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Objective and technical fields:
Productive test of drip irrigation system including infiltration water losses beneath root layer, providing irrigation water productive use, watering efficiency increase, land use efficiency raising, soil moistening regularity, high yield achievement.
Objectives: Study of technical, operational and technological particularities of drip irrigation system (DIS) for cotton irrigation and practical recommendations development on DIS operation and cotton growing under DIS.
Scientific and technical approach:
Problem of water deficit in the region can be solved by water saving technologies application. DIS could be attributed to this technology. Study of technical and technological particularities of DIS is very important for water saving and land productivity increase.
Environment characteristics:
Pilot site is located within semi-arid steppe with sharply continental climate. Frost-free period duration is 182-185 days. Sum of effective temperatures is 4300 oC per year. Mean temperature in January is –2 oC (min –34 oC), in July +26 oC (max +45 oC). Precipitation is 415 mm, including 140 mm during growing season.
Geomorphology: Alluvial plain constituted by quaternary deposits. Relief is hilly plain with 0.003-0.01 slope. Soils: meadow-grey with the spots of slightly salinizated soils. Salinity type is chloride-sulphate, chlorine-ion content is to 0.04 %. According to mechanical composition it is middle and heavy loam with permeability coefficient 0.18-0.65 m/day, on low elevation places 0.18-0.4 m/day.
Soil 1 m-layer volume mass is 1.20-1.47 g/cu.cm, specific mass is 2.67-2.69 g/cu.cm, limited field capacity is 22-24 % to soil mass; withering moisture is 5-7 % of mass.
Groundwater level depending on locality relief varies from 3 to 20 m. Water salinity is 3-15 g/l. Chemical composition is sulphate-hydrocarbonate-magnium-calcium. Water-bearing rocks are alluvial loam and pebble-gravel with sand filling.
Parameters of Pilot Projects and Technical Solutions:
Field observations over water distribution during waterings by DIS along surface tubes-moisteners (by volumetric method), water supply dynamics through DIS (by water-meters), pressure within the system (by manometers). For determination of norm and schedule of irrigation soil moisture indices were used (tensiometers of american production or thermostat-weight method for moisture definition within root layer), i.e. next waterings were appointed by achieving soil pre-irrigation moisture 70 % of FFMC or Israeli method was applied where watering duty (Mn) was calculated multiplying evaporativity (mm/day) by irrigation interval (day) and by water pressure within the leaves (atmosphere), determined by barocamera “Arimad”.
Water duty and irrigation norms were recorded by water-meters (DIS) and weirs of Chipoletti (furrow irrigation).
For better soil moistening two first waterings were performed by duty 250-300 cu.m/ha and last two waterings by 50 % of calculated norm. Phenological observations were executed following common methodology. As a control site an adjacent field with furrow irrigation (15 ha) was selected with similar parameters (plants density, furrow width, fertilisers, etc.).
Fertilisation through DIS was executed: NH4NO3 solution 160-200 kg/ha, nitrogen 25 kg/ha. On control site fertilisers doses were the same (before three first waterings by norm 50-70 kg/ha).
Methodology:
Pilot site area is 100 ha. DIS of Israeli production was installed including pumping station, distributors, watering hoses with drippers. Water was supplied from settlings by submersible electric pumps of “Iona Uspis” company with capacity 100 kW and discharge 164 cu.m/hour under head 4-7 atm. Pumping station is eqquipped by hydrocyclon which separates sand particles (discharge 200 cu.m/hour) and by 6 filters with quartz sand for silt particles absorbtion. Pumping station includes also water-meters, manometers, valves, fertilisators and herbilisators and small jet-pumps for solution supply.
Watering hoses with drippers of button-type “Katif” were joined with ditributors by special connectors, at the end hoses were closed by plugs. Watering hoses diameter is 20 mm, distance between drippers is 100 cm, dripper’s discharge is 2.0-2.3 l/hour under pressure within hoses 2.6-3.0 atm. Watering hoses were laind in each second furrow (furrow spacing was 90 cm). Hoses demand was 5550 m per year.
Results:
DIS within 1992-1995 of its operation was reliable and workable. Certain accidents were discovered:
a) electric motor bearings were replaced twice;
b) fine filter breakage;
c) certain joinings, connectors were distroyed;
d) plastic jet-pump within fertilisator required to be replaced every 3-4 years;
e) 3-5 % of watering hoses should be replaced;
f) hydrants breakage due to tractors raid.
Pumps provided head pressure 5.6-5.9 atm and after hydrocyclon and filters 3.8-2.9 atm. That allowed to supply 11-12 cu.m/hour water per hectare. Water supply regularity was high – each dripper gave 2.1-2.2 l/hour. Within the control site overmoistening at the beginning of the furrow and undermoistening at its end was recorded.
Irrigation norms under DIS were (cu.m/ha): 2600 (1992), 2700 (1993), 4280 (1994), 2910(1995) to compare with 6400-7200 cu.m/ha within control site. Waterings duty were (cu.m/ha): from 300-340 to 120-160 and depended on irrigation schedule. Irrigation interval was 3-5 days under DIS and 18-30 days in control. Within 1994 16 waterings by DIS were performed (June 18 – August 24) by water duty 160-340 cu.m/ha with irrigation interval 4-5 days and irrigation norm 4280 cu.m/ha. Within the control site 4 waterings (water duty 1300-2000 cu.m/ha, irrigation interval 19-23 days) were performed by irrigation norm 6800 cu.m/ha.
Source of moistening under dripper has elliptic shape on depth of 20-30 cm. Moisture decreases on bigger distance from dripper: 16-22 % of volume (distance 60 cm, depth 20-40 cm); 10-15 % (distance 90 cm, depth 30-80 cm). During irrigation interval (3-5 days) moisture exhaustion occures and mentioned zones lose 35-55 % of initial moisture. Under dripper on depth 10-20 cm moisture content is 26.5-31.5 %; on depth 40-50 cm – 25-27.5 %; on depth 70-80 cm – only 9.6-14.7 %. In dry furrows on the same depth moisture is 5.0-9.2 % (10-20 cm); 12.0-12.9 % (40-50 cm); 9.2-10.1 % (70-80 cm). Cotton root growth in direction of wet furrows is noted.
Phenological observations did not discover difference in main stem growth, plants density and boxes weight. DIS influences only on ripe elements number: 8.6 versus 7.8 (1992); 9.3 versus 5.5 (1994). This difference provided higher yield: 0.22 t/ha growth (1992); 0.21 t/ha (1993); 1.5 t/ha (1994); 1.7 t/ha (1995). Cotton yield was (t/ha) under DIS and furrow irrigation: 2.37 and 2.15 (1992); 2.28 and 2.07 (1993); 3.22 and 1.72 (1994); 1.82 and 1.65 (1995) respectively. Cotton technological property improvement was not discovered.
Physical evaporation under DIS did not exceed 27 % of evapotranspiration; under furrow irrigation it was 35 % and more. Field watering efficiency under DIS increases up to 0.95; operator’s productivity is 50 ha per season (usually 12-15 ha).
Advantages of DIS are the following: water saving, yield growth, cultivations cut down, soil compaction, soil moisture regulation.
Disadvantages are as follows: necessity of highly qualified staff, dependence on fuel and electric energy availability and high price.
On the base of investigations recommendations were developed on DIS operation and cotton growing technology under DIS.
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