Bioponics—An Organic Closed-Loop Soilless Cultivation System: Yields and Characteristics Compared to Hydroponics and Soil Cultivation

Abstract

Sustainable food production has become increasingly important. Soilless cultivation systems offer several advantages, such as water and nutrient use efficiency, and can be implemented where traditional agriculture is impossible. Bioponic systems use locally or regionally available nutrient sources from organic waste streams (either fluid or solid) and can thus contribute to closing nutrient cycles locally. Bioponics harnesses the metabolic processes of microorganisms which release nutrients from organic matter. This study aimed to set up a bioponic system, by using biogas digestate concentrate and biochar as nutrient sources, and promoting nutrient release from the organic sources by including a biofilter in the system. The development of water quality, plant growth, and quality was monitored extensively. In addition, the influence of either the fungal biocontrol agent Trichoderma atrobrunneum or UV-C treatment of the nutrient solution on plant health and growth was investigated. Three cultivation cycles with Lactuca sativa (“HAWKING” Salanova®) in bioponic (BP), hydroponic (HP), and soil (SO) cultivation were performed. The study showed that healthy lettuces could be produced in BP systems, using a biogas digestate concentrate and biochar as nutrient sources, despite salt accumulation in the nutrient solution. In plant sap analyses, lettuces cultivated in BP systems contained less nitrate but more ammonium and chloride. The yield of the lettuces grown in the BP systems was intermediate, compared to the HP and the SO. The fungus, T. atrobrunneum, strain, T720, survived in soil and soilless cultivation systems. Compared to the HP and the SO systems, the shoot height of lettuces grown in the BP system, with the application of Trichoderma, was significantly increased. In SO systems with Trichoderma application, a significantly higher chlorophyll and flavonoid content, but significantly lower shoot height was observed. The fresh weight of lettuce roots was significantly higher in HP systems with Trichoderma treatment. Cultivating plants by using organic waste streams requires commitment and experience from producers. In BP systems, a biofilter (either within the system or externally, to increase nutrient levels) can help to rapidly convert the ammonium-rich fertilizer to plant-available nutrients. Unlike conventional HP systems, in BP systems, nutrients are released slowly over time, requiring close monitoring and adjustments. In conclusion, healthy lettuces for human consumption can be produced in BP systems, and the application of the biocontrol agent used has some beneficial influence on plant growth.

A Low-Tech Approach to Mobilize Nutrients from Organic Residues to Produce Bioponic Stock Solutions

“…The yield of lettuce grown in bioponic solution was only one fifth (21%) of the lettuce yield when grown in the Hoagland solution. This was lower than most other published results for yields of bioponically grown lettuce, relative to mineral nutrient solution grown lettuce as reported by Gartman et al [22], Williams and Nelsons [52], Liedl [10], and Atkins and Nichols [55], who obtained 72%, 63%, 56%, and 23%, respectively.…”

“…This may have additionally reduced plant growth and could be an explanation for the equally reduced plant growth in the spiked bioponic solution, despite a good NH 4 + :NO 3 − ratio. Increasing the nutrient concentration in the bioponic solution in order to increase yield, as proposed by Gartman et al ( 2023) [22], can, therefore, not be applied to the present study. A more promising approach could be diluting the solution or reducing the number of microorganisms by suitable measures.…”

“…Neither Williams and Nelson [52], Liedl et al [10], nor other studies [22,55] described a high microbial load leading to a strongly developed biofilm on the roots, potentially reducing their oxygen supply and hosting pathogens, like Pythium spp., which can cause root rot [57]. This may have additionally reduced plant growth and could be an explanation for the equally reduced plant growth in the spiked bioponic solution, despite a good NH 4 + :NO 3 − ratio.…”

“…Accordingly, Shinohara et al (2011) [16] were able to nitrify all NH 4 + in an aerated aqueous solution containing soluble fish-based fertilizer. Further, the combination of anaerobic digestion for mineralization and a subsequent aerobic treatment for nitrification has been investigated in several studies [8,12,21,22]. However, problems such as phytotoxicity, high pH, and low and imbalanced nutrient concentrations, causing poor plant growth, also occurred regularly with aerobically produced bioponic solutions [8,11,12,21,22].…”

Reducing the risks associated with the ingestion of vegetables grown on soils contaminated with trace metal elements through the application of soil amendments: Results of experiments in Lubumbashi/Democratic Republic of the Congo.

“…Studies carried out by (MunungaKatebe et al 2023) showed that the level of contamination, pollution and enrichment of each market garden was not the same, as the majority of gardens were contaminated. We therefore recommend that urban market gardens in Lubumbashi with extremely high levels of contamination, as well as those with exceptionally high levels of pollution, use soilless production techniques such as conventional hydroponics or bioponics to guarantee the quality of the vegetables produced in their gardens to safeguard human health(Dhawi 2023;Gartmann et al 2023;Magwaza et al 2020;Mai et al 2023). The Congolese government must ensure that planning for urban agriculture in the country takes into account the implications of pollution and high levels of contamination on the potential risk posed by market gardens.…”