The skyrocketing cost of nitrogen is spurring a lot of interest among farmers in alternative nitrogen sources, and there aren't very many, says Charles Mitchell, Auburn University Extension agronomist. Mitchell spoke about alternative nitrogen sources at the recent East Alabama Cotton Production Meeting in Marvyn.
“We need nitrogen, and most of our nitrogen sources are in the ammonium form,” says Mitchell. “We know that nitrogen is essential for making protein, and protein is essential for making cotton.”
Unfortunately, he says, there are only a few alternative sources of nitrogen available to farmers. “We've known for 110 years now, thanks to Alabama's Old Rotation, that we can produce two-plus bales of cotton year in and year out just on legume nitrogen, such as from a clover or vetch cover crop. But this takes planning and a lot of management if a grower wants to utilize legume nitrogen in his production system,” he says.
Broiler litter is another option, says Mitchell. “We have 2 million or so tons of broiler litter in Alabama, and we once said it was a 3-3-2 fertilizer, but it has gone higher. On the average, chicken littler is about a 3-4-3 fertilizer. The average phosphorus and potassium levels have gone up,” he says.
Thirteen years of research have shown that broiler litter is a good source of fertility for cotton, he says. “I've been told that you can buy poultry litter at just about any poultry farm in north Alabama for less than $10 per ton. But that won't get it to central or south Alabama,” says Mitchell.
Five years of research in central Alabama looked at nitrogen rates versus yield, comparing ammonium nitrate and broiler litter, and the total nitrogen in broiler litter was close behind ammonium nitrate in yields, he says. “We got our maximum yields at about 108 pounds of broiler litter nitrogen and 120 pounds of ammonium nitrate.”
About two-thirds of the broiler litter nitrogen applied this year is going to be available for this year's crop, says Mitchell. “It takes about 180 pounds of nitrogen as broiler litter to give use the same cotton yield as 120 pounds nitrogen as ammonium nitrate.
“In our experiment, all of the broiler litter was put out at planting. Ammonium nitrate was put out in split applications, just as we recommend. But don't count on much residual nitrogen from broiler littler.”
The bottom line, says Mitchell, is that broiler litter is a good alternative nitrogen source for cotton. “If you use it, the NRCS nutrient management code states that all nutrients should be put out no more than 30 days prior to planting the crop. I get calls from growers in north Alabama wanting to know if they can put out chicken litter in January and plant corn in April. But that's not the way to do it.
“In our tests, we always put out broiler litter within two to three days of planting the crop. Treat it as you would any fertilizer. That's going to involve storing it. We thought we could get by with just piling it up out in the field. In one of our tests, we piled up broiler litter and covered it to see if we could store it out in the weather. But it soaks up rain like a sponge. If you have chicken litter delivered to your farm, you had better cover it up or you'll lose it. It's not a pretty sight when it becomes saturated with water, and it's impossible to spread.”
Urea is another alternative source of nitrogen, and it's the cheapest source of fertilizer nitrogen other than anhydrous ammonia, says Mitchell.
“It's about a 46-0-0 fertilizer. It's a good source of fertilizer to use, and the reason it's so inexpensive is because of the process used in making it. It's a relatively inexpensive process compared to that used to make ammonium nitrate. Any nitrate is expensive compared to an ammonium source, and urea is all ammonium.”
Biuret, says Mitchell, is a feed-grade urea that is used as a supplemental source of nitrogen, sprayed on cotton leaves in late summer.
“Dry urea is the most concentrated source of solid nitrogen available. It's fairly water soluble. If you mix it with water at the maximum concentration, you'll get a 23-percent nitrogen solution. You'll get only a 19-percent ammonium nitrate solution. If you mix urea and ammonium nitrate together, you can get up to a 32-percent solution. That's the liquid fertilizer we're using — one-half ammonium nitrate and one-half urea.”
Another advantage of dry urea compared to ammonium nitrate is that urea can be applied over cotton leaves and it won't burn the plant, whereas ammonium nitrate will burn anything if some moisture is present, he says.
“Urea also is pretty stable in high humidity. It will tolerate humidity of 75 percent before it starts to absorb water. Ammonium nitrate has a critical level of humidity of 59 percent.
“The big problem with urea is its volatilization. It can go back into the air as a gas, and that generally occurs under certain conditions.”
Whenever urea reacts with a small amount of moisture in the soil, urease is formed, explains Mitchell. “Ammonium gas then is formed, and it goes back into the air — that's how we lose it. All plants have urease in them.
Residue from no-till and organic matter on the soil surface give us urease. Surface-applied urea in the presence of urease can result in volatilization loss.”
Water is required for dissolving urea, he says. “If you have plenty of moisture, it'll wash on into the soil. The higher your soil pH, the greater your chances of losing urea to volatilization. The worst-case scenario would be if you were using urea in the middle of the summer, it's hot and dry, but you've had enough humidity to give you heavy dew.
“In addition, you're on pastureland with a lot of residue on the surface, and your soil pH is above 7. If you broadcast urea on the surface, and you don't get rain for about two weeks, you could get about a 50-percent loss.”
On the other hand, if you put out urea early in the spring, you get a one half-inch rain within three days, and urea is broadcast on tilled land, you'll get almost no loss, he says.