Submitted to: American Society of Agronomy Meetings
Publication Type: Abstract Only
Publication Acceptance Date: 10/30/2001
Publication Date: 10/25/2001
Citation: Dontsova, K., Johnston, C.T., Norton, L.D. Ammonia absorption by soil clays saturated with CA and MG. CD-ROM. Charlotte, NC: American Society of Agronomoy Meetings. 2001. Interpretive Summary:
Technical Abstract: It is well known that the surface acidity of clay minerals is affected by the type of exchangeable cation. More electronegative cations result in greater surface acidity due to enhanced polarization of water molecules. In this study we measured the surface acidity of one specimen clay and two soil clays, with and without organic matter, exchanged with Ca and Mg. We determined the surface acidity by quantitatively measuring the protonation of ammonia to ammonium. FTIR and gravimetric data for self supporting clay films were obtained simultaneously. Equilibrium constants were determined for ammonia protonation. We observed that water absorbed on Mg-exchanged soil clays was more strongly hydrogen bonded compared to that of Ca clays. Related to this, more ammonia was retained on the Mg-clay than on Ca-clay at high humidity. Conversely, at low relative humidities similar amounts of ammonia were absorbed on Ca and Mg treated clays. Surface acidity of all the clay samples was considerably greater at low relative humidity. Increased retention of ammonia in the form of ammonium at high water content may benefit agricultural production and the environment by reducing the ammonia lost through nitrification and leaching.