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Objective and technical fields:
Reduction of field water losses, raising the labor productivity under furrow irrigation and raising cotton yield on the lands with high inclination (more than 0,01).
Objective: Elaboration of the furrow irrigation technology for cotton from subsurface irrigation network with flexible irrigation pipelines of small diameter guaranteeing differential irrigation by through furrows depending on the degree of their roughness and compaction.
Scientific and technical approach:
Perfection of the technology of irrigation from the network of flexible irrigation pipelines with due regard for the technology of cotton growing and change of water-physical properties of furrow soil on the lands with high inclination. Experiment includes selection of optimal elements of the technology of through furrow irrigation taking into account types of furrows guaranteeing uniform moistening of the field and reduction of water losses for surface release.
Environment characteristics:
Climate is continental. Average annual temperature is 16,9 0C, in July it is +29oC. Annual precipitation is 650-700 mm. Relative air humidity is 48%, evaporativity is 1854 mm per year. Relief is slightly corrugated, predominating inclination is 0,01-0,02, maximum inclination is 0,05-0,06.
Soils are mostly loess and loess-like loam 25-30 m sick.
Soils are cinnamon-colored - calcareous, heavy loam. For 0-100 cm soil layer minimum moisture capacity is 24,5%, porosity is 45,8%, density is 1,3-1,5 g/cm3, soils are non-salinized. Depth of water table is more than 3 m, salinity of ground waters is less than 1 g/l. Average inclination in the direction of irrigation is 0,03-0,02. Irrigation water is given from Baypazin reservoir on the Vakhsh river, turbidity is almost zero, salinity is less than 0,5 g/l.
From the canals water is given to the fields by the system of subsurface pipelines. From pipelines water is distributed among irrigation furrows by hydrants through irrigation hoses. Hoses of large diameter (250-300 mm) with big watering outlets are used, which cause large water releases and soil erosion. For this reason and in connection with the fact that tail escapes do not operate, banks of the Yavansu river are fell, which make lands unusable.
Parameters of Pilot Projects and Technical Solutions:
Area of the experimental plot: gross area was 120 ha, net area was 110 ha. On the whole territory cotton was grown with 0,6 m row-spacing. Subsurface self-head irrigation network was used made of asbestos-cement pipes (diameter - 400 m) 1,5-2,5 km long. Pressure was 2-3 m in the head, 40-50 cm in the tail of the system, distance between pipelines was 400 m, hydrants were installed each 120 m. Efficiency of the subsurface network was 0,9-0,95. Technical condition was good. For irrigation flexible kapron pipelines with the diameter of 200-150 mm were used, irrigation outlets with the diameter of 10 mm were made each 1,2 m in pipelines of 150 mm diameter and each 0,6 m in the pipelines of 200 mm diameter. Complete set of irrigation equipment included 4 pipelines 205 m long each, 2 pipelines of 150 mm diameter and 2 pipelines of 200 mm diameter. Simultaneous irrigation was made on the area of 9,6 ha. Irrigation pipelines were installed with inclination of 0,003.
Methodology:
During inter-row cotton cultivation furrows compacted by tractor and not compacted (friable) are formed which alternate in succession. Furrows of different compaction and roughness with 0,6 m row-spacing, formed during inter-row cultivation on the lands with high inclination significantly influence velocity and movement of jets in furrows, i.e. while in some furrows jets are only reaching the end of furrows, in other furrows water is already being released.
The most simple measure for reduction of water release under furrow irrigation is provision of free water flow from upper to lower furrows. In this case only water released from furrows in the end of the field is lost.
Free flow of released water from upper to lower furrows is possible during water supply to furrows from subsurface and surface irrigation pipelines. Under this water supply the length of through furrows can be 400-800 m equal to optimal length of tractor bout.
Therefore three variants of irrigation technologies are possible: 1) irrigation through friable furrows; 2) irrigation through compacted furrows; 3) irrigation through all furrows. According to the calculation method the elements of furrow irrigation technology for 3 irrigation variants were determined.
On the experimental plot irrigation was made with due regard for the degree of furrow compaction and their specific absorption after preliminary study of the reaching of erosion-safe irrigation jets along a dry furrow and analysis of these data. In experimental variants irrigation was made through furrows 480 m long, simultaneously from 4 levels, irrigation front was 200 m.
