Beware of Nitrates in Corn Silage

Dry conditions may cause high nitrate levels in corn silage. High nitrate levels can lead to nitrate poisoning and the formation of toxic silo gas.

• Any condition which kills the leaves while the roots and stems remain active (drought, overcast, weather, hail, grazing or trampling, frost)
• Prolonged drought followed by rain
• High nitrogen fertilization caused by heavy fertilizer or manure applications or following legume plow down

Under these conditions, plants accumulate high levels of nitrates. When eaten by animals, the nitrates are converted rapidly to nitrites which are absorbed into the blood stream. Nitrite in the blood alters the way the blood carries oxygen. This causes rapid breathing, fast and weak heartbeat, muscle tremors, staggering and death if corrective steps are not taken quickly.

In normal growing conditions, much of the nitrate is taken up by the cobs and converted to protein. When there are few (or no) cobs, nitrate content of the stalks will be higher. Use caution when green chopping corn this year as nitrates may be considerably higher than normal. Higher cutting height will help, as nitrates are more concentrated in the bottom 4 to 6 inches of the stalk. Ensiled corn has 25% to 65% lower nitrate levels than fresh cut material.

When high nitrate forage is ensiled, deadly nitrogen dioxide gas (silo gas) can be produced within hours! Silo gas is heavier than air, so it settles in low points in the silage pack and in feed rooms at the base of the silo. The gas may be visible as a reddish to yellowish-brown haze around the silo base, and has a bleach-like odour.

Protect yourself, your staff and your family from this dangerous poison. If someone must enter the silo to level or cover the silage, do it immediately after filling and leave the blower running while anyone is in the silo. Do not enter the silo for at least three weeks after ensiling. Post a sign at the silo chute as a reminder of the danger. Silo gases can be deadly!

If you suspect high nitrates in the corn, have it tested by a forage-testing laboratory. Sample after ensiling and when fermentation is completed (at least 3 weeks).

For information about safely entering a silo, refer to the Ontario Farm Safety Association factsheet called "Silo Gas Dangers".

Related Links

• Silo Gas Dangers (pdf)