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Objective and technical fields:
Provision of the efficient use of lands and irrigation water during development of sloped terraced and other lands for gardens and vineyards. The objective of studies is elaboration and testing of the technology for low-head drip irrigation of orchards through furrows girdled around a trunk without fine water treatment using polyethylene pipes of 4 mm diameter as outlets. For uniformity of water supply along the length of an irrigation pipeline orifices of pipes-outlets were made lower than the piezometer line by the value of the calculated head.
Scientific and technical approach:
Studies included elaboration and testing of the new irrigation method for orchards which is a variety of the drip irrigation. This method guarantees local moistening of terraced subsident slopes and other lands using turbid water and does not require high head in the irrigation system. For this purpose the following studies were carried out: study of irrigation regimes for peach-trees, almond-trees and pomegranates 4-6 years old; parameters of the irrigation technique through girdled furrows; hydraulic operational regime of irrigation pipelines and pipes-outlets; regime of the irrigation system operation; agrarian practices of gardening with low-head drip irrigation.
Environment characteristics:
The pilot plot is situated in Vakhsh valley with sharply continental climate. Maximum temperature in July is 46oC-47oC and higher, minimum temperature is -25oC-26oC, average annual temperature is 15,7oC-15,9oC. Sum of positive temperatures (above 10oC) is 4500-5800oC. Average annual relative air humidity is 45-50%. Duration of the frost-free period is 220-275 days. Precipitation falls mostly in late autumn, winter and spring, annual precipitation is 160-300 mm.
Soils are loess subsident non-salinized, lightly loam, volume weight of 1 m soil layer is 1,25 t/m3, minimum moisture capacity is 19,0-20,5%, depth of water table is more than 80 m, ground waters are fresh. Irrigation of the plot is made from the irrigation canal with salinity less than 0,7 g/l, type of salinity is hydrocarbonate-calcium, sometimes it is sulphate-hydrocarbonate calcium, content of suspended particles is 1,5-3,0 g/l.
Relief is hilly, inclination is 0,2-0,45. The conditions of the plot are typical for the area of 150-200 th. ha of lands in Vakhsh valley.
Parameters of Pilot Projects and Technical Solutions:
The system consists of a pump station, carrier, main, distributory and irrigation pipelines, pipes-outlets, furrows manually cut around a trunk (girdled furrow) and surface reinforced spillway channels for water release during flushing of irrigation pipelines. The head necessary for irrigation pipelines is 1,5-2 m. The system is subsurface, pipes-outlets are made near each plant, their height follows the line of the piezometer head, flow rate of an irrigation pipeline is selected depending on the flow rate of pipes-outlets and their number for one pipeline. Fine water treatment is not required which allows to reduce investments and expenditures for the system operation.
From the carrier pipeline of 200 mm diameter water is pumped to the metallic reservoir located at the highest place of the plot, than under the head of 1-1,5 m water flows to the main polyethylene pipeline of 160 mm diameter 240 m long laid along a crest of the hill and then it is given to the distributory metallic pipelines of 100 mm diameter laid at the depth of 0,7 m for the biggest inclination of a slope perpendicularly to the main pipeline each 60 m. Average length of a distributory pipeline is 270 m, their number is 8. From distributory pipelines under the small head (1,0-1,5 m) water flows to irrigation polyethylene pipelines of 20 mm diameter laid along terraces at the depth of 0,4 m. Water is given to the plants from furrows manually cut around a trunk (girdled furrows) through pipes-outlets of 4 mm diameter fixed into irrigation pipelines in the distance equal to the space between trees in a row. The space between trees in a row is 4 m (almond-trees and peach-trees) and 2 m (pomegranates). Uniformity of water distribution is provided by the same head over orifices of pipes-outlets through installation of their head lower than the piezometer line in the distance equal to the calculated head. Big orifices of pipes-outlets allow to use turbid water for irrigation, to regulate flow rate of an outlet depending of soil permeability.
Trees are planted on the terraces with 0,02 inclination, width of terraces is 2,0 m, space between trees in a row: 2 m (pomegranates) and 4 m (peach-trees and almond-trees). Row spaces are not sown.
The source of irrigation is Kumsangir canal branch, salinity is 0,7 m, water turbidity is 1,5-3,0 g/l.
Calculated flow rate for a pipe-outlet is 50 l/hour. Flow rate of an irrigation pipeline is 1500 l/hour (50 x 30) for irrigation of pomegranates and 750 l/hour for irrigation of peach-trees and almond-trees.
Gross area of the experimental plot is 15 ha, net area is 13 ha. The plot consists of 9 sections of simultaneous irrigation: 5 sections of pomegranates, 3 sections of peach-trees and 3 sections of almond-trees. Output of the pump station is 54000 l/hour which provides simultaneous irrigation of 36 terraces of pomegranates (app. 0,8 ha) or 72 terraces of peach-trees and almond-trees (app. 1,6 ha) from 1 distributory pipeline. Net width of the irrigation front was 72 m for pomegranates and 144 m for peach-trees and almond-trees.
