全人工光型植物工廠中低鉀、低鈉與低硝酸鹽水耕栽培萵苣之研究

Cultivating Hydroponically Grown Lettuce with Low Potassium, Sodium and Nitrate Concentration in Plant Factory with Artificial Lighting

本研究以香波綠萵苣（frill-ice lettuce）為栽培對象，選定每百克萵苣鮮重之鉀、鈉與硝酸鹽含量上限分別為80，30與250 mg，三項數值均低於上限值者以三低萵苣稱之。本研究在台大植物工廠內使用湛水式水耕系統（Deep Flow Technique, DFT）進行栽培，使用LED為人工光源，平均光量為200μmol．m^(-2)．s^(-1)、光期16小時、日夜溫25/20℃、二氧化碳濃度1200μmol．mol^(-1)。對照組為栽培全程（由播種至採收42天）使用1.5倍強度（EC=1.2 mS．cm^(-1)）的山崎養液萵苣配方，其它三個處理組分別為採收前三、前兩與前一週更換為無鉀配方（以硝酸銨取代山崎養液配方中的硝酸鉀），第五個處理組為採收前兩週將養液更換為清水。結果顯示，對照組鮮重為108.67 g，每百克鮮重之鉀離子含量為365.52 mg。清水處理組僅降低鉀含量約48%，仍遠高於選定的上限值且鮮重也降低69%，此處理方式在商業上為不可行，不僅鉀離子未達標，鮮重也損失過大。採收前兩週進行無鉀養液處理組鮮重為56.20 g，每百克鮮重之鉀離子含量約為36.96 mg。本研究開發出兩種栽培流程，分別可生產生食用與熟食用的三低萵苣，前者可降低鉀含量約90%，但鮮重約降低48%；後者可降低鉀含量約46%，鮮重降低約20%。 Patients with end stage renal disease (ESRD) often experience hyperkalemia, a condition that requires limiting their dietary intake of potassium. As fresh vegetables are the largest source of potassium intake for people, it is vital to produce vegetables with low potassium concentration for ESRD patents. Prior studies was conducted in Japan about low-potassium vegetable production demonstrated that some products are low in potassium but high in sodium. The objective of this study was to develop an operating procedure which would enable the growth of low potassium, low sodium and low nitrate lettuces without scarifying too much of the fresh weight. The frill ice lettuces were grown in a plant factory with artificial lighting (PFAL) using hydroponic system with deep flow technique (DFT). The lettuces were grown in an environment with average light intensity of 200．μmol．m^(-2)．s^(-1), light period of 16 hours, day/night temperatures of 25/20°C and carbon dioxide concentration of 1200 μmol．mol^(-1). The Yamasaki solution for lettuce with 1.5 strength (EC=1.2 mS．cm^(-1)) was used from sowing to harvest (totally 42 days) as the control group. Other three treatments were to replace potassium nitrate with ammonium nitrate three, two and one week before harvest and the fifth treatment was to replace nutrient solution with tap water two weeks before harvest. Results showed that the potassium concentration and fresh weight for the control group is 365.52 mg per 100 g fresh weight and 108.67 g per plant, respectively. The tap water treatment was not recommended because the loss of fresh weight was too big and the reduction of potassium concentration was not accepted. Two cultural procedures were recommended and they are for ＂ready to eat＂ and ＂eat after cook＂ lettuces. This study showed the potential of producing low potassium (＜ 80 mg per 100 g fresh weight), low sodium (＜ 30) and low nitrate (＜ 2500 ppm) frill-ice lettuce in a PFAL.