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Objective and technical fields:
Elaboration of set of measures on water use improvement and soil salinization prevention on base of land drainability increase and leaching by means of close and open horizontal drainage construction over the rice engineering system. Reclamation efficiency, drainage workability under drifting soils determination. Soil water-salt regime management.
Scientific and technical approach:
Prevention of soil salinization, irrigated lands productivity increase through land drainability strengthening and salt removal by means of managible close horizontal drainage construction.
Meaning: Elaboration of set of measures on close horizontal drainage construction over rice system to raise irrigated lands productivity.
Environment characteristics:
Geomorphology: AmuDarya alluvial plain. Relief is slightly corrugated with slope 0.0003-0.0004. Lithology: Multilayer thickness of quaternary sediment overlaid by loam (1.5-2.5 m) with permeability coefficient 0.02-0.35 m/day. Groundwater level was initially 1.8-2.5 m, in spring 1.3-1.5 m. Soils initially were strongly to slightly salinizated, sulphate-chloride and chloride-sulphate. Salt content within arable layer (0-60 cm) was salinized on average 2.8 % on solid residue and 1.0 % on chlorine-ion.
Average annual temperature is 12-13 oC. Period without freezing duration is 190 days. Relative air humidity is 46-51 %. About 40 % of annual precipitation occures in spring (March-May), 24-30 % in autumn (September-November), 20-27 % in winter (December-February) and 9-13 % in summer under their average annual value 87 mm. Average wind velocity is 3-3.5 m/sec achieving sometimes 10-15 m/sec.
Parameters of Pilot Projects and Technical Solutions:
Total area of pilot site is 145 ha. Area of close horizontal drainage is 33.91 ha, rest of area is covered by open horizontal drainage. Close drainage extent is 1774 m, open drainage 3510 m. Distance between drains is 206-230 m, drains depth is 2 m.
Crop pattern: rice 70 %, fodders 30 %. Total extent of irrigation network is 5120 m. Efficiency is 0.75. Canals are earthen; discharge is 140 l/sec (minimum) and 260 l/sec (maximum). Irrigation regime technology irrigation by flooding. Irrigation norm varied from 19.6 to 23 th. cu.m./ha (fields 141, 142) and from 25.1 to 30.9 th. cu.m./ha (fields 143-148).
Methodology:
Field observations on water, salt and water-salt balance elements movement within unsaturated zone, groundwater and irrigated land as a whole. For this purpose within the experimental plot the permanent balance stations were established equipped by metering devices.
Results:
Rice planting was started in 1977. Rice sorts were: Dubovsky-129, Uzros-59 and Uzbeksky-5. Water duty to checks was 165.4-21.84 l/sec. Irrigation hydromodulus was 5.26-1.3 l/sec/ha including those necessary to support stable water horizon within the checks 1.61-0.77 l/sec/ha. Drainage modulus was 0.70-0.80 l/sec/ha and release hydromodulus was 1.03-0.08 l/sec/ha. Soils were strongly to slightly salinizated. Salt content for 4 years of irrigation decreased from 332.3 to 58.2 t/ha, i.e. almost by 6 times and for chlorine 8-9 times. Further changes in soil salinity did not occure. Biggest salt removal was observed during growing season.
Observations of drainage and irrigation water quality showed that within the field under close drainage salt influx with water supply was 19.9 t/ha while within the fields under open drainage it was 23.2 t/ha. Salt removal by close drainage was 29.5 t/ha, by open 39.9 t/ha.
Agroclimatic data during observation period were the following: sum of temperatures in 1982 was 3287 oC, 1983 3304 oC, 1984 3210 oC and according to the phases:
- shoots appearance 193 oC;
- bushing 534 oC;
- blooming 1501 oC;
- ripening 846 oC;
- full ripening 192 oC.
Average irrigation norm during 1977-1984 for site under close horizontal drainage was 21.3 th. cu.m./ha, under open horizontal drainge 28 th. cu.m./ha.
Water expenses were the following:
- Soil water absorbtion at the beginning of flooding 9.05 %;
- evaporation from water surface 22.66 %;
- transpiration 27.99 %;
- vertical filtration 28.07 %;
- lateral filtration 3.59 %;
- technical losses 2.35 %;
- release 6.29 %.
Actual rice water consumption coefficient was 262-623; hydrotechnic coefficient (cu.m/1 oC) 3.85; total water consumption was 9778-12996 cu.m/ha; average value was 12105 cu.m/ha.
Rice height during observation period was as follows:
- minimum 56-93 cm;
- maximum 86.7-135 cm;
- biological yield 2.48-5.90 t/ha;
- bunker yield 2.17-4.77 t/ha.
Groundwater level before vegetation period was 1.4-2.3 m and average velocity of level depletion after water release was 2.7-6.3 cm/day. Salinity of irrigation, ground- and drainage water varied as follows:
- Irrigation canal: 0.65-0.94 (solid residue); 0.13-0.33 g/l (chlorine);
- Check: 0.99-4.07 (solid residue); 0.35-0.45 g/l (chlorine);
- Wells: 2.75-5.07 (solid residue); 0.62-0.84g/l (chlorine);
- Observation wells: 1.23-3.01 (solid residue); 0.26-1.01 g/l (chlorine);
- Close drainage outlet: 1.74-4.58 (solid residue); 0.49-0.93 g/l (chlorine);
- Piesometer: 12.41 (solid residue); 3.2 g/l (chlorine);
- Drains: 2.5-3.34 (solid residue); 0.35-1.1 g/l (chlorine);
- Collectors: 1.48-2.71 (solid residue); 0.37-0.80 g/l (chlorine);
- Takhtacupyr collector: 1.85-3.35 (solid residue); 0.38-0.98 g/l (chlorine);
- Field canals: 0.9 (solid residue); 0.26 g/l (chlorine);
- Upper system: 1.28 (solid residue); 0.26 g/l (chlorine).
Zone of water and salt exchange spreads for 100-115 m.
As a conclusion it is worth to note that close drainage use for two fold regulation of groundwater and water-salt regime allows to save irrigation water. Due to groundwater regulation within 1981-1984 within the site under close drainage 5.5-7.9 th. cu.m./ha or 21.9-25.6 % water was saved or average 24.24 % per hectare.
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