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 (682KB)
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104,194,000 Yen (FY1998 20,735,000 Yen)
Based on a series of on-site water and salt balance experiments, it was proved that the ordinary eight-year rotation system and the over-irrigation to the rice fields together with an inappropriate drainage management have accelerated the salt accumulation and concurrently increased abandoned farmlands in the Lower Syr Darya River region. A remarkable finding was obtained on the salt behavior in rice fields, and this denies the hypothesis that rice cultivation practice in arid area is effective for leaching accumulated salts.
In order to overcome problems on secondary salinization, the following remedial measures are recommended:
1) to avoid mixed cropping with rice and upland crops and to unify either upland crops or rice in an irrigation block to control groundwater table, 2) to decrease conveyance and field application losses through improved canal construction and management performance, introduction of canal-lining and improved land-leveling performance, 3) to maintain and operate drainage canals to function, especially installation of drain pipes across dikes for connecting fields and field-drains might enhance subsurface drainage function, 4) to introduce bio-drainage along canals and around farm lots for preventing waterlogging and salinization, 5) to develop design and management technique of evaporation pond for better effluent management at the outfall of each irrigation block, and 6) to conclude international water and/or drainage rights agreements among riparian countries and to enact a basin-basis management regulation to control water withdrawal and drainage.
Secontary salinization, Irrigation system management, Water balance, Salt balance, Eight-year cropping system