Abstract: Laboratory and field experiments were conducted to determine the effects of different material ratios on nitrogen loss during biogas fermentation and yieldimproving effects of application of biogas fertilizer on crops. The results showed that the average nitrogen loss of biogas fermentation was 482%. Available N in the biogas liquid after the fermentation was increased by 254 times than that before the fermentation. Available N in the biogas liquid after the fermentation accounted for 621% of total N. Available N in the biogas liquid for the biogas fermentation was 513 times greater than that for the compost fermentation. Nitrogen loss in the biogas liquid for the biogas fermentation was in the following order: Treatment 1(pig manure∶straw=4∶1)(997%)> Treatment 2(pig manure∶cow dung∶straw=1∶1∶05)(434%)> Treatment 3(pig manure∶cow dung∶human fxces=3∶1∶1)(268%). Available rate of N in the biogas liquid for the biogas fermentation was 415 times greater than that for the compost fermentation. Under different soils， the yieldincrease rates of rice， corn， wheat， cotton， and rape with application of biogas fertilizer were 65%-157% with an average value of 1138%．

Key words: biogas fermentation, compost fermentation, nitrogen loss, biogas fertilizer, yieldimproving effect