available working surface, vehicle clearance and turning space |
| Expected tonnes of fresh forage per hour, including the peak | Determines how much spreading and compaction must be completed while trailers keep arriving |
| Crop type, dry matter and chop characteristics | Helps anticipate material that is unusually dry, springy, wet or difficult to spread |
| Packing tractor or loader operating weight | Establishes the available compaction weight, separate from the machine's lifting capacity |
| Number of vehicles and the work each performs | Shows how much time the machines will actually spend packing rather than pushing or waiting |
| Delivery and exit arrangements | Helps keep reversing trucks and packing machinery on coordinated routes |
| Wall condition, drainage, lighting and access | Identifies hazards before machinery begins climbing the forage surface |
Inspect concrete walls for movement or cracks and confirm that the floor, approach and drainage are sound. Agree on traffic directions, unloading locations and a clear communication method between truck drivers and packing operators. A designated supervisor should be able to reduce the incoming delivery rate when the surface begins to accumulate thick piles.
3. Spread Forage in Thin Layers and Maintain a Progressive Wedge
The packing process works best when each load can be distributed before the next load buries it. Instead of building a deep heap and flattening it later, move the fresh crop into a shallow layer over a gradually advancing wedge.
Aim for loose, freshly spread layers no deeper than about 15 cm (6 inches) before the first packing passes. The South Dakota State University corn silage harvesting guidance uses this limit as a practical packing recommendation. Crop condition and the working area may call for thinner layers.
A workable filling sequence is:
- Direct the arriving trailer to the designated unloading area and keep the truck separate from active tractor paths.
- Spread the load across the planned working width, preventing thick ridges at the walls or discharge points.
- Run the packing machine over the new layer in an organized pattern, with adjacent wheel paths covering the surface.
- Repeat passes while maintaining a stable ramp, then introduce the next thin layer.
- Adjust unloading or harvesting when the incoming crop starts accumulating faster than the team can spread and pack it.
The progressive wedge should provide a safe route for the machinery. A commonly cited maximum ramp steepness is one unit of rise over three units of horizontal run (1:3, or 3:1 run-to-rise), equivalent to roughly 18°. Gentler slopes may be necessary for the equipment, surface conditions and site. Penn State's horizontal silo safety guidance and the University of Wisconsin's drive-over pile guidance describe this approach.
4. How Much Packing Tractor Weight Do You Need?
Select packing machinery around the peak delivery rate and the hours available for compacting each load. During high-volume harvest periods, several tractors or loaders may be needed to maintain thin-layer packing.
Calculate a starting weight requirement
A widely used planning guideline is approximately 800 lb of packing tractor weight for each US short ton of fresh forage delivered per hour. In metric units, this is approximately 0.4 metric tonne of packing machinery for every metric tonne per hour of incoming crop.
Estimated total packing weight (metric tonnes) ≈ peak fresh-forage delivery (tonnes/hour) × 0.4
| Peak fresh forage delivery | Initial packing weight estimate |
|---|---|
| 50 tonnes/hour | About 20 tonnes |
| 75 tonnes/hour | About 30 tonnes |
| 100 tonnes/hour | About 40 tonnes |
| 150 tonnes/hour | About 60 tonnes |
For example, with 100 tonnes of fresh forage arriving each hour, the guideline points to approximately 40 tonnes of total packing machinery weight. This might involve more than one suitable machine. Equipment needed for spreading, reversing and traffic management must also be considered: a loader that spends much of its shift pushing material may contribute less effective packing time than a dedicated packing tractor.
The estimate is a starting point for planning, based on University of Vermont Extension's packing-weight guidance and Utah State University's silage storage recommendations. Final arrangements depend on forage dry matter, layer depth, compaction time, available working width and measured density.
Evaluate the machines already on the farm
Assess the actual operating weight, including any manufacturer-approved ballast or counterweights, together with tire configuration, traction, stability, rollover protection and time available for packing. Follow the machine and tire manufacturers' limits for inflation pressure and added ballast.
Wheel tractors and suitable wheel loaders are common packing machines. Tracked equipment may be useful for handling or spreading material under certain conditions, but its ground-contact characteristics differ from those of wheeled machines. Where existing equipment is insufficient, the practical options are to add suitable packing capacity, improve the division of work or reduce the delivery rate.
