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Objective and technical fields:
Reduction of soil erosion, increase of irrigators’ labor productivity while irrigating cultivated crops on sloping lands.
Objective: To develop soil-conservative irrigation technology using mobile irrigation system for conditions of complex relief.
Scientific and technical approach:
Determination of the parameters of soil-conservative furrow irrigation technique under conditions of sloping lands and development of irrigation facilities to obtain these parameters during irrigation.
Importance of the study: Determination of the parameters of soil-conservative furrow irrigation technique, which provide protection of fertile layer from intensive erosion, and the parameters of mobile irrigation system for conditions of sloping lands.
Environment characteristics:
The climate of the Hissar valley is sharply continental. Average annual temperature is 14-16oC, sum of positive temperatures is 4442-4860oC. Frost-free period is 225-240 days. Annual precipitation is 595-705 mm. Evaporativity is 1280-1680 mm/year. Relative humidity varies from 17-25% in summer to 60-90% in winter.
Soils of foothill part of the Hissar valley include loess loam. In sloping hilly and smooth areas of foothills diluvial and alluvial-proluvial loess loam prevails, its subsidence is more than 50 cm. Thickness is 30-60 m. Relief is complex, slopes are 0,02-0,1, length of slopes varies from 50-70 to 400-500 m. Permeability coefficient is 0,42-0,56 m/day. Ground water are not contained within thickness above 20 m. Soils are non-salinized. There are light- and middle-loamy gray soils. Humus content in upper horizon is no more than 1,5-2,0%.
Parameters of Pilot Projects and Technical Solutions:
Area of irrigated lands with high slope (0,02-0,10) is more than 200 th.ha. There are 36,8 th.ha of such lands in the Hissar valley. Water is supplied by open canals from pumping stations placed at a depth of 50-200 m and more below their head. Water is distributed by pipe network. However, due to subsidence of soils and high hydraulic heads these network was wrecked during first years of development. Now, watering is done by temporary surface irrigation network and is accompanied by erosion and gully formation.
In four pilot plots the mobile irrigation system was used. It consists of automatic flow off-take regulator (1 piece), distributive reservoirs (4 pieces), conveying hoses (4 pieces, length is 70-120 m), irrigation hoses (4 pieces, length is 60-100m), silt ejector (1 piece). This system was developed for irrigating a module plot, area of which is 60-92 ha, duty of water is 20-45 l/sec. Erosion-safe irrigation stream for 0,02-0,10 slope of furrow is 0,025-0,090 l/sec.
Methodology:
Field studies and observations of water movements on the surface and within aeration zone, water balance elements, soil erosion and washing down. Development, laboratory and field studies of the elements of mobile irrigation system (MIS). For these purposes the representative permanent pilot plots, area is 10-60 ha, were selected. Combined observations of water balance elements and irrigation technique, soil erosion and washing down were conducted in these plots. Technological parameters and reliability of MIS operation were studied. Laboratory studies were conducted in hydraulic laboratory and in a model area of hydro-reclamation department of the Tajik Agrarian University. Results of the studies were systematized and passed for development of soil-conservative furrow irrigation technology on sloping lands by MIS use.
Results:
Sloping lands were mainly developed in seventies. During project implementation, as a result of soil subsidence, high heads in the system and destructive erosion processes, up to 95% of pipe irrigation system were wrecked. As a result of intensive erosion and washing down of upper horizon (up to 25-200 t/ha during irrigation period) cotton productivity decreased by 10-15%, vine productivity decreased by 10-12%, maize for silage productivity decreased by 40%, etc. Extended development of sloping lands using primitive furrow irrigation technology caused ground water level rise in lower plots and intensive siltation of their irrigation network. Gully formation was observed in dozens of plots amounted to 1 hectare.
Development of soil-conservative irrigation technology was directed towards urgent solution of all these problems before introduction of alternative irrigation methods. It was determined, that total water consumption in sloping lands was by 15-20% more than in neighboring plain areas. Under 5200 m3/ha of total evaporation and 930 m3/ha of deep release irrigation norm accounted for 5776 m3/ha. Depending on slope, under other equal conditions, surface release accounts for 25-40% of net irrigation norm and 8-15% under MIS use. Precisely defined irrigation schedule foresees 6-7 waterings with 800-1200 m3/ha irrigation depth and 6300-7100 m3/ha irrigation norm. Irrigation in slopes begins at the end of May -early June, that is 8-10 day earlier than in neighboring plain areas. The following elements of soil-conservative furrow irrigation technique for 0,02-0,05 slope (in exceptional case - 0,10) were determined: length of furrow is 60-120 m, irrigation stream is 0,025-0,090 l/sec, duration of watering is 36-48 hours. Recommended elements of irrigation technique allow to preserve and promote increased fertility while reducing degree of erosion and washing down during irrigation period from 25-200 t/ha to a level of annual natural soil reproduction determined by soil balance calculations in irrigated lands within 5-7 t/ha. This allowed to increase cotton productivity up to 3,6 t/ha or by 20-34%.
Applicability of the elements of soil-conservative irrigation technique is provided by mobile irrigation system. The parameters of MIS elements were determined:
- diapason of discharge of automatic regulator is 3-50 l/sec;
- required discharge of MIS is 20-45 l/sec;
- diameter of conveying hoses is 150-250 mm;
- diameter of irrigation hoses is 70-100 mm;
- diameter of outlets is 3-5 mm.
Regulation of irrigation stream uniformity under conditions of complex relief was provided by head regulating spreaders placed in a distances calculated by developed methods.
Sweepings keeping conic net placed in the head of conveying hose was developed and tested to protect hose outlets from obstruction. The length of such hose depends on discharge and accounts for 2,0-2,5 m. Use of the net provides reliable operation of irrigation hoses and prevents getting of seeds and weeds with irrigation water into a field.
Turbidity of irrigation water varies from 0,5 to 1,5-2,0 g/l. This often leads to siltation of irrigation hoses. For hose washing a silt ejector for flexible hoses was developed and tested. The ejector allowed to replace manual washing by hydromechanic one and to reduce duration of washing to 10. MIS is developed to irrigate the module plot, area of which is 92 ha at 0,02-0,04 slope and 60 ha at 0,05-0,06 slope. MIS is moved from distant points of the module plot by tractor.
Technological maps of irrigation by MIS are developed at different slope lengths: 320-400 m, 160-200 m, 80-100 m.
Recommendations on MIS development for different relief conditions are given.
Recommended technology is developed for irrigation of lands with high slopes of different configuration and for irrigation of highlands.
An economic effect of MIS according to expenditures is 48,6-274,2 rouble/ha (in prices of 1984).
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