Irrigated Rice Systems Research Articles

Основные принципы проектирования рисовых оросительных систем

Основные принципы проектирования рисовых оросительных систем

Основные положения экологически сбалансированного водопотребления рисовых оросительных систем в Краснодарском крае

Основные положения экологически сбалансированного водопотребления рисовых оросительных систем в Краснодарском крае

ФОРМУВАННЯ ГІДРОГЕОЛОГО-МЕЛІОРАТИВНОЇ ОБСТАНОВКИ НА РИСОВИХ ЗРОШУВАЛЬНИХ СИСТЕМАХ ПРИДУНАВ'Я ТА ШЛЯХИ ПІДВИЩЕННЯ ЇХНЬОЇ ЕКОНОМІЧНОЇ ЕФЕКТИВНОСТІ З УРАХУВАННЯМ ПОГОДНО-КЛІМАТИЧНИХ РИЗИКІВ

The analysis of the main reasons for the unsatisfactory hydrogeological-reclamation state of the Danubian rice irrigation systems was carried out and the ways of its improvement due to the increase of drainage ability of irrigated lands of rice systems were considered. On the saline lands of the rice systems of the Danube delta drainage network is the main means of active and directed influence on the water-salt regime of the reclaimed area, formation of the regime of groundwater level, both in the growing season and in the not irrigated period for rice and attendant crops. Drainage network is essentially a determining factor in the formation of productivity of agricultural lands. An analysis of the efficiency of the drainage operation on the rice systems of the Danube Delta has shown that drainage built in accordance with the design standards that were in force at the time of construction does not provide uniform drainage ability in the area and the soil profile of rice fields. This is one of the main reasons for their unsatisfactory hydrogeological-reclamation state and reducing the yield of rice and attendant crops. By conducting optimization calculations according to the expense indicator, taking into account that optimal vertical filtration rate for the Danubian rice irrigation systems is at the level of 6...8 mm/day the optimal distance between the drains – 100 m was determined. Constructive improvement of existing rice systems with the drainage network in the form of open drains and distances between them – 250...500 m can be accomplished through the installation of additional separate closed drain-collectors. These drain-collectors are appropriate to arrange along the checks, with the set distance. For reducing the value of the vertical filtration rate in the drainage zone where it reaches 25 mm/day it is advisable to practice maintaining of water levels in the drainage network. Consequently, it is possible to achieve a reduction of the filtration rate to 4…5 mm/day. Developed measures and corresponding reconstruction of rice systems will enable to maintenance of satisfactory hydrological and hydrogeological regimes,ensure uniform salinity of soils during the cultivation of flooded rice, create favorable conditions for oxidation-reducing processes and maintenance of favorable ecological-reclamation state on the system.

DEVELOPMENT OF APPROACHES TO WATER RESOURCES MANAGEMENT IN THE LOWER KUBAN TO ENSURE WATER USER REQUIREMENTS IN LOW‐WATER YEARS†

ABSTRACTThe Lower Kuban River Basin experiences an acute shortage of water resources during the growing season. Every third year is a low‐water period. The complex layout of rice irrigation systems requires reliable forecasting and skilful management. This article presents the results and methodology for determining the optimal operational modes of the Lower Kuban irrigation and drainage systems based on multi‐criteria analyses and trade‐off theory that ensure the reliable functioning of the water resource system taking into account contradictory requirements of water users and restrictions aimed at preserving the Kuban River Basin ecosystem.The methodology is based on multi‐criteria analysis and hydrodynamic modelling with the application of the ‘operating structures' module, which, according to a given hierarchy of priorities, allows the water users to fulfil the requirements for discharges and water levels during the determined time period at water intake sites and outlets within the river network. The developed computational technology allows a reasonable compromise to be reached in the process of negotiations between water users and water basin authorities. © 2019 John Wiley & Sons, Ltd.

Agrogenic soil evolution of rice agrolandscapes

This paper describes soil chronosequence studies relating to fertility evolution of meadow-chernozemic (Gleyic Chernozem) soil of the Kuban region. The research has been conducted in the rice irrigation system of Krasnoarmeysky district, Krasnodar Krai. Over the course of 80 years with 12-year intervals, soil was sampled from pits from the plots/checks with permanent rice cultivation, or with crop rotation as well as from fallow land. Changes of morphological, physical and physico-chemical soil characteristics were studied. Rice paddy cultivation results in removal from the plow layer organic substances, carbonates, mineral elements, and silt particles, i.e. of the components responsible for stable soil development in the irrigation system. This illustrates the expression of dehumification, lessivage, and degradation soil processes with rice cultivation permanently as a monoculture or in a crop rotation during the chronosequence study. Deterioration of the soil physical condition is one of ever-increasing factors.

