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This article in AJ

  1. Vol. 70 No. 2, p. 295-298
    Received: Apr 23, 1977

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Comparative Toxicity of Nitrapyrin and 6-Chloropicolinic Acid to Radish and Cucumber under Different N Nutrition Regimes1

  1. Diane J. Sander and
  2. A. V. Barker2



Nitrapyrin, 2-chloro-6-(trichloromethyl)pyridine, is a nitrification inhibitor used to maintain fertilizer N in the ammonium form in order to reduce leaching and denitrification losses of N from soil. Nitrapyrin and its metabolite, 6-chloropicolinic acid, are phytotoxic, and ammonium injury to plants is frequently greater when nitrapyrin is added to the soil. The objectives of this study were to investigate the phytotoxicity of nitrapyrin and 6- chloropicolinic acid under different N nutrition regimes (15 meq/liter of NO3-N. NH4-N, or NH4-N with pH buffering to 7 with CaCO3) and to see if either compound affected the phytotoxicity of ammonium ions. Radish (Raphanus sativus L. ‘Cherry Belle’), and cucumber (Cumumis sativus L. ‘SMR-18’), were grown in sand culture in a greenhouse. Plant nutrients and the inhibitors (10 ppm) were supplied in solution, and CaCO3 was mixed with the sand. Radishes were uninjured by nitrapyrin or 6-chloropicolinic acid. Ammonium-N (15 meq NH4-N/ liter) nutrition produced toxicity symptoms in radish and decreased root yields. Buffering of pH partially corrected the ammonium toxicity to roots and fully corrected it for shoots. Nitrapyrin and 6-chloropicolinic acid restricted cucumber growth. Visible symptoms of nitrapyrin toxicity appeared as constricted zones on the stem base and as white areas on petioles of first true leaves. Toxicity of 6-chloropicolinic acid appeared as curling on younger leaves and marginal burn on older ones. Cucumber growth was restricted by ammonium-N nutrition. Buffering of pH corrected the toxicity of ammonium-N and picolinic acid but not that of nitrapyrin.

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