Evaluation of macro algal biomass and extracts for soil improvement and plant growth stimulation of Sorghum bicolor

Author: Takarir Faatema Sheliya

Sheliya, Takarir Faatema, 2022 Evaluation of macro algal biomass and extracts for soil improvement and plant growth stimulation of Sorghum bicolor, Flinders University, College of Medicine and Public Health

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Marine macroalgae are plant-like organisms regarded as a valuable natural bioresource in a variety of agricultural applications. Applications in agriculture improved the physical and chemical qualities of soil. The agricultural value of marine macroalgae is further enhanced by their ability to produce a diverse range of biologically active biocidal compounds effective in boosting protection against plant-infecting diseases.

The literature review, which is a component of the presented research, covers characteristics of prospective macroalgal agricultural applications. Commercial production and utilization of certain marine macroalgal chemicals with interesting biotechnological value, such as biofertilizers, bio stimulators, and soil conditioners, are emphasized and addressed in detail.

In the research component of this project, Undaria pinnatifida, a brown alga was used as a bio-fertilizer to investigate its effect on the growth of Sorghum bicolor. A greenhouse growth trial with Sorghum bicolor seeds was carried out with different biofertilizer treatments, such as Seasol fertiliser treatment, Algardis (derived from post-fucoidan extracted biomass of the brown seaweed Fucus vesiculosus), Undaria pinnatifida biomass, microwave-assisted extracts of Undaria pinnatifida biomass at 40, 60, and 80oC, compost (positive control), and unfertilized nutrient-poor topsoil (negative control). N, P, K, and C contents of pre-seeded (except for the Seasol treatment) and end of growth trial soils were determined using inductively coupled plasma optical emission spectrometry (ICP-OES) and elemental analysis, respectively.

A total of 24 pots (25 cm diameter) were set up in a randomized design in a greenhouse in triplicate * eight treatment combinations with daily rotation. The light intensity was between 500-600 µmol m-2 s-1 set to a photo period of 16:8-hour light/dark cycle at a set temperature of 28ºC during the day and 18ºC at night. To only account for the contribution of C to plant growth, soils, except for 3 pots of topsoil that served as a negative control, were fertilised with the respective fertiliser with N, P, and K levels brought to the same levels as found in compost soil. Pots were only fertilised once prior to seeding except for compost soil (positive control) and unfertilised topsoil (negative control).

Highest growth of Sorghum bicolor was achieved in compost soil, but water holding capacity (WHC) was highest in topsoil fertilised with Undaria pinnatifida biomass, 40, 60, and 80oC extracts, and Seasol treatment. In comparison between unfertilised topsoil and compost soil the unfertilised topsoil (negative control) had the highest C (41.5 g/kg) content on day 0, and compost soil (positive control) had the highest N (1.3 g/kg), P (1.32 g/kg), and K (3.14 g/kg) content on day 0. The C content was much higher in U. pinnatifida biomass in compare to all other treatments at before seeding day-0. After 56 days (post-harvest), an increased soil elemental nutritive value was noticed. The concentrations of N (4.4 g/kg), P (1.455 g/kg), K (3.377 g/kg), and C (56 g/kg) of compost soil were increased, while N (1.6 g/kg), C (24.86 g/kg), and P (0.37 g/kg) contents in unfertilised topsoil (negative control) decreased, as did the N (1.566 g/kg), C (25.33 g/kg), P (0.57 g/kg), and K (3.22 g/kg) contents of the Algardis treatments. Post-harvest K (2.883 g/kg) and P (0.779 g/kg) contents were higher compared to starting conditions for treatments fertilised with Undaria biomass and K (3.345 g/kg), C (25.733 g/kg), and N (1.633 g/kg) contents for Undaria biomass MAE 40, 60, and 80˚C, N (1.266 g/kg), and C (22.9 g/kg) concentrations were lower for the latter treatments. Postharvest C (1.633 g/kg) and N (25.733 g/kg) concentrations were higher for topsoil fertilised with MAE 40˚C extracts compared to MAE obtained at 60 and 80˚C.

The plants were grown in compost soil (positive control) Algardis, Seasol, Undaria biomass, and Undaria MAE 40, 60, and 80℃ treatments. Seeds of Sorghum bicolor sown in the unfertilised topsoil (negative control) did not germinate. Best growth was observed for seeds germinated in compost soil, followed by Algardis, Seasol, and Undaria biomass treatments, while Undaria MAE 40, 60, and 80℃ treatments did not support growth to the same extent.

Plants grown in compost soil had higher above and below ground biomass, followed by Algardis, Seasol, and Undaria biomass treatments. There was no increase in the development of above and below-ground biomass between the fertilisation regimes using the MAE extracts.

In conclusion, fertilisation with Seasol with compost soil shows the best result, and the treatment with Undaria pinnatifida biomass and the Algardis liquid extract of the brown macroalga Fucus vesicolosus (Marinova) treatments supported growth to the same extent were the best alternative options to Seasol and can be used for the cultivation of Sorghum bicolor. Whilst in theory, Undaria pinnatifida biomass and Algardis can be cost-effective, eco-friendly, and easily available, techno-economic and life cycle analyses are required to demonstrate cost-effectivity and environmental sustainability.

Keywords: Marine macroalgae; bio-stimulants; Undaria pinnatifida, sustainable agriculture, Algardis, Sorghum bicolor, Fucus vesiculosus, Water holding capacity (WHC).

Subject: Biotechnology thesis

Thesis type: Masters
Completed: 2022
School: College of Medicine and Public Health
Supervisor: Kirsten Heimann