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A study of fertilizers made from separately collected sanitation streams found no systematic crop-yield disadvantage compared with mineral fertilizers. That is evidence that the recycled products examined can perform agronomically—not proof that every recycled fertilizer is interchangeable with every conventional product. Nutrient composition, processing, crop, soil and application all affect whether a particular product is suitable.
What the study found
An announcement from the Institute for Social-Ecological Research (ISOE), published on 13 October 2026, reports that researchers found no systematic yield disadvantage across the recycled fertilizers examined. Yields were generally significantly higher than in unfertilized controls. The finding applies to the products and trials analyzed; it does not show that all recycled fertilizers produce identical results to all mineral fertilizers.
The products came from resource-oriented sanitation systems (ROS), which separately collect nutrient-rich streams from human excreta, treat them and recover materials for potential agricultural use. Rather than treating “recycled fertilizer” as one uniform input, the study characterized products individually.
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How much evidence the analysis covered
ISOE reports that the researchers compiled more than 450 data sets from over 200 sources across 32 countries. Of these, 13 types of recycled fertilizer had enough information for detailed characterization. The agronomic analysis was a separate quantitative meta-analysis: it combined 134 data sets from 68 sources, covering 31 crop species and field, pot and hydroponic trials.
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The size and range of this evidence base make the findings relevant across multiple crops and trial settings, but the pooled result does not erase differences among products or conditions. The announcement does not provide individual results for each fertilizer type, crop or trial, so it cannot establish a universal performance ranking.
Why one recycled fertilizer may perform differently from another
Feedstock and treatment shape what a recovered fertilizer contains and how it behaves. The announcement notes variation in nutrient content, nutrient form and concentration, as well as pH, salt content and organic-matter proportion. These properties can affect both nutrient availability and suitability for a particular crop, soil and management practice.
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For a farm or other user evaluating a specific product, the relevant comparison is not simply “recycled versus conventional.” It is whether the product’s characteristics match the intended use. Useful factors include:
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- Growing conditions: The crop, soil and application practice, including how the product fits into the broader nutrient-management plan.
- Product quality: Feedstock, treatment and reliable characterization of properties such as pH, salt and organic matter.
- Safety evidence: Hygiene controls and relevant contaminant testing for the specific product and its production process.
- Approval: Whether the product is permitted for the intended agricultural use under applicable local rules.
What the announcement says about safety
For the products examined, ISOE reports that heavy-metal concentrations were predominantly low and comparable to those in established fertilizers. That finding should not be read as a blanket safety determination for every product or every contaminant. The announcement says evidence on organic contaminants, including pharmaceutical residues and PFAS, remains incomplete and does not allow a similarly comprehensive assessment across all product groups.
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Hygienic safety is also tied to feedstock and treatment conditions. A yield result alone cannot establish that a product is safe to handle or apply. Users need product-specific quality information and applicable safety and approval requirements.
What would make wider agricultural use practical
The authors identify reliable characterization and integration into agricultural quality-assurance and regulatory systems as practical challenges. They call for comparable testing methods, robust quality criteria and organizational frameworks. Those steps would help users evaluate products consistently and determine where they are appropriate.
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ISOE’s announcement characterizes phosphorus recovery from sewage sludge and sewage-sludge incineration ash as already regulated within conventional wastewater systems, while saying comparable agricultural-use and approval pathways for ROS systems are still lacking. This is the authors’ characterization, not a complete account of the law in every jurisdiction; requirements depend on location and intended use.
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Martina Winker of ISOE said the key question is the fertilizer’s properties for a particular application, rather than whether it comes from a conventional or recycled stream. The study’s conclusion therefore supports evaluating recovered products on their measured quality and agronomic fit, not assuming that their origin alone determines their performance.
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Study details
The paper is by Corinna Schröder, Franziska Häfner, Ariane Krause, Moritz Hallama and Martina Winker: “Recycling fertilizers from resource-oriented sanitation systems: product-level characterization and meta-analysis of agronomic performance,” published in Frontiers in Environmental Science, volume 14, article 1843173 (2026). The findings summarized here are those reported in ISOE’s 13 October 2026 announcement.
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