Soil water characteristic curves were determined using a pressure-membrane extraction apparatus for the soils collected on five different plantations

i.e.

pure fir forest(Cunninghamia lanceolata)

fir and pine(Pinus massoniana) mixed forest

and three other mixed broad-leaved forest(Schima superba×Cinnamomum camphora×Lithocarpus glaber×Liquidambar formsana

Schima superba×Lithocarpus glaber and Cunninghamia lanceolata×Pinus massoniana×Schima superb) in Simian Mountain of Chongqing City.The results show that the empirical equation(θ=aS-b) proposed Gardner(1970) described well the relationship between soil moisture contents and soil water suctions for all the soils from the five forests with coefficients of determination greater than 0.99.In terms of the fitting parameter a values

the soil water retention capability of the five forest soils as in order from high to low were Cunninghamia lanceolata×Pinus massoniana×Schima superba(a=0.328)

Schima superba×Cinnamomum camphora×Lithocarpus glaber×Liquidambar formsana(a=0.248)

Cunninghamia lanceolata(a=0.225)

Schima superba×Lithocarpus glaber(a=0.218)

and Cunninghamia lanceolata×Pinus massoniana(a=0.206)

respectively.According to the regression equations

the soil water suction upper limit of soil available water was approximately 0.03 MPa.The specific water capacity indicated that soil available water decreased substantially when the suction is greater than 0.15 MPa

which implies that 0.15 MPa might be the critical value for differentiation of readily available water and slowly available water.According to the a×b values(the product of fitting parameter a and b

which equals to the specific water capacity when the soil suction S=1.00×105 Pa) and readily available water contents

although no obvious trend has been identified in the variations of soil water supply capability for different soil layers of five plantations

the soil water supply capability of five plantations in order from high to low were as followed: Schima superba×Cinnamomum camphora×Lithocarpus glaber×Liquidambar formsana(ab=0.065

readily available water 11.704)Cunninghamia lanceolata(ab=0.062

readily available water 10.677)Schima superba×Lithocarpus glaber(ab=0.058

readily available water 10.485)Cunninghamia lanceolata×Pinus massoniana×Schima superba(ab=0.058

readily available water 10.003)Cunninghamia lanceolata×Pinus massoniana(ab=0.056

readily available water 9.980).