Summary
This 152-year longitudinal analysis of archived samples from the Park Grass Experiment reveals divergent trends in soil iodine and selenium retention between limed and unlimed control plots, with differences broadly attributable to atmospheric inputs. Herbage offtake of both elements was negligible relative to soil concentrations, yet a positive correlation between soil and plant concentrations suggests shared bioavailability controls. The findings indicate that under intensive agriculture with soil pH management and phosphate/sulphate fertiliser use, grazing animal iodine requirements are unlikely to be met through herbage alone.
UK applicability
These findings are directly applicable to UK grassland and mixed farming systems, as they are based on a long-running UK field experiment under representative soil and climate conditions. The conclusion that herbage iodine concentrations may be insufficient for grazing livestock has immediate relevance to UK farm management and animal health policy.
Key measures
TMAH-extractable selenium and iodine concentrations in soil (0–23 cm depth) and herbage (μg/kg); soil-to-plant transfer factors; herbage yield; growing season rainfall; soil pH
Outcomes reported
The study measured historical trends in iodine and selenium concentrations in soil and herbage from 1876 to 2008 across plots with different fertiliser and manure amendments, and with and without liming. It assessed how soil amendments, rainfall, crop yield and soil chemistry changes affected retention and bioavailability of these micronutrients.
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