Leaching of atrazine 6-chloro-N-ethyf-N#x2032;-(methylethyl)-1,3,5-triazine-2,4-dlamine and terbuthylazine 6-chloro- N-(1,1-dirnelhylethyt)-N#x2032;-ethyl-1,3,5-triazlne-2,4-diamine was studied in 23 soils by means of the soil thick-layer leaching method. The equivalent of 4 kg ai ha#x2212;1of both herbicides was leached with water equivalent to 129 mm rain Distances leached were measured qualitatively in bioassays with the test plantTnfolium repensL. Leaching distances in different soils varied from 6#x2013;20 cm for atrazine, and from 2#x2013;16 cm for terbuthylazine. Atrazine leached at least 10 cm in 13 soils, while terbuthylazine did not move from the zone of application in 12 soils. Of the five soil properties assessed by means of simple regression, organic matter content (C) and P-reversion were significantly correlated with the leaching distance of atrazine, and C with the mobility of terbuthylazine. Relationships between herbicide leaching and either total clay content or soil pH were relatively weak. The combination of organic matter content and soil pH in multiple regression analysis gave the best prediction of leaching for atrazine (R=0.85) and terbuthylazine (R= 0.42). It is suggested that the regression models incorporating C and pH be used for rapid ranking of soils regarding their leaching indices for the two compounds The models may prove useful for preliminary identification of soils which are prone to leaching of the herbicides.
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