Effects of Nitrogen Sources on Seedling Growth and Quality of the Chinese Guger Tree (Schima superba Gard. et Champ.)

Seedlings of Schima superba Gard. Et Champ. were raised in dibbling tubes containing a mixed medium of vermiculite, peat, pearlite and forest soil (V/V, 1:1:1). Liquid fertilizers composed of different ratios of ammonium and nitrate were applied to the dibbling tubes twice a week for five months and then the tubes were hardened by reducing water supply for three months. Seedling quality was determined according to its morphological attributes (seedling height and root collar diameter) measured periodically, and physiological attributes (chlorophyll and nutrient content) measured in October 1993 (at five months) and January 1994 (at eight months). Changes in the chemical properties of the medium (pH and concentration of N. P. K. Ca, and Mg) were examined at the end of the fertilization (at five months) and hardening (at eight months) periods. The early growth in height and root collar diameter, and physiological attributes of seedlings fertilized with a combines nitrate and ammonium mixture appeared better than those with only a single nitrogen form alone. Of the single nitrogen forms, ammonium had a better effect on growth than nitrate. When nitrate us was as the sole nitrogen source, seedlings grew slowly and showed interveinal chlorosis, which may have been induced by a nutrient imbalance. In late autumn, hardening induced increased accumulation of nutricnts which sould benefit and improve seedling quality. Since the nutrient content of the medium was too low to support seedling growth, fertilization was required for the dibbling tube system. As to nitrogen sources, ammonium acidified the medium, while nitrate alkalized the medium. For raising healthy seedlings, the medium in dibbling tubes should be monttored for changes in pH and nutrient status.