Nitrogen and Phosphorus Loss From Wild Rice Stem Cultivation in Dianshanhu Region,Shanghai and Their Pollution Load

A multi-plot run-off experiment was carried out in a paddy field cultivated with wild rice stem(Zizania caduciflora) and rice in rotation and with wild rice stem alone under conventional fertilization in Dianshanhu Region to study N and P losses and their non-point source pollution load.Results show that discharge of the non-point source pollutants,nitrogen and phosphorus,occurred mainly in the period from June to September.The mean mass concentration of TN in drainage could reach as high as 130.0 mg·L^-1,mainly in the form of NH₄⁺-N,which came mainly from inorganic fertilizer.During the wild rice stem growing season,the mean mass concentration of TP in drainage was in the range of 0.104-0.777 mg·L^-1,mainly in the form of particle,which accounted for 73.5% ~90.3% of TP(except for August).Furthermore,TN non-point source pollution load of the rotation system and the mono-cropping system was 134.8 and 88.6 kg·hm^-2·a^-1,respectively.Both were higher than those from other cropping systems in the Taihu Region,while TP non-point source pollution load was 1.52 and 1.06 kg·hm^-2·a^-1,respectively,lower than the average level of the common cropping systems in the Taihu Region.So it is important to set control of the use of nitrogen fertilizer and the nitrogen loss as priority for control of agricultural non-point sources pollution in the Dianshanhu Region.