Hydroponic Fertilizer Supply for Basil Using Controlled-release Fertilizer

Urban Farm DB summary

To simplify nutrient management in small-scale hydroponics, three experiments tested whether controlled-release fertilizer (CRF) could support basil (Ocimum basilicum) with a single application per crop cycle. All seven commercial CRF products tested (including Osmocote Bloom and others) showed an initial rapid nutrient release followed by a plateau, but release rates over 11 weeks varied from 60% (ammonium phosphate) to 100% (magnesium sulfate). Two commercial N-P-K CRF products supplied less calcium and magnesium than a typical water-soluble fertilizer (WSF) solution. In a growth-chamber experiment, plants grown for four weeks under CRF treatments yielded less than half the shoot fresh weight of WSF-grown plants and showed calcium-deficiency and micronutrient-toxicity symptoms confirmed by tissue analysis, with the CRF solution's electrical conductivity rising to a maximum of 5.4 dS/m. A custom "Blend" combining CRF macronutrients with WSF micronutrients was then tested: at double concentration, it produced shoot fresh weight (241 g per four plants) comparable to WSF (244 g) with healthy tissue nutrient levels, whereas commercial CRF products designed for soil or container production proved unsuitable for hydroponic use.