Maize for Silage
Insight 303


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Once maize silage harvest commences it is important that the chopped material is compacted into a stack or bunker, and covered and sealed as rapidly as possible. This bulletin gives details on all aspects of maize silage storage.


Maize silage can be stored in a bunker or an above ground silage stack. Field measurements have shown that the average density of a New Zealand maize silage stack (no walls) is approximately 200 kgDM per cubic metre with a range of 150 - 275 kgDM per cubic metre. The average density of a New Zealand maize silage bunker is approximately 225 kgDM per cubic metre with a range of 175 - 300 kgDM per cubic metre. Overseas research has shown that the target drymatter density for both stacks and bunkers is 250 kgDM per cubic metre.

Storage space

The approximate amount of storage for different amounts of maize silage is given in Table 1 below:

Table 1: Storage space required for maize silage

Amount of maize silage
(tonnes of DM)
Approximate storage space required (cubic metres)
  Stack Bunker
25 125 111
50 250 222
75 375 333
100 500 444
125 625 556
150 750 667

Figure 1 (below) shows a good bunker or stack management technique. The first step is to work out how far into the face you need to feed. Next scoop out the lowest section of the silage. Then using the bucket blade, chip down the silage one section at a time starting at the bottom.

Building new bunkers and stacks

Build your bunker or stack on a firm base away from hedges, trees and major drains. Choose a site that you will have access to all year round.. Feed-out costs will be reduced if the bunker or stack is built close to where the maize silage will be fed. The size of the face of the stack or bunker should match the rate of feed-out. Ensure the stack is built so that you can feed across the face of the stack every two to three days taking at least half metre each time from the face.

New bunkers (in-ground)

Ensure that there is a drain around any high ground above the bunker intercepting any surface water entering the stack site. Slope the walls outward by making the top slightly wider than the base. This allows easier compaction right up to the walls. Maize silage can be stored in bunkers that have dirt walls. However, in some soil types when the water table rises, a large amount of water can enter the bunker through the walls. Water then accumulates at the bottom of the bunker wetting the silage and destroying its quality. To avoid this happening, it is a good idea to dig a ditch around the base of the wall and put in some form of drainage (clay tiles or plastic pipe). Backfill the ditch with gravel and direct drainage away from the site. For more information on bunkers or stacks refer to Pioneer Technical Insight No. 320: Designing a maize silage bunker or stack.

Permanent bunker or stack sites

Plan to carry out any maintenance of permanent bunker or stack sites well before harvest. Crumbling dirt walls should be re-cut to give a straight, clean edge. If you have a permanent bunker or stack site that you use each year, clean out residues of last year's silage. Repair any damage to the floor of the stack that may have occurred during feeding out the previous season.


Arrange for silage making supplies e.g. cover, tape and Pioneer® brand silage inoculant. Discuss with your contractor where you will build the silage stack and who will do the stack work. Where required, widen gateways, culverts and/or races to allow easy and safe access for the silage harvester and silage transport units. Check overhead electric fence and power wires and tree branches have plenty of clearance for these large machines. Ensure that there are enough tires to completely cover the stack once harvest is finished.

Compaction equipment

Good compaction is the key to making top quality silage. Take into account the rate at which the silage is being harvested when planning machinery requirements for compaction. Compaction is a function of vehicle weight, rolling time, and depth of spread of harvested material. Remember that wheeled vehicles have a higher weight per surface area and achieve better compaction than tracked vehicles of an equal weight. If a small tractor that you plan to use has duals, remove the outside wheels, increase the tyre pressures and attach weights.

Silage covers

Use a new, high-quality plastic cover. Make sure that you have silage tape that is compatible with the cover.

Pioneer® brand silage inoculant

Most contractors can apply Pioneer® brand silage inoculant through the harvester. If your contractor can’t apply inoculant, it can be sprayed over each load as it is dumped at the stack. Use a sprayer that has been washed thoroughly to remove any chemical residues.

Harvest and first load checking of drymatter percentage

Contractors can adjust chop length and kernel processor settings to suit the drymatter of the crop that is being harvested. Use the following “squeeze test” method to check if the above settings are correct for the moisture level of the maize silage being harvested.  

Thesqueeze test"

A good method of testing whether the chop length that you are using is correct for the moisture level is to take a handful of the maize silage and squeeze it. The palm of your hand should feel moist after applying pressure. If you can squeeze water out of the silage, you are almost certain to have run-off from your stack. Request that the chop length is increased and the processor backed off, then retest. If no improvement is gained when the machine is set to maximum chop length, either cease harvesting and wait for the crop to mature further or contact your local Pioneer representative toll-free on 0800 PIONEER (0800 746 633) for information on ensiling a wet maize silage crop.    

If there is no moisture evident when you squeeze a handful, and when you release the material it does not stay compressed, the maize is too dry and/or the chop length is too long. Request that the chop length is shortened and the processor gap is checked. If the machine has reached its minimum settings and no improvement is gained, special steps must be taken to ensure a good fermentation takes place. Contact your local Pioneer representative toll-free on 0800 PIONEER (0800 746 633) for information on ensiling a dry maize silage crop.

Spreading loads

Fill the bunker or stack as quickly as possible to minimise exposure to the air. Where possible, fill in a wedge shape (Fig 1). This will give good compaction and minimise the amount of time that the maize silage is exposed to the air. Spread each load into a 100 - 150 mm layer so that it can be compacted properly. If large loads are being delivered to a stack site, dump the loads in front of the stack. Build the stack by taking small loads to the stack layering as you go to achieve the desired shaping.

Figure 1: Filling in a wedge shape


After the last load has been delivered continue compacting until the surface of the stack or bunker is firm to the point where the lugs on the tractor wheels sit above the stack surface. The surface shouldn’t have any obvious soft patches

Placing cover

Cover the stack as soon as possible after the stack is compacted. The quicker air is excluded from the stack, the lower the loss in silage feed value. Consider safety aspects (e.g. power lines, buildings etc.) if attempting to place stack cover in windy conditions. Ensure enough staff are on hand to keep control of cover.

Seal around the base of silage stacks by placing a layer of sand, dirt or lime. If the cover must be joined, ensure that joints are sealed well. Where possible, avoid a large overlap as condensation can form between the layers of plastic and drip into the silage causing spoilage. Weigh down your silage cover firmly with tyres that are touching or sand bags placed closely together.

Rat, mice and pukeko control

Rats, mice and pukekos can make holes in the cover exposing the silage to the air and causing spoilage. Keep the area around the stack tidy and free of long grass and weeds where rats and mice can reside. Place rat baits in bait stations on the ground at each side of the stack. If pukekos are a problem, you will need to apply to Fish and Game for a permit to control them if you are outside game bird shooting season.

Holes in the cover

Inspect the stack regularly and mend any holes that develop in the cover with silage tape.

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The information in this publication is general in nature only. Although the information in this publication is believed to be accurate, no liability (whether as a result of negligence or otherwise) is accepted for any loss of any kind that may arise from actions based on the contents of this publication.

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Revised: Jan 2020
Expires: Jan 2022