Crust formation leads to development of a dense hard layer on soil surface which effectively retards seed germination and water intake. Various remedies have been proposed to overcome this difficulty. The purpose of this study was to examine the effects of polyacrylamide (PAM), pumice and straw, applied as amendments, on some characteristics of soil crust (0-10mm) and water infiltration into soil under sprinkler and surface irrigation simulated in soil columns at laboratory. The columns were prepared by evenly packing (Db=1.4 gr/cm3) of the soil (Coars-loamy, mixed (calcareous) mesic, fluventic) in PVC tubes of 15 and 25 cm long and 15 cm diameter. Pumice at the rates of %1 and %3 and wheat straw equivalent to 2.1 and 5 tons/ha were well mixed with 0-5cm layer of soil in each column. PAM was dissolved (50 and 100 mg/lit) in tap water of EC=0.5 ds/m and SAR=2.2. Soil columns were watered either by a rainfall simulator or by continuous flooding of soil surface by application of a 2 cm head of water. Infiltration was measured during the experiment until steady state intake was realized, then the soil surface allowed to eventually dry and to crust. Bulk density (Db) of 0-10mm layer and penetration resistance were measured by clod and cone penetrometer, respectively. All amendments, irrespective of application rates, significantly (P<0.01) redauced Db of 0-10mm surface layer and increased its porosity. Db’s averaged over amendment type and application rates were 1.36, 1.67 for sprinkling and flooding as compared to 1.82 for untreated soil, implying that amendments acted more effectively in reducing surface densification under sprinkling rather than flooding. Penetration resistance (Pr), measured 2,4 and 6 days after irrigation behaved similar to Db. Pumice %1 resulted in lowest resistance of 3.25 kPa as compared to 4.51 kPa in untreated soil, which indicates a significant differences at %1 level. Regarding water retention behavior, only pumice %3 significantly increased moisture content at 10 kPa suctions as compared to untreated soil (0.22 versus 0.19 g/g, respectivity).
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