Forum on the Caspian, Aral and Dead Seas-Perspective of Water Environmental Management and Politics

Irrigation Management on Paddy Based Agriculture in the Deltas of the Aral Sea Basin

Yoshihiko Ogino, Hiroyuki Takaishi (University of Osaka Prefecture),
Hiroki Ohue (Ehime University) and Kyoichi Otsuki (Tottori University)

1. Irrigation Management Situation in Paddy Areas in the Deltas of the Aral Sea Basin

In order to study irrigation management problems associated with paddy based crop rotation system, the following three cases were picked out for each river basin, namely, the deltas of the Ili river (Akhadara region), Syrdarya (Kzyl Orda), and Amu Dar'ya (Nukus).

The Bakhbaktie state farm was planned for reclamation in the period when Khunaev was first secretary of Kazakhstan in 1966. When the Kapchagai dam was completed in 1970, the state farm started to run with 5,000 settlements in 8,400 ha farm lands.

The standard crop rotation system based on rice farming system is as follows; 2 years rice + 1 year mixed sowing barley and alfalfa + 2 years alfalfa + 1 year rice + 1 year fallow (not normally but temporarily depending on soil salinity condition). Rice is cultivated 3 times in every 7 to 8 years, which means 3/7.5, that is, rice is cultivated 40% over the total acreage of farm land. In fact in the state farm, rice is cultivated in 2,800 ha over the total irrigated farm land of 6,726 ha which is equivalent to 41.6%.

The irrigation coefficient is defined as the ratio of the acreage of actual irrigated land to total farm acreage of the state farm, so in this case the value is 0.8.

Official documents state that water requirement for rice is 35,000 m³/ha per year, and for barley and others it is 7,500 m³/ha in a year. But in fact, with water amounting to 40,000 to 50,000 m³/ha per year, no other crops than rice, such as barley and alfalfa, are irrigated at all. These crops other than rice are supplied with water from ground water in a form of subsurface irrigation. Massive water supply to rice (after land is cropped with non-rice crops such as barley and alfalfa) is necessary to leach away salts accumulated during non-rice cropping period.

When land was reclaimed along with irrigation canals and ditches, the land located higher than the irrigation water level remained unreclaimed because water supply to such land was impossible due to gravity. The land located in the lower depression where drainage was not possible also remained unreclaimed due to the fear of waterlogging and, consequently, soil salinization.

Reclamation works were completed in 1961 when the Kzyl Orda weir (maximum discharge rate 450 m³/sec, service area 495,000 ha) was constructed. Cherybizakh state farm was located on the left bank of the Syrdarya and the irrigated area is 7,000 ha with a population of 4,000 (800 households).

(1) the crop rotation system is the same as in case 1. The acreage of rice cultivation (2,755 ha) is about 40% of total irrigated lands (7,055 ha).

According to irrigation managers (farmers), the purpose of irrigation is to maintain a high ground water table (1.5 m below the ground surface) so that moisture supply in the fields of non-rice crops such as barley and alfalfa is possible
by subsurface irrigation with capillary action. However, during this process, within two or three years, salts accumulate sufficiently to damage non-rice crops on the soil surface so that really abundant water supply at the time of paddy helps to leach away the accumulated salts from the surface soil. Such process is repeated in the deltas.

Nukus collective farm is located in the northern part of Nukus City with 100,000 ha of total farm land and a population of 50,000 today. The collective farm has been reclaimed for the purpose of supplying foodstuff to the people living in the Nukus City area since 1963.

(2) irrigation coefficient is 45% of which the irrigated farm land is about 45,000 ha (rice is cultivated in 22,000 ha and upland crops in 23,000 ha).

(3) water requirement is 24,000 to 25,000 m³/ha in a year for rice, 12,000 m³/ha in a year for cotton.

As mentioned above, high lands and low-lying depressions were not reclaimed as irrigated lands at the time of land development, so that irrigation coefficients range from some 50 to 75% in the deltas of the Aral Sea. Within the irrigated lands, some 40% of total irrigated lands are cultivating rice and 60% are for non-rice crops. For simplification, suppose that a state farm or collective farm serves 10,000 ha of the total land which is divided into 2,400 ha of rice paddy and 3,600 ha of non-rice crops such as barley and alfalfa as rice based farming system.