INTERRELATION BETWEEN STRUCTURAL YIELD ELEMENTS AND TECHNOLOGICAL INDICATORS OF WHOLEGRAIN AND MILLED RICE IN NEW RICE CULTIVARS

Background. To obtain sustainable and high rice yields, it is crucial to select the best cultivars adapted to the cultivation in the main rice-growing areas. Combining high yields and technological quality indicators of wholegrain and milled rice is of vital importance. The practical solution of such an important task largely depends on successful breeding work. Materials and methods. Eight rice cultivars were evaluated in competitive trials in 2016–2018. Experimental plots were arranged within the rice irrigation system of the All-Russian Rice Research Institute in Belozerny Settlement, Krasnodar Territory. During the growing season, the following traits were visually evaluated: plant density, resistance to lodging, disease and pest infestation, and uniformity of crops. Screening and discarding operations on the plots planned for harvesting were followed by making model sheaves of 10–15 plants each for biometric analysis. Technological characteristics of wholegrain and milled rice were measured according to GOST 10843-76 and GOST 10987-76 standards. The results were mathematically processed and proved reliable. Results. Four promising cultivars ‘VNIIR 10244’, ‘VNIIR 10275’, ‘VNIIR 10279’ and ‘VNIIR 10282’ with a set of economically useful traits significantly exceeding the standard reference (st) ‘Flagman’ were selected. Their yield was 9.0 t/ha; 1000 grain weight: 29.3; 28.1; 30.4 and 26.3 g; hull percentage: 17.7; 19.7; 19.5 and 21.4%; and wholegrain content: 88.5; 93.5; 89.4 and 97.8%, respectively. Significantly high yields of these cultivars are due to the optimal number of fertile spikelets (150–160 pcs), panicle density (9.8–12.6 pcs/cm), and significant weight of grain from the main panicle (3.7–4.4 g), with an average sterility of 14.2–20.3%. A close positive correlation of yield traits with wholegrain content was observed in cvs. ‘VNIIR 10282’, ‘VNIIR 10279’, ‘VNIIR 10276’ and ‘VNIIR 10275’ (r = 0.92– 0.98). An inverse relationship between yield and kernel fissuring was observed in most genotypes, which testifies to the potential possibility of increasing their yield without the risk of reducing milled rice yield or wholegrain content. Conclusion. The evaluation resulted in identifying four promising rice cultivars: ‘VNIIR 10244’ and ‘VNIIR 10279’ (large-grain), ‘VNIIR 10275’ and ‘VNIIR 10282’ (medium-sized grain). They significantly exceeded the standard reference ‘Flagman’ in a set of economically useful traits: yield and its structural elements as well as technological characters of wholegrain and milled rice quality. The best of the selected genotypes according to the optimal ratio of the studied traits will be submitted to the State Variety Trials in 2019–2020.

Continuous Flooding or Alternate Wetting and Drying Differently Affect the Accumulation of Health-Promoting Phytochemicals and Minerals in Rice Brown Grain

Climate changes impose adoption of water-saving techniques to improve the sustainability of irrigated rice systems. This study was aimed, by a two-years side-by-side comparison, at verifying the hypothesis whether “Alternate Wetting and Drying” (AWD) affects the concentrations of health-related compounds and minerals in brown grains of three japonica rice (Oryza sativa L.) cvs (‘Baldo’, ‘Gladio’, and ‘Loto’) usually grown in temperate areas in continuous flooding (CF). Due to the rotational turns in water distribution imposed by local authorities and to the weather behavior, different AWD timing and severity occurred in the two years of the study. AWD induced in both seasons yield losses in ‘Baldo’ and ‘Gladio’ but not in ‘Loto’. In the brown grains of ‘Loto’, AWD increased the concentrations of total tocols, γ-oryzanol, flavonoids, and the antioxidant activity. AWD affected the concentrations of minerals, particularly increasing copper, cadmium and nickel, and decreasing manganese, arsenic and zinc. In the sensitive cultivars, ‘Baldo’ and ‘Gladio’, AWD seems to affect plant yield, rather than for severity of the dry period, for prolonged absence of ponded water that exposes plants to cooler temperatures. The selection of suitable cultivars, like ‘Loto’, tolerant to AWD-related stresses, could combine environmental, yield-related, and nutritional benefits improving the product quality.

