9de Macale MAR,Vlek PLG.The role of Azolla cover in improving the nitrogen use efficiency of lowland rice.Plant and soil,2004,263(1/2):311-321.
10Vlek PLG,Fugger W,Biker U.The fate of fertilizer N under Azolla in wetland rice//Proceedings of the 2nd ESA Congress.Warwick,UK:Warwick University,1992:376-377.