The effect of iodine on soils and plants

Summary. 1 No definite evidence of partial sterilisation with iodine was obtained when a number of different soils were treated with various combinations and strengths of iodine, the bacterial numbers with different treatments varying either very little or inconsistently. A suggestion of beneficial action with iodoform was obtained, if the right conditions could be found. 2 Germination of tomato seeds in ?sick? soils was not affected by treatment with iodine in sodium iodide, and the initial vigour of treated and untreated plants was very similar. 3 The loss from ?damping off? of tomato seedlings was not reduced by treatment before sowing, over a wide range of concentrations of iodine in sodium iodide. 4 Germination of mustard is either inhibited or badly checked by strong doses of iodine. In the latter case some of the plants eventually make a striking recovery and ultimately surpass the untreated controls in green and dry weight. If some time elapses between treatment and sowing the toxic action of iodine disappears and the mustard is unaffected, showing neither the initial toxic effect nor the later recovery and stimulation. 5 Barley is decidedly more sensitive than mustard to the toxic action of iodine, as germination is inhibited by a smaller dressing. With an amount of iodine that allows the seeds to germinate, though checking them badly, the plants frequently die off and never make the recovery nor show the stimulation of mustard under similar circumstances. With various intervals between treatment and sowing barley is still killed off at a time of sowing and with a strength of iodine that allows mustard to make its greatest recovery. 6 The various means whereby iodine may be put out of action in the soil are discussed and the suggestion is made that iodine might possibly have some specific and effective action if means could be found to prevent it from being converted from the elemental state so rapidly as appears usually to be the case. 7 Although no definite partial sterilisation effect has been obtained and though mustard and barley show little or no significant reaction, the possibility is not excluded that other agricultural crops, e.g. mangolds and sugar beet, might be benefited by the use of small amounts of iodine in addition to the usual fertilisers.