Nitrogen is important for crop growth and production. Managing this valuable input for maximum plant availability is critical to ensure optimum economic returns while minimizing the potential for negative environmental effects. Urea is the standard N fertilizer product for rice production, and it is a major component of liquid N sources such as urea ammonium nitrate (UAN) solutions used widely in the south. Urea is a high analysis (44-46% N) granular N fertilizer that is ultimately converted into ammonium and nitrate, the plant available forms of N. The N in urea is subject to loss by volatilization to ammonia gas if it begins to break down on the soil surface. Several factors including soil temperature, soil moisture, soil pH, wind-speed, cation exchange capacity, organic matter, and humidity influence the rate of ammonia volatilization.
Agrotain ([N-(n-butyl) thiophosphoric triamide] abbreviated NBPT) became commercially available around the year 2000. It slows urea breakdown by controlling the urease enzyme. This allows growers more time from urea application until the next rain or irrigation event needed to incorporate the fertilizer into the soil. At higher rates Agrotain can minimize ammonia volatilization losses for up to 14 days. Note that Agrotain only stabilizes N from loss against ammonia volatilization. Agrotain will not provide stabilization from the other N loss mechanisms once the urea fertilizer is incorporated into the soil and urea is converted into ammonium. The ammonium will convert to nitrate in the soil and may be lost via leaching, or lost through denitrification in saturated soil conditions.
Claims have been made regarding the ability of several other products to stabilize N from loss. One claims to stabilize N from both volatilization losses and nitrification losses by increasing the cation exchange capacity around the urea fertilizer. Several university laboratory and field experiments, including some in Mississippi have not verified this claim. Another product claims to control volatilization losses is a polymer coating to slow release. However, in our tests, it dissolved in water as rapidly as untreated urea, and in lab and field studies, volatilization and denitrification losses were not minimized. Two other products with the same active ingredient propose to stabilize N by cation exchange reaction with calcium. This mechanism has yet to be verified in the scientific community. Furthermore, there was no control of N loss by volatilization in laboratory studies.
As stated earlier, the N in urea can be lost from the soil surface to the atmosphere through volatilization of ammonia. Once urea is incorporated into the soil, it can be converted to ammonium. Where oxygen is present (aerobic soils) such as in corn production, the ammonium can be converted to nitrate and lost to leaching or denitrification when soils become saturated with standing water. In rice production, the ammonium can be stabilized by establishing a permanent flood within a few days after application.
Research has shown the active ingredient NBPT can control volatilization losses. Products that have the active ingredient DCD or nitrapyrin at the appropriate rates can slow the conversion of ammonium to nitrate, thus providing stability against the loss of leaching and denitrification.
The choice you make regarding the N-stabilizer product can be likened to car insurance. For many people, insurance premiums are never capitalized on because accidents have not occurred. However, if the accident does occur, you want the insurance to provide stability against repairs or replacement. In crop production, N losses cannot be predicted; however, when conditions promote loss, be sure you have a product that is proven to insure N will be available to the plant rather than in the atmosphere or in the closest stream.