Abstract: Based on the data of climate, topography, soil, and remote sensing ima ges, and by using the universal soil loss equation (USLE) and geographic informa tion system (GIS) techniques, the spatiotemporal dynamic changes of vegetation’ s soil conservation value in Yuyang District of Northern Shaanxi were analyzed. The results showed that in 1978〖KG-*2〗-〖KG-*7〗2005, the total mean annual ve getation’s soil conservation value in the District increased by 28037×106 yuan, with an inc rement about 676%, among which, 365% increment was in 1978〖KG-*2〗-〖KG-*7〗19 89 and 228% increment was in 1989〖KG-*2〗-〖KG-*7〗2005. The increment of the total vegetation’s soil conservation value in wind-blown sand region was abou t 17 times as that in loess hilly-gully region, while the mean per unit veget ation’s soil conservation value in loess hilly-gully region was about 46 times as that in sand-blown region. In Yuyang District, its outer suburb had th e highest mean per unit vegetation’s soil conservation value, followed by subur b, and urban area, but its suburb had the highest increment of total vegetation ’s soil conservation value, followed by urban area, and outer suburb.

Key words: Oryza sativa, Allelopathy, Resources competition, Nitrogen stress, Econiche, Allelopathy-competition separation based bioassay (ACS)