5. Plan Packing Passes Without Creating Unsafe Traffic
Each thin layer needs repeated wheel coverage across the usable surface. An operator who repeatedly drives down the center can leave lower-density strips at the sides, while tight turns and wheel spin may disturb material that has already been packed.
Organize the work so that successive tire tracks cover adjacent strips, with suitable overlap and repeat passes according to the packing plan. Use gradual direction changes on firm material, keep loader buckets low during movement and avoid crossing the route of a reversing delivery vehicle.
When multiple tractors are used, allocate working zones and establish right-of-way and radio or visual signals. Experienced operators should work with rollover protective structures and seat belts as appropriate to the machinery. The Journal of Dairy Science review of silage safety discusses rollover hazards, coordinated machinery movement and the importance of keeping the loader bucket low.
What about the bunker walls and corners?
Edges and wall junctions commonly receive fewer effective passes and can have lower density. They deserve deliberate attention during each layer, rather than a rush to correct the edges after the bunker is full.
Inspect wall stability and clearly identify the safe working boundary before filling. Keep the forage surface below the top of retaining walls, provide visible wall markers where suitable and plan routes that allow the operator to cover the accessible edge without placing wheels above an unsupported drop or loading an unsafe wall. The required stand-off distance and turning method depend on the machine, structural conditions and actual layout.
Keep all ground personnel outside the active packing area and away from retaining-wall edges while heavy machinery is moving. Establish clear communication between drivers and the site supervisor. If the available equipment cannot reach an edge safely, have an experienced silo contractor review the filling geometry and traffic plan.
6. How Do You Check Whether the Silage Is Dense Enough?
A daily packing log tells the manager whether the process was followed. Density testing tells the manager what was achieved at the sampled location. Using both makes it easier to improve the next filling operation.
Record the process while filling
A simple shift sheet should include:
- Date, shift, crop and representative dry matter measurement.
- Tonnes delivered and the hours over which they arrived, including peak periods.
- Packing machine IDs, actual working weights and time spent packing.
- Approximate loose layer depth and whether wheel coverage reached all safe operating zones.
- Weather, equipment interruptions, changes to the traffic plan and temporary covering.
- Sections completed, final packing and cover installation time.
The key comparison is whether the incoming delivery rate stayed within the packing plan. An unusually high arrival rate combined with thick layers is an early warning that compaction may be uneven.
Measure and interpret dry matter density
For a sample with known mass and volume:
As-fed density (kg/m³) = sample fresh mass (kg) ÷ sample volume (m³)
Dry matter density (kg DM/m³) = as-fed density × dry matter fraction
For example, a sample with an as-fed density of 800 kg/m³ and 30% dry matter has a dry matter density of:
800 × 0.30 = 240 kg DM/m³
This corresponds to approximately 15 lb DM/ft³. A 35% DM sample would need approximately 686 kg/m³ as-fed density to reach the same dry matter density.
Density varies across a bunker. A representative assessment should consider more than one location, including safe access to areas near the sides and center. For meaningful sample-volume measurements, use a trained forage-testing service with suitable coring equipment and dry matter analysis. Open silage faces can collapse without warning; operators should not climb or stand beneath them to collect samples. University of Kentucky's bunker silo management guidance covers safe sampling and feedout-face precautions.
After the bunker is opened, note recurring hot spots, loose areas, mold, unusual odors and the condition of the cut face. These observations help interpret the packing and storage history, although fermentation, sealing and feedout practices also affect the final result.
7. What If Harvest Deliveries Are Faster Than the Packing Crew?
The clearest sign is a growing backlog of forage that can no longer be spread into shallow layers before the next trailer arrives. At that point, the shift supervisor needs to restore an achievable working rate.
First, control the incoming flow. Let the crew spread and compact the accumulated material, and change the unloading schedule or harvester pace. If the same bottleneck repeats, add an appropriate packing machine or allocate a separate machine to moving forage so the primary tractor can spend more time packing.
Watch for four situations:
| Situation | Immediate priority | Planning response |
|---|---|---|
| Trucks arrive faster than the forage can be spread | Avoid large heaps and restore thin-layer work | Reduce deliveries or add effective spreading/packing capacity |
| One tractor is continually pushing and rarely packing | Reassign tasks so packing receives enough time | Add a suitable machine or redesign unloading flow |
| Rain makes the ramp slippery or creates standing water | Stop unsafe vehicle movements and protect the exposed forage | Address site drainage and cover suitable completed areas |
| Equipment breaks down during filling | Move people and vehicles to safe positions; protect completed packed material | Arrange repairs or replacement before restarting the normal intake rate |
For a prolonged interruption, finish and cover a safely accessible completed section as soon as practicable. Temporary plastic cover can protect the surface from rain and oxygen while filling is paused; seal and weight it appropriately without exposing staff to falls or moving machinery. University of Wisconsin Extension's pile-construction guidance discusses temporary covering during rainfall delays.
