Abstract: Taking the herbaceous layer vegetation in Shapotou area as test object, this paper studied its species richness, abundance, coverage, height growth, and aboveground biomass under effects of different nitrogen (N) fertilization levels. Oneyear observation showed that comparing with the control, all N fertilization treatments except 50 g N·m^-2had positive effects on the species richness. With increasing N fertilization level, the species abundance decreased, with a decrement of 86.7% in treatment 50 g N·m^-2, and the species coverage decreased after an initial increase, with the maximum in treatment 20 g N·m^-2 and having a significant difference (P<0.05) with the control. The responses of heig
ht growth to N fertilization levels varied with plant species. Aboveground biomass was higher at low N fertilization level but lower at high fertilization level. In a word, low N fertilization level benefited the community biodiversity and productivity, while high N fertilization level had restriction effects.

Key words: Alfalfa, Dry matter yield, Yield characteristics, Diversity