Irrigation engineering module 1

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Irrigation Engineering

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Irrigation engineering module 1

  1. 1.  80% human body made up of water. 7/25/2014 1 Dr. L. S. Thakur
  2. 2. On average we have sufficient water to meet human needs. The problem is water distribution. We distinguish between water quality and quantity problems. 75% earth’s surface covered with water, only 3%, is fresh., with only 1% water available for human consumption. 7/25/2014 2 Dr. L. S. Thakur
  3. 3. Region Total Population w/o Access to Water (%) Absolute No. of People w/o Access to Water (in millions) Africa 54 381 Latin America & Caribbean 20 97 Asia & Pacific 20 627 Western Asia 12 10 Total 26 1115 7/25/2014 3 Dr. L. S. Thakur
  4. 4. Dr. L. S. Thakur C i v i l E n g i n e e r i n g D e p a r t m e n t B I T S e d u c a m p u s w w w . l a l i t s t h a k u r . c om Irrigation Engineering Module 1 7/25/2014 4 Dr. L. S. Thakur
  5. 5. Outline Necessity of irrigation Scope of irrigation engineering Benefits and ill effects of irrigation Irrigation development in India Types of irrigation systems Soil-water plant relationship: Classification of soil water- soil moisture contents- depth of soil water available to plants-permanent and ultimate wilting point 7/25/2014 5 Dr. L. S. Thakur
  6. 6. What is Irrigation Engineering  Irrigation is the artificial application of water to the soil for the purpose of supplying the moisture essential for plant growth  It is used to assist in growth of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall.  Irrigation is often studied with drainage, i.e. the natural or artificial removal of surface and sub- surface water from a given area. 7/25/2014 6 Dr. L. S. Thakur
  7. 7. What is Irrigation Engineering Irrigation engineering: involves  Conception,  Planning,  Design,  Construction,  Operation and  Management of an irrigation system. 7/25/2014 7 Dr. L. S. Thakur
  8. 8. Historical Perspectives  Ancient civilizations rose over irrigated areas  Egypt claims having the world's oldest dam, 108m long, 12m high, built 5,000 years ago  6,000 years ago, Mesopotamia supported as many as 25 million people.  The same land today with similar population depends on imported wheat for food 7/25/2014 8 Dr. L. S. Thakur
  9. 9. Historical Perspectives  Nile River Basin (Egypt) - 6000 B.C.  Tigris-Euphrates River Basin (Iraq, Iran, Syria) - 4000 B.C.  Yellow River Basin (China) - 3000 B.C.  Indus River Basin (India) - 2500 B.C.  Maya and Inca civilizations (Mexico, South America) - 500 B.C.  Salt River Basin (Arizona) - 100 B.C.  Western U. S. - 1800’s 7/25/2014 9 Dr. L. S. Thakur
  10. 10. Necessity of Irrigation  Insufficient rainfall  Uneven distribution of rainfall  Improvement of perennial crop  Development of agriculture in desert area 7/25/2014 10 Dr. L. S. Thakur
  11. 11. Challenges for Irrigation & Drainage Engineers  Depletion of natural resources (soil and water)  Salinization of soil  Lower productivity of soil: tax records from Mesopotamia barely yields were 2500L/ha, now only ¼ to ½ this value.  Dissertification 7/25/2014 11 Dr. L. S. Thakur
  12. 12. Benefits of Irrigation  Increase in crop yield  Protection from famine  Cultivation of superior crops  Elimination of mixed cropping  Economic development  Hydro power generation  Domestic and industrial water supply 7/25/2014 12 Dr. L. S. Thakur
  13. 13. 7/25/2014 13 Dr. L. S. Thakur
  14. 14. Disadvantages/ Ill – Effects of Irrigation  Rising of water table  Formation of marshy land  Dampness in weather  Loss of valuable lands 7/25/2014 14 Dr. L. S. Thakur
  15. 15. Irrigation & Technology  Hi-tech control: tensiometers, controls and automation of irrigation and water application.  Use of remote sensing for irrigation scheduling and prediction of yield  New job oppurtunities 7/25/2014 15 Dr. L. S. Thakur
  16. 16. Role of Civil Engineers  The supply of water at farm turnout  Water storage  Water conveyance  Supplying water WHEN needed and by the QUANTITY needed – irrigation scheduling  Drainage: surface and sub-surface 7/25/2014 16 Dr. L. S. Thakur
  17. 17. Purposes of Irrigation  Providing insurance against short duration droughts  Reducing the hazard of frost (increase the temperature of the plant)  Reducing the temperature during hot spells  Washing or diluting salts in the soil  Softening tillage pans and clods.  Delaying bud formation by evaporative cooling  Promoting the function of some micro organisms 7/25/2014 17 Dr. L. S. Thakur
  18. 18. Different Uses of Water  consumptive usage is diversion + consumption of water through transforming it into water vapor (where it is “lost” to the atmosphere), letting it seep into ground, or significantly degrading its quality. For eg.: Residential, Industrial, Agricultural, Forestry  non-consumptive usage Do not reduce water supply &, frequently, do not degrade water quality. Examples: Fisheries use water as a medium for fish growth, Hydroelectric users extract energy from water, Recreation may involve using water as a medium (example: swimming) and/or extracting energy from water (examples: white- water rafting, surfing), Transportation is especially important use of water in the tropics. 7/25/2014 18 Dr. L. S. Thakur
