Summary of research project: |
Objective and technical fields:
To develop equipment for middle- and strongly-subsident loess soils, which provides irrigation water supply and consists of flexible conveying pipelines and watering hoses laid on irrigated land for a period, when intensive subsident deformations are appeared, and then replaced by permanent ones.
Development and application of technological processes for gradual irrigation development of middle- and strongly-subsident loess soils to obtain stable crop yields from the very first year of land development.
Scientific and technical approach:
Development of technical facilities and technological processes for gradual irrigation development of middle- and strongly-subsident loess lands with different relief conditions based on use of temporary mobile intra-farm irrigation system consisted of of flexible pipelines and watering hoses laid on irrigated land for a period, when intensive subsident deformations are appeared, and then replaced by permanent irrigation system, on selection of rational elements of furrow irrigation and provision of faster use of new developed lands in agriculture.
Importance of the study: Elaboration of technological processes for development of structurally unstable loess soils with different relief conditions, which provide reliable preservation of reclamation facilities from destruction caused by uneven subsident deformations of irrigated field, keeping high land use efficiency and even moistening within the length of furrow and provide stable crop yields from the very first year of land development.
Environment characteristics:
The state farm is located in Garauta natural landmark, the south-west part of Tajikistan, lower riches of Vakhsh river. The natural landmark is a wide plateau semi-desert plain, formed by loess proluvial and alluvial-proluvial rocks.
Environment characteristics of the plot are typical for the most part of south Tajikistan with middle- and strongly- subsident soils and middle corrugated micro-relief.
Average annual air temperature is 16-16,5oC, maximum is in July - +26,3oC, minimum is in January -24oC. Total sum of temperatures of frost-free period is , on the average, 5130oC. Frost-free period is 180-200 days. Total sum of positive temperatures (more than 10oC) is 2800-2900oC. Average annual precipitation is 158 mm, including 77mm in April-October.
The plot contains proluvial deposits, slope is 0,005-0,03. Lithology: Quaternary deposits of big thickness (more than 300 m). Water-bearing layers are at a depth of 33-52 m, permeability coefficient is 0,2-0,4 m/day. Subsident features of loess rocks are characterized by large dispersion of relative subsidence values 0,01-0,16 under natural pressure. Porosity is 47-55%.
There are light gray soils on sandy loam and loam deposits with 70-98% of silt particles. Gray soils are characterized by low content of humus (2%), high carbonate content and gypsum presence. Type of salinity is chloride-sulphate, solid residue is 0,6-1,8%. Salinity of ground waters is 6-8 g/l.
Density characteristics of soil are the following: angle of internal friction is 27-31o, cohesive force is 0,01-0,04 MPa.
Parameters of Pilot Projects and Technical Solutions:
Area of the pilot plot is 125 ha (gross) and 121 ha (net). Irrigation water was supplied to the plot by conveying pipelines from flumes, then to the furrows by watering polyethylene hoses.
Every year there were five waterings with the following depths of water (gross): 2,4-3,2 th.m3/ha in first 3-4 years of development, 1,8-2,8 th.m3/ha in next irrigation years. Duration of watering is 32-40 hours. Irrigation norms (net) were 8,2-10,3 th.m3/ha (net) and 10,6-14,4 th.m3/ha (gross).
Waterings were done with different combinations of irrigation stream, slope along the furrow and duration of irrigated land use in agriculture. Irrigation stream for middle slope (0,018) varied from 0,1 to 0,15 l/sec. For such slopes irrigation streams, which more than 0,15 l/sec, cause erosion of furrow bottom and over-removal (limit is 10t/ha per year) of mineral elements from the end of furrow. For middle slope (0,014) irrigation streams equal to 0,14-0,18 l/sec were studied.
