2018 ASHS Annual Conference

Drawbacks of synthetic fertilizers led us to explore wastewater-grown algae as biologically based alternative. Such algae may allow for the recycling of polluting nutrients for use as fertilizer. Six formulations of extruded algal pellets comprising various amounts of polylactic acid, soy flour, biochar, and wastewater-grown algae were compared as fertilizers for African marigold (Tagetes erecta L.) and gerbera daisy (Gerbera jamesonii Bolus ex Hooker f.). A synthetic, controlled-release fertilizer (CRF), and a commercially available co-product of wastewater treatment, also were studied. Fertilizers were incorporated throughout the root-zone at 641.2 g N·m–3, the rate of N that corresponded to the CRF label recommendation. Plant growth index, shoot dry weight, and shoot nutrient concentrations, as well as substrate pH and EC, were measured after 40 and 64 d for marigolds and gerbera daisies, respectively. Extruded bio-based fertilizers increased the dimensions and weights of shoots of both species compared to those measures of unfertilized plants and of plants supplied with the commercially available co-product of wastewater treatment. Growth of plants provided with certain extruded bio-based fertilizer formulations were similar to those measures of plants fertilized with CRF. Nutrient deficiency symptoms and associated insufficient nutrient concentrations of shoots were evident in plants provided some formulations of bio-based fertilizers and the commercially available co-product of wastewater treatment. Bio-based fertilizers did not negatively impact substrate pH or EC. Overall, extruded bio-based fertilizers were effective fertilizers, though our results show that growth of marigolds and gerbera daisies depends on the formulation of these materials. We conclude that use of algae as a source of biologically sequestered and recycled nutrients has potential for reducing environmental impacts associated with nutrient management of horticultural crops.