浮萍对稻田田面水中氮素转化与可溶性氮的影响

浮萍是稻田田面水中大量存在的典型水生植物，本试验采用室内培养的方法，以采自浙江省嘉兴市双桥农场的青紫泥水稻土为例，探讨了不同初始密度的浮萍对稻田施尿素后田面水尿素水解及可溶性氮浓度的影响。结果表明，浮萍可明显加快田面水尿素态氮的水解过程，对照、低浓度浮萍（D1）和高浓度浮萍（D2）处理中尿素水解速率常数k分别为0．02，0．03，0、04／h；试验前期，浮萍将大量的铵态氮（NH4^＋-N）吸收同化后储存于体内．而从第12天（D2处理）和15天（D1处理）开始，由于浮萍的释氮作用导致田面水中NH4^＋-N浓度逐步回升，同时硝态氮（NO3^--N）浓度也明显增加，说明浮萍在田面水氮索浓度较高时可大量积累氮索而浓度较低时可以向田面水中释放氮素，这有利于降低施肥初期田面水氮素流失潜能和保证施肥后期作物的氮营养供应。

Influence of Duckweed on N Conversion and Dissolved N in Floodwater after Urea Application into Paddy Field

Duckweed is one of the key hydrophyte in floodwater which may effect N transformation in paddy field.It studied the influence of duckweed in different density on N conversion in floodwater after urea application through greenhouse culture.Soil was colleted from Shuangqiao farm,Zhejiang province,which was one of the typical paddy soil in Hangjiahu plain.The results showed that duckweed would accelerate urea hydrolization and the velocity constant of urea hydrolization in control,low-density duckweed(D_1) and high-density duckweed(D_2) treatments were 0.02,0.03 and 0.04/h,respectively.In the first days of the experiment,duckweed may uptake and assimilate large amount of NH~ _4-N and then save them,however,from the 10~(th) day(in D_2 treatment) and the 12~(th) day(in D_1 treatment),part of N was released from duckweed and then NH~ _4-N and NO~-_3-N in floodwater increased obviously.It was indicated that duckweed could save part of N when large amount of N was applied into paddy field while release N when N concentration in floodwater was very low,which was helpful for reducing N rainfall potential and providing N nutrient for paddy rice persistently.