Many cattlemen have had to adjust their pasture fertilization habits in recent years, because the old standby is no longer available. Ammonium nitrate had been the nitrogen source of choice, but fears that it could be used as a weapon have led to increased regulation; as a result, many smaller dealers no longer carry it.
Dr. Rob Kallenbach, University of Missouri Extension Forage Specialist, noted almost all of the response from a nitrogen fertilizer application happens in the 6-8 weeks following that application. “For spring hay, we would typically make that application in the middle of March,” he said. “If we want to try to increase fall growth, which tends to be a bigger limitation in pasture systems, we would make a lot of applications from the middle of August to the early part of September.”
Dr. John Jennings, professor and forage specialist for University of Arkansas Cooperative Extension, told Ozarks Farm & Neighbor that removal of ammonium nitrate has led to urea becoming a bigger source of nitrogen in forage agriculture, which has led to some adjustments. “In late winter and spring, when the ground is still cool, nitrogen performance will be basically the same for urea and ammonium nitrate, pound for pound,” John said.
There are other alternatives, including calcium nitrate and ammonium sulfate, but they’re more costly per pound of nitrogen. Another possibility would seem to be use of Agrotain, an additive that controls nitrogen releases. However, John said, “The Agrotain work that we have done, and Dr. (Nathan) Slaton has done at the University of Arkansas on forages, hasn’t shown it to be cost-effective.”
Even in the summer, if a producer can apply urea just before a rain, the nutrient gets dissolved in the soil and losses are minimized. That can be a tricky proposition; still, said John, urea is often cheaper than ammonium nitrate, and that can compensate for the volatilization losses. “When you look back at some of the research data where urea and ammonium nitrate have been compared on Bermuda grass, the losses are seldom more than 20-25 percent; most of the time they’re in the range of about 10 percent,” he said.
Producers can eliminate the need for nitrogen applications to pastures if they inter-seed enough legumes. John said, “In hay fields, you need a higher proportion of legumes in there to make up the difference in the yield, because that’s usually what you’re depending on for your winter feed, so there still might be some nitrogen application on the grasses there. If they can maintain a really good stand of clover, red clover or alfalfa particularly for hay, those will work out and make a nice hay crop as well.”
Many producers in this part of the country, of course, get their nitrogen from the readily available supplies of chicken litter. “If you decide to use manure like poultry litter, it’s not as dense a fertilizer in terms of when we apply at the surface,” he explained. “We have a lot more material there at the surface. And in those steep slopes and areas where we may have over applied it, we can get into some runoff issues.” That means producers should steer clear of applying litter on steep grades and near waterways.
