Summary of research project: |
Objective and technical fields:
Introduction of rational irrigation technology for crops of rice crop rotation using salinized drainage waters, which provide favorable meliorative state of irrigated lands and their high productivity. Management by salt regimes of soils and ground waters, while using drainage waters for irrigation and leaching the lands as well as management by drainage flow quality.
Scientific and technical approach:
Perfection of irrigation schedule, watering technology with the use of salinized drainage waters based on field and laboratory experiments. The task consists of drainage water quantity and quality management and scientifically grounded proposal on optimization of meliorative regimes and increase of irrigated lands productivity.
Environment characteristics:
The climate is sharply continental. Average annual air temperature is 14 -16 oC, total effective air temperature is 2200 - 2400 oC, frost free period is 185 - 195 days, total average annual precipitation is 160 - 200 mm, evaporativity is 1200 - 1400 mm, relative air humidity is 50 - 63%.
Relief: slightly corrugated valley with 0,0003 - 0,0005 slope.
Lithology - up to 5 meters loam, sandy clay loam soils with sand interlayers. Thickness of top deposits is from 35 to 80 meters; permeability coefficient (PC) = 1-30 m/day.
Thickness of water-bearing layer is 10-25 m; PC = 50-200 m/day.
Depth of ground waters bedding is 1,5-3,0 m, salinity is 1-25 g/l. Type of ground waters by chemical composition is chloride-sulphate and sulphate-chloride, by cations - sodium-magnesium and sodium. Salinity of drainage waters is 1-10g/l, type - chloride-sulphate.
Pilot Projects and Technical Solutions:
Area of a pilot plot is: gross - 48 ha, net - 40 ha. Crops pattern is the following: rice - 52-57%, alfalfa - 43-48%. Irrigation network has a form of open earthen canals, efficiency is 0,6 - 0,65.
Technical state of the network is satisfactory, drainage network has a form of open horizontal drains. Specific length is 38 - 40 m/ha.
Depth of drains is 2 - 2,2 m, depth of headers is 3 - 3,5 m.
Methodology:
A balance method was used for studying the environmentally safe irrigation technologies for crops of rice crop rotation, depth of draining, water-salt regime of soils, meliorative effect of open horizontal drainage. Water-salt regime and balance on the pilot plot were considered in relationship with irrigation schedule, degree of soil salinization and irrigation water salinity, drainage effect and variation of ground waters level. Checking experimental data on reliability and their processing were performed by a method of mathematical statistics using dispatching/control and regressive analysis. Mathematical calculations of field and laboratory materials are made using computers. The pilot plot was equipped with measuring devices for all parameters of water-salt regime and balance formation.
Results:
Irrigation norm of water for rice in light and medium loamy soils, where drainage modulus is about 1,0-1,1 l/sec/ha, was accounted for 24200 - 25600 m3/ha. In heavy loamy soils the drainage modulus drops to 0,5 - 0,7 l/sec/ha and duty of water decreases - 20600-21350 m3/ha. Specific water expenditures per 0,1 t of rice grain under watering by irrigation water (1 - 1,25 g/l) was 410 - 500 m3 and under watering by drainage waters with 2,5 g/l salinity was 800 - 910 m3. Level of soil moisture is maintained at 78 - 85% HB during alfalfa cultivation. For alfalfa of first growing year it was done 3 waterings with norm of water at 800 - 900 m3/ha, second growing year - 5 waterings with norm of water at 900 - 1200 m3/ha. Under irrigation by water with salinity of more 2 g/l leaching requirements were EB = 1,1 - 1,35.
A maximum value of transpiration at 5060 - 5800 m3/ha was recorded under rice watering by irrigation water (1,0 - 1,5 g/l), minimum - 3880 - 4400 m3/ha - under watering by drainage water (2,6 - 3,0 g/l). Evaporation from water surface within the growing period depends on air temperature, its humidity, dense of rice and irrigation water salinity. The largest evaporation value is recorded under watering by drainage water (6550-6880 m3/ha), the minimum (6150 - 6300 m3/ha) - under watering by river water.
