Soil NO3-N analysis in Ca(OH)2 extracts by the chromotropic acid method
1989
Haby, V.A.
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 Cl- 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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