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Objective and technical fields:
Water consumption rate decrease and irrigated lands productivity increase on the base of drip irrigation system insertion. Objectives: water use improvement, water consumption cut down, soil water-salt regime management on the background of vertical drainage.
Scientific and technical approach:
Soil water -salt regime optimization on the base of irrigated land drainage improvement, water consumption rate decrease. Experiment’s meaning is the drip irrigation technology adaptation to local conditions and elaboration of measures on its efficiency increase.
Environment characteristics:
Climate is sharply continental. Average annual air temperature is 13-15 oC. Annual precipitation is 150-230 mm. Evaporativity is 1200-1400 mm. Positive temperature higher than 14 oC is kept within 6 months. Relative air humidity in winter is 80-85 %, in spring 70 -75 %, in May 30-40 %, in July - 20 %. Relief is represented by slightly waved plain with slope 0.002 -0.003. Cover sediments are quaternary multilayer depositions consisting of loam, sandy loam, clay. Total thickness is 7 -15 m. They are underlaid by gravel -pebble with thickness 12 -18 m. Loam permeability coefficient is 0.2-0.5 m/day, for sandy loam is 0.10-0.12 m/day. Loam water specific yield is 0.10-0.12; sandy loam and sands 0.11-0.15. Groundwater level in spring was 1.0-1.5 m, in autumn - 3.0-3.5 m. Water salinity was 1-2 g/l. Salinity type was chloride-sulphate. Salinity of water, pumped out by vertical drainage was 0.8 -1.2 g/l, salinity type was chloride-sulphate. During 5 years drainage water salinity almost did not change. Soils are medow-grey, humus stock within the upper 0.6 m -layer changed from 0.7 to 1.0 %. Mobile nutrient elements content was as follow: phosphorus -2 -5 mg/100 g of soil; nitrogen 4.5 -8.5 mg/100 g of soil. Salinization level of certain horizons of 1.5 m -thickness of soil varied within 0.09 -0.12 %. Volume mass changed from 1.4 to 1.5 kg/cu.cm; specific mass - 2.66 -2.71 g/cu.m, full field water capacity (MMFC) was 20.9 -23 %.
Parameters of Pilot Projects and Technical Solutions:
Pilot plot area was 500 ha (450 ha net) . Land use efficiency was 0.8. Pilot plot has been constructed by Israel firm in spring 1992. Main crop is cotton. Water intake was performed from the vertical drains and flume network. Mains (diameter 70 -120 mm) were burried in the center of irrigated fields on the depth of 0.9 -1.1 m. Every 21.5 m distributive tubes (diameter 40 mm) were connected. Irrigation pipes were connected from two sides (diameter 16 mm) and had length 230 -280 m. Distance between irrigation pipes was 1.8 m, distance between drippers was 1 m. Working pressure was 0.2 -0.25 MPA. Drippers’ discharge was 2.3 l/min for 1 m of length, hole diameter was 0.94 mm. Moistening regularity along the irrigation pipe was 0.9; between different fields -0.8. Treatment was combined: settle -cans and screens (battery of sandy and rotational filters).
Methodology:
Field investigations of water and salt movement, mobile forms of nutrients, moistening regime, soil water-salt regime under irrigation by surface and drainage water. Pilot plot was equipped by means of water accounting and measurement, soil moisture sensors, irrigation automated management. All operations on cotton growing were performed under Israel specialists supervision. For drip irrigation technology reclamation efficiency multicriterial. Analysis of field investigations was applied.
Results:
Pilot plot has been constructed on the lands of state farm «Ikan». Before its construction cotton yield was 2.3 - 2.7 t/ha. Annual water supply was 6 -7 th.cu. m/ha, irrigation norm was 4.5 -5.4 th. cu.m/ha. Water storage irrigation norm was 1.4 - 1.6 th. cu.m/ha, irrigation norm was 4.5 -5.4 th.cu.m/ha and leaching rate was 1.3 -1.5 th.cu.m/ha. Soil moisture before irrigation was 65 -70 % of FFMC. Average annual salt content change was within the limits of 3 t/ha. Sustainable tendency for salt stock decrease was noticed. (B + Oc) to (T + N) ratio varied as 0.9 -1.1. Groundwater overflow from loam to gravel-pebble sediments was 1000 -1500 cu.m/ha and back -1800 2500 cu.m/ha. Drip irrigation system was functioning within 2 years (1992 -1993). In 1994 1996 drip irrigation system was functioning within one site and was served by local specialists. In 1992 water -storage irrigations were not performed. Vegetation irrigations were executed since June 12 till August 30. Number of irrigations was 11 -12. Watering duty was 360 -430 cu.m/ha, irrigation norm was 4.2-4.5 th.cu.m/ha. In 1993 water -storage irrigation was performed by norm of 1.5 th. cu.m/ha, number of irrigations was 10, watering duty was 380 -410 cu.m/ha, irrigation norm was 4.0 th.cu.m/ha, start of irrigation - June 10, end of irrigation - September 5. In 1995 water -storage irrigation was 1.5 th.cu.m/ha, number of irrigations -10; watering duty 380-420 cu.m/ha, irrigation norm 4.0 t.cu.m/ha. Beginning of irrigation - June 10, end of irrigation -August 20. Threshold of moisture before irrigation was 0.6 0.7 of FFMC, in a furrow and 0.55 -0.65 FFMC outside of furrow.
After irrigation soil moisture increased to 0.85 -0.95 FFMC in a furrow and 0.66 -0.7 outside of it. Fertigation was performed during irrigation. During 3 years of drip irrigation system application nutrient mobile forms stock did not change practically and under furrow irrigation they were cut down on 20 -30 %, that coincides with mineral fertilizers’ insertion dynamics. In 1992 amount of fertilizers was 450 kg/ha, in 1993 - 350 kg/ha. Root zone (1.5 m) salinity did not change practically and varied as 0.09 -0.11 %.. At the second year of operation of the drip irrigation system Israel specialists decided to raise cotton yield due to shift of the irrigation end from August 10 -15 to September 5. This operation lengthened time of cotton ripening and the most part of yield remained under snow. Cotton yield was 2.5 t/ha in the first year, 1.5 t/ha at the second year and 2.6 t/ha at the third year. Average yield was 2.45 t/ha.
Starting from 1994 number of working wells began to reduce due to higher prices for pumping equipment and electric energy. In 1996 vertical drainage system was stopped. Within the period 1995 -1996 reclamation processes tendency changed and soil salinization increased: under drip irrigation on 0.1 %, under furrow irrigation - on 0.15 %.
During two first years of drip irrigation water supply plus precipitation (6.0 -6.5 th.cu.m/ha) to total evaporation (6.3 6.8 th.cu.m/ha) ratio was 0.88 -1.03. Differences in cover loam and gravel -pebble layers salinity and direction of flow change defined negative salt balance. In 1995 water supply was cut down on 800 -1000 cu.m/ha due to vertical drains operation time decrease and water supply plus precipitation to total evaporation ratio was 0.78 -0.95 that led to secondary salinization. Root zone balance as a whole became positive on salt accumulation within 2 -3 th/ha/year. Drip irrigation efficiency was determined from comparison between 1988 -1991 and 1992 -1994 agricultural production obtained respectively under furrow and drip irrigation.
Main result of scientific investigations is water consumption reduction on 20 %, irrigated lands water -supply improvement, hand labour cut down. Economic effect was 200-500 rouble/ha.
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