Summary of research project: |
Objective and technical fields:
More exact definition of drainage parameters, development of measures on deep waters level decrease and salinity control based on increase of lands drainability and leaching through subsurface horizontal drainage construction and proposals on its improvement
Scientific and technical approach:
Control of deep waters level, settlements logging, soil salinization and increase of lands productivity are based on strengthening of drainability and leaching regime of irrigation. Importance of the study consists in scientifically grounded measures on improvement of environmental and reclamation state of irrigated lands and water-logged settlements, water use and soil’s water-salt regime management.
Environment characteristics:
The pilot plot is located in south part of Kolkhozabad district below the Kumsangyr canal. There is a plain surface, which slightly lowers southward and to the west. Height above sea level is 373-392 m.
Climate is semi-desert continental with very hot, dry long summer and mild soft winter. Average annual air temperature is 15,7 oC. Average annual precipitation is 270 mm. Average annual relative air humidity is 62%. The plot belongs to the third bottom of the Vakhsh river, slope is 0,004-0,007. It has smooth relief and contains loess sandy loam, sands and loam.
There are mainly non-salinized light gray soils. Value of dry residue in deep waters varies from 1,2 to 5,2 g/l, on the average 3 g/l. Type of salinity is sulphate. Deep waters are recharged by seepage from irrigation channels and infiltration in fields. Regime of deep waters is characterized by high level during growing period, maximum depth is in May-June. Amplitude of fluctuation depends on a depth of deep waters below 3 m and accounts for 1,5-2 m. According to field observations, during growing period deep waters level is characterized by wide fluctuations and mounts to 0,4-0,5 m from surface.
Parameters of Pilot Projects and Technical Solutions:
Irrigated area of the plot is 90 ha (net), 95 ha (gross). Length of subsurface drainage is 6185 m (planned), 6086 m (actual), 67,2 m/ha (specific). Drain spacing varies from 60 to 140 m. Depth of drain is 1,6-3,5 m. Pipes are ceramic, asbestos-cement. Filter is sandy-gravel. During reconstruction an open irrigation system was replaced by flumed one, its length was 3050 m. Specific length is 76,2 m/ha, efficiency is 0,84.
Methodology:
Field studies and observations of the dynamics of deep waters, movement in soils of salts from aeration zone, accounting of drainage waters and study of the chemical composition and salinity of ground and drainage waters. The plot was equipped with meters to keep regular observations. Regime of deep waters was observed from 13 wells, depth is 2-10m. Salt sampling was done up to the depth of 2,0 m in 9 fixed salt lots. In order to identify influence of drains on desalinization the geochemical line was drilled twice a year. Hydrometric observations were conducted in 6 drains. Besides field observations, data of water related and agricultural institutions were used.
Results:
Studies on the pilot plot show, that existing drainage network due to its small depth (1,0-2,5 m) does not influence the character of water table and available drains during field works are dry.
Deep waters are recharged mainly by infiltration of irrigation and shallow waters pumped out by wells of vertical drainage as well as by precipitation.
Analysis of deep waters level regime shows, that the higher level is observed in summer-autumn period and accounts for 1,1-2,5 m.
Salinity of deep waters varies within 1,1-3,9 g/l, mainly 3,0 g/l. Type of salinity is sulphate-calcium, sulphate-chloride-calcium-sodium. Content of sulphate-ion varies from 762 to 2914 mg/l.
Salinity of the lower water-bearing horizon varies from 3,4 to 7,1 g/l. Type of water, practically in all wells, is sulphate-chloride-calcium, rarely - magnesium.
Permeability coefficient varies within 0,7-0,82 m/day in sandy loam and 3,4-6,5 m/day in sands.
Results show, that water inflow per 1 km of drain varies from 0,95 to 5,2 l/sec, and average runoff modulus is 0,027 l/sec/ha. It is identified, that percolation coefficient of top deposits is 0,03-1,25 l/day.
Average irrigation norm during growing period accounts for 10020 m3/ha. Water intake under system’s efficiency of 0,8 accounts for 12500 m3/ha. Water release under modern irrigation method is no more than 840 m3/ha.
Observation of drainage outflow allowed to assess indirectly permeability of deposits. Water permeability was higher than planned one. In drains 2-D-7 and 2-D-8 average drainage modulus within the growing period accounts for 0,38-0,57 l/sec/ha, i.e. 2,7 times higher than planned one. The highest average monthly values, 0,65-0,73 l/sec/ha, were observed in May-July, i.e. when the level of deep waters is highest. During ungrowing period water flow in drains reduces by 8-11 times. The best results were obtained in drains 2-D-9 and 2-D-11. Here average drainage modulus within the growing period accounted for 0,29-0,34 l/sec/ha, that was considerably higher than planned. During ungrowing period specific values of drainage outflow decreased to 0,5-0,15 l/sec/ha. Average values accounted for 0,19-0,23 l/sec/ha, in drain 2-D-7 - 0,34 l/sec/ha. According to conducted analysis, considerable inflow during growing period is accounted by over-irrigation.
After drainage construction hydrochemical state was also improved. Deep waters salinity was more than 3,8-4,3 g/l before drainage construction and 2,5-3,0 g/l in 1987-1988. Content of chlorine-ion accounted for 0,033%, before drainage construction - 0,068%.
Operation of the pilot plot under cotton cultivation allowed the following:
- to increase land use efficiency, which was 0,85 in 1988;
- to create high drainability of irrigated lands. Annual volume of drainage outflow varied from 13,8 to 15,3 th.m3/ha. Drainage outflow within the years varied within 0,23-0,79 l/sec/ha. Average drainage modulus within the growing period was 0,34 l/sec/ha;
- to provide high rate of deep waters level decrease after leaching and irrigation. Rate of deep water level decrease in the pilot plot was 20-30 cm/day while in non- and weakly drained ones was 4-7 cm/day;
- to maintain level of deep waters at a certain optimal depth. Deep waters level was equal to 1,5-2,0, that was 0,4-0,8 m lower than in surrounding areas;
- to establish high rate of soil desalinization under leaching and leaching regime of irrigation;
- to form negative water-salt balance. For 3 years of drainage work with leaching regime of irrigation salt storage in 0-100 cm reduced by 3,5 times from total salt amount;
- to reduce and make even salinity of deep waters within 1-2 g/l;
- to increase cotton productivity in sowing areas from 2,4 to 3,1 t/ha.
Above mentioned is confirmed by the results of the studies. In 1988 application area of intensive water saving irrigation technologies accounted for 1149 ha. Productivity of raw cotton was, on the average, 3,26 t/ha or 0,16 t/ha higher than in previous 5 years (3,1 t/ha). Cotton productivity in the pilot plot was 0,19-0,32 t/ha higher than it was planned. Due to increase in quantity of fiber sale price in 1988 was 1158 rouble/t or 127 roubles more than in previous 5 years (1983-1987).
As a result, an economic effect from intensive technology application accounted for 1145 th. roubles. Annual expenditures for cotton cultivation were decreased: 1951 rouble/ha in 1983-87, 1924 rouble/ha in 1988.
Besides, there was irrigation water saving as compared with previous years, especially in the pilot plot .
An economic effect accounted for, on the average, 800 rouble/ha in 1988.
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