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Having NH3 issues in dry soils?

Jeff Caldwell 11/04/2011 @ 10:17am Multimedia Editor for Agriculture.com and Successful Farming magazine.

Though rains have fallen over the last week in much of the Corn Belt, it's been an awfully dry fall in the region. And now, that could affect how much fertilizer you can put down before winter sets in.

There are a lot of questions about whether soils are too dry. True, it's dry, and that definitely has an effect on how anhydrous ammonia, for example, is taken up by the soil. You can still put NH3 down in dry soils if you make sure it's being absorbed and not lost.

The good news is drier soil is capable of holding more NH3 than if it's damp, according to Iowa State University agronomist John Sawyer. And, you're less apt to lose anhydrous immediately after applying it in dry soils, since you won't be causing sidewall smearing with injection knives, typically an easy track for anhydrous to escape the soil before absorption.

But, there are other dangers; anhydrous moves further in the soil after injection. And, if your soil's on the dry and cloddy side, that can make it easy for the NH3 to escape before it can react with the soil and be absorbed.

"The problem with dry soil and low moisture is that soil moisture is needed to temporarily hold ('go into solution') the ammonia so it can become attached to clay or organic matter as ammonium," Sawyer says. "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. Therefore, proper depth of injection and good soil coverage are a must for application into dry soils.

"Movement toward the soil surface can also occur for some time after application if the soil dries and the knife track 'opens up' as the soil dries. A similar movement within the soil can occur if the soil breaks into clods at application and there are large air voids left in the soil," he adds. "These conditions can result in greater ammonia concentration toward the soil surface, and greater potential for loss to the atmosphere at or after application."

The best way to keep that anhydrous in the soil in dry conditions is to make sure your knife tracks are covered, adds University of Illinois Extension soil fertility specialist Fabian Fernandez.

"The biggest concern should not be whether there is enough moisture in the soil to react with ammonia, but rather how moisture conditions impact the sealing of the ammonia knife track," he says.

So, what's the best way to know if you're losing too much anhydrous? The good thing is it's fairly easy to smell. "The easiest way to test whether your process is adequate is to go back to the field after an application path and smell for ammonia," Fernandez adds. "While the human nose is very sensitive to this smell, it is impossible to quantify how much is being lost. However, if one can still smell ammonia a few hours later, the best thing to do would be to wait for better application conditions. If there is no smell, there is a good chance that nitrogen loss from the application is minimized."

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