RICE CULTIVATION IN AMUR REGION

Rice plays an important role in the modern diet of Russian people. It occupies a leading position in area, yield, and gross grain harvest among all cereal crops. The aim of the research is development of optimal irrigation regimes that ensure rational use of water resources in southern agricultural zone of Amur Region. Setting and conducting field and laboratory experiments, system approaches and modern research methods were used. The article presents the results of studies on rice cultivation under different irrigation regimes. In the southern zone of Amur Region, along with water regimes of 70, 80, 90% of FMC, differentiated rice irrigation regimes were studied, combining differentiation of presumed humidity thresholds and wetting depth of active soil layer 75...85% of FMC (0.4 and 0.6 m); 80% of FMC (0.4 and 0.6 m). In addition, various flooding regimes of rice field (short and intermittent flooding), seeding rates, timing of sowing, rice cultivars were studied. Obtaining a rice grain yield of more than 4 tons per hectare is ensured by application of mineral fertilizers in the dose of N120P30K30 and seeding rate of 5 million seeds. Optimum seeding time was set from 20 to 25 May. Based on the results of the research, irrigation water was saved, as well as yield increased by optimizing irrigation rice regimes using sprinkling by differentiating presumed moisture thresholds and wetting depth. When rice was cultivated under flooding system of irrigation, it was established that regime of shortened flooding turned to be optimal. When sprinkling in conditions of southern agricultural zone of Amur Region, differential irrigation regime of 75...85% of FMC in active soil layer was 0.4 and 0.6 m.


INTRODUCTION
Rice is one of the most important crops in diet of Russian people. It occupies a leading position in area, yield, and gross grain harvest among all cereal crops. The demand for rice is increasing every year. Growth and stabilization of grain production in Amur region can help in solving problem of providing the population with own grain by increasing crop diversity. Amount of heat and light in the southern zone of Amur Region is sufficient to cultivate rice. Rice cultivation can contribute to increasing grain production in the area. According to the Ministry of Agriculture of the Russian Federation, area suitable for cultivating rice in the Far East is at least 240 thousand hectares. Thus, not only the population of this region, but also all of Eastern Siberia, can be provided with rice grains [1][2][3]. Currently in the Far Eastern Federal District rice is cultivated only in Primorsky region, but production is not enough to meet the growing food needs of the Far East [4]. Therefore, the relevance of our research is determined by the need to develop effective water regimes for rice cultivation in compliance with principles of water conservation and environmental safety requirements of production.
The aim of the research is the development of optimal irrigation regimes that ensure rational use of water resources in the southern agricultural zone of Amur Region.

MATERIALS AND METHODS
Field research has been conducted since 2005 on experimental field of Far East State Agrarian University, p. Gribskoye of Blagoveshchensk district of Amur region, located in the zone of Gribskoye irrigation system. Observations and records have been documented, while observing the requirements of techniques of the experimental case [5][6][7]. We studied water regime of soils: pre-irrigation soil moisture content of 70, 80, 90%, 75-85% of field moisture capacity (FMC) (0.4 and 0.6 m); 80% of FMC (0.4 and 0.6 m); 80% of FMC (0.6 m) (control) -sprinkling, shortened flooding: creating a water layer of 0.10...0.12 m after sowing, after 0.10...0.12 m seedlings till tillering phase, decreasing water layer to 0.05m before tubing phase, increasing water layer to 0.15 m until the end of milk ripeness (control); intermittent flooding: after sowing 0.10 m (10 days), then water removing, after emergence 0.07 m (2...3 days), water removing, then 0.10...0.12 m and maintained till tillering phase, water layer decreasing up to 0.05 m (10 days), increasing water layer to 0.15 m and maintaining until the end of grain ripeness; intermittent flooding: creating a layer of water 0.12 m after sowing, no water in rice field during 7 days, on the 8th day the whole cycle repeats. Then 0.10...0.12 m to tillering phase, followed by a water decreasing to 0.05 m (10 days), further increasing water layer to 0.15 m and maintaining till the end of grain milky ripeness. Fertilizer doses were control without fertilizers; N 60 Р 30 ; N 90 P 30 K 15 ; N 120 Р 30 К 30 . Seeding rates were 4 million (control); 5 and 6 million of seeds. Rice cultivars: dry-bottomed (early cultivar 'Volgogradskiy' of Research Institute of Irrigated Agriculture, high-yielding, resistant to sharply continental climate), and rice cultivars regionalized in Primorsky Krai, which are related to early ripening groups: round-grained -'Dariy 23', 'Priozerny 61'; longgrained -'Khankaisky 429', 'Khankaisky 52', 'Lugovoy', 'Rassvet' and 'Kaskad' with high technological and culinary quality. Sowing terms: 10.05-15.05; 20.05-25.05; 30.05-04.06.
The soil cover of the site is represented by meadow-brown soils. The density of soil in calculated layers (0.6 m) is 1.33 t/m 3 , the lowest moisture capacity of the soil is 22.50%, porosity is 49.18%. Humus content is low 2.13%, easily hydrolyzable nitrogen is 2.7 mg/100 g, mobile phosphorus content is 37.8 mg/kg, exchange potassium content is 122.5 mg/kg.
The years of research differed significantly in the magnitude and distribution of atmospheric precipitation, which made it possible to assess effectiveness of the irrigation regimes studied.
Rice cultivation in field experiments was carried out on the basis of existing zonal recommendations supplemented by variants of studied methods. To control weed vegetation a broad spectrum post-emergence herbicide Segment was used.

