Summary of research project: |
Objective and technical fields:
Increase of irrigated hectare productivity within the system of all-the-year-round land use. To determine an optimal irrigation schedule for fine-fiber cotton, which provide high and qualitative yields of raw cotton (first sort of fiber) at minimum irrigation water expenditures, in connection with irrigation schedule of intermediate crops.
Scientific and technical approach:
On the base of existed theories and irrigation scheduling practices develop the most optimal irrigation schedule for fine-fiber cotton and examine effect of this regime parameters on qualitative and quantitative changes in crop productivity, saving of irrigation water, labor and equipment during cotton cultivation.
Environment characteristics:
The plot is located in the southern-west part of the Vakhsh valley. There are five terraces, characterized by flat and mountainous relief. Direction of the general slope of land surface is southern. Climate is characterized by sharp fluctuations in air temperature during the daytime, low relative air humidity in summer, plenty of radiation, low precipitation (294 mm/year). Average monthly air temperature in coldest month (January) is 0,5-0,9 oC, in warmest one (July) is 28,3-29,0 oC, absolute minimum temperature is -25...-26 oC, absolute maximum temperature is 46-47 oC, average annual temperature is 15,7-15,6 oC. Frost-free period is 190-235 days. Total sum of positive temperatures (more than 10 oC) is more than 4200 oC. Average annual relative air humidity is 36-50%. Average annual wind speed is 0,8-1,9 m/sec. There are 54,8% of old irrigated light gray soils, 24,8% of gray-meadow ones and 20,4% -other types. Consistency of top 2 m is 2,61 t/m3, volume mass is 1,24-1,34 t/m3. 0-100 cm of soils are non-salinized. Minimum moisture capacity of 1m layer is 22,01% of dry soil mass, maximum hygroscopicity is 3,31%. Permeability of 1 m layer for the first hour of watering is 362 m3/ha. Ground waters are deeply bedded (they are not found on the depth of 12,5 m). Slopes of the surface are mainly 0,01-0,03, rarely 0,003-0,007. Source of irrigation is the Vakhsh river, salinity of water is not more than 0,5 g/l.
Parameters of Pilot Projects and Technical Solutions:
Irrigated area of the pilot plot is 4 ha (net). The main cultivated crop is fine-fiber cotton, intermediate crops are barley and perko. Water is supplied through furrows from open earthen network, the length of irrigated furrow is 130 m. Water flows are released through an open spillway. Water turbidity varies within 5-0,5 g/l. Water discharge on the plot accounted for 25-30 l/sec, initial irrigation stream was 0,15 l/sec, changed one - 0,005 l/sec.
Methodology:
Field studies were conducted according to SoyuzNIKHI methods. Area of each plot with one-stage layout under four-times repetition was 624 m2 . Field studies on influence of initial soil moisture on evapotranspiration and productivity of fine-fiber cotton were conducted for five alternative irrigation schedules at the following calculation layers: 70 cm - during the phases before flowering and maturity, 100 cm - from flowering till fruit formation. 1st alternative - establishing the dates and depths of irrigation during growing period according to existed recommendations; 2nd - establishing the dates and depths of irrigation during growing period under soil moisture decrease to 60%; 3rd - establishing the dates and depths of irrigation during growing period under soil moisture decrease to 70% from germination till fruit formation, during maturity 60%; 4th - establishing the dates and depths of irrigation during growing period under soil moisture decrease to 70% from germination till flowering, to 80% from flowering till fruit formation and 60% during maturity; 5th - establishing the dates of irrigation according to integral discharge rating curve (DRC) recommended by K.D. Domullokhodzjanov. In all alternatives tillage, weed control, plants feeding with fertilizers were carried out according to adopted technological scheme for cotton cultivation.
Cotton was sowed after harvesting of intermediate crops.
Duty of water and its release in plots were accounted by volumetric method and by weirs. Soil moisture was determined by thermostat-balanced method with neutron moisture meter and by ohmic method (with tensiometers). Before watering moisture was measured three times at the depth of 1,5 m, each ten days up to the depth of 3 m.
While conducting field studies on 20 plots the following tasks were solved: 1 - study of natural and reclamation conditions of the plot; 2 - development of an optimal irrigation schedule for fine-fiber cotton under all-the-year-round land use and determination of its influence on growth, development and productivity of cotton; 3- determination of water balance’s components for cotton field; 4 - identification of relationships between evapotranspiration and meteorological factors; 5 - determination of cost-effectiveness of an optimal irrigation schedule for fine-fiber cotton.
Results:
Generalization of long-term studies showed, that during cotton cultivation the most important factor influencing the yield formation is moisture of active layer. Under conditions of all-the-year-round land use, due to harvesting of intermediate crops sowing of cotton is delayed on 10-15 days from an usual one. The late watering of intermediate crops forms uniform moistening of a field and provides uniform germination. Therefore, the date of first watering is delayed on 10-15 days and leads to water saving.
The most optimal alternative is to irrigate cotton when the soil moisture is 70-70-60%. There were 11 waterings for this alternative: by three waterings from germination till the beginning of flowering and maturity, depth of irrigation was 770 m3/ha; five waterings from flowering till maturity, depth of irrigation was 1230 m3/ha, i.e. the scheme of irrigation was 3-5-3. Irrigation norm accounted for 10,6 Th.m3/ha, evapotranspiration was 10,8 Th.m3/ha. Average monthly biophysical coefficients of cotton evapotranspiration (water discharge per 1oC of average daily temperature, m3/ha) accounted for 0,91 m3/ha/oC in May, 3,48 m3/ha/oC in July, 1,46 m3/ha/oC in October. Bioclimatic coefficients of cotton evapotranspiration (water discharge per 1 Mb of average daily deficit of air humidity, m3/ha) accounted for 0,77 , 4,63 and 1,75 m3/ha/Mb respectively. Biological coefficient for irrigation period, on the average, is equal to 2,18 m3/ha/Mb.
It was determined, that there are close exponential relationships between 10-day evapotranspiration of fine-fiber cotton (E10-day) and sum of average daily air temperatures for 10-day period (T10-day), sum of average daily deficit of air humidity (D10-day):
E10-day = 2,266 * 0,001 T10-day^2,202
E10-day = 0,407 * D10-day^1,288
Implementation of the optimal irrigation schedule (70-70-60%) provided 4,268 +0,05 t/ha of row cotton, that is 0,93 t/ha more than in control. Specific irrigation water expenditures accounted for 2500 m3/t, that is 15% less as compared with control.
Cost-effectiveness of the optimal irrigation schedule implementation was 787 roubles/ha (in prices of 1984).
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