Summary
This controlled field trial examined how applying different types of sheep excreta affects selenium uptake by perennial ryegrass across soils varying in organic matter. Counter to expectations, excreta application either maintained or reduced grass selenium concentration and accumulation, with particularly marked reductions in high organic matter soils receiving faeces, likely mediated by selenium sorption and microbial reduction. The findings suggest direct animal supplementation is more effective than manure application for sustaining ruminant selenium intake through forage.
UK applicability
These findings are directly applicable to UK sheep farming systems, where manure application is standard practice and forage selenium status is a known constraint on ruminant and human nutrition. The results indicate that relying solely on excreta recycling may not address selenium deficiency in grazing livestock, supporting the case for targeted mineral supplementation strategies in UK pastoral systems.
Key measures
Selenium concentration in perennial ryegrass tissue (ICP-MS analysis); total selenium accumulation in grass; soil organic matter content; excreta type (urine, faeces, or combination); source of animal selenium supplementation (organic vs. inorganic)
Outcomes reported
The study measured selenium concentration and total accumulation in perennial ryegrass grown in soils of differing organic matter content, following application of sheep urine and/or faeces from animals supplemented with organic or inorganic selenium sources. Biogeochemical mechanisms underlying selenium availability were investigated through wet chemistry analysis.
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