Herbicide Concentration in Runoff and sediment from Experimental plots of Highland Cultivated Areas

Abstract

Bromacil, 2,4-D, dalapon, DCPA, diuron, linuron and oxadiazon at the rates of 4 kg ai/ha, 4 kg ae/ha, 8 kg ae/ha, 8 kg ai/ha, 4 kg ai/ha, 2 kg ai/ha and 2 kg ai/ha, respectively, were applied to cultivated soil of 8 to 10% and 25 to 28% slopes during the middle of rainy season at Royal Ang Khang Highland Agriculture Research Station, Fang district, Chiang Mai. At 8 to 10% slope the maximum concentration of bromacil, 2,4-D, dalapon, DCPA, diuron, linuron and oxadiazon detected in runoff were 29.1, 38.4, 809.7, 36.4, 110.7, 280.0 and 49.3 g/L, respectively. At 25 to 28 % slopes the maximum concentration of bromacil, 2,4-D, dalapon, DCPA, diuron, linuron and oxadiazon detected in runoff were 29.4, 31.3, 763.9, 6.9, 46.8, 65.3 and 10.7 µg/L, respectively. The maximum concentrations of herbicides in runoff were observed within a few days after application and were drastically reduced which might be attributed to half life or persistence and leaching of herbicides in soil. The average amount of bromacil, 2,4-D, dalapon, DCPA, diuron, linuron and oxadiazon in water phase were 67.4, 56.2, 76.5, 32.1, 37.7, 64.2 and 69.2% of total amount of herbicides detected in both water and soil sediment phases, respectively. The maximum concentration of herbicides detected in runoff water were applied to sandy loam soil and leaves of test plants. No phytotoxicity of herbicides were observed except those of bromacil, linuron and oxadiazon when applied to leaves. Total losses of herbicides from both sloped were less than 2% of applied rates except 2,4-D loss was less than 6%. All herbicides moved vertically to 7.5 to 15.0 cm depth. Except bromacil, the other herbicides moved laterally with runoff to surface of adjacent (non treated area) slope base. The persistences of bromacil, 2,4-D, dalapon, DCPA, diuron, linuron and oxadiazon were 117, 30, 30, 180, 180, 241 and 241 days respectively.