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Objective and technical fields:
Reduction of soil erosion, raising the productivity of irrigators’ labor during irrigation of clean tilled crops on sloping lands. Objectives: elaboration of a soil-protecting irrigation technology for clean tilled crops with application of a portable irrigation system under the conditions of the complicated relief.
Scientific and technical approach:
Determination of the parameters of soil-protecting elements of a furrow irrigation technique under the conditions of sloping lands and elaboration of irrigation equipment for guarantee of these parameters during irrigation.
Significance of the investigations: Determination of the parameters of soil-protecting elements of a furrow irrigation technique guaranteeing preservation of a fertile soil layer from intensive erosion and a portable irrigation system under the conditions of sloping lands.
Environment characteristics:
Area of irrigated lands with high inclination (0,02-0,10) in the Republic is more than 200 th. ha. In Gissar valley such lands occupy the area of 36,8 th. ha. Water is delivered to irrigation schemes by open canals to which water is supplied by pump stations located 50-200 m and more lower than the level of their head. Water distribution among irrigation schemes was to be carried out by a tubular irrigation system, but it broke because of soil subsidence and high hydraulic pressure in the first years of cultivation and irrigations were made using a temporary irrigation system.
The climate of Gissar valley is sharp continental. Average annual air temperature is 14-160C, duration of a frost-free period is 225-240 days, sum of positive temperatures is 4442-48600C. Annual precipitation is 595-705 mm, evaporativity is 1280-1680 mm. Relative air humidity varies from 17-25% in summer to 60-90% in winter.
Soils in a foothill part of Gissar valley are loess and loesslike loams. On gently hilly and smooth surfaces of the foothills there are mostly diluvial and alluvial-proluvial Middle Quaternary loesslike loams, their subsidence is more than 50 cm. Their sickness is 30-60 m. Relief is complicated, inclination of irrigated plots are 0,02-0,1 and more, length of slopes varies from 50-70 to 400-500 m. Coefficient of permeability is 0,42-0,56 m/day. To the depth of 20 m ground waters were not discovered, soils are non-salinizated. Soils are slightly and middle-loam ordinary gray soils. Humus content in the upper layer does not exceed 1,5-2,0%.
Parameters of Pilot Projects and Technical Solutions:
Testing-production plot in the cattle-farm«Leningrad» in Gissar district.
Soils are dark gray soils (upper level) and loess middle loams. Exposion is north, inclination is 0,03-0,17. Water is supplied by a pump station Chuzy-2 to a distributing channel from Big Gissar Canal. The main crop is cotton. Irrigations were made to the furrows 70-80 m long with 0,12 inclination and 100 m long with 0,05 inclination. Flow rate of irrigation jets flowing to furrows was 0,02-0,04 l/sec.
Area of plots where study of water balance elements and an irrigation technique were carried out was 1,3-1,5. Area of plots where elements of a portable irrigation system and irrigation technologies were carried out was 60-100 ha.
A portable irrigation system includes: 1 automatic controller of flow rate; 4 distributing reservoirs; 4 feeder hoses 70-120 m long and 4 watering hoses 60-100 m; 1 silt ejector. The complete set is meant for sloping lands with the complicated relief. In this case an irrigation scheme is divided into module plots. Depending on the degree of a relief complication the area of a module plot can be 60-92 ha. On one module plot waterings were made using 4 complete sets of a portable irrigation system, 1 set per each 16 ha. Flow rate for the irrigated plot was 20-45 l/sec. Flow rate for non-eroding watering jets with inclination of furrows equal to 0,02-0,10 was 0,025-0,090 l/sec.
