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Objective and technical fields:
Establishment of possibility and efficiency of drainage saline water use on the places of its formation to cut down drainage outflow. Soil water-salt regime and drainage effluent quality management under saline water utilisation for irrigation and leaching.
Scientific and technical approach:
Development of irrigation regime, soil water-salt regime based on field experiments. Main meaning of experiment is drainage outflow quantity and quality management and irrigated land productivity increase.
Environment characteristics:
Climate is sharply continental. Average annual air temperature is 13-15.6 oC, in July - 27 oC. Annual precipitation is 76-133 mm. Aridity coefficient is 17-32. Evaporativity is 1000-1180 mm. Relative air humidity is 55-65 %.
Relief: slightly corrugated plain.
Lithology: - loam, clay, sandy loam with thickness 20 m. Cover sediments' thickness is 10-15 m. Permeability coefficient is 0.9 m/day. Aquifer thickness is 5-15 m. Permeability coefficient is 3-5 m/day.
Separating layer thickness is 12-25 m, its permeability coefficient is 0.01-0.20 m/day.
Drainability is low under natural conditions. Groundwater level is 1.0-2.5 m, water salinity is 5-50 g/l. Water chemical composition is chloride-sulfate. Drainage water salinity at the beginning of its operation was 5-10 g/l.
Parameters of Pilot Projects and Technical Solutions:
Pilot site area is 102 ha (94 ha net). Cultivated crops: cotton - 54-69 %; corn - 7-15 %; vegetables and melons - 5-13 %. Irrigation network - concrete flumes with efficiency 0.96-0.98. Technical state is satisfactory. Drainage network - open horizontal drains. Drain's density is 45 m/ha, depth is 2.5-3.0 m; depth of collectors is 4.0 m.
Methodology:
Field observations on water and salts movement and unsaturated zone's water-salt balance elements measurement. Study of soil water-salt regime formation and drainage effluent quality. Pilot plot was equipped by water-meters. Multicriterial analysis and forecast calculations were used to process data obtained.
Results:
During growing period there were 5-6 irrigations by norm 660-2000 cu.m/ha. Autumn-winter leaching irrigations had norm 2000-3400 cu.m/ha. Annual water supply was 7650-11500 cu.m/ha.
Moisture before irrigations was supported at the level of 0.7-0.8 FFMC. Water-salt balance desalimizating flow within unsaturated zone was 2500 cu.m/ha. Salt removal varied from 5 to 20 t/ha. Irrigation leaching regime within the annual EB: EET was 1.1-1.35. Total evaporation was 890-910 mm. Drainage outflow was 4000-6100 cu.m/ha. Average annual drainage modulus was 0.09-0.21 l/sec/ha. During July-August drainage modulus increased to 0.4-0.5 l/sec/ha; the same picture could be observed in January after leaching.
Drainage effluent salinity was 2.0-4.4 g/l. Within the control site its salinity was 0.5-0.9 g/l. The pilot site is located in the tail part of irrigated scheme and drainage water is used for irrigation. Within the pilot site common and partial water-salt balances were negative and have desalinizating type.
Gradual soil desalinization is achieved during the experiments from 1.5 to 0.6-0.8 % for sum of salts. Salt stock within 3 m-layer decreased from 680 to 400 t/ha for a solid residue.
The more intensive harmful salts (NaCl, NaSO4, MgSO4) and non-toxic salts (CaSO4) ratio increased.
Groundwater salinity decreased from 8-10 to 4-4.5 g/l.
Soil water-physical properties did not change, they only slightly varied.
Nutrient elements were accumulated. Soil-absorbing complex was improved within the pilot site as well as on control one. Absorbed sodium was 4-5 %, calcium - 65 %, that is favourable for crop cultivation. Cotton yield increased from 0.7-0.8 (1977) to 2.8-3.0 t/ha (1986).
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