Evaluation of N Volatilization Losses From Enhanced Efficiency Fertilizers in Rice Production.

In drill-seeded, delayed flood rice production, the most important nitrogen (N) fertilizer application is the application applied just before permanent flood establishment. This fertilizer application timing is the most important because the largest amount of fertilizer N is applied at this time and it has the largest potential for loss. The nitrate (NO3-) form of nitrogen is unstable under flooded, anaerobic conditions and will be lost through a process called denitrification. Because of this loss potential, only fertilizers that contain N in the ammonium (NH4+) form, like ammonium sulfate (21-0-0), or fertilizers that break down into the ammonium form, like urea (46-0-0), are recommended in rice production. Urea is the most commonly used N fertilizer source because it is the cheapest per pound of N. The only problem with urea is the potential for it to turn into ammonia (NH3) gas if it is left exposed on the soil surface for an extended period of time. Studies conducted at the Rice Research Station over the last several years have shown that when urea is left on the soil surface for a 10 day period of time prior to permanent flood establishment volatilization losses can range between 17 to 30%. Unfortunately, in commercial rice production in Louisiana, it may take 10 or more days for a flood to be established on some of the larger fields. In these situations, a urease inhibitor containing the active ingredient N-(n-butyl) thiophosphoric triamide, or NBPT for short, is recommended. The urease inhibitor slows down the breakdown of urea to the ammonium-N. Because it temporarily delays the breakdown of urea, it also temporarily delays the potential for ammonia volatilization losses. In 2012 a urease inhibitor product containing the active ingredient NBPT, was released by the Helena Chemical Company. This product was tested at two application rates, 3 and 4 quarts of product per ton of urea. Two rates of the N-Fixx were evaluated because the label states that a 2 or 3 quart per ton of urea application rate can be used. The N-Fixx treated urea was compared to Agrotain Ultra (KOCH Fertilizer, LLC) treated urea at a rate of 3 quarts per ton of urea. Agrotain Ultra is an established and proven NBPT containing urease inhibitor product that has been used in commercial rice production for several years. Approximately 17% of the cumulative applied N from the untreated urea fertilizer was lost in the 10-day period prior to permanent flood establishment. The Agrotain Ultra treated or the N-Fixx treated (3 or 4 quarts) ureas were used, less than 5% of the cumulative applied N from the fertilizers was lost over the same 10-day period prior to permanent flood establishment.