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  Eur.J.Hortic.Sci. 85 (5) 321-328 | DOI: 10.17660/eJHS.2020/85.5.3
ISSN 1611-4426 print and 1611-4434 online | © ISHS 2020 | European Journal of Horticultural Science | Original article

Urban farming in indoor settings: Nitrate limits compliance check of leafy green vegetables under LED lighting

M. Gräf1, R. Stangl1, R. Hood-Nowotny2 and A. Kodym3
1University of Natural Resources and Life Sciences, Institute of Soil Bioengineering and Landscape Construction, Vienna, Austria
2University of Natural Resources and Life Sciences, Institute of Soil Research, Vienna, Austria
3University of Vienna, Department of Pharmacognosy, Vienna, Austria

SUMMARY
In urban farming, the cultivation of leafy vegetables hydroponically under artificial light in indoor settings offers the possibility of decentralized food production. For food safety, the European Commission issued a regulation “EU NO1258/2011” to stipulate the maximum levels for nitrate in food. We conducted this study to determine, whether leafy vegetables grown in indoor settings can comply these nitrate limits. The air temperature, relative humidity and light intensities for all treatments were maintained at 23±2°C, 45±10% and 120±10 μmol m-2 s-1 at a photoperiod of 16 hours, with two different light spectra: red-blue (RB) vs. red-green-blue (RGB). Fresh food biomass, nitrate, nitrogen and SPAD readings of three different leafy vegetables (cabbage, pak choi, and rocket) were analyzed. The nitrate limits were met by all species, but are high compared to plants traditionally soil cultivated. Furthermore, a significantly reduced nitrate accumulation was found for the species rocket under the RGB treatment compared to the RB. This study proposes the integration of green light to red and blue in urban indoor farming, as a strategy to reduce the nitrate content of selected vegetables and to improve food quality and make it consumer-friendly.

Keywords artificial light, hydroponic, indoor farming, nitrate accumulation, soil-less

Significance of this study

What is already known on this subject?

  • Nitrate values in leafy vegetables are subject to large fluctuations. Nitrogenous fertilisers and light conditions are the two main factors driving those, both factors which can be regulated under controlled environment.
What are the new findings?
  • The nitrate content of the species rocket, cabbage and pak choi was within the limits set by the European Commission, which were cultivated hydroponically in a household setting under artificial light. Moreover, lower nitrate accumulation was found for all species under the RGB-LED compared to the RB-LED, but significantly only in rocket.
What is the expected impact on horticulture?
  • In addition to red and blue light, the wavelength range between 500–600 nm should be considered when designing LEDs for the cultivation of leafy vegetables.

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E-mail: michael.graef@boku.ac.at  

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Received: 11 February 2020 | Accepted: 24 June 2020 | Published: 21 October 2020 | Available online: 21 October 2020

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