Parallel to the line of distributory pipelines at the distance of 1 m from them reinforced discharge furrows were made where the ends of all irrigation pipelines closed by plugs were arranged.
Methodology:
Objectives and tasks of field and laboratorial studies were determined; alternative solutions of problems on determination of the irrigation regime, hydraulic parameters of the irrigation system, elements of the girdled furrow irrigation technique were selected.
For determination of the irrigation regime and water requirements for pomegranates, peach-trees and almond-trees of different age (4-6 years of intensive growth and development, biomass accumulation) irrigation was made after reduction of soil moisture down to 70% of minimum moisture capacity in 1 m soil layer, area of moistening was 3-7 m2. Soil moisture was measured with thermostat-weight method. Water consumption was studied using 3-8 plants with 4 repetitions.
Elements of the irrigation technique (size of an irrigation furrow, diameter of a girdled furrow, water permeability of a furrow, soil moistening by 1 furrow) were measured with study of moistening contours.
Hydraulic parameters were calculated using existing relations with due regard for particularities of water supply and were tested on a test bench consisted of a pipeline and outlets with a space of 2-5 m.
Parameters of the system operation (flushing regime, uniformity of water supply) and particularities of crop agrarian practices under this irrigation method were determined during an irrigation season.
Water discharge was measured by calibrated water meters and with the volumetric method, meteorological parameters were measured by meteorological devices, data were processed with the method of variational statistics.
For assessment of the efficiency of the new method the furrow irrigation method of 5-6 year old pomegranates was used as a control variant. Furrows were 60 m long, their flow rate was 0,1 l/sec., irrigation was made also according to the preirrigation soil moisture equal to 70% of minimum moisture capacity.
Results:
As a result of studies it was discovered that low-head drip irrigation can be used on the soils with different texture and permeability, for irrigation fresh water is preferable, water turbidity can be up to 3,5-4,0 g/l. Inclination of irrigation pipelines should be 0,005-0,05, their diameter should be 16-25 mm, their length should be 60-100 m, flow rate depends on the number of pipes-outlets and can be 500-5000 l/hour. Flow rate of pipes-outlets is 10-100 l/hour.
The method of hydraulic calculation of the irrigation system was elaborated and tested under the experimental conditions including: measurement of the flow rate of pipes-outlets depending on soil permeability, age and sort of plants; height of installation of pipes-outlets, their length and place of orifices; diameter and length of an irrigation pipeline; and necessary water pressure in its head.
Nonuniformity of water flow from pipes-outlets did not exceed 10-15%.
Flow rate of irrigation pipelines was regulated by valves made in their head, uniformity of water flow was very high (90-95%).
On the plot 0,8 ha of pomegranates and 1,8 ha of peach-trees and almond-trees were irrigated simultaneously. Duration of the pump station operation was 18-20 hours per day, duration of the plot irrigation of simultaneous irrigation was 8-10 hours.
Efficiency of the irrigation technique was 0,9-0,95 (losses took place during flushing of pipelines which were less than 10-15% of the irrigation norm).
Main parameters of a girdled furrow for the conditions of the plot were:
for peach-trees and almond-trees of 4-6 years old: diameter of a girdle was 1-1,3 m, section was trapezoidal, width was 5-12 cm in the bed and 10-20 cm at the top, depth of filling was 3-15 cm;
for pomegranates of 4-6 years old: diameter of a girdle was 0,9-1,0 m, section was trapezoidal, width was 5-12 cm in the bed and 10-20 cm at the top, depth of filling was 3-15 cm.
Relations were found for determination of the flow rate of pipes-outlets depending on soil permeability, parameters of girdled furrows, age and sort of a plant. On light soils flow rate of pipes-outlets should be 30-70 l/hour.
For provision of the determined regime of soil moistening irrigation period starts at the end of April and lasts till October.
For peach-trees depth of irrigation was 300-560 l/plant, 20-22 water gifts were made, irrigation norms were 7800-10200 l/plant. For almond-trees of 4-6 years old depth of irrigation was 275-490 l/plant, 19-20 water gifts were made, irrigation norms were 6200-8400 l/plant. For pomegranates of 4-6 years old depth of irrigation was 225-425 l/plant, 23-21 water gifts were made, irrigation norms were 5600-7700 l/plant.
Data on the system operation were gathered including operational regime of the irrigation system and its flushing, and agrarian practices of grown plants. It was proved that the yield of pomegranates of 5-6 years old rose by 35%, gross irrigation norm decreased by 20-25%, net irrigation norm decreased by 5-8% comparing with the furrow irrigation. Surface release under furrow irrigation was 15-18%, it was absent under the new irrigation method.
This irrigation system can be recommended for irrigation of gardens and vineyards on flat and slope lands especially on the soils with high filtration.
The system was constructed and had been successfully operated till 1991 on the area of 31 ha in the districts of Khatlon province.
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