Drought-stressed corn harvested for silage poses three major problems: Lower tonnage, high-nitrate levels that can raise toxicity levels, and lower nutritive value.


"This can be a difficult choice because the cost and availability of alternative forage sources must be weighed against the harvest cost and salvage value of the crop," says William Kautz, director of technical services for Chris Hansen Biosystems in West Allis, Wis.


"Studies on severely stressed corn with no appreciable ears have shown a feeding value about 70 percent of normal corn silage," he says. "Studies on moderately stressed corn have found comparative feeding values from 80 percent to 95 percent of normal corn silage."


Use these guidelines for harvesting high-nitrate corn silage:

  • Ensile the crop when it has reached 65 percent to 68 percent moisture. Check moisture content prior to harvest because it may drop rapidly as the plant begins to die.
  • If a good rain is received after a prolonged dry period, wait three to five days before chopping.
  • Since most nitrates are concentrated in the bottom portion of the stalk, consider chopping 12 to 18 inches off the ground. "That way, you will leave the highest concentration of nitrates in the ground," says Dan Schauff, dairy nutritionist at Agri-King in Fulton, Ill.
  • Ensure that optimum numbers of desirable lactic-acid-producing bacteria are present for rapid, efficient fermentation by using a high-quality silage inoculant.

Precautions to take for successful feeding of high-nitrate corn silage:

  • Have the silage analyzed for nitrate content prior to feeding.
  • A nitrate nitrogen content of 500 to 1,000 parts per million is considered "marginally high," Schauff says. It is safe to feed, but you may want to dilute it down with other forages. 
  • Levels above 1,000 parts per million are considered "high." At levels between 1,000 to 1,500 parts per million nitrate nitrogen, it's safe to feed to non-pregnant animals, but its use in pregnant animals should be limited to 50 percent of total-ration dry matter. Dilute with other forages.
  • At levels higher than 1,500 parts per million, consult with a nutritionist on proper dilution levels.
  • Rumen microbes can adapt to high-nitrate corn silage over time. The first two to three weeks are especially critical, as cows adapt to drought-stressed silage.