Development of a bioassay for liquid organic fertilisers using Azolla filiculoides: A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Horticultural Science with Honours

Abstract

The number of liquid organic fertilisers are increasing on the market. Some of these fertilisers claim to contain plant growth hormones; the growth promotion of these products has not been proven in most cases. Lemna species has been investigated as a potential bioassay for liquid organic fertilisers, but nutrient storage and sterile culture techniques made it unsuitable. Azolla is sensitive to both inorganic nutrients and organic compounds. A protocol was developed for the use of Azolla as a bioassay; the starting weight of 0.5 g, 10 replicates per treatment, experiments run for 9 days without a change of the International Rice Research Institute nutrient solution, at the concentration of nutrients recommended. Azolla floating in solutions of liquid organic fertilisers responded in different ways, in solutions at concentrations recommended by the manufacture the Azolla died. Fungi grew over the surface of the Grotech in the growth cabinet where ideal conditions (25°C and humid) were provided for fungal growth. Foliafeed killed Azolla at all concentrations tested, which may be due to micronutrient toxicity. As the concentration of Maxicrop decreased (3 ml Litre⁻¹ to 0.38 ml Litre⁻¹ ) the dry matter production of Azolla increased by 12%. Spray applications of Maxicrop (11 ml of a 3 ml Litre⁻¹ solution) significantly increased {p<0.05) the dry weight of Azolla in water by 12% above that of the control (water only). The application of plant growth regulators had mixed effects, indole acetic acid, at a concentration that had previously increased growth (0.1 μg ml⁻¹ ) did not affect the fresh weight but significantly decreased the dry weight of Azolla (p<0.05). Benzylaminopurine had no affect on either fresh or dry weight, while gibberellic acid and abscisic acid decreased the fresh and dry weights. The sensitivity of Azolla to plant growth regulators needs to be assessed further before the non-nutritional effects of the plant growth hormones can be tested.