Geo-Environment Science

The information of electric conductivity (EC) was investigated as an indicator for estimating total nitrogen concentration (T-N) in irrigation water. Water quality indicators, such as T-N, EC, and concentration of metallic elements and anions, were measured at rice terraces in Hoshino village, Yame-gun, Fukuoka prefecture, Japan. The rice terraces were located in 3 different water systems. The result showed a positive correlation between EC and T-N. Thus, linear regression equations were calculated to estimate T-N by using EC as an independent variable. Coefficients of the slope and the intercept in the regression equations were different among water systems. The slope of a regression equation, which represented the rate in change of T-N against EC, was the largest in Hirouchi area, followed by Rokuri and Fujiyama areas. Next, the effect of ion concentration in irrigation water was investigated to identify the reason that the regression equations had different coefficients among water systems. T-N had a strong positive correlation with SO_4^<2->, Ca and Mg. It was examined that the correlation with SO_4^<2-> was caused by ammonium sulfate, which was used for fertilizer. The correlation with Ca and Mg was explained by elution of Ca^<2+> and Mg^<2+> from soil at the locations of high NO_3-N concentration. N0_3-N accounted for large portion in T-N in this study. Also, it was examined that trees around a water system would be a possible factor that affected soil components (ion amount). From the above consideration, it was indicated that T-N could be estimated by a linear regression equation for each water system based on the EC information.