Ammonia (NH 3 ) emission from nitrogen (N) fertilizers used in agriculture decreases N uptake by the crop and negatively impacts air quality. In order to better understand the factors influencing NH 3 emission from agriculture, this research was conducted with four major soils used for potato production: Biscayne Marl Soil (BMS, pH 7.27), and Krome Gravelly Loam (KGL, pH 7.69) from Florida; and Quincy Fine Sand (QFS, pH 6.65), and Warden Silt Loam (WSL, pH 6.46) from Washington. Potassium nitrate (KNO 3 ), ammonium nitrate (NH 4 NO 3 ), ammonium sulfate ((NH 4 ) 2 SO 4 ) or urea ((NH) 2 CO) sources were evaluated for ammonia volatilization at 75 kg N ha −1 rate. The soil water regime was maintained at either 20 or 80% of field capacity (FC), and incubated at 11, 20 or 29°C. Results indicated that NH 3 volatilization rate at 20% FC was 2 to 3-fold greater than that at 80% FC. The cumulative volatilization loss over 28 days ranged from 0.21% of N applied as NH 4 NO 3 to 25.7% as (NH 4 ) 2 SO 4 . Results of this study demonstrate that NH 3 volatilization was accelerated at the low soil water regime. Moisture quotient (Q) is defined as a ratio of NH 3 emission rate at 20% FC to that at 80% FC both at the same temperature. The peak Q values of NH 3 volatilization were up to 20.8 for the BMS soil at 20°C, 112.9 for the KGL soil at 29°C, 19.0 for the QFS soil at 20°C, and 74.1 for the WSL soil at 29°C, respectively. Thus, maintaining a suitable soil water regime is important to minimize N-loss via NH 3 volatilization and to improve N uptake efficiency and air quality.

Emission of N as NH3 is the primary gaseous loss of N from N sources applied to soils. Knowledge of NH3 volatilization, however, in relation to temperature is incomplete. Soils used in this study were a Biscayne marl soil (BMS) and Krome gravelly loam (KGL) from Florida, and Quincy fine sand (QFS) and Warden silt loam (WSL) soils from Washington. These soils were amended with either KNO3, NH4NO3, (NH4)2SO4, or urea, and incubated at 11, 20, or 29°C under 20 or 80% field capacity (FC) soil water regimes. A change in the rate of NH3 emission corresponding to a 9°C change in temperature is expressed as the temperature quotient (Q9), which describes the temperature effect on rates of NH3 volatilization. At 20°C, the cumulative NH3 emission at 20% FC was up to 8.1‐fold greater than that at 80% FC. The Q9 values of NH3 emission from the WSL soil were up to 10‐fold greater than those from the other three soils amended with either (NH4)2SO4 or NH4NO3 The Arrhenius activation energy (Ea) was about 188 J mol−1 for the WSL soil but ≤42 J mol−1 for the other soils. Volatilization from the WSL soil was highly temperature dependent. These results indicate that Q9 and Ea could be used as indices for N management for crop production to minimize NH3 emissions. Further research is needed, however, to verify the above relationships across a wide range of soils and agroclimatic regions.

Dead plant tissues and ash from a prescribed fire play an important role in nutrient balance and cycling in the Florida Everglades ecosystem. The objective of this study was to assess the dynamic changes in total phosphorus release (TPr) from ash or tissues of either cattail (Typha domingensis Pers.) or sawgrass (Cladium jamaicense Crantz) to water. Natural-dead (senesced-dead) and burning-dead (standing-dead due to a prescribed fire) cattail and sawgrass were collected from highly (H) and moderately (M) impacted zones in the Florida Everglades. This experiment was conducted by incubation and water-extraction of the materials in plastic bottles for 65 d at room temperature (24 +/- 1 degrees C). Results showed that 63 to 88%, 17 to 48%, 9 to 20%, and 13 to 28% of total P (TPp) were released as TPr from cattail and sawgrass ash, cattail tissues from the H zone, cattail tissues, and sawgrass tissues from the M zone, respectively. TPp means total P of plant tissues, whereas TPr is total P release from the tissues or ash. Most of the TPr was released within 24 h after burning. The quick release of TPr observed in this experiment may help explain the P surge in the surface water immediately following a fire in the marsh. These findings suggest that prescribed burning accelerates P release from cattail and sawgrass. They also imply that it is very important to keep the water stagnant in the first 24 h to maximize the benefits of a prescribed fire in the Everglades.