Evaluation of Soilless Substrates for Organic Lettuce Production with Water-soluble Organic Fertilizers

Consumer demand for organic vegetables has been increasing over the decades and containerized production with soilless substrate has been gaining attention recently due to ease of integration with controlled environment agriculture (CEA). However, limited research has evaluated organic substrates under liquid organic fertilization. This study evaluated six organic substrates: peatmoss with perlite (peat-perlite), coir, wood fiber (WF), wood fiber–coir mix (WF-coir), fine-grade pine bark (FG bark), and medium-grade pine bark (MG bark) for lettuce ( Lactuca sativa L.) production under molasses-based liquid organic fertilization (Expt. 1). The second experiment evaluated peat-perlite, coir, WF-coir, and FG bark as substrates for lettuce grown in larger containers with a similar fertigation protocol amended with calcium chloride. Biomass production, nutrient availability, and leaf nutrient content were measured. In Expt. 1, head fresh (112.8 ± 6.2 g) and dry weights (6.3 ± 0.3 g) did not differ among lettuce grown in peat-perlite, coir, WF, FG bark, and MG bark; however, lettuce grown in FG bark had greater fresh weight and greater dry weight than in WF-coir. Head diameter was lower in WF, WF-coir, and MG bark (30.1 ± 0.5 cm on average) compared with peat-perlite (36.7 ± 0.6 cm). In Expt. 2 with reduced root restrictions, fresh weight did not differ among substrates; however, dry weight was 28% greater in peat-perlite (13.9 ± 0.6 g) than in other substrates. In both the experiments, peat-perlite supported better leaf nutrient status, whereas peat-perlite and coir provided greater nutrient availability than the other substrates.