When operations resume, inspect the exposed or previously covered material and follow a site-specific plan for handling any heated, visibly spoiled or contaminated layer. The next loads should return to thin-layer spreading and a stable traffic pattern. Long shutdowns may justify completing and sealing the current section rather than repeatedly opening it.
8. Finish Packing and Protect the Completed Bunker
After the final load, allow the planned finishing passes over all safe working areas, shape the surface for drainage and cover the completed forage promptly. Check that the covering lies close to the forage and is secured at seams, walls and edges. Water runoff should be directed away from the stored crop and bunker wall junctions.
The packing crew should complete the agreed sealing arrangement and confirm the following before handing over the bunker:
- All planned loads have been spread and packed.
- No unsafe high pile or unsupported machine route remains.
- Wall junctions, drainage routes and the working surface have been inspected.
- Cover installation has been completed and recorded.
- Any areas needing later monitoring have been marked on the bunker plan.
Document the final passes and cover installation in the shift record. Review density samples and feedout observations later to improve the packing plan for the next harvest.
9. Silage Pit Packing Checklist
| Stage | What to confirm | Person responsible |
|---|---|---|
| Before harvest | Bunker condition, routes, drainage, machinery weights and peak delivery estimate | Farm or harvest supervisor |
| First deliveries | Safe progressive wedge and loose layers around 15 cm or less | Filling operator |
| Every load | Material spread promptly and the surface covered by repeat packing passes | Packing operator |
| Each shift | Tonnes per hour, actual packing time, crop dry matter and equipment faults | Shift supervisor |
| Wall and edge work | Safe working boundary, stable walls and no exposed drop-off under wheels | Site safety lead |
| Rain or breakdown | Traffic stopped where unsafe; completed forage protected | Shift supervisor |
| End of filling | Final packing passes, surface drainage and cover installation | Storage crew |
| Later review | Representative density and documented feedout observations | Farm manager / qualified testing service |
Frequently Asked Questions
How thick should each layer be when packing silage?
A useful target is about 15 cm (6 inches) or less before packing. Spread the forage uniformly and complete repeated passes before adding the next layer. Very dry or difficult-to-pack material may require extra attention to layer depth and compaction time.
Is a 15–18 tonne loader enough for a bunker silo?
That depends mainly on the peak hourly delivery rate and how much time the machine actually spends packing. Using the 800 lb per US ton/hour planning guideline, 100 metric tonnes of forage per hour calls for approximately 40 metric tonnes of total packing weight. A smaller harvest may be workable with less equipment.
What density should corn silage reach in a bunker?
A widely used benchmark is at least 240 kg dry matter/m³ (15 lb DM/ft³), with approximately 288 kg DM/m³ (18 lb DM/ft³) as a stronger target. Evaluate multiple locations and interpret results alongside forage properties, sealing and storage performance.
Can a packing tractor drive directly along the bunker wall?
The safe driving route depends on wall stability, forage height, equipment dimensions and the available working width. Plan wheel coverage of accessible areas while keeping machinery away from unsupported edges and hazardous wall loading. Experienced operators and a site-specific traffic plan are essential.
What should a farm do if filling is interrupted by rain?
Stop work if traction or visibility makes machinery movement unsafe. Protect completed packed forage with a suitable temporary cover if filling is paused, keep water out of the bunker and inspect conditions before restarting. Restore thin-layer packing when deliveries resume.
Conclusion
Successful silage packing depends on the flow of chopped forage, thin and consistent layers, enough time under the packing equipment, and safe traffic throughout the bunker. Record the harvest conditions and packing work, then use density and feedout observations to refine the process for the next season.
Once the bunker is opened, the stored forage becomes part of the daily feeding program. NexAgri offers TMR mixers for dairy feeding to combine silage with other ration ingredients according to herd size, batch volume and feeding schedule. For a dairy feeding equipment enquiry, share your herd numbers, main forage ingredients and feeding layout through NexAgri Solutions.
