OBJECTIVES Ammonia volatilization is an important mechanism of nitrogen (N) loss from soils which is dependent on several soil and management factors. This research was conducted with Biscayne Marl Soil and Krome Gravelly Loam from Florida and Quincy Fine Sand and Warden Silt Loam from Washington to determine ammonia volatilization at various temperatures and soil water regimes using either KNO 3, NH 4 NO 3, (NH 4 ) 2 SO 4 or urea applied to the soil at 75 kg N ha -1 rate. Soil water regime was maintained at either 20% or 80% of field capacity (FC), and incubated at either 11, 20 or 29 o C which represent the minimum, average and maximum temperatures, respectively, during potato growing season in Washington. Results indicated that the ammonia volatilization rate at 20% FC soil water regime was 2- to 3-fold greater than that at 80% FC. The cumulative volatilization loss over 28 days accounted for 0.21% loss of N applied as NH 4 NO 3. This loss increased to 25.7% for (NH 4 ) 2 SO 4. Results of this study demonstrate that NH 3 volatilization was significantly accelerated at low soil water regimes. Thus, maintaining near optimum soil water regime is important to minimize volatilization loss of N and to improve N uptake efficiency in addition to its direct effects on plant growth and nutrient uptake. ABSTRACT RESULTS Low-Soil Moisture Dramatically Drives Up Ammonia Volatilization Guodong Liu 1, Y.C. Li 1 and A. K. Alva 2 1 University of Florida-TREC, SW 280 St, Homestead, FL 33031, USA; 2 USDA-ARS N Bunn Rd., Prosser, WA 93305, USA Phone: (305) x355 FAX: (305) (1) To estimate NH 3 volatilization rates from soil for potato production (2) To quantify the effects of soil moisture and temperature on NH 3 emission (3) To identify relationships among soil types, soil moisture levels and incubation temperatures on NH 3 volatilization Figure 2. Cumulative ammonia volatilization from different N sources applied to four soils incubated at 20 o C at either 20% or 80% FC soil water regimes. MATERIALS AND METHODS 2. Incubation and sampling A schematic diagram of the basic elements of the apparatus used to trap ammonia emission from fertilized soils. A. 1 ml 45 mg N/ml (equivalent to 75 kg ha -1 ) was added onto 300 g dry soil surface at the bottom by a micropipette. B. a sponge spiked 800 µl trapping solution (He et al, 1999) was inserted in the mouth of the 500 ml plastic bottle to trap the volatilized ammonia. C. a small sponge spiked 150 µl was inserted into a short pour spout of the screw cap on the bottle to protect the bottle from any contaminations from the outside air. Incubation temperatures: 11, 20 and 29 o C. Soil water content was adjusted to either 20% or 80% field capacity (FC). Sampling time: after 1, 3, 7, 14, and 28 days of incubation. B C A Figure 3. Higher soil pH quickly drives up ammonia volatilization from different N sources at 20% FC much more dramatically than that at 80% FC at either 11, 20 and 29 o C. CONCLUSIONS Results of this study revealed that N volatilization loss was significantly influenced by the effects of soil type, soil water content, fertilizer, and temperature treatments. Across all N sources, and soils used in this study volatilization loss was greater at lower soil water regime than that at near field capacity soil water regime. Among the N source, NH 3 volatilization was greater from ammonium sulfate or urea as compared to that from either ammonium nitrate or potassium nitrate source. Furthermore, NH 3 volatilization was greater from high pH soils sampled from Florida as compared to that from the slightly lower pH soil sampled from Washington. This difference could also be influenced by other soil properties including soil texture and biological activities. ACKNOWLEDGEMENTS This research was supported by the Florida Agricultural Experiment Station and a grant from USDA-ARS. REFERENCES 1.Alpkem Corparation RFA methodology for ammonia nitrogen. A303-S020. Alpkem Corporation, Clackamas, Oregon. P. 7 2.Cabrera ML, SC Tyson, TR Kelley, OC Pancorbo, WC Merka and SA Thompson Soil Sci. Soc. Am. J. 58: FAO, 2001, Global estimates of gaseous emissions of NH 3, NO and N 2 O from agricultural land. 4.Fenn, LB and LR Hossner IN: Advances in Soil Sciences (ed. BA Stewart) Springer-Verlag, New York, Berlin, Heidelberg, Tokyo. Pp He, ZL, A.K. Alva, D.V. Calvert and D.J. Banks Soil Sci. 164: Soils tested pH = 7.27 pH = 7.69 pH = 6.65pH = 6.46 pH = 7.27pH = 7.69pH = 6.65pH = Ammonia analysis In AutoAlanyzer III according to EPA, Method (EPA, 1993). Figure 1. Dynamical rates of ammonia volatilization from different N sources applied to four soils incubated at 20 o C at either 20% or 80% FC soil water regimes. Vertical lines at each data point represent the standard error of the mean. 1. Dynamical rates of NH 3 emission 2. Cumulative NH 3 emission 3. Effects of soil pH and incubation temperature on NH 3 emission