Summary of research project: |
Objective and technical fields:
Improvement of water use through optimization of the irrigation regime and determination of maize water requirements.
Objectives: elaboration and optimization of the irrigation regime for maize guaranteeing maximum and good yield and high efficiency of water and land resources use under the conditions of the third irrigation module region. Control of maize irrigation regimes and raising the productivity of irrigated lands under the conditions of the deficiency of water and other resources.
Scientific and technical approach:
Study of the irrigation regime, water consumption, water balance and productivity of maize on the basis of field studies. Studies included improvement of water use planning and management, and scientifically grounded recommendations on the irrigation regime of maize and raising the productivity of irrigated lands.
Environment characteristics:
The collective farm is situated in Vakhsh valley at the height of 329-445 m above sea level. Duration of the warm period is 250-310 days. Sum of positive temperatures (above +10oC) is 4500-5800oC. Maximum temperature reaches 46-47oC. Annual precipitation is 143-297 mm, precipitation for the period from April to September is 45-77 mm. Relative air humidity is 47,0-56,0%, it decreases down to 22% for the period from July to August. Annual evaporativity is 1469-1950 mm. Average annual wind speed is 1,2-2,1 m/sec. The territory of Vakhsh valley is divided into 6 terraces. The third terrace where the experimental plot is situated has been the main area of cultivation and irrigation since ancient times. Its widths reaches 18-20 km. Concerning microrelief the territory of the plot is a plain. Topsoils are mostly old-irrigated bright gray soils. Soils are attributed to middle loam. Volume weight in 0-200 cm soil layer is 1,30-1,48 g/cm3, specific weight is 2,60-2,65 g/cm3, soil porosity is 43,3-50%. The least moisture capacity is 22,4% in 0-70 soil layer and 22% in 0-100 cm soil layer. Soil permeability is 1,0 cm per 6 hours. Inclination is 0,005-0,025. Depth of water table is big. The source of irrigation is Vakhsh canal, water salinity is 0,24-0,27 g/l of sulphate-hydrocarbonate-calcium type.
Parameters of Pilot Projects and Technical Solutions:
The area of the experimental plot was 2,0 ha. Area of introduction was 6580 ha. Land use efficiency was 0,90-0,93. Irrigation network was made of concrete flumes, its efficiency was 0,85-0,92. Technical state was satisfactory. Specific length was 55 m/ha. Irrigation was made through furrows 100-120 m long. Irrigation was made according to preirrigation soil moisture.
Methodology:
Field studies on soil moisture regime, irrigation scheduling and norms, incomes and expenditures of the water balance, ground waters, crop water requirements for the growing season, maize growth, development and productivity. The plot was provided with measuring and accounting equipment. Phenological and biometrical observations were made using the methods of VNIIK (1980) and SoyuzNIKHI (1973). Systems, sequential and complex analyses of results were used. For optimization of the irrigation regime for UZPSK-704 (1983-1985) and VIR-156TV (1986-1988) maize hybrids the following irrigation variants were compared: 1 - water gifts were made according to recommendations (control); 2, 3, 4 - water gifts were made according to soil moisture - 70-70-70; 70-80-70; 80-80-70% of the normal soil moisture.
Results:
Every year vegetative irrigation was made with the water storage irrigation, its depth was 1300-1500 m3/ha. It was discovered that if preirrigation soil moisture was increased, number of water gifts and irrigation norm for maize increased, too, average depth of irrigation decreased. In the control variant on the average for the years of studies 5 water gifts were made with the irrigation norm of 4609 m3/ha (UZPSK-704) and 4416 m3/ha (VIR-156 TV). Soil moisture before irrigation decreased down to 50-51% of the normal soil moisture. In other variants number of water gifts varied from 7 to 10, depth of irrigation was 597-922 m3/ha and the irrigation norm was 4416-6335 m3/ha. Under experimental conditions the difference between the irrigation norm of a net and gross field was 1,29-1,33 times. Surface release was 7-17%, deep discharge was 9-20%, evaporation was assumed as 10% of the depth of irrigation.
