Summary
This long-term field study evaluated the impacts of recycling biosolids (digested sludge cake) to agricultural land at four contrasting English sites over 20 years. Biosolids application significantly increased soil organic matter by 10–17%, available water capacity by up to 10%, and key nutrients (nitrogen, phosphorus, sulphur), whilst also doubling earthworm populations in low-metal treatments, with no observed adverse effects on crop quality, suggesting biosolids recycling is a viable means of maintaining soil fertility and organic matter.
UK applicability
The study was conducted across four English sites with differing soil types and agroclimatic conditions, making the findings directly applicable to UK agricultural practice and policy on sustainable biosolids recycling. Results support the evidence base for maintaining biosolids recycling as part of a sustainable agricultural landbank strategy in the United Kingdom.
Key measures
Soil organic matter (% increase), light fraction SOM (mg kg⁻¹), available water capacity (% increase), water infiltration rate, aggregate stability, total nitrogen (% increase), extractable phosphorus (% increase), total sulphur (% increase), earthworm numbers and weight
Outcomes reported
The study measured changes in soil physical, chemical, and biological properties after 20 years of biosolids application, including soil organic matter, nutrient content, water capacity, and earthworm populations. Crop quality was monitored to assess any adverse effects.
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