Summary of research project: |
Objective and technical fields:
Considering the possibility of high lucerne yield in the rice crop rotation with preservation and improvement of the reclamation state of irrigated lands. Creation of optimal conditions for growing the main crop (rice).
Scientific and technical approach:
Elaboration of the irrigation regime on the basis of field tests. Prevention of the seasonal restoration of salt in the rooting zone, increase of the soil fertility, control over ground water movement and consideration of the possibility of their participation in sub-irrigation.
Environment characteristics:
Kzyl-Kum irrigation scheme is situated between the modern delta of the Syr Darya in the east and Kzyl-Kum desert in the west. It begins from Chardara reservoir and stretches to the north along the left bank of the river. The territory is a flat plain, slightly lowering in the northern direction, inclination is 0,0002-0,003. Relief is flat of a terracelike slightly bench character. The soils include cretaceous, tertiary and quaternary deposits. Quaternary deposits are divided into ancient (or lower) and modern (or upper) alluvial formations. It includes 2 layers: the upper sandy loam layer 3 m deep and the lower sand layer 60 and more m thick. Before the development of the scheme ground waters were of the riverside type. After the development of the scheme for rice crop rotation the ground water regime became of the irrigation type. Fluctuation of water table varies from 0,5 to 3,0 m depending on artificial factors. Ground waters are mostly slightly salinizated. On the testing plots there are mostly meadow-gray soils, their distinctive feature is stratification and heterogeneity. Water-physical properties of an aeration zone are the following: volume weight is 1,43-1,47 g/cm3, specific weight is 2,70-2,75 g/cm3, total porosity is 46-50%, the least moisture capacity is 21,5-25,0%, coefficient of permeability is 0,24-0,30 m/day. Salt content in 0-140 cm soil layer was 29-72 t/ha, in 0-60 cm layer was 14,4-35,3 t/ha which was 50-60% from the total salt content.
The region is attributed to Kzyl-Kum sub-zone of a dry hot zone of deserts and semi-deserts. Average annual precipitation is 165-210 mm. Total precipitation for a warm period (t>10oC) is 60-70 mm. Thermal regime of a warm period (April-November) is characterized by considerable amplitudes of temperature reaching 45oC. Sum of positive temperatures (t>10oC) is 4600-4800oC with the duration of 200-210 days. During the described period relative air humidity did not exceed 45-35%, minimal humidity (18%) was in July-August. The number of days with the relative air humidity less than 30% was 180. Humidity deficit varies from 8-9 mb in April to 32 mb in July.
Parameters of Pilot Projects and Technical Solutions:
The testing plot with the area of 35-40 ha had a rice irrigation system with rectangular checks of the Krasnodar type. A rectangular check was 150-200 m wide and 800-100 m long with the area of 12-15 ha. Average area of checks is 3-4 ha. Checks are located across a rectangular field and have their own water outlet and importation works. As a rule, leveling of checks is broken after rice growing, differences of check surface height reach 15-20 cm. Irrigation release canals are of a two-side command.
Methodology:
Field tests on studying an irrigation regime included observations over the soil moisture, the depth of water table, green mass growth, development of a root system, phenology, change of the physical-mechanical composition, water-physical and chemical soil properties, quality of irrigation, drainage and ground waters, climatic conditions. For this purpose the pilot plot was provided with measuring and accounting equipment. Results of studies were processed using the methods of mathematical statistics, which allowed to determine accuracy and reliability of tests.
Results:
Irrigation influences significantly on the yield of lucerne. The most economically efficient irrigation regime of lucerne is when soil moisture in the rooting zone is maintained at the level of 90% of the natural soil moisture. During a growing period 2-4 irrigations are necessary with the irrigation norm equal to 1200-1400 m3/ha. This irrigation regime guarantees yield of 9,26-10,44 t/ha. Determined dependence (W = 2557,1-4,92 H, where W is the moisture content in 0-60 cm soil layer, m3/ha; H - depth of water table, cm) allows to definite the irrigation norm and schedule. Differences between calculated and actual irrigation norms are stipulated by the absence of inclination of the check surface, complicated microrelief and necessity to create a sufficient hydraulic head. Corrections for the calculated irrigation norms are 3-5 with check flooding, 2,5-3,0 with furrow irrigation, 1,2-1,3 with sprinkler irrigation. Irrigation water expenditures for lucerne growing in the rice crop rotation are a little less than in lucerne growing in usual rice crop rotations in the south of the Republic. With the total water consumption equal to 7,8-10,2 th. m3/ha, the share of irrigation water in it is 55-67%. Irrigated lucerne raises soil fertility. Humus content increased by 3-3,5 times. Phosphorus content increased by 61-64%, nitrogen content increased by 30-35%. In 2 years of lucerne growing rice yield was 6,8-7,3 t/ha, while in the crop rotation without lucerne irrigation it was 35-40% less. In spite of leaching of soils during rice growing, by the lucerne growing season they had been attributed to slightly salinizated with a solid residual in 0-60 cm layer equal to 1,676. During lucerne growing without irrigation salt restoration took place up to 2,180%, while on the plot with irrigated lucerne salt content decreased down to 1,345%. During lucerne growing ground water salinity varies from 1,310 to 1,558 h/l.
Comparing actual irrigation norms and actual water income to soil with irrigation it should be said that only 24,5-26,4% of water of the irrigation norm is necessary for moistening the rooting zone of the soil with maintenance of its moisture at the level of 90% of the full field moisture capacity.
The ordinate of the hydromodulus for the first year lucerne is 0,45-0,58 l/sec per 1 ha. Irrigation interval was 40-45 days on the average.
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