  19. 19. Irrigation Development in India  Among Asian countries India has largest arable land (40%).  Only USA has more arable land than India.  In a monsoon climate and an agrarian economy like India, irrigation has played a major role in the production process. There is evidence of the practice of irrigation since the establishment of settled agriculture during the Indus Valley Civilization (2500 BC). 7/25/2014 19 Dr. L. S. Thakur
  20. 20. Irrigation Development in India  These irrigation technologies were in the form of small and minor works, which could be operated by small households to irrigate small patches of land and did not require co-operative effort.  In the south, perennial irrigation may have begun with construction of the Grand Anicut by the Cholas as early as second century to provide irrigation from the Cauvery river. 7/25/2014 20 Dr. L. S. Thakur
  21. 21. Irrigation Development in India  At beginning of 19th century, there was large no of water tanks in peninsular India and several canals in northern India were build.  The upper Ganga canal, upper Bari Doab canal and the Krishna and Godavari delta system were constructed between 1836-1866.  During the last fifty years, gross irrigated area (GIA) of India has increased more than three fold from 22 to 76 million Hectares. 7/25/2014 21 Dr. L. S. Thakur
  22. 22. 7/25/2014 22 Dr. L. S. Thakur
  23. 23. Irrigation Development in India  Groundwater irrigation in India developed during the period of green revolution and contributed much in increasing the gross irrigated area of the country.  In the last five decades, groundwater irrigation has increased from 5 million hectares to 35million hectares. 7/25/2014 23 Dr. L. S. Thakur
  24. 24. Classification of Irrigation Schemes  Irrigation projects in India are classified into three categories  major  medium &  minor according to the area cultivated. 7/25/2014 24 Dr. L. S. Thakur
  25. 25.  Major irrigation projects: projects which have a culturable command area (CCA) of more than 10,000 ha but more than 2,000 ha utilize mostly surface water resources.  Medium irrigation projects: projects which have CCA less than 10,000 ha. But more than 2,000 ha utilizes mostly surface water resources.  Minor irrigation projects: projects with CCA less than or equal to 2,000 ha. utilizes both ground water and local surface water resources. Classification of Irrigation Schemes 7/25/2014 25 Dr. L. S. Thakur
  26. 26. National Water Policy  Our country had adapted a national water policy in the year 1987 which was revised in 2002.  The policy document lays down the fact that planning and development of water resources should be governed by the national perspective. 7/25/2014 26 Dr. L. S. Thakur
  27. 27. Aspects Related to Irrigation from Policy  Irrigation planning either in an individual project or in a watershed as a whole should take into account irrigability of land, cost-effective irrigation options possible from all available sources of water and appropriate irrigation techniques for optimizing water use efficiency.  close integration of water use and land use policies.  Water allocation in an irrigation system should be done with due regard to equity and social justice.  Concerted efforts should be made to ensure that the irrigation potential created is fully utilised.  Irrigation being the largest consumer of fresh water, the aim should be to get optimal productivity per unit of water. 7/25/2014 27 Dr. L. S. Thakur
  28. 28. Types of Irrigation Systems Irrigation Systems Flow Irrigation Perennial Irrigation Inundation Irrigation As Per Sources Direct Irrigation eg. Weir Storage Irrigation eg. Dam Combined Irrigation eg. Dam & Weir Lift Irrigation Well Irrigation Lift Canal Irrigation 7/25/2014 28 Dr. L. S. Thakur
  29. 29. Types of Irrigation Systems Based on way water is applied to agricultural land  Flow irrigation system: where the irrigation water is conveyed by growing to the irrigated land.  Direct irrigation  Reservoir/tank/storage irrigation  Lift irrigation system: irrigation water is available at a level lower than that of the land to be irrigated and hence water is lifted up by pumps or by other mechanical devices for lifting water and conveyed to the agricultural land through channels flowing under gravity. 7/25/2014 29 Dr. L. S. Thakur
  30. 30. Types of Irrigation Systems On the basis of duration of the applied water  Inundation/flooding type irrigation system: In which large quantities of water flowing in a river during floods is allowed to inundate the land to be cultivated, thereby saturating the soil.  The excess water is then drained off and the land is used for cultivation.  It is also common in the areas near river deltas, where the slope of the river and land is small. 7/25/2014 30 Dr. L. S. Thakur
  31. 31. Types of Irrigation Systems  Perennial irrigation system: In which irrigation water is supplied according to the crop water requirement at regular intervals, throughout the life cycle of the crop.  The water for such irrigation may be obtained from rivers or from wells. 7/25/2014 31 Dr. L. S. Thakur
