Summary of research project: |
Objective and technical fields:
Water use improvement through optimization of irrigation schedule and determination of cotton water requirements. Determine for soil-climatic conditions of the Gissar valley an optimal calculated layer for cotton cultivation under accelerated method of soil moisture measurement. Irrigation scheduling and irrigated lands productivity increase under conditions of water and other resources deficit.
Scientific and technical approach:
Study of the dynamics of soil moisture, irrigation schedule, crop requirements, water balance’s elements and cotton productivity based on field experiments. Importance of the study consist in improvement of crop requirements planning and management, increase of cotton productivity and development of scientifically grounded recommendations on irrigation scheduling.
Environment characteristics:
The plot is located in Gissar valley, 850-900 m above sea level. Climate is sharply continental. Maximum air temperature is 43-44 oC (in July), minimum is -24-30 oC. Average annual temperature is 14,1-15,1 oC, sum of positive temperatures (more than 10 oC) is 2192-2510 oC. Frost-free period is 220-240 days. Average annual relative air humidity is 46-53%, in summer - 31-42%. Annual precipitation is 560-788 mm, mainly in late autumn, winter and spring. Evaporativity varies from 1341 to 1690 mm. Average annual wind speed is 1,5-2,8 m/sec. Quantity of strong wind days (v > 15m/sec) is 5-15. There are dark gray, meadow-gray and brown-calcareous soils. The valley is divided by ravines and river systems. Plain part contains thick layer of alluvial-proluvial deposits followed by conglomerates and sandstone. In 1960 and 1964-66 experiments were conducted in dark gray soils with deep groundwater’s level (4,5 -5 m). Slope of the plot from the South to the North is 0,012-0,015. Top field water capacity in 0-70 cm is, on the average, 23,6% of absolutely dry soil weight, in 0-100 cm - 23,4%, volume mass is 1,37 and 1,39 g/cm3 respectively. In 1961-63 studies were conducted in gray-meadow soils with shallow ground waters level (1,5-3 m). Top field water capacity in 0-70 cm and in 0-100 cm is 23,1 and 23,4% respectively. Source of irrigation is Big Gissar Canal (BHC), salinity of water is no more than 0,7 g/l. Water store under top field water capacity at the depth of 0-100 cm is 2892 m3/ha, wilting percentage is 6,8%, soil porosity is 47,8%. Soil texture: semi-loam.
Parameters of Pilot Projects and Technical Solutions:
Irrigated area of the pilot plot is 2 ha. The plot consists of 20 lots. Area of each lot is 192-461 m2. Scheme of crop spacing is 60x14x1. Land use efficiency is 0,90. Water is supplied through furrows from open earthen network. Efficiency of canals is 0,88-0,92. Length of irrigation furrow is 100-120 m. Irrigation dates, depths and norms were determined according to irrigation schedules, which were dependent on calculated layer.
Methodology:
Field studies and observations of irrigation schedule, water balance’s elements, cotton growth, development and productivity. Different calculated layers were studied for irrigation timing ( 70-100-70 (control), 70-70-70, 50-50-50 cm) and determination of irrigation norms (70, 100, 130 cm). The methods for soil moisture measurement were studied as well. Preirrigation soil moisture was 65% before flowering, 70% during flowering-fruit formation, 65% during maturity. Observations were conducted according to SoyuzNIKHI (1961) methods. The pilot plot was equipped with meters to keep regular observations. Irrigation water was accounted by Cipolletti weir with 12,5 and 25 cm sills. Systems analysis of obtained data, mathematical processing and technical and economic justifications were made.
Results:
While optimazing cotton irrigation schedule, change of a size of calculated layer causes corresponding changes in the parameters of irrigation schedule.
