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Soil Science Society of America Journal Abstract -

Soil NO3-N Analysis in CA(OH)2 Extracts by the Chromotropic Acid Method


This article in SSSAJ

  1. Vol. 53 No. 1, p. 308-310
    Received: May 26, 1988

    * Corresponding author(s):
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  1. V. A. Haby 
  1. Texas A&M Univ. Agric. Res. and Ext. Center, P.O. Drawer E, Overton, TX 75684-0290



Methodology and instrumentation improvements have contributed to the increased use of nitrate-nitrogen (NO3-N) analysis of soil extracts for predicting crop N requirements. This research was conducted to determine the accuracy of the modified chromotropic acid (CTA) procedure for NO3-N in saturated Ca(OH)2 extracts of soils. Sixty-two soil sample extracts were analyzed for NO3-N by the CTA method modified to eliminate oxidizing agents, NO-2, and possible interferences from CI- and Fe. Results were compared with the same samples extracted and analyzed by use of the phenoldisulfonic acid method (PDSA). Comparison indicated the two methods were in close agreement (slope = 0.92 and r2 = 0.94). The graph of CTA NO3-N concentration vs. absorbance at 410 nm followed Beer's Law. The modified CTA method, combined with Ca(OH)2 extraction of soil NO3-N, is described in detail and presented as a standard.

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