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Objective and technical fields:
To identify climate changes regularities and to assess cotton water requirements for differernt years of land development for watering and irrigation norms correction.
Scientific and technical approach:
To determine total evaporation value on base of heat balance method. To define water consumption process stabilization according to the period of development.
Environment characteristics:
Climate is sub-tropically continental. Average air temperature is 14.5 -16.2 oC, maximum is 46 -50 oC ( summer). Average relative air humidity is 16 -17 % in summer. Wind velocity is 2.1 -3.5 m/sec within growing period. Precipitation is 146 -535 mm growing from desert to mountains. Evaporation from water surface is 1100 -1300 mm.
Relief: slightly corrugated plain.
Lithology: quaternary sediments of alluvial, proluvial and diluvial origin.
Soils : loess loam and sandy loam (15 -16 m), which is underlaid by gravel (few meters). Mechanical composition of soil to depth 4 -4.5 m shows loam, sandy loam and sand. Soil volume mass within unsaturated zone is 1.33 -1.4; specific weight -2.4 -2.64 g/cu.cm. Permeability coefficient is 0.8 m/day. Under irrigation physical properties of soil significantly changed. Volume mass increased and porosity decreased. Soil permeability before development (1974) was 0.91 m/day, in 1976 -0.29, in 1977 -0.26 m/day. Soils are slightly salinizated, sulphate. Groundwater salinity is 10 -20 g/l, chlorine -ion content does not exceed 1.2 g/l; level depth was 7.5 -8.0 m initially, 3.5 -4 m after 1 year. In 1977 level was within 2.13 m (February) -1.28 m (August).
Parameters of Pilot Projects and Technical Solutions:
Site area is 104 ha (100 ha net).
Crop is cotton: irrigation was performed in furrows.
Irrigation network - canal with concrete lining, technical state is good. Site is located between two collectors with depth 3.0 m.
Methodology:
Site was equipped by means of measurement of all parameters of heat and water balance by devices for water accounting.
Multicriterial analysis was used to process data obtained.
Results:
Field observations in 1974 showed that average summer temperature is 2.5 0C lower comparatively with desert; relative humidity 2 -13 % higher; wind velocity within 0 -2 m layer is 0.6 -1.6 m/sec lower.
Total evaporation during July -September 1974 was 234 mm; from cotton field in 1975 -1977 it was 1035, 905 and 805 respectively. Bioclimatic coefficient was for May -0.4; June -0.7; July -1.04; August -1.07; September -0.96. Irrigation norm in 1975 was 10970; in 1976 -10330, in 1977 -12733 cu.m/ha. Watering depth was for given period 1200 -2900 cu.m/ha; number of waterings -5 -6; irrigation interval was 15 -20 days. Soil moisture before irrigation was from 13 % (depth 0 -20 cm) to 30 % (150 -175 cm); after irrigation: 35.4 % (0 -25 cm) and 24.8 % (150 -175 cm).
Cotton field of the 3-rd year (1977) water balance was as follow: water depth -1273.3 mm, precipitation -12.3 mm, evaporation -879.3 mm, water outflow from unsaturated zone 477.1 mm.
Following conclusions can be drawn from field investigations’ result:
- Irrigation of new lands provokes decrease of average-monthly air temperature on 2-5 oC.
- Irrigation impact on thermal regime is observed all over the growing period.
- Maximum air temperature is observed in June -July.
- Absolute air humidity on irrigation field is 5 -11 higher than on desert.
- Heat expense for evaporation after irrigation increases 2 -3 times at the beginning of vegetation.
- Total evaporation volume depending on human activity changes during May -September from 1035 mm (1-st year) to 905 mm (2-nd year) and 805 mm (3-rd year).
- Evaporation from water surface during June -September 1975 was 1236 mm, 1976 -1103 mm, 1977 -1071 mm.
- Cotton yield in 1975 was 1.01 t/ha, in 1976 -1.8 t/ha, in 1977 -2.8 t/ha.
- Cotton irrigation norm within two first years of land development should be 25 -30 and 12 -15 % higher to compare with old developed land.
- The third year is practically a year of land development completion.
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