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Phenological observations of rice growth stages, plant density, determination of crop structure by the method of Gossortoseti (1995), photosynthetic indicators of crops according to the method of A.A. Nichiporovich (1979,1985) were carried out in the field experiments. Humus content was determined by the method of I.V. Tyurin and B.A. Nikitin in the modification of CINAO in accordance with GOST 26213-84, aqueous and salt pH -according to potentiometric method in accordance with GOST 26483-90, total nitrogen -according to Kornfeld, easily hydrolyzed nitrogen -by the method of M.M. Konova and I.V. Tyurin, mobile phosphorus and potassium -according to B.P. Machigin -GOST 26205-91. In determining water-physical properties of the soil granulometric composition was studied according to the method of N.A. Kachinsky, density of solid phase -pyknometric method, soil density -method of cutting ring, and field moisture capacity (FMC) -by flooded areas.
Analyzes for determination of water-physical and agrochemical properties of soils were carried out in agrochemical laboratory of Department of Ecology and Soil Science of Far East State Agrarian University and in laboratory of Soybean Research Institute.
Weed infestation of seedlings and before harvesting was carried out by applying a marking -0.25 m 2 in 10 replicates. Water balance calculations for rice checks were carried out according to the method of Rice Research Institute (1979). Total water consumption -by A.N. Kostyakov (1975).

RESULTS AND DISCUSSION
We found that irrigation frequency varied during experimental years, depending on irrigation regime and cultivar [6,7].
To maintain soil moisture at the level of 70% of FMC depending on meteorological conditions in 2005-2007 it was required to conduct 5...8 waterings with a rate of 670 m 3 /ha. Increase in pre-irrigation humidity threshold to 80% of FMC was accompanied by increase in number of waterings to 8...12 with irrigation rate of 450 m 3 /ha. Maintenance of 90% of FMC in calculated soil layer was achieved by 11...15 waterings with a rate of 220 m 3 /ha. In 2008, all irrigation water for entire growth season was used during 8 waterings, in 2009 -during 6 waterings and in 2010 -during 10 waterings (Table 1).
Total water consumption of irrigated rice under different weather conditions varied from 6,179...9,199 m 3 /ha. The greatest average for research years was noted in the variant with maintaining soil moisture of at least 90% of FMC and amounted to 8630 m 3 /ha.
As field studies showed, the most favorable for rice cultivation in terms of water availability was 2013, when precipitation during the growing season was 166 mm higher. In the variant of differentiated moistening in 2013, it was necessary to conduct 2 vegetative waterings with irrigation rate 560 m 3 /ha for cultivar 'Khankaisky 429' and 530 m 3 /ha for cultivar 'Rassvet'. In 2011, in the same variant, it was necessary to conduct 8 watering operations with the rate of 2,060 m 3 /ha for cultivar 'Khankaiskiy 429', 6 waterings with the rate of 1560 m 3 /ha for cultivar 'Rassvet'; in 2012, irrigation rate was 1,810 m 3 /ha and 1,560 m 3 /ha for 'Khankaiskiy' and 'Rassvet', respectively ( Table 2).  In structure of the total water consumption of rice varieties under different irrigation regimes, share of atmospheric moisture over whole growing season in 2011 was 54.5...72.1%, in 2012 -62.8...74.6%, in 2013 -87.5...97.9%. The results of field studies showed that soil moisture is used only in the initial period of rice development, and it accounts for about 1% of total water consumption. The share of irrigation water in the structure of rice total water consumption varied 10.0-15.1% (in 2013) to 50.9...57.1%.
The results of the research showed that the optimal parameters of rice irrigation regime during sprinkling are formed under differentiated moistening: maintaining the pre-irrigation humidity at level more than 75% of FMC in 0.4 m layer during the sowing -tillering period, in 0.6 m layer -at level more than 85% of FMC during tillering -wax ripeness of grain, which contributes to reduction of irrigation water costs for obtaining projected grain yield.
The water balance of rice card-check is represented by income and expense items. In the incoming part there is an irrigation norm, which is supplied to maintain necessary water layer in checks, and precipitation. The expenditure part includes balance items used to maintain water layer in checks, water consumption, filtration, leakage, flow, and technological water removing.
In structure of water balance of irrigation card-check, the largest water consumption  Table 3).
The highest irrigation rates 12,534 m 3 /ha and 11,249 m 3 /ha were established in the third variant with intermittent flooding for 'Khankayskiy 429' and 'Rassvet', respectively. The lowest irrigation rates were established at shortened flooding regime (9,811 m 3 /ha and 8,758 m 3 /ha for 'Khankayskiy' and 'Rassvet' cultivars, respectively), which is connected primarily with check flooding scheme and water layer.
The study of influence of seed rates on rice yield showed that the maximum yield was obtained at a rate of 5 million seeds. Increase in seed rate resulted in high plant density which consequently led to yield decrease.