Growth and Tissue Elemental Composition Response of Spinach (Spinacia oleracea) to Hydroponic and Aquaponic Water Quality Conditions

Abstract

Spinach (Spinacia oleracea, cv. Carmel) was grown in a conventional glass greenhouse under three different nutrient solution treatments. Lighting and temperature conditions were identical. Six growing systems were used to provide a duplicate trough system for each of these three treatments. Six crops (referred to as trials) were harvested from each system over a two month time period. Two treatments received hydroponic nutrient inputs, with one treatment at pH 7.0 (referred to as H7) and the other at pH 5.8 (referred to as H5), and the third treatment was aquaponic (referred to as A7), receiving all of its nutrients from a single fish tank with koi (Cyprinus carpio) except for the addition of chelated iron. The pH of the systems were regulated by adding K2CO3 to the aquaponic systems, and KOH to the hydroponic systems. Plants were harvested at a marketable size for baby-leaf spinach. Comparisons made between the treatments were total yield (fresh weight and dry weight), leaf surface area, tissue elemental content, and dry weight to fresh weight ratio. Despite some differences in nutrient solution and tissue composition, it was found that dry weight biomass yield values were not different in pairwise comparisons between treatments (A7 vs. H5: p=0.59 fresh weight, p=0.42 dry weight). Similarly, surface area results were not different between treatments. Statistically non-different biomasses were achieved in the A7 and H5 systems for both dry weight and fresh weight. The important comparison is A7 vs. H5, because the H7 treatment is at a pH rarely used in hydroponics, and received slightly more light due to its greenhouse position.