Summary of research project: |
Objective and technical fields:
Expedient use of irrigation water under rice crop ponding and, on this base, reduction of water diversion. To develop irrigation schedule for rice, the irrigation norms and optimal periods to stop water supply in checks during pre-harvesting.
Scientific and technical approach:
Water consumption of a rice field is determined on the base of biological features of adapted rice sorts, climatic, soil and hydrogeological conditions of the object. Development of recommendations on rice irrigation schedule, irrigation norm’s components and optimal periods to stop water supply in checks during pre-harvesting. The recommendations will provide increase of irrigated lands productivity and profitability of farms.
Environment characteristics:
Climate is sharply continental, characterized by large annual and daily amplitudes of air temperature. Highest daily fluctuations, up to 11-17 oC, are in summer. Average annual air temperature is 8,9 oC. Frost-free period is 180 days. Total sum of positive temperatures at more than 10 oC is 3700. Annual precipitation is 120 mm. Relative air humidity in April-October is 40-26%. Average monthly water temperature in the Syrdarya river in April is 10,6oC, in May - 17,7oC. The state farm is located in the Syrdarya river’s delta adjacent plane. Relief is slightly corrugated. Soils are alluvial-meadow and meadow-bog with humus content at 1,14-1,54%. Soils texture : heavy loam and clay. Soils are middle permeable. Amplitude of annual fluctuations of ground waters is 1-3 m. Developed soils are non-salinized, low and heavy salinized. Type of salinization is sulphate chloride. Ground waters salinity varies from 1 to 10g/l and more, mostly 1-3 g/l.
As a result of big amount of released water (due to flowing waters) gross irrigation norms increased to 50-70 Th. m3/ha. This led to overwork of diversion network, raise of ground waters, secondary salinization of soils and crops productivity reduction. Salinization of lands accounted for 70-80% of total area. Rice productivity reduced from 4,2-5,0 t/ha to 1,8-3,0 t/ha.
Parameters of Pilot Projects and Technical Solutions:
Irrigated area is 12000 ha (gross), 9360 ha (net). Land use efficiency is 0,78. Specialization of farm is rice-growing and cattle-breeding. Water supply is done by left-bank canal and its distributors in earthen channels. Form of field system is of Krasnodar type. Area of a field is 20-30 ha, area of a check is 2-3 ha. Discharge of ditches is 200-300 l/sec. Depth of check releases is 1,5 m, ground ones - 2,0-2,5 m. Efficiency of irrigation network is 0,74. Average irrigation modulus of rice accounted for 2,2-2,8 l/sec/ha. Maximum irrigation modulus (during initial ponding and creation of water layer) for field was 18,8 l/sec/ha, for rice field - 4,8 l/sec/ha.
Methodology:
Field studies of micro-climate, water movement in checks, salts in aeration zone, ground waters in fields and adjacent territory as a whole. Three stationary balance plots, area is 900 m2, were created for regular observations of check ponding technology, water temperature, precipitation, water release, salt balance, ground waters, evaporation from water surface and transpiration, saturation of soils in aeration zone, plants growth and development, quality of yield formation. The study of three types of ponding: permanent, shorten and interrupted was conducted. Materials of the study were processed using methods of mathematical statistics. Studies of irrigation schedule were conducted in non-salinized and salinized soils within 1964-1970. For field studies there were selected fields, typical for the scheme, which were equipped with weirs, gauges, balance platforms with pans, meteorological station, observation well and piezometers, phenological platforms.
