Summary
This field trial evaluated whether dewatered dairy processing sludge could replace mineral fertilisers for phosphorus and nitrogen supply in grassland systems. All sludge types applied at 40 kg-P ha⁻¹ produced comparable yields and phosphorus uptake to mineral treatments, with phosphorus index maintained at adequate levels. Iron-precipitated and calcium-precipitated sludges showed advantages for nitrogen availability in early harvests, suggesting these by-products could support nutrient recycling without compromising crop performance.
UK applicability
The study was conducted in the United Kingdom on soils representative of dairy farming regions, directly addressing UK grassland management and the challenge of sustainably valorising dairy processing by-products. Findings are immediately applicable to UK farm practice and food industry nutrient recycling policy.
Key measures
Grass yield, phosphorus and nitrogen uptake, Morgan's soil phosphorus index, soil phosphorus availability, crop phosphorus concentration
Outcomes reported
The study assessed phosphorus and nitrogen fertiliser replacement value of four types of dairy processing sludge applied to grassland at field scale over one growing season, measuring crop yield, nutrient uptake, and soil phosphorus status. Four sludge types (Al-precipitated, Fe-precipitated, and two Ca-precipitated variants) were compared against mineral fertiliser treatments.
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