For prediction of the irrigation scheduling for maize the relation between soil moisture and concentration of leaf cellular sap was found:
Y= - 0,131 X + 16 , where Y is concentration of leaf cellular sap (%, dry substance) and X is soil moisture (%).
It was found that at the panicle emergence stage the depth of root penetration reached 120 cm under irrigation according to low soil moisture and 90 cm under irrigation according to high soil moisture. At the stage of full ripeness the depth of root penetration was 170 cm under irrigation according to low moisture and 120 cm under irrigation according to high (80-80-70) soil moisture. Air-dried root mass increased up to 156 g/plant (UZPSK-704 maize hybrid) and up to 126,7 g/plant (VIR-156 TV maize hybrid). Depending on irrigation regimes stalk height at the stage of full grain ripeness was 241-341 cm (UZPSK-704 hybrid) and 190-272 cm (VIR-156 TV hybrid). Leaf area varied from 33,2 to 63,3 th. m2/ha (UZPSK-704 hybrid) and from 24,8 to 53,1 th. m2/ha (VIR-156 TV hybrid). Dry biomass was 14,75-26,83 t/ha (UZPSK-704) and 12,95-22,50 t/ha (VIR-156 TV). Grain percentage in a dry biomass was 43,7-39,2% (UZPSK-704 hybrid) and 40,0-33,1% (VIR-156 TV hybrid). Duration of the period from sprouting to full grain ripeness was 113-118 days for UZPSK-704 hybrid with the required sum of positive temperatures equal to 1627-1718oC, and 100-105 days for VIR-156 TV hybrid with the required sum of positive temperatures equal to 1532-16290C. Average density of plants was 53,5 th./ha. Weight of grain in a corn-cob was 120-196 g (UZPSK-704) and 122-168 g (VIR-156 TV). It was discovered that for growing of UZPSK-704 maize hybrid irrigation according to soil moisture (70-80-70% of the normal soil moisture) is the best. In this case 9 water gifts were necessary with the irrigation norm of 6003-6343 m3/ha. Under this regime the yield was maximum (10,35 t/ha). For VIR-156 TV maize hybrid this regime (70-80-70% of the normal soil moisture) was optimal. With optimal water supply the grain yield of VIR-156 TV hybrid was 7,59 t/ha.
Study of the total water requirements with a water balance method showed that the main balance income was the irrigation norm: it was 72,5-89,9% for UZPSK-704 hybrid and 87,4% (average) for VIR-156 TV hybrid. Percentage of moisture used from soil stock in 0-200 cm layer was on the average 12% (UZPSK-704) and 8,2% (VIR-156 TV), the rest part of a water balance included precipitation. Depending on the preirrigation soil moisture total water requirements varied from 6289 to 7993 m3/ha (UZSPK-704) and from 5280 to 7160 m3/ha (VIR-156 TV).
The relation between yield of grain and total water requirements was found. If yield of grain increased from 6,25 to 10,75 t/ha, total water requirements increased from 6,45 to 7,6 th. m3/ha, i.e. yield of grain increased by 1,72 times while total water requirements increased only by 17,8%. This relation was expressed by the parabola equation for UZPSK-704 hybrid. Correlative relation was 0,98-0,05. For VIR-156 TV relation between grain yield and water requirements was linear with the correlative coefficient r = 0,79-0,14. If yield increased from 45,1 to 77,0 t/ha, total water requirements increased from 5180 to 7200 m3/ha. For calculation of the total water requirements biophysical and biological coefficients were specified. Biophysical coefficient was 2,38 m3 per 1oC for UZSPK-704 hybrid and 2,44 m3 for VIR-156 TV hybrid. Biological coefficient was 3,16 m3/1 mb for UZSPK-704 hybrid and 3,11 m3/1 mb for VIR-156 TV. Using the optimal irrigation regime for UZSPK-704 hybrid guarantees net profit of 479,5 ruble/ha (prices of 1988) with profitability of 72,8%. Using the optimal irrigation regime for VIR-156 TV hybrid guarantees net profit of 229,9 ruble/ha (prices of 1988) with profitability of 38,0%.
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