Effects of Organic Fertilizer on Bok Choy Growth and Quality in Hydroponic Cultures

Kazuki Kano,Yumi Eguchi,Hiromitsu Odani,Songying Zhou,Makoto Shinohara,Hiroaki Kitazawa,Keitaro Suzuki,Ani Widiastuti,Yufita Dwi Chinta,Tatsuo Sato

doi:10.3390/agronomy11030491

Abstract

Effects of corn steep liquor (organic fertilizer, OF) and conventional chemical fertilizer (CF) on the growth and yield of bok choy (Brassica rapa var. chinensis) in summer and autumn hydroponic growing systems were compared. When OF and CF were applied with the same amount of total nitrogen in summer cultivation, there was no significant difference between yields; however, the growth rate in OF was slower than in CF. When OF was applied with twice the amount of nitrogen in CF (OF2), bok choy growth and yield were significantly inhibited in summer cultivation, likely owing to dissolved oxygen deficiency and different rates of nitrification and nitrogen absorbance by the plant root. Although the contents of potassium, calcium, and magnesium in bok choy showed no difference among the three treatments in both cultivation seasons, the carbon/nitrogen ratio tended to be higher in OF and OF2 than in CF. Lower nitric acid and higher ascorbic acid content was found in OF and OF2 than in CF. Overall, our results suggest that a comparable yield is expected by using the same nitrogen amount with a conventional recipe of chemical fertilization in autumn cultivation. However, further improvement of hydroponic management is needed in summer cultivation.

Highlights

Chemical fertilizers are commonly applied in hydroponics cultivation systems for Chinese vegetables including bok choy (Brassica rapa var. chinensis) [1] during summer and autumn
To achieve success in multiple parallel mineralization, two conditions are required: the hydroponic solution must be under an aerobic condition and the organic materials must be applied continuously in small amounts, wherein the application is combined with compost
Organic fertilizer resulted in lower nitric acid and higher ascorbic acid content

Summary

Introduction

Chemical fertilizers are commonly applied in hydroponics cultivation systems for Chinese vegetables including bok choy (Brassica rapa var. chinensis) [1] during summer and autumn. The accumulation of phytotoxic compounds and the deficiency of dissolved oxygen both inhibit plant growth [2,3,4,5] Due to these disadvantages, the utilization of organic fertilizers in hydroponics has not been viable until the development of the multiple parallel mineralization technique by Shinohara [6]. The utilization of organic fertilizers in hydroponics has not been viable until the development of the multiple parallel mineralization technique by Shinohara [6] This technique allows the decomposition of organic materials, such as bonito soup, rapeseed oil cake, corn oil cake, fish meal, dried brewer’s yeast, fermented tomato foliage, and methane fermentation digest, in hydroponic solution without causing the accumulation of phytotoxins and dissolved oxygen deficiency. The microorganisms in the compost facilitate the mineralization of nitrate ions and prevent the accumulation of phytotoxic compounds [7,8]

Methods

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Discussion

Conclusion