Comparing Gibbs Energy Relationships for Ammonia Volatilizations from Agricultural Soils for Potato Production

Soil drought, that can be enhanced by global warming increases ammonia (NH3) volatilization. This laboratory study was conducted with two soils: Krome Gravelly Loam (KGL) from Florida and Warden Silt Loam (WSL) from Washington State and two fertilizers: Ammonium sulfate [(NH4)2SO4] or ammonium nitrate (NH4NO3). Two water regimes including 20 and 80% Field Capacity (FC) were used at 20°C which is the average temperature in the potato growing season in Washington State. The data demonstrated that variation in NH3 volatilization subject to different soil water regimes can be explained by changes in Gibbs free energy of Nitrogen (N) fertilization in soils with varying water contents. The absolute values of Gibbs free energy of (NH4)2SO4 or NH4NO3 applied to soil at 20% FC soil water regime were 5-fold greater than at 80% FC. Accordingly, the equilibrium constant (K) of deprotonation of ammonium ions in soil solutions at 20% FC was 3,000or 50-fold greater than that at 80% FC for (NH4)2SO4 or NH4NO3, respectively. Nitrogen loss via NH3 volatilization was 4-to 7-fold greater at 20% FC than that at 80% FC. This study suggests potential acceleration of NH3 volatilization from soils under drought. Therefore, optimal water management is critical to mitigate NH3 volatilization from agricultural soils.