Summary of research project: |
Objective and technical fields:
Salinity control and land productivity rise on the basis of increased drainability and leaching under ground water dam and draining base level limiting by the Kayrakkum reservoir.
Scientific and technical approach:
An optimal management by soil water-salt regime through development of reclamation-environmental regimes for land productivity and farm profitability rise.
Environment characteristics:
The object is located in West Fergana and joins to the south-west bank of the Kayrakkum reservoir as irregular contour extended in the middle and narrowed along the edges. The climate is dry continental. Average annual temperature is 14,4oC. Precipitation is 150 mm/year, mainly related to Autumn-Spring. Sum of positive temperatures is 5000oC. Duration of wind period at a rate of 15 m/sec is more than 60 days. Evaporativity is 1300-1500 mm/year. The plot is located in a foothill plain inclined in south-north direction to the reservoir. Lithology of the profile is characterized by pebble sediments with sandy loam and loam interlayers. Thickness of fine-grained soils increases from 2 to 40 m downward the slope. Slopes are 0,001-0,003. Ground waters are bedded at a depth of 1,5-3,5 m with toxic salts content equal to 1,0-2,5 g/l, type is chloride-sulphate. Permeability coefficient in pebble horizons is 10-20 m/day. Permeability coefficient of fine-grained soils decreases to 1,0-0,025 m/day. In the frontier between the scheme and the reservoir draining base level increased by 19-21 m due to its filling (1961) and ground water slope reduced. Inflow of drainage effluent to reservoir became difficult.
Ground water level depends on water availability, supply and head in reservoir. In ordinary years, when water level in reservoir is close to normal pool level, ground water level is 1,5-2,0 m. In low water level years under water drawdown (more than 6 m) ground water level decreases to 1,5-2,0 m.
Water-salt balances are complex due to changes in ratio of income and expenditures within observed years. It should be noted, that expenditures, deep release, have a low ratio, only 1-,3%. Over 7 years of salt balance accountings the rest was positive. In connection with general water management situation in the Syrdarya river basin salinity of irrigation water in the scheme increased from 0,6 g/l in 1955 to 1,8 g/l in 1974-1975. Salinity of drainage waters used for irrigation is more than above. Drainage modulus is, on the average, 0,26 l/sec/ha, that is 2-3 times less than water release by collectors, which is 0,85 l/sec/ha in high water level years and 0,52 l/sec/ha in low water level years. Salinity of drainage waters equal to 4-4,8 g/l is dissolved by irrigation water supplied from Big Fergana Canal and from vertical drainage wells. In low water level years this influence of irrigation water is lower. Type of drainage waters is chloride-sulphate. In income and expenditures ratio of toxic salts (MgSO4, Na2 SO4, NaCl) is approximately equal and in release ratio of non-toxic salts deposited in soils is reduced.
Specific and volume weight is 2,62-2,77 g/cm3 and 1,21-1,55 g/cm3 respectively. Porosity reduces from 58,3 to 40,7% downward the profile. Water permeability decreases from 6,0 to 3,9 cm/hour, moisture-holding capacity (MC) increases - 2840 m3/ha in 0-1 m layer. Irrigation depths are 820 m3/ha, leaching requirements are more than 1100 m3/ha. There are gray and meadow slightly-, middle- and strongly- salinized soils, salinity type is chloride-sulphate-sodium. Gypsum content is 0,9-1,3%, carbonate content is 2%. In absorption complex equal to 10-12 ml per 100 g magnesium cation prevails.
Parameters of Pilot Projects and Technical Solutions:
Area of the scheme is 6000 ha. It consists of four farms with 3 main plots (20x20 m) selected and 3 deep (depth is 2 m) and 6 shallow (depth is 0,5 m) wells for soil and ground water samplings during spring and autumn. Ground water level was measured. A range of experimental leachings was done in model areas. In special experiments leaching requirements on the background of optimal and half norms of fertilizers were studied. Influence of different norms of fertilizers on toxicity of dissolved salts was studied. In 20 points of the scheme samples of irrigation and drainage waters were taken. More than 70% of inter- and on-farm irrigation network is laid in earthen channel. Efficiency of the network is 0,55-0,6. Specific extent of drainage network is 36 linear meter/ha. 50% of drainage network of a depth of 1,5-2,5 m is in unsatisfactory condition, especially in the bank zone of the reservoir.
In south frontier of the scheme from mountainous side a line of vertical drainage wells was constructed to catch deep release from Arkin scheme (Kyrgyz Republic).
Methodology:
Field studies, observations and special experiments were conducted in the scheme. Solution of the main objectives of the project is based on water-salt balance calculations for the scheme. Materials of water related institutions were used jointly with analysis and calculations. Observations, accountings and samplings were conducted regularly during short- and long- term periods within 3-7 years. Experimental studies were conducted during 3 years. System analysis of the results was used.
Results:
Obtained results allow to form negative soil water-salt balance, to manage the efficiency of leaching and irrigation in salinized soils, to determine and regulate depths and salinity of ground waters. Ways to reduce toxicity of residual salinity by fertilizing are found. Reclamation-agronomic characteristics of soils were determined. It allows to develop measures on their optimization as well as soil salt regimes under different degree of leaching. Possibilities of salinized drainage water use for irrigation are studied. Character of reclamation-environmental processes within the scheme is determined. Role of ground water inflow from the mountainous side of irrigated lands and ground water dam, created by the Kayrakkum reservoir, is determined. Applicability of systems approach for analysis of reclamation regimes is studied.
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