Biological nitrification denitrification and nitrogen loss in rice field ecosystem Nutrient balance in rice field ecosystem of northern China Effect of hydroquinone and dicyandiamide on N2O and CH4 emissions from lowland rice soil Rice field ecosystems in northern China Ⅱ. Study of symbiotic nitrogen fixation of Azolla in rice-Azolla combination systems Rice field ecosystems in northern China Ⅰ. Structural study of rice-Azolla combination systems