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The Effect of Ammoniacal Nitrogen on Lettuce (Lactuca sativa) and Radish (Raphanus sativus) Plants¹

ABSTRACT

The relationship of the growth of radish and lettuce plants to pH, NH₃, and NH₄⁺ concentration of the nutrient solution was determined by the use of stepwise multiple regression. Data were collected from plants grown in nutrient solutions with a factorial arrangement of pH (6, 7, and 8) and ammonical nitrogen (0, 10, 20, 30, 40, 60, and 90 ppm of N). The equations obtained for radish and lettuce, respectively, were: Y = 0.479 + 0.00242 X₁³ + 0.0207 X₂ – 0.605 X₃ + 0.0133 X₃³ + 0.0200 X₄ – 0.000746 X₄² + 0.00000551 X₄³ and Y = 5.571 – 0.551 X₁ – 0.00111 X₂³ – 0.605 X₃ + 0.0171 X₃³ + 0.0428 X₄ – 0.000753 X₄² + 0.00000327 X₄³ where Y was grams of dry matter/plant, X₁ was pH, X₂ was H⁺ cone x 10⁷, X₃ was NH₃ conc. (ppm of N) and X₄ was NH₄⁺ conc. (ppm of N). Both equations were significant at the 0.5% level and had R²'s of 0.575 and 0.646, respectively. The response of the two species to pH and H⁺ differed, with radish having its optimum growth at pH 8 and lettuce at pH 7. Their responses to NH₃ and NH₄⁺ were very similar. Growth was reduced as the NH₃ conc. increased and was increased as the NH₄⁺ conc. increased to an optimum level of 17 ppm of NH₄⁺-N for radish and 36 ppm for lettuce.

¹ Contribution from the Department of Vegetable Crops, University of California, Davis 95616. Presented before Div. S-4, Soil Science Society of America, Aug. 17, 1971, at New York, N.Y.

² Staff Research Associate, Assistant Olericulturist, and Professor of Vegetable Crops, respectively.

Received for publication September 27, 1971. Accepted for publication January 6, 1972.