Studies on the Growth of Citrus Seedlings with Different Forms of Nitrogen in Solution Cultures.

Abstract

Freshly emerged pineapple sweet orange seedlings were successfully grown for periods up to 15 months in aerated solutions with N supplied as (NH4)2 SO4. Such plants were healthy and essentially equal to others grown with all or part of their N supply from NO3 provided the development of excess acidity was prevented. Somewhat greater root development occurred when NO3 was the source of N. When the solution pH was maintained near 4-0, growth was reduced irrespective of form of N. Greater reduction in growth occurred in the NH4 cultures than in the NO3 cultures; however, greater acidity also existed due to the opposite trends in pH shifts as a result of absorption. The reduction in growth was paralleled by a reduced concentration of base cations in the foliage. Reduced K, Ca and Mg concentrations were associated with increased H-ion concentration, while the shift from NO3 to NH4 reduced the K and Ca only. It seems probable that these effects are largely coincidental with and not the primary cause of reduced growth under high acid conditions.