降低潮汐式淹灌系統之養液溫度允許於較高氣溫環境下栽培波士頓萵苣

Abstract

萵苣為溫帶作物，建議的生長氣溫在23℃或以下，此為台灣夏季需仰賴進口，也是使用人工光型植物工廠栽培時降溫成本高的原因。本研究旨在探討於植物工廠內使用冰水機是否允許波士頓萵苣(Lactuca sativa L.) 於較高的環境溫度下栽培，以利成本的降低。本研究首先探討潮汐式淹灌(Ebb and Flood, E&F)與湛液式養液循環法 (Deep Flow Technique, DFT)對栽培的影響與使用前者時適當的淹灌頻度，其次確立養液有控溫時的氣溫的上限，也對養液穩定控溫對於提高產能的重要性提出栽培結果的證明，也對於傳統育苗方式提出修改的建議，亦證明新育苗方式的優越性。 相同養液溫度 (20℃) 下，氣溫由23升至 28℃可使鮮重提升且降低降溫成本；育成期維持氣溫/液溫為28/23與28/20之組合在收穫鮮重上無顯著影響，但前者之冰水機能耗可減少約 80%，雖空調成本略升，但兩項成本合計，前者比後者約降低 20%。冰水機性能若能提高，兩者的差異會縮小。 本研究建議栽培波士頓萵苣可使用潮汐式淹灌系統，以變頻空調維持室內氣溫於28℃，以冰水機調控養液溫度於23℃，每 15 分鐘啟動一次循環泵浦，漲潮與落潮時間各半，室內二氧化碳濃度維持於 1200 ppm，養液pH 與EC 分別維持於6.0 與1.3 mS.cm-1。播種後育苗期14 天 (LED，PPF 為150 μmol.m-2.s-1，給光24 小時)，育成期21 天(T5 螢光燈管、色溫6500 K、PPF為 200 μmol.m-2.s-1，給光16小時)，總計 35 天可得約 105 g 的鮮重且在為期21 天的育成期中內循環風扇、抽水泵浦、人工光源、空調與冰水機等五種耗電設備合計之能源成本約為 0.122 元g-1。如果循環風扇及人工光源的效率與冰水機的性能係數得以提高，且能將環控室的空間充分運用來提高產能，能源成本可降為約0.048元 g-1。

Taiwan need to import lots of lettuce during the summer season due to the fact that lettuce prefer cool temperature (less than 23℃) to grow. It is also the reason that the plant factory with artificial lighting (PFAL) required lots of energy to remove the heat load. The focus of this study is to investigate on temperature of aerial and root zone environmentof semi-head lettuce (Boston or Butter head lettuce, Lactuca sativa L.). The hypothesis is that by applying chiller to reduce temperature (T) of nutrient solution allows lettuce to be grown at higher temperature, leading to lower energy cost. Two circulating systems include Ebb and Flood (E&F) and Deep Flow Technique (DFT) were investigated. Proper frequency when using E&F also under investigation. When the root zone can be controlled at 20℃, the upper limit of aerial T was found. Some evidence was found regards keeping root zone T stable is very important to get high yield. A modified plug tray was developed to improveyield. At same root zone T, aerial T increase from 23 to 28℃enhanceplant growth leading to increase of fresh weight and reduce energy cost. There is no significant difference on fresh weight when aerial/root zone T are at 28/23 or 28/20. However, the 28/23 treatment reduced the energy consumption of chiller by 80% but increase energy consumption of AC, leading to a 20% reduction of totalenergy consumption in removing heat. If the COP of the chiller can be improved, the difference among two treatments can be minimized. The suggested protocol to grow Boston lettuce is as follows: Ebb and Flood system, chiller and AC system with inverter should be used. The nutrient solution should be controlled at 23℃ using chiller, the UP and DOWN time of recirculating pump can be set at 7.5 minutes each, indoor CO2 concentration kept at 1200 ppm. The pH and EC are 6.0 and 1.2 mS.cm-1. LED is used at Seedling stage, the PPF is 150 with continuous light for 14 days. Tubular florescent lamps with color temperature of 6500 K are used for mature stage production after transplanting. The PPF is 200 and light period is 16 hours per day for 21 days. At DAS equals 35, the expected harvest fresh weight is around 105 g. The total electricity costs of circulating fans, pump, artificial light, AC and chiller for 21 days from transplanting to harvest is 0.122 NT$ per gram of produce. Assuming the efficiency of circulating fans, artificial lamps, COP of chiller and amount of production area can be increased, the energy cost drop to 0.048 NT$ per gram of produce.