Ammonia Volatilization and Denitrification Losses of Urea-Nitrogen Stabilizers from Two Contrasting Soils.

Urea-nitrogen (N) fertilization in crop production agriculture is a major source of ammonia (NH₃) volatilization and denitrification of nitrous oxide (N₂O).  Urea-N stabilizers (urease and/or nitrification inhibitors and slow-release N-fertilizers) might reduce these gaseous-N emissions from soils; however, their effects can vary with soil texture.  Laboratory incubations were conducted to investigate the influences of stabilized urea-N fertilizers on emissions of NH₃ and N₂O from Ulen sandy loam and Bearden-Kindred silty clay loam soils. Treatments include (i) unamended control, (ii) conventional urea, (iii) urea plus NBPT [N-(n-butyl) thiophosphoric acid triamide, urease inhibitor], (iv) urea plus nitrapyrin (NP) [2-chloro-6-(trichloromethyl)-pyridine, nitrification inhibitor], (v) urea plus NBPT and DCD (Dicyandiamide, nitrification inhibitor), and (vi) polymer coated urea. The soils were amended with urea N-fertilizers (each at rates to achieve 224 kg N ha^-1, except control), and incubated in airtight 1 L mason jars at constant temperature (20 °C) and moisture content (60% of soil water holding capacity) for 140 days. Phosphoric acid (0.5 M) traps were used for absorbing and determining NH₃ emissions from the soils.  Headspace air from the jars was collected, and analyzed for N₂O concentration using a DGA-42 Dani Master gas chromatograph fitted with ⁶³Ni-electron capture detector. Measurements for NH₃ and N₂O emissions were taken on days 1, 3, 5, 7, 10, 13, 16, 20, 24, 31, 38, 59, 80, 108, and 140 after treatment application. At the termination of the experiment, soils are analyzed for inorganic N (NH₄⁺-N and NO₃^-- N) contents using an automated Timberline TL2800 ammonia analyzer. The results from the study will estimate likely effects of soil texture on emissions of NH₃ and N₂O from different urea-N fertilizers.