Abstract
The concentrations and loadings of herbicides were investigated in two paddy fields (C and F) located around Lake Biwa. Herbicide loss was calculated from cumulative loadings from May to June (2003 and 2005), and the amounts of herbicide applied determined using a questionnaire were estimated to be 1.72% for Pretilachlor, 13.0% for Cafenstrol, 11.3% for Daimuron, 0.024% for Esprocarb, 8.0% for Molinate and 44.8% for Simetryn in C in 2003, and 16.9% for Daimuron and 14.3% for Mefenacet in F in 2005. Specific loss was calculated from herbicide loss, and average discharge on nonrainy days was obtained for seven paddy fields including C and F. To estimate herbicide loss, the multiple regression analysis used water solubility, Henry's law constant and soil adsorption constant as independent variables and specific loss as a dependent variable. The analysis of seven paddy fields showed a relatively low multiple correlation coefficient between the observed and calculated values. However, the analysis dividing the seven fields into two soil groups (Brown and Gray lowland soil group, and Gley soil group) improved the multiple correlation coefficient. In both soil groups, the most important contributor to herbicide loss was the adsorption constant of soil.
