Summary
This 1984 study compared nitrogen fertilisation strategies on nitrate accumulation in leafy vegetables, finding that composted farmyard manure—a slow-release source—produced significantly lower nitrate concentrations than equivalent NPK applications in spinach, Swiss chard, head lettuce, and corn salad. Findings were corroborated by analysis of products from paired conventional and organic growers. Whilst compost-grown vegetables typically yielded less, cultivar selection could equalise yields, suggesting a low practical risk of excessive nitrate even at high compost doses (300 kg N/ha).
Regional applicability
The study predates modern UK regulations on nitrate limits in food and water, yet its findings on slow-release organic nitrogen reducing nitrate bioaccumulation remain relevant to UK organic and regenerative farming practice. Applicability to contemporary UK temperate horticulture is high, though modern cultivars and agronomic practices may differ.
Key measures
Nitrate concentration (mg/kg or similar), crop yield, nitrogen application rate (kg N/ha)
Outcomes reported
Nitrate concentrations in leafy vegetables (spinach, Swiss chard, head lettuce, corn salad) were measured under pot and field trials comparing composted farmyard manure versus NPK fertiliser application. Crop yields and variety-specific responses were also assessed.
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