A control plot, area located beside the pilot plot is also 125 ha. It was developed by a traditional way - after thorough grading and construction of subsurface irrigation network. Water was supplied from subsurface conveying pipelines, then in furrows by temporary ditches in earthen channels. Area of one watering in the control plot was 18-22 ha under two ditches operation. Irrigation streams for middle slope were 0,12-0,18 l/sec, duration of watering was 72-80 hours, irrigation water releases from the ends of furrow were 35-67%.
Methodology:
Problem of irrigation development and agricultural use of irrigated lands located in loess subsident soils with different relief conditions was solved in the following stages:
First stage - during intensive subsident deformations - land grading to prepare lands for use in agriculture, water supply to the field by stable flexible pipelines, then to furrows by watering hoses, obtaining the yields at the beginning of irrigation development.
Second stage - during stabilization of water-physical and other soil characteristics - construction of permanent irrigation system using traditional materials (e.g. asbestos-concrete pipes) laid in a safe depth and crop irrigation by hoses.
Taking into account above mentioned, there were field studies and observations of water movement in soil and within furrows, measurement of all parameters of irrigation technique and technology in middle- and strongly- subsident loess soils in order to determine duration of moistening and to select rational length of furrow at the initial stage of irrigated land development. Depth of moistening was determined by a well drilled to a depth of moistening, the elements of furrow irrigation technique were determined under various combinations of irrigation streams, lengths of furrow and slopes. Deformation of irrigated lands surface under moistening by irrigation water was studied by systematic grading of changed ground levels.
Two ditches were functioning simultaneously within the pilot plot. At the initial stage they consisted of flexible pipes laid on land surface and equipped with light hydrants along the length, then - subsurface pipelines with hydrants. Hydrants are joined by polyethylene (or kapron) hoses, diameter is 150-200 mm, diameter of outlet, placed every 60 cm (row spacing), is 10-15 mm. Diameters of the hoses and slopes are selected to provide rate of water flow in the head of hose, under maximum irrigation stream, equal to 0,8-1,5 m/sec. Irrigation streams in outlets of the hose are regulated in the head of hose (by hydrant).
In each ditch there are four hoses, length is 150-200 m. Discharge of ditch is 150-200 l/sec, of one hose - 37-50 l/sec. Area of one watering is 8-12 ha for each ditch.
Results:
Analysis and generalization of the results of studies on use of lands with middle- and strongly- subsident soils allowed to make the following conclusions:
- physical and mechanical characteristics of irrigated lands are changed within the depth of moistening during land development. Porosity falls down to 42-48%, relative subsidence decreases to 0,01, density of dry soil increases up to 1,50-1,56 g/cm3. Permeability coefficient is 0,06-0,1 m/day;
- duration of intensive subsident deformations under irrigation is 3-5 years. Under similar soil conditions the less period of subsident deformations is observed in well graded areas, which have small slopes (less than 0,008), with well permeable soils;
- soil permeability decreased, mostly in first 3-4 years, by 4-5 times;
- for loess loam of light and middle texture the following elements of furrow irrigation technique are proposed: at the initial stage of development for 0,01-0,03 slope length of furrow is 70-80m, irrigation stream is 0,125-0,15 l/sec. In 3-4 years, when water-physical characteristics of soil are stabilized, length of furrow is 100-120 m, irrigation stream is 0,15-0,20 l/sec. For above elements coefficient of moistening uniformity along the furrows is 0,85-0,9. This can be achieved when a ratio of duration of watering to time required for irrigation stream to reach the end of furrow is not less than 4-6. Per cent of water releases from the end of furrow is 8,5-25%. Efficiency of irrigation is 0,69.
- average long-term productivity of cotton was 3,18 t/ha, that is 0,77 t/ha more than in control plot. Land use efficiency was 0,074 more and accounted fore 0,975. Irrigation water saving as compared with control plot was 1200 m3/ha. Thus, the profit accounted for 94,4 rouble/ha (in prices of 1984). Specific irrigation expenditures were 367 rouble/ha (in prices of 1984). Annual economic effect from irrigation, taking into account additional net area irrigated by saved water, was 559 rouble/ha.
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