Summary of research project: |
Objective and technical fields:
Study of the dynamics of water and salt transportation in an aeration zone under various irrigation technologies, and improvement of methods of reclamation regime control on irrigated lands.
Scientific and technical approach:
An irrigation technology influences significantly the dynamics of formation of irrigation water infiltration losses, salt transportation rate, migration of nutrients and organic matters. Studies included elaboration of an irrigation technology guaranteeing control over the reclamation regime of irrigated lands.
Environment characteristics:
Shaulder irrigation scheme is a part of West Tian Shan province, its climate is sharply continental, thermal regime is high, air is dry. Average annual temperature is 11,9oC. Average perennial precipitation is 238 mm, relative air humidity is 53%. Studied territory is characterized by complicated alternation of deposits with different lithological and permeability properties. Soils are made of quaternary deposits. Lower rocks which are the regional negative confining bed, are tertiary-cretaceous deposits. Soils are red-colored gypsum-bearing clay with conglomerate, limestone, sandstone and sand pans. Topsoil of the studied territory is attributed to the subtype of light gray soils.
Parameters of Pilot Projects and Technical Solutions:
Soils of the testing-production plot (TPP) and lysimeters have a heavy texture where physical clay content in 0-150 cm layer is 50,08-66,12%, consistence is 1,35-1,58 g/cm3, consistence of a solid phase is 2,48-2,54 g/cm3, porosity is 36-43%. Content of nutrients in 0-20 cm layer includes 0,072-0,081 of gross nitrogen; 0,142-0,209 of phosphorus, 0,22-0,88% of gypsum, 5,37-7,0% of carbonates. In an absorbing complex structure calcium cations predominate, they are 78,7% of the total structure. In the meliorated layer of the TPP salt content is predetermined by its distance from drains. The plots located near drains and a main drain (40-50 m) have a minimum degree of salinity. In 0-100 layer it is 0,437-0,700%, chlorine ions content is 0,048-0,200%. Salinity is of a chloride-sulphate type. Among toxic salts sulphates of magnesium and sodium predominate which are 44-52% of the total salt content; sodium chlorides are 18,1-24% of the total salt content.
Methodology:
The dynamics of the water and salt transportation processes, migration of nutrients and organic matters under various irrigation regimes were determined by lysimeters and on the TPP. During tests the main attention was paid to determination of quantitative values of infiltration water flow rate, volume of infiltration waters, intensity of ground water recharge to an aeration zone, migration of salt, nutrients and organic matters. Maize irrigation norms were the following: on the TPP: 88, 100 and 1200 m3/ha; on lysimeters: 350, 500 and 1000 m3/ha.
Results:
The results of studies show that during irrigation infiltration losses of irrigation water are inevitable. The maximum losses for the TPP were after initial moisture replenishment irrigation before maize planting with the irrigation norm equal to 2000 m3/ha. In this case infiltration waters reached 800-1000 m3/ha and caused decrease of the salt content. Once the depth of irrigation was reduced, infiltration losses of irrigation water decreased. Under the leaching irrigation regime with the irrigation norm equal to 1200 m3/ha, infiltration losses were 400-480 m3/ha. During irrigation of maize with the irrigation norm equal to 1000 m3/ha, infiltration losses decreased down to 300-350 m3/ha with the depth of irrigation equal to 800 m3/ha - 200-250 m3/ha. The dynamics of infiltration losses under different irrigation regimes predetermines rate of soil salt specific yield which was estimated by salinity of infiltration waters. Average salinity of infiltration waters was 18,5 g/l (the depth of irrigation was 800 m3/ha), 17,0 g/l (the depth of irrigation was 1000 m3/ha), 15,6 g/l (the depth of irrigation was 1200 m3/ha). The rate of soil salt specific yield was increased with the simultaneous reduction of the depth of irrigation due to reduction of the velocity of infiltration water flow in a meliorated soil layer. This fact is proved by lysimeters. With the depth of irrigation equal to 350 m3/ha and initial soil moisture equal to 80-85% of the normal moisture, the velocity of infiltration water flow varied from 0,003 m/day at the beginning to 0,00015 m/day at the end of infiltration: the depth of irrigation equal to 500 m3/ha increased the velocity of infiltration water flow which reached 0,015 m/day; with the depth of irrigation equal to 1000 m3/ha the amplitude of variations of infiltration water velocity was 0,024 m/day. An irrigation regime also influences the intensity of the ground water recharge to an aeration zone between irrigations. With the depth of irrigation equal to 1000 m3/ha and initial soil moisture equal to 65-70% of the normal soil moisture, the intensity of the recharge increased up to 0,001-0,0015 m/day. Thus, results of studies showed that through change of the depth of irrigation and an irrigation technology it is possible to control reclamation processes with the same volume of water.
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