  32. 32. Some Important Terms for Irrigation  Culturable Command Area (CCA): The gross command area contains unfertile barren land, alkaline soil, local ponds, villages and other areas as habitation. These areas are called unculturable areas. The remaining area on which crops can be grown satisfactorily is known as cultivable command area (CCA). Culturable command area can further be divided into 2 categories  Culturable cultivated area: It is the area in which crop is grown at a particular time or crop season.  Culturable uncultivated area: It is the area in which crop is not sown in a particular season. 7/25/2014 32 Dr. L. S. Thakur
  33. 33. Some Important Terms for Irrigation  Gross command area (GCA): The total area lying between drainage boundaries which can be commanded or irrigated by a canal system. G.C.A = C.C.A + unculturable area  Water Tanks: These are dug areas of lands for storing excess rain water.  Water logged area: An agricultural land is said to be waterlogged when its productivity or fertility is affected by high water table. Depth of water-table at which it tends to make soil water-logged and harmful to growth and subsistence of plant life depends upon height of capillary fringe. The height of capillary fringe is more for fine grained soil and less for coarse grained ones. 7/25/2014 33 Dr. L. S. Thakur
  34. 34. Some Important Terms for Irrigation  Outlet: This is a small structure which admits water from the distributing channel to a water course of field channel. Thus an outlet is a sort of head regulator for the field channel delivering water to the irrigation fields.  Permanent wilting point: or the wilting coefficient is that water content at which plants can no longer extract sufficient water from the soil for its growth. 7/25/2014 34 Dr. L. S. Thakur
  35. 35. Soil Water Plant Relationship Vocabulary Terms  Potable- drinkable, free from contaminants.  Irrigation- addition of water to plants to supplement water provided by rain or snow.  Water Cycle – the cycling of water among the water sources to surface, to atmosphere, back to surface.  Precipitation – falling products of condensation in the atmosphere, as rain, snow, or hail.  Evaporation – to change from a liquid or solid state to a vapor or gas.  Saturate – this happens to soil when water is added until all the spaces or pores are filled. 7/25/2014 35 Dr. L. S. Thakur
  36. 36. Gravitational Water Super Fluous Water Easily Available Water Wilting Limit Oven Dried Soil Water Available With Difficulty Field Capacity Wilting Coefficient Ultimate Wilting Hygroscopic Water Water Not Available Available Water/ Capillary Water Soil Water Plant Relationship 7/25/2014 36 Dr. L. S. Thakur
  37. 37. Soil Water Plant Relationship Types of Groundwater  Gravitational – also called “free water.” - This is the water that drains out of the soil after it has been wetted.  This water moves downward through the soil because of the pull of gravity.  This water also feeds wells and springs. 7/25/2014 37 Dr. L. S. Thakur
  38. 38. Soil Water Plant Relationship Types of Groundwater  Capillary – water that moves into and is held in the soil by capillary forces (or pertaining to the attraction or repulsion between a solid and a liquid).  Plant roots can absorb or take up this moisture.  The size of the soil pore will influence the amount of water held by capillary forces. - Provides most of the moisture for plant growth. 7/25/2014 38 Dr. L. S. Thakur
  39. 39. Soil Water Plant Relationship Types of Groundwater  Hygroscopic - very thin water films around the soil particles.  These films are held by extremely strong forces that cause the water molecules to be arranged in a semi- solid form.  This water is unavailable to plants. 7/25/2014 39 Dr. L. S. Thakur
  40. 40. Soil Water Plant Relationship How is Soil Water Classified?  Hygroscopic Water is held so strongly by the soil particles (adhesion), that it is not available to the plants.  Capillary Water is held by cohesive forces greater than gravity and is available to plants.  Gravitational Water is that water which cannot be held against gravity. As water is pulled down through the soil, nutrients are "leached" out of the soil (nitrogen) 7/25/2014 40 Dr. L. S. Thakur
  41. 41. Soil Water Plant Relationship Levels of Water in Soil  Saturation Point – the moisture point at which all of the pore spaces are filled with water.  Occurs when an area receives a lot of rain on a daily basis and the water does not get absorbed by plants, evaporation is at a low do to the lack of sunlight, and runoff areas (ditches, drains) are to capacity. 7/25/2014 41 Dr. L. S. Thakur
  42. 42. Soil Water Plant Relationship Levels of Water in Soil  Field Capacity – the maximum amount of water left in the soil after losses of water to the forces of gravity have ceased and before surface evaporation begins.  Occurs when the soil contains the maximum amount of capillary water. 100 SampleSoilDriedtheofWeight SoilofVolumeCertainainRetainedWaterofWeight CapacityField          7/25/2014 42 Dr. L. S. Thakur
  43. 43. Soil Water Plant Relationship Levels of Water in Soil  Wilting Point – the point at which the plant can no longer obtain sufficient water from the soil to meet its transpiration needs.  At this point the plant enters permanent wilt and dies.  Available Soil Water – that amount present in a soil which can be moved by plants.  It is designated as the difference between the field capacity and the wilting point. 7/25/2014 43 Dr. L. S. Thakur