As operation and management by farmers in state farms, only paddy rice fields are irrigated. Supposing that the amount of water applied to the rice paddy is 50,000 m³/ha in a year, ground water level rises up to 1.5 m below from the soil surface. This ground water is available to irrigate noun-non-rice crops. If an adjacent influence area of ground water is assumed to be 20% of total land, then the acreage of the influence area is 2,000 ha.

The evapo-transpiration rate (ET) for each type of field is shown in column 2 in table 1, with an irrigation term of 100 days. Of the total 120 million m³ of water applied to the rice paddy, 24 M m³ is consumed in the paddy, 30 M m³ in non-paddy fields, 16 M m³ in others, 8 M m³ in the adjacent influence area of ground water, and the last 42 M m³ is held in the ground water respectively, as shown in column 4 in table 1. Water application efficiency is defined as the ratio of consumptive use of water (ET) to the total application of water, so the value is (24+30)/120=0.45 (45%). If the water of 42 M m³ held in ground water is necessary to irrigate non-rice crops, the value becomes in that case (24+30+42)/120=0.80 (80%). The 42 M m³ of water held in ground water is shared in equal depth of 420 mm.

Column 5 in table 1 shows the total depth (in mm) of consumptive water use in each type of land uses. The conceptual model of paddy based crop rotation system in the deltas of the Aral Sea basin is shown in figure.1.

By using the conceptual model for this kind of irrigation management in the rice based agriculture in the deltas, improvement of irrigation management and systems are concluded as follows.

Type of lands	Acreage	Net-consumption (ET)		Gross-consumption
	ha	mm/day	M m³	mm/year	M m³/year
paddy	2,400	10	24	1,420	34
non-paddy	3,600	8	30	1,220	44
other uses	4,000	6	16	820	33
influence area	2,000	4	8	400	8

Total water supply 120 M m³ Ground water supply 42 M m³

In the deltaic area in the Aral Sea Basin, rice is cultivated in rotation with non-rice crops such as barley and alfalfa. In
an irrigation command, some 60% is cultivated and 40% is uncultivated as these areas are too high to receive irrigation water by gravity or too low and therefore would suffer from severe waterlogging and soil salinity. Within the 60% of irrigated cropped area, some 24% is planted with rice and 36% is planted with non-rice crops in rotation with rice. The Actual irrigation practice is to supply only irrigation water to rice fields which raise the ground water table to be absorbed by non-rice crops. Virtually no surface irrigation water supply is given to non-rice crops.

Water applied to rice fields raises the ground water table in the entire area, covering even non-agricultural areas amounting to 40% of the total command area. The ground water table adjacent to the command area is also raised. This means that the irrigation water supply to rice fields is consumed by non-rice crops in the form of sub-irrigation, as well as it is consumed in non-agricultural and adjacent areas.

Abundant water supply (approximately 500 mm) is needed for rice areas during the initial period of rice cultivation after rotation to non-rice crop has finished, for leaching accumulated salts during non-rice cropping periods. To improve irrigation (water application) efficiency the following measures are considered effective:

1) To reclaim non cropped areas (amounting to some 40% of entire irrigation command) where the ground water table
is raised high enough to promote evaporation loss. For this purpose, however, proper land leveling and drainage system must be implemented.

2) To introduce proper surface irrigation practices for non-rice crops (e.g., furrow irrigation) to avoid reliance on water supply from ground water table which is raised by water supplied to rice crops. As farmers are not used to such irrigation practices, it may take considerable time to modify the irrigation practice.

3) Under the current irrigation practice, massive irrigation supply to rice crops appears to be necessary as:

ii) water is supplied to non-rice crops from raised ground water table. It is highly desirable, however, to examine ways and means to increase irrigation efficiency, including reducing irrigation water supply and water losses during water delivery.

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