The Runoff Loss Of Nitrogen And Phosphorus In Paddy Wetland

The loss of nitrogen and phosphorus in constructed wetland of paddy field is an important part of agricultural non-point source pollution,which has many negative effects on water quality,but there have been few studies systematically revealed the pattern and mechanism of nitrogen and phosphorus runoff loss.Therefore,five different fertilizer application levels including 0%（F0）,50%（F1）,70%（F2）,100%（F3）,and 150%（F4）were set up in the constructed wetlands of paddy field in Changsha County,Changsha.Through 1.5 years of high-frequency monitoring,the runoff nitrogen and phosphorus loss pattern were revealed from the aspects of nitrogen and phosphorus form transformations,concentration dynamic changes,loss load and risk sensitive periods,and the loss mechanisms were discussed from fertilization levels and rainfall.This study can provide theoretical basis and practical suggestions for the reduction and control nitrogen and phosphorus runoff loss in paddy wetlands,and the development of agriculture tourism with both ecological and economic benefits.The results show:（1）The form of total nitrogen in the surface water of paddy field is mainly dissolved nitrogen,the concentration of ammonium nitrogen in the dissolved nitrogen is high,the concentration of nitrate nitrogen is very low,and the particulate phosphorus is the main part of total phosphorus.The nitrogen and phosphorus concentrations in the surface water increased significantly with the application of chemical fertilizer,and the nitrogen and phosphorus concentration in the water decreased in a single exponential decay equation with the days after application of basic fertilizer and top dressing.（2）The runoff loss of total nitrogen and total phosphorus were 19.99 kg N ha^-1and 1.72 kg P ha^-1,respectively.The dissolved nitrogen was mainly form in total nitrogen,accounting for 70%～77%,the others were particulate nitrogen,accounting for 23%～30%.The main form of total phosphorus runoff loss in the paddy wetland was particulate phosphorus,accounting for 59%～68%,the others were dissolved phosphorus,accounting for 32%～41%.（3）The application of chemical fertilizer significantly increased nitrogen and phosphorus concentrations and runoff losses,especially the dissolved nitrogen and particulate phosphorus.The risk sensitive period of nitrogen loss is 0～5 days after application of base fertilizer and 0～10 days after topdressing.The risk sensitive period of phosphorus loss is 0～15 days after the application of base fertilizer in early rice season,and 0～5 days after the application of base fertilizer in late rice season,and when the accumulated rainfall is large within 5 days.The agronomic utilization rate,apparent utilization rate and comprehensive benefit of F2 treatment were the highest of the five treatments.The comprehensive benefit of late rice is higher than that of early rice.It is of practical significance to reduce and control the loss of nitrogen and phosphorus in the constructed wetland of subtropical paddy field,and the development of sightseeing agriculture with both ecological and economic benefits.