Monitoring of flooding of rice irrigation systems via laser scanning and digital imaging

The paper presents the study of various technologies to monitor flooding of rice irrigation systems and hydraulic engineering structures as such. It considers planning and prospects of improvement through the introduction of modern systems of laser scanning and digital imaging. It also analyzes the condition of planning works on rice fields in Lower Kuban. This year it is planned to sow 134.5 thousand hectares of rice this year in Krasnodar Krai, which is nearly 8 thousand more than last year. The region produces 87% of rice in Russia. Rice irrigation systems within the rice cultivation region cover huge territories with different agrometeorological and hydro-reclamation conditions. The cultivation of this culture is critical in relation to humidity of top soil, its temperature and surface microrelief. Rice industry in Krasnodar Krai is still reviving. Today the productivity of this culture in Russia makes about 200 thousand tons of grain annually. This is quite sufficient to satisfy the domestic needs of the country. Russia even has an opportunity to import about 50 thousand tons of grain annually. The total length of flood embankment from the Krasnodar reservoir to the mouths of the Kuban and the Protoka rivers is 650 km. Since 1998 and till present, the flood embankment systems were examined several times to detect sites in unsatisfactory technical condition threatening the emergency burst. Technical condition of the flood embankment system of the Kuban and the Protoka rivers is considered emergency. The design of rice irrigation systems is based on the modular principle satisfying the integrated approach to internal network. It is recommended to introduce the new way of planning thus ensuring the maximum approximation of surfaces of rice fields to a horizontal surface.

Perancangan Sistem Pompa Irigasi Pembangkit Listrik Tenaga Surya (PLTS) Untuk Pertanian Subak Semaagung

In general the average rice harvest in Indonesia is three times in one year with a rice age of 115-120 days. Subak is an organization owned by farmers in Bali that specifically regulates traditional rice field irrigation systems. Subak Semaagung every year there is a shortage of water on agricultural land. Subak area of approximately 55 hectares consisting of six groups of farmers called "tempek". Agricultural water supplied to each tempek interchangeably because the water supply is very limited, so any tempek can only grow rice once in 2 years. The situation is very difficult for farmers to maintain their own rice fields with a limited water supply, so that the fields in the Subak has been largely abandoned. Previously, the Ministry of Agriculture has provided assistance in the form of diesel-powered irrigation pump system, but the diesel-powered water pumping systems are only used for 1 year because it requires a very complicated way of operational and fuel costs are enormous. This research will be designed water pump system Solar Power Plant (PLTS) for more effective than previous diesel pump. From the discussion and analysis has been done that with an area of 300 m2 can be mounted solar panels monokristaline 52.14 kW with a maximum capacity of solar modules totaling 158 units, inverter 33 kW two units, and Submersible pumps SP 60-9 two units. So that the result of the calculation of water that can be lifted inthe dry season every day is 1.275.000/liters/day. With a total investment cost of solar power water pumps Subak Semaagung ????????1.168.137.010.

Greenhouse Gases from Irrigated Rice Systems under Varying Severity of Alternate‐Wetting and Drying Irrigation

Core Ideas Rice cultivation under flooded conditions is a significant source of methane. Increasing drying severity decreased methane by 41 to 71% compared to flooded conditions. Drying beyond a certain level did not result in further methane emission reductions. Co‐management of nitrogen and drying time ensured that N2O emissions remained low. Increasing drying severity resulted in no reduction in grain yields. Rice (Oryza sativa L.) is normally grown under flooded conditions and is a significant source of methane (CH4). Alternate wetting and drying (AWD) is one practice which has shown promise to reduce CH4 emissions and global warming potential (GWP). Under AWD, the soil is allowed to dry periodically during the growing season. In this 2‐yr field study, three different severities of drying were compared to a continuously flooded condition to quantify effects on rice yields, greenhouse gas emissions, GWP and yield‐scaled GWP (GWPY). The AWD treatments in order of increasing drying severity were: Safe‐AWD (AWDS) where plots were reflooded when the perched water table fell 15 cm below the soil surface (volumetric water content of 41 to 44%); and AWD35 and AWD25 where plots were reflooded when the soil volumetric water content reached approximately 35 and 25%, respectively. Each of these treatments received two drying cycles (all occurring between 45 d after planting and heading). Grain yields and cumulative N2O emissions (close to zero) did not vary significantly among treatments. The AWDS reduced CH4 emissions by 41% and the AWD35 and AWD25 by 56 to 73% and 60 to 67%, respectively. Since only CH4 differed between treatments, AWD reduced GWP and GWPY by the same relative amount as CH4. Increasing drying severity reduced CH4, GWP and GWPY emissions up to a point (AWD35) but continued drying (AWD25) did not further reduce CH4 emissions. Given the high early season CH4 fluxes, drying earlier may result in greater reductions of CH4 in wet seeded rice systems but this requires further study as there may be negative effects such as increased N2O emissions.

