The effects of sodium polyacrylate(SP) on soil

water-holding capacity at different suctions of sand

silt and clay were evaluated by using centrifugal Method.Five rates of SP

0.0%

0.01%

0.08%

0.2%

and 1%(on dry weight basis)

were added to these three soils.The effects of SP on yield and WUE of winter wheat and the following maize were studied.SP was dusted on the upper layer with 2gm/m2after the wheat was sown and the maize was planted on the field without any treatments after the wheat was harvest.The results show that the amount of water retained by the soil at each suction over the range of 0.01MPa to 1.5 MPa significantly increased with increase of SP;The effects on sand were more obviously than silt and clay;It is suggested the concentrations of SP be controlled from 0.08% to 0.2% by weight and the best rate is 0.2% of each soil.Then the capillary prosity of sand

silt and clay were increased 138.61%

37.22%

62.70% respectively compared to the CK.Without added irrigation

the yield and WUE of SP treated wheat were increased 4% and 5.7% respectively compared to the CK while increased 1% and-1% respectively with added 28.5mm irrigation at filling stage.The yield and WUE of the maize planted on the SP treated plot were increased-0.5% and 3% respectively compared to CK.The effect of SP on the yield and WUE of maize was less obviously than on the wheat.