The absorption and movement of sodium chlorate when used as an herbicide
1933
Loomis, W.E. | Smith, E.V. | Bissey, R. | Arnold, L.E.
1. Serum chlorate apparently penetrates readily all of the external surfaces of the plant with the exception of unusually heavy cuticle or corky layers and may be expected to gain entrance to the plant whether applied to the leaves, to herbaceous stems, to rhizomes, or to roots. 2. The data presented indicate that the movement of sodium chlorate within the plant is principally in the xylem and is most rapid in the direction of the transpiration stream. With the higher transpiration rate of plants growing in moist soil and moderately dry atmosphere, there was a more rapid spread of chlorate throughout the plant, whether it was applied to a portion of the top or to the soil about the roots. Removing the phloem did not appreciably hinder the movement of sodium chlorate, but checking transpiration by vaselining the leaves or holding the plants in humid atmosphere sharply reduced the movement. 3. Sodium chlorate, whether applied to the soil directly or reaching it in the drip and leachings from sprayed plants, has persisted in the soil in an apparently unchanged form for 2 1/2 years. This chlorate was washed into the subsoil by rainfall and, perhaps because of the lower temperatures, it was particularly persistent when large quantities of the salt were allowed to accumulate in an unleached subsoil. Sodium chlorate in the soil solution may be absorbed by the roots and rhizomes of plants and translocated to the tops so that both tops and roots are killed by the toxin. The efficacy of this herbicide seems to be related to this continued action which may finally result in the death of persistent perennials. 4. The removal of sodium chlorate from the soil by leaching is possible, but large volumes of water are required and the evidence points to the decomposition of the salt as the principal cause of its disappearance. Decomposition is fairly rapid in moist soil at temperatures above 20 degrees C, but may be very slow in cool dry soil. This behavior of the chlorate can be used to advantage both in assuring a continued action on persistent weeds and in avoiding excessive accumulation of chlorates in soils in which decomposition is normally slow.
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