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  • MK3 Optimising cascades

    of hydropower

    AGRICULTURE & IRRIGATION

    ANNEX C:

    CROP WATER REQUIREMENT AND IRRIGATION SCHEDULE

    December 2012 Paradis Someth Timo Rsnen

  • Authors Paradis Someth (ITC), Timo A. Rsnen (Aalto)

    Produced by Mekong Challenge Program for Water & Food Project 3 Optimising cascades of hydropower for multiple use Lead by ICEM International Centre for Environmental Management

    Suggested citation Someth Paradis and Rsnen Timo. 2012. Annex to Land Use Suitability for Agriculture in the Sesan Catchment: Crop Water Requirement and Irrigation Schedule. Project report: Challenge Program on Water & Food Mekong project MK3 Optimizing the management of a cascade of reservoirs at the catchment level. ICEM International Centre for Environmental Management, Hanoi Vietnam, 2013

    More information www.optimisingcascades.org | www.icem.com.au

    Image Cover image: Ou Chum upper reservoir, Rattanakiri (Photo Peter-John Meynell). Inside cover: Wet season irrigation canal, Lower Sesan, Cambodia (Photo Peter-John Meynell)

    Project Team Peter-John Meynell (Team Leader), Jeremy Carew-Reid, Peter Ward, Tarek Ketelsen, Matti Kummu, Timo Rsnen, Marko Keskinen, Eric Baran, Olivier Joffre, Simon Tilleard, Vikas Godara, Luke Taylor, Truong Hong, Tranh Thi Minh Hue, Paradis Someth, Chantha Sochiva, Khamfeuane Sioudom, Mai Ky Vinh, Tran Thanh Cong

    Copyright 2013 ICEM - International Centre for Environmental Management

    6A Lane 49, T Ngoc Vn| Tay Ho, HA NOI | Socialist Republic of Viet Nam

    http://www.optimisingcascades.org/http://www.icem.com.au/
  • WLE MEKONG| Optimising cascades of hydropower (MK3) Landuse Suitability for Agriculture in the Sesan. Annex C: Crop Water Requirement and Irrigation Schedule

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    TA BLE OF CON TEN TS 1 INTRODUCTION ........................................................................................................................... 2

    2 DATA AND METHODS.................................................................................................................. 2 2.1 Water balance in paddy fields ...................................................................................................... 2 2.2 Crop evapotranspiration .............................................................................................................. 2 2.3 Effective rainfall ............................................................................................................................ 3 2.4 Rainfall and temperature data ..................................................................................................... 3 2.5 Rice growth stage and crop coefficient ........................................................................................ 3 2.6 Soil type ........................................................................................................................................ 3 2.7 Irrigation scheduling ..................................................................................................................... 4

    3 RESULTS ...................................................................................................................................... 5

    4 FINAL REMARKS .......................................................................................................................... 6

    REFERENCES ....................................................................................................................................... 7

  • WLE MEKONG| Optimising cascades of hydropower (MK3) Landuse Suitability for Agriculture in the Sesan. Annex C: Crop Water Requirement and Irrigation Schedule

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    1 IN TRODU CTION

    Soil water balance for the paddy fields was calculated using FAO CROPWAT 8.0 (Allen et al., 1998 ) for 2001-2007. The main purpose of this soil water balance analysis is to calculate rice crop water requirements and irrigation schedules for the wet and dry seasons for two sites in the Sesan catchment, where are supposed to be high suitability for paddy rice cultivation. The data and methodology used for water balance calculations together with the main results are explained in this report.

    2 D A TA A ND METH OD S 2 . 1 W A T E R B A L A N C E I N P A D D Y F I E L D S

    The water balance in a paddy field was calculated by field storage and water volumes entering and leaving the field. The field storage consisted of ponded water and soil moisture . The inflow to the field consisted of precipitation , irrigation , surface inflow and seepage inflow , while the outflow was composed of crop evapotranspiration , infiltration , surface outflow and seepage outflow . Therefore, the water balance equation was

    is the change of field storage and all terms are expressed either in mm or in m3. The water

    balance for the paddy fields was calculated for the whole irrigated area in two selected locations for both the rainy and dry season.

