The Effect Of Applying Controlled Drainage On Salt And Water Balance In Yinnan Irrigation District

In North America, controlled drainage is considered as one of the best agricultural management practices (BMP). Controlled drainage is based on crops' tolerance ability, by constructing controlled structures such as weirs etc., to reduce water quantities drained to downstream water bodies in proper time, with the purpose of lowering pollution and protecting environments. Aimed at the presence of Yinnan Irrigation District's excessive drainage and water environment's pollution, taking advanced foreign drainage practices as references, and through elaborate design and detailed preparation in advance, this thesis is based on the controlled drainage experiment in Xiwei, Yongning. By 4 months' controlled drainage experiment, rice's water requirement in one growing season, drainage water quantities of rice field, salinity values of water in different depth of observation wells and in drainage ditch have been gained. Calculating and analyzing these materials, and comparing controlled drainage with conventional drainage, some conclusions are drawn as following.1. By improving control measures during applying controlled drainage, relative ideal data and conclusions are gained.2. Based on salt and water balance, along with crop tolerance to salt, the result tests that adopting controlled drainage in Yinnan Irrigation District is feasible.3. During the period of experiment, the effect of controlled drainage is evident. Taking drainage water quantity per unit area as the index to compare, the average value of drainagewater drained from controlled drainage areas is 49.5% less than from conventional drainage areas, and underground drainage reduces 45.9%, so the effect of controlled drainage on Irrigation District is evident.4. During the period of growing season, groundwater table takes on obvious periodicity The period of underground water table can be divided into three stages: (1) low water table stage (before the middle of May), (2) high water table stage because of irrigation (from the middle of May to early September), (3) relatively low water table stage (from early September to early October). At the same time, the water table in the area of controlled drainage is 1.8cm higher than conventional drainage. During the tropical July controlled drainage raised 2.6cm water table, and its effect is also sure.5. During the period of conservation, salts of different water table depth in controlled drainage area vary evidently, but only 0.69% higher than conventional drainage area. Yet salts in drainage ditch rise more obviously, because the value of controlled drainage area is 11.67% higher than that of conventional drainage area. The salinity value of both in different depth of observation wells and in drainage water, downstream water body is far below than the rice's tolerance values, so controlled drainage has the potential for raising underground water table.6. By analyzing the salt and water balance in the zone of controlled drainage after adopting controlled drainage, the salt introduced is less than outputted, so the zone of controlled drainage is still in balance.7. Based on controlled drainage experiment in rice field, an idiographic management strategy is put forward.Awarded by national science foundation project (50209015) , the effect of controlled drainage on water quality improvement...