Summary
This comparative study evaluated ten composts varying in feedstock material, composting method, and maturity using integrated biological and chemical assessment protocols. The analysis reveals a fundamental trade-off: composts from nutrient-rich sewage sludge exhibited high heavy metal burdens and phytotoxic effects despite superior nutrient profiles, whilst composts from yard waste and household sources demonstrated better agronomic performance with good-quality humus despite lower absolute nutrient levels. The findings underscore the importance of feedstock selection in balancing nutrient delivery with contaminant risk and biological efficacy.
UK applicability
These findings are directly relevant to UK composting policy and practice, particularly regarding the use of sewage sludge-derived composts in agriculture and horticulture. The results align with UK Quality Protocol for the Production and Use of Quality Compost from Source-Separated Biodegradable Waste, which restricts heavy metal concentrations, and may inform decisions about home and community composting schemes.
Key measures
Seed germination rate, plant root growth intensity, macro- and micronutrient content, heavy metal presence, humic substance quality and quantity
Outcomes reported
The study compared 10 different composts using biological tests (seed germination, root growth) and chemical analysis (macro/micronutrient content, heavy metals, humus quality). Results showed sewage sludge-based composts had highest nutrient and heavy metal content but inhibited plant growth, whilst yard trimmings and household waste composts showed superior biological performance despite lower nutrient levels.
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