Immobilization of ammonium and nitrate and their interaction with native N in three Illinois Mollisols |
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Authors: | F Azam F W Simmons R L Mulvaney |
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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 |
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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. |
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Keywords: | Mollisol N interaction N availability N fertilizers N immobilization N mineralization |
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