Retention and Fixation of Ammonium and Ammonia in Soils

Abstract

Large quantities of N in the form of Ammonium (NH4 +) and Ammonia (NH3) are being used to increase crop production in agriculture. The reactions involved and the nature of the complexes formed when NH4 + and NH3 are brought into contact with soil materials are of interest from both agronomical and theoretical viewpoints. This chapter reviews the nature of NH3 adsorption by clays and organic matter. It discusses the fixation of NH4 +. The chapter considers the cation exchange with emphasis on NH4 +. The adsorption affinity of univalent cations to soil colloids usually increases with decreasing size of the hydrated ions. The thermodynamic treatment of cation exchange reactions can give valuable information about the reaction mechanisms in ideal systems.