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Toxicity of Preplant Anhydrous Ammonia to Germination and Early Growth of Corn: II. Laboratory Studies¹

Laboratory experiments were conducted to determine concentrations of NH₃ in soil which are toxic to germination and early root growth of corn (Zea mays L.). In one experiment seeds were germinated in soil uniformly mixed with a given rate of anhydrous ammonia, and in another experiment roots were grown into successive layers of soil containing increasing amounts of NH₃. Germination and early growth was retarded when soil [NH₃ + NH₄⁺)-N concentration reached 944 ppm (pH 3.1) and essentially completely inhibited when it reached 1,628 ppm (pH 9.0). Roots grew through 3-cm layers of soil containing 1,172 ppm (NH₃ + NH₄ ⁺)-N (pH 8.4), but did not grow into layers containing 1485 ppm (NH₃ + NH₄⁺)-N (pH 8.7). Radicles stunted by NH₃ were thicker and had more branching than those of control plants. Root tips which encountered toxic amounts of NH₃ had a brown, scorched appearance.

Key Words: Nitrogen rate • pH • Root growth

² Formerly Graduate Fellow (now Biometrician, Geigy Agricultural Chemicals, Ardsley, New York, 10502) and Professor of Soil Fertility.

Received for publication October 3, 1969.