    In this study, surface drainage, runoff and seepage from one plot to another is assumed as negligible since these parameters are not available at the time of the study, and especially in Cambodia, paddy fields are characterised by high bunds without drainage and water is distributed and used very carefully. Therefore, the consumptive use principally consisted of crop evapotranspiration and infiltration. Watanabe (1999) also reported that, in a plot-to-plot irrigation system, water consumption consisted principally of total evapotranspiration and total infiltration. Hence, supply terms are only precipitation and irrigation.

    2 . 2 C R O P E V A P O T R A N S P I R A T I O N Rice crop evapotranspiration ( ) is one of the most important factors for evaluating water consumption in the paddy fields. In this study, was estimated by the single crop coefficient approach (Allen et al., 1998):

    where is crop evapotranspiration (mm/day); is crop coefficient; is reference evapotranspiration (mm/day) and daily calculated by the FAO Penman-Montheith method using minimum and maximum temperature. Other parameters are estimated using the temperature:

    where is net radiation at the crop surface (MJ/m2/day); is soil heat flux density (MJ/m2/day); is mean daily air temperature at 2 m height (C); is wind speed at 2 m height (m/s); is mean saturation vapor pressure (kPa); is actual vapor pressure (kPa); is slope of vapor pressure curve (kPa/C); and is psychrometric constant (kPa/C).

  • WLE MEKONG | Optimising cascades of hydropower (MK3) Landuse Suitability for Agriculture in the Sesan. Annex C: Crop Water Requirement and Irrigation Schedule

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    2 . 3 E F F E C T I V E R A I N F A L L Effective rainfall was calculated by USDA Soil Conservation Service, for decade (daily rainfall is aggregated per decade) as follows:

    for mm

    for mm

    2 . 4 R A I N F A L L A N D T E M P E R A T U R E D A T A The daily rainfall and temperature data required for paddy field water balance calculations were derived from the hydrological model calibrated for Sesan River catchment (for description of hydrological modelling see Annex 1). We used two locations in the Sesan catchment to extract the rainfall and temperature data in order to take into account the differences in hydroclimate within the basin. The location 1 was selected from the central part of Lower Sesan basin in Cambodia and the location 2 was selected from the central part of Upper Sesan Basin in Vietnam. The two locations were selected also so that they reflect the hydroclimate of existing or potential future agricultural areas. The two locations for hydroclimate data were following:

    Location 1 (Cambodia): Latitude: 13.862 N Longitude: 106.616 E Altitude: 108 m

    Location 2 (Viet Nam): Latitude: 14.444 N Longitude: 107.9 E Altitude: 600 m

    2 . 5 R I C E G R O W T H S T A G E A N D C R O P C O E F F I C I E N T Two types of rice varieties were selected for the crop water requirement and irrigation scheduling: medium variety of 125 days for wet season rice and early variety of 105 days for dry season rice. Growing date started from 15 May for wet season rice, while from 01 December for dry season rice for the two selected sites. The root depth for these types of rice ranged from 30 cm to 70 cm. Crop establishment is transplanting for Cambodia and direct sowing for Vietnam. Therefore, nursery stage is only applicable to irrigation in Cambodia. Growing length and crop coefficient (Kc) for both rice varieties of each development stage were adopted as follows:

    - Wet season rice (146 days): 21 days and Kc = 0.60-1.10 for nursery stage, 60 days and Kc = 0.50-1.10 for vegetative stage, 25 days and Kc = 1.00-1.20 for reproductive stage, and 40 days and Kc = 0.70-1.05 for late season stage.

    - Dry season rice (119 days): 14 days and Kc = 0.50-1.00 for nursery stage, 55 days and Kc = 0.60-1. 05 for vegetative stage, 20 days and Kc = 1.00-1.20 for reproductive stage, and 30 days and Kc = 0.70-1.00 for late season stage.

    2 . 6 S O I L T Y P E Soil type was assumed to be Sandy Loam for Site 1 (Cambodia) and Loam for Site 2 (Viet Nam). Puddling depth was set to 0.30 m for both sites. Maximum percolation was set to 3.1 mm/day for Sandy Loam in Cambodia and 3.4 mm/day for Loam in Viet Nam.

  • WLE MEKONG | Optimising cascades of hydropower (MK3) Landuse Suitability for Agriculture in the Sesan. Annex C: Crop Water Requirement and Irrigation Schedule

    4

    2 . 7 I R R I G A T I O N S C H E D U L I N G There were two applications of irrigation scheduling for land preparation. First application (pre-puddling) brought the soil to saturation and second application (puddling) is for flood

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