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

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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.
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