Summary of research project: |
Objective and technical fields:
Determination of optimal elements of the furrow irrigation technique for cotton with deep volume loosening of compacted gray soils.
Objectives: improvement of water use and control of soil water regime, raising the productivity of irrigated lands with deep volume loosening through selection of irrigation jets and furrow length guaranteeing uniformity of field moistening and reduction of water losses
Scientific and technical approach:
Study of movement and moistening of soil profile along the length of an irrigation furrow, variation of soil permeability in the different years after deep loosening. Elaboration of water-reclamation and technological recommendations on raising the productivity of irrigated lands, irrigation water and water saving.
Environment characteristics:
Climate is continental. Amplitude of temperature is 40-50oC. Annual precipitation is 680 mm. Sum of positive temperatures equal to 4100-3200 0Ñ and long frost-free period (220-230 days) allow to grow various crops.
In Yavan valley hydrogeological conditions determine many of soil properties (degree and nature of salinity, moisture saturation etc.). They determine meliorative measures as well.
Practically all cultivated soils in Yavan valley are compacted. Small pores (3-5 mmk) predominate (24-28%), pores measuring less than 3 mkm are 18-20% (this determines unproductive soil moisture content). Coefficient of permeability at the depth of 0-3,0 m is 0,2-0,4 m/day, it decreases as a result of various artificial compaction (including irrigation compaction) - soils become unproductive with poor permeability.
Parameters of Pilot Projects and Technical Solutions:
Area of the experimental plot is 15 ha. Average inclination in the direction of irrigation is 0,015, grown crop is cotton. The plot is 400 m wide and 375 m long. Soils are dark gray, heavy loam. At the depth of 30 cm from the surface there is a compacted layer with poor permeability 10-20 cm sick which prevents normal moistening of soil profile at the studied depth (0,7-1,0 m), extends the duration of irrigation, increases surface release and irrigation erosion. For elimination of these negative effects in autumn of the previous year on 3/4 part of the experimental plot deep volume loosening had been made without turning over a furrow layer for the depth of 0,6 m; on the rest part of the plot usual ploughing had been made at the depth of 25-30 cm. After that for 3 years usual ploughing was made on the whole area of the plot.
Water was given to the plot from the subsurface irrigation network. Distance between subsurface pipes was 400 m, they were laid along the borders of the plot; distance between hydrants-outlets was 125 m or 3 hydrants for the plot. Irrigation was made by flexible kapron pipelines of 250 mm diameter from 3 levels. Width of irrigation front was 100 m and the plot was divided into 4 parts 100 m wide, length of each level was 125 m. For collection and release of surface water an open ditch was made at the end of each level. Irrigation was longitudinal, on the maximum inclination.
Source of irrigation was the Vakhsh river, water salinity was 0,7 g/l, water turbidity was 0,5-1,5 g/l.
In spring before cotton sowing the plot was leveled and harrowing was made. Cotton was sown by usual sowers with row-spacing equal to 0,6 m.
Methodology:
Objectives and tasks of field and laboratorial studies were determined. Elements of the furrow irrigation technique with deep volume loosening were determined on the basis of natural observations over irrigation, moisture flow in soil, water filtration and surface release. For study of moisture flow in soil and moisture absorption the plot was divided into 3 levels each 125 m long, each level was divided into 4 sections 100 m wide. Thus, the experiment included 4 variants of 3 repetitions, in each repetition there were 4 even furrows. In the first variant (control, without loosening) irrigation jet flow rate was recommended equal to 0,12 l/sec; in the second variant (with loosening) irrigation jet flow rate was 0,12 l/sec.; in the third variant (with loosening) irrigation jet flow rate was 0,25 l/sec.; and in the forth variant (with loosening) irrigation jet flow rate was 0,35 l/sec.. Irrigation schedule was determined on reduction of soil moisture to 70% of minimum moisture in 70 cm layer during the stages before blooming and ripening and in 100 cm layer in the stage of blooming-fruit formation; depth of irrigation was determined on restoration of moisture up to 100% of minimum soil moisture in the studied layers. Moisture was determined with the thermostat-weight method. Flow of irrigation jets was registered each 2 hours after beginning of irrigation.
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. Duration of experiments was 4 years.
Results:
Volume loosening on irrigated lands increased soil porosity, accumulation of precipitation and additional moisture accumulation in soil. Coefficient of permeability rose by 2-3 times. Effect of deep loosening remained for 3 years with gradual decrease of filtration and permeability of soil. In the year of loosening effect water content increased by almost 2 times, first water gift of cotton was made 15-17 days later, irrigation intervals extended by 1-3 days. Gross irrigation norm in the year of loosening reduced by 44%, in the second year it reduced by 30%. Analysis of water flow in a furrow showed that irrigation jet (0,12 l/sec, variant 2) recommended for usual soil treatment with deep loosening reached the end of a furrow in 30-28 hours exceeding control variant by 2,3-3,0 times in the first year after loosening, in 20-22 hours in the second year, in 10-12 hours in the third year, which was equal to the control variant. Duration of the reaching of irrigation jets in the third variant (irrigation jet with flow rate of 0,25 l/sec) was 8-10 hours in the first year after loosening, 4-5 hours in the second year and 2-3 hours in the third year. Duration of the reaching of irrigation jets in the fourth variant was 5-6 hours in the first year after loosening, 3-4 hours in the second year and 1,5-2,0 hours in the third year.
Irrigation efficiency in the control variant (without loosening) was 0,57-0,59. Water losses were the following: 40-47% for infiltration, 26% for surface release and 10% for evaporation. Optimal variant with loosening was irrigation jet with 0,25 l/sec. flow rate, its efficiency was 0,6-0,81, tail release decreased by 1,4-2,5 times, losses for evaporation decreased by 4-7 times. At the same time deep release increased by 1,5-3,0 times. Irrigation erosion decreased by 3-4 times on the average for 2 years after loosening. Cotton yield increased by 25% in a year after loosening, by 7% in the second year and in the third year it was the same as in the control variant.
During irrigation in the fourth variant (irrigation jet with 0,35 l/sec. flow rate) intensive erosion of soil and increased surface release took place. Efficiency of this variant was 0,56-0,62. Efficiency of the second variant because of water infiltration was low (0,35-0,41).
Uniformity of moistening was 0,7-0,8 in the control variant, 0,4-0,5 in the second variant, 0,7-0,8 in the third variant and up to 0,9-0,95 in the fourth variant.
Calculated net depth of irrigation was 800-1000 m3/ha, gross depth of irrigation was: 1450-1820 m3/ha in the control variant, 2300-2900 m3/ha in the second variant, 1200-1400 m3/ha in the third variant and 1450-1820 m3/ha in the fourth variant.
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