| Summary: | 碩士 === 國立臺灣大學 === 生物產業機電工程學研究所 === 99 === This study aims at developing protocols for the production of three types of hydroponic grown lettuce with low nitrate content in plant factory. The initial goal is to produce lettuce with more than 100 g in fresh weight and lower than 2000 ppm in nitrate content which agree with EUs regulation.
Two types of nutrient solution and three levels of concentration were investigated for the production in seedling stage. For other production stages, besides types of nutrient solution and levels of concentration, various daily light integral (DLI) and light quality were investigated especially for the last 7 days before harvest, which termed ‘de-Nitrate’ stage.
Five batches of experiments on Boston lettuce (Latuca sativa var. Capitata)were conducted and in total 21 treatments were investigated. Among these 21 treatments, there are 13, 5 and 2 treatments capable of producing Boston lettuce in 35 days with upper part fresh weight greater than 100 g, with nitrate lower than 2500 ppm and with nitrate lower than 2000 ppm, respectively. Also, there are 5 treatments capable of producing products with fresh weight greater than 100 g and with nitrate lower than 2500 ppm. Among these 21 treatments, there is only one treatment meet the preset goal of this study. The treatment codes in three production stages (based on planting density) were listed below:
Stage 1 (From seeding to day 14): N1_E1.2_F230_D20
Stage 2 (From day 15 to 28): N1_E1.2_F270_D16
Stage 3 (From day 29 to 35): N1_E0.2_LRB270_D17
A experiment on loose leaf lettuce (Lactuca sativa var. crispa)was conducted and in total 2 treatments was investigated. Both treatments were capable of producing products with fresh weight greater than 140 g and with nitrate concentration lower than 1800 ppm. But one treatment encountered tip burn problems. The one without tip burn was proposed. Treatment codes in three production stages were listed below:
Stage 1 (From seeding to day 14): N1_E1.2_F230_D20
Stage 2 (From day 15 to 28): N1_E1.2_F230_D13
Stage 3-1 (From day 29 to 35): N1_E0.2_LRB230_D13
Stage 3-2 (From day 36 to 42): N1_E0.2_LRB270_D17
An experiment on green oak leaf lettuce (Lactuca sativa L. var. crispa cv. green oak LS-049)was conducted and in total 2 treatments was investigated. Both treatments were capable of producing products with fresh weight greater than 140 g. but only one treatment with nitrate concentration below 1100 ppm, much lower than the other treatment, which is higher than 4000 ppm. The proposed treatment codes in three production stages were the same with previous crop listed above.
In summary, using red and blue LED as light source with DLI at 17 or 13 mol/m2/day, using Yamazaki formula at EC equals 0.2 mS/cm for the last 7 days before harvest, the nitrate concentration of three types of lettuce can be kept below 2000 ppm, and the fresh weight of upper part of Boston lettuce can be kept greater than 100 g and leaf lettuce and green oak leaf lettuce can be kept greater than 140 g.
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