Abstract: Gully is an important kind of erosional landform in watershed on the northern Loess Plateau and has a profound effect on the surface processes,such as the hydrological,vegetational,geomorphologic and ecological processes.In order to clarify the response of three soil physical parameters (soil bulk density BD,saturated hydraulic conductivity Ks and soil moisture content SMC) to the gully topographical conditions,slope position and soil depth,in this study three sampling transects at the bottom,edge and nearby bank of an erosional gully were designed,and 40 sampling sites were designed.At every site,the undisturbed soil cores were sampled at three soil layers: 0-10 cm,10-20 cm and 20-30 cm,and they were regarded as surface,sub-surface and shallow soil layers respectively.The data of BD,Ks and SMC were obtained using the constant water-head method and oven-drying method.The results are as follows: ① Topographical conditions significantly or highly significantly affected the values of BD,Ks and SMC,and these three parameters fluctuated in a wave-like trend along the slope length.The BD values at the gully edge and bank were decreased slightly with the increase of slope length.Except the soil surface on the gully edge,the SMC on the downslope was significantly higher than that at the middle and upper slope; ② On the gully edge and bank,the variation trend of Ks and BD at different soil layers was opposite to that at the gully bottom; ③ At every soil-depth layer,SMCs on the gully edge and bank were significantly different from those at the gully bottom,and they were always lower on the gully edge than those on the gully bank.The results mentioned above indicated that the spatial pattern of BD,Ks and SMC on the slope were changed with the distribution of gully,and the influence of specific topographical conditions of the slope-gully unit on the soil physical parameters could not be neglected.

Key words: gully, soil bulk density, soil saturated hydraulic conductivity, soil moisture content, Loess Plateau