Make a plan for drought-stressed corn silage in 2018

Hot, dry weather conditions can damage corn and have the potential for toxic levels of nitrates in corn silage.

Drought-damaged corn
Drought-damaged corn. Photo by Phil Kaatz, MSU Extension.

Corn silage harvest will soon be in full swing and livestock producers should be aware of the potential for excess levels of nitrates due to the prolonged moisture stress, high temperatures and low humidities during this year’s growing season.

Nitrate accumulation is the major concern

Producers making plans to harvest corn silage due to drought damage should be aware of major issues associated with nitrate accumulation in the plants. This increase in nitrates has the most significance following the recent rainfall events over Michigan in the past two weeks. High producing corn hybrids having high amounts of nitrogen fertilizer and manure application prior to drought conditions will be prone to excess nitrate in harvested corn silage.

As the corn plants recover, nitrates are taken up at levels greater than they can assimilate. This causes excess amounts of nitrate in the plant that can be toxic to livestock. This is especially important if farmers are feeding green-chopped corn or corn silage. To minimize risk, generally wait two weeks before harvesting the silage.

Ensiling corn silage will reduce the amount of nitrates in the plant materials by one-third to one-half during the ensiling process. However, even with corn silage stored in bunker silos for several weeks, it is difficult to predict levels of nitrates in drought-stressed corn silage.

What conditions lead to increased nitrates?

There are types of questions to ask prior to chopping corn silage to help producers determine whether they have the potential for nitrate toxicity.

  • Heavy nitrogen fertilization or manure application. The more nitrogen that is available, the greater the potential for increased nitrate accumulation.
  • Cloudy weather will increase the potential for nitrates due to reduced activity by enzymes that convert nitrate into amino acids and, later, proteins.
  • Deficiencies of nutrients such as phosphorus, potassium, molybdenum and manganese increase the concentrations of nitrate. Root uptake of nitrate continues, but growth is limited causing nitrates to accumulate.
  • Rainfall after prolonged moisture stress just prior to harvest can increase the amount of nitrates in plant materials. To minimize risk, generally wait two weeks before harvesting the silage.
  • Frost damage on all corn, including droughty corn, can have elevated levels of nitrates if harvested two to six days following a heavy frost. Silages following heavy frost conditions should be tested and treated the same as drought-stressed corn silage.

Harvest recommendations

Corn silage should be harvested at normal recommended moisture levels, regardless of growing conditions (see Table 1). Drought can affect the whole plant moisture content. When drought slows plant growth and delays maturity, the moisture content will be higher than suggested by the appearance of the crop. When a drought occurs at the end of the season, moisture levels may be lower than normal. Even though drought-damaged corn may appear dryer than normal, whole plant samples are the only sure-fire way to know the current moisture levels of the crop.

Harvest height is typically set at 4 inches. Increasing the height to improve silage quality is usually not profitable, since the improvement in quality rarely offsets the yield loss.

Table 1. Recommended moisture levels for corn silage structures.

Silo type

Recommended moisture content (%)

Upright silo


Upright "oxygen-limiting" silos


Horizontal silos


Bag silos


Corn silage samples can be submitted to the Michigan State University Soil and Plant Nutrient Laboratory to determine nitrate content of your plant materials. A representative sample should be dried and sent in a paper bag to the laboratory. Wet samples should be delivered directly to the laboratory.

What are safe nitrate levels?

The potential problems associated with high nitrate levels in corn silage include possible asphyxiation and death of animals consuming excess nitrates. Founder, the inflammation of the hoof's internal connective tissue, can also affect livestock, especially dairy cows, causing lameness and off-feed problems. This condition may dramatically decrease milk production and result in high cull rates of affected cows.

When in doubt about potential nitrates in forages, always sample affected feedstuffs.

Table 2. Guidelines for feeding forages to livestock based on nitrate nitrogen and nitrate concentrations.

Nitrate nitrogen NO3-N (ppm)

NO3 (ppm)

Feeding recommendation

Less than 1,000

Less than 4,400

Not toxic.



Limit feed to less than 50 percent of the ration dry matter.



Limit feed to less than 25 percent of the ration dry matter. Do not feed to pregnant cattle.

Greater than 4,000

Greater than 17,600

Toxic, do not feed.

Source: Kurt Steinke, MSU

For more information, contact Phil Kaatz at or 810-6678-0341.

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