C. Non-freezing period duration is 170 days. Annual precipitation is 350 mm; relative air humidity 50-70 %, in summer it decreases to 40 %. Surface slope is 0.0023 from south to north.
Proluvial-alluvial sediments are widely spread. They are presented by light, middle and heavy loam with thickness of 20 m. pilot plot is located in zone with unsatisfactory surface run-off and bad internal groundwater outflow. Before land development groundwater level was on depth 0-3 m, on low elevated places 0-1 m; groundwater salinity was 10-50 g/l, more seldom 2-5 g/l. Type of salinity is sulfate. Grey-medow and medow soils prevail. Soils are salinated to depth of 13-14 m (area 76 ha).
Soil layer 0-1 m is strongly salinated. Average salt content is as follow: 0-1 m - 1 %; 1-2 m - 1.05 %, 2-3 m - 0.68 %. Salinity type is sulfate-calcium-sodium, sulfate-sodium-calcium, magnesium-calcium-sodium.
Parameters of Pilot Projects and Technical Solutions:
Leaching area is 25 ha (1972-1974), 41 ha net (1976-1977). Over the plot with area of 25 ha three drains are dug with length of 600-714 m and distance between drains 220 m, depth 3.0 m.
Pilot plot with area of 76 ha is located within the fourth field of IV rotation and limited by: open collectors with depth 4.5 m and distance between them 918 m from the east and west; flume canals from the south and north.
Plot's dimensions are 900x840 m. permanent horizontal drains are parallel to the canal and have following size: width - 180 m, depth - 3.5 m. Temporary drains have following parameters: width - 50 m, depth - 1.5 m and extend in longitudinal direction. The plot is divided into 5 fields with 15-16 checks within each of them. Investigations were carried out within the third field.
Methodology:
Field observations of water, salt movement, water-salt balance components, within the layer of 3.5 m, groundwater level, drainage performance dynamics. For this purpose within two fields (area 25 ha) three transects of observation wells were drilled to observe groundwater level dynamics and its salinity. Sampling was made over 15 points within every field; chemical analysis and moisture sampling was made between the checks and in 5 points over each field. Weirs were established for drainage water accounting. Flooded rice planting influence on adjacent areas' reclamation state was observed over 7 observation points within each field. Within the third field (75 ha) equipment for irrigation and drainage water accounting has been established.
Observations of soil salinity have been carried out over 42 points within the horizons each 20 cm to 1 m and 50 cm to 3.5 m. In the same points observations of groundwater level and salinity were performed. Sampling was made twice a year before and after leaching.
Water-physical properties of soil within three soil profile were determined. Three wells have been drilled to the depth of 20 m with sampling for chemical analysis each 50 cm to depth of 5 m and each 100 cm to depth of 20 m.
Nutrient elements dynamics has been studied over three points with sampling over horizons: 0-5; 5-10; 10-20; 20-40 and 40-60 cm.
Flooded rice planting influence on adjacent areas' reclamation state was determined in 13 points with soil sampling for chemical analysis to depth of 3.5 m, groundwater level and salinity within the growing period. Phenological observations were carried out over rice plants and yield.
Results:
Leaching through flooded rice planting with permanent drainage parameters: B=220 m, t=3 m, B/t=73.3 and drainage flow rate 0.23-0.63 m/day, leaching rate 9.5; 11.8 and 2.7 (first field), 12.6 (second field) th.cu.m/ha led during three first three years to soil desalinisation of 1 m-soil layer. To the end of the second year soil was fully desalinisated. Within the layer 1-2 m and 2-3 m desalinisation process was continuing within all three years, groundwater salinity was decreased from 29.5 to 16.6 g/l within the first field and from 19.0 to 8.0 g/l within the second field. Water expenses for leaching 0.1 % salt from the 1 m-soil layer were 1300 cu.m/ha for the 1-st field and 3308 cu.m/ha for 2-nd field.
Leaching through flooded rice with permanent drainage (parameters: B=180 m, t=3.5 m, B/t=51.4) and temporary one (parameters: B=50 m, t=1.5 m, B/t=31.2) water removal rate by permanent drainage 0.3 cm/day, by temporary one - 1.2-1.3 cm/day and leaching duty 24.5 th.cu.m/ha (net) led to soil 1 m-layer desalinisation from strongly salinated to slightly salinated; 1-2 m layer from strongly salinated to middle salinated; 2-3 m layer remained middle salinated. Groundwater salinity decreased from 26.5 to 16.1 g/l. Water expense for leaching 0.1 % from 1 m-soil layer was 3045 cu.m/ha. Leaching during the second year by duty 22 th.cu.m/ha (net) promoted further salt leaching from 2 m-layer.
Desalinisation influence depth under capital leaching and intensive drainage is 10 m, beneath this depth salt accumulation has occured.
Between the fields on bermas and waves intensive salt accumulation has being occured.
Land use efficiency was 0.54 because about half of an area was occupied by temporary drains, bermas and waves.
Toxic salts stock within the balance layer 0-3.5 m have decreased on 265 and 62 tn/ha, respectively for 1-st and 2-nd years.
Toxic salts removal by permanent drainage outflow was 71 and 50 tn/ha and by temporary one - 142 and 95 tn/ha, respectively for 1-st and 2-nd years.
Drainage outflow by permanent drainage was 4.7-5.1 th.cu.m/ha and by temporary one - 13.4-15.4 th.cu.m/ha.
Due to high drainability of the pilot plot adjacent lands were not subjected to soil salinisation within the 0-3.5 m layer, groundwater level or salinity changes.
Main result of investigations is an experience of leaching through flooded rice application, which has positive as well as negative consequences. Positive sides are as follows: high leaching effect and possibility to gain within the first year high yield of rice and profit. Negative side is that this method is too expensive in terms of land, water and human resources; promotes toxic salts removal through drainage outflow to the surface, increases surface water salinity and impacts negatively downstream areas.
