Air November 7, 2001

Thank you Gary, and good morning everyone. It’s been warm, quite a bit warmer than normal the past couple of weeks. It sounds like that’s about to change though. Cooler weather would certainly be nice, and I don’t think anyone would be upset if we had some rain. A quick reminder about KSU Swine Day, November 15th at the Manhattan Holidome. Call me if you have any questions.

With the warmer than normal weather - normal for this time of year is daytime highs around 58 and overnight lows in the mid 30s - soil temperatures have not cooled down as quickly as normal. Alfalfa has been slow to go dormant and producers are hesitant to apply anhydrous ammonia. We know that fall applied nitrogen can be subject to leaching and even denitrification. Our rule of thumb has always been to not apply anhydrous ammonia when soil temperatures are above 50 degrees. As of yesterday afternoon, we had soil temperatures at four inches depth of at least 55 degrees. So do we apply anhydrous, or not. Well, the truth is, that 50 degrees is not a switch at which loss will or won’t occur. As temperatures cool down in the fall, the bacteria that convert anhydrous ammonia to forms that are more easily lost, start to slow down in activity. The slow down starts to occur at 70 degrees and by the time the soil is under 50, the bacteria’s activity is very minimal. There will still be some activity clear down to freezing, it just isn’t enough to worry about. At 55 degrees, and colder weather approaching, I would not hesitate to be applying anhydrous. Under a worst case scenerio, it would stay warm for another month and you might lose 10% of your nitrogen. This would also require there to be extensive enough rain to actually leach some of the ammonia that has been converted to nitrate. Ammonia doesn’t leach very easily, nitrates do. Okay then, how about surface applications of liquid or dry nitrogen sources on to brome grass. Do we wait for cooler weather or apply it anyway. I’d go ahead and start fertilizing the bromegrass and fescue. Nitrogen losses to ammoniafication have generally been way over stated. The general feeling now is that under worst case field scenerios, you could lose 15%. It won’t happen this fall. Colder weather is coming, so get that fertilizer applied!

This is Chuck Otte, Geary County Extension Agent, with Ag Outlook 2001.

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