Summary of research project: |
Objective and technical fields:
To study how macro-relief (terracing) of rice field influences the irrigation norm, salt regime of soils, hydrochemical regime of surface and ground waters, rice productivity. Scientific justification of optimal parameters of rice fields macro-relief for achievement of high yields of rice under reclamation state improvement.
Scientific and technical approach:
Study of an influence of rice checks terracing on a value of infiltration, water salinity, salt regime of soils and rice productivity; study of water and salt balance of the rice check in relationship with macro-relief . Economic justification of the parameters of rice field relief. Determination of the optimal parameters of rice field macro-relief.
Environment characteristics:
Climate. Considered region is related to Kzylkum sub-zone of dry hot zone of deserts and semi-deserts. Total annual precipitation according long-term data is 165...200 mm, the largest amount is fixed in Spring and Autumn. Total precipitation for a warm period with air temperature of more than 10oC accounts for 60...70 mm, the smallest amount is fixed in July (2 mm) and September (1 mm). Total positive air temperature for a period, when air temperature is more than 10oC, accounts for 4600...4800oC, duration 200..210 days. Evaporativity is 1100 - 1200 mm. Relative air humidity in winter is 70...76%, in other period is not more than 34...45%, a minimum value 18% is in July...August. Number of days with relative air humidity less than 30% is 180. Deficit of air humidity grows from 8...9 Mb in April to 32 Mb in July.
Relief. Kzylkum scheme is a plate valley, lightly lowering in north-west direction with 0,0002...0,0003 slope. Height above sea level is 200...250 m. Relief is smooth, has a light bench terraced nature. There are two bottoms and modern flood plain on the scheme’s territory.
Lithology of the scheme has a uniform nature. The lowest layer includes gray and yellow-gray fine-grained sands with thin interlayers of clay, sandy loam and loam, sometimes with coarse sediments (gravel, shingle, etc.). Top layers include yellow-brown loam and sandy loam with clay and sand interlayers. Thickness of loamy layer varies from 0,5 to 3 meters. Soil texture consists of top loams, thickness of which is up to 3 m, and bottom sands - up to 60 m and more. Permeability coefficient (PC) from soil surface is 0,21...0,35 m/day. PC of bottom sandy loam layers is 1,4...1,6 m/day and sands - 2,4 m/day. Level of ground waters in spring accounts for 1,6...2,5 m, in growing period - 0,6...1,8 m. Salinity of ground waters is 1,87...8,14 g/l. Type of salinity is chloride-sulphate. Permeability varies from minimum (11 mm/hour) in loamy soils to maximum (100 mm/hour) in eolic sands.
Parameters of Pilot Projects and Technical Solutions:
The irrigated area is 33 ha. Specialization of farm is rice-growing. Water supply and release are done by earthen canals. Crops rotation has a following scheme: 1. Rice, 2. Rice, 3. Alfalfa, 4. Alfalfa, 5. Rice, 6. Rice, 7. Rice, 8. Fallow lands (barley). Irrigation schedule, developed by KazNIIrice, for rice and alfalfa was common for the Kzylkum scheme. Rice in the pilot plot was cultivated under shorten ponding regime. UZROS-59 sort was sowed.
Methodology:
The base for study of physical processes, which proceed under adjoining checks and identification of causality of rice productivity reduction, comprises a method of conjugate observations for objective factors of terracing, including: difference of water-salt balances in high and low checks; rate and direction of infiltration from surface in symmetric points of rice checks; difference in ground waters regime; biometrics and rice productivity. The pilot plot was equipped with water meters, balance platforms, piezometers and observation wells.
Results:
Effectiveness of water use in rice irrigation systems of the Syrdarya basin depends, to a considerable degree, on parameters of rice field relief. Lowering of checks terracing increases uniformity of infiltration processes improving reclamation regime of soils and ground waters, allows agrotechnical measures, which provide rice productivity increase and reduction of irrigation water expenditures, to be implemented more effectively.
Terracing of adjoining checks in rice irrigation systems of the Syrdarya river basin is about 90 cm. In Kzylkum scheme terracing of about 35 cm accounts for 45%, from 35 to 80 cm - 40%, from 80 cm and more - 15%. In high checks with positive terracing of up to 80 cm the rate of infiltration accounts for 140...200 m3/(day.ha), in low checks - drops to 20...40 m3/(day.ha). Both at positive and negative excessive terracing reclamation and nutrient regimes of soils are deteriorated, in first case this is caused by considerable washing of nutrient elements by water flows, in second case - insufficient aeration. In both cases this leads to yield arrears. An optimal rate of infiltration is 60...90 m3/(day.ha), which is maintained in checks with terracing of not more 35 cm and provides rice productivity within 4,8...7,3 t/ha.
Water-salt studies ascertained influence of rice field macro-relief on irrigation norm, which accounts for 23,0 th.m3/ha and more in high checks with up to 80 cm terracing and 21,6 th.m3/ha in low checks. This is caused by different value of infiltration, which, in its turn, influences the change of water salinity in ponding depth and ground waters. In high checks water salinity in ponding depth varies within 1,2...1,5 g/l, in ground waters - 1,5...2,5 g/l, in low checks - 2,8...3,5 g/l and 3,6...8,2 g/l respectively, water salinity in irrigation source is 1,1 g/l. Altitude of checks on a map and value of vertical infiltration determines salt regime of soils. In high checks with positive terracing and water discharge for infiltration of 100...180 m3/(day.ha) the salt regime is determined by type of desalinization, salt removed during growing period from 1,6 m of soil accounts for 10...11 t/ha; in low checks with negative terracing and water discharge for infiltration of less than 40 m3/(day.ha) the salt regime is determined by secondary salinization with salt storage during growing period of 5...18 t/ha. According to materials of the research, equations and models were worked out. They describe relation of rice productivity to terracing, irrigation norm, water salinity in check, value of infiltration. A range of factors, which influence prevalently the yield formation, were identified. An economic assessment of rice field relief influence on rice system productivity shows, that the damage from arrears of rice yield accounts for 346...510 US$/ha under checks terracing of 35 cm more.
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