Thus, experiments (1961) in the control (1st alternative) included 5 waterings according to the scheme 1-3-1, in 2nd alternative - 6 waterings according to the scheme 1-4-1 and in 3rd alternative - 7 waterings according to the scheme 1-5-1. For the control irrigation intervals were 19-29 days, for 2nd alternative - 14-19 days, for 3rd alternative - 10-18 days. Average duration of watering was 41,0; 31,4 and 27,9 hours respectively. Water release varied from 4,5 to 36% of irrigation depth. Actual irrigation norm accounted for 5870 m3/ha in the control, 4859 m3/ha in 2nd alternative, i.e. 1011 m3/ha less than in the control. The same regularities were obtained in other years. 7 years (1960-66) of studies showed the following results.
In massive, homogeneous, slightly flaky soils cotton roots extend to the depth of more than 2 m. However, the main mass of active roots is located in upper fertile layers. At the depth of 0-30 cm roots accounts for 50-61% of their total amount, in 0-70 cm - 75-85%. Accordingly, the main amount of water is extracted from 0-70 cm. When ground waters are deeply bedded (4,5-5 m), water discharge is 80-90% of total one from 0-100 cm. Water discharge from 100-150 cm is low and accounts for 3-4% of total crop requirement. Under mentioned conditions, 0-100 cm of soil layer are over-watered under watering depth of 1000-1100 m3/ha. More effective waterings are done with decreased depths under 0-70 cm calculated layer, which provide normal water supply to the plants while saving irrigation water.
Decrease of calculated layer during watering to 70 cm does not considerably affect the quantity of waterings (for 7 years number of waterings was increased , on the average, on 0,3), but allows to reduce substantially irrigation water expenditures. Water saving, as compared with above mentioned calculation of irrigation depths connected with moistening of 100 cm, accounts for 1100 m3/ha or 20%.
Influence of waterings, under decreased to 70 cm calculated layer, on crop productivity within experimental years is different. For 7 years there were, on the average, additional 0,08 t/ha of a yield. Decrease of calculated layer to 70 cm promoted acceleration of maturity and increase in yield of first harvesting in all experimental years. For 7 years in this alternative yield of first harvesting was higher, on the average, on 0,37 t/ha, in some years (1960, 1963, 1966) - on 0,52-0,81 t/ha. While decreasing calculated layer, pre-freezing yield increased accordingly on 0,31 t/ha, in some years (1960, 1963) - on 0,36-1,05 t/ha.
Reduction of irrigation norm, while decreasing calculated layer, is explained by saving and productive use of water by plants from root zone and better use of soil water from lower horizons. This is confirmed by water balance of the cotton field and the values of water requirements coefficients, which are lower (1180 m3/t) in alternatives with 70 cm calculation layer.
Total crop requirements is also changed depending on a value of calculated layer. In experiments a value of total crop requirements was 6352 m3/ha under 0-70 cm calculated layer, 7377 m3/ha under 0-100 cm layer. Reduction of crop requirements, while decreasing calculated layer to 0-70 cm, accounted for, as compared with 0-100 cm layer, 14,4%.
There is relationship between the yield of raw cotton and total crop requirements, which is established. Yield of raw cotton increases from 4,2 to 5,86 t/ha while raising total crop requirements from 5,6 to 7,3 Th. m3/ha. Further rise does not lead to increase of the yield. Relationship is parabolic.
In order to calculate total water requirements of cotton bioclimatic and biophysical coefficients were determined. In optimal alternative (0-70 cm) biophysical and bioclimatic coefficients were equal to 1,51 and 0,75 respectively.
Further increase of calculated layer up to 130 cm is characterized by greater increase of irrigation water and reduction of total and pre- freezing yield of raw cotton.
Watering according to the moisture of 0-50 cm soil layer by the depths, calculated for moistening of 0-70 cm layer, gives the results similar with alternatives, where dates and irrigation depths were determined under 0-70 cm layer.
Due to higher yield of first and pre- freezing harvesting and increase of raw cotton variety state, watering by reduced depths under 0-70 cm calculated layer provided additional 47,88-68,18 roubles per hectare. Additional income from irrigation water saving was not included.
Production testing of irrigation timing according to the moisture of 0-70 cm layer showed high efficiency.
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