Summary of research project: |
Objective and technical fields:
Precising of drainage parameters, development of measures on heavy salinized lands reclamation. Leaching of salinized soils with precipitation using close horizontal drainage. Determination under field conditions of an efficiency of different constructive elements of drains and proposals on their improvement.
Scientific and technical approach:
Salinity control is based on drainability of developed areas and leaching of lands with precipitation. Importance of the study: Determination under field conditions of an efficiency of different constructive elements of drains and proposals on their improvement.
Environment characteristics:
The climate is characterized by dry hot summer and rainy winter. Average annual temperature is 15,4oC. Frost-free period is 228 days. Total average monthly precipitation is 563,3 mm. Relative humidity is 55-70%, in summer - 26-30%. The pilot plot is located within the plane prolluvial plain of the Toirsu river. Relief is smooth, slope is 0,00-0,003, in some areas - 0,004-0,005. Lithology: loam with clay, sandy loam, sand and pebbles interlayers. Permeability coefficient is 0,1-0,2 m/day for loam, 0,8 m/day for sandy loam and sands. Ground waters level is 0,0-2,0 m. Salinity is 15-20 g/l. Type of water is sulphate, sulphate-chloride. Ground waters below the lower horizon are artesian. Piezometric head is 0,5-2,0 m on land surface. Permeability is 2,6-7 m3/day. Gradient of head is 0,1-0,2, salinity of artesian waters is 2-45 g/l. Soil surface belongs to hydromorphic group. Type of soils is gray-meadow. Carbonate content is 7-20% of the weight. Soil texture is coarse-silt, heavy loam, within the profile - alkaline 7,9-8,7. Volume mass varies from 1,35 to 1,61 g/cm3, porosity is 39,1-49,3%, in vertical direction - 0,11-0,44 m/day, in horizontal one - 0,07-0,35 m/day. Soils are strongly salinized, below the arable layer salinity is 0,66-1,326% of dry soil weight. Type of salinity is sulphate-chloride, rarely - sulphate.
Parameters of Pilot Projects and Technical Solutions:
Irrigated area is 400 ha. Length of close drainage is 29692 m (planned), 14034 m (actual), 37,8 m/ha (specific). Drain spacing varies from 105 to 155 m. Depth of drain is 3,5-4,0 m, pipes are polyvinilchlorine (PVC), ceramic, pipe-filters are 150 and 200-300mm. Filters are sandy-gravel.
Methodology:
Field studies and observations of the movements of aeration zone and ground waters in soils, accounting of drainage waters and study of the chemical composition and salinity of ground and drainage waters. Studies were conducted on a fixed balance plot (its area is 75 ha). The plot was equipped with meters to keep regular observations. Regime of ground waters was observed from 38 wells, depth is 2-10m. Salt sampling was done up to depth of 200 m in 15 fixed salt lots. Hydrometric observations were conducted in outfalls of 18 effective drains. 8 drains were taken for salt sampling. Besides field observations, data of water related and agricultural institutions were used.
Results:
Soils of the pilot plot are salinized, with high level of ground waters and weak natural drainage. It is located in the middle of non-irrigated lands of a collective farm specialized on boharic farming. Productivity of cultivated wheat under unirrigated conditions was 10-13%.
It was planned to cultivate cotton and alfalfa on the pilot plot. According to calculations after putting the lands into irrigation productivity of cotton in the first year should be 1,35 t/ha. In the forth year of irrigation productivity of cotton should be 2,25 t/ha. Construction of systematic drainage and irrigation allowed the following:
- to accelerate putting the developed lands into irrigation. Considerable amount of precipitation (550-650 mm) in winter-spring period provides deep infiltration (2,5-3,0 m) of ultra-fresh waters, it causes an intensive leaching in the root zone and leads to lightly and middle salinized soils under initial 1,5-2% of salt content for one period of moistening. Rational use of such factor allows to develop salinized lands without thorough leaching;
- to create in developed lands high drainability. Regime of drainage outflow and salinity without irrigation is directly connected with climatic factors. The maximum drainage outflow was in April. Value of drainage outflow varied from 0,03-0,05 l/sec/km to 5,16 l/sec/km. Modulus of drainage outflow was 0,01-0,03 l/sec/ha. Salinity varied within the year according to ground waters regime. Salinity of drainage waters was 66 g/l in 1981, 35 g/l in 1985, 29 g/l in 1990.
