Summary
This 152-year analysis of the Park Grass Experiment reveals how soil management practices and environmental factors influence iodine and selenium dynamics in grassland systems. Liming increased the loss of both micronutrients from soil, whilst phosphate and sulphate fertilisers reduced herbage concentrations through ion competition and growth-dilution effects. The findings suggest that in intensively managed, pH-controlled pastures, herbage alone is unlikely to meet the iodine requirements of grazing livestock.
UK applicability
These findings are directly applicable to United Kingdom grassland and pasture management, particularly for livestock farming systems where soil pH is actively managed. The results highlight a potential micronutrient gap in grazing animals reliant on forage from improved grasslands, with implications for animal health and productivity in UK pastoral regions.
Key measures
TMAH-extractable selenium and iodine concentrations in soil (0–23 cm) and herbage; soil-to-plant transfer factors; herbage yield; growing season rainfall; soil pH and chemical properties
Outcomes reported
The study measured long-term trends in iodine and selenium concentrations in soil and herbage samples from the Park Grass Experiment (1876–2008), assessing the effects of mineral fertilisers, organic manures, liming, rainfall and crop yield on retention and bioavailability. Results showed that liming reduced soil iodine and selenium retention, phosphate and sulphate fertilisers suppressed herbage concentrations through ion competition and yield dilution, and herbage uptake of both elements remained negligible relative to soil stocks and atmospheric inputs.
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