Abstract
The European Green Deal proposes the reuse of any kind of waste that can be safely repurposed; sludge may also be reused as a biosolid. The present research aims to evaluate a biosolid made from sludge, originating from a wastewater treatment plant (WWTP) for its effect on tomato growth and enhancement of tolerance against the phytopathogenic fungus Fusarium oxysporum f. sp. radicis-lycopersici (Forl). Peat and/or two soil types were amended with biosolid (0, 80 and 160 tons/ha) to form substrates on which tomato plants were grown either under controlled conditions, in a growth chamber or outdoors, in a net protected area. Plant growth and disease parameters were recorded 4–7 weeks after application of Forl inoculum in the substrates. Results showed that biosolid addition enhanced plant growth and increased tolerance against tomato foot and root rot caused by Forl. Specifically, fresh weight, root weight, stem height and leaf number of tomato plants in Forl-inoculated soils that had received biosolid, were increased when compared to Forl-inoculated control soils. Forl resulted in higher disease severity on plants grown outdoors in biosolid plus clay soil than in biosolid plus sandy soil, while the opposite occurred under controlled conditions where higher disease index was recorded on plants grown in peat plus sandy soil than in peat plus clay soil. These findings strongly suggest that this biosolid may act as an organic fertilizer and possible stimulant of tomato tolerance against Forl, and the effect is soil type dependent. Therefore, this biosolid should be considered for its possible use in agriculture according to the principles of circular economy and waste minimization. • Biosolid addition enhances tomato growth in different substrates and conditions. • Disease is less severe on plants grown on soil mixed with biosolid. • In the outdoors trial biosolid renders higher disease tolerance in sandy soil. • Fusarium disease is less aggressive on tomato plants grown on biosolid mix. • Tolerance to disease is higher in sandy soil+biosolid than in clay soil+biosolid.
Highlights
The main disposal method of sludge produced by wastewater treatment plants (WWTP), has been landfilling due to its relatively low cost
The findings strongly support the evidence that this biosolid may act as an organic fertilizer and as a possible stimulant of tomato tolerance against Forl
For the data obtained from tomato plants grown under controlled conditions, analysis of variance (ANOVA) results showed that the biosolid levels, inoculum levels and peat mixtures along with the interactions “biosolid by inoculum” and “inoculum by peat mixture” had a statistically significant effect, at P≤0.05, on the parameters disease index, fresh weight, root weight, stem height and number of leaves
Summary
The main disposal method of sludge produced by wastewater treatment plants (WWTP), has been landfilling due to its relatively low cost This method has been abandoned in many countries because of strict environmental regulations Precautions should be taken when using sludge-based biosolids as soil amendments, in order to avoid soil pollution with toxic metals and toxic organic compounds or soil contamination with dangerous pathogens (Clarke et al 2016; Gonzalez-Ollauri et al 2020) For this reason, European legislation has set limit values for metals of toxicological concern when sludge is used for fertilization (Council Directive 86/278/EEC)
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