Shallow Aggregate Ebb-and-Flow System for Greenhouse Lettuce Production

摘要

A novel soilless technique for the production of lettuce was developed and evaluated for its viability for ornamental greenhouse growers adapting their ebb-and-flood irrigation benching systems to diversify into growing lettuce, without having to purchase the conventional nutrient film technique (NFT) or deep flow technique (DFT) hydroponic systems. The experimental design was a three by four factorial, with three treatments for aggregate depth (19, 38, and 57 mm) and four treatments for irrigation frequency (once every 1, 2, 4, or 8 hours), for a total of twelve treatment combinations. Each treatment was replicated three times in a randomized complete block treatment design. Prior to each replication, seeds of 'Rex' lettuce were planted in phenolic foam sheets and grown until the emergence of four true leaves on each seedling was noted. Sixteen seedlings were then transplanted into each shallow-aggregate ebb-and-flood (SAEF) system. After 42 days, shoot diameters and chlorophyll content were measured and shoots were harvested, weighed fresh, and then dried to acquire their dry weights. Aggregate depth and irrigation frequency were demonstrated to significantly affect lettuce shoot diameter, chlorophyll content, as well as fresh and dry weight. The treatment with 38 mm of aggregate and irrigated every 2 hours resulted in significantly higher average fresh and dry shoot weights than all other treatments. The treatment with 57 mm of aggregate and irrigated every 8 hours resulted in significantly lower average fresh and dry shoot weights than all other treatments as well as the lowest average shoot diameters. Chlorophyll content was significantly higher in the 57 mm treatment irrigated every 8 hours than in all other treatments, and the 19 mm treatments irrigated every 1 and 2 hours produced the lowest average chlorophyll content. There were no significant differences in shoot fresh weight, dry weight, chlorophyll, or diameter among the plants grown in optimal SAEF, DFT, or NFT treatments. Therefore, the SAEF system can be considered a viable alternative to produce uniformly marketable lettuce shoots reliably.