  44. 44. Soil Water Plant Relationship The Hydrolic (Water) Cycle  Water is constantly moving through the atmosphere and into and out of the soil.  Soil moisture is one portion of the cycle which can be controlled to the greatest extent by affecting the soil. 7/25/2014 44 Dr. L. S. Thakur
  45. 45. Soil Water Plant Relationship How Does Water Enter the Soil?  through pores in the soil  sandy soils have the largest pores, but are often filled with other material  medium textured soils (loamy) have good water entry properties  clays, pores swell shut when they get wet 7/25/2014 45 Dr. L. S. Thakur
  46. 46. Soil Water Plant Relationship  Water Holding Capacity – is a soil property which represents the amount of water a soil can retain after it has been saturated by rain and downward movement has ceased.  Transpiration – the process by which water, as a vapor, is lost by living plants.  Translocation – the process by which water moves through a plant from the roots to the leaves.  Wilting Point – the moisture content of a soil in which growing plants wilt and will not recover after water is added. 7/25/2014 46 Dr. L. S. Thakur
  47. 47. Soil Water Plant Relationship  Evapotranspiration - the combination of water that is lost from the soil through evaporation and through transpiration from plants as a part of their metabolic processes  Adhesion – the attraction of two different molecules (water to soil)  Cohesion – the attraction of two similar molecules (water to water) 7/25/2014 47 Dr. L. S. Thakur
  48. 48. Soil Water Plant Relationship Depth of Soil Water Available to Plants dw d The depth of water stored in the root zone of soil may be determined as follows: Let, d = depth of root zone d = unit weight of dry soil w = unit weight of water Unit weight of soil = (1 x d) x d Unit weight of water = (1 x dw) x w 100 SampleSoilDriedtheofWeight SoilofVolumeCertainainRetainedWaterofWeight CapacityField        7/25/2014 48 Dr. L. S. Thakur
  49. 49. Soil Water Plant Relationship    d d CF d ww    1 1 ..   CapacityField dd w d w   CapacityFieldcapacity,fieldat  dSdw Depth of water held by soil at permanent wilting point PointWiltingPermanent dS PWP)-(F.C.WaterAvailableofDepth  dS PWP)-(F.C.75.0soilofrWater/meteAvailableReadilyofDepth  S If the water content of the soil at lower limit of the readily available moisture is mo, the readily available depth of water is  om-F.C. dS 7/25/2014 49 Dr. L. S. Thakur
  50. 50. Soil Water Plant Relationship Water Holding Capacities of Soils The amount of water a soil can retain is influenced by:  soil texture  soil structure  organic matter. 7/25/2014 50 Dr. L. S. Thakur
  51. 51. Soil Water Plant Relationship Soil Texture  The smaller the soil particles, the greater the soil’s water holding capacity. Clay has more water holding capacity than sand.  Small soil particles (clay) have more small pores or capillary spaces, so they have a higher water holding capacity. Large soil particles (sand) have fewer capillary spaces, therefore less ability to hold water. 7/25/2014 51 Dr. L. S. Thakur
  52. 52. Soil Water Plant Relationship Soil Structure  A soil structure has a direct correlation to the amount of water it can retain. Organic Matter  Organic matter aids in cementing particles of clay, silt, and sand together into aggregates which increases the water holding capacity.  Decomposition of organic matter also adds vital nutrients to the soil. 7/25/2014 52 Dr. L. S. Thakur
  53. 53. Soil Water Plant Relationship Proportions of Soil Constituents 7/25/2014 53 Dr. L. S. Thakur
  54. 54. Soil Water Plant Relationship 7/25/2014 54 Dr. L. S. Thakur
  55. 55. Soil Water Plant Relationship Bulk Density (b) b = soil bulk density, g/cm3 , Ms = mass of dry soil, g Vb = volume of soil sample, cm3 , Typical values: 1.1 - 1.6 g/cm3 Particle Density (p) p = soil particle density, g/cm3 , Ms = mass of dry soil, g , Vs = volume of solids, cm3 , Typical values: 2.6 - 2.7 g/cm3 )/( 3 cmg V M b s b  )/( 3 cmg V M s s p  7/25/2014 55 Dr. L. S. Thakur
  56. 56. Soil Water Plant Relationship Porosity () %1001 soilofvolume poresofvolume           p b    Typical values: 30 – 60% 7/25/2014 56 Dr. L. S. Thakur
  57. 57. Soil Water Plant Relationship Soil Moisture Content  The soil moisture content indicates the amount of water present in the soil.  It is commonly expressed as the amount of water (in mm of water depth) present in a depth of one metre of soil.  For example: when an amount of water (in mm of water depth) of 150 mm is present in a depth of one metre of soil, the soil moisture content is 150 mm/m 7/25/2014 57 Dr. L. S. Thakur
  58. 58. Soil Water Plant Relationship Water in Soils  Soil water content Mass water content (m) m = mass water content (fraction) Mw = mass of water evaporated, g (24 hours @ 105oC) Ms = mass of dry soil, g s w m M M  7/25/2014 58 Dr. L. S. Thakur
  59. 59. Soil Water Plant Relationship Volumetric water content (v) v = volumetric water content (fraction) Vw = volume of water, Vb = volume of soil sample At saturation, v =  As = apparent soil specific gravity = b/ w (w = density of water = 1 g/cm3) As = b numerically when units of g/cm3 are used b w v V V  msv A   7/25/2014 59 Dr. L. S. Thakur
