Exploitation of Liquid Digestate as the Sole Nutrient Source for Floating Hydroponic Cultivation of Baby Lettuce (Lactuca sativa) in Greenhouses

Abstract

Sustainable agriculture relies on replacing fossil-based mineral fertilizers, which are highly cost-energetic to produce, and demand extensive use of scarce natural resources. Today, agronomic practices within the concept of circular economy are emerging and, as such, the exploitation of digestate as a biofertilizer and soil amender is extensively investigated. This study aimed at evaluating the agronomic potential of liquid digestate as the sole nutrient source for hydroponic cultivation of baby lettuce in greenhouses. Growth rate, physiological responses, concentration of secondary metabolites, and nutrient uptake were compared between baby leaf lettuce grown in digestate in concentrations of 5, 10, and 20% diluted in water (either with or without pH adjustment) and in Hoagland solution (control). Results showed that the production yield was negatively correlated with the concentration of the added digestate. Nevertheless, the antioxidant capacity was significantly enhanced in 5 and 10% liquid digestate treatments compared to the control. Additionally, the nutrient composition in the baby leaf lettuce and the reduction in nutrient concentrations in the growth media demonstrated efficient mineral uptake by the plants. Thus, the application of liquid digestate as a fertilizer in hydroponic systems is a promising practice to recover residual resources, leading to the transition towards more sustainable greenhouse production.

The Effects of Different Combinations of Cattle Organic Soil Amendments and Copper on Lettuce (cv. Rufus) Plant Growth

“…The reduction in micronutrients in the lettuce leaves could likely be ascribed to their lower solubility due to the higher digestate pH compared to the soil one (Table S1), as reported by Olszyk et al [68], who observed a decrease in Fe, Mn, and Zn concentrations, mainly, in lettuce plants grown in the presence of several biochars as amendments. Similarly, a reduction in Fe uptake was detected in baby leaf lettuce under different digestate [69,70]. The addition of a low Cu concentration (M+Cu and D+Cu) caused in the plant leaves a twofold increase in Cu uptake with respect to the control (S).…”

Assessing the Different Economic Feasibility Scenarios of a Hydroponic Tomato Greenhouse Farm: A Case Study from Western Greece

“…In addition, an important research need could be the development of varieties that pertain to this cultivation method in Greece and also to resolve issues with regards to waterborne diseases. A specific type of such technologies could be new ways for valorizing recycled water in hydroponics, such as the combination of aquaponics with plant growing in greenhouses [53], or the use of alternative substrates in the framework of a circular economy [54], both of which are being investigated in Greece. This would also allow for the better monitoring of water quality, thus decreasing the danger for waterborne diseases.…”

Evaluation of a Small-Scale Anaerobic Digestion System for a Cattle Farm under an Integrated Agriculture System in Indonesia with Relation to the Status of Anaerobic Digestion System in Japan

“…In this regard, Reuland et al [25] stated that the digestate liquid provided better conditions for plant growth than unseparated digestate. In addition, Ntinas et al [26] demonstrated the efficient application of digestate liquid from livestock manure as a fertilizer for the hydroponic cultivation of baby lettuce grown in a greenhouse using a floating system. Similarly, Levin et al [27] confirmed that the liquid fraction from cow manure exhibited better fertilization performance for cucumber due to the fast release of nutrients (i.e., nitrogen) to the plants.…”