Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
11/4/99
Contacts:
Michael L. White, Adair County Extension, (515) 743-8412,
x1mikew@exnet.iastate.edu
Elaine Edwards, Extension Communication Systems, (515)
294-5168, eedwards@iastate.edu
Anhydrous Ammonia (NH3) Application
AMES, Iowa -- American farmers will spend up to $1.5 billion on nearly five million tons of anhydrous ammonia (NH3) for next year's crop, with Iowa producers using almost one-fifth of that total. Some will choose to apply NH3 this fall for any number of reasons: to ease their spring workload; to take advantage of favorable NH3 prices and payment programs; to run on dry soil this fall to reduce soil compaction; or, simply because the weather is favorable.
"There are disadvantages to fall applications of NH3. Fall application rates cannot be tailored to spring moisture conditions and planting dates. Cropping plans may change over winter," said Mike White, Iowa State University Extension field crop specialist. Lower corn yields can result when NH3 is applied (at equal rates) in fall versus spring, according to Iowa State University and University of Minnesota yield data. And, above normal moisture and/or soil temperature in late fall or spring increases the risk of nitrates leaching into ground water and streams.
"Crop residue cover also is affected by the tillage action of NH3 application. It's estimated that protective soybean residue losses from NH3 application equipment are between 30 percent and 50 percent, dramatically increasing the risk of winter and spring soil erosion in fragile residues," White said. "And although few producers raise corn on corn, between 10 percent and 40 percent of corn residues can be destroyed with fall NH3 application."
Nitrate detections in streams after spring rains has become increasingly common. Fall-applied NH3 tends to have a higher potential than spring-applied NH3 of adding to nitrate detections. To increase the efficiency of NH3 applications, ISU recommends applying NH3, liquid nitrogen or dry nitrogen forms of fertilizer in the spring, or as in-season sidedress applications.
"Not only is timing important, proper application is another key factor in making NH3 inputs profitable," White said. (Using an approximate NH3 cost of $220 per ton this fall and a $7 per acre application fee, a typical 120 lb. of nitrogen applied per acre will cost around $23.) If producers do decide to apply NH3 in the fall, ISU recommends that they should wait until the soil temperature has dropped to 50°F or below at a depth of four inches. A nitrogen inhibitor like "N-Serve" also should be considered for soils prone to nitrogen losses.
Understanding the properties of NH3 is important for proper application. When applied in the field, the physical properties of NH3 (unlike liquid sprays or solid granules), undergo constant change. NH3 contains 82 percent nitrogen and 18 percent hydrogen, and it begins to boil at -28°F, so it must be stored as a liquid, under pressure. Each pound of NH3 that vaporizes is capable of freezing about 4 pounds of water. Such extreme physical properties make NH3 a challenging product for producers to handle and apply accurately and evenly, or in precision farming environments.
"Many producers over-apply NH3 because they are uncertain of actual application rates due to poor distribution by equipment," White said. "If improved application equipment could reduce typical applications by 5 percent, U.S. producers would be able to pocket a direct savings of $65 million annually."
In a 1993 University of Nebraska study, 61 NH3 applicators were randomly checked for their rate per acre application accuracy. The 44 applicators without electronic controllers had an average variation of plus or minus 16 percent of the intended application rate. The NH3 applicators with electronic controllers did a little better job. Their average variation ranged plus or minus 7.4 percent. A 1997 cooperative study conducted by Iowa State University, Successful Farming and Continental NH3 Products, found that even greater variation was possible among knives on the same applicator.
Researchers found that the manifold used on most NH3 applicators is the primary reason for knife-to-knife variation. Most manifolds are simply hollow chambers with outlet holes on the perimeter. NH3 immediately begins to vaporize into a gas as it moves out of the tank, through the hoses and into the manifold. The vapor interrupts the flow of liquid nitrogen to the hoses and knives, which disrupts uniform distribution. Often two, three or, sometimes, even four times more NH3 goes to one knife compared to another. ISU researchers have found that the type of manifold used and the way the hoses are connected to it can greatly reduce knife-to-knife variation. The researchers also found that knife-to-knife variability in NH3 application tends to decline as the manifold pressure increases. Even simple things like making sure the knives are all of the same make and free of flow obstructions can drastically reduce knife-to-knife variation.
"Applying NH3 can pay big dividends, but it's important that producers and dealers understand the equipment they are using, and that they apply NH3 when conditions are right," White said.
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