Effects of cultivation method and nitrogen application rate on key enzyme activities of nitrogen metabolism at early milky stage and grain yield of rice

• WANG Heting, 
• DONG Hui, 
• QI Longchang, 
• LI Xuesong, 
• WANG Teng, 
• SONG He, 
• CHEN Song, 
• DONG Zhaorong, 
• ZHANG Xiufu