Effects of Carbon Source on Immobilization and Chemical Distribution of Fertilizer Nitrogen in Soil1
- Kenneth R. Kelley and
- Frank J. Stevenson2
Three C sources (glucose, a phenolic glycoside, and catechol) were added to soil along with 15N-labeled (NH4)2SO4 in an incubation study to determine effects of aliphatic and phenolic substrates on transformations of fertilizer N. Microbial utilization of the C substrates resulted in a rapid depletion of available mineral N, with maximum immobilization of soil and tracer N after 6, 10, and 20 d in the glucose-, phenolic glycoside-, and catechol-amended soil, respectively. A close relationship was observed between clay-fixed nonexchangeable 15NH+4 and KCl-extractable (exchangeable + soluble) 15NH+4 during incubation (r2 = 0.91**). The nonexchangeable 15NH+4 was readily released and immobilized during microbial utilization of the added substrates. Availability ratios indicated that the immobilized 15N at the point of maximum incorporation into the microbial biomass was from 3.5 to 8.0 times as susceptible to mineralization as the native soil N. Net mineralization of 15N was accompanied by a decrease in amino acid-15N, an indication that synthesis and decomposition of microbial protein were closely related to the level of available mineral N. Higher levels of acid-insoluble 15N in the phenolic glycoside- and catechol-amended soil were attributed to condensation reactions involving amino compounds and substrate-derived polyphenols. Overall, microbial transformations were more important than substrate effects in determining the distribution of immobilized 15N after 120 d of incubation.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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