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

Daniel Vandam,Michael Timmons,David De Villiers,Tyler Anderson

doi:10.3390/horticulturae3020032

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 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 (H5), and the third treatment was aquaponic (A7), receiving all of its nutrients from a single fish tank with koi (Cyprinus carpio) except for chelated iron. System pH was regulated by adding K2CO3 to aquaponic systems and KOH to hydroponic systems. Comparisons made between treatments were total yield, leaf surface area, tissue elemental content, and dry weight to fresh weight ratio. 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. The important comparison was that A7 achieved the same growth as H5, the conventional pH with a complete inorganic nutrient solution, despite unbalanced and less than “ideal” nutrient concentrations in the A7 condition.

Highlights

Hydroponics is a method of growing plants using mineral nutrient liquid solution without soil.The method of application of the nutrient solution to the roots varies widely [1]
We found no statistical differences in our biomass results, which were normally distributed as shown in Tables 4 and 5, between the A7 and H5 treatments, (A7 vs. H5: p = 0.59 fresh weight, p = 0.42 dry weight, n = 84) even when total flat mass was measured (Table 4c)
This study brought to light the idea that non-optimal nutrient conditions for spinach growth using nutrient rich water from a fish RAS can still produce the quality and quantity of product that a carefully controlled inorganic hydroponic nutrient solution produces

Summary

Introduction

Hydroponics is a method of growing plants using mineral nutrient liquid solution without soil.The method of application of the nutrient solution to the roots varies widely [1]. Hydroponics is a method of growing plants using mineral nutrient liquid solution without soil. Aquaponics is a method of growing plants hydroponically using nutrients provided from an aquaculture system. Aquaponics makes multiple uses of resources such as water and nutrients [2,3]. Hydroponics uses inorganic nutrient fertilizers, while aquaponic treatments rely on fish waste, which has the potential to be at less or more than ideal concentrations for plants. Aquaponics uses fish recirculating waters or mineralized waste discharge to generate the nutrients needed by plants, meaning the nutrient composition is not formulated to exact concentrations and can be less stable [6]. Growing plants aquaponically uses nutrients that would otherwise be lost from a fish system, which has an added value in marketing to a certain class of consumers. The plants help filter the fish water and help to reduce nitrate which can be toxic to some fish salmonid species at elevated levels, e.g., greater than 40 mg/L [3]

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