Loss of Amide Herbicides in Runoff Water and Sediment and Their Persistence in Soil

Abstract

Abstract
Alachlor and butachlor at the rate of 4.0 kg ai/ha metolachlor at the rate of 3 kg ai/ha, and propanil at the rate of 6 kg ai/ha were applied to the cultivated soil of 8-10 and 25-28% slopes during the middle of rainy season at Royal Angkhang Highland Agriculture Research Station, Fang district, Chiangmai. The soils of the 8-10 and 25-28% slopes were clayloam and clay, respectively. At the 8-10% slope site the maximum concentrations of alachlor, butachlor, metolachlor, and propanil in the runoff were 46.1, 61.5, 65.0 and 86.3 µg/L respectively. At the 25-28% slope site the maximum concentration of alachlor, butachlor, metolachlor, and propanil in the runoff were 18.5, 15.5, 51.4 and 70.3 µg/L, respectively. The highest amounts of water, soil, and herbicides were lost from both sites 1 to 3 days after application. The average amount of alachlor, butachlor, metolachlor, and propanil in the water phase were 66.4, 52.2, 68.0 and 54.9% of the total amount of herbicides found in the combined sediment and water phases, respectively. The maximum concentrations of herbicide were applied to leaves and to sandy loam soil where test plants were grown under greenhouse condition. Plant dry weight were reduced significantly by all herbicides when foliar application was practiced. The plant dry weight were not affect by soil application of herbicides. This indicating that all the chemicals were adsorbed by clay particle and organic matter. Total losses of all herbicides were less than 0.5% of the applied rates. The downward movement of the herbicides to the depth of 7.5-15 cm. was as follows: metolachlor > propanil > alachlor > butachlor which was in correlation with their water solubility. The persistence of alachlor, butachlor, metoachlor, and propanil in the soil of the treated area which could be detected by gas chromatography were 180, 180, 117, and 30 days after application, respectively.