Lymnaeid Snail Vectors of Fascioliasis, Including the First Finding of Lymnaea neotropica in Ecuador, Assessed by Ribosomal DNA Sequencing in the Southern Zone Close to the Peru Border.

Fascioliasis is a freshwater snail-borne zoonotic trematodiasis of high pathogenicity and wide veterinary repercussions. In South America, moreover, it causes serious public health problems, with high human infection rates in Andean countries. Ecuador offers a worrying risky scenario due to its physiography, including many human infection reports and animal endemicity throughout its Andean highlands. Endemic areas with increasing animal fascioliasis were surveyed for lymnaeid snails in the province of Loja, southern Ecuador, close to the border of Peru, the country known to present the widest human fascioliasis endemic zone. The altitude of the sampling sites ranged between 150 and 1770m a.s.l., and their location was close to human villages. Biotopes surveyed were characterized according to fascioliasis transmission needs. The species Lymnaea schirazensis and L. neotropica were identified by rDNA ITS-2 and ITS-1 sequencing. The non-transmitting L. schirazensis combined haplotype agreed with populations of this species previously reported from northern Ecuador. The finding of the efficient vector L. neotropica is reported for the first time in Ecuador and suggests a passive introduction from neighbouring Peru by uncontrolled livestock transport. Rice irrigation system implementation, lymnaeid finding on Taraxacum (dandelion) plants which are consumed fresh in salads by people, and Saccharum (sugarcane), whose bark is peeled off with the teeth, represent potential infection sources for humans. The closeness to the Cajamarca human hyperendemic area in northern Peru, where the same two lymnaeids have been also found and triclabendazole resistance reported, is an additional risk to be considered regarding the livestock transborder exchange.

EVALUATION OF AGRO-AMELIORATIVE CONDITION OF THE MAIN TYPES OF SOILS OF RICE CROP ROTATION

Relevance of research. The most common irrigation regime for rise in the world is constant flooding.
 Soils of rice crop rotation undergo significant changes during the construction of rice irrigation systems, and during their operation. This leads to the formation of so-called "rice soils" that is the result of the transformation of full-profile soils, which were partially or completely disturbed when planning and building rice checks. Keeping the water layer in the field for 4-5 months leads to irreversible changes in the morphological, physical and chemical soil properties. Therefore, it is relevant to determine the indicators of the soil cover, taking into account the features of the soils of rice crop rotations, in order to prevent the development of degradation processes and increase the productivity of rice crop rotation.
 The purpose of the study is to determine the main indicators of soil cover of rice crop rotation and their testing on a rice irrigation system with an area of ​​190 hectares.
 Methods and methods of research. During the study the following methods were used: field method - to study the basic soil properties; laboratory one - to study of physical and chemical, ameliorative, agrochemical soil properties and chemical composition of irrigation, subsoil, drainage and waste water; mathematical and statistical, comparative and retrospective - to evaluate the study results of the basic soil fertility indices.
 The research was carried out in the area of a rice irrigation system with 8-field crop rotation, where the proportion of rice does not exceed 50%. Rice was grown in accordance with the technology of rice growing, taking into account environmental protection requirements. For the companion crops, commonly used cultivation technologies were used. The system has been operated in a project mode for 50 years. The soil cover of the investigated system is represented by dark chestnut alkalized (72.9 hectares), meadow solonetz(18.9 hectares) and meadow chestnut alkalized (75.8 hectare) soil types.
 Research results. On the basis of analysis of retrospective data of monitoring study of the main indicators of agro-amelioration status of soils under rice crop rotation, the indicators of soil condition for the main soil types of rice irrigation systems were determined: groundwater level, groundwater mineralization, content of light-soluble salts in arable layer, chlorine ions content in soil-water extract, toxic salt content, soil salt balance, humus content, the content of easily hydrolyzed nitrogen compounds, the density of upper humus layer, the content of air-dry aggregates, content of water-stable aggregates.
 Conclusions. The approbation of the developed soil condition indicators on the rice irrigation system of the Rice Institute of the National Academy of Agrarian Sciences was carried out, which enabled to identify the main problems and specify the ways to overcome them. In the areas with meadow chestnut alkalized and meadow solonetzsoil types, it is necessary to increase their drainage capacity, namely to repair drainage networks. In the whole area of the investigated rice irrigation system, it is necessary to increase the proportion of perennial legumes and fallow land in the crop rotation, to do soil slitting or other types of mechanical soil treatments to improve its structural and aggregate composition, in particular, the content of air-dry soil aggregates in size of 0.25-10,00 mm and water-stable soil aggregates larger than 25 mm.