Water discharge for percolation depends on natural drainability of an area, percolation characteristics of soils and altitude of plots. Water discharge in first plot accounted for 10600 - 10800 m3/ha, on second one - 6950 7400 m3/ha.
Water discharge for aeration zone saturation depends on depth of ground waters bedding, initial moisture , water-physical characteristics of soils, and varies within 2600 - 3400 m3/ha.
Drainage waters are forming at expense of release and drainage ones, their salinity varies within 1,4 - 4,5 g/l during irrigation period and increases during non-irrigation one. Type of drainage water with salinity of about 2,5 g/l is sulphate, more 2,6 g/l - chloride-sulphate.
Maximum yield of rice equal to 5,00 - 5,43 t/ha was achieved while watering till its full ground cover by irrigation water, then - by mixture - irrigation water with drainage one with 2,0 - 2,4 g/l salinity. While watering by drainage water with salinization of more 2,5 g/l rice yield falls to 2,5 - 2,8 t/ha. Under watering with salinity of more 2,5 g/l, reduction of rice plants growth, crops density decrease, hollow kernels increase were observed and growing period was prolonged on 5-9 days.
While watering rice and alfalfa by water with salinity of 1-2,4 g/l, ground waters are being desalinized on 1,2-2,0 g/l from initial value, and under salinity of more 2,5 g/l there is increase of ground waters salinization on 0,6 - 1,8 g/l.
In light and middle loamy soils after 3-year rice cultivation while watering by water with salinity of 1-2,4 g/l 0-300 cm of soil were desalinized. In 0-100 cm layer salt content was reduced from 0,35 to 0,06 % or 6,4 times, in 100-200 cm layer - from 0,206 to 0,068, i.e. more than 3 times. 0-100 cm were desalinized by chlorine as well - from 0,019 to 0,010%. Salts removed from 0-300 cm accounted for 84,8 t/ha, i.e. 58% from initial content. Desalinization was caused by washing of toxic salts of sodium-sulphate on 55%, sulphate- magnesium - on 56%, sodium-chloride - on 37%as well as non-toxic salts of calcium- sulphate - on 76,1%.
While watering by drainage water with salinity of 2,6-3,0 g/l, after 3-year rice irrigation salts content in 0-300 cm layer was increased from 0,39 to 0,43%, including by chlorine - from 0,018 to 0,023%.
The total stock of salts in 0-300 cm layer due to toxic salts of magnesium sulphate (from 8,3 to 15,1 t/ha) and non-toxic salts of calcium sulphate (from 26,8 to 43,0 t/ha) increased from 139,7 to 167,8 t/ha, i.e. on 20%.
However, 0-100 cm layer was desalinized from 4,8 to 37,6 t/ha.
In heavy loamy soils while watering by water with salinity of 1-2,4 g/l after 3-year rice cultivation 0-300 cm layer was desalinized from 0,38 to 0,33%, including by chlorine - from 0,018 to 0,012%. The total amount of salts decreased on 76,4 t/ha or on 36% from initial content. However, desalinization is occurred mainly in upper 0-150 cm . In 160-300 cm amount of salts increased on 30,6 t/ha or 15%.
While watering by drainage water with salinity of 2,6-3,0 g/l after 3-year irrigation of rice in 0-300 cm soil profile salt content increased from 163,9 to 220,1 t/ha or 1,4 times. Salinization of soils occurred in the whole 0-300 cm layer. Amount of salts in arable horizon (0-40 cm) increased on 12,8 t/ha, i.e. two times from initial content. Their qualitative content was deteriorated as amount of toxic salts of magnesium-sulphate increased 2,2 times, magnesium chloride - 1,6 times, sodium sulphate - 1,3 times.
There were no big changes in water-physical characteristics of soil under long-term drainage waters use, a little increase of specific mass and density was observed in upper 0-40 cm. Reduction of nutrient elements during rice cultivation and their increase during alfalfa growth.
While watering by drainage water with salinity up to 2,5 g/l content of absorbed sodium accounts for 4-7%, within 3-6g/l - up to 12-18% against sum of soil-absorbing complex.
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