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Objective and technical fields:
Development of measures on water use improvement and prevention of soil salinization on the base of irrigation regime parameters and water-storage irrigations optimization for different level of soil and groundwater salinization. Soil water-salt regime management by means of vegetation and water-storage irrigations; drainage outflow decrease by drainage load lowering.
Scientific and technical approach:
Soil water-salt regime regional management’s limits definition by means of field experiments on the base of negative salt balance formation. Field investigation meaning is suggested measures’ parameters optimization for land productivity increase and water consumption rate decrease due to soil salt specific yield increase.
Environment characteristics:
Climate is sharply continental. Average annual relative air humidity is 50-55 %. Winter is moderate, spring is short with precipitation about 100 mm which is 35-50 % of annual value. Summer is very dry and hot. Maximum temperature is 450C and relative air humidity is 15 %. Autumn is warm. In summer precipitation does not exceed 25 % of annual value. Temperature in July is 27-29oC. Average decade temperature higher than 14oC is kept during 6 months (mid-April-mid-October). Average – monthly wind velocity is 4-6 m/sec. Evaporativitys is 1200-1400 mm/year.
Pilot site soils are grey heavy and light loams which are underliaid by gravel-pebble sediments. Permeability coefficient is 10 times higher for gravel-pebble comparatively with cover loam.
Relief is flat with slope 0,003-0,005. Volumetric mass of 1 m – layer varies within 1,35-1,48 g/cu.cm; specific mass is 2.69-2.71 g/cu.cm.
Permeability coefficient average meanings for soil surface were 0.35, on depth of 30 cm - 0,8 and 1 m - 0,50 m/day. Soil and groundwater salinity type was chloride-sulfate with unsaturated zone depth of desalinization (allowable limits 0,3 %) 0.5; 1.0; 1.5; 2.5 m and upper groundwater horizons salinization level, respectively; 13; 15,5; 10,5; 6,0 g/l. Groundwater level during the growing period was 2,3 m and during non-growing period - 3,5 m.
Parameters of Pilot Projects and Technical Solutions:
Pilot plots' area was 70 ha including 10 ha of first stage development.
Open drainage density within the first plot was 45 m/ha, within the second plot drainage extent was 2400 m, its density was 40 m/ha. Distances between drains were 100, 200, 300 m, drain depth 2.5-3.0 m. Tubes were asbestes-cement, screens - sandy - gravel. Open drainage density (1c-1, DC-16) was 20 m/ha. Total drainage density was 60 m/ha. Groundwater level regime was observed through 10 sets of piezometers and 70 wells whose transects were positioned perpendicular to the main drains. Irrigation network was represented by open earthen canals with density 20 m/ha.
Methodology:
Water and salt movement regularity within the system "soil - groundwater" under unsaturated zone's depth of desalinization changes was defined by field observations.
Pilot plots were equipped by means of measurement and accounting. Multicriterial analysis for processing of data collected was applied.
Results:
State farm “Timiryazev” lands have been developed since 1960 without drainage. Within 5 years of their exploitation about 70 % of land was lost due to secondary salinization. More than half of these lands became strongly salinizated.
Start of collectors’ construction has been done in 1963 and drainage construction - in 1964. Before collector-drainage network construction groundwater level was 1,5-2 m, after construction – 3 m. Piezometric head has been decreased from 0.1-0.2 to 0.03-0.1 m.
Collector-drainage system’s designed parameters provided high regularity, of soil desalinization all over the area between drains, groundwater level sustainable regulation within 1.0-2.0 m under capital leaching (rates more than 8 th.cu.m/ha); 2.0-2.5 m under water storage irrigations; 3.0-3.5 m within the autumn period before leaching and water- storage irrigations.
Drainage outflow modulus varied within the limits 1.0-1.5 l/sec/ha under leaching; water- storage irrigations were 0,2-0,5 l/sec/ha; in autumn period 0.0-0.4 l/sec/ha.
Average annual drainage modulus (without regard to leaching period) was 0.05-0.11 l/sec/ha.
Water-storage irrigations were performed mostly in spring by depth of 1.5-1.6 th. cu.m./ha. Moisture before irrigations was supported at the level of 0.7-0.8 FFMC. Irrigation depths were 0.9-1.5 th. cu.m./ha. Total evaporation was 8.0-9.0 th. cu.m./ha. Calculated and leaching irrigation regimes were tested. Calculated regime has been established by bioclimatic method. Leaching regime – by increasing of irrigation depth on 20-30 %.
Given regimes reclamation efficiency study showed as follow:
- under initial depth of soil desalinization 0.5-0.6 m (allowable limits are 0,3 % on toxic salts) irrigation leaching regime provided salt stock decrease within the upper 1 mlayer on 9-11 t/ha, within the unsaturated zone (3 m) on 12-15 t/ha. After 3 years salt stock decreased respectively on 20-25 t/ha and 30-40 t/ha;
- under initial depth of soil desalinization 1.0-1.1 m during the first year of irrigation leaching regime application salt stock decreased respectively on 10-13 t/ha and 20-25 t/ha. During the first year of irrigation it increased on 7-10 t/ha within the upper 1 m – layer and on 10-15 t/ha within the unsaturated zone and after three years of irrigation respectively 15-20 and 25-30 t/ha;
- under initial depth of soil desalinization 1.5-1.6 m salt movement velocity was slowing down. Within the first year of irrigation leaching regime application salt stock decreased on 3-5 t/ha within 1 m – layer, 5-8 t/ha within unsaturated zone; after 3 years of irrigation, respectively 6-9 t/ha and 10-15 t/ha. Under calculated irrigation regime salt stock increased on 5-7 t/ha within the upper 1 m – layer and 7-10 t/ha within unsaturated zone; after 3 years of irrigation, respectively, on 10-15 and 15-20 t/ha;
- under initial depth of soil desalinization 2,5-3 m during 3 years of leaching regime salt stock decreased on 6-8 t/ha within upper 1 mlayer and 10-15 t/ha within the unsaturated zone.
In the first case water supply and precipitation (10.0-11.0) to total evaporation (8.6 – 9.0 th. cu.m./ha) ratio was 1.1-1.3 and in the second case it was 0.9-1.0 (7.6-8.0) to (8.0-8.5 th. cu.m./ha).
Negative water-salt balance has been established within all thickness of cover sediments (8-15 m) on background of effective drainage (salt removal was 10-20 t/ha) under leaching regime, and positive water-salt balance under calculated irrigation regime (salt removal 2-3 t/ha). Higher rate of salinization of the upper 1 m – layer occurred due to vertical salt exchange within the cover sediments but not due to its inflow with irrigation or groundwater.
Under irrigation leaching regime, when salt stock within the root zone was sustainably cut down, cotton yield varied within wide limits 2.4-3.0 t/ha and was dependent not on initial depth of desalinization but on soil physical properties. Under volumetric mass within soil root zone 1.45-1.5 g/cu.cm and soil desalinization depth 1.5-3.0 m cotton yield was 2.4-2.6 t/ha but under mass of 1.4-1.45 g/cu.cm and soil desalinization depth 0.5-1.0 m yield increased to 2.8-3.0 t/ha.
Main result of investigations is soil desalinization acceleration and water supply cut down due to prophylactic leaching replacement by water-storage irrigation and water use rate decreasing under unsaturated zone’s desalinization depth increase. Economic effect was 200-300 rouble/ha.
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