  60. 60. Soil Water Plant Relationship Equivalent depth of water (d)  d = volume of water per unit land area d= (vA L)/A = vL  d = equivalent depth of water in a soil layer  L = depth (thickness) of the soil layer 7/25/2014 60 Dr. L. S. Thakur
  61. 61. Soil Water Plant Relationship Volumetric Water Content & Equivalent Depth (d) Wet Weight of Soil, g Dry Weight of Soil,g Volume of Water,cc Wet Soil Sample Dry Soil Sample Water – = Bulk Volume, cc Equivalent Depth 7/25/2014 61 Dr. L. S. Thakur
  62. 62. Soil Water Plant Relationship Volumetric Water Content & Equivalent Depth (d) Typical Values for Agricultural Soils 7/25/2014 62 Dr. L. S. Thakur
  63. 63. Soil Water Plant Relationship Water-Holding Capacity of Soil Effect of Soil Texture Dry Soil Gravitational Water Available Water Unavailable Water Water Holding Capacity Silty Clay LoamCoarse Sand 7/25/2014 63 Dr. L. S. Thakur
  64. 64. Soil Water Plant Relationship Soil Water Constants  For a particular soil, certain soil water proportions are defined which dictate whether the water is available or not for plant growth which are called as soil water constants.  Saturation capacity: This is the total water content of the soil when all the pores of the soil are filled with water. It is also termed as the maximum water holding capacity of the soil. At saturation capacity, the soil moisture tension is almost equal to zero. 7/25/2014 64 Dr. L. S. Thakur
  65. 65. Soil Water Plant Relationship  Field capacity: this is water retained by an initially saturated soil against force of gravity. Hence, as gravitational water gets drained off from soil, it is said to reach field capacity. At field capacity, macro-pores of soil are drained off, but water is retained in the micropores. 7/25/2014 65 Dr. L. S. Thakur
  66. 66. Soil Water Plant Relationship Two stages of wilting points are recognized which are:  Temporary Wilting Point: this denotes the soil water content at which the plant wilts at day time, but recovers during right or when water is added to the soil.  Ultimate Wilting Point: at such a soil water content, the plant wilts and fails to regain life even after addition of water to soil. 7/25/2014 66 Dr. L. S. Thakur
  67. 67. Soil Water Plant Relationship  Permanent Wilting Point: plant roots are able to extract water from soil matrix, which is saturated up to field capacity. However, as water extraction proceeds, moisture content diminishes and negative pressure increases. At one point, plant cannot extract any further water and thus wilts. 7/25/2014 67 Dr. L. S. Thakur
  68. 68. Soil Water Plant Relationship It must be noted that the above water contents are expressed as percentage of water held in the soil pores, compared to a fully saturated soil. 7/25/2014 68 Dr. L. S. Thakur
  69. 69. Soil Water Plant Relationship Soil at saturation capacity moisture content 100% After draining out of gravitational water, soil at field capacity Gravitational water Gravitational water Capillary Water (Available Water) After extraction of available water by plants After drying in oven moisture content 0% Capillary Water (Available Water) Hygroscopic water 7/25/2014 69 Dr. L. S. Thakur
  70. 70. Soil Water Plant Relationship  Available Water Water held in the soil between field capacity and permanent wilting point i.e. “Available” for plant use  Available Water Capacity (AWC) AWC = fc - wp Units: depth of available water per unit depth of soil, “unitless” (in/in, or mm/mm) Measured using field or laboratory methods 7/25/2014 70 Dr. L. S. Thakur
  71. 71. Soil Water Plant Relationship  Soil Hydraulic Properties & Soil Texture Values can vary considerably from these within each soil texture Soil Texture fc wp AWC in/in or m/m Coarse Sand 0.10 0.05 0.05 Sand 0.15 0.07 0.08 Loamy Sand 0.18 0.07 0.11 Sandy Loam 0.20 0.08 0.12 Loam 0.25 0.10 0.15 Silt Loam 0.30 0.12 0.18 Silty Clay Loam 0.38 0.22 0.16 Clay Loam 0.40 0.25 0.15 Silty Clay 0.40 0.27 0.13 Clay 0.40 0.28 0.12 7/25/2014 71 Dr. L. S. Thakur
  72. 72. Soil Water Plant Relationship  Fraction Available Water Depleted (fd) (fc - v) = soil water deficit (SWD) v = current soil volumetric water content  Fraction Available Water Remaining (fr) (v - wp) = soil water balance (SWB)            wpfc vfc df              wpfc wpv rf   7/25/2014 72 Dr. L. S. Thakur
  73. 73. Soil Water Plant Relationship  Total Available Water (TAW) TAW = (AWC) (Rd) TAW = total available water capacity within the plant root zone, (inches), AWC = available water capacity of the soil, (inches of H2O/inch of soil), Rd = depth of the plant root zone, (inches) If different soil layers have different AWC’s, need to sum up the layer-by-layer TAW’s TAW = (AWC1) (L1) + (AWC2) (L2) + . . . (AWCN) (LN) L = thickness of soil layer, (inches) , 1, 2, N: subscripts represent each successive soil layer 7/25/2014 73 Dr. L. S. Thakur
  74. 74. Soil Water Plant Relationship  Depth of Penetration Can be viewed as sequentially filling the soil profile in layers  Deep percolation: water penetrating deeper than the bottom of the root zone  Leaching: transport of chemicals from the root zone due to deep percolation 7/25/2014 74 Dr. L. S. Thakur
  75. 75. Water Requirements of Crops  Depth of water applied during irrigation  Duty of water and delta improvement of duty  Command area and intensity of irrigation  Consumptive use of water  Evapotranspiration  Irrigation efficiencies  Assessment of irrigation water 7/25/2014 75 Dr. L. S. Thakur
