Forty years of revegetation using mainly
Caragana korshinskii at Shapotou Desert Experimental Research Station near Lanzhou
has established a dwarf\|shrub and herbaceous cover on sand dunes. Situated in southeast Tengger Desert at 1330 m elevation, it has an average annual rainfall of 191 mm with 83% received in May\|September. Precipitation, as the sole source of water replenishment in the semi\|arid area, plays a pertinent role in sustaining the
desert ecosystem. The redistribution of infiltrated moisture through percolation, root extraction and evapotranspiration pathways was investigated. Experiments were conducted in the growing season for 45 days (17 August to 30 September 2001) on revegetated sand dunes. TDR probes were inserted horizontally at the depths of 5, 10, 20, 40, 60, 80, 100, 120, 140, 160, 180, and 200 cm layer below the ground surface in the dwarf\|shrub of
Caragana korshinskii community to record volumetric soil moisture at hourly intervals. Other essential meteorological and soil parameters were evaluated. Seven rainfall events each of 1 5～40 7 mm intake occurred during the experimental period. Rainfalls were sporadic with widely different intensities. For the 40 7 mm rainfall episode with 3 4 mm/h maximum intensity and 5 4% antecedent volumetric soil moisture, maximum infiltration rate attained 0 42 mm/min. Infiltration rates varied greatly with individual rainfall quantity and antecedent soil moisture, with drier soil profile facilitating infiltration. Relationship between infiltration rate and rainfall intensity is linear, with infiltration rate at 10 times the magnitude of rainfall intensity. At rainfall intensity <0 46 mm/h, no soil moisture is gained. Root withdrawal of soil water and evapotranspiration (reaching 69%～90% of precipitation) restricted the wetting front penetration. A 40 mm rainfall at 1 50 mm/h intensity permitted wetting to 60 cm depth; a similar 40 7 mm rainfall at a lower 0 49 mm/h intensity limited wetting to <40 cm. The concentration of roots at about 140 cm depth imposed a diurnal moisture cycle there, with moisture depletion in daytime and replenishment at night by internal transfer from adjacent layers.