Evaluating a Controlled-Release Fertilizer for Plant Establishment in Floating Elements for Bioretention Ponds

In bioretention ponds proposed to manage urban runoff, floating elements with anchored macrophytes plants improve nutrient and pollutants removal and provide aesthetic benefits. To prompt the establishment and initial growth of plants in floating elements with substrate, the application of Osmocote (a controlled-release fertilizer) in tablet form was proposed. In a confined environment, eight treatments were compared, combining two substrates (peat and zeolite at a ratio of 1:1 or 2:1 v/v), two levels of fertilization (without or with addition of Osmocote plus tablets; 5 g plant(-1)), and the presence or absence of Mentha aquatica L. plants. For about 16 weeks, the amount and quality of water, along with plant growth and nutrient content, were monitored. The results showed better plant growth when Osmocote was supplied, with no effect of the substrate. The presence of the plant produced the almost total uptake of the nutrients contained in the tap water and released by the fertilizer. This indicates that the use of a controlled release fertilizer can improve plant growth without compromising water quality, hence being a valuable solution to promote plant establishment usable as routine practice when a bioretention basin is vegetated with floating elements with substrate.