Characterization of chemically fixed nitrogen-15-labeled liquid anhydrous ammonia and of biologically immobilized nitrogen-15 in typical Illinois mollisols
He, Xin-Tao
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https://hdl.handle.net/2142/20000
Description
Title
Characterization of chemically fixed nitrogen-15-labeled liquid anhydrous ammonia and of biologically immobilized nitrogen-15 in typical Illinois mollisols
Author(s)
He, Xin-Tao
Issue Date
1990
Doctoral Committee Chair(s)
Mulvaney, Richard L.
Department of Study
Crop Sciences
Discipline
Crop Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Agronomy
Chemistry, Agricultural
Environmental Sciences
Language
eng
Abstract
An investigation was carried out into the chemical nature and further transformation of fixed liquid anhydrous NH$\sb3$ with emphasis on chemical fixation of NH$\sb3$ by soil organic matter. For this purpose, $\sp{15}$N-labeled liquid anhydrous NH$\sb3$ was injected into a Drummer soil. The fixed $\sp{15}$NH$\sb3$ was sequentially extracted with 0.15 M Na$\sb4$P$\sb2$O$\sb7$ and 0.15 M KOH, and the extracted N was fractionated into humic acid (HA) and fulvic acid (FA). The residual soil was then extracted with 0.1 M NaOH and 99% (v/v) dimethyl sulfoxide (DMSO). The FA fraction was further separated into low molecular weight (LMW) and high molecular weight (HMW) components by equilibrium dialysis, and into generic FA and nonhumic substances by sorption-desorption from XAD-8 resin. The results show that: (1) chemical fixation by soil organic matter accounted for 36% of the total fixed NH$\sb3$; clay fixation accounted for 52%; (2) of the chemically fixed NH$\sb3$-N, 55% was recovered in the FA fraction and 17% as HA by sequential extraction with Na$\sb4$P$\sb2$O$\sb7$ and KOH, 11% was further recovered by extraction with NaOH and DMSO, and 17% remained as humin; (3) most of the N extracted by Na$\sb4$P$\sb2$O$\sb7$ and KOH was recovered in the FA fraction of which about three-fourths occurred in either the LMW fraction or as nonhumic substances; (4) about 13% of the newly fixed NH$\sb3$ was available to soil microorganisms, and 22% was potentially available to higher plants; and (5) incubation with glucose led to stabilization of the newly fixed NH$\sb3$ through biological immobilization.
Additional studies dealt with characterization of biologically immobilized N. For this purpose, a Flanagan soil was incubated with $\sp{15}$N-labeled (NH$\sb4$)$\sb2$SO$\sb4$ and glucose for 7 days, following which HA, FA, and humin fractions were obtained by sequential extraction with Na$\sb4$P$\sb2$O$\sb7$ and KOH. The HA was further fractionated into organic phase, aqueous phase, and residue by extraction with 45% aqueous phenol. Selective enrichment of newly immobilized N was observed in the residual HA after phenol extraction. The humic fractions may be ranked as follows according to selectivity ratio: HA-KOH $>$ FA-Na$\sb4$P$\sb2$O$\sb7$ $>$ humin $>$ HA-Na$\sb4$P$\sb2$O$\sb7$ $>$ FA-KOH. Results of acid hydrolysis and fractionation studies showed considerable differences in the distribution patterns between the newly immobilized $\sp{15}$N and native soil N.
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