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0References
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Turchenyuk V.A.
Ph.D., associate professor
Rokochynskyy A.M.
Professor
Prykhodko N. V.
Assistant
Mendus S.P.
Ph.D., associate professor
Zaiets V. V.
Senior lecturer
National University of Water and Environment, m. Rivne, Ukraine
THE EFFICIENCY OF DANUBE RICE IRRIGATION SYSTEMS DRAINAGE AND WAYS OF ITS IMPROVEMENT
ABSTRACT
In the article the analysis of the main reasons of poor land reclamation condition of Danube rice irrigation systems territory. The questions of improving water-air and salt regimes of soils by increasing filtration through placement of land drainage were considered.
Keywords: efficienAcy of drainage, reclamation condition, rice irrigation system
The natural reclamation condition of irrigation rice systems (RIS) is determined by a number of factors, foremost of which is natural (climatic factors) and technological (irrigation norm, structure and parameters of irrigation and drainage networks, etc.). The research results [3,4,8,10] Indicate that the most significant impact on the natural reclamation condition of RIS provides drainage network that determines the intensity and direction of filtration processes which occur during prolonged over wetting of soils by using irrigation
flooding. Drainage network in RIS directed on formation of their water regime and in a significant degree determines the productivity of agricultural lands.
Drainage that arranged on rice irrigation systems must meet the following basic requirements:
- create the optimal filtration rate on rice field;
- provide required draining norm after water discharge at least 0.8 m and bringing it to 1.5 ... 1.7 m at the beginning of a new irrigation season;
- in the case of soil salinity to desalinate root layer to permissible salt concentration of no more than 3 years of operation;
- exclude the possibility of soil salinization on the reclamation fields and fields occupied accompanying cultures.
Rice irrigation systems in Ukraine, including in the Danube Delta were built for irrigation by known scheme Krasnodar card type (CCT) and card checks a broad front of flooding and water discharge (CCBF) with unilateral and bilateral command mostly open irrigation and drainage channels, the distance between them depending on the soil and hydrogeological conditions was 200 ... 500 m in some areas up to 900 meters at a depth of drains 1,5...1,7 m.
Because of prolonged drainage network use under the influence of numerous factors it was deformed [1,4,5]. Such channels can't affect the quality of watersalt regime of soil under rice cultivation, especially in times of accompanying culture growing when you need to provide the critical depth of groundwater level, which for conditions of the Danube Delta is 1,3... 1,5 m.
Analysis of the efficiency of the drainage on rice systems of the Danube Delta showed that drainage, built according to current construction and building standards do not provide sufficient filtration rate of rice fields, and that is one of the main reasons for their poor environmental and reclamation condition and reducing the yield of rice and accompanying cultures.
An important indicator of the efficiency of the drainage network and one of the main indicators the reclamation condition of systems is the drawdown depth of groundwater level for end of irrigation period to limits its stability and the beginning of spring field work associated with what intensity of redox soils processes.
Scientists I. Zhovtonog and O. Oleinik [7] established pattern changes harvest rice on the depth of groundwater in outside vegetation period in natural conditions from which it follows that the depth of the ground water level about 1m in the autumn-winter period the harvest of rice was 20 ... 30 cwt/ha, with a depth of 1, 5 m - 40 ... 50 cwt/ha, with a depth of 2.0 ... 2.5 m - 70 ... 80 cwt/ha.
Similar results for the conditions of Kuban were received by I. Prykhodko [9]. He found that when groundwater level (GWL) was 0,7 ... 1,0 m rice harvest was 3 ... 4 t/ha, while GWL was 1.5 m - 4 ... 5 t / ha, when GWL 2 m - 5 ... 6 t /ha. According to him lowering of groundwater level to a depth of 2.5 m does not increase the yield of rice and it is also 5 ... 6 t / ha.
V. Dudchenko [2] has established the empirical direct dependence between the groundwater level of outside vegetation period and yield of rice (r = 0,962). So
at a depth of 1.5 m and below ground water does not affect the yield of rice. If their level is above this point, the rice yield is reduced, and at the location of ground-water at a depth of 50 ... 60cm from the soil surface of rice yield is reduced to zero.
This conclusion is supported by the research conducted by S. Goncharov [1] for conditions of Danube RIS. His researches suggest that at the checks where groundwater level in the period between irrigation lie deeper soil-reclamation conditions favorable for rice and the fertility of the soil better. The depth of the root aeration of soil between irrigation is important to eliminate the effects of wetland processes and restore its fertility.
So to get rice yield within 40...50 cwt/ha the depth of groundwater level at the beginning of the growing rice season shall be not less than 1,5m. Providing such depths in rice systems where the drainage network open, deep drainage channels should be 2.0...2.5 m, which in most parts of the RIS is almost impossible because of its fast deformation.
