| Taking the Qingtongxia irrigation district at the Yellow River upstream as an example, based on the monitor experiment material, this paper has analyzed the migration characteristics of nitrogen and phosphorus in the water conveyance system, the field system and the drainage system in the irrigations district. The results showed that, the concentrations of nitrogen and phosphorus showed increasing tendency in the water conveyance system and the increasing extent related to the channel substrate and content of nitrogen and phosphorus. In the field system, the fertilizer application process has a great influence on the concentration of nitrogen and phosphorus in farmland irrigation drainage and soil. During the crop growing period, nitrogen content in the soil above 60 cm changes greatly, total phosphorus content in the soil changes slightly correspondingly. In the drainage system, the concentrations of nitrogen and phosphorus showed decreasing tendency, from the end of farm ditch to outlet of agricultural drain, the concentration of ammonia nitrogen, nitrate nitrogen and total phosphorus in the agricultural drain decreased by 25%,41% and 45% respectively. Affected by livestock and poultry breeding pollution and so on, the concentration of nitrogen showed increasing tendency in mainstay drainage ditch. |
