Tips for Crop Watchers
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Moisture-Stressed Crops and Nitrate Potential - Issue 11, Volume 6—July 29, 2005
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Corn with low grain yield potential or high percentage of barren ears often contains toxic levels of nitrate.
In corn, highest levels of nitrate are found in the stalk (lower 12 to 18 inches of the stalk contain more nitrate) and
lowest levels are in the ear.
Levels are high just before tasseling and then drop after pollination during grain set.
Nitrate levels are higher in the morning. Also, the nitrate level is elevated for a few days right after a rain as it causes the
plant to take up soil nitrates very quickly. Allow about 5 days after a rain for the plant to convert nitrate to plant protein.
A qualitative field test can indicate whether nitrates are present above or below 1000 ppm.
A laboratory analysis can indicate the specific level of nitrate present in a sample.
Ensiling high nitrate forage and allowing the material to complete the normal fermentation process (2 to 3 weeks) will
reduce the nitrate level by one-third to one-half. Testing for nitrates by a lab after fermentation has been completed is
also recommended.
Nitrate-nitrogen level (dry matter basis) of less than 1,000 parts per million is generally considered “safe” for livestock
rations.
Purdue University suggests 1 ton of corn silage (70% moisture) per foot of barren or immature corn plant, excluding the
tassel.
Be sure the silage is at the correct moisture for the storage method you use.
In addition to corn, sudangrass, sorghum-sudangrass, pearl millet and certain weeds (including pigweed, smartweed,
ragweed, lambsquarter, and nightshade) can accumulate toxic levels of nitrate.
Baling does not reduce the nitrate level as compared to ensiling (see comment above regarding fermentation). If drought
damaged crops (especially if nitrogen was applied) are baled or green-chopped, test the forage for nitrate levels.
More on Moisture-Stressed Crops and Nitrate Potential - Issue 12, Volume 6—August 12, 2005
In Issue 11 (July 29), we discussed moisture-stressed crops and nitrate potential. Additional guidelines or management
strategies are provided here:
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Corn plants take up nitrogen with water uptake, therefore with water deficient plants, corn leaves “fire” due to lack of
nitrogen.
Plants accumulate toxic levels of nitrate when soil nitrogen levels are high and available, but the plant is unable to
utilize it (or convert it to plant protein).
Symptoms of nitrate poisoning in livestock (incoordination, difficult breathing, muscular weakness, coma, and death)
are related to the lack of oxygen in tissues.
Nitrate does not accumulate in the grain.
Toxicity of nitrate varies among livestock of various ages, diets, and health status.
Be sure all pesticides applied to the crop are cleared for silage use.
A list of laboratories that test forages for nitrates is available at Extension offices. Try to obtain a representative forage
sample and then send the fresh sample (1 pint-1 quart) in a sealed, airtight plastic bag. Ideally, it is best to take a sample
directly to the laboratory; if this isn’t possible then freeze it and ship it frozen. Once the sample arrives at the laboratory,
analysis should be completed in 2-3 days.
For corn silage, be sure to wait until the corn plant dries to the correct moisture content for the storage method you use:
o Bunker or bags = 30-35 percent dry matter
o Conventional silo = 35-45 percent dry matter
o Oxygen limiting silo = 45-55 percent dry matter
• The fermentation process will reduce the nitrate level. Use the hand-squeeze test to determine if the plant contains too
much moisture. If water drips from the squeezed sample, corn silage is too wet for ideal fermentation.
Tips for Crop Watchers can be found on the web at http://web.extension.uiuc.edu/RockfordCenter/newsletters/morrisonj