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Nitrogen Sources for a Tough Spring - from Mike Roegge

Posted by John Fulton -

It sure looks like Mother Nature wants to keep winter around a bit longer than many of us would prefer. Officially, spring begins March 20th, but many producers are hoping that spring weather will arrive sooner. We're going to need as many days as possible to get quite a few field operations completed before planting can commence: fall (now spring) tillage, eliminating ruts in fields or parts of fields, fertilizer to apply, manure to spread, etc.

Most areas saw very little fall anhydrous ammonia applied. Which means the NH3 system will be fully stressed this spring. I think most folks realize that not all fields will get NH3 applied prior to planting, it's just not possible to get over that many acres in a timely fashion without delaying planting. Thus we need to be examining the use of alternative nitrogen sources and timings.

Of the 3 main nitrogen sources, NH3 is the most commonly used. It's cheaper and is applied below the surface, which can reduce N losses (but not all). Urea and liquid are the other two sources. Both have been used in the past with similar results to NH3, if used correctly.

When nitrogen is applied to the soil, it breaks down into ammonium and then nitrate. These are the two forms that the corn crop uptakes. And nitrate is the form that can be lost (leaching or denitrification) from the soil. Comparing the 3 N sources, note that NH3 takes the longest amount of time to break down compared to ammonium and nitrate. While liquid N is half ammonium and nitrate, which means it can be lost the quickest. The longer we can keep nitrogen from breaking down to nitrate the more protected it is from loss through leaching or denitrification.

In terms of potential N losses, all forms are vulnerable. N is lost in one of several ways: 1) under saturated soil conditions, nitrate can be converted to a gas by soil microbes (denitrification); 2)nitrate can be leached out; or 3) if left on the soil surface, N can convert to a gas. Nitrogen stabilizers (N-serve, Instinct, Agrotain, etc.) can be used to reduce some of these potential losses.

1) If the soil is saturated and any of the N has been converted to nitrate, soil microbes will cause nitrate to be converted to a gas and lost. But only the portion of the N that has converted to nitrate.

2) If water is moving through the soil profile and any of the N has been converted to nitrate, leaching can occur, and tile lines take it out of the field. Again, only nitrate can be leached.

3) If left on the soil surface, with warming soil temperatures, heavy residue and high evaporation occurring, urea can be lost through volitization. This doesn't happen immediately, but, depending upon the above factors, within 7-14 days. Urea is found not only in dry urea but also in liquid N, as 50% of liquid N is urea.

No system is foolproof. So take precautions- Apply liquid or dry N sources at planting time, not weeks ahead. Consider using nitrogen stabilizing products. Incorporate liquid and dry if not expecting rain within 7 or so days. Consider using some of the coated urea products as the coating will prevent N loss for 4-8 weeks, although you might want to incorporate to prevent movement of the granules off the field. Sidedressing is the most efficient method of applying N, and you can actually reduce your normal rate.

All 3 nitrogen sources have been used with success. It's just that you have to manage them differently. HN3 is injected, which eliminates surface loss. But you can lose NH3 via leaching or denitrification. Urea, if not incorporated (by tillage or rain) within 7-10 days can be lost via volatilization under certain conditions. Use of coated urea will reduce that loss. Liquid N is half urea and half equal portions of ammonium and nitrate. The nitrate portion is vulnerable immediately to loss (as described above).

Be aware, you'll more than likely have to use one of these alternative sources this year. Make sure you plan ahead for best results. For instance, spinners may not be as precise at application, so a double spread may be necessary. Just be prepared.

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