In nutrient solution, 2,3,6-trichlorobenzoic acid (2,3,6-TBA) was less toxic to oats than either 2-methoxy-3,6-dichlorobenzoic acid (dicamba) or 3-amino-2,5-dichlorobenzoic acid (amiben). The latter two herbicides were similar in phytotoxicity.
In soil, dicamba was the most phytotoxic in each of four soils used, while 2,3,6-TBA and amiben were similar in toxicity in all soils except the organic soil, in which amiben was less phytotoxic than 2,3,6-TBA. In the sandy soils the same amount of herbicide was required to reduce the growth of oats by 50% as was required in nutrient solution, but considerably higher amounts were required in the organic soil. This reduction in phytotoxicity was attributed to adsorption of the herbicides in an unavailable form by the organic matter of the soils, amiben being adsorbed to a greater extent than 2,3,6-TBA or dicamba. Practically no adsorption occurred on the clay colloids of the various soils.
In persistence studies, amiben was more subject to apparent microbial decomposition than 2,3,6-TBA or dicamba. Decomposition was more rapid in the organic soil than in the clay or sandy soils. In leaching studies, the three herbicides were readily washed out of columns of the various soils. Differences in movement of herbicide in these soils could be related to the rate of water movement through the soil.