Summary of research project: |
Objective and technical fields:
Definition of the soil-reclamation processes tendency under irrigation by saline drainage effluent within the place of its origin. Objectives: Drainage effluent quality and soil water-salt regime management under saline water use for irrigation
Scientific and technical approach:
Prevention of soil salinization under saline water use for irrigation by means of drainage effluent quality improvement; soil salt-water regime development on the base of experimental data. Major meaning of investigation is drainage effluent quality management under its use for irrigation and recommendations’ development on soil productivity increase.
Environment characteristics:
Climate is continental. Average annual rainfall is 250-400 mm. Average air temperature is +13oC. Relative air humidity is 50-70 %, evaporation - 800-900 mm/year. Relief is slightly undulated. Collective farm is located within the Chu river alluvial valley. Lithology is presented by loam, underlaid by pebble layer. Cover depositions thickness is 10-14 m. Their permeability is 0,2-10 m/day. Groundwater level depth is 6-10 m up to 10-15 m. Soil mechanical composition shows middle loam, somewhere there are sandy loam massifs. Soil is carbonaceous along all profile. Carbonate content in ploughed layer is 8.2 %. Soil response is alkaline, pH is 8,2- 8,7. Groundwater salinity is 2,5-3,5 g/L, chemical composition is sulfate-hydrocarbonaceous, on some places salinity achieves 20-35 g/L . Underground flow is 5-10 l/s from 1 sq.km. Drainage effluent salinity is 1,5-4 g/L.
Parameters of Pilot Projects and Technical Solutions:
Pilot plot area is 84 ha. Alfalfa share is 76 %, winter wheat -24 %. Irrigation network-concrete flums: drainage network- open horizontal drains with depth 3,5-4 m. Eight wells with depth 40-50 m were used for groundwater observations.
Methodology:
Field observations of salt movement under fresh and saline water irrigation, groundwater level and salinity, irrigated land water-salt balance. Study of saline water impact on soil-reclamation processes tendency and rate; forecast of soil salt regime under irrigation by fresh and saline water.
Results:
Fresh water with chemical composition of hydrocarbonate calcium and salinity 0,42 - 0,49 g/L was used on the control site. On the pilot plot which is located in tail part of the Atbashy irrigation system, drainage effluent of sulfate-magnesium composition and salinity 1,8 - 2,2 g/lL was used with content of soda 0.8 mg.ekv/l. Irrigation rate was 6000 cu.m/ha for alfalfa and 2800 cu.m/ha for corn. Specific feature of soil salt regime is soda formation and soil sodification. Soil porosity is 0,45- 0,55; density is 1,19-1,48 g/cm3 , permeability 0.15-0,50; height of capillary raise is 2,3-2,7 m. Soil moisture before irrigation was kept at 70-80 % of full moisture. The control site’s ploughed layer’s absorbtion volume is 7.09-9,82 mg.ekv/100 g and on the depth of 100-150 cm it is 7,6-8,04 mg.ekv/100g. At the beginning of growing period soil sodification according to sodium content was 3,8 % on the control site, at the end of growing period -5,92 %; in the spring on the pilot plot - 4,46, after growing period - 10,01 %. Within the pilot site common and partial salt balance is positive and tends to gradual salinization and soda accumulation. Gipsum in soil is not available, soil-reclamation processes are characterized by sodium accumulation in soil- absorbing complex and calcium destruction. Saline water use for irrigation led to drainage effluent salinity increase. At the end of growing period under fresh water irrigation common salt content in the soil 1 m - layer decreased on 26-30 %, soda in soil is not available. Under saline water irrigation salt content decreased mainly at expense of Ca(HCO3)2 . But residual soda increased 0,5-1,5 times and soda NaCO3 - 0,03 mg.ekv has appeared, which promotes sodium accumulation increase in soil-absorbing complex 1,5-2 times and calcium content decrease on 10-46 %. Under mentioned above irrigation regimes land meliorative conditions are worsening that is proved by alfalfa and corn yield decrease. For soil-reclamation processes forecast calculations special software set is developed. For soil sodification prevention special measures are developed on chemical reclamation of drainage effluent with gipsum additives. PH is decreased by these measures from 8,6-8,7 up to 8,0-8,1 and calcium accumulation exceeds over sodium.
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