The role of water and irrigation is vital in cultivation of rice in Iran . The dominant method of irrigation in paddy fields in Iran is continuous flooding which changes to periodical method in time of water deficiency. Cracks are the main problem in periodical irrigation. The amount of water required in periodical irrigation method is several times greater that flooding irrigation. Crop residues in paddy fields are able to prevent establishment of cracks and their intensity. I the present research, effect of different levels of crop residue on soil hydraulic characteristics and control of amount and intensity of cracks in some paddy Soils of Guilan Province is studied. The experiment was performed as split-split plots based on complete randomized blocks design, using four soil textures and three replications. Soil texture as the main factor, in 4 levels, rice stem residues as sub- factor in 7 levels (0, 2, 3, 4, 5, 6 and 7%) and soil moisture stages in dry and wet conditions as sub-sub-factor in 5 levels (primary stage (T 1 ), initial crack stage (T 2 , crack area = 13-17 cm 2 ), final crack stage (T 3, crack area = 55-59 cm 2 ), final cracks get back to the initial stage (W 1 ), and crack disappearance (W 2 )) were considered. Effect of addition different levels of rice residues on moisture content, bulk density, resistance to penetration of a penetrometer (i.e. compaction), height of soil (subsidence and swelling), volume of soil, number of days for crack formation, volume of water used in wet stage, and saturated hydraulic conductivity of soils were studied. The results showed that soil texture, levels of crop residues, crack treatment and their interaction have significant effect (p 0.01) on moisture content, bulk density, penetration, height of soil, volume of soil, and days to crack formation. Increasing the level of rice residues, caused moisture content, height and volume of soils to increase with respect to control, and decreased the bulk density. Addition of rice residues increased generally the penetration of soil and delayed the crack formation. In drying stage of soil samples, from T 1 to T 3 , moisture content, and height and volume of soil was decreased. In wetting stage, from W 1 to W 2 , moisture content, height and volume of soil was increased. In drying stage, bulk density, penetration days to crack formation, from T 1 to T 3 , increased. In wetting stage, bulk density and penetration, from W 1 to W 2 , was decreased, but days to crack formation was increased. In silty clay soil, addition of 2 and 3%
