Efficacy of s-Triazines as Influeced by Adsorbtion and Mobility of Various Soils

Abstract

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 simazine > dimethametryn > atrazine =ametryn. The average rates of all herbicides were requited to produce 80% weed control across herbicides were in the order Kampang Saen clay > Kampang Saen silty loam > Nampong sand. The efficacy of herbicides were correlated with CEC values but negatively correlated with % sand contents. These results indicated that soil with high CEC value required high rate of s-atrazines. But soil with high sand content required low rate of herbicides. Laboratory experiments indicated that adsorption of herbicides were in the order dimethamethyn > simazine> atrazine = ametryn. While adsorption of dimethametryn and simazine were correlated with CEC values. The adsorption for 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 atrazine > simazine > ametryn > dimethametryn. 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.