the study of nitrate dispersivity in sandy soil using hydrus-1d model

the increasing use of nitrogen fertilizers due to high dynamics of nitrate in the soil would be a serious threat to groundwater, and therefore, to thuman health. this study is aimed to investigate the disperdivity values of nitrate in the coarse, medium and fine sandy soils in the short travel distance of 20, 40 and 80 cm in vitro using the hydrus-1d model. for this purpose, pure potassium nitrate salt solution under the sustainable regime with concentration of 160 (mg/lit) was added to the soil columns as persistent contaminants, then for extracting the needed parameters the concentration of output nitrate in three different porosities volumes were measured and breakthrough curves were plotted for each column. the results showed that dispersivity increases as the soil particle size increases. also, by increasing the average travel distance in medium and coarse sands nitrate disperdivity values increased. but in the fine sand the disperdivity values decreased as the transmission distance increased. the disperdivity values for fine, medium and coarse sand were from 30/50 to 42/55 cm, 57/06 to 68/51 cm, and 68/50 to 97/06 cm, respectively. the average model error percent (er) was less for fine sandy soil, and coefficient of determination (r2) was relatively more for fine sandy soil than the coarse and medium sandy soils, which means the lower error value and higher precision of the overall process in simulation of nitrate transfer in this model for the fine sandy soils.