Moisture Quotients for Ammonia Volatilization from Four Soils in Potato Production Regions

Ammonia (NH3) 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 NH3 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 (KNO3), ammonium nitrate (NH4NO3), ammonium sulfate ((NH4)2SO4) or urea ((NH)2CO) sources were evaluated for ammonia volatilization at 75 kg N ha 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 NH3 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 NH4NO3 to 25.7% as (NH4)2SO4. Results of this study demonstrate that NH3 volatilization was accelerated at the low soil water regime. Moisture quotient (Q) is defined as a ratio of NH3 emission rate at 20% FC to that at 80% FC both at the same temperature. The peak Q values of NH3 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 NH3 volatilization and to improve N uptake efficiency and air quality.