Ammonium nitrate fertilizer is an effective source of nitrogen for crop growth. Unfortunately, in the hands of terrorists, it can also be used as a raw material for producing a bomb capable of killing many innocent people. Since the Oklahoma bombing, law enforcement officials have imposed tighter controls on the transport and distribution of this fertilizer. In 2005, several local fertilizer dealers stopped selling ammonium nitrate because of new Coast Guard rules regulating its movement on the Mississippi River. Urea is the most common dry N fertilizer substitute for ammonium nitrate. Although it too could be used to produce bombs, terrorists have not successfully used urea because it becomes very unstable after mixing with the other bomb-making ingredients.

Effective crop N management with urea may be different from ammonium nitrate. Urea (45% N) contains more nitrogen per unit weight than ammonium nitrate (32% N). This saves on freight costs because less material is needed per acre. The major disadvantage of urea is that it can be lost by volatilization when broadcast on soil without incorporation. The worst-case scenario is urea applied on the surface of warm, wet, high-pH (recently limed) soil with windy weather and no rain, tillage, or irrigation for a couple of weeks. Farmers and agriculture chemical dealers have questions concerning the amount of N loss that can occur from urea. How much is lost on dry soil and what effect does a light rainfall or irrigation (< ½-inch) event before or after application have on N loss from urea? Are N fertilizer additives such as "NBPT" ((N-(n-butyl) thiophosphoric triamide, AgrotainTM ) or humic acid effective in reducing volatilization?

In 2005, we began a research project to learn more about urea losses in wheat, cotton, and rice. Wheat was top-dressed with N in the spring following a rain the previous day. Wheat yields per acre from the fertilizers and additives were 40 bu (control), 54 bu (urea), 62 bu (urea +Agrotain [NBPT]), 63 bu (ammonium nitrate), 44 bu (UAN 32%), 61 bu (UAN + Agrotain). We have not harvested cotton tests with fertilizer treatments applied at cotton cotyledon and 7th node growth stages. Thus far, cotton petiole nitrate and leaf chlorophyll meter readings have not indicated significant benefits from fertilizer additives (NBPT and Humic Acid) under the weather conditions that they were used in 2005.