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Objective and technical fields:
Development of the set of measures on soil water-salt regime regulation by means of effective technology and technique of leaching on background of close horizontal drainage threngthened by open one. Investigation of reclamation efficiency of 2-stage leaching of strongly salinizated soils.
Study of processes of desalinization of hardly-meliorated strongly salinizated soils depending on filtration rate of leaching water.
Development of calculation method and technology of 2-stage leaching.
Scientific and technical approach:
Prevention of soil salinization, soil and water productivity increase, based on land drainability, leaching regime of irrigation promotion. Scientific ground of measures on soil water-salt regime management.
Environment characteristics:
Pilot plot is located within new developed part of Golodnaya Steppe in state farm “Gagarin”. Lithology: Loam, clay, sandy loam, sand (60 m). Soils: Grey-meadow, middle and heavy clayer. Volumetric mass increases downward: 1.36 (20 cm)-1.73 (80 cm) and 1.62 g/cu.cm (1.5 m). Specific mass varies within 2.71-2.84 g/cu.cm. The least moisture capacity is 37-40 %; water specific yield is 0.08. Soil permeability coefficient for 1 m-layer is 0.03-0.06 m/day, for layer 1-4 m – 0.05-0.12 m/day. Sum of toxic salts within 4 m-thickness is 0.7-1.9 %; chloride – 0.14-0.4 %; sulphate – 1.2-1.9 %. Salinization type is chloride-sulphate. Pilot site’s soils are very strongly salinizated with high gipsum content.
Groundwater salinity is 40-60 g/l; chemical composition is chloride-sulphate-magnesium-sodium.
Parameters of Pilot Projects and Technical Solutions:
Field investigations of spatial quantity-quality interrelation of hydrodynamic and hydrochemical processes of soil desalinization under capital leaching, modelling of filtration flow hydrodynamic characteristics.
Salt desalinization processes were studied by lisimeter. Three times measurements were executed under head gradients: 5; 1; 0.7; 0.3; 0.2; 0.1; 0.05 and 0.01.
Observations of water and salt balance elements were executed. Salt availability parameters were defined by means of field measurements.
Methodology:
Field investigations were executed within 78 ha pilot site in two versions: two stage leaching and flooding under the same parameters of close horizontal drainage of depth 3.0-3.5 m and distance between drains 125 m. Temporary drains were constructed: within the first stage – every 10 m, within the second stage – every 20 m with depth of 0.8-1.0 m. Field size within the first stage was 10x30 m, second stage – 20x30 m. Water supply technology – from field to field over the chain. Time of water supply: 1st stage - 25.09.75-12.01.76 (110 days), 2nd stage – 01.04.76-10.05.76 (40 days), total – 150 days. Within the control field – 25.09.75-21.02.76.
Permanent observations on groundwater regime, drainage outflow dynamics, water supply, soil calculated layer’s salinity were performed. Hydrodynamic characteristics of filtration flow were obtained by piesometric network, modelling and calculations. Filtration rate depended on distance from temporary drain axis. Optimal filtration rate was proved by modelling of leaching processes.
Leaching within each version was performed until filtrate salinity 4-5 g/l under water duty 18.9-20.0 th.cu.m/ha and duration 8.5-20 days. Leaching rate under filtrate’s salinity 9 g/l was determined which corresponds to extreme value of toxic salt content – 0.3 % (16-20 t/th.cu.m/ha).
Results:
Results of investigations are the following:
- Relationship between salt availability and filtration rate is established (under leaching of grey-meadow soil – a=1.1 under V=0.005 m/day; 1.6 under V=0.035 m/day and 2.0 under V=0.25 m/day);
- Filtration scheme under conjunctive operation of deep close and shallow temporary drainage was studied. It was found that filtration rate distribution irregularity coefficient under two-stage leaching was 1.75 (control – 4.25). Filtration rates were highest near drains (14-15 mm/day) and minimum – between drains (8-8.5 mm/day);
- 2-stage leaching method reclamation efficiency was grounded. Its application increases 1.7 times salt removal provides 1.5 m-layer regulary desalinization to the toxicity limit, decreases significantly salt content on depth of 2-3 m, saves irrigation water (about 5 th.cu.m/ha) and cut down leaching duration (on 15-20 %);
- On the base of salt balance salt content within 0-4 m-layer decreased under 2-stage leaching on 376 t/ha (control – 216 t/ha);
- 2-stage leaching calculation method and application technology on base of leaching norm assessment, duration calculation and work composition over the stages;
- Technical-economic calculations showed that annual effect was 202.1 rouble/ha. 2-stage leaching method was inserted within new developed zone in Golodnaya Steppe.
The following recommendations were given:
- 2-stage leaching method is expedient for Golodnaya and Djizak Steppes conditions where soils are badly permeable (Kp=0.1-0.003 m/day), different in mechanical composition and upper layers salinization is 0.8 % of toxic salts;
- Within the first stage of leaching temporary drainage is executed taking into account filtration rate 7-10 mm/day creation between drains, drainage parameters: depth 0.8-1.0 m; distance – 10 m; within second stage – 20 m;
- Under soil salinization chloride-sulphate and sulphate type and toxic salts content 0.4 % within 1 m-layer between furrows 1st stage leaching is executed; 2nd stage is executed under toxic salts content 0.3 %;
- Soil desalinization is achieved within 100-150 days.
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