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Objective and technical fields:
To determine reclamation efficiency of operative-reliable drainage, its constructive elements under conditions of multilayer soils by means of systematic observations on soil water-salt regime dynamics with different depth drainage and distances between drains.
Scientific and technical approach:
Creation of necessary artificial drainability strengthens leaching impact and provides physical evaporation cut down due to groundwater level decrease during the period of intensive evaporation, commonly providing irrigation regime organization and high leaching efficiency.
Environment characteristics:
Geomorphology: ancient alluvial AmuDarya valley with slope 0.0003-0.0004. Lithology: multilayer quaternary sediments with thickness of 1.5-2.5 m constituted by loam and clay with permeability coefficient 0.19 m/day which in turn underlaied by fine- grained sand with permeability 1-3 m/day and thickness 35-40 m. Groundwater salinity is 5-19 g/l (average mean is 8.8 g/l). Level depth is 2-2.5 m: during growing period it is 1-1.5 m, during leaching - 0-1.2 m. Salt content within the ploughed layer is 2.8 %. Soils are strongly salinizated. Before drainage construction desalinization was performed by heavy irrigations (2000-2500 cu. m/ha) under total rate 11-13 th. cu.m/ha and spring leaching by rate 4-7 th. cu.m/ha. Cotton yield was 1.0-1.2 t/ha.
Parameters of Pilot Projects and Technical Solutions:
Field observations on reclamation situation change under artificial drainability, which is provided by systematic operative- reliable drainage, were executed. Close horizontal drainage within the area 303.7 ha with drain depth 1.5-2.0-3.0 m and distances between drains 150-300 m. Total drains’ extent is 9136 m, its density is 30 m/ha.
Drainage design standard: asbestos-cement, concrete and ceramic pipes. Drainage construction method is half-mechanized, so-called ‘shelf-method’. Irrigation network - small ditches, irrigation technique - furrow for all crops except grass and rice (by flood).
Agricultural crops: cotton (60 %), rice- 10 ha. Pilot site has triangular shape, its borders are middle-distributors P-8 and Kazakh-Yab and in-farm collector «Parallel».
Methodology:
For systematic observations of soil water-salt regime and groundwater dynamics the pilot site was equipped by water-meters and observation wells. 19 piesometric sets were installed on depth from 2.5 to 50 m (2-7 wells in each set).
77 single wells had depth 2.5-3.0 m and were positioned along single transects. Field investigations allowed to definite 1968-1970 water-salt balance.
Results:
Pilot site’s area was represented by non-irrigated lands with surface salinization. It is located among irrigated lands and surrounded by irrigation canals that create high inflow and load on drainage. Pilot site creation with cultivation mostly cotton, rice and perennial grass permitted:
- to increase land use efficiency from 0.56 in 1967 to 0.8 in 1970;
- to create high drainability. Drainage outflow was 14.4-15.6 th. cu. m/ha under total water supply 22.3-26.2 th. cu.m/ha. Inflow from outside was 29.5 %;
- to provide high groundwater level decrease velocity after irrigation and leaching. Groundwater level decrease velocity was 10-20 cm/day while within the non-drained lands it was 3-6 cm/day;
- to support optimal groundwater level; during growing period it was 0.3-0.7 m lower to compare with adjacent sites.
- to create close hydraulic connection within all cover sediments thickness and active water-salt exchange zone under drainage and canals operation. Drainage impact zone is 250-300 m and 40-50 m in vertical direction, creating upward flow of water and salts from beneath when irrigation is absent. Under irrigation zone of upward flow is 1419.5 m, from salts removed from the soil 55-65 % is withdrawn from lower horizons;
- to accelerate soil desalinization under leaching. During 4 years 80 t/ha salts were removed from available 232 t/ha; during the first year -108 t/ha, second year - 30 t/ha. Allowable limit for chlorine - ion was achieved to the end of the first year;
- to form negative water -salt balance. Salt removal was 34 t/ha within the first year, 29.2 t/ha in the second year and 12.4 t/ha in the third year. During 4 years of drainage operation salt content within the 0-100 cm layer was decreased 4 times on chlorine -ion;
- to decrease groundwater salinity to 3.5-4 g/l ;
- to determine active zone of water -salt exchange as 35-50 m;
- to raise cotton yield from 1.0 to 4.8 t/ha. Main result is water consumption rate decreasing from 23-25 to 17-18 th. cu. m/ha. Water saving was achieved due to cessation of heavy leaching rates 7.0 th. cu.m/ha and its replacement by water-stock irrigation (1.5 th. cu.m/ha). Economic effect was 500-550 rouble/ha.
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