Results:
In 1964-66 studies of rice irrigation schedule in non-salinized soils were conducted. Shorten type of ponding was recognized as the best out of 3 investigated ones. Under shorten type of ponding the checks are flooded, immediately after rice sowing, to the depth of 10-15 cm for 3-4 days, then water is not supplied. In the period of the young growth (with formation of clear rows) the checks are again flooded to the depth of 10-15 cm. During tillering the water is not supplied. When the water level drops to 5 cm, water is again supplied in order to maintain this depth till the end of tillering. After tillering the depth is maintained at 10-15 cm till the full milk stage of grain maturity. Water in checks is not released and kept for evaporation and transpiration. Such regime of ponding provided the following:
- aerobic conditions during germination and sprouting. In comparison with control (permanent ponding) crops density increases on 7-11%, crop productivity - on 3,8-6,0% and is equal to 4,4-5,2 t/ha;
- reduction of water intake as flowing waters in checks did not give expected effect and led to irrigation norms increase. Thus, irrigation norms increased , on the average, on 8400 m3/ha and in some schemes - up to 20 Th. m3/ha. Observations of micro-climate, water temperature in ditches and checks showed, that under sharply continental conditions water in checks did not become cooler than an optimal one and, vice versa, temperature of water supplied from ditches is always higher in morning hours. Flowing waters increased unproductive part of discharge;
- reduction of watering period on 8-9 days and, consequently, reduction of irrigation water discharge, on the average, on 1700 m3/ha. Determination of an optimal period to stop water supply (during the milk stage of maturity) provided an optimal soil drying for machinery harvesting without losses in yield and grain quality. A minimum soil moisture in 0-40 cm during the phase of full maturity accounted for 75,4% of field capacity. Gradual lowering of water depth in checks does not influence the plants. Under soil moisture at 75-80% of field capacity the consistence of soil is 8-9 kg per 1 cm2. There are only tracks after combines and other transport and, while keeping water till wax and full maturity, the depth of the tracks increases up to 15-27 cm and more. This causes skidding and reduction of productivity;
- increase of the optimal values of rice irrigation norm’s components. Water discharge for evaporation and transpiration for early rice was 7000-8900 m3/ha, for middle one - 9400 m3/ha and for late one - 11000 m3/ha. Depending on thickness of aeration zone, discharge for saturation accounted for 3400-4900 m3/ha. Water losses for seepage, depending on hydrogeological conditions, were 3500-8600 m3/ha. Irrigation norm under cultivation of early and middle rice was 18,0-24,8 Th. m3/ha and 27,2 Th. m3/ha respectively. Under cultivation of rice in primitive irrigation system irrigation norm was 38,5 Th. m3/ha, in productive scheme - 51,8 Th. m3/ha.
In salinized soils the studies were conducted in 1967-70. It is determined, that an optimal variant of rice ponding in heavy salinized soils and salt-marshes of sulphate-chloride type is a permanent ponding with variable depth of water from sowing till milk stage of maturity. After sowing the checks are flooded to the depth of 10-15 cm, then in three days the water is released completely. This cycle is repeated 2-3 times till tillering. After tillering, depth of ponding is 10-15 cm till full milk stage of maturity. Between tillering and bursting water in checks is released 3-4 times on 50% of ponding depth. Such regime of ponding provided the following:
- an optimal water regime for plants growth and development, highest yield and lowest water discharge. Complete or partial water release from checks during initial phase of rice development promoted desalinization of top soils in the zone of seeds sprouting. Releases reduced toxicness of soil solution. At the same time, flowing waters (50% of water supply) did not provide complete water exchange in checks as there were stagnation areas, where weak growth, development and even withering of plants were observed;
- desalinization of soils under rice. In checks located near group releases of 2,0-2,5 m depth, more than 1,5 m of soil were desalinized. Salt removal by solid residue was 62-80%, by chlorine - 92-96%. While cultivating rice repeatedly, in checks near group releases 1,5 m profile was desalinized further on 30-70%, by chlorine - on 33-60%. On the background of field releases, 0,5 m, on the average, were desalinized. Salts removal by solid residue was 35-45%, by chlorine ion -54-86%;
- reduction of rice water consumption. Irrigation norms, taking into account complete release and partial replacement of water in checks, during cultivation of early rice were 23-28 Th.m3/ha, including 4,3-5,6 Th.m3/ha for top soils leaching. Leaching requirements under flowing waters is 8-11 Th. m3/ha. In low salinized soils during initial period, after creation of 10-15 cm layer, one complete release is sufficient and, before the phase of bursting, 1-2 times replacements of water on 50% of ponding depth are required.
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