The researches of many authors [3,7,10] found that drainage should provide not only regulation of the GWL depth but also the filtration rate needed to create a good filtration conditions of rice soils under check during the growing season. Long-term field research on the Danube RIS has shown that in areas where the checks filtration rate was negligible rice yield was smaller. The yield of rice was higher at sites check, situated at a distance of 60 meters from the drains, where the average rate of filtration of water in the upper layer of soil ranged from 0,005 to 0,01m/day. Where it was more or less than these values rice yield was lower. Authors [3,7,8] also noted that on the rice yield has a particular impact filtration conditions of soil in rice growing season, of which the direction and intensity of soil processes. They proved that in the vegetation rice period on the whole check surface must be provided rate of filtration in the top layer of soil within 5...7mm/day.
Different rate of filtration across the width of rice field causes the big difference in groundwater salinity and salt content of the soil, leading to the availability of various reclamation conditions within a single check and different yield of rice.
The researches of filtration from irrigated rice field surface of the Danube Delta [4,5,10] showed that the higher filtration rate (from 4 to 20 mm/day) observed on the part of the rice fields, the so-called near-drains zones up to 50 m from drains in the absence of the staff in the drainage channels and in accordance with the maximum amount of pressure gradient.
Then, by mid-distance between drains, rate of filtration is within 1...2 mm/day and practically absent, as shown in Figure 1.
to c
S £
OJ a > g
o
(D
"3
U f—
16 14 12 10 8 6 4 2
vî 1
2
3
♦ ----
0
50
100
150
200
250
300
Distance from the drainage channels on cards-checks, m
Fig.1. The rate of vertical filtering on cards-checks, depending on the distance between the drainage channels: 1
- B = 200 m, 2 - B = 250 m, 3 - B = 500 m
In other words to create favorable reclamation conditions in the rice fields drainage network must provide desalinization of soil root layer by washes with water layer, to provide the optimal conditions for soil aeration, to provide the optimal filtration rate (5...7 mm/day) in the topsoil around a check during the rice growing season. Such depth of GWL and filtration rate in the corresponding periods of the growing season of rice and other cultures of rice crop rotations ensure the removal of soil salt solutions and at the same time not allow leaching of soil nutrients.
One of the main causes of negative processes in soils of RIS and reducing of soil fertility and yield of rice is the inability of the drainage network to maintain the required drainage norm in between-irrigation period and the required filtration rate. The shallow drainage channels (1,5...1,7 m), built in 200...500 m cannot provide the necessary filtration conditions and aeration of top layers of soil.
Our research and calculations showed that a favorable air-water regime of the soil for the Danube RIS can be achieved by adding to a drainage closed collectors, arranged by card check (Figure 2).
1 V3
L I N
i ^ 1 1 f
^J^'
IT
l-l
ifTIi
o
T
Fig.2. The construction of the card-check with closed drainage-collector:
1 - separating irrigation canal; 2 - irrigation-discharge; 3 - water supply building; 4 - discharge structure; 5 -the main channel fault; 6 - Card drainage channel fault; 7 - gateway controller; 8 - closed collector-drainage; 9 -regulatory structure
Depth favorites such drains, based on the required rate of drainage in between-irrigation period should be at least 2 m. Placing of closed drains reduces the distance between the open drainage channels up to 100...125 m instead of the existing 200...500 m. Calculations of dynamics the groundwater level decrease in conditions of Danube RIS equipped with closed drainage, showed that the draining process of the rice fields in period after irrigation is more intense. Reduction of groundwater to a depth of 1,5 m passes much faster and is 20-50 days, and it's almost in 2...3 times reduces the period of drainage. Improvement of drainage network construction makes it possible to extend the period of favorable groundwater level standing in the between-irrigation period in 30-100 days, bringing it to a total duration of 200-220 days. This creates conditions for the full oxidation of recovered toxic products for the new irrigation season. Formed in the growing season saline after the discharge of water from the surface of the check rapidly descend to the bottom of the soil profile. The intensity of this process and the depth of draining determine the effectiveness of the rice irrigation system.
Equipping rice field by closed drainage will also affect the intensity of vertical filtering process under rice during its growing season.
In our opinion, based on the analysis of the research of filtering, which were held by a number of scientists [4,5,8,10] to create optimal air and water-salt regime of soil aeration zone the filtering intensity in the rice growing season should be sufficiently high and evenly throughout the area of irrigation field, and the filtration process should be managed.
This construction of irrigation fields with drains of closed type help to strengthen filtration of irrigated cards that provide even soil desalinization throughout the area under growing flooded rice, fast and deep draining of rice-checks in between-irrigation period, maintaining the groundwater level in the period below the critical depth that creates favorable conditions for the occurrence of redox processes.
The proposed construction of the irrigation cardcheck will provide an opportunity to reconstruct the existing rice systems with little investment, because it does not require a placement of systematic drainage, greatly increase the efficiency of drainage network and will make it possible to manage the draining in the different phases of crop growth and in between-irrigation period.
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