Preliminary study on change of some chemicals of acid sulfate soils under rainfed and irrigated riceland   Jumpol Yuvaniyama, Sarayuth Thanacharoentham Jurai Thongmark and Charoen Charoenchamratcheep   ABSTRACT       Preliminary study on the change of some chemicals propertics of acid sulfate soils under rainfed and irrigated riceland was carried out in Rang-sit soil series- very acidphase. These selected areas are located at Tambon Donyor, Muang district, Tambon Sai-Moon and Tambon Bang Look-Sua, Ongkarak district, Nakhon-Nayok province during 1991 - 1992. The propose of this study is to test the drainage canal hypothesis and the change of some chemical properties of acid sulfate soil solution and soil that could be applied for water management planning on acid sulfate area. The remarling requirement plus leaching or flushing and irrigation should be considered from the results of this study. The chemical parameters such as pH, EC, Fe++, Al+++, SO4=, and soluble acid from rainfed and irrigated riceland have some correlation in both positive and negative to the duration of sampling time and the distance of each site from the drainage canal. Most of the results from those chemical parameters follow the drainage canal hypothesis. Some of them that do not follow are due to the effect of drainage canal on the oxidation of secondary pyrite as reacidification process especially on irrigated riceland.       Keywords : acid sulfate soils, rainfed, irrigated, rice