Abstract
Perennial ryegrass was grown in pots in a sandy loam soil, into which iodide, elemental iodine or iodate had been incorporated at a rate of 20 mg I/kg. The uptake of iodine into the herbage was much greater from iodate than from the other two forms. Replacement of 5 % of the soil by well‐decomposed farmyard manure reduced uptake from all three forms of iodine more than ten‐fold. Similar replacement by chalk reduced uptake from iodide but increased uptake from iodate. The recovery of added iodine in three successive harvests of ryegrass ranged from 0.03% for elemental iodine in combination with soil + FYM to 2.16% for iodate in combination with soil + chalk.