利用大型径流场研究太湖地区稻季氮素的径流排放

Nitrogen Loss via Runoff from Paddy Field Using the Large Catchment Area in Taihu Region

为准确评价稻季氮素径流排放对水体环境的影响,建立一面积为714m2的大型径流场。通过测定降雨、灌溉输入氮量以及稻田径流氮排放量,研究在常规施肥、灌溉条件下太湖地区乌栅土上稻田施氮肥对水体环境的影响。结果表明,稻季径流氮中主要为溶解无机氮,所占比例达69.2%～91.4%,颗粒氮、溶解有机氮比例很低;氮素径流排放主要发生在苗期,稻季后期排放量较少;径流氮排放量低于降雨和灌溉氮素输入量,用较高氮浓度水体灌溉稻田可能是减少周围水体氮总量的有效方法;与同期进行的原状土柱试验比较发现,将田埂高度由6cm增加到8cm,稻季径流量和氮素径流排放分别降低73.4%和约90%。降雨输入氮在研究该地区水体富营养化时不容忽视。

A 714 m^2 large catchment was established for estimating exactly the effect of N loss via runoff from paddy field in Wushan soil on ambient water body. Nitrogen in rainfall and irrigation were monitored at the same time. The results showed that the proportions of DIN （dissolved inorganic nitrogen） to TN （total nitrogen） in runoff were 69.2%-91.4%, while the proportions of PN （particle nitrogen） and DON （dissolved organic nitrogen） were very low. Most of the runoff N discharge occurred at seedling stage. The amount of N discharge from runoff during the whole rice season was 12 kg N·hm^-2 and 1.64 kg N·hm^-2 in 2001 and 2002, respectively, which was lower than the sum of the amount of N inputted by rainfall and irrigation. NPS （non-point source pollution） did not occur in this experiment, while the paddy field became the constructed wetland intercepting the part of nitrogen in irrigation. Irrigating the paddy filed using the water with relatively higher N concentration might be the effectire measurement to reduce the total amount of nitrogen in the water body around the paddy field. Compared with the results of the field experiment with profile-undisturbed monolith lysimeters, it was indicated that enhancing the ridge of field from 6 cm to 8 cm could reduce the amount of runoff and N discharge via runoff by 73.4% and about 90%, respectively. The concentration of DN in each rainfall was higher than 0.2 mg N·L^-1（the threshold concentration of N for inland water eutrophication）. The nitrogen inputted by rainfall has an ecological significance on the water body eutrophication.