Water was supplied to the portable irrigation system from the open canal through a floating automatic semi-constant flow regulator. Feeder hoses made of reclamation fabric 80-100 m long were put down on the slope with the biggest inclination (0,03-0,12) and on joints they were connected with distributing reservoirs. Watering polyethylene hoses 80-100 m long with watering holes (1 per each 60 cm) were connected with watering bell-sockets of reservoirs and put down transversally to a feeder hose. The distance between watering hoses were equal to a length of furrows with 0,002-0,03 inclination. Head in feeder hoses did not exceed the height of a distributing reservoir, i.e. less than 0,8 m and in watering hoses it was not more than 0,6 m. Surplus head in a watering hose with inclination considerably exceeding calculated head, was regulated by head regulating spreaders.
The distance between portable irrigation systems was 160-200 m. The area of simultaneous watering by a portable irrigation system was 2,7-5,4 ha, its seasonal productivity within a module plot was 16 ha.
3 USSR licenses were given for the design of the elements of a portable irrigation system.
Methodology:
Observations over the elements of a water balance and an irrigation technique were carried out in 3 variants:
Variant 1 - irrigation through ordinary furrows from discharge furrows (control)
Variant 2 - irrigation through zigzag microfurrows from a watering hose
Variant 3 - irrigation through ordinary furrows from a watering hose
Cotton water consumption on sloping lands were compared with the same value on adjoining flat plots. For this comparison study of cotton water consumption on a flat plot in the distance of 3 km from the main testing plot was made in cooperation with specialists of «Agriculture» Research Institute.
Intake rate of soil was determined on sections of furrows 1 m long. Samples for study of soil moisture were taken before and after each irrigation and at the end of each ten-day period. Moisture was measured using a thermostat-weight method and NIV-2 device. Volume of water supply and release from the ends of furrows was measured by a weir and using a volumetric method. Slope wash was measured through taking samples for study of turbidity using a thermostat-weight method. Water flow velocity in furrows was measured using a coloring method and a stop-watch.
Phenological observations over growth and development of cotton plants were made at the end of each ten-day period since sprouting till harvesting.
Plant transpiration was measured at the end of each ten-day period and before and after each irrigation. For this measurement VLTK-500 scales were installed on a testing plot and they were protected from possible wind. Weighting plants was made 4 times per day: in 8, 13, 17 and 24 o’clock.
Elaborated design of the elements of a portable irrigation system was studied under laboratorial and field conditions, on a model platform using existing standard methods and devices. Water flow velocity in the hoses was measured by a Pito tube; head was measured by piezometers; filling and ellipticity of hoses were measured by a ruler; velocity of waves in a feeder hose was measured by a stop-watch.
Representativeness of the selected plots in Gissar valley was estimated through making a flow chart of features for 7 main parameters taking into account geomorphology and properties of soils.
Time expenditures for irrigation and other technological elements were measured by timekeeping while performing operations.
Results:
Sloping lands were developed mostly in seventies. During the period of project fulfillment up to 95% of an irrigation network was wrecked as a result of subsidence, high head in the network and erosion. As a result of intensive erosion and wash of the upper layer of soil (up to 25-200 t/ha per an irrigation season) cotton yield was reduced by 10-15%, grapes yield - by 10-12%, maize yield - by 40% etc. Cultivation of sloping lands using primitive irrigation technology through furrows caused raise of a water table on lower located plots and intensive silting of irrigation systems on them. Gullying appeared on many fields and made plots with the area up to a hectare unusable.
The main objective of elaboration of a soil-protecting technology was solution of above-mentioned urgent problems, introduction of alternative irrigation methods for sloping lands.
As a result of investigations it was discovered that total water consumption on sloping lands is 15-20 % more than on adjoining flat areas. It is caused by better aeration and less preirrigation water content in soil. With total evaporation of 5217 m3/ha, deep outflow of 930 m3/ha, evaporation during irrigation of 577,6 m3/ha, precipitation of 648 m3/ha and using soil water by cotton, net irrigation norm was 5776 m3/ha. Under similar conditions cotton irrigation norm for the flat control plot was 4337 m3/ha and total water consumption was 5867,7 m3/ha which is 15% less than on the sloping lands (6724,6 m3/ha).
