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This article in SSSAJ

  1. Vol. 56 No. 3, p. 961-966
    Received: May 23, 1991

    * Corresponding author(s):
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Corn Growth as Affected by Suspension Fertilizers Containing Fluorosilicic Acid

  1. F. J. Sikora ,
  2. J P. Copeland,
  3. E. F. Dillard and
  4. J. R. Burnell
  1. Agricultural Research Dep.
    Chemical Research Dep., National Fertilizer Environmental Research Center, Tennessee Valley Authority, Muscle Shoals, AL 35660-1010



Fluorosilicic acid (H2SiF6) is a suggested additive to suspension fertilizers produced from monoammonium phosphate (MAP) to prevent gelling of the suspension. A greenhouse study was conducted to determine if F added to soil via P suspension fertilizers was detrimental to corn (Zea mays L.) growth. The F sources consisted of reagent-grade NH4F, NH4SiF6, and three P suspension fertilizers. Equilibria constants and measurements with a F- ion selective electrode (ISE) indicated SiF62- dissociates to H4SiO4 and F- at pH > 4 and total F concentration <1 mM. Therefore, only F- needed to be considered as a potential toxic component in soils. At an initial soil pH of 5.8, an 11% dry-matter weight decrease was observed when a suspension fertilizer with 89 g F kg−1 was added to soil to supply a rate of 170 mg F kg−1 soil. An adequate level of F in P suspension fertilizers is between 16 and 23 g kg−1 and this level did not affect corn dry-matter weight with application rates ≤ 32 mg F kg−1 soil. At high soil F-application rates from 30 to 170 mg F kg−1 soil, F was not suspected to be the phytotoxic agent since F concentrations in corn tops were all <0.4 mg kg−1. There was a significant correlation between soil Al and F extracted with water, which led to a hypothesis that decreased corn growth was due to Al phytotoxicity.

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