Nitrate Testing of Corn for Green Chop or Silage

Denise L. Schwab, Extension Beef Field Specialist, Southeast Iowa

Problem Statement

Due to the drought conditions in extreme eastern Iowa, there was a lot of concern about the nitrate level in corn for green chop feed or silage.  Horror stories of producers in the area losing cattle due to nitrate poisoning further increased the level of concern.  The drought conditions have forced cattlemen to feed hay for a majority of the summer, which means they are looking for additional feeds for the fall and winter.  Since corn yields are extremely low, green chopping corn or ensiling corn are the first feed to consider.

Programmatic Response

A quick-test for the presence of nitrates in corn stalks has been done in Illinois in the past, and was currently being conducted in their drought areas.  For one day we set up to check corn stalks for nitrates.  Producers were invited to bring five average corn stalks from a field that was intended to be green chopped or chopped for silage.  They were informed that this was simply a quick test to determine the presence or absence of nitrates on that day.

Twenty-seven producers from six counties brought in 169 corn stalk samples to test.  Stalks were cut in half below the ear and recorded if an ear was present or not.  Sixty-seven percent of the samples were positive for nitrates at the 6‰ mark, 64% at the 12‰ mark, 53% at the 18‰ mark, 33% at the 24‰ mark, and 21% at the 36‰ mark.  The decrease in nitrates as you move up the stalks was consistent with research data.  Ninety-five percent of the stalks bore some type of an ear, although some were small and had few kernels.  Seventy percent of the plants with ears tested positive for nitrates.  This was inconsistent with research data that showed that stalks with ears are less likely to have nitrate concentration problems.

Producers then discussed options for feeding the forage as green chopped forage or ensiled silage.  Producers with positive samples below the 12‰ mark were encouraged to set their chopper head high.  Those with nitrates throughout the plan were encouraged to test the silage after a 3-5 week ensiling process before feeding to cattle.  Sixteen of the 27 producers were strongly encouraged to test their silage after the fermentation process and prior to feeding.


Producers were extremely appreciative of the effort to test their corn for nitrates.  Several indicated they were planning to test the silage before feeding it to cattle.  One producer was put at ease that it was safe to harvest his corn as green chop feed for cattle.

One dairy producer indicated that they were currently feeding green chop from the same field that tested positive for nitrates.  She also indicated that the blood urea nitrogen level in their milk tank had increased significantly shortly after they started green chopping, and we could clearly show that it was due to the nitrate levels in the corn they were chopping.

Several were planning to chop their corn for silage and start feeding it immediately to cows.  They were convinced to wait until the silage went through the fermentation process and to get an accurate test for analysis before feeding.

Several producers have called since the testing day asking for additional quick tests.

September 13, 2005   
107 - Iowa Beef Center

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