Organic Waste-Based Fertilizer in Hydroponics Increases Tomato Fruit Size but Reduces Fruit Quality.

Dmitry Kechasov,Michel J Verheul,Anush Panosyan,Martina Paponov,Ivan A Paponov

doi:10.3389/fpls.2021.680030

Dmitry Kechasov, Michel J Verheul + Show 3 more

Open Access

https://doi.org/10.3389/fpls.2021.680030

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Abstract

In regions with intensive agricultural production, large amounts of organic waste are produced by livestock animals. Liquid digestate from manure-based biogas production could potentially serve as fertilizer if integrated with closed horticultural irrigation systems. The aim of this experiment was to investigate how fertilizer based on liquid biogas by-products of pig manure digestion can affect the growth and production of tomato plants. Integration of a nitrification bioreactor presumes a significantly lower concentration of nutrient solutions and a higher level of oxygenation than classical mineral cultivation. Therefore, additional controls were included. We compared plant growth and fruit quality traits of tomato plants grown in a hydroponic solution with organic fertilizer with two levels of mineral fertilizer. The tomatoes grown with organic waste-based liquid fertilizer showed reduced growth rates but increased mean fruit size, resulting in no significant change in total yield compared with high-mineral cultivation. The growth rate was similarly reduced in plants cultivated with low-mineral fertilizer. Plants cultivated with organic waste-based fertilizer had high Cl− concentration in xylem sap, leaves, and, ultimately, fruits. The leaves of plants cultivated with organic waste-based fertilizer contained higher concentrations of starch and soluble carbohydrate and low concentrations of phosphorous (P) and sulfur (S). The plants grown with organic waste-based or low-mineral medium showed significantly poorer fruit quality than the plants cultivated with the high-mineral solution. The low-mineral treatment increased xylem sap contribution to fruit weight because of higher root power. The organic waste-based fertilization did not change the root power but increased fruit size. In conclusion, organic waste-based cultivation is a possible solution for sustainable plant production in greenhouses. However, additional adjustment of nutrient supply is required to improve fruit quality.

Highlights

In northern latitudes, year-round cultivation of high-value vegetables, such as tomatoes, can only be conducted in greenhouses
Tomato cultivation in a closed re-circulating hydroponics system using organic waste-based fertilizer and an integrated nitrification bioreactor was confirmed in this study to produce yields comparable with those achieved with current hydroponic technology
We found that (I) organically cultivated plants had a lower growth rate compared to plants cultivated with conventional nutrition, and this was related to the low concentrations of essential nutrient elements in the organic waste-based nutrient solution; (II) fruits of organically cultivated plants were larger in size, that was related to greater availability of Cl− in the nutrient solution of organic hydroponics and subsequently higher Cl− accumulation in the fruits; (III) tomato plants grown with an organic waste-based nutrient solution accumulated more carbohydrate in the leaves; and (IV) fruits cultivated with organic waste-based fertilizer or a low-mineral treatment had lower quality than fruits cultivated with the highmineral nutrient solution

Summary

Introduction

Year-round cultivation of high-value vegetables, such as tomatoes, can only be conducted in greenhouses. Tomatoes are grown in soilless cultures using nutrient film techniques (NFT) or rockwool slabs with drip irrigation. Closed-cycle soilless systems, where all leachate is recycled, can further reduce fertilizer run-off by 30–40% compared with open-cycle systems (Montesano et al, 2010). Current disinfection procedures (e.g., heat treatment, ozone, hydrogen peroxide, and UV radiation) are not sustainable (Maessen and Verheul, 2016) These treatments create a sterile root environment, making roots prone to invasive diseases and increasing potentially explosive disease outbreaks. Experiences with organic growth systems have shown that the development of diseases is seldom explosive in these systems This might reflect the natural non-sterile biological environment that promotes a root zone that is more resistant to invasive diseases

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