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Fall anhydrous ammonia application

Posted Tuesday, November 8, 2011, at 9:25 AM

Soil temperatures are still above recommended levels (50 degrees and cooling 4-inch temperature) for the fall application of anhydrous ammonia. Another problem that is of concern is the dry soil. First, there are reports or remarks of the soil being so hard that it is difficult to the machinery to penetrate the soil. Secondly, is the question whether anhydrous should be applied to dry soils?

Dry soil can hold ammonia. Even air dried soil contains some moisture. Ammonia dissolves readily in water, but it is held or retained in soil by clay and organic matter. Soil moisture is needed to temporarily hold the ammonia until it can become attached to clay or organic matter as ammonium. If dry soils are cloddy and do not seal properly, the ammonia can be lost at injection, or seep through the large pores between clods after application. Proper depth of injection and good soil coverage are a must for application into dry soils, according to John Sawyer, Iowa State University. Wing sealers immediately above the outlet port on the knife can help close the knife track, limit the size of the retention zone, and reduce vertical movement of ammonia. Closing disks can reduce ammonia loss by covering up the injecti0on track with soil that traps the ammonia as it moves to the soil surface. Reducing application rate or narrowing the knife spacing reduces the concentration of ammonia in each injection band. If oils are dry and in good physical condition, they hold more ammonia than soil that is moist.

The potential is usually low for fall-applied ammonia to damage corn seed or seedlings. However, if the soil remains dry (and limits nitrification), the ammonia is injected shallow or there is poor soil structure (ammonia placed near the seed location), or the rate of application is high, then it is possible for ammonia damage. The best cure is to inject deep enough with friable soil coverage to get adequate soil separation between the point of ammonia injection and the depth where corn seed will be planted or offset ammonia bands from future corn rows.

One of the best ways to see if there is ammonia loss at time of application is to use your nose. Be aware of what is happening if you apply anhydrous ammonia. If you make an application round in the field, and you still smell ammonia from that application, then you should make adjustments or wait for better conditions. If the soil is breaking into clods, there isn't good coverage of the knife tracks with loose soil, and ammonia is escaping, then stop and either change the way the equipment is working or is set up, or wait until the soil has better structure or moisture.

Recent rainfall makes fall application of anhydrous more attractive. Soil temperatures are still hovering around 50 degrees. The weather forecasts are calling for cooler temperatures which would be good for fall application.



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As our local University of Missouri Agronomy Extension Specialist, Crook has been writing a column for the print edition Agriculture page for the past three years and we will now be sharing it on our web version. Crook has a bachelor and masters degree in agronomy from University of Missouri and received his doctorate in Agronomy from Kansas State University. He was in soybean variety development research for 22 years for various seed companies and has been Saline County's agronomy specialist for 10 years.
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