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Objective and technical fields:
Determination of water consumption and diversion norms and their components in rice growing with horizontal drainage. Raising the soil efficiency of rice fields and rice productivity.
Scientific and technical approach:
Determination of the components of a rice irrigation norm and rice field water balance under field conditions with horizontal drainage. Detection of parameters of subsurface horizontal drainage guaranteeing optimum land-reclamation regime and raising the soil efficiency of rice fields.
Environment characteristics:
Climate has a big thermal potential: sum of positive temperatures (when t >10oC) can be 4600-4800o. Average annual temperature is 12,0-12,5oC, the hottest month is July (average monthly temperature is 27,3oC). The highest precipitation is in spring-winter season, the lowest precipitation is in summer-autumn season. Total precipitation for a warm period (t > 10oC) is 60-70 mm. The highest relative air humidity is in winter months (77-82%), the lowest one is in summer months (31-33%). Relief is uniform. Inclination in the north direction is 0,0002-0,0003. Soils are made of alluvial deposit of the Syr Darya river. The distinctive feature of meadow-gray soils is stratification and heterogeneity. Cover deposit is loams with clay and sandy loam interlayers. Its depth can be up to 3 m, coefficient of permeability is 1,45 m/day. Underlying rocks are fine-grained sands (their depth can be up to 60 m), coefficient of permeability is 12 m/day. Cover loams have the following water-physical properties: volume mass is 1,38-1,51 g/cm3, specific mass is 2,62-2,72 g/cm3, total porosity is 44-47%, the least moisture capacity is 18,5-22,7% to the weight of the absolutely dry soil. Salt content in a soil layer 3 m deep before development was 0,313-2,094%, including chlorine ions - 0,045-0,182%; sulphates - 0,115-1,195%; sodium - 0,072-0,262%, calcium - 0,021-0,346%. Before development salinity of ground waters of chloride-sulphate type was 4,4 g/l and laid at a depth of 5 m from day surface. By the degree of natural drainability the territory of the scheme is slightly drained. Total subsurface runoff does not exceed 300 mm/year.
Parameters of Pilot Projects and Technical Solutions:
Irrigated area is 80 ha. Open drain spacing is 400 m, subsurface drain spacing is 100 to 600 m. Average depth of subsurface horizontal drainage is 1,6 m. Irrigation network with density of 30 m/ha includes group distributors and check ditches with earthen channel.
Methodology:
Field studies of the components of water consumption norms with horizontal drainage, elements of water and salt balances, reclamation condition of rice fields. Systems analysis of the results of studies. The plot was provided with necessary metering and accounting equipment.
Results:
Studies showed that drainage type and parameters influence a rice irrigation norm and water balance of a rice field. In rice growing drainage outflow on the plot with open drainage was 3000 m3/ha in the period of development, 2 100 m3/ha in the period of operation (or 12-11% of the duty of water). On the plot with subsurface horizontal drainage it was higher and changed considerably depending on drain spacing. Drainage outflow in subsurface horizontal drains with drain spacing equal to 400 m was 6100 m3/ha in the period of development and 5500 m3/ha in the period of operation (or 24-26% of the duty of water). Studies showed that this variant was the most efficient. Water expenditures per unit of output were minimum and rice yield was maximum. Rice yield was 5 t/ha in the development period and 6 t/ha in the operation period.
In rice growing by flooding water demand mainly depends on evapotranspiration and percolation. Total rice water consumption made up of water surface evaporation and water transpiration of plants depending on the climatic values varied from 10 300 m3/ha to 11 700 m3/ha on the plot with open horizontal drainage (OHD) and from 10 400 m3/ha to 11 900 m3/ha on the plot with subsurface horizontal drainage (SHD) with drain spacing equal to 400 m (optimum variant). Percolation characterizing the degree of drainability of the territory was 7 300 - 8 200 m in OHD variant and 6 100 - 7 300 m3/ha in SHD variant.
In rice irrigation except water expenditures per total water consumption and percolation on a rice field considerable amount of water is used for saturation of soils in the aeration zone especially in the first years of the development of virgin lands. On the testing production plot with horizontal drainage initial soil saturation in the first year of the development of irrigated lands was 5 600 m3/ha in OHD variant and 5 500 m3/ha in SHD variant; in the second year it fell down to 3 300 m3/ha in OHD variant and 3 500 m3/ha in SHD variant.
Not taking into account precipitation which in Kzylkum irrigation scheme is insignificant in the period of rice growing (less than 500 m3/ha) and falls very seldom, we can consider that water consumption norms of rice on the testing production plot in the operation period was 21 000 - 22 500 m3/ha in SHD variant and 20 000 - 21 500 m3/ha in OHD variant. It is necessary to note that rice yield on the plot with SHD was 20-30% higher than on the plot with OHD in all the years of studies and was 5-6 t/ha. Water diversion on the plot with SHD in the operation period was 5 000 - 5 500 m3/ha (25-26% of the water balance expenses), water diversion from the plot with OHD in the operation period was 2 000 - 2 200 m3/ha (11-12% of the water balance expenses).
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