結萵苣為我國第二大外銷蔬菜，自2013年迄今之年平均外銷量皆超過1萬公噸。惟結球萵苣在溫度偏高環境易出現頂燒症生理病害，常導致棄收損失，而施肥不當被認為是主要因素。為克服該問題本研究以改變氮肥及鉀肥施用量，建立合理化施肥制度，評估可否有效降低該生理病害發生。結果顯示結球萵苣春期作及秋期作適量減少肥料總用量與降低氮/ 鉀肥施用比率之合理化施肥措施，可有效避免頂燒症發生，惟部分試區相同栽培期之平均葉球重顯著低於農民慣行施肥組。蘿蔓萵苣春期作以相同策略合理化施肥亦可有效降低頂燒症發生，但種植不同品種即可避免頂燒症發生。因此本研究證實氮/ 鉀肥施用比率之合理化施肥策略，在降低或避免頂燒症發生具顯著效果。
創新內容：鉀肥為促進結球萵苣葉球發育之重要營養元素，土壤中鉀肥不足易增加結球不良之風險，本研究在結球發育之前仍維持高氮/ 鉀比之肥料施用，但在結球發育之後則改變為低氮/ 鉀比之肥料施用，為合理化施肥之主要應用策略。
Rational Application of Fertilizer in Lettuce to Reduce Tipburn Rate
Hsieh, M. H. and C. W. Lin
Iceberg lettuce is the second largest export vegetable, with an average exceeding 10,000 tons per year in Taiwan since 2013. Romaine lettuce is another kind of vegetable for future exportation. Tipburn is a widespread physiological disorder of lettuce, with the symptom of necrosis on margins and inner leaves of the head. In addition, tipburn is a feature of rapid growth in summer due to high temperatures, which enhance calcium deficiency. Inadequate fertilization is a major cause of calcium deficiency in lettuce. To overcome this problem, we evaluated the effects of fertilization on heading characteristics and tipburn rate by both reducing the nitrogen and increasing potassium after head formation. Using this method, the total amount of applied fertilizer decreased. Results showed that tipburn did not occur in iceberg lettuce with the rational application of fertilizer. However, some trials showed that the yield was lower than that of the conventional fertilizing treatment. In romaine lettuce, the tipburn rate was lower with the rational application of fertilizer than the conventional fertilizing treatment in spring cropping for one cultivar. However, no tipburn occurred in the heat tolerant cultivar with both treatments. This research has proven that reducing the ratio of nitrogen to potassium in the fertilizer is an effective approach to reduce or nullify the tipburn rate in iceberg and romaine lettuce.
What is already known on this subject?
The previous research has proven that supplementary calcium applications by foliar sprays did not effectively increase calcium levels or reduce tipburn and is not recommended for tipburn control. In addition, the disorder is often associated with the application of too much nitrogen in leafy vegetables in Taiwan.
What are the new findings?
This is the first report to evaluate the growth and fruit production of papaya from cuttings in two different facilities, plastic greenhouse and net house in Taiwan.
What is the expected impact on this field?
Crops with even a small percentage of tipburn are often abandoned. Adjusting the ratio of nitrogen/potassium fertilization will be an effective approach to solve this problem.
Key words: Iceberg Lettuce, Romaine Lettuce,
Rational Application of Fertilizer, Physiological Disorder
Accepted for publication: April 11, 2016