Location: Agricultural Systems ResearchTitle: Comparing gibbs energy relationships for ammonia volatilizations from agricultural soils for potato production
|LIU, GUODONG - University Of Florida|
|LI, YUNCONG - University Of Florida|
Submitted to: American Journal of Environmental Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2013
Publication Date: 10/1/2014
Citation: Liu, G., Li, Y., Alva, A.K. 2014. Comparing gibbs energy relationships for ammonia volatilizations from agricultural soils for potato production. American Journal of Environmental Sciences. 10(1):19-25. DOI: 10.3844/ajessp.2014.19.25.
Interpretive Summary: Loss of ammonia (NH3) from soil is termed as ‘volatilization’ loss. This loss can be significant, which impacts the nitrogen budget, under certain conditions such as: high pH soils, method of application and/or incorporation of ammonium containing nitrogen fertilizers etc. Several soil factors, including soil water content, influence the rate of this loss. When ammonium (NH4) form of nitrogen is applied to soil, there are three steps processes which include: dissolution of ammonium containing fertilizer, transformation of NH4 to NH3, and transformation of NH3 in solution into gas form of NH3, which is then subject to loss from the soil into atmosphere. In this study, NH3 volatilization loss was evaluated from two different soils, predominantly used for potato production in Washington and in Florida (a gravelly loam soil and a silt loam soil) subjected to either 20 or 80% field capacity water content, with application of ammonium sulfate and ammonium nitrate. The loss of ammonia from the soil at 20% field capacity water content was 4 to 7 – fold greater than that at 80% field capacity soil water content. Gibbs free energy is a thermodynamic parameter that indicates the rate of a given reaction. The Gibbs free energy values for the nitrogen sources used in this study were 5 – fold greater at extreme soil water stress (20% field capacity) as compared to that at 80% field capacity soil water content. This study demonstrates that Gibbs free energy can be used as a good indicator for rapid prediction of ammonia volatilization loss from the soil.
Technical Abstract: 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 3,000- or 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.