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This article in SSSAJ

  1. Vol. 73 No. 4, p. 1268-1275
     
    Received: May 16, 2008
    Published: July, 2009


    * Corresponding author(s): tlrobert@uark.edu
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doi:10.2136/sssaj2008.0165

Direct Steam Distillation as an Alternative to the Illinois Soil Nitrogen Test

  1. T. L. Roberts *a,
  2. R. J. Normana,
  3. N. A. Slatona,
  4. C. E. Wilsona,
  5. W. J. Rossa and
  6. J. T. Bushongb
  1. a Crop, Soil, and Environmental Sciences Dep., 115 Plant Science, Univ. of Arkansas, Fayetteville, AR 72701
    b USDA-NRCS, 4900 Oklahoma Ave. Ste. 300, Woodward, OK 73801

Abstract

Development of the Illinois Soil N Test (ISNT) has rejuvenated the search for a soil-based N test to measure potentially mineralizable soil N. Accurate quantification of amino sugar N has been achieved using the ISNT, but issues concerning sample variability and analysis time have led to the discovery of a 10 mol L−1 NaOH direct steam distillation (DSD) procedure. Our primary objective was to determine if DSD could be used as a reliable alternative to the ISNT. Laboratory experiments were conducted to compare the two methods based on recovery of N from pure organic compounds, specificity tests to determine amine group hydrolysis, and recovery of 15N-labeled glucosamine N added to soils. Both methods recovered appreciable amounts of amino sugar N from pure compounds and the ISNT had a higher recovery of N from all amino sugar compounds. Recovery of N from glutamine and asparagine was higher using DSD. Direct 15N techniques for recovery of glucosamine N added to six soils showed no significant difference between the two methods within a soil, but resulted in significant differences among soils. Glucosamine-15N recovery significantly and positively correlated with soil total N. Although the ISNT and DSD measure different amounts of amino sugar N and transition amino acid N, they recover relatively the same amount of hydrolyzable N for a given soil, indicating that differences between the methods may not be that significant as both appear to quantify a pool of potentially mineralizable N. Direct steam distillation appears to be a viable alternative to the ISNT in correlation and calibration of crop response for N-fertilizer recommendations due to the short analysis time per sample (∼6 min) and the accurate estimation of potentially mineralizable N.

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