Effect of Grow Medium and Hydroponics Fertilizer on Iceberg Lettuce (Lactuca sativa var. capitata) Cultivation

Iceberg lettuce (Lactuca sativa var. capitata), which belongs to the family Asteraceae, is a globally renowned vegetable, particularly in salads for its crisp texture, mild flavor and perceived health benefits. Iceberg lettuce remains relatively uncommon in Sri Lanka, and the cultivation is confined to cooler climates. However, there are gaps in the recommendations of fertigation protocols for hydroponics Iceberg lettuce cultivation. Therefore, this research was conducted to examine the influence of selected grow media and fertigation options on the vegetative growth and yield of Iceberg lettuce grown in the hydroponics system, “grow bag culture” in controlled environment agriculture. The research was carried out in a soft plastic-covered greenhouse under a mild climatic region in the higher attitudes (in Lindula), Sri Lanka. The experiment design was a single factor Completely Randomized Design (CRD) with six treatment combinations of grow media and fertigation options. Grow media compositions varied with different ratios of topsoil, coco-peat, rice hull charcoal, and compost. Vegetative growth was assessed during 1 to 7 weeks after transplanting (WAT). At the final vegetative stage, leaf area, chlorophyll concentration, leaf nitrogen content, plant fresh weight and dry weights were determined through destructive sampling. Percentage head formation was assessed at 9 – 11 WAT. At harvesting, yield parameters, head fresh weight, dry weight, head diameter and height were assessed. The results revealed significant variations in plant height, leaf parameters, and head characteristics among treatments, highlighting the effect of fertilizer mixtures and grow media on plant growth and head formation. Leaf color and chlorophyll content of Iceberg lettuce leaves indicated a lesser treatment effect. Substrate parameters, including pH, electrical conductivity, bulk density and water holding capacity, varied significantly among treatments and have a notable influence on the final yield. Treatment (T4) (which contained coco-peat: rice hull charcoal: topsoil at 1:1:2 ratio) and fed with half the strength of standard Alberts fertilizer dosage (F2) was the overall best combination for Iceberg lettuce cultivation. The information generated would be useful for revising the farmers’ guide on hydroponics Iceberg lettuce with respect to the selection of grow media and management of fertigation.