Soil water content and potential of the 0-200 cm soil profile in Robinia pseudoacacia forest land were observed continuously with a neutron moisture meter and a negative pressure meter to study the soil water characteristic curve (SWCC) and soil water potential characteristics in the Loess Hilly Region from April 1

2015 to October 31

2015

and the gray relational grade of soil water potential in different soil depths and months were analyzed by gray relational analysis. The results showed that: (1) Soil water characteristic curve (SWCC) at different soil depths could be well described by the Gardner power function. The fitting parameter a was in the order of the surface layer (0.103 8) > the middle layer (0.094 4) > the deep layer (0.086 0)

while parameter b followed the order of the surface layer (0.284) < the middle layer (0.291) < the deep layer (0.298). (2) According to the SWCC

soil water constant of the artificial R. pseudoacacia forest land was as follows: average field capacity and wilting coefficient was 25.53% and 8.42%

respectively

and the maximum effective water range was 17.11%. Normally

when the soil water suction was 0.1 MPa

soil water supply capacity was characterized by the specific water capacity. The value was in the order of surface layer (56.73%) > middle layer (53.74%) > deep layer (50.84%) in the artificial R. pseudoacacia forest land. (3) The vertical spatial distribution of soil water potential of the artificial R. pseudoacacia showed that the water potential of the surface soil layer increased from -0.21 MPa to -0.08 MPa

the middle layer soil water potential fluctuated greatly

and the deep layer soil water potential was stable

being around -1.14 MPa. The grey relational grade analysis showed the order of R12 (0.899 8) > R23 (0.711 5) > R13 (0.702 8). The results showed that the relationship between the surface layer and the middle layer of the artificial R. pseudoacacia forest land was close

the relationship between the deep layer and the middle layer was the second

and the relationship between the surface layer and the deep layer was the worst. (4) Soil water potential of the 0-200 cm soil layers in the artificial R. pseudoacacia forest land decreased from April to June

then increased significantly from July to August

and decreased again from September to October. The grey relational grade of soil water potential in each month showed the order of R10 (0.868 9) > R05 (0.806 7) > R09 (0.780 4) > R07 (0.676 3) > R06 (0.654 8) > R08 (0.611 4). The soil water potential variation trends in May

September

and October were similar to that in April. In contrast

the soil water potential variation trends in June

July

and August were different from that in April.