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Immobilization of ammonium and nitrate and their interaction with native N in three Illinois Mollisols
Authors:F Azam  F W Simmons  R L Mulvaney
Institution:(1) Department of Agronomy, University of Illinois, 61801 Urbana, IL, USA;(2) Present address: Soil Biology Division, Nuclear Institute for Agriculture and Biology, Faisalabad, Pakistan
Abstract:Summary Three Illinois Mollisols were incubated for 2 weeks at 25°C after treatment with different amounts of glucose and/or 15N-labelled (NH4)2SO4 or 15N-labelled KNO3. The objectives were: (1) to compare the immobilization and interaction of NH inf4 sup+ –N and NO inf3 sup- –N with the native soil N, and (2) to study the relationship between immobilization of applied N and the added N interaction. As determined, immobilized N refers to forms not extractable with 2 MKCl (immobilized 15N+clay-fixed 15NH inf4 sup+ ). In all cases, both NH inf4 sup+ –N and NO inf3 sup- –N were actively immobilized and transformed into organic forms in the presence of glucose. In the absence of glucose, a higher proportion of NH inf4 sup+ than NO inf3 sup- was recovered in organic forms. Although the three soils differed considerably in the amounts of applied N immobilized, similar trends in N immobilization were observed. A positive added N interaction occurred with all soils, the magnitude increasing with the rate of N addition. In the absence of glucose, higher added N interactions were obtained for NH inf4 sup+ than NO inf3 sup- , whereas there was very little difference between NH inf4 sup+ and NO inf3 sup- in the presence of glucose. The results indicate that under conditions of rapid immobilization (e.g., in the presence of glucose), NH inf4 sup+ and NO inf3 sup- will show comparable interaction with the native soil N, whereas in unamended soil, the extent of this interaction will be greater with NH inf4 sup+ than with NO inf3 sup- . Significant correlations were observed between applied N immobilized and the added N interaction only in one soil having a high initial mineral N content.
Keywords:Mollisol  N interaction  N availability  N fertilizers  N immobilization  N mineralization
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