Irrigation management strategies to increase water productivity in Oryza sativa (rice) in Uruguay

Traditional rice irrigation systems in Uruguay are fully irrigated and early continuously flooded irrigation accounts for a high volume of water used. The purpose of this study was to determine irrigation techniques that increase irrigation water productivity (WPi) allowing a reduction in water input without negatively affecting grain yield in Uruguay. Ten experiments were conducted over a six-year period from 2009 to 2015, in three experimental units located among the major rice growing regions. Treatments included: early continuous flooding (C), alternate wetting and drying (AWD), intermittent flooding until panicle initiation (IP) and intermittent flooding during all crop growth period (I). All treatments were planted on dry soil. In treatment C flooding started 15–20 days after emergence and a water layer of 10 cm above the soil surface was maintained throughout all the crop cycle. In treatments IP and I, the water level alternated between 10 cm and 0 cm and was re-established when the soil was still saturated. The AWD treatment allowed the soil to dry periodically (water depletion of 50% of soil available water) until panicle initiation. IP and I over three seasons led to significant savings in irrigation water inputs in the North and Central regions (averaged 35% or - 3986 m3 ha−1) in relation to C. In the East region, AWD allowed for a 29%(-2067 m3 ha−1) water saving in relation to the control over four seasons but determined a significant yield loss of 1339 kg rice ha−1 (15% reduction) in relation to C. WPi was increased by 0.25 kg m−3 (23%) in IP and 0.68 kg m−3 (62%) in I, in relation to the control C. Whole grain percentage was significantly reduced with I in the North region only. Techniques that maintained the soil water at saturated conditions like intermittent flooding, allowed a reduction of water input with no significant effects on grain yield, which led to a significant increase in WPi.

JUSTIFICATION OF RICE WATERING METHODS AND CROP CULTURES

The article discusses the need for the use of resource-saving and environmental protection systems of agriculture in the rice growing of the Krasnodar Territory. Due to the fact that rice irrigation systems located in the Krasnodar Territory are outdated, and projects aimed at the reconstruction of these systems do not always meet ecological-landscape principles, the efficiency of their use has decreased, which leads to environmental and economic problems such as as salinization, reduction of soil fertility and reduction of agro-resource potential of land. To eliminate these problems arising in such conditions, certain costs are necessary, which reduces the profitability of rice cultivation and can lead to the ruin of farms. To avoid these problems, a number of activities are being carried out, which consider possible solutions to these problems, aimed at expanding the functional capabilities of rice irrigation systems through reconstruction projects that will yield high yields and increase the efficiency of using natural resources, such as water and land.

Agro-Environmental Evaluation of Irrigation Water from Different Sources, Together with Drainage and Escape Water of Rice Irrigation Systems, According to its Impact on Maize

Agro-Environmental Evaluation of Irrigation Water from Different Sources, Together with Drainage and Escape Water of Rice Irrigation Systems, According to its Impact on Maize

