水耕氮肥濃度對荔枝開花及結果的影響

Effect of Nitrogen Concentrations of Hydroponic Media on Flowering and Fruiting of Litchi (Litchi chinensis Sonn.)

秋末冬初荔枝持續生長的營養枝條尚未花芽創始，而起因常被認為與水份充分供應有關，但氮素溶解於水而為植株所吸收亦會導致此種現象。荔枝著果率低的原因也常被推測與氮素供應有關。為釐清水份與氮素對荔枝開花結果的影響並準確控制氮素供應，本研究利用水耕栽培系統對‘黑葉’高壓苗進行0mg/l（對照），14mg/l及42mg/l的氮素濃度處理。開花表現以14mg/l處理最佳，每株開花枝條比率約為其他處理的兩倍；且第一支花穗至最後一支花穗萌出期間隔最短，花穗抽出最為整齊；花穗長度亦顯著較42mg/l及0mg/l處理為長。然而在花穗形態方面，僅0mg/l處理為純花穗。結果表現以14mg/l處理最佳，不管是在幼果期（果徑約為1公分）或成熟果階段，均有最高的結果枝條比率，42mg/l處理初期結果枝條比率很差，0mg/l處理則在果實發育階段落果嚴重。氮素會直接影響荔枝開花與結果的表現，若氮素管理得當並有一段適當的低溫，則即使荔枝處於高的水份狀態亦有花芽創始。對荔枝花芽創始而言，最適當的氮素處理濃度應較14mg/l略低，但14mg/l氮素處理對荔枝花穗發育及結果較為適當。著果期葉片分析的資料顯示，隨著處理氮素濃度的增加，葉片內氮與鈣的含量隨之增加，但可溶性醣、磷、鎂、鋅的含量卻呈下降的趨勢，鉀、鐵含量以0mg/l處理最高，錳含量似不受處理中氮素濃度的影響，而銅含量則以42mg/l處理最高，澱粉含量以14mg/l處理最高。這些結果顯示足夠的碳水化合物應是14mg/l處理結果率較高的原因之一。

Air layered litchi plants of cv. Haak Yip were grown in hydroponic solutions containing 0 (control), 14, 42 mg/l nitrogen to study the effect of nitrogen concentrations on flowering and fruiting. At 14 mg/l N, the percentage of flowering shoots per tree was about two fold when compared with the other two treatments and resulted in the longest average length of panicles. The panicles grown from 14 mg/l and 42 mg/l N treatments were leafy. At 0 mg/l N, however, the panicles, though shorter then the usual length, were leafless, the result of normal flower initiation. Fruiting was best at 14 mg/l N treatment, also. Whether in young or mature fruit stage, the percentage of fruiting shoots was highest at 14 mg/l N treatment. Poor fruit setting occurred at 42 mg/l N. At 0 mg/l N, heavy fruit drop occurred during fruit development stage. The result of this study indicated that nitrogen per se did have direct influence on the processes of flowering and fruiting in litchi. The most suitable nitrogen concentration for flower initiation might be lower than 14 mg/l. However, for flower development and fruiting, 14 mg/l nitrogen supplied might be suffient. As concentrations increased, N Ca contents increased in leaves but soluble sugar P Mg Zn were in the opposite direction. K Fe were highest in 0 mg/l N. Cu was highest in 42 mg/l N. No significant difference in Mn content among three treatments. Starch content was highest in 14mg/l N treatment. Adequate carbohydrate might be one of reasons why 14 mg/l N treatment got better fruit set and development.