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Concentration of NH₃(aq) Required for Incipient NH₃ Toxicity to Seedlings¹

ABSTRACT

Short term experiments with sudangrass (Sorghum sudanensis L.) and cotton (Gossypium hirsutum L.) were conducted in a growth chamber to determine incipient toxic levels of NH₃(aq). Sudangrass seedlings were grown for 14 days in potted Lucedale sandy loam surface soil treated with different rates of N from NH₄OH, (NH₄)₂SO₄, and (NH₄)₂HPO₄. Root growth of cotton seedlings was measured over a 3-day period in split-root experiments in which the upper portion of the root medium was a sandy loam surface soil and the lower portion was either a nutrient solution or a treated soil at various levels of pH and ammoniacal-N. Symptoms of NH₃ toxicity were evident on sudangrass foliage at NH₃(aq) concentration in the soil solution in situ of 0.17mM and greater; there was no evidence of NH₃ toxicity at 0.13mM and less. Symptoms of NH₃ toxicity on cotton roots were evident in soil solutions in situ at NH₃(aq) concentrations of 0.24mM and greater but not at 0.17mM and less; in nutrient solutions, symptoms were evident at 0.22mM NH₃(aq) but not at 0.16mM. The critical concentration for incipient NH₃ toxicity was concluded to be 0.15 to 0.20mM NH₃(aq).

¹ Contribution from Department of Agronomy and Soils, Auburn University Agr. Exp. Sta., Auburn, Alabama. Part of a dissertation submitted by the senior author in partial fulfillment of requirements for the Ph.D. degree.

² Assistant Professor and Professor of Soils, respectively.

Received for publication August 4, 1969. Accepted for publication October 24, 1969.