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Objective and technical fields:
Study of autumn-winter and spring leaching irrigation, leaching rate to prevent soil salinization on background of close horizontal drainage.
Identification of autumn-winter and spring leaching irrigation reclamation efficiency in soil desalinization, irrigation water saving and influence on cotton yield.
Scientific and technical approach:
Development of technology of autumn-winter and spring leaching, soil and groundwater desalinization, soil and water productivity increase, based on field tests.
Meaning of experiments: scientific ground of leaching rate to prevent soil salinization under leaching by furrows on background of close horizontal drainage to improve water use and manage soil water-salt regime.
Environment characteristics:
Relief: Slightly corrugated, slope is 0.0025 to north-west. Altitude is 430 m.
Climate: Sharply continental. Average annual temperature is 13-14.8oC. Precipitation is 89-172 mm. Evaporativity is 1050-1160 mm. Relative air humidity is 57-65 %.
Lithology: Quaternary sediments represented by: loam (2.5 m), coarse sand (13.5 m), gravel with sand filling (22 m), loam alternated with sand (38-60 m). Clay content is 20-30 %, permeability coefficient is 0.3-0.6 m/day. Loam is light and middle. Soil is middle salinizated, chloride-sulphate type, meadow with groundwater level 2.0-2.4 m. Groundwater salinity is 4.6-5.1 g/l on solid residue and 0.1-0.12 g/l on chlorine.
Soil content of humus is 1.5-1.95 %, common nitrogen is 0.137-0.201 % and common phosphorus is 0.115-0.157 %.
Total area of pilot site is 6.12 ha. One field size is 10800 sq.m (36x300 m).
Parameters of Pilot Projects and Technical Solutions:
Pilot site’s area is 160 ha (gross) or 153 ha (net).
Crop pattern: cotton – 76 %, corn – 6 %, alfalfa – 1.5 %, melon – 3 %.
Irrigation network – concrete flumes with efficiency 0.92-0.95. Technical state is satisfactory. Close horizontal drainage density is 40 m/ha, total length is 6400 m. Distance between drains is 280 m. Drain depth is at the head 2.7 m, at the tail – 3.0 m. Drainage pipes are asbestos-cement. Groundwater observations were performed in 4 points. Groundwater outflow was 0.2-0.3 l/sec/ha, and during leaching – 0.5 l/sec/ha.
Methodology:
Field observations after water and salt movement; water-salt balance elements of unsaturated zone measurement.
Pilot site was rigged by means of measurement and accounting. Soil moisture content and salinity were measured by sampling.
Test versions:
Version 1. Autumn leaching by checks by rate of 1500 cu.m/ha (control);
Version 2. Autumn leaching by checks by rate of 2500 cu.m/ha;
Version 3. Spring leaching by checks by rate of 1500 cu.m/ha;
Version 4. Autumn leaching by furrows by rate of 2500 cu.m/ha;
Version 5. Spring leaching by furrows by rate of 1500 cu.m/ha.
Over all versions before leaching in autumn ploughing was executed to depth of 40 cm followed by loosening to depth of 60 cm. Annually before leaching 3 versions of checks and 5 versions of furrows were performed. Check’s size depending on slope was 0.05-0.06 ha (length 25 m x width 20 m), furrow length was 330 m, width – 0.9 m.
Autumn-winter leaching was performed within the 1st and 2nd versions by rate of 1500-2500 cu.m/ha and within the 4th version into furrows by rate of 2500 cu.m/ha. Leaching was performed since 15 till 22 of January.
Water-stock irrigations within the 3rd version were performed by checks by rate of 1500 cu.m/ha and within the 5th version – into the furrows by rate of 1500 cu.m/ha since 10 till 14 of March.
Results:
In 1986 after leaching was found, that from 1 m-layer salts were washed out: in the 1st version – 23.2 %, 2nd – 30 %, 3rd – 17.3 %, 4th – 24 %, 5th – 16.7 % of initial amount. After leaching by rate of 1500-2500 cu.m/ha chlorine-ion content was 0.004-0.007 %.
Reason for low salts’ removal under spring leaching by checks and furrows within all versions of the test by rate of 1500 cu.m/ha is salts’ raise to the surface from lower horizons inspite of better salt solution and washing out under higher temperature. That is why soil secondary salinization in spring is more intensive to compare with winter. Inspite of these disadvantages salt content before cotton sowing within 1 m-layer does not exceed 1.24-1.26 % and chlorine-ion 0.004-0.006 % of dry soil weight. This content is suitable for cotton yield.
Leaching efficiency significantly depends on groundwater level position. In 1986 before leaching groundwater level was 2.37-2.48 m, after leaching within 1, 2, 4 versions of the test (30.01.1986) it was 0.86 m; in spring before leaching within 3, 5 versions (5.03.1986) it was 1.86 m. During leaching groundwater outflow was 0.5-1.5 l/sec/ha. Spring leaching was performed on March 10-14, 1986. During this period groundwater level was on 1.26 m (20.03.1986). During sowing period groundwater level was 1.7 m. Cotton sowing was undertaken on April 7, 1986. Cotton sort was "Tashkent-6".
During cotton sowing soil moisture within 1st version within the 0-40 cm-horizon was 19.0 %; within 1 m-layer - 20.3 %; within 2nd version - 22.4-23.9 %; within 3rd version - 22.4-24.2 %; within 4th version - 20.7-22.6 %; within 5th version - 21.0-22.3 %.
The same conformity was kept during leaching and after it in 1987, 1988. But during growing season of 1987, 1988 inspite of leaching by rate: in 1986 - 3865 cu.m/ha; in 1987 - 2870 cu.m/ha; in 1988 - 3396 cu.m/ha gradual secondary soil salinization occurred.
Salt accumulation value varies within the test versions in 1987 from 0.193 % (version 5) to 0.26 % (version 4) and 0.303 % (version 3). Chlorine-ion content increase at the end of growing period was observed.
The same phenomena was noticed in 1988. At the same time annual gradual soil desalinization was observed.
Due to slow soil desalinization yield growth varied within the test versions within the limits 10-15 %, i. e. was in average for 3 years: 0.23 t/ha in 2nd version, 0.35 t/ha in 4th version, 0.17 t/ha in 5th version. Within the 3rd version where spring leaching was performed by rate 1500 cu.m/ha cotton yield was 2.53 t/ha which is 0.04 t/ha lower to compare with control field. Thus for central Fergana conditions under relatively close to surface groundwater (1.5-2.2 m) further soil desalinization may be achieved by means of winter-spring water-storage irrigations and leaching by rate of 1.5-2.5 th.cu.m/ha and vegetation irrigations by norm of 950-1100 cu.m/ha, providing at least 3-4 irrigations by norm 3.5-4.0 th.cu.m/ha.
Experiments showed that best time for water-storage irrigations is March and for leaching - January and February.
As technological approach the best was leaching by checks where soil salinization during the growing season is slower (version 1) than by furrows (version 5).
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