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Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Vegetable growers have been primary users of ammonium nitrate to supply additional nitrogen. With this material, there is little concern about volatile loss of nitrogen when it is applied on the soil surface and irrigated or rained in. However, ammonium nitrate is difficult to obtain these days, so vegetable growers are left looking for alternatives. Many are using urea. When urea is spread on the soil, there is the potential for volatile nitrogen loss as the urea is converted into the ammonium form. This can be quite significant when soil temperatures are high, as they are now. Losses can range from 10 to 25 percent within two to three days when soil temperatures are near 75oF, and the urea is not irrigated or rained in with a 0.5 inch or more of water.
Urea can be treated with the product Agrotain, which is a urease inhibitor, to slow the rate of conversion of the urea into the ammonium form. By doing this, it reduces the potential for volatile nitrogen loss. Agrotain can be quite effective for at least two weeks. During this time period, there is usually a good probability of measurable rainfall to move the urea into the soil. So if you are using urea as a surface broadcast, consider having it treated with Agrotain or pray for rain right after the application. Note, when urea is incorporated into moist soil, volatile nitrogen loss should be minimal and use of Agrotain will not be necessary.