| In order to explore the function and mechanism by using the super absorbent polymer to improve soil water-holding characteristic, put three types of super absorbent polymers with different dosages (0.05%, 0.10% and 0.50%) into sand soil without aggregate pore, to measure the soil moisture content of each treatment under different suctions, successfully fitted soil water characteristic curve by V-G model, and acquired the results of the soil water characteristic curve parameter and main water constants for each treatment. The results indicate that: (1) After using the super absorbent polymer, except the soil unavailable water had no significant change, the saturated soil water content, field capacity, gravity water and available soil water in all treatments had significantly increased. When we used 0.50% super absorbent polymer, the field capacity in this treatment was 3～4.7 times higher than the control group. Using the super absorbent polymer, the water-holding capacity in middle and low water suction segment was significantly improved, that was the soil pore for holding water. (2) The soil water characteristic curve for each treatment was moved to the right, the water-holding capacity in each suction section was increased. The n value was total less than the control group, which indicated that super absorbent polymer can significantly improve the soil water-holding capacity in the dehydration process. (3) After using the super absorbent polymer, the soil added absorbent water mainly derived from gravity water and available water. When we use 0.05% of the super absorbent polymer, the proportion of the gravity water in each treatment was high than 60%. With the dosages increasing, the proportion of the gravity water was decreased and the available water was increased. It indicated that mechanism of super absorbent polymer to the soil water-holding characteristic was mainly embodied the increase of the proportion of water held by capillary pore. When use low dosage, the soil gravity water can be significantly improved, but with the increase of the dosage, the soil available water was significantly improved. (4) Comprehensively compared the improving effect of the super absorbent polymer type, the B3 with 0.50% dosage was the best improvement effect. From this, even though the super absorbent polymer was a kind of substrate with strong ability of moisture-absorbing by molecule, it can be greatly changed the water-holding capacity by soil pore and increase available soil water capacity. So it should be given great attention and widely used. |