Objectives Experiments were conducted to investigate the effects of different concentrations of seaweed extract on the yield and quality of hydroponic Chinese kale (Brassica alboglabra Bailey) in greenhouse.
Methods The hydroponic experiments were carried out in Horticultural Experiment Base in South China Agricultural University. The initial nutrient solution was 1/2 strength Hoagland solution. In the preliminary experiment, the tested seaweed extract fertilizer was diluted by 800, 1000 and 1200 folds in the nutrient solution, respectively, which was refreshed once a week. According to the results of the preliminary experiment, the seaweed extract was diluted by 1200, 1400, 1600, 1800 and 2000 folds in the nutrient solution in the following main experiment, and the nutrient solutions would not be changed during the whole experiment. The plant biomass was measured, and the contents of soluble sugar, soluble protein, nitrate and vitamin C were determined, and the 2, 2-diphenyl-1-picrylhydrazyl, ferric-reducing antioxidant power, contents of total phenolics, total flavonoids, glucosinolates and mineral elements of Chinese kale were analyzed.
Results In the primary experiment, the three dilution treatments all inhibited the growth and the biomass of Chinese kale significantly, and the dilution folds of 800 and 1000 decreased significantly more than that of 1200 fold. In the main experiment, the plant growth and quality showed extremely sensitive to the concentration of seaweed extracts. The growth and biomass of Chinese kale only increased significantly in treatments of 1400 and 1600 dilution, and the contents of nitrogen, phosphorus, calcium, potassium and sulfur, the contents of total phenolic compounds, total flavonoids and FRAP, the antioxidant capacities merely increased significantly in dilution treatment of 1400 fold, all above were not affected in other dilution treatments.
Conclusions The hydroponic Chinese kale is extremely sensitive to the concentration of seaweed extract in the nutrient solution. Over high concentration of seaweed extract will inhibit the growth and biomass of Chinese kale significantly, while too low concentration would not have the expected promotion effects. When the tested seaweed extract is diluted by 1400 folds in the nutrient solution, it will stimulate the growth and biomass accumulation, enhance the photosynthetic pigment contents, the nutrition quality and the anti-oxidance ability. In addition, adding seaweed extract once at the initial will not need changing the nutrient solution during the whole culture period.
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