Struvite fertiliser offers a sustainable solution for recycling of phosphorus for crop growth without altering the soil resistome
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Background
The reserves of rock phosphate, used to produce fertilisers, are being exhausted by the ever-increasing pressure to meet the food demands of a growing world population. Sustainable alternatives are urgently needed, and struvite, a renewable phosphorus fertiliser recovered from waste streams such as animal manure, offers a promising solution. However, other manure-derived fertilisers have been associated with the promotion of antimicrobial resistance (AMR) in soil, raising concerns about whether struvite might pose similar risks. Despite this, the impact of struvite on the soil resistome remains poorly understood.
Methods
This study assesses the AMR risk associated with Xiamen struvite (XIA), produced from piggery wastewater, compared with two commercial fertilisers: Crystal Green (CG) and Triple Super Phosphate (TSP), and an untreated control soil. Following a three-month fertilisation period, rhizospheric soils were analysed using mass spectrometry to investigate antimicrobial residues in the soil, and shotgun metagenomics and culture-based assays, and bacterial isolate characterisation to identify bacterial AMR linked to the treatments. Notably, this is the first study to apply culturing methods to investigate struvite’s impact on AMR.
Results and conclusions
While XIA struvite soil fertilisation led to an increase in total culturable bacterial load, (CFU/g), there was no evidence of antimicrobial residues detected in soil, as confirmed by mass spectrometry. Metagenomic profiling further revealed no significant alterations to antimicrobial resistance genes (ARGs) across all treatments, including CG, TSP, and untreated controls. Culture-based analysis supported these findings, with tetracycline-resistant bacteria undetected and only minimal resistance observed to erythromycin, florfenicol, and neomycin. Although resistance levels to amoxicillin, streptomycin, and trimethoprim were higher in XIA-treated soils, this appeared to reflect a broader increase in microbial load rather than selective enrichment of resistant strains. These data suggest that piggery-derived struvite does not impose a clear AMR risk in soil and performs similarly to conventional fertilisers. While it appears to increase total bacterial load, there is no evidence of selective enrichment for AMR bacteria. However, variability in antimicrobial and ARG content across studies highlights the need for standardised production specifications for struvites to ensure safety and consistency. This study provides the most comprehensive assessment to date of struvite’s AMR implications, supporting its potential as a safe, sustainable fertiliser and contributing valuable insights to inform regulatory guidance.
