In the semi-arid hilly region of South Ningxia Hui Autonomous Region

three-year

seven-year

eleven-year

and nineteen-year old alfalfa fields and seven-year old alfalfa fields at uphill

middle slope

and downhill were taken as study objects.The dynamics of the dried soil layer(0—5 m) and soil moisture and nutrients were analyzed.The results show that both slope position and plant age affected soil moisture contents.The average moisture content of 0—5 m soil profile on the uphill alfalfa field was 6.34%

which was substantially lower than that on middle slope and downhill fields.The average moisture contents in 0—5 m soil profile decreased on the alfalfa fields as in order of three-year

seven-year

nineteen-year

and eleven-year

and soil drying index(SDI) decreased as in order of uphill

middle slope

downhill and three-year

seven-year

nineteen-year

and eleven-year.The dying degree declined as soil depth increased.After the alfalfa aged

soil moisture content could recover but took a long time.On all the alfalfa fields in this study

the average content of soil organic matter

total N

available N

total P

available P

and available K all increased in the fields from uphill to downhill.As the soil depth increased

the soil organic matter

total N

available N

total P

and available P decreased.As the age of alfalfa increased

the soil organic matter

total N

total P

available P

and available K exhibited a declining trend

but the available N increased first and then decreased with the age of alfalfa in the field.When alfalfa field was very old

the soil organic matter and total N began to accumulate but was still at a relatively low level.