Summary of research project: |
Objective and technical fields:
Development of measures for salinity control on the basis of land drainability increase by vertical drainage construction.
Objective: To determine the reclamation effectiveness of this type of drainage in multi-layer soils. Soil water-salt regime management for creation and rehabilitation of its productivity.
Scientific and technical approach:
Salinity control and increase of land and water productivity through drainability strengthening. Importance of the study consist in scientifically grounded measures for improving management of soil water-salt regime and reclamation-environmental processes by effective vertical drainage combined with rather shallow poor surface horizontal drainage.
Environment characteristics:
The climate is subtropical continental. Average annual temperature is 15,5oC, sum of positive temperatures is 5500-6000oC. Frost-free period is 234 days. Precipitation is 290 mm/year. Evaporativity is 1500-1600 mm/year. The plot is located in an active zone of salt accumulation and belongs to the third alluvial bottom of the Vakhsh river. Relief has a form of bowl. The plot is divided into the north-east part with 0,01 slope and the west slight sloping part with 0,0017 slope. Lithology: multilayer top of 6-11 m fine-grained soils and below there are pebbles, more than 100 m, with sand interlayers. Permeability coefficient is 10-20 m/day. Fine-grained soils include the inter layered loam, sandy loam and clay, their permeability coefficient is 1,0-0,025 m/day.
Ground waters are contained mainly at a depth of 0,5-3,0 m. Salinity of ground waters is very high, more than 100 g/l in the south-west part of the plot. In the canal adjacent zone salinity is less than 3-5 g/l. Salinity equal to 10-24 g/l prevails. Within the roof of pebble horizon salinity of ground waters is 10-15 g/l. Type of ground waters is chloride-sulphate-calcium. Ground waters head raises from 0,2 to 0,6 m to the center of the bowl.
There are alkaline, salinized irrigated gray and meadow soils. Before the development the area consisted of 72% of alkaline soils, 15% of heavy salinized soils and 13% of low- and non-salinized soils. Salt storage in 0-2 m amounted to 800 t/ha and NaCl content was 150 t/ha. Type of salinity is chloride-sulphate and sulphate-chloride. In low levels of relief there are thick gypsum horizons - almost 40% of the plot area belongs to middle- and heavy- gypsum-bearing horizon. Soil texture: fine loam in the canal adjacent zone and heavy loam in central part of the bowl. The higher the gypsum content the lower the soil absorption, from 10-12 to 7-9 ml per 100 g of soil. Alkaline soils contain 40-50% of sodium. Volume and specific weight of soil is 1,28-1,72 and 2,48-2,81 g/cm3 respectively. Porosity varies from 37 to 58%. In gypsum-bearing horizons the higher the gypsum content the lower the specific mass, 2,8-2,4 g/cm3 , and the lower the volume mass, from 1,5-1,6 to 1,3 g/cm3. Permeability coefficient of gypsum-bearing light-, middle- and heavy- loam varies accordingly from 6-12 to 1-2 m/day. Permeability coefficient of clay with low gypsum content is 0,025 m/day, for clay with middle and high gypsum content - 0,5-1,0 m/day.
Parameters of Pilot Projects and Technical Solutions:
Irrigated area is 400 ha. Specific length of irrigation network is 20 m/ha. Specific length of waste and drainage ramified network is 22 linear meter/ha, depth is 1,0-2 m, drain spacing is 200-600 m. Around the central part of the bowl three vertical drainage wells, up to a depth of 51 m, with 1 km distance between them as a battery of triangular shape were constructed. Drains were equipped with pumps ATN-14.
Methodology:
Field studies and observations of water and salt movement, measurement and study of water-salt balance’s elements and agro-reclamation parameters of leached and irrigated lands. System analysis of the results of studies, based on balance calculations and hydro-dynamic schemes was used. The pilot plot was equipped with water and salt meters and with piezometric network in fine-grained soils and within pebbles horizon. Total quantity of piezometric points is 35. Initial soil survey(in 1957 and 1963) and repeated one(in 1968) were conducted.
Results:
Under influence of reclamation the pilot plot was desalinized and development of 320 ha of salinized soils became possible. As a result of 5 year pumping, area with ground water salinity equal to 5g/l increased from 28 to 61%. Areas with ground water level at 1m (43%) were completely vanished, at a depth of 1-3 m decreased from 85 to 13%. In rest area 87% of ground water level was lower than 3m. Artesian waters of pebbles inflowed in fine-grained soils in the amount of 8-13 th. m3/ha were replaced by reverse ground water flow. Command zone of one vertical well is 200 ha. Pumping forms cone of water-table depletion up to a depth of 20-30m, rate of ground water level decrease in a well is 2,8 m/day, within 150 and 300 m distance is 0,75 and 0,50 m/day respectively. Ground waters are restored to their initial state over 30 days after stopping the pumping. Over 5 years average water balance was with negative rest equal to 1756 m3/ha. Portion of vertical drainage accounted for 44%. Difference of income and expenditures was 75 t/ha per year and, taking into account income with artesian waters, was 50 t/ha. 72% of total salt removal relates to vertical drainage. Drainage removed 43% of outside salts and 57% of salts directly from fine-grained horizon.
Over 5 years, water balance in 1967 characterized by high precipitation had positive rest equal to 700 th.m3/ha, that was 2 times more than additional precipitation. Average annual water supply in high- and low- water level years varied within 9,96 and 13,24 th.m3/ha respectively, precipitation was 13,54 and 15,4 th.m3/ha.
Equipment of vertical drainage wells by electric pumps allowed to obtain capacity of well equal to 100-140 l/sec under operation coefficient equal to 0,6 during growing period and pumped volume equal to 5 mln.m3/ha. Salinity of pumped waters reduced from 10 to 3,5 g/l. Salt was mobilized from a depth of more than 50 m. Multiple changes in well operation and stopping promoted inclusion of salts into artificial geochemical flow and caused aeration of dried soil zone. During leaching, mostly under rice cultivation, desalinization proceeds in the whole fine-grained zone.
Specific expenditures for vertical drainage wells construction accounted for 750-770 rouble/ha, for operation - up to 25 rouble/ha (in prices of 1983-1984). Agricultural production became profitable in 3rd development year under governmental expenditures for drainage construction and operation.
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