Too late for nitrogen applications

By Blake Jackson

The optimal time to apply nitrogen fertilizer to encourage fall forage growth has passed, according to John Lory, the University of Missouri Extension’s state nutrient management specialist. Applying nitrogen now will not enhance growth and could increase the risk of nitrate buildup in forages.

Lory advises that nitrogen applications should be made in late summer, ideally before August 15th. "Delaying applications after Aug. 15 reduces the probability that the applied nitrogen will maximize yield in cool-season forages such as tall fescue," he explains.

Missouri pastures are currently experiencing dry conditions, with minimal forage growth. No significant rainfall is expected through October 28th, and as of October 17th, 83% of the state is classified as abnormally dry, with 53% facing moderate drought or worse, according to MU Extension state climatologist Zachary Leasor.

“In these conditions, there is little chance that nitrogen fertilizer applications will increase fall growth,” Lory states. "Spending money on nitrogen fertilizer this late in the season under these dry conditions is high risk, low value. Don’t do it."

Many farmers are tempted to apply nitrogen later than MU Extension recommends, particularly if there has been good rainfall through September. However, with current dry conditions, the potential for fall growth is slim.

Even if rainfall comes by November, shorter days and cooler temperatures will still limit growth, notes MU Extension state forage specialist Carson Roberts.

Moreover, up to half of the nitrogen applied now could be lost through ammonia volatilization, Lory warns. Tall fescue won’t respond to any remaining nitrogen until next spring. "If you apply nitrogen now, you are applying to promote spring growth," Lory adds, suggesting that it’s more efficient to apply nitrogen in spring when growth is more likely, allowing for better fertilizer use.

Additionally, nitrogen application at this time could raise the risk of nitrate accumulation in forages, which is dangerous for cattle and other ruminants.

Tim Evans, MU Extension’s state specialist in animal health and veterinary toxicology, explains that nitrogen taken up by cool-season grasses after rain may lead to dangerously high nitrate levels, potentially fatal for grazing animals.

Evans also emphasizes that the only cattle that have already been fed that day should be introduced gradually into new pastures. The first animals introduced to new pastures should be nonpregnant cattle.

Roberts suggests now is a good time to take soil samples and apply lime if needed, preparing for frost-seeding legumes such as red clover, which naturally fix nitrogen and increase yields.

For more information, visit MU Extension publication “Nitrate Problems in Livestock Feed and Water”.

Photo Credit: gettyimages-jacqueline-nix