Transport of Triazine Herbicides in Runoff from a Hillside

Abstract

The triazine herbicides were applied to the cultivated clay loam and clay soils of 8 - 10 and 25 - 28% slopes, respectively at the rate 4 kg (ai) ha in teh middle of the rainy season at Royal Angkhang Highland Agriu Agricultlure Research Station, Fang District, chiangmai, High amounts of herbicides were lost from both slopes 1 to 3 days after application but the loss from 8 - 10% slope were higher. At 8 - 10% slope the maximum concentrations in the runoff were atrazine 64, cyanazine 19, simazine 247, and metribuzin 99 ug/1. At 25-28% slope the maximum concentrations in the runoff were atrazine 67, cyanazine 29, simazine 378, and metribuzin 70 ug/1. The avereage amounts in water phase were atrazine 43, cyanazine 68, simazine 46, and metribuzin 72% of the total amount of herbicides found in both sediment and water phases.
The maximum concentration of herbicides were applied to leaves and to sundy loam soil where test plants were grown under greenhouse conditions. No herbicide reduced plant dry weight when applied to leaves indicating that the herbicides were not taken up by leaves. Atrazine, cyanazine, and simazine did not reduce plant dry weight when applied to soil. This is believed to be due to theadsorption of herbicides onto soil colloids. However metribuzin reduced plant dry weight when applied to sandy loam soil indication that metribuzin needs soil with higher organic matter and clay to act as adsorbents.
Total loss of atrazine, cyanazine, and metribuzin on the slopes were less than 1% of applied rate rrspectively while simazine was lost at less than 4%. All herbicides were leached to 7.5 to 15 cm depth at 20 days after application. The herbicides also move laterally on the soil surface to adjecent nontreated slope base. Their persistence in soils were equal to those of the treated area. Persistence of atazine, cyanazine, simazine, and metribuzin in soil of treated area were 117 days on 8 - 10% slope and 180 days on 25 - 28% slope, respectively.