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The Effects of Phosphorus and Organic Matter on the Concentration of Certain Decomposition Products of Cyanamid in Tobacco Plantbeds¹

ABSTRACT

Field experiments were conducted to determine the effects of superphosphate and organic matter in preventing the accumulation of toxic residues where Cyanamid was used for weed control in tobacco plantbeds on heavy silt loam soils of central Kentucky. Toxic materials or conditions in some cases following treatment with Cyanamid resulted in stunted tobacco seedlings or even death. Soil conditions where seedling injury was noted include soil pH above 8 and ammonium-N concentration exceeding 350 ppm. of soil at seeding time (about April 1). Three-fourths pound per square yard of 20% superphosphate applied with the Cyanamid decreased soil pH and ammonium-N concentration, resulting in improved plant growth. Organic matter decreased soil pH and ammonium-N content, but not until May which is too late for seeding.

In laboratory studies ammonium ions from the decomposition of Cyanamid were more readily leached from the soil when superphosphate or other materials supplying cations had been added. Leaching ammonium-N from the soil resulted in improved plant growth particularly when superphosphate had been used. In greenhouse studies ammonium-N in soil was found to be toxic to tobacco seedings, particularly at high soil pH as occurs when Cyanamid (equivalent to 70% calcium hydroxide) is applied to soil in sufficient quantity to act as a weed control agent.

¹ Contribution from the Agronomy Department, University of Kentucky, Lexington, Kentucky, published with the permission of the Director of the Kentucky Agr. Exp. Sta. Appreciation is expressed to the Agr. Chem. Div. of the American Cyanamid Co. for a grant in partial support of this investigation.

² Formerly Graduate Assistant, Agronomist, Agronomist, and Plant Pathologist, respectively.

Received for publication February 14, 1956. Accepted for publication June 27, 1956.