Flow rate of irrigation jets was 0,15 l/sec., working head was equal to 2-3 diameters of an irrigation pipeline.
Results of theoretical investigations and processing of data obtained during field studies were the basis for testing the technology of differential through furrow irrigation of cotton, which included: maximum-non-eroding irrigation jet, furrow length during the reaching period, furrow length during the period of additional moistening, duration of irrigation jet reaching, duration of additional moistening, duration of water gift and optimal technologies for each water gift including operation of hydrants and irrigation pipelines.
On the basis of study of absorption and irrigation jet reaching in furrows of different degree of roughness the optimal variant was chose for each water gift providing maximum irrigation technique efficiency and uniform moistening.
Determination of water-physical properties of soil, hydraulic studies, study of the elements of an irrigation technique and irrigation regime and biometric investigations were carried out using common methods and recommendations. Agronomic practices of cotton growing were used according to recommendations of Agricultural Ministry of the Republic. Data were processed by the methods of mathematical statistics.
Systems analysis of obtained results was used.
Results:
For irrigation according to determined variant irrigation technologies for through furrow irrigation for each water gift were made. The first water gift was made in spaces between rows through furrows compacted by tractor wheels, other water gifts were made through all types of furrows, water from odd pipelines was given to each furrow, water from even pipelines was given only to friable furrows. Irrigation was made simultaneously from 4 levels of pipelines in through furrows 480 m long. For reduction of surface release in the period of additional moistening some of the pipelines were turned off and released water from upper levels was used in lower levels.
Experimental variant of irrigation was compared with 2 control variants. The following control variants were used: irrigation by interrupted jet (base control) and existing irrigation technology (farm control).
In control variants the first water gift was made through friable furrows, other water gifts were made through all furrows. Furrows were 120 m long. Average flow rate of irrigation jets was 0,15 l/sec.
In the experimental and «base control» variants 6 water gifts were made with irrigation interval equal to 13-22 days; in the variant «farm control» 4 water gifts were made with irrigation interval equal to 22-23 days.
Duration of each water gift in the «base control» variant was the same as in the experimental variant equal to 24-60 hours, in the «farm control» variant it was 2-4 days.
In the experimental variant irrigation norm was 7066 m3/ha including 1166 m3/ha (16,5%) for surface release; in the control variants irrigation norm was 8491 m3/ha and 12279 m3/ha including 2338 m3/ha (27,5%) and 4235 m3/ha (34,5%) for surface release. Irrigation norm on the experimental plot was 20% less than on «base control» plot and 74% less than on «farm control» plot. Using the technology of through furrows resulted in reduction of surface release by 2 times comparing with irrigation by interrupted jet and by 3,63 times comparing with the «farm control» variant.
Together with study of water use in the field turbidity of released water was measured. According to measurements, 7,8 t of melkozem was removed from each hectare of the experimental plot. This value was 10,5 t/ha for the «base control» plot and 37 t/ha for the «farm control» plot. Thus, during through furrow irrigation and irrigation by interrupted jet soil erosion for the growing season did not exceed recommended permissible limits (10-12 t/ha).
Results of data processing showed that variability of depth of irrigation along a through furrow estimated by variation coefficient was 7-12% which proved good uniformity of field moistening, actual coefficient of moistening uniformity was 0,85-0,90.
Cotton yield in the first variant was 3,08 t/ha and the difference was 0,08 t/ha comparing with the «base control» variant and 0,39 comparing with the «farm control» variant. Minimum significant difference in yield was 0,24 t/ha. Difference in yield between the experimental and «farm control» variants was significant, difference in yield between the experimental and «base control» variants was not significant, i.e. they were equivalent.
Labor expenditures of irrigators for the growing season on the experimental plot were 24% less than on the «base control» plot and 13% less than on the «farm control» plot.
Annual profitability (in prices of 1984) was 394 ruble/ha comparing with the «farm control» variant and 102 ruble/ha comparing with the «base control» variant.
Profitability of the proposed technology was achieved by increased land use efficiency, reduced labor expenditures, decreased diameters of irrigation hoses, reduced water losses and raised cotton yield.
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