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Mineralizable Soil Nitrogen: Amounts and Extractability Ratios
Author(s) -
Juma N. G.,
Paul E. A.
Publication year - 1984
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1984.03615995004800010014x
Subject(s) - chemistry , loam , ammonium , hydrolysis , permanganate , incubation , nitrogen , sulfuric acid , soil water , nuclear chemistry , chloroform , chromatography , inorganic chemistry , biochemistry , organic chemistry , environmental science , soil science
Studies were conducted on a 15 N‐labeled Weirdale loam, a Dark Gray Chernozemic soil (Boralfic Boroll) to (i) determine the amounts of N released by several methods previously used to obtain an estimate of potentially mineralizable N, (ii) determine their 15 N enrichment and extractability ratios, and (iii) compare the results from the above with the N mineralized during incubation and NH + 4 released by the chloroform fumigation incubation technique. The NH + 4 ‐N accumulated during 10 d in fumigated soils accounted for ∼1% of total N, was highly labeled, and had extractability ratios of 6.6 to 7.4. These ratios were similar to ones obtained for N mineralized during incubation of unfumigated soils. Ammonium‐N extracted with dilute acidic permanganate solution (0.01 M KMnO 4 in 0.1 or 0.5 M H 2 SO 4 ) accounted for 0.72 to 0.84% of total N and had extractability ratios ranging from 3.4 to 3.9. A stronger solution of acidic permanganate extracted more N that was less enriched. Dilute sulfuric acid extracted NH + 4 and organic N that had extractability ratios of < 3. Ammonium‐N released by autoclaving the soil accounted for ∼1% of total N and had extractability ratios ranging from 0.6 to 0.9. Acid hydrolysis showed that 72% of total N was hydrolyzable, 32% was amino acid‐N and 20% was NH + 4 released on hydrolysis. The extractability ratio for NH + 4 released on hydrolysis was 1.7 and was significantly ( P < 0.01) greater than extractability ratios of hydrolyzable N and amino acid‐N. The similarity and high extractability ratios of NH + 4 released after fumigation and NO ‐ 3 ‐N accumulating during aerobic incubation indicated that the fumigation extracted a biologically meaningful fraction. The biomass was responsible for only 15 to 25% of the net N mineralized during a 12‐week incubation. Results indicated that (i) extraction of a highly labeled N pool in soil can only partly explain the source of N being mineralized, (ii) N is mineralized from several pools, and (iii) there is a remote possibility that a single extractant can extract the variety of N compounds undergoing mineralization and immobilization in soil.