青楓及樟樹容器苗生產關鍵技術之探討

景觀樹木在園藝產業上具有相當重要之地位，其生產潛力相當可觀。常見的苗木生產方式分成田間生產和容器生產。田間生產分為裸根移植苗和土球包裹苗，出貨前需要斷根、修枝，常造成苗木生長勢衰落和存活率低等問題。為了改善苗木品質，容器育苗技術為臺灣未來景觀綠化應用的發展趨勢。容器生產又分為實生型容器苗和容器化苗，生長迅速、節約土地及成活率高等為其優點，但根系限縮容器內，為了確保容器苗的正常生長，需要在其生長過程中適時適量補充水分和養分。實生型容器苗受容器效應影響，生長速度較田間生產慢；容器化苗地植時不受容器效應影響，生長速度較快，惟臺灣苗木業者移植前常過分修枝，並於地上部地下部尚未平衡時出售，致使苗木品質和存活率沒有明顯上升。本試驗擬就灌溉和氮肥試驗，設法加快小苗培育的速度，再就容器化苗移植前的修剪作探討，期能加快生產進程並提升臺灣的苗木品質。灌溉試驗以2種介質和4種不同灌溉時機作為處理。介質分別是田土和田土加椰纖(v/v=1:1)，兩介質保水力不同，灌溉頻度亦不同(S>S+C)；灌溉時機分別是介質含水量降低至15%、25%、35%和45%時進行灌溉。結果顯示，青楓冬季生長受阻，且介質含水量維持15%和25%以上的青楓冬季落葉後無法重新長葉；樟樹則無明顯休眠期。青楓和樟樹之介質含水量降低至35%時為最佳灌溉時機，約為田間容水量的65%，此時青楓和樟樹在株高、莖徑、冠幅和分枝數有較好的表現，樟樹的地下部表現亦佳，惟樟樹應斟酌使用追肥，避免植物生長旺盛或灌溉淋洗導致介質肥份不足，進而造成生長速度趨緩、苗木品質變差。氮肥試驗每週施用一次氮肥，氮素濃度分別是0、4、8、16、32 mM。結果顯示，氮肥濃度對正值落葉期的落葉樹種青楓影響不大，而常綠樹種樟樹則是一年四季皆有影響。樹種不同對氮肥濃度的喜好也不同，氮肥濃度過低造成苗木品質低弱，氮肥濃度過高則造成生長延緩，地下部衰弱。青楓建議施用的氮肥濃度為4-8 mM左右，樟樹則是較需要肥份的作物，建議濃度為8-16 mM。如欲增加分枝數，則可提高施用的氮肥濃度，青楓建議使用8-16 mM，樟樹則可提高至16-32 mM。修剪比例試驗則分為移植前重修剪(移除90%枝葉)和移植前輕修剪(僅移除枯枝、病枝)兩處理。結果顯示，輕修剪處理於試驗初期面臨較嚴重的乾旱逆境，存活率較低，但脫離乾旱逆境後有較佳的新根發展。試驗結束時，輕修剪處理的莖徑變化和光合作用皆優於重修剪處理，有利於移植後的再生長。建議移植前進行適當的微量修剪，雖需較繁複的管理，但後續的新根發展和苗木品質較佳，有助於對抗栽植地的逆境。綜合上述結果，青楓於介質含水量低於35%時灌溉，並施以氮素濃度4-8 mM的養液，欲增加分枝數則提升濃度至8-16 mM；樟樹於介質含水量低於35%時灌溉，並施以氮素濃度8-16 mM的養液，欲增加分枝數則提升濃度至16-32 mM，且應斟酌使用堆肥，避免因頻繁灌溉或生長旺盛造成營養缺乏。移植前應進行適當的微量修剪，克服乾旱逆境後，可擁有較佳的新根發展和苗木品質。

關鍵字

容器苗；容器化苗；灌溉；氮肥濃度；移植；修剪

並列摘要

Trees play important role in landscape, and thereby the tree production for landscaping owns great commercial values. Conventional tree nurseries grow trees in field and in pots. Due to the fact that the transplantation of the field-grown trees often accompany with a great loss of root and increase vulnerability to post-transplantation shocks for trees, the techniques of producing high quality containerized trees will become the major option for Taiwanese nurseries in the future. Containerized tree can be categorized into container-grown seedling and containerized seedling. These two types of seedlings have the advantages of fast growing, land area saving and high survival rate, but since their root system is restricted by container, proper irrigation and nutrient should be supplied routinely for maintaining normal growth and development. The container-grown seedling is started from container, which limited the tree growth by the container effect, consequently the growth rate is slower than field-grown trees. The containerized tree seedlings are originally grown in field, so the growth rate is faster than the container-grown seedlings. However, Taiwanese tree nurseries often heavily prune seedlings before transplanting the field-grown seedlings into container as well as the containerized seedlings are sold when their underground and upper-ground part have not reach a balance yet. This results in low tree quality and survival rate. This study applied various irrigation and nitrogen fertilization practices to accelerate the tree seedling growth, and investigated the pruning methods before transplantation to container, hoping to improve the speed and quality of tree production in Taiwan. The irrigation experiment employed two different growth media and four different irrigation timings. The media used were field soil (S) and a equal-volume mixture of field soil with coconut fiber (S+C). The timings of irrigation were set at the media water content dropped to 15%, 25%, 35% and 45%. The result showed that the growth of green maple ceased in winter, and the green maple with the irrigation timing at 15% and 25% soil water content did not flush out new leaves after leaf abscission in winter. Camphor trees did not exhibit an evident dormancy. Green maple and camphor tree had best growth performances characterized by tree height, stem diameter, canopy width and branching numbers when irrigated at the timing of 35% soil water content, which was 65% of the field water capacity. Adding additional fertilizers should be cautious on camphor trees to avoid over-growth and over-irrigation that could even reduce the nutrient level in soil. The nitrogen fertilizer was applied weekly with the concentrations of 0, 4, 8, 16 and 32 mM. The result showed that the different concentrations of nitrogen did not have evident effect on the green maples growth during their defoliation period, but had significant effect on camphor tree growth year round. Different tree species had different optimum nitrogen concentration. The suggested nitrogen concentration level for green maple was 4-8 mM and for camphor tree was 8-16 mM. When increasing branching numbers became a priority, the suggested nitrogen concentration was 8-16 mM for green maple and 16-32 mM for camphor tree. The pruning experiment employed heavy pruning (90% shoot removal) and light pruning which merely removed dead branches and infected branches. The result showed that the lightly-pruned trees suffered from more severe drought stress in the beginning of the experiment than the heavily-pruned tree, but once they overcome the stress, the root establishment was better than the heavily-pruned trees. On the other hand, the secondary growth and photosynthesis of the lightly-pruned tree were better than the heavily-pruned trees, which favored the growth after transplantation. In shorts, although light pruning required more labor works and better management than heavy pruning, its created higher tree quality and decreased the vulnerability to stresses. Above all, to create the best tree quality of green maple, it was suggested to be irrigated when the soil water content dropped below 35%, with 4-8 mM nitrogen fertilization for regular growth and 8-16 mM for more branching numbers. To create the best quality of camphor, the trees was suggested to be irrigated when the soil water content dropped below 35%, with 8-16 mM nitrogen fertilizer for regular growth and 16-32 mM for greater branching numbers. Adding additional fertilizers shall be cautious to avoid over growth or nutrient insufficiency. Light pruning is suggested before transplantation. The light-pruned trees should be well-managed to overcome drought stress, and the consequent tree quality was higher than heavily-pruned trees.