Micro-organisms in vertical lettuce cultivation systems

In vertical lettuce cultivation, the presence of micro-organisms plays a role, in addition to the substrate.

Vertical cultivation systems have a higher spatial efficiency and enable cultivation in places where this is not possible with traditional cultivation techniques.

Effect of substrate and types of bacteria

Peat is a popular, yet unsustainable substrate. Therefore alternative substrates are being explored. However, the impact of these alternative substrates on the cultivation of plants, but also on the bacterial communities in the rhizosphere, has not or insufficiently been studied.

Lettuce cultivation For his master thesis, led by ir. Thijs Van Gerrewey and Prof. Danny Geelen of the Faculty of Bioscience Engineering, Ghent University, Seppe Top studied the effect of both the type of substrate as well as the composition of the types of bacteria that are present in the rhizosphere. The study looked into yield (fresh weight and dry weight), into health-promoting substances such as phenols and certain antioxidants, as well as into undesirable substances such as nitrate.

Seppe Top: “The results confirm prior research. Bacteria in the rhizosphere and substrates influence each other and together they influence the crop.”

The best yield was obtained using a substrate containing composted green waste. The higher yield was linked to a lower dry matter content, and lower phenol concentrations. There was no direct influence on the antioxidants measured. The substrate with a mixture of black peat, coconut fibre, composted green waste, sand and gum arabic resulted in the highest yield with an average phenol concentration.

The potential role of soil as well as rhizosphere bacteria was investigated by adding mixtures of bacteria to the nutrient solution. Depending on the origin of the bacterial mixture, positive or negative effects on yield and quality were observed.

Prof. Danny Geelen: “The importance of substrate choice has clearly been confirmed by this research. Even though it was also demonstrated that bacterial communities in the rhizosphere exhibit an effect, further research is needed to determine their composition and their effect on other quality parameters. In this way, the yield and quality of lettuce in a vertical cultivation system can be further improved.”

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