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Objective and technical fields:
Prevention of soil salinization on base of land drainability improvement, leaching regime of irrigation, leaching.
Objectives; Soil water-salt regime management improvement on background of different types of drainage; irrigation-drainage system efficiency increase; irrigation water use improvement.
Scientific and technical approach:
Prevention of soil salinization on new developed lands, irrigation-drainage systems’ efficiency improvement are based on appropriate drainability creation by construction of drainage and leaching regime of irrigation providing optimal soil water-salt regime and balance.
Environment characteristics:
Climate is sharply continental. Average air temperature in July is 30-32 oC, maximum 47-50 oC. Average annual temperature is 15.8 oC. Annual precipitation is 180-280 mm. Relative air humidity within growing period is 33-40 %, in July 18-22 %. Evaporativity is 1200-1300 mm within the growing season.
Geomorphology: Alluvial and alluvial-proluvial plain of the Kashkadarya delta. There are two aquifers within drainage active influence zone: quaternary and ancient quaternary. Ancient quaternary sediment roof is impermeable layer.
Lithology: Cover loam (20 m), sand with interlayers of sandy loam and clay. Sand permeability coefficient is 10-15 m/day, loam – 0.4 m/day.
Groundwater before land development was saline everywhere, sulphate-chloride, with salinity 10-16 g/l. Level depth was more than 5 m.
Before land development non-salinizated and slightly salinizated soils encompassed 70 % of area.
Parameters of Pilot Projects and Technical Solutions:
Irrigated area is 145 th. ha, net – 96423 (cotton – 63 %, alfalfa – 9 %, grain – 8 %, corn – 5 %).
On-farm irrigation network – concrete upon polyethylen film (efficiency is 0.96-0.97). Specific extent is 22 m/ha, concrete network extent is 2.5 m/ha. Irrigation norm for cotton at beginning of development was 7.7-8.1 th. cu.m./ha, for alfalfa 9.3-11 th. cu.m./ha depending on soil composition and groundwater depth. Water supply is performed from Karshi and Ulyanov mains.
Drainage network is represented by vertical, horizontal close and combined drainage. There were 65 vertical drains at the moment of investigations beginning.
Well specific yield is 2.1-3.1 l/sec/m, discharge is 25-35 l/sec. Close horizontal drainage has extent 1348 km, drain’s depth is 3-3.5 m, distance between drains is 200-250 m. Combined drainage is represented by small experimental sites.
Methodology:
Field observations on all water-salt balance elements of unsaturated zone, groundwater and irrigated lands as a whole. Special balance contour with area 145000 ha was singled out. Within this contour typical farms, within the farms – experimental sites were assigned. Within these sites detailed observations on water salt movement and irrigation regime were carried out. All the territory is equipped by means of water and salt accounting.
Results:
Intensive land development initiated quick raise of groundwater level (5-7 m/year). Before development over 85 % lands groundwater level was deeper than 5 m. Within the observation period groundwater level was mainly on depth 1-3 m. Groundwater level raise was accompanied by groundwater desalinization, areas with water salinity 20 g/l decreased, land with salinity 0-5 g/l increased. Artesian water inflow did not change (+ 200-700 cu.m/ha). Land development provoked salinizated lands area reduction and increase of non-salinizated lands from 28220 to 58434 ha.
Salts maximum shifted from depth of 1.5-2 m to the surface (45-100 t/ha), mainly concentrating within 1 m-later (89.6-162.4 t/ha). In spite of groundwater level average depth 2.83 m and salinity 20 g/l lands of state farm # 11 remained middle and strongly salinizated.
Water duty was 17-22.7 th. cu.m./ha with tendency to decrease and irregularity in space. Within the balance farms it decreased from 22500 to 17170 cu.m/ha (state farm 3) and from 28300 to 13400 cu.m/ha (state farm 14), exceeding norms assumed by the project.
Water consumption regime does not correspond to actual water supply on irrigation norm as well as its seasonal distribution: water-storage irrigation was combined with leaching, number of irrigations was cut down, norms were increased and not differentiated according to soil composition and salinization level.
Total evaporation within growing season decreased from 10250 to 8070 cu.m/ha.
Drainage outflow exceeds expected values and achieves 3.7-4.8 th. cu.m./ha (average meaning is 2.5-2.7 th. cu.m./ha). Salt removal by drainage outflow exceeds 86-100 t/ha, minimum salt removal (2-12 t/ha) is observed within the farms where groundwater is lower than drain’s depth.
Observations show that drainage outflow accepted by collectors 2-10 times exceeds primary drains’ outflow.
Analysis shows that about 50 % of drainage effluent is constituted by released water (collectors Dagut, ŢĘ-6, ÂĘ).
Water-salt balances show that unsaturated zone’s soil and groundwater desalinization rate is satisfactory under water supply to drainage outflow ratio 0.34, in spite of partially not working drainage. Within the area with huge salt stock it was not possible to create sustainable soil desalinization in spite of drainage outflow achieving 4220 cu.m/ha (state farm 9, 1977) and average groundwater level equal 2.4 m while drainage removed huge amount of salt annually: 59.7 t/ha (state farm 9); 51.46 t/ha (state farm 10). Forecast water-salt calculations show that under big salt stock beneath groundwater level and keeping existing water supply groundwater level should be support at 2.6-2.7 m.
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