Mineralization of organic fertilizer for improved plant nutrient availability in hydroponics

Lucie Půstová

Master's thesis

Abstract:

There is an increasing interest in using organic fertilizer for hydroponic plant production, due to its lower greenhouse gas emissions, lower accumulation of harmful toxins in food, and greater resource recycling potential than mineral fertilizers. However, there are major limitations to the use of organic fertilizer in hydroponics, which mostly center around nutrient availability and nitrogen. Nitrogen in organic fertilizer is predominantly present in organic compounds, which need to undergo mineralization to become plant available. In soil, microorganisms are responsible for this and subsequent nitrification. The lack of microorganisms in hydroponics means that nutrients bound in organic compounds become available to plants only very slowly, limiting growth and inducing deficiencies. A parallel mineralization and nitrification method used in previous studies employs soil as a source of microorganisms and, through an incubation process, organic nitrogen compounds are broken down by the microorganisms. This thesis draws inspiration from this method and tests various sources of inoculum found in Denmark, including agricultural soils, compost soil, and seawater, to test the effect on ammonium and nitrate concentrations in organic fertilizer. In the incubation experiment of this thesis, successful nitrification was induced by the end of week 3, when almost all of the ammonium had been oxidized in the compost soil inoculum treatment. This inoculum, which produced the highest nitrate levels in week 3, was selected for the hydroponic plant growth experiment with Brassica rapa subsp. chinensis. After 27 days of treatment, plants grown with mineral fertilizer showed the highest biomass accumulation and no deficiency symptoms. Plants grown with the incubated organic fertilizer had a higher shoot and total fresh weight than the (non-inoculated) organic fertilizer treatment while displaying fewer visual symptoms of deficiency and having higher leaf concentrations of potassium and iron. Overall, this study shows that organic fertilizer, with the proper inoculation and mineralization, can be successfully used in hydroponic plant production.

Keywords

Brassica rapa subsp. chinensis, microbial nitrification, mineralization, organic fertilizer, nitrate, Hoagland solution, hydroponics, vinasse, bok choy

Language used: English

Date on which the thesis was submitted / produced: 17. 4. 2023

Thesis defence

• Date of defence: 15. 5. 2023
• Supervisor: Ing. Filip Mercl, Ph.D.
• Reader: Pavel Klouček, Ph.D.

Czech University of Life Sciences Prague

Faculty of Agrobiology, Food and Natural Resources

Master programme:
Sustainable Agriculture and Food Security