Reviewed irrigation scheduling for cotton under the conditions of sloping lands of Gissar valley includes 6-7 irrigations with norms equal to 800-1200 m3/ha each and an irrigation norm equal to 6300-7100 m3/h. Irrigation on slopes begins at the end of May - at the beginning of June 8-10 days early than on flat lands.
Parameters of soil-protecting elements of an irrigation technique were determined with inclination of 0,02-0,05 (exceptionally up to 0,10): length of furrows is 60-120 m, irrigation jets are 0,025-0,090 l/sec., duration of watering is 36-48 hours. Depending on inclination, using a portable irrigation system surface release is 8-15% of a net irrigation norm. It was discovered that uniformity of moistening along the whole length of a furrow highly depends on the ratio of the reaching duration of a watering jet to the total duration of watering. If this value equals to 0,08 uniformity of moistening approximates 1, if it equals to 0,16 uniformity is 0,75. In irrigation through zigzag microfurrow uniformity of moistening was 0,85-0,75 which is explained by lengthening of the way of a watering jet and bigger period of its reaching the end of furrows.
Efficiency of an irrigation technique measured as a ratio of a net irrigation norm to a gross depth of irrigation taking into account water filtration deeper than the calculated soil layer. In irrigation from discharge furrows due to bigger duration of a watering and large release from the ends of furrows efficiency was 0,62-0,67. In irrigation from hoses, after reaching, watering jets were two times reduced and releases from the upper level flowed to the furrows of the lower level. Due to this method efficiency of an irrigation technique was increased up to 0,88-0,91.
Recommended elements of an irrigation technique allowed to preserve and helped to raise fertility, reducing erosion and soil wash to the level of a natural annual soil reproduction equal to 5-7 t/ha (with irrigation from a portable irrigation system) while with irrigation from a temporary irrigation system it was 25-200 t/ha for an irrigation season. This allowed to raise cotton yield up to 3,60 t/ha or by 20-34%.
Keeping to the parameters of soil-protecting elements of an irrigation technique was ensured by using a portable irrigation system. The following parameters of the elements of a portable irrigation system were determined:
- discharge range of an automatic regulator - 3-50 l/sec.;
- watering flow of a portable irrigation system complete set - 20-45 l/sec.;
- diameter of feeder hoses - 150-250 mm;
- diameter of watering hoses - 70-100 mm;
- diameter of watering holes - 3-5 mm.
The least uniformity of watering jets with the maximum inclination of 0,02 and minimum piezometeric head of 0,2 m was 87,8%. That was guaranteed by regulation of jet discharge by head regulating spreaders installed along the length of a watering hose each 6-20 m and more (depending on the inclination).
For protection of watering holes of hoses from obstruction a litter-gathering conical net was designed and tested which was installed in the head of a feeder hose. The length of such net depends on the flow rate and can be 2,0-2,5 m. Its application allows reliable work of watering hoses and prevents getting of weed seeds to the field together with irrigation water which reduces manual labor during inter-row cultivation.
Turbidity of irrigation water varied from 0,5 to 1,5-2,0 g/l which caused silting of water hoses. For flushing of hoses a flushing device for flexible hoses was designed and tested. This device allowed to change manual flushing by hydromechanical one and reduced duration of flushing up to 10 times.
A portable irrigation system is intended for a module plot with the area of 92 ha with inclination equal to 0,02-0,04 and 60 ha with inclination equal to 0,05-0,06. A portable irrigation system was moved from remote parts of a plot on a tractor-chassis T-16.
Technological maps of irrigations from a portable irrigation system were developed with different lengths of slopes (320-400 m, 10-200 m, 80-100 m), recommendations on designing a portable irrigation system for different environmental conditions were given.
Recommended technology is intended for irrigation of lands with high inclination of different configuration and area in highland regions.
Economical efficiency of a portable irrigation system according to the expenditures is (in prices of 1984) 48,6-274,2 ruble/ha.
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