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Objective and technical fields:
Irrigated lands' productivity increase at expense of reclamation improvement. Analysis of reclamation regimes with regard to crop yield, drainage systems workability and their regime.
Scientific and technical approach:
Assessment of VDS operation regime, its technical state, crop irrigation regime, irrigation water quality impact on ecological-reclamation processes.
Meaning: Methodological and practical recommendations on reclamation regime and VDS operation improvement.
Environment characteristics:
Climate is dry, semi-desert, windy. Precipitation is 119 mm, relative air humidity in simmer is 26-28 %; temperature achieves 32 oC.
Landscape: moderately corrugated plain with slope 0.0005-0.0006.
Lithology: Cover loam (4-12 m), sandy loam, sand with permeability coefficient is 0.5-4 m/day, water specific yield is 0.09-0.11. Cover is underlaid by gravel-pebble thickness (3-30 m), with permeability coefficient 10-50 m/day. Below it conglomerates and pebbles lay.
Territory is slightly drained. Main source of groundwater formation is irrigation water infiltration, its expense is due to outflow and evapotranspiration. Water is sulfate-sodium, magnesium-chloride-sulfate-sodium and calcium-chloride-sodium.
Soils are hydromorphic with spotted salinization within lower elevation places. Salinization is chloride-sulfate.
Parameters of Pilot Projects and Technical Solutions:
Water supply is performed from canal Shakhrud to the field by in-farm irrigation network. Efficiency of mains is 0.9-0.96, intra-farm canals 0.75-0.85, on-farm canals 0.7-0.79.
Share of cotton in crop pattern is 67-75 %. Land use efficiency is 0.85-0.77, irrigated land efficiency is 0.8-0.5.
There is a VDS consisting of 127 wells, which was constructed mainly in 1970-1978. Well's diameter is 1000 mm, depth is 20-25 m, discharge is 20-35 l/sec, specific yield is 6.7 l/sec/m.
Open horizontal drainage density is 32 m/ha and drain depth is 2.43 m.
Methodology:
Design of water-salt balance, measurement of actual discharges and specific yields of VDS wells.
Results:
VDS operation within pilot site in Kagan district permitted:
- groundwater level regulation within 2.7-2.9 m;
- cover loam drainability 1200-2300 cu.m/ha per year achievement;
- groundwater salinity decrease from 20-40 to 5-10 g/l;
- pumped water salinity increase from 1.3 to 3.5-8.5 g/l;
- non-salinizated and slightly salinizated land area of 95.4 % achievement;
- groundwater level decrease 0.10-0.22 m/day;
- cotton yield achievement 1.85-2.19 t/ha against initial 1.23-1.27 t/ha, growth is 0.62-0.82 t/ha.
However by 1981-1982 these processes were slowed down:
- irrigation water salinity in 1988 was 0.85-1.47 g/l against 0.5-0.8g/l in 1970;
- groundwater average level within the growing period was 2.09-2.57 m;
- most wells operate 15-25 years, their discharge decreased due to colmatation on 33 % or 18 l/sec;
- specific water duty within growing season varied within 4.8-8.2 th.cu.m/ha which is close to standard; within non-growing period it was from 2.7 to 3 th.cu.m/ha against 3-4 th.cu.m/ha real needs;
- total drainability, created by open and vertical drainage, was 1800-2300 cu.m/ha;
- common water-salt balance was negative (-1.11-1.55 t/ha). Main source of salt was irrigation water (8.9-9.1 t/ha).
Under these conditions soil salinization restoration has started. Slightly salinizated lands were 74.3 %, middle salinizated lands - 15.18 %, strongly salinizated - 10.52 %.
Cotton yield varied from 1.2 to 2.54 t/ha.
On base of forecast calculations and water-salt balance recommendations are developed for reclamation regime and VDS operation improvement providing:
- water supply to irrigated field 8600 cu.m/ha;
- pumped water volume 2280 cu.m/ha;
- groundwater depth regulation in growing season within 2.1-2.66 m; in spring 1.8-2.45 m, in autumn - 2.7-2.85 m;
- salt stock annual decrease within unsaturated zone on 89.4 t/ha.
These measures will allow to stabilise ecological-reclamation processes and increase crops yield.
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