  76. 76. Water Requirements of Crops  The term water requirements of a crop means the total quantity of all water and the way in which a crop requires water, from the time it is sown to the time it is harvested.  The water requirement of crop varies with the crop as well as with the place.  The same crop may have different water requirements at different places of the same country. 7/25/2014 76 Dr. L. S. Thakur
  77. 77. Water Requirements of Crops Factors affecting Water Requirement  Water table: high water table less requirement, vice versa.  Climate: In hot climate evaporation loss is more, hence requirement more, vice versa.  Ground slope: ground is steep, the water flows down very quickly and soil gets little time to absorb, so requirement more. If ground is flat less requirement.  Intensity of irrigation: if intensity of irrigation for a particular crop is high, then more area comes under the irrigation system and requirement is more, vice versa. 7/25/2014 77 Dr. L. S. Thakur
  78. 78. Water Requirements of Crops  Type of soil: sandy soil water percolates very quickly, so requirement is more. Clay soil retention capacity is more, so less requirement.  Method of application of water: surface method more water is required to meet up evaporation. In sub surface and sprinkler method less water required.  Method of ploughing: In deep ploughing less water required, because soil can retain moisture for longer period. In shallow ploughing more water required. 7/25/2014 78 Dr. L. S. Thakur
  79. 79. Water Requirements of Crops Base  Base is defined as the period from the first to the last watering of the crop just before its maturity.  Also known as base period.  Denoted as “B” and expressed in no of days. Crop Base in Days Rice 120 Wheat 120 Maize 100 Cotton 200 Sugarcane 320 7/25/2014 79 Dr. L. S. Thakur
  80. 80. Water Requirements of Crops Delta  Each crop requires certain amount of water per hectare for its maturity.  If the total of amount of water supplied to the crop is stored on the land without any loss, then there will be a thick of water standing on the land.  This depth of water layer is known as Delta for the crop.  Donated by “Δ” expressed on cm. Kharif Crop Delta in cm Rabi Crop Delta in cm Rice 125 Wheat 40 Maize 45 Mustard 45 Groundnut 30 Gram 30 Millet 30 Potato 75 7/25/2014 80 Dr. L. S. Thakur
  81. 81. Water Requirements of Crops Delta if a crop requires 10 waterings at an interval of 20 days with each watering of depth 12.5 cm then delta = 10 * 12.5 = 125 cm and base period can be calculated as B = 10 * 20 = 200 days   in hectaregrowingiscropwhichonlandofArea metre-in hectarerequiredwaterofquanityTotal Delta 7/25/2014 81 Dr. L. S. Thakur
  82. 82. Water Requirements of Crops Duty Duty of water is defined as no of hectares that can be irrigated by constant supply of water at the rate of one cumec throughout the base period. Denoted as “D” and expressed in hectares/cumec. Varies with soil condition, method of ploughing, method of application of water. 1 cumec-day = 1 m3/sec for one day. Crop Duty in hectares/cumec Rice 900 Wheat 1800 Cotton 1400 Sugarcane 800 7/25/2014 82 Dr. L. S. Thakur
  83. 83. Water Requirements of Crops Method of Expressing Duty Number of hectares /cumec of water can irrigate during base period eg. 1000hectares/cumec Total depth of water Number of hectares /million cubic metre of stored water (for tank irrigation) Types of Duty Gross Duty: duty of water measured at head of main canal. Nominal Duty: duty sanctioned as per schedule of irrigation dept. Economic Water Duty: duty of water which results in maximum crop yield Designated Duty: duty of water assumed in an irrigation project for design of canals. 7/25/2014 83 Dr. L. S. Thakur
  84. 84. Water Requirements of Crops Factors affecting Duty  Soil characteristics: if soil of the canal bed is porous and coarse grained, it leads to more seepage loss and low duty. If soil is compact and close grained, seepage loss will less and high duty.  Climatic condition: when atmospheric temp. of command area becomes high, the evaporation loss is more and duty becomes low and vice versa.  Rainfall: if rainfall is sufficient during crop period, less quantity of irrigation water shall be required and duty will more and vice versa. 7/25/2014 84 Dr. L. S. Thakur
  85. 85. Water Requirements of Crops  Base period: when base period is longer, the water requirement will be more and duty will low and vice versa.  Type of crop: water requirement of various crops are different. So the duty also varies.  Topography of agricultural land: if land has slight slope duty will high as water requirement optimum. As slope increases duty increases because there is wastage of water. 7/25/2014 85 Dr. L. S. Thakur
  86. 86. Water Requirements of Crops  Method of ploughing: deep ploughing by tractor requires less quantity of water, duty is high. Shallow ploughing by bullocks requires more quantity of water, duty is low.  Methods of irrigation: duty is high in case of perennial irrigation system as compared to inundation irrigation system. Because in perennial system head regulator is used.  Water tax: if some tax is imposed on the basis of volume of water consumption, the farmer will use the water economically, duty will be high. 7/25/2014 86 Dr. L. S. Thakur