- to decrease ground waters level. Annual amplitude of ground waters level fluctuation before drainage construction varied within 1,0-1,5 m. It was 70-115 cm after drainage construction, while locating stably at the depth of more than 1,74-2,3 m. With the beginning of irrigation in drain systems rate of ground water level decrease accounted for 40-60 cm/day, on 3-5th day of irrigation - 10-18 cm/day, in 10 days - 5-7 cm/day;
- to create high rate of soil desalinization in aeration zone. Construction of systematic drainage without irrigation caused desalinization processes. For 2 years of drainage work without irrigation area of non-salinized and slightly salinized lands in 0-10 cm accounted for 45-47% of total one. In 100-200 cm intensity of desalinization accounted for 10-20% per year of initial salt content. The most intensive desalinization was in 0,25-0,5 cm. For 3-4 years of close drainage work rate of desalinization decreased in 0,50 cm layer, increased in 50-100 cm and was practically unchangeable in 100-200 cm. The main reduction of soil salinization was caused by dissolving and leaching of sodium and magnesium sulphate. Salts removal from 0-50 cm accounted for 70-90%, from gypsum horizon (75-100 cm) - 44-57%, from 100-150 cm - 60-70%, from lower 150-200 cm - 25-30%. Initial salt content was 1-2% of soil weight. Chlorine content in 0-75 cm decreased from 0,174-0,205% to 0,08-0,016% (on 91-86%), sulphate content decreased from 0,50-0,77% to 0,06-0,07% (on 87-92%), sodium content decreased from 0,20-0,27% to 0,03-0,06% (on 75-90%). Content of hydrocarbonate-ion increased within the profile on 24-37% and mounted to 0,03-0,06% of the weight. For five years of drainage work salinization reduced to 0,15-0,25% in 0-100 cm layer. Within September 1980-August 1981 intensity of salts removal varies from 90 to 744 g/sec, 243-2000 t/month accordingly, specific value is 69,4 t/km (4,6 t/ha) - 570 t/km (38 t/ha) per month. For a year salts removal accounted for 9404 t (on the average 179,1 t/ha) under average monthly intensity at 223,9 t/km or 14,9 t/ha. Average specific intensity of salts removal in the zone of systematic drainage accounted for 29,85 t/ha/month in January-May 1981, 15,3 t/ha in 1985, i.e. salt storage decreased. The main mass of removed salts, 1-95% of the weight, consist in sodium chlorides and sulphates: SO24 - 32-36%, Cl - 27-28%, (Na+K)- - 32-36% of the total amount of ions;
- to reduce and make even ground waters salinty within 2,0-3,0 g/l. Regime of ground waters salinity after drainage construction was under stable desalinization within many years. The most intensive reduction of salinity was in an area with high salinization. Value of desalinization was 8-10 g/l in the first year, 15-20 g/l in the second one. In the third year there was stabilization of desalinization rates mounting to 13-20 g/l. When the ground waters are close (up to 2,5 m) desalinization accounted for 0,3-2,5 g/l per year.
With the beginning of irrigation salt regime of soils changed. Its qualitative and quantitative characteristics are connected with parameters and technical state of drainage. In lands with technically defective drains secondary salinization of soils was observed with the beginning of irrigation due to increase of salts coming with irrigation water. Secondary salinization of soils was caused by imperfect drains (small depth, defects in drainage lines) and their incorrect operation. As a whole, area of non-salinized soils reduced on 4% and increased on 0,3%. Due to unstable situation and complex economic conditions observations on the pilot plot were stopped since 1990.
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