氮肥施用量與採收前光照處理對設施栽培圓葉萵苣生長與硝酸鹽含量之影響

Effects of Nitrogen Fertilizer Amounts and Lighting Treatment before Harvest on Growth and Nitrate Content of Lettuce (Lactuca sativa) under Protected Structures

蕭巧玲(Chiao-Ling Hsiao) ； 何佳勳(Chia-Hsun Ho) ； 楊純明(Chwen-Ming Yang)

《台灣農業研究》 70卷4期 (2021/12) Pp. 299-309

https://doi.org/10.6156/JTAR.202112_70(4).0006

摘要

葉菜類蔬菜對於硝酸鹽的蓄積除了遺傳因子控制之外，栽培過程中的氮肥管理及光照亦是2項影響植體硝酸鹽含量變化原因。本研究於行政院農業委員會農業試驗所農場之簡易塑膠布設施內進行，探討於4種氮肥處理下，在採收前以輔助人工光源調節設施內光環境對圓葉萵苣「明豐3號」（Lactuca sativa cv. 'Ming Feng No. 3'）生長及硝酸鹽含量之影響。試驗係以發光二極體（light-emitting diode; LED）及省電燈泡（energy-saving light bulb; ELB）為人工光源，計有藍光LED（LED_B）、紅光LED（LED_R）、藍紅光LED（LED_(3B:1R)）、紅藍光LED（LED_(3R:1B)）及省電燈泡（ELB）等5種，另以不照光（no light）為對照，共計6種光照處理。試驗結果顯示，在30 kg N．ha^(-1)及203 kg N．ha^(-1)兩種較低氮肥處理下圓葉萵苣植體具有較低硝酸鹽含量，當氮肥提高至346 kg N．ha^(-1)及376 kg N．ha^(-1)雖可獲得較高生長表現（包括株高、地上部鮮重及葉數），但亦使植體蓄積較多硝酸鹽。此4種氮肥處理植株於採收前6 h進行不同光照處理時，經與不照光處理比較，可發現4種氮肥處理搭配輔助光照皆有降低硝酸鹽含量之效果。其中，在376 kg N．ha^(-1)氮肥處理下，以LED_B及LED_(3B:1R)可使硝酸鹽分別降低14%及23%。又將376 kg N．ha^(-1)氮肥處理植株於採收前4 h及6 h，分別以LED_B、ELB進行光照處理，結果顯示皆可減少圓葉萵苣植體硝酸鹽，且兩處理間無顯著差異。經分析葉片淨二氧化碳交換速率（視同光合作用速率）與植體硝酸鹽含量間之相關性，結果顯示兩者間呈現顯著的二次曲線關係，即硝酸鹽含量隨著光合作用速率的升高而呈曲線型下降；當光合作用速率提高至4.5 μmol CO_2 m^(-2) s^(-1)以上時，植體硝酸鹽含量可維持於3,000 mg kg^(-1)（3,000 ppm）以下。綜合本研究結果，顯見氮肥施用量將明顯影響圓葉萵苣植體生長量及硝酸鹽含量，若於採收前進行額外輔助光照處理，將可獲得調降硝酸鹽含量效果，而於相近效果下，則以4 h光照時間較6 h者可節省用電成本。

關鍵字

硝酸鹽 ； 葉萵苣 ； 光環境 ； 發光二極體 ； 氮肥

並列摘要

Accumulation of nitrate content in leafy vegetables is affected by not only genetic factors but also nitrogen (N) fertilization and lighting conditions during plant growth. Pot experiments were conducted under a protected structure covered with plastics in an experimental farm located in the Taiwan Agricultural Research Institute. Four amounts of N fertilizers were applied during growing period of lettuce (Lactuca sativa cv. 'Ming Feng No. 3'). Supplemental lighting was provided by different artificial light sources at 4 or 6 h before harvest. A total of 6 supplemental lighting treatments using light-emitting diode (LED) and energy-saving light bulb (ELB; a compact fluorescent lamp) were used as light sources and plants treated with no light as a control. Results showed that plants treated with N fertilizer at a rate of 30 and 203 kg N．ha^(-1) had comparatively lower nitrate contents than those of higher N inputs. Increasing the amount of N fertilizer promoted plant growth. Plants after being applied with higher N rates (346 and 376 kg N．ha^(-1)) showed better growth, in terms of traits of plant height, aboveground fresh weight and leaf number, however, higher N generated a greater nitrate accumulation. The contents of nitrate were compared in lettuce plants after being treated with 6 h of supplemental lighting of blue light LED (LED_B), red light LED (LED_R), 3 blue/1 red mix LED (LED_(3B:1R)), 3 red/1 blue mix LED (LED_(3R:1B)), or ELB before harvest. The results indicated that a lower nitrate content was found in plants treated with supplemental lighting prior to harvest in all 4 nitrogen application rates, compared to that of plants without light treatment. At the highest nitrogen rate of 376 kg N．ha^(-1), the nitrate content reduced by 14% and 23% with the treatments of LED_B and LED_(3B:1R), respectively. No difference was found among plants treated with 4 h and 6 h of supplemental lighting of either LED_B or ELB in plants applied with 376 kg N．ha^(-1). The relationship between photosynthetic rate (i.e., net CO_2 flux) and nitrate content was curvilinear, in which nitrate content was decreased curvilinearly with the increasing of photosynthetic rates in leaves of lettuce. At photosynthetic rate greater than 4.5 μmol CO_2 m^(-2) s^(-1), nitrate content was maintained in less than 3,000 mg kg^(-1) (3,000 ppm). Accordingly, this study demonstrated the effects of nitrogen fertilization on nitrate content and growth performance in lettuce. To further reduce nitrate content at time of harvesting, a supplemental lighting by artificial light sources for 4 h prior to harvest would be as effective as that of 6 h to save energy cost.

並列關鍵字

Nitrate ； Lettuce (Lactuca sativa) ； Light environment ； Light-emitting diodes (LEDs) ； Nitrogen fertilization