Covering maize silage: how to ensile and cover maize properly

Maize silage that heats up at the face costs you feed and milk. Maize ferments easily, but maize silage is sensitive to heating. Every mistake at harvest, rolling and covering shows up later at the silage face.

When do you harvest maize for silage?

First choose a maize variety that suits your soil and your region. Some varieties do better on sandy soils, others on clay, and not every variety ripens equally early. Talk to your seed supplier or crop adviser.

Harvest the maize when it has 32-36% dry matter. That is the advice in the maize handbook of Wageningen University & Research (WUR). Above 32% there are no more effluent losses, and above 36% the risk of heating and mould during feeding increases. Maize that is too wet ferments more slowly. Maize that is too dry is hard to compact, holds more air and heats up faster. There is also a lot you can do before harvest: see improving maize silage quality.

How do you ensile maize?

1. Work cleanly. Make sure the apron and the access route are clean, so no sand gets into the silage.
2. Chop at 6-8 mm (WUR maize handbook). Short-chopped maize compacts better and faster than long-chopped crop. The drier the maize, the shorter you chop.
3. Take your time rolling. Use enough weight and capacity, so little oxygen stays in the silage. Roll layers of 30 to 40 cm at 3 to 4 km/h. More tips are in silage compaction tips.
4. Filling over two days? On the second day, only start rolling once there is a new layer of maize on top. If you drive straight over the old layer, you squeeze out the CO2 that has built up and bring fresh air into the silage.
5. Roll the silage evenly and finish the top smooth and slightly rounded, so no water stays on it (WUR). With Silage Safe you give the silage a rounded profile, so the water runs off through the drainage.

How do you cover maize silage?

1. Cover straight after rolling. The sooner the pit is sealed, the sooner fermentation gets going and the less chance heating has.
2. Use side-wall plastic if the walls of your pit aren't watertight, so no water runs into the maize along the wall. With Silage Safe you leave at least 20 cm of plastic on the floor.
3. Lay underlay film over the full width. It clings tightly to the maize and makes the pit more airtight.
4. Use a new top sheet. Old plastic may have holes.
5. Secure the cover tightly, especially on the edges. That is where the maize is least well compacted and most air gets in.
6. Check after a few weeks. The silage settles a little more. Pull the plastic and the cover tight again, so no air pockets form.

The full step-by-step plan for covering is in the guide covering a silage pit.

A large maize silage pit can also be covered without heavy lifting. At Jennissen in Den Dungen (NL), a 90 x 14 x 4 metre maize silage pit is covered with Silage Safe. They used to spend an hour every week shovelling soil off the pit. Now they open it in five minutes. "We're saving a lot of time and no longer have problems with heating."

Why must rainwater stay out of maize silage?

Good maize silage usually has a pH of 4.0 to 4.2 (WUR maize handbook). Rainwater is much less acidic than good silage. If it runs into the silage, the pH rises in that spot and moulds and bacteria get a chance. You often see this at the bottom and along the walls. Make sure there is good drainage in and around the pit and let the water run out along the wall.

See how the drainage in the bottom hem of the covers works on our product information page. What else you can do about rainwater in silage is in a separate article.

Why does maize silage heat up faster?

Maize contains a lot of sugar and starch. Yeasts live on them as soon as oxygen gets in after opening. The drier the maize, the greater the risk: according to the WUR maize handbook, above 36% dry matter the risk of heating and mould during feeding increases. Good rolling, covering straight away and a high enough feed-out rate help. All tips are in preventing silage heating.

What should you watch out for after covering and when opening?

• Keep the pit closed for at least 4 weeks (WUR), preferably 6. By then the maize has fermented enough and is stable.
• Keep the feed-out rate high enough: at least 2 metres per week in summer and at least 1.5 metres per week in winter. So when you fill the pit, work out how high the silage can be for that feed-out rate.
• Keep the silage face tight and smooth, and don't leave loose maize lying in front of the face.
• Check the cover for holes, for example from birds or rats.