Goosegrass: Morphophysiological Characterization Under Water Excess Conditions

ABSTRACT: Eleusine indica (L.) Gaertn. (goosegrass) is a grass species that has global prominence as a weed in areas typical of the soybean crop. However, its dispersion in recent years has been reported expressively for areas of poorly drained soil, in which irrigated rice is cultivated (lowlands). Little is known on its behavior and biology in this different ecosystem. This study aimed to evaluate if Eleusine indica can survive and withstand flooding. The experimental design was a completely randomized (two-way), in which two E. indica biotypes, one from the uplands (without flooding) and the other from the lowlands (with flooding), were submitted to three soil water conditions: 50 and 100% water retention capacity and soil under water depth. Photosynthetic and gas exchange parameters (photosynthetic rate, stomatal conductance, intercellular CO2 concentration, transpiration, water use efficiency, and assimilation rate by Rubisco) were determined. Morphological diversity of biotypes was evaluated through descriptors. The existence of typical lowland biotype could not be characterized. However, both biotypes were able to survive, develop, and generate seeds in a flooded environment in the irrigated rice system.

Scientific substantiation of the directions of conflict resolution in the area of recovery of rice irrigation systems in the territory of Kherson region

Scientific substantiation of the directions of conflict resolution in the area of recovery of rice irrigation systems in the territory of Kherson region

The efficiency of cultivation of winter wheat using leaf treatments with mineral fertilizers and growth stimulants

The elements of agricultural technology for the cultivation of winter wheat have been developed. These elements provide sustainable yields of winter wheat after application of mineral fertilizers and growth stimulants under the conditions of “waste” fields of the rice irrigation system (deposit). It was established that the maximum yield for three years was in the variant B2 (Master + Megafol) - 5.00 t/ha, that is 1.24 t/ha (33%) more than in the control variant. The highest level of profitability was after treatment with Lignohumate (100 g/ha) - 215.1%, that is 72.2% higher than in the control variant.

Reuse of return flows and its scale effect in irrigation systems based on modified SWAT model

Return flows in irrigation systems are often reused contributing to overall efficiency. To investigate the fate of return flows and the scale effects of reuses, the SWAT (Soil and Water Assessment Tool) model was modified to better represent the characteristics of paddy rice irrigation systems, which includes a simulation module for automatic multi-source irrigation (AMSIM). The modified SWAT model was used to simulate the hydrological processes in the Yangshudang (YSD) watershed of the Zhanghe Irrigation System (ZIS) in China. Furthermore, we proposed a method to calculate the amounts of return flows and the reused amount based on the output of the model. The sub-basins nesting method was used to divide the study area into six scales. We calculated the rainfall & irrigation water reuse rates (ηI+P) and the irrigation water reuse rates (ηI) at different scales and analyzed the changes of these two indicators over different scales. The results revealed that the modified SWAT model succeeded in simulating hydrological processes in a paddy rice irrigation system. ηI+P and ηI increased with the increase of scale. ηI+P was higher in the wet years and lower in the dry years, while ηI was higher in the dry years and lower in the wet years. The reason for increase of ηI+P and ηI as the scales increases were due to the fact that the return flows was repeatedly intercepted by downstream paddy fields, farm ponds, and drainage channels at larger scales, This reuse rates however reach the upper limit at a scale of 3500 ha, after which ηI+P and ηI no longer increase.

Flow regime shapes seasonal patterns of fish species richness and abundance in main and branch channels of a rice irrigation system

Current modernization of an irrigation system degrades fish habitats in quantity and quality and is a significant concern for biodiversity conservation and management of ecosystem services in rice farming landscapes. Irrigation systems consist of various types of channels, whose hydrological and hydraulic heterogeneities can contribute to the coexistence of diverse fish species in this flooded habitat. We compared seasonal patterns of fish species richness and abundance between main and branch channels which have different functions in an irrigation system with different flow temporality and magnitude: the main channels (mean width 425 cm and mean discharge 0.467 m3/s in irrigation period) and the branch channels (176 cm and 0.115 m3/s, respectively). The branch channels are small and temporary, but densities of fish species richness and abundance were not smaller than the main channels during the irrigation period. Further, clear positive hysteretic loops in species richness and abundance with discharge were found in the branch channels, which indicates that fish species richness and abundance gradually increased with discharge during this hydroperiod. Water velocity strongly constrained species richness and abundance in the main channels but not in the branch channels partially because of slow-flow patches at microhabitat scale with a larger vegetation coverage. We also found that the main channels provided deeper habitats in the non-irrigation period and contributed to maintain fish species richness and abundance. Therefore, managing both the main and branch channels as an indispensable, interconnected channel network can be a key for fish habitat conservation in an irrigation system.