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As determined by bioassay of segmented soil columns, a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), N-butyl-N-ethyl-a,a,a-trifluoro-2,6-dinitro-p-toluidine (benefin), and 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) varied in their leachability in a clay loam soil, even though their water solubility is the same. Nitralin was by far the more easily leached, benefin was least leached, and trifluralin slightly more so than benefin. Four A-in or more of water readily leached nitralin deep enough into the soil in amounts great enough to adversely affect the root growth of sensitive crop plants. Trifluralin and benefin were leached into the soil in relatively minute amounts, and these amounts were not great enough to affect root growth of sensitive crop plants when at least 0.5-in of untreated soil separated the seed from the layer of soil in which the herbicides had been mixed. The apparent breakdown product of nitralin present in moist soil was leached as readily as nitralin.

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No abstract

Field screening methods were developed which proved very reliable in accurately assessing the potential of herbicides during the first year of testing. Under conditions imposed by these methods, the herbicides usually exhibited maximum toxicity, thereby indicating which ones might be potentially hazardous in growers' fields when crop tolerance is lowered by adverse growing conditions. Of the 29 crop uses suggested by the data, 16 are registered by the USDA and are now in current use. Of these 29, 26 were indicated during the first year of testing and substantiated by data from an additional 1 to 4 years of testing.