Efficacy of s-triazines as influenced by adsorption and mobility of various soils
1991
Rungsit Suwanketnikom | Ronnayoot Sattayanikom (Kasetsart Univ., Bangkok (Thailand). Faculty of Agriculture. Dept. of Agronomy)
Field experiments were conducted on Kampang Saen clay, Kampang Saen silty loam and Nampong sand in 1987 and 1988 to study the efficacy of atrazine, ametryn, dimethametryn and simazine and the influence of various soil parameters on s-triazine efficacy. The average rates of all herbicides were required to produce 80 % weed control at 8 weeks after application were in the order simazinedimethametrynatrazine=ametryn. The average rates of all herbicides required for 80 % weed control across herbicides were in the order Kampang Saen clayKampang Saen sitly loamNampong sand. The efficacy of herbicides were corrrelated with CEC values but negatively correlated with % sand contents. Soil with high CEC value required high rate of s-triazines. But soil with high sand content required low rate of herbicides. Laboratory experiments indicated that adsorption of herbicides were in the order dimethametrynsimazineatrazine=ametryn while adsorption of dimethametryn and simazine were correlated with CEC values. The adsorption of atrazine and ametryn were correlated with % clay, % organic matter content and CEC values respectively but negatively correlated with % sand content. Rf values indicated that mobility of herbicides were in the order atrazinesimazineametryndimethametryn. Furthermore the movement of herbicides were correlated with % sand content but negatively correlated with all soil parameters. The herbicide efficacy, adsorption and mobility did not get into the same order suggested that efficacy of herbicides could not only be attributed to differences in soil adsorption and mobility but also molecular toxicity and environmental factors
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