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.以蛭石（vermiculite）、泥炭（peat）、珍珠岩（perlite）与森林土（forest soil）按体积比（V/V, 1:1:1）混合作为育苗基质，将木荷（Schima superba Gard. Et Champ.）幼苗定植于点播育苗管（dibbling tubes）中。每周向点播育苗管施加两次不同铵态氮与硝态氮配比的液体肥料，持续5个月；随后通过控水3个月对幼苗进行炼苗处理。 通过定期测定幼苗的形态指标（苗高与地径（root collar diameter））与生理指标（叶绿素含量（chlorophyll）与养分含量（nutrient content））评估幼苗品质，其中生理指标分别于1993年10月（施肥5个月时）与1994年1月（炼苗3个月后，即总培育时长8个月时）完成测定。分别于施肥阶段结束（5个月时）与炼苗阶段结束（8个月时），测定育苗基质的化学性质变化，包括pH值以及氮（N）、磷（P）、钾（K）、钙（Ca）、镁（Mg）的浓度。 施用铵硝混合肥料的幼苗，其早期株高、地径生长表现与生理性状均优于仅施加单一氮源的处理组。在单一氮源处理中，铵态氮对幼苗生长的促进效果优于硝态氮。当仅以硝态氮作为唯一氮源时，幼苗生长缓慢且出现脉间失绿症状，该现象可能由养分失衡引发。 晚秋时节的炼苗处理可促进幼苗体内养分积累，进而改善并提升幼苗品质。由于初始育苗基质的养分含量过低，无法支撑幼苗正常生长，因此点播育苗体系需配合施肥操作。就氮源类型而言，铵态氮会酸化育苗基质，而硝态氮则会碱化基质。为培育健康壮苗，需定期监测点播育苗管内基质的pH值与养分状态变化。