Characteristics of nitrogen leaching of rice-wheat rotation field in Taihu Lake area

A lysimeter experiment was conducted in Taihu Lake area to study nitrogen leaching of rice-wheat rotation under different nitrogen application rates.The results showed that nitrogen was leached away mainly in the form of NO^-₃-N,not NH⁺₄-N,and it occurred in the wheat growing stage.Of the total nitrogen leached,43%～72% was NO^-₃-N with a concentration range from 20 to 110 mg/kg.Nitrogen content in the solution and loss from leaching increased gradually with fertilizer applications.The amount of total NO^-₃-N loss from tested land was17.8～58.5kg/hm²,its average loss was 39.2kg/hm² and net NO^-₃-N loss was 5.5～40.7kg/hm²,which accounted for 3.7%～12.2% of total fertilizer applied.Compared with using fertilizer only,straw combined fertilizer can reduce the nitrogen leaching while fertilizer combined manure can increase the nitrogen leaching in soil.Except for few samples taken at early rice growing stage,the concentrations of NO^-₃-N and NO⁺₄-N in leaching from rice field were 1mg/kg and 0.5mg/kg,which were lower than those from the wheat field.