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Objective and technical fields:
Drip irrigation method productive test, measuring regularity of soil moistening, infiltration water losses, water productive use, irrigation efficiency, land use efficiency. Significance: Study of drip irrigation technical and technological peculiarities, efficiency of different cotton irrigation regime and recommendations’ preparation.
Scientific and technical approach:
Problem of water resources deficit can be solved by water saving technologies development and among other drip irrigation method. Study of its efficiency under Central Asian conditions is very important.
Environment characteristics:
Relief: flat alluvial plain constituted by quaternary sediments thickness with slope 0.002-0.003. Soils: light grey soil, slightly salinizated. Salinization type is sulfate-chloride; chlorine-ion content is 0.02 %. Mechanical composition shows light loam; permeability coefficient is 0.49-0.81 m/day.
Soil volumetric mass of 1 m-layer is 1.16-1.29 g/cu.cm, specific mass is 2.54-2.62 g/cu.cm, full field moisture capacity 22-24 % to soil mass, withering moisture 5-7 %. Groundwater level is 2.9-3.6 m. Humus content within 0-25 cm-layer is 0.61 %, total nitrogen – 0.05 %, phosphorus – 0.13 %, potassium – 1.82 %, C:N ratio is 7:7.
Pilot site is located within the zone of dry steppes with sharp continental climate. Average annual precipitation is 229 mm from which 167 mm coincide with November-March. Period without freezing is 220-226 days. Positive temperatures sum is 4779-5094 oC.
Parameters of Pilot Projects and Technical Solutions:
Field investigations of water discharge during irrigations along watering hoses (by volumetric method), water-supply dynamics through the system (by water-meters), pressure inside the system (by manometers). Investigation scheme was as follow: moisture before irrigation 65-65-60 % of FFMC, 70-70-60 % and 75-75-60 %. Soil moisture was determined by mecury (local) and american tenziometers and also by thermostat-weight method on selected soil samples. Study of certain agrotechnical methods of cotton growing under drip irrigation system’s (DIS) operation (soil tillage, sowing arrangement, fertilisation, harvesting) has been fulfilled. Main characteristics of a new irrigation equipment are described. Watering depth and irrigation norm by water-meters and Chipoletty weirs (furrow irrigation) were registrated.
To create better moistening the first irrigation through DIS was executed by duty 250-300 cu.m/ha and two last waterings by 50 % reduced duty. Working time of DIS and agricultural technique was registrated. Phenological observations of cotton “Yulduz” field, yield accounting and its quality identification were executed according commonly accepted methodology.
Adjacent field was taken as a control site. Its area is 10 ha and it was irrigated by furrows with all other similar to pilot site parameters. Annual fertilisation was equal for two sites: 250 kg/ha nitrogen and 180 kg/ha phosphorus.
Methodology:
Pilot site (area is 65 ha) is equipped by DIS supplied by Israeli firm “Plastro Gwat”. Set of DIS technical means consists of: pumping station, system of mains and distributive pipelines, hoses with drippers. Irrigation water was taken from the basin-setting tank (20x100x3 m) by electric pumps with capacity 180 cu.m/hour creating pressure inside pipeline 4-6.5 Ata.
Pumping station is connected with hydrocyclon, which separates sand particles (capacity 200 cu.m/hour) and 6 filters with special quartz sand which absorbs silt fractions from irrigation water.
Irrigation hoses with button-type-drippers “Katif” were connected with pipelines by special connectors and were closed at the end of furrow by plugs. Irrigation hoses diameter was 16 mm, drippers were positioned on them every 70 cm, every dripper’s productivity was 2.0-2.3 l/hour under pressure inside hose 2.5-3.0 atmospheres. Watering hoses were laid inside every second furrow (distance between furrows 90 cm). Hose demand for a ha was 5550 m.
Results:
Drip irrigation technique and technology study showed its high efficiency in Uzbekistan. DIS supplied by Israeli firm “Plastro Gwat” was reliable and effective. Annually 23-26 waterings were performed through DIS during growing period. The best on moisture regime was version 70-70-60 % of FFMC, which gave biggest yield (to 4.38 t/ha against 3.27 t/ha within the control field). The first irrigations through DIS were started at the end of June or at the beginning of July and completed at 10-15 September, irrigation interval was 3 days.
In 1993 24 waterings were performed by duty 110-160 cu.m/ha, irrigation norm under version 65-65-60 % of FFMC was 2800 cu.m/ha, version 70-70-60 % - 3110 cu.m/ha, version 75-75-60 % - 6200 cu.m/ha (5 irrigations) on the control field. Moistening regularity was rather high, pressure inside irrigation hoses was 2.9 Ata on a distance of 0-100 m from pipeline and 2.7-2.8 Ata on a distance of 100-200 m, that provided water discharge by 1 dripper 2.16-2.18 l/hour on a distance of 0-100 m and 2.12-2.13 l/hour on a distance of 100-200 m. Totally 14-15 cu.m/hour water was supplied through DIS.
Within the control field irregular moisture distribution was discovered – overmoistening at the beginning of the furrows and undermoistening at the end of the furrows. Moistening source under drippers had elliptic shape and moistening center on depth of 20-25 cm. Arround this center zones of different moistening are located. On distance of 600 cm from center moisture of 20-35 cm horizon is 17-20 %; on 90 cm within the horizon 30-60 cm moisture is 10-16 %. It is worth to notice that cotton roots develop in direction of moistening center that allows to plants to absorb water actively from the point between the furrows.
Phenological observation and yield accounting showed that the best version on cotton productivity was version 70-70-60 %, where highest yield was obtained (3.62 t/ha in 1992; 4.38 t/ha in 1993; 4.31 t/ha in 1994) against the control yield under furrow irrigation (3.29 t/ha in 1992; 3.27 t/ha in 1993; 3.36 t/ha in 1994). Analysis of cotton fibre technological quality discovered better indices (rupture tension 4.4 g/s against 4.2 g/s in control).
Balance structure shows that drip irrigation gives 42-52 % water saving.
Agrotechnical assessment has found:
a) decrease of cultivations number on 63 % (3 cultivations instead of 8) and mechanized work on 5.8 machine/hour/ha;
b) decrease of hand labour expenses on 21 % (22.5 man/day/ha instead 28.3);
c) DIS allows to regulate operatively soil calculated horizon moistening at the expense of increase or decrease of irrigation norm;
d) DIS increases nitrogen fertiliser use efficiency on 18-20 %;
e) DIS provides significant water saving under scheme 70-70-60 %: 3810 cu.m/ha in 1992, 3090 cu.m/ha in 1993 and 3420 cu.m/ha in 1994;
f) DIS contributes to cotton yield increase, which was under scheme 70-70-60 % 3.62 t/ha against 3.29 t/ha in 1992; 4.38 t/ha against 3.27 t/ha in 1993; 4.31 t/ha against 3.96 t/ha in 1994.
Drip irrigation shortages are as follows:
a) necessity of highly qualified staff;
b) dependance DIS on energy or fuel availability;
c) necessity of permanent control;
d) high cost of DIS (2.3-2.9 th.US$/ha, which returns after 4-5 years under cotton yield more than 4.0 t/ha.
World experience (USA, Israel, Australia, etc) shows DIS advantages and achievements in cotton yield (4.5-5.5 t/ha).
Investigations permitted to develop recommendations on cotton growing technology under drip irrigation in Uzbekistan.
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