Summary of research project: |
Objective and technical fields:
Determination of water consumption and diversion norms and their components in rice cultivation on the background of vertical drainage. Raising the available water supply and rice productivity.
Scientific and technical approach:
Determination of the components of a rice irrigation norm and rice field water balance under field conditions on the background of vertical drainage. Control of drainability in the territory during growing period and control of ground waters level during ungrowing one in order to create favorable reclamation regimes in rice fields and achieve stable yields.
Environment characteristics:
Climate of the object is characterized by low precipitation: average annual precipitation accounts for 165-210 mm. From April to October, excluding its late ten-day period, an average daily air temperature is more than 10oC. Total sum of positive air temperature for this period is equal to 4600-4800oC. Average annual air temperature is about 12oC. Relative air humidity varies from 31-33% in summer to 77-82% in winter, evaporativity - from 255-280 mm to 15-20 mm respectively. An annual deficit of natural moisture availability is about 1180 mm.
Considered object is a plate valley with 0,0002-0,0003 slope. Lithology is determined by two-layer quaternary sediments: top layer - small-grained soils, thickness is up to 3 m, Permeability Coefficient (PC) from surface is about 0,37 m/day, bottom layer - sands, thickness is up to 60 m, PC is 12 m/day. Ground waters are contained in the first from land surface horizon, which is spred all over the region and consists of unpermeable clay rocks of paleogene-neogene age. Water-bearing rocks are small- and fine- grained sands of river genesis Direction of ground waters flow coincides with direction of the Syrdarya river flow and has 0,0006-0,0007 slope. In respect to degree of natural drainability a scheme, where the pilot plot is located, related to poor drained area. Total ground waters flow accounts for 290-300 mm/year. Before the beginning of the study, ground waters depth was, in average, 4,5 m. Salinity of ground water top layers was equal to 1,2-2,2 g/l, in the depth of 10-50 m - 0,8-1,5 g/l. Type of waters are sulphate-chloride, rarely sulphate. The main mass of salts was located in top 1,5 m layer of cover sediments, consisted of loams with clay and loamy sands interlayers. Salt content was 0,31-0,40% by solid residue, including 0,065-0,075% of chlorine ions, 0,104-0,187% of sulphates, 0,069-0,083% of sodium, 0,012-0,026% of calcium. Type of salinization was sulphate-chloride. Water-physical characteristics of cover sediments were the following: volumetric mass is 1,41-1,54 g/m3, specific mass is 2,63-2,72 g/m3, porosity is 43-47%, minimum moisture capacity is 18,6-25,0%, permeability coefficient from 1m depth is 1,54 m/day, from 2m depth is 1,76 m/day.
Parameters of Pilot Projects and Technical Solutions:
Irrigated area is 238,4 ha. An area of one well operation is 80-100 ha or one crop rotation field. Vertical drainage well (VDW) parameters are the following: depth is 50m, drilling diameter is 1270 mm, total length of slit filter is 20 m. Capacity of a well is 40-60 l/sec. Irrigation network includes ditches and group distributors in earthen channel.
Methodology:
Field studies for determining formation factors of the components of water consumption and diversion norms on the background of vertical drainage, elements of water and salt balances, reclamation condition of rice fields. Systems analysis of the results of studies. The plot was equipped with necessary meters and accounting devices.
Results:
Rice on the pilot plot was cultivated under shorten irrigation regime, which is mostly correspondent to its physiological features. In order to determine water consumption norms of rice there were special studies on determining its components: initial saturation of soils, evaporation, transpiration and infiltration.
Saturation of aeration zone to the potential moisture capacity of soil is an inevitable process under creation of water layer on a surface of rice check. It was dropped from 5830 m3/ha in 1975 to 2700-2800 m3/ha in 1978-1979. Water expenditure for evaporation and transpiration from rice fields in different years varied within 4300-5390 m3/ha and 5840-6470 m3 /ha respectively, total water consumption was 10140-11860 m3/ha. Portion of transpiration in total value of water consumption has being increased during growing period and evaporation from water surface has being decreased.
Study of infiltration in rice field and determination of its optimal value allows to clarify water consumption norm of rice. According to results of the studies, highest rice yields were achieved on the plots, where vertical drainage maintained infiltration in checks within 6-9 mm/day. Value of infiltration in checks dropped from 10750 m3/ha in 1975 to 7820 m3/ha in 1979. Water consumption norms were 27,0-27,5 th. m3/ha during development and 21,0-23,0 th. m3/ha during operation.
Drainage flow during development accounted for 12,0 th. m3/ha, during operation - 10,0 th. m3/ha. Water diversion from rice field was quite lower as water from vertical drainage well was used for rice irrigation (average salinity of drainage water during growing period was 0,82-1,36 g/l ). Water diversion from rice field accounted for 7,5-8,0 th. m3/ha during development and 5,5-6,0 th. m3/ha during operation.
There are two periods within the regime of vertical drainage in the rice system: growing and ungrowing. During growing period the wells must maintain an optimal water-air, salt and nutrient regime of soils, provide favorable conditions for rice growing, increase available water supply and reduce deficit of irrigation water at expense of drainage water use from VDW. During growing period VDW at 40-60 l/sec capacity can supply 3500-6500 m3/ha of water for 80-100 ha area. During ungrowing period the wells must maintain level of ground waters at 2,0-2,5 m depth. At such levels, as studies showed, secondary salinization of soils in aeration zone is not allowed and arable layer is not dried up. Rice yield were, as a rule, higher than 5 t/ha.
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