2019 ASHS Annual Conference

Hydroponic producers are seeking information on effective organic fertilizers for leafy greens and herbs. Because organic fertilizers contain plant or animal by-products, nutrients must be mineralized into plant available form. Commercially available microbial inoculants or naturally prepared materials (e.g. vermicompost extract) may aid mineralization. The objective of this project was to determine the impact of one conventional and two organic fertilizers with and without microbial inoculants on nutrient solution elemental content and yield of baby leaf spinach (cv ‘Carmel’) and basil (cv ‘Genovese’) in deep water culture hydroponics. Styrofoam rafts containing 40-cells with soilless germination mix were sown with one seed in each 2.5x2.5 x4.4 cm (LxWxH) cell. Upon germination (cotyledon emergence), rafts were floated in 35-L hydroponic tubs. Crops were grown for three sequential cycles during which time the same nutrient solutions used, but with additions of fresh nutrient solution daily to make up for lost water. In each crop cycle, plants were harvested at 13 and 18 days after floating for spinach and basil, respectively. In experiment 1, spinach was grown with one of six treatments: Sonneveld’s conventional fertilizer at 150 ppm N (control), control + non-aerated vermicompost extract at 10% by volume (NVE, Worm Power, LLC), Hydroser organic seaweed based fertilizer at the label rate (Qingdao Seawin Biotech Group Co., LTD.), and Hydroser + NVE. Plant fresh weight (FW) was greatest and not significantly different for control and control + NVE averaging 3.1 and 3.4 g·plant^-1, respectively. For these two treatments FW did not vary by crop cycle. For Hydroser, FW was smaller than control and declined with crop cycle, and averaged 1.3 g·plant^-1. For Hydroser + NVE, FW was smaller than control for cycles 1 and 2 (averaging 1.9 g·plant^-1) and was similar to control for cycle 3 (3.2 g·plant^-1). According to nutrient solution analysis, the NVE supplied some nitrate, plus NVE led to enhanced conversion of ammonium to nitrate by later crop cycles. In a second experiment, basil and spinach were grown with control, Hydroser, Pre-Empt organic fertilizer at label rate (Coastal Fertilizer & Supply, Inc.), and Pre-Empt + TerraBella commercial root microbial inoculant (AquaBella Organic Solutions, LLC). Basil was less responsive to fertilizer treatments, FW averaged 77, 87, and 97% of control for Hydroser, Pre-Empt, and Pre-Empt + TerraBella. For spinach, FW averaged 44, 45, and 46% of control for Hydroser, Pre-Empt, and Pre-Empt + TerraBella.