Abstract:In order to offer a scientific base and reference to rational utilization and large scale planting for introduced switchgrass (Panicum virgatum L.) in the semiarid conditions on the Loess Plateau,we investigated the photosynthetic dynamic variation,aboveground biomass production and soil moisture content profile distribution under three different row spacings,which were 20 cm（L20）,40 cm（L40） and 60 cm（L60） on terrace land in loess hilly gully region.The results indicated that:(1)The curves of diurnal variation in net photosynthetic rate (Pn) had double peaks,showing obvious midday depression.The first peak appeared at 10:00,and the second peak for L40 appeared at 14:00,while for L20 and L60 treatments it appeared at 16:00.The daily mean values order of Pn was as follows:L60>L40>L20.The midday photosynthesis depression under each row spacing was due to non stomatal factor limitation.(2)The diurnal variation in WUE was similar to Pn,and the peak values appeared at 10:00 and 14:00 respectively under the three row spacing treatments,and the daily average order was L60>L40>L20.(3)Soil volumetric moisture vertical distribution was similar under each row spacing,showing increased firstly,and decreased,and then increased with soil depth.Except in 0～50 cm soil layer,soil water storage in the other layer was not significant different among the three row spacings.Total soil water storage in 0～380 cm decreased with row spacing,showing that:L20>L40>L60.(4)The aboveground biomass order for the three row spacing was L20>L60>L40.Although the leaf Pn was lower,the biomass production and soil water storage were significantly higher under L20,all these results suggested that the optimum row spacing was 20 cm for switchgrass on terrace land in loess hilly gully region.