A University of Missouri fertility specialist says his aerial photographs of corn experiencing nitrogen deficiency typically show deficiency occurring in strips in at least half of the fields he surveys. These streaks always correspond to common swath widths of fertilizer applicators.
That leads Peter Scharf to believe there is a serious, increasing problem with uneven distribution of nitrogen fertilizer.
"This problem sticks out like a sore thumb when nitrogen loss occurs, because the
areas receiving low nitrogen rates have a light-green or yellow-green color that is very visible," Scharf says. "But the uneven applications are still happening in years with low nitrogen loss, and potentially are causing yield loss in those years as well."
Uneven Application of Granular N Sources
Granular nitrogen sources — urea and ammonium nitrate — are increasingly susceptible to uneven application, Scharf says, because more and more of our supply of granular nitrogen is imported. Urea imports more than doubled from 1997 to 2007.
"Imported granular nitrogen is more susceptible to uneven application due to the increased handling that these materials go through," the fertility specialist says. "Every time granular nitrogen is handled, especially when it goes through an auger, forces on the granules tend to break them into smaller pieces.
Scharf says the urea and ammonium nitrate he has handled over the past 15 years increasingly is in the form of fine particles. With most granular nitrogen applications made using spinner spreaders to throw the fertilizer, the dust can't be thrown very far.
"When spreading material with a lot of fine particles, the rate immediately behind the spreader will be much higher than the rate at the edge of the pattern," Scharf says. "This results in streaks of high and low nitrogen availability, which can be seen in aerial photographs of corn fields that have experienced nitrogen loss.
"The corn in the nitrogen-deficient streaks will have lower yields due to this deficiency."
Spreading Granular N Evenly
There are several potential solutions to the problem of uneven application of granular nitrogen, Scharf say.
One is the use of air-boom spreaders.Fine particles can be blown down the boom tubes on a stream of air to produce a relatively even application.
"This is a pretty good solution, except that I’ve heard from operators that the fine
materials will collect at the places where the boom folds, clogging it up," Scharf says. "My understanding is that these places are difficult to access and clean.
"Maintenance costs and operator fatigue are also issues with air-boom spreaders, and I’ve heard several people who have these applicators say that they intend to go back to using spinner spreaders in the future."
Scharf says one option for producers is to inspect the fertilizer material before agreeing to purchase it. This requires time and hassle, along with a backup plan of how to proceed if the fertilizer material is not up to par, Scharf says.
Another possibility is to screen out the fine particles and only apply the larger particles, but Scharf says it would require a plan for how to still get value out of the fine particles, and how to charge enough extra to cover the labor and management costs of implementing this solution.
The last option, Scharf says, is to "double-spread," which can either be done by spreading in narrower swaths than the machine is designed for; or by spreading a half-rate in one direction and then spreading the other half crosswise to the first.
"This practice certainly helps to even out applications, but it’s potentially very
expensive because it cuts the applicator’s total acreage by as much as half," Scharf says. "It makes it harder to pay for the applicator and cuts into precious field time, especially in a year like this one, when very little fertilizer was applied in the fall. Applicators will be going full bore this spring when conditions are right — and even when they aren’t — to catch up.
Scharf says the long-term solution is to re-granulate the dry nitrogen that is imported. This will take advantage of low natural gas prices — and therefore fertilizer production costs — elsewhere in the world while still delivering a quality product that can be spread evenly on crops.
"Until producers are willing to pay a premium for this product, and someone invests in the infrastructure to make it happen, we’ll have to get by with other solutions," Scharf says.
Uneven Application Of Anhydrous Ammonia
Streaks associated with uneven applications of anhydrous ammonia are narrower than those associated with granular nitrogen, Scharf says, and may also be less common.
"I’ve seen them both parallel to the row and at an angle to the row," he says. "I hear a wide range of opinions about how to get even nitrogen applications from anhydrous ammonia."
Scharf says work done by Gerry Gogan, formerly of Farmland, showed clearly that the main problem with uneven distribution of anhydrous ammonia was poor splitting at the manifold. Progress has been made in manifold design over
the past 15 years.
Manifolds with interior structures that are designed to swirl the ammonia around the manifold chamber improve distribution, Scharf says from reports he's obtained, as do vertical dam manifolds. At the high end, he says the pumping and metering systems provide the most thorough solution; however, they can be
"With old-style manifolds that put out uneven rates, randomizing the hoses can
undo a lot of the damage," Scharf says. "If one manifold port is putting out a low rate, the port next to it is likely to put out a low rate as well.
"If the hoses from these two ports go to adjacent knives, then both knives will be putting out low rates and the corn in between will not get as much nitrogen as intended. If one is putting out a low rate and the other a high rate, the corn will be much happier."
Other practices, such as making all hoses the same length, inspecting knives for burs and blockage, and replacing knives regularly can all help to make applications more even, Scharf says, but are considerably less important than how evenly the material stream is split by the manifold.