Summary of research project: |
Objective and technical fields:
Planning and implementation of water use with due regard for soil-reclamation and hydrogeological conditions and efficiency of an irrigation technique of an irrigated field. Objectives: Improvement of water use and increasing efficiency of irrigation schemes.
Scientific and technical approach:
Determination of irrigation norms and increasing efficiency of irrigated lands on the basis of optimization of irrigation norms with due regard for soil-reclamation and hydrogeological conditions and efficiency of an irrigation technique to achieve optimum water-salt regime on an irrigated field.
Environment characteristics:
Climate is sharp continental resulting in high annual and day amplitudes of temperature and instability of climatic data in time. Duration of a warm period (t > 100C) varies from 177 to 192 days. Sum of positive temperatures (>100C) varies from 3500 to 41000. Precipitation is low, 109 to 159 mm, in dry years precipitation can be only 50-70 mm per year, 10-30 mm in a warm period. Evaporativity is 1300-1600 mm. Moistening factor is 0,06-0,08. An irrigation scheme is situated in the valley of an ancient delta-flood plain and the first bottom of the Syr Darya. Relief is flat. Inclination is 0,0005-0,001. Regarding hydrogeological conditions, irrigated lands are situated in the area of difficult inflow and outflow of ground waters with depth of water table and regime depending on local conditions. Depth of water table on 40% of the irrigated area is lower than 3 m; on 42% it is 2-3 m; on 18% it is 1-2 m. Salinity of ground waters varies widely from 1-3 g/l to 3-5 g/l and more. Type of salinity is sulphate-chloride and chloride-sulphate. Irrigated lands in the Lower Syr Darya have mostly hydromorphic soils: alluvial meadow and meadow-bog soils; less often - desert, sand and takyr soils. 65% of the irrigated area have middle-loam and light-loam soils, 20% have heavy-loam soils. There are 33% of soils with no and slight salinity, soils are saline on more than 50% of irrigated lands. Type of salinity is chloride-sulphate and sulphate-chloride. Density of the drainage network is 40-45 m/ha.
Parameters of Pilot Projects and Technical Solutions:
Kzyl-Orda left-bank irrigation scheme is situated on the left bank of the Syr Darya. It is a narrow strip 135 km long and 30-60 km wide which stretches from Kzyl-Orda gauging station to Djusaly station. In 1980 the irrigation scheme included 13 rice-growing farms. Total area of the irrigated lands in this period was 85 000 ha. The area of the pilot testing plot included 7 ha under rice and 5 ha under lucerne. Water is abstracted by Kzyl-Orda dam which was put into operation in 1956. Water is delivered by left-bank main canal 140 km long, its capacity is 210 m3/sec. Rice systems are mainly of Krasnodar type, in some parts of the scheme systems with rectangular checks and wide flooding were made.
Methodology:
Field tests on study of an irrigation regime for crops of the rice crop rotation. On testing areas a series of observations and studies was carried out on the water-salt regime of soils; all elements of a water balance; growth, development and productivity of plants under different regimes of moistening and meteorological conditions. Testing areas were provided with lysimetering and water accounting equipment. Methodology of a problem solution was a systems analysis of the results of field observations and studies using experimental data gathered in other irrigation schemes with the same environmental conditions.
Results:
Irrigation regime for rice on saline soils (the area was 5 ha) was studied in 3 variants: 1. Constant flooding, without running water and release (control); 2. The same conditions as for the control plot but with running water equal to 50% of the total duty of water; 3. Constant flooding but with periodic changing of water in checks. The norm of irrigation for the control plot was 18300 m3/ha, rice yield was 1,88 t/ha. Average salinity of water in checks was 1,67 g/l. In the second variant the norm of irrigation was increased by 9860 m3/ha, rice yield was 2,45 t/ha, salinity of water in checks fell on the average for the irrigation season down to 1,41 g/l. With running water (50% of the total duty of water) from the soil layer 0-10 cm deep 10,4 t/ha salt was washed, i.e. 39% of the total wash from that level. The most rational variant for saline soils is constant flooding with periodic changing (release) of water depending on the degree of its salinity in checks and drainability of soils. Under this irrigation regime after planting of rice a check is flooded with a layer 10-15 cm deep; in 3 days release (changing) of water is carried out. The cycle is repeated 2-3 times till the stage of bushing out; during this stage the water layer is 5 cm deep; after this stage the water layer is increased up to 10-15 cm and periodically 50% of the water depth in checks is changed (4-6 times depending on the degree of salinity of water). Rice yield under the rational regime of irrigation was 2,75 t/ha. Net norm of irrigation on the average for the years of studies was 25 000 m3/ha including 35,9% for evapotranspiration, 16,1% for initial saturation, 30,0% for filtration and 18,0% for surface release. Gross irrigation norm of the field was 37 000 m3/ha. Depth and degree of desalinization of soils depended on the degree of drainability of rice fields. With check releases desalinization happened on the average for the depth of 0,5 m. Salt removal on solid residual was 35-45%, and on chlorine-ion it was 54-86%. With release collectors (depth of drains was 2,5 m) desalinization happened for the depth of more than 1,5 m. Salt removal on solid residual was 62-80%, on chlorine-ion it was 92-96%. Intensity of soil desalinization rises with increase of soil drainability. Therefore application of more efficient drainage raises intensity of soil desalinization by 1,5-2,0 times and reduces restoration of their salinity in an ungrowing season by 2 times.
Study of the irrigation regime of rice on saline soils showed that after their cultivation soil content of salt is sharply reduced, regarding degree of salinity they become slightly saline. However, after replacement of rice by lucerne in crop rotation soil salinity is restored as a result of intensive evaporation of ground waters and bad drainability of soils. For the tests on study of the irrigation regime of lucerne on saline soils irrigation norms were assumed to be 1,5-2,0 times bigger than calculated ones (mp); determined preirrigation soil moisture was not less than 80% of normal moisture, on the control plot with 80% of normal moisture net mp = 750 m3/ha; gross mp = 100 m3/ha. The highest salt accumulation in a root zone was on the plot where irrigations were made with calculated norms (control). Under such conditions for the whole growing season salt content in a soil layer 1 m deep increases by 1,6 times. The highest salinization happens in the upper layer 0,3 m deep, for which coefficient of season salt accumulation equals to 2,08. If depth of irrigation is 1,5 times higher, it reduces intensity of salt accumulation in a root zone of soil. Coefficient of the seasonal salt accumulation for topsoil is reduced down to 1,40, and for the layer 1 m deep - down to 1,5. If depth of irrigation is 2 times higher, it reduces intensity of salt accumulation in the whole zone of soil and especially in the layers 0-0,3 and 0-1,0 m deep. Coefficient of the seasonal salt accumulation for topsoil is reduced down to 1,10,-1,12, for the layer 1 m deep - down to 1,10-1,14; for the layer 1,5 m deep - down to 1,39-1,51. Heavy irrigation leads to salt removal from the root zone of soil. Thus, if m = 1,5 mp, quantity of removed salt from the layer 1 m deep is 3,0-4,9 t/ha, and if irrigation norms are increased by 2 times quantity of removed salt is 4,4-7,8 t/ha. Favorable salt regime for the plots with m = 1,5-2,0 mp predetermined yield of lucerne. It was 8,8-10,2 t/ha, which was 1,5-3 t/ha more than on the plot where m = mp. Thus, for creation of the favorable salt regime on saline soils it is necessary to use leaching irrigation regime of lucerne increasing irrigation norms at least by 1,5 times. Irrigations should be made with reduction of soil moisture content not less than 80% of the normal moisture.
|
