Toxicity of arsenic, borax, chlorate, and their combinations in three California soils

does not appear. First page follows. Introduction In weed control it is often desirable to apply two or more chemicals at the same time. Where, for example, both annuals and deep-rooted perennials occur, arsenic and chlorate combined may be used for complete sterilization. In such cases one must know the reciprocal effects of these reagents in order to use them with any assurance of success. This paper describes experiments designed to show the toxicity of three common herbicides used two and three at a time in three California soils. Toxicity Studies Tests on the toxicity of sodium arsenite and sodium chlorate (2)4 and sodium borate (3) used separately, in these soils have been published and the technique has been described. Briefly, it consists in growing indicator plants, Kanota oats in this case, in soil cultures in No. 2 cans. The chemicals being studied are added to the air-dry soil, dissolved in sufficient water to bring the soil to its field capacity. The cultures are then seeded and grown for 30 days, at which time the height and fresh weight of the indicator plants are recorded. In the preliminary toxicity tests (2), (3) concentration series were used covering the complete range from 0 to 100 per cent toxic and beyond, so that cultures were included that showed no plant growth even after several croppings. In the present experiments two arbitrary growth levels were selected: the 50 per cent level at which growth was reduced to approximately one-half that of the untreated checks, and the 10 per cent level at which growth was correspondingly reduced to a low value. The concentrations used to produce growth at these two levels were derived from the original toxicity curves, the data from the first runs with the three chemicals being computed in terms of percentage of checks. Table 1 gives the values expressed as parts per million in terms of the air-dry soil. For the borax they have been converted to the hydrous form that contains 47 per cent water by weight.