養液溫度對水耕網紋洋香瓜生長與發育之影響

Abstract

甜瓜(Cucumis melo L.)為世界重要一年生草本蔬菜作物。植物根部對溫度敏感，溫室水耕網紋洋香瓜(Cucumis melo L. var. reticulatus)有夏季根溫過高問題，且水耕植株根部對養分與水分的吸收不受限制也不易調節。相較於降低溫室整體環境溫度，單純降低水耕植株根部溫度之範圍較小、消耗能源較少，而更經濟實用。快速降低根溫可在不改動養液配方下，減少根部對水分的吸收。因根溫控制對湛水式水耕網紋洋香瓜果實品質之影響於國內外均尚無完整研究，故本論文於全年三季分別觀察養液控溫處理對網紋洋香瓜 ‘Earl's Favorite’ 地上部各生理參數之影響，以確定各季最佳果實品質之適當根溫；並於春夏作與夏秋作之果實肥大期與成熟期進行短暫低根溫處理，確認改善果實品質之效果，亦探討短暫低根溫處理與NaCl處理間之差異。以湛液式(deep flow technique, DFT)水耕栽培系統與修改之沈養液配方栽培 ‘Earl’s Favorite’，利用水冷式冷水機、加溫棒、循環水系統、不鏽鋼蛇管進行降溫或升溫處理。結果顯示，於春夏作與秋冬作維持根溫在28～31℃可使根系生理機能正常，抵禦地上部氣溫逆境，增進果實品質與消費者購買意願。夏秋季栽培維持根溫在此範圍使果實過重、過大，並破壞網紋美觀。故進一步研究控制水分吸收。春夏季與夏秋季栽培時，於果實肥大期與成熟期短暫低根溫處理可以限制水分吸收，使果實重量維持在適售範圍，但品質不佳；而春夏季處理短暫低根溫差-5℃兩天或三次NaCl皆較對照組提升果實品質，而此兩處理之間，除可溶性固形物外，其他品質上並無差異，且果實甜度與鹹度、以及消費者購買意願亦無差異。故短暫低根溫溫差-5℃兩天處理並無比NaCl處理更佳之效益，而NaCl處理可提升果實品質，且未增加果實鹹味。

Melon (Cucumis melo L.) is an important annual herbaceous vegetable crop. The roots of melon plants are sensitive to temperature. Hydroponic melon grown in the greenhouse suffers from high root temperature in summer. Nutrients absorption and water uptake by roots of hydroponic plants are hard to be limited and controlled. Compared to lowering ambient temperature in the greenhouse, simply lowering root-zone temperature of hydroponic plant is more economical and practical owing to smaller range and less energy consumption. Rapidly lowering the root temperature reduces water uptake and nutrient absorption without changing the formula of nutrient solution. The effect of controlling root-zone temperature of deep flow technique (DFT) hydroponic netted muskmelon (Cucumis melo L. var. reticulatus) on fruit quality is not studied worldwide. The present thesis aimed at the effect of controlling root-zone temperature on various physiological parameters to determine the suitable root temperature for the best fruit quality of netted muskmelon ‘Earl’s Favorite’ in 3 seasons separately. Short low root-zone temperature treatments at the fruit enlargement and maturation stages in spring-summer and summer-autumn seasons were also conducted to confirm the improving effect on fruit quality. In addition, the difference between short low root-zone temperature treatment and NaCl treatment was also investigated. ‘Earl’s Favorite’ was cultivated with DFT hydroponic system and previously modified Shen nutrient formula. Nutrient temperatures were controlled by water-cooled chiller, heating rod, circulating water system and stainless steel coil. The results showed that in spring-summer and autumn-winter seasons controlling the root-zone temperature at 28~31°C could maintain the normal physiological function of root system, tolerate the temperature stress aboveground and ultimately increase fruit quality and consumer purchase intention. However, in summer-autumn season, maintaining the root temperature in this range caused the fruits too heavy and too large, and the netting deterioted. So further study on controlling water uptake was conducted. In spring-summer and summer-autumn seasons, short low root-zone temperature treatment could limit water uptake and keep the fruit weight within salable range but with poor fruit quality. When netted muskmelon was treated with temperature difference of -5°C for two days or 3 times of NaCl in the spring-summer season, both treatments showed higher fruit quality compared with the control. While between these 2 treatments, non-significant difference was shown in most items of fruit quality and consumer purchase intention. Hence short low root-zone temperature treatment did not have better effect than 3 times of NaCl applications which improved fruit quality and did not increase the salty taste of fruits.