Evaluation of hydroponic systems for organic lettuce production in controlled environment

Authors: CHOWDHURY, MILON - The Ohio State University; SAMARAKOON, UTTARA - The Ohio State University; Altland, James

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/19/2024
Publication Date: 8/6/2024
Citation: Chowdhury, M., Samarakoon, U., Altland, J.E. 2024. Evaluation of hydroponic systems for organic lettuce production in controlled environment. Frontiers in Plant Science. 15. Article 1401089. https://doi.org/10.3389/fpls.2024.1401089.
DOI: https://doi.org/10.3389/fpls.2024.1401089

Interpretive Summary: Organic hydroponics is a crop culture method in controlled environment agriculture (CEA) that uses organic substrate and organic nutrient solutions derived from plant and animal sources, along with the biological pest controls. Due to easy handling and availability of irrigation equipment, CEA growers prefer to use liquid organic fertilizer instead of substrate incorporated fertilizers. However, there are major differences regarding the nutrient ion availability between organic and synthetic fertilizers. This study was aimed to determine a compatible hydroponic system through lettuce cultivation using a liquid organic fertilizer under controlled environment conditions based on the growth performance, leaf tissue nutrients, and nutrient solution analysis. Four distinct hydroponic methods were selected: nutrient film technique (NFT), deep water culture (DWC) (liquid culture systems), Dutch bucket (DB), or regular plastic container (RPC) (substrate-based systems). ‘Green Butter’ lettuce was grown using a liquid organic fertilizer (Espartan) for four weeks. Shoot growth parameters and root growth parameters were measured. Substrate-based hydroponic systems (i.e., DB and RPC) demonstrated superior performance in terms of growth parameters and mineral composition. Despite the high growth and mineral composition, the substrate-based hydroponic system leached more nutrients, indicating a need for optimization. This study provides empirical evidence supporting the potential use of liquid organic fertilizer in CEA and the importance of selecting proper soilless cultivation methods for food production. We also suggest substrate-based hydroponic systems are a better option for screening liquid organic fertilizers for future use.

Technical Abstract: Organic farming methods, including the use of organic substrates, fertilizers, pesticides, and biological control, are gaining popularity in controlled environment agriculture (CEA) due to economic benefits and environmental sustainability. However, despite several studies focusing on the preparation and evaluation of liquid organic fertilizers, none have explored the compatibility of these fertilizers with different hydroponic systems. Therefore, the objective of this study was to evaluate lettuce production using a liquid organic fertilizer under different hydroponic systems. Four distinct hydroponic methods were selected: nutrient film technique (NFT), deep water culture (DWC) (liquid culture systems), and Dutch bucket (DB), regular plastic container (RPC) (substrate-based systems). ‘Green Butter’ lettuce was grown using a liquid organic fertilizer (Espartan) for four weeks. Shoot growth parameters (e.g., shoot width, number of leaves, leaf area, foliar chlorophyll content, fresh weight, and dry weight) and root growth parameters (e.g., root length, fresh weight, and dry weight) were measured. The growth difference of lettuce under the DB and RPC systems was negligible, but the growth in RPC was 29% to 60% and 15% to 44% higher than the NFT and DWC systems, respectively, for shoot width, number of leaves, leaf area, shoot fresh weight and dry weight. Root parameters were nearly identical for the NFT and DWC systems but significantly lower (21% to 94%) than the substrate-based DB and RPC systems. Although lettuce grown in the NFT system showed the least growth, its mineral content in the leaf tissue was comparable or sometimes higher than that of substrate-based hydroponic systems. In conclusion, the tested liquid organic fertilizer is suitable for substrate-based hydroponic systems; however, further evaluation of different liquid organic fertilizers, and crop species is required.