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Objective and technical fields:
Development of methods for strongly salinizated lands desalinisation under difficult hydrogeological and soil conditions by means of autumn-winter leaching, leaching regime of irrigation and strong soil drainage on background of vertical drainage.
Objective: Soil water-salt regime management, their productivity improvement.
Scientific and technical approach:
Soil desalinisation and its productivity improvement is achieved by creation of such water supply to drainability ratio which provides optimal rate of soil desalinisation and root zone moisture content support within the growing season.
Environment characteristics:
Climatic parameters are as follows:
Average annual precipitation is 324 mm, maximum occures in March (59 mm), minimum in August (1 mm). 73-84 % rainfall occures within spring-winter time. Duration of period without freezing is 202-208 days. Sum of positive temperatures is 4300-4400 oC. Long-term average temperature is 13.4 oC, in January -2.2 oC, in July +27.9 oC. Average long-term evaporativity values: annual - 1217 mm, within the growing period (IV-X) - 1073; minimum evaporativity is 18 mm (January), maximum - 222 mm (July).
Relief: Slightly corrugated plain with slope 0.0003-0.0005.
Lithology: Alluvial sediments, cover loam (18-25 m, permeability coefficient is 0.07-0.1 m/day) underlaid by sand-gravel-pebble thickness (50-100 m, permeability 40-45 m/day). Site is characterised by inflow prevailing over outflow on 1000-1500 m/ha. Artesian water head in 1964-1969 was 0.65 m lower than groundwater level, before VDS construction it was 0.5-1.0 m higher.
Underground outflow was 20 cu.m/day/ha or 7000 cu.m/ha per year, actual drainage modulus was 0.23 l/sec/ha.
Average groundwater level was 2.03 m, within growing season it was 1.8-2.2 m, within non-vegetation period 2.5-3.5 m.
Groundwater salinity was in 1969 5-8 g/l, its type was chloride-sulphate.
Soils: Grey-meadow, middle loam with gypsum stratum on depth 0.7-1.5 m. Unsaturated zone soils (0-3 m) have the following water-physical characteristics: specific weight is 1.3-1.5 g/cu.cm; porosity is 40-47 %; full field moisture capacity 32-35 %; maximum hydroscopy is 7.2-9 % from soil volume. Arable layer permeability is 0.15-0.2 m/day, for gypsum stratum 0.01-0.02 m/day. Under initial conditions soils were strongly salinizated. 1 m-layer salinity was 2.03 % on solid residue and 0.16 % on chlorine; within 1-2 m-layer it was 1.28 % and 0.11 % respectively. Salinization type was sulphate and chloride-sulphate.
Parameters of Pilot Projects and Technical Solutions:
Pilot site's area is 17 ha. Main crop is cotton. There were 28 vertical drainage wells in operation. Water supply was performed from Shuruzyak canal, from vertical drains, from collector Shuruzyak. Wells depth is 65-80 m, well discharge is 100-200 l/sec, specific yield is 10-15 l/sec/m. Irrigated area was 1538 ha with land use efficiency 0.78; non-irrigated - 1462 ha with efficiency 0.16.
Methodology:
Field observations on all elements of water-salt balance of unsaturated zone, groundwater and irrigated area as a whole. Site was equipped by all necessary equipment for groundwater level, piesometric head, water supply measurement.
Soil sampling for water and salt content were performed regularly.
Results:
VDS construction was started in 1958-1960. Irrigated lands constituted 15 % and were strongly salinizated. Well construction was completed to 1965. Along with number of wells increase land use efficiency and water supply increased too. VDS operation led to positive changes of water-salt regime dynamics, to groundwater level deeper position, groundwater outflow downward into sand, soil desalinisation. Development of soil desalinisation was started in 1964 with spring leaching by rate 10200 cu.m/ha. Water pumped by vertical drains was used with salinity 1.3-1.4 % on solid regime and 0.3-0.4 % on chlorine. Cotton was sown after leaching.
Irrigation norm within the first year was 5780 cu.m/ha. Since autumn leaching was regularly performed by rate 2.8-3.6 th.cu.m/ha; within growing season - by rate 4.8-6.5 th.cu.m/ha. Water duty to the field (net) with regard to rainfall (B+O) varied from 11 to 12.5 th.cu.m/ha under total evaporation (N+T) 7.8-8.5 th.cu.m/ha. These conditions allowed:
- to provide groundwater overflow from cover loam into pumped aquifer 3.8-5.7 th.cu.m/ha per year;
- to regulate groundwater level; it was regulated within 1.2-3.5 m and piesometric head was 2.2-
3. 5 m; in 1964-1969 it was 0.4 m lower than groundwater level;
- to regulate groundwater level by rate of 0.02-0.025 m/day;
- to manage by unsaturated zone and cover loam desalinisation rate by means of creation of downward filtration of irrigation and groundwater due to pumping from underlaying horizons. Average drainage modulus was 0.1-0.37 l/sec/ha;
- to achieve soil desalinisation at expense of non-vegetation leaching and leaching regime of irrigation in combination with VDS. After 5 years of development salt content within 1 m-layer was 1.21 % against initial 2.1 %, chlorine - 0.027 % against initial 0.16 %. Salt content within 2 m-layer (unsaturated zone) within the period of autumn 1963 - autumn 1964 was respectively: 1.16 % against 1.8 % on solid residue and 0.027 % against 0.13 % on chlorine. Leaching regime of irrigation was supported: (B+O)/(N+T)=1.25-1.4;
- to decrease groundwater salinity from 15 to 4-5 g/l and stabilise it at this level;
- to perform all cover loam thickness desalinisation; desalinizate groundwater from 16-17 to 5-6 g/l;
- to create stable negative water-salt balance of unsaturated zone over all territory of state farm. In 1963 water-salt balance was positive, but since development started in 1964 it became negative. Salt removal within 1964-1969 from unsaturated zone was 73-37 t/ha per year;
- to rise cotton yield from 0.5 to 2.5 t/ha;
- economic efficiency was 270-290 rouble/ha.
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