  87. 87. Water Requirements of Crops Methods of improving duty  Proper ploughing: Ploughing should be done properly and deeply, so that moisture retaining capacity of soil is increased.  Methods of supplying water: this should be decided according to the field and soil conditions.  Furrow method – crops shown in row  Contour method – hilly area  Basin method – for orchards  Flooding method – plain lands 7/25/2014 87 Dr. L. S. Thakur
  88. 88. Water Requirements of Crops  Canal lining: to reduce percolation loss the canals should be lined according to site condition.  Transmission loss: to reduce this canals should be taken close to the irrigable land as far as possible.  Crop rotation: crop rotation should be adopted to increase the moisture retaining capacity and fertility of the soil.  Implementation of tax: the water tax should be imposed on the basis of volume of water consumption. 7/25/2014 88 Dr. L. S. Thakur
  89. 89. Water Requirements of Crops Total Quantity of Water Required (WR) = consumptive use (A) + conveyance losses (B) + special needs (C) 7/25/2014 89 Dr. L. S. Thakur
  90. 90. Water Requirements of Crops Depth of Water Applied during Irrigation (dw) Where d = depth of root zone, F.C. = field capacity, mo = lower limit of readily available moisture content  o w d w mCFdd  ..   7/25/2014 90 Dr. L. S. Thakur
  91. 91. Water Requirements of Crops If Cu is rate of daily consumptive use, frequency of irrigation is days)(in u w w C d f  7/25/2014 91 Dr. L. S. Thakur
  92. 92. Water Requirements of Crops seconds)(in q dA t w  Irrigation Time Required The frequency once decided need to be applied in the form of water with the time of supply being given also of equal importance otherwise sacrificing the planning of irrigation on the whole t = time required to pump water dw = depth of water to be applied in m mo = required moisture content to bring soil moisture at FC A = area to be irrigated in sq. m. q = discharge in cumecs 7/25/2014 92 Dr. L. S. Thakur
  93. 93. Water Requirements of Crops Relation between Base, Delta and Duty Let, D = duty of water in hectare/cumec, B = base in days, Δ = delta in m From definition, one cumec of water flowing continuously for “B” days gives a depth of water Δ over an area “D” hectares. i.e. 1 cumec for 1 days gives Δ over D/B hectares. 7/25/2014 93 Dr. L. S. Thakur
  94. 94. Water Requirements of Crops or 1 cumec for B days gives Δ over D/B hectares. or 1 cumec for 1 day = (D/B) × Δ hectare – meter 1 cumec- day = (D/B) × Δ hectare – meter ----- (i) Again, 1 cumec- day = 1 × 24 × 60 × 60 = 86400 m3 = 8.64 hectare – meter ------- (ii) (1 hectare = 10, 000 m2) From (i) & (ii) = (D/B) × Δ = 8.64 Δ = (8.64 × B)/ D = in m 7/25/2014 94 Dr. L. S. Thakur
  95. 95. Water Requirements of Crops Command Area "The area which lies on down stream side of project to which water can reach by gravity action." There are the three types of commanded areas.  Gross Commanded Area (G.C.A): The Gross commanded area is the total area lying between drainage boundaries which can be irrigated by a canal system. 7/25/2014 95 Dr. L. S. Thakur
  96. 96. Water Requirements of Crops  Cultivable Commanded Area (C.C.A): It is the net area, which can be irrigated by a canal system. It includes all land on which cultivation is possible, though all area may not be under cultivation at the time. G.C.A. = C.C.A. + Uncultivable area  Irrigable Commanded Area (I.C.A): It is the part of cultivable commanded area, which can be irrigated. All the C.C.A. cannot be irrigated because of high elevation. 7/25/2014 96 Dr. L. S. Thakur
  97. 97. Water Requirements of Crops Intensity of Irrigation  It is the ratio of area irrigated per season to total irrigable areas or small projects is based on this. Crop Period  It is the time in days, that a crop takes from the instant of its sowing to that of its harvesting. Rabi Crops  Crops sown in autumn (October) and harvested in spring (March). Eg. Wheat, Coriander, Fenugreek, Mustard, Chick Pea, Potato, Oats 7/25/2014 97 Dr. L. S. Thakur
  98. 98. Water Requirements of Crops Kharif Crops  Crops sown in beginning of southwest monsoon and harvested in autumn. Eg. Cotton, juwar, seaseme, castor, soyabean Kor Watering, Depth & Period  The first watering after the plants have grown few centimeters high is known as kor watering, the depth of water applied as kor depth and the portion of the base period in which it is required is kor period. 7/25/2014 98 Dr. L. S. Thakur
  99. 99. Water Requirements of Crops Paleo  Defined as the first watering before sowing of any crop to make the soil ready for sowing. Intensity of Irrigation  Defined as the percentage of culturable commanded area proposed to be irrigated during a year. Crop Ratio  Ratio of area of land irrigated during rabi and kharif also known as rabi – kharif ratio. 7/25/2014 99 Dr. L. S. Thakur
  100. 100. Water Requirements of Crops Time Factor  Ratio of number of days canal run to number of days of irrigation period. Outlet Factor  Defined as the duty at the outlet < duty at field considering transmission losses. Capacity Factor  Ratio of mean supply to full supply of canal. 7/25/2014 100 Dr. L. S. Thakur
