A comparative leaching experiment of saline soil using undisturbed core samples ( 20 cm in diameter and 74 cm in length) with and without a hardpan was carried out following the conventional method of water supply. The samples were collected in salt-affected farmland in the Syrdarya region of Uzbekistan, with a hardpan formed at a depth of 30 cm. Another sample, without a hardpan, was plowed manually to a depth of 40 cm. A 24 -day leaching experiment with total water supply of 300 mm demonstrated clear differences between the two sample types. The amounts of leached water were 98 . 7 mm for with-hardpan and 223 . 6 mm for without hardpan samples and the amounts of salt leached from samples were estimated as 276 mg cm-2 (discharge ratio: 16 . 4 %) and 597 mg cm– 2 ( 35 . 8 %), respectively. However, after the experiment ( 72 days), saturated hydraulic conductivity of samples without a hardpan at depths of 30– 60 cm was reduced to one-200 th of that before the experiment. This suggested that hardpans could form not only by tractor compaction but also soil slaking and precipitation of gypsum by leaching operations. It is necessary to develop methods to maintain the effects of breaking the hardpan and confirm their validity through on-site testing.
