Effects of Hydrogen Peroxide on Organically Fertilized Hydroponic Lettuce (Lactuca sativa L.)

Vanessa Lau,Neil Mattson

doi:10.3390/horticulturae7050106

Abstract

Hydroponic production typically uses conventional fertilizers, but information is lacking on the use of organic hydroponic fertilizers. Development of microbial communities and biofilm that can reduce dissolved oxygen availability is a difficulty with organic hydroponics. One potential solution is the use of hydrogen peroxide (H2O2) which can reduce microbial populations and decompose to form oxygen. However, information is lacking on the impact of hydrogen peroxide on hydroponic crop performance. The aim of this study was to determine the effects of H2O2 concentrations in deep water culture hydroponics by assessing how it affects plant size and yield in lettuce (Lactuca sativa L.) “Rouxai”. In this experiment, three H2O2 treatments, namely the application of 0, 37.5 or 75 mg/L H2O2 to 4 L aerated hydroponic containers with either conventional or organic fertilizer, were compared. The containers had either fish-based organic fertilizer (4-4-1, N-P2O5-K2O) or inorganic mineral based conventional nutrient solution (21-5-20, N-P2O5-K2O), both applied at 150 mg/L N. Three replicates of each H2O2 treatment–fertilizer combination were prepared resulting in a total of eighteen mini hydroponic containers each with one head of lettuce. There were two growth cycles: fall 2018 and spring 2019. When added to conventional fertilizers, both 37.5 mg/L and 75 mg/L of H2O2 led to stunted growth or death of lettuce plants. However, when 37.5 mg/L of H2O2 was applied to organic fertilizers, the lettuce yield nearly matched that of the conventionally fertilized control, demonstrating that the application of H2O2 has the potential to make organic hydroponic fertilization a more viable method in the future.

Highlights

Marketed as a technologically revolutionary and sustainable way to grow produce, the employment of hydroponic methods in greenhouses and “plant factories” is gaining traction globally [1]
In the fall trial, dissolved oxygen (DO) levels were recorded each day to track the degradation of H2 O2 within the rootzone (Figure 2)
Conventional fertilizer with 75 mg/L H2 O2 led to the greatest sustained levels of DO, and in the organic treatments DO levels degraded more quickly after each addition

Summary

Introduction

Marketed as a technologically revolutionary and sustainable way to grow produce, the employment of hydroponic methods in greenhouses and “plant factories” is gaining traction globally [1]. The disposal of chemically fertilized wastewater from these systems can leach into the environment and over time, degrade ecosystems as well as contaminate clean water sources [4,5]. An alternative to these conventional fertilizers is the use of organic fertilizers derived from plant and animal byproducts such as seaweed extract, manure or hydrolyzed fish emulsion [6] which require the development of microbial communities to mineralize complex organic compounds to make them plant available [7,8]. It is believed that the suspended organic matter which can develop on plant roots can clog pumps/recirculation lines, reduce oxygen and nutrient uptake by roots and deplete nutrient solution oxygen levels [13,14,15]

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Discussion

Conclusion