  101. 101. Water Requirements of Crops Types of Soil  Alluvial soil: formed by deposition of silt carried by river water during flood. Silt is formed due to weathering action of rocks by heavy current of river water in the hilly regions. Found in Indo –Gangetic plains, Brahmaputra plains. 7/25/2014 101 Dr. L. S. Thakur
  102. 102. Water Requirements of Crops 7/25/2014 102 Dr. L. S. Thakur
  103. 103. Water Requirements of Crops 7/25/2014 103 Dr. L. S. Thakur
  104. 104. Water Requirements of Crops  Black soil: originated by weathering action on rocks like granite, basalt etc. Mainly found in AP, MP, TN, Gujarat. They are sticky when wet and very hard when dry. Suitable for cultivation of cotton. 7/25/2014 104 Dr. L. S. Thakur
  105. 105. Water Requirements of Crops  Red soil: formed by weathering action of rocks of igneous and metamorphic group. Water absorbing capacity very low. Found in Karnataka, TN, Orissa, WB, Maharashtra etc. 7/25/2014 105 Dr. L. S. Thakur
  106. 106. Water Requirements of Crops 7/25/2014 106 Dr. L. S. Thakur
  107. 107. Water Requirements of Crops  Laterite soil: formed by weathering action of laterite rocks. Yellowish red in color and having good drainage property. Found in Kerala, Karnataka, Orissa, Assam etc. 7/25/2014 107 Dr. L. S. Thakur
  108. 108. Water Requirements of Crops Consumptive Use of Water  It is defined as total quantity of water used for the growth of plants by transpiration and the amount of lost by evaporation.  It is also known as evapo-transpiration.  Expressed in hectare-meter or as depth of water in m.  The value of consumptive use of water is vary from crop to crop, time to time, place to place. 7/25/2014 108 Dr. L. S. Thakur
  109. 109. Water Requirements of Crops Evapotranspiration a) Evaporation: The process by which water is changed from the liquid or solid state into the gaseous state through the transfer of heat energy. b) Transpiration: The evaporation of water absorbed by the crop which is used directly in the building of plant tissue in a specified time. It does not include soil evaporation. c) Evapotranspiration, ET: It is the sum of the amount of water transpired by plants during the growth process and that amount that is evaporated from soil and vegetation in the domain occupied by the growing crop. ET is normally expressed in mm/day. 7/25/2014 109 Dr. L. S. Thakur
  110. 110. Water Requirements of Crops Factors that affect Evapotranspiration  Weather parameters  Crop Characteristics  Management and Environmental aspects are factors affecting ET Weather Parameters: The principal weather conditions affecting Evapotranspiration are:  Radiation  Air temperature  Humidity and  Wind speed. 7/25/2014 110 Dr. L. S. Thakur
  111. 111. Water Requirements of Crops Crop Characteristics that affect ET :  Crop Type  Variety of Crop  Development Stage  Crop Height  Crop Roughness  Ground Cover  Crop Rooting Depth 7/25/2014 111 Dr. L. S. Thakur
  112. 112. Water Requirements of Crops Management and Environmental Factors :  Factors such as soil salinity,  Poor land fertility,  Limited application of fertilizers,  Absence of control of diseases and  Pests and poor soil management  May limit the crop development and reduce soil Evapotranspiration. 7/25/2014 112 Dr. L. S. Thakur
  113. 113. Water Requirements of Crops  Other factors that affect ET are ground cover, plant density and soil water content.  The effect of soil water content on ET is conditioned primarily by the magnitude of the water deficit and the type of soil.  Too much water will result in water logging which might damage the root and limit root water uptake by inhibiting respiration. 7/25/2014 113 Dr. L. S. Thakur
  114. 114. Water Requirements of Crops Determination of ET  Evapotranspiration is not easy to measure.  Specific devices and accurate measurements of various physical parameters or the soil water balance in lysimeters are required to determine ET.  The methods are expensive, demanding and used for research purposes.  They remain important for evaluating ET estimates obtained by more indirect methods. 7/25/2014 114 Dr. L. S. Thakur
  115. 115. Water Requirements of Crops Water Balance Method  Water Balance or Budget Method is a measurement of continuity of flow of water. It consists of drawing up a balance sheet of all the water entering and leaving a particular catchment or drainage basin. The water balance equation can be written as: ET = I + P – RO – DP + CR + SF + SW Where: I is Irrigation, P is rainfall, RO is surface runoff, DP is deep percolation, CR is capillary rise, SF and SW are change in sub-surface flow and change in soil water content respectively 7/25/2014 115 Dr. L. S. Thakur
  116. 116. Water Requirements of Crops Lysimeter Method  A water tight tank of cylindrical shape having dia about 2 m and depth about 3 m is placed vertically in ground. The tank is filled with sample soil. Bottom of the tank consists of sand layer and a pan for collecting surplus water. The consumptive use of water is measured by the amount of water required for the satisfactory growth of plants with in tank. Cu = Wa – Wd (Cu = consumptive use, Wa = water applied, Wd = Water drained off) 7/25/2014 116 Dr. L. S. Thakur
  117. 117. Water Requirements of Crops 7/25/2014 117 Dr. L. S. Thakur
  118. 118. Water Requirements of Crops Simplified Pathway of Water in an Evapotranspiration Measuring Apparatus GRASS SOIL Water Added (A) Rainfall (R)Evaporation (PE) