investigation of nitrate leaching changes trend below the root zone in karaj farms with geographic information systems

high quantity of chemical fertilizer use in farms to increase production but low efficiency irrigation leaches part of nitrate and follows groundwater pollution. in this research, extra water below root zone as deep percolation collected with point drains which installed interface of natural drainage zone and agricultural soil in university of tehran research farms. then, concentration of nitrate (no3-n) measured in the water quality laboratory. results showed nitrate concentration changed between 0.15 to 289 ppm. in this study, nitrate leaching trend to karaj groundwater and reasons is considered. finally, initial soil nitrate measuring, usage of modern irrigation methods with high efficiency, prediction of rainfall time and fertilizer management in fields recommended to preventing of groundwater degradation quality trend.