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Agronomy Journal Abstract -

Automated Determination of Chlorides in Soil and Plant Tissue by Sodium Nitrate Extraction1


This article in AJ

  1. Vol. 76 No. 3, p. 371-374
    Received: May 9, 1983

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  1. T. P. Gaines,
  2. M. B. Parker and
  3. G. J. Gascho2



An accurate, precise, and fast automated method for determining Cl in large numbers of soil and plant samples was needed in the confirmation that Cl toxicity was the cause of leaf scorch, a new disorder of soybean [Glycine max (L.) Merr.] grown on Atlantic Coast Flatwoods soils of Georgia. The method described involves the use of 0.1 M NaNO3 as an extractant for soil and plant tissue samples with Cl being determined colorimetrically on a Technicon Auto-Analyzer. Several studies including evaluation of extractants, shaking time, soils of varying texture, tissues of plants, and varying amounts of sample- and carbon-weights were conducted to compare the proposed method with available methods of Cl analysis. Recovery of Cl after KCl was added to soils was 97% using 0.1 M NaNO3. Chloride concentrations in water and 0.1 MHNO3 soil extracts could not be accurately determined due to turbidity and acidity interferences. Recovery of Cl from soils by the NaNO3 extractant was not aflected by shaking times of 5, 10, and 20 min. Ten days after soils were incubated with KCI the NaNO3 extractant was as effective in extracting CI(84%) as Mehlich No. 1 double acid extractant was in extracting K (86%). The NaNO3 extractant was equally effective in extracting Cl from sandy clay, sandy clay loam, loamy sand, and sand soils. Most of the error in the method was in the extraction procedure rather than in the measurement by the Auto-Analyzer. The NaNO3 extraction method compared favorably to the longer ashing method for leaf samples, but ashing was more accurate for seed samples. Fifty samples per hour can be determined by the Auto-Analyzer.

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