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Objective and technical fields:
Soil salinization prevention on basic of land drainability improvement, leaching and leaching regime of irrigation. Objectives: water use improvement, soil water-salt regime mangement, irrigated lands productivity increase on background of vertical drainage.
Scientific and technical approach:
Soil salinization prevention and land productivity increase on basic of land drainability increase and salt removal by groundwater pumping providing soil water-salt regime optimal management.
Meaning: Development of the set of measures on irrigated land productivity increase and water saving.
Environment characteristics:
Climate: Low precipitation (250-350 mm) and it irregularity within a year. Relative air humudity is 55 -60 %, in summer 25 -30 %. Sum of positive temperatures is 4000-4100 oC. Average annual temperature is 12.5 -13 oC. Absolute maximum is 44 oC, minimum is -30 oC.
Lithology: loam (26 m), middle grained sand (32 -34 m), gravel-pebble (110-140 m). Permeability coefficient for loam is 0.1 -0.5 m/day, for aquifer 30 -50 m/day.
Groundwater level varies within 1.7-2.2 m (growing season) and 2.5 - 4.26 m in autumn. Interrelations between ground and artesian water are different and difference between groundwater level and artesian head varies from -2 m to +3 m.
Soils: middle loam. Soils are salinizated; within 3.5 m layer solid residual is 1.2 -0.7 %, chlorine -ion 0.033 -0.01 %. Downward salinity decreases to 0.1 % (solid residual) and 0.0099 % (chlorine). Salinization type is chloride -sulphate. Total salt stock in soil (40 -80 % of area) exceeds allowed content by 1.5 -2.5 times.
Parameters of Pilot Projects and Technical Solutions:
Irrigated area is 2975 ha (net). Land use efficiency is 0.85. Main crop is cotton. Water supply is performed from canal K -2a. Experimental site area is 50 ha, under cotton -32 -34 ha. Number of vertical drainage wells is 12. Only 4 of these wells influence experimental site. Wells’ depth is 60 -70 m; discharge 78 -85 l/sec, specific yield -8 -12 l/sec. Screens are perforated steel tubes with gravel filling. Workability coefficient is 0.8 -0.85.
Methodology:
Balance sites were established for field investigations by area of 50 and 22.3 ha, where regular observations were carried out on water and salt movement, irrigation water accounting, VDS operation parameters measurement. These sites were equipped by observation wells with depth 5 -7, 18 -20, 35 -45. Multicriterial analysis was used to process data.
Results:
On balance site “Navoiy” under intensive operation of vertical drains with workability coefficient 0.70 -0.80 and discharge 80 -100 l/sec favorable conditions for downward water movement were created. Two maximum positions of groundwater level were observed: 1.7 -2.2 m under autumn -winter leaching and 2.5 -4.2 m in autumn. Difference between artesian and groundwater level is 2.4 m within 240 m from drain; water lowering rate is 1.8 -2.4 cm/day; within 1700 m from drain they are: 2.1 m and 1.5 cm/day respectively. Ground and pumped water salinity dynamics is low. Groundwater salinity is 2.5 -4.7 g/l (chlorine -0.11 -0.54 g/l); outside of irrigated area water salinity is 11.5 g/l (chlorine 1.37). Pumped water salinity did not change (0.67 -1.0 g/l); artesian water salinity is 1.4 -3.8 g/l. Salinity type is sulphate -chloride under low salinity and chloride -sulphate under high one.
Cover sediments salinity is (0 -3.5 m) 1.2 - 0.7 % (chlorine 0.033 -0.01 %), downward it decrease to 0.1 % (chlorine 0.0099 %).
By 1972 due to salt re -distribution below 3 m salinity increased to 0.133 % (chlorine 0.233 %). Within active zone (0-4 m) salt accumulation depends on leaching regime of irrigation.
Analysis of water -salt balance for 1970 -1971 showed that under leaching rate 2200 cu.m/ha plus precipitation (2120 cu.m/ha); groundwater outflow 1609 cu.m/ha and salt removal of 7.2 t/ha were provided. But insufficient water supply in 1971 (2 irrigations by norm 3700 cu.m/ha under total evaporation within this period 4040 cu.m/ha) provoked inflow of 1637 cu.m/ha into unsaturated zone and salt influx of 10.5 t/ha. Results of investigations show that soil desalinization sustainable process can be supported by high drainability under leaching regime of irrigation (7 -8 th. cu.m/ha), that provides 15-20 t/ha salt removal from active zone. As a result of VDS insertion in 1966 -1972 cotton yield increased from 1.24 to 2.14 t/ha. On the old irrigated zone of Golodnaya Steppe on background of VDS operation it is possible to regulate operatively soil water-salt regime.
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