STRAIGHT FROM THE HORSES MOUTH

Duane A. Lienemann

 UNL Extension Educator,

 Webster County

January 5, 2011 Edition
Crop Production Clinics: These clinics provide valuable information to help crop producers and agribusiness professionals improve their profitability and safety. The clinics will feature presentations from extension specialists and educators on soil fertility, soil water and irrigation management, crop production, ag. business management & policy, pesticide safety, and disease, insect and weed pest management. The Crop Production Clinics also be a primary venue for individuals to renew their license for Commercial & Noncommercial Pesticide and Private Pesticide Applicators. The clinics closest to producers in the south central Nebraska is in Kearney on January 6 and in Hastings on January 10. You can find more information and all locations by going to: http://cpc.unl.edu/.  I get a lot out of the clinics. I think you will too.
Warm Winter Weather & NH3: Can you believe this winter weather. You have to love it, but you know we will pay for this- and it may not be just weather. Most farmers I know put on fertilizer this fall. Of course there are many advantages, with the most obvious being that fall fertilizer application spreads out the workload so that there’s more time to focus on corn planting in the spring. Secondly, wet spring weather sometimes prevents producers from applying anhydrous ammonia in the spring ahead of planting, and forces them to apply more expensive sources after planting or compact their soil. Equally important for many growers have been issues with ammonia availability at times in the spring the past year or two.
Despite those advantages, a fall application of anhydrous ammonia involves some risks, and we may be seeing one of those hit us because of the nice weather we have been experiencing this winter – so far. This is due to the potential for higher nitrogen (N) loss in the spring following fall application, as a result of nitrification of the ammonium during winter and very early spring and subsequent leaching, or denitrification. I think maybe we should explore that a little bit.
When anhydrous ammonia is applied to the soil, it quickly reacts with water to form ammonium hydroxide. A large portion of the ammonia is converted to ammonium and can be bound to clay and organic matter particles within the soil, primarily through the cation exchange process. As long as the nitrogen remains in the ammonium form, it can be retained on the exchange capacity of the soil, and does not readily move in most soils, so leaching is not an issue. Now this is assuming that the soil temperature is consistent with normal winter temperatures.
At soil temperatures above freezing, ammonium is converted by specific soil microbes into nitrate-N through the activity of nitrosomonas bacteria which is responsible for transforming ammonium to nitrite, which is then rapidly transformed to nitrate. Temperatures below 50°F reduce this considerably. Since this conversion is a microbial reaction, it is very strongly influenced by soil temperatures and perhaps by soil pH. The higher the temperature, the quicker the conversion will occur.
We apply fertilizer in the fall because we normally will have soils which are, or soon will be, cold enough to limit nitrification. In this part of the country we also have medium to fine texture soils that give us the ability to fall apply under normal conditions. Higher pH soils also aid in the decision. We do this even though we know of the risks. The risk for nitrification with the onset of warm winter weather however can be reduced with fall fertilization if a nitrification inhibitor is used. Specifically the use of a nitrification inhibitor such as N-Serve can help reduce N losses from fall N applications under specific conditions, particularly during periods when soil temperatures warm back up for a period after application.
Without the inhibitor farmers may find that extended warm weather accentuates one of the potential downsides of fall application of N in that nitrification can begin in late February and March, and essentially be complete before the corn crop takes up much N in late May and June. This will be especially true if we get significant rainfall this spring and may be helped if the forecast holds for a dry spring. If N is applied closer to the time of corn planting, or after corn has been planted, a higher percentage of the N is likely to still be in the ammonium form during the wet periods of late spring. So do we wish for early rain or not?
While many farmers in our area have practiced good stewardship in making their applications of fall Nitrogen, the unseasonably warm temperatures so far this winter could potentially cause a significant loss of nutrients. With the warm weather we have been experiencing, while very welcome, we may have a potential problem in that it is not letting that early applied nitrogen freeze up and rest for the duration of the winter. We are probably slowly using up our inhibitor if that is part of our management plan. We’re in good shape right now, but if warmer weather continues, farmers could see nitrogen loss as early as February. We may see the need this coming spring of using side dressing of nitrogen. Often times 30-40 pounds is worth 15-20 bushels more. What is the best thing right now for that fall applied nitrogen? The simple answer is cold temperatures and snow.
I think farmers are doing a great job in watching their nitrogen, and other nutrients, it may pay them to also watch loss potentials in their fields. Never before has proper crop nutrition been more important. With the current corn prices, farmers are putting the economics to it because $5-$7 corn just can’t be short of nitrogen. It just doesn’t make sense economically with the current state of the markets. I think that soil testing may be a management tool that our area farmers may want to implement this coming year. We could have the perfect storm for nitrogen loss even if we don’t get spring rains.
The preceding information comes from the research and personal observations of the writer which may or may not reflect the views of UNL or UNL Extension. For more further information on these or other topics contact D. A. Lienemann, UNL Extension Educator for Webster County in Red Cloud, (402) 746-3417 or email to: dlienemann2@unl.edu or go to the !website at: http://www.webster.unl.edu/me