Summary of research project: |
Objective and technical fields:
Development of rational technology of soil desalinization by means of horizontal drainage, leaching and irrigation leaching regime. Definition of drainage design efficiency in multilayer soils.
Scientific and technical approach:
Acceleration of soil desalinization and its productivity restoration, irrigation water saving.
Importance: Leaching technology’s parameters optimisation, depth of soil desalinization within unsaturated zone and groundwater aquifer establishment.
Environment characteristics:
Pilot site is located within the alluvial plain with slope 0.002-0.003. Sediments are represented by quaternary, tertiary and cretaceous depositions. From the surface it is heavy loess loam and from the depth 3-5 m middle and light loam. Cover loam thickness is 10-17 m. Permeability coefficient of heavy loam is 0.3-0.6 m/day, middle loam 0.5-1.2 m/day, light loam 1.0-1.7 m/day. Loam is underlaid by gravel-pebble sediment with sandy filling. Their thickness is 8-15 m; permeability coefficient varies within 40-100 m/day. Before drainage construction groundwater level was on depth of 1.5-2.0 m, and after its construction 2.5-3.0 m. Groundwater salinity was 7-14 g/l, salinity type was chloride-sulphate. Before drainage construction these lands were not used for crop growing and were strongly salinizated. Salt content in upper 1 m-layer of soil was 0.8-2.0 %, within the second 1 m-layer it was 0.6-1.8 %. Salinity type was chloride-sulphate. Maximum salt accumulation was observed within the upper 1 m-layer of unsaturated zone.
Parameters of Pilot Projects and Technical Solutions:
Pilot plot’s irrigated area was 135 ha including 60 ha of the first stage, 75 ha – the second stage. Close drainage extent for the first site was 2400 m, density – 40 m/ha; distance between drains – 100; 200; 300 m; depth was 2.5 m within the head and 3.0 within the tail. Tubes were asbestos-cement, screens – sandy-gravel. The site is surrounded by collectors P-3, P-3-II, K-1 and DC-16. Their density is 20 m/ha. Groundwater regime was observed through 60 observation wells. Water exchange between different aquifers was observed through special sets of wells with depth of 3.5; 10; 15 and 20 m. Number of sets was 10. Open drainage extent was 2750 m, specific extent – 36.5 m/ha; for collectors – 13.5 m/ha. Drain depth was 2.5-3.0 m, for collectors – 3.5-4.0 m. Groundwater regime was investigated through 85 observation wells with depth of 5 m.
Methodology:
Field researches were performed through water and salt movement study, unsaturated zone water-salt balance elements’ and groundwater measurements. Pilot sites were equipped by water-meters by which permanent measurements were undertaken. Multicriterial analysis was used to process collected data.
Results:
Pilot plot’s irrigated lands are introduced by strongly salinizated soils. For soil desalinization autumn-winter leaching or rice planting were used. For non-salinizated soils development cotton planting was used.
Horizontal drainage construction allowed:
- to create highly drainable lands by leaching and irrigation leaching regime. Drainage outflow volumes within the pilot sites were 25-36 % of water supply, but taking in consideration groundwater overflow from cover loam to gravel-pebble sediments and their seepage into the drainage they increased to 70 % of water supply;
- to provide higher velocity of groundwater level decreasing after leaching and vegetation irrigations, which varied within 8-10 cm/day. Before drainage construction if did not exceed 4 cm/day;
- to support groundwater level below critical depth (more than 2.5 m) and guarantee its quick lowering after water-storage and vegetation irrigations;
- to use good hydraulic connections between different quaternary aquifers for strengthening of salt removal from unsaturated zone and groundwater upper layers under leaching, water-storage and vegetation irrigations;
- to establish rational depth of unsaturated zone desalinization under leaching by heavy leaching rates: 4.5 th. cu.m./ha (50 % of calculated rate by V.Volobuev); 8.5 th. cu.m./ha (calculated rate); 14 th. cu.m./ha (50 % higher than calculated rate); 26 th. cu.m./ha (2.5 times higher than calculated rate); under rice planting – 41 th. cu.m./ha (5 times higher than calculated rate); in the first case soil desalinization (to allowed limits 0.3 %) has occured to 0.5 m downward; in the second case – to 1.0 m; in the third case – 1.5 m; in the fourth case – 2.5 m; in the fifth case – 4 m. Specific water discharge for 1-th of salt removal from 1 m-layer were respectively: 45, 76, 82, 147, 532 cu.m, and from 3 m-layer: 82, 76, 65, 84, 105 cu.m. Groundwater salinity increased respectively : from 8.5 to 13; 9-15.5; 8-10.5; 8-6.5; 9.5-6 g/l;
- to form negative water-salt balance. Under leaching rate 4.5-41 th. cu.m./ha salt removal from unsaturated zone and quaternary sediments by drainage outflow was 10-150 t/ha and by underground flow which discharged by seepage into drains – 15-160 t/ha. Under multilayer soils horizontal drainage reclamation efficiency 2 times exceeded indices obtained on the experimental sites.
The main investigations’ result is definition of horizontal drainage reclamation efficiency and rational depth of soil desalinization under leaching; water use improvement at expense of water consumption rate cut down and surface water unregulated runoff use within non-growing period; acceleration of soil desalinization and cotton yield increase to 2.0-2.5 t/ha, cereals 4.0-4.5 t/ha, corn 6.0-7.0 t/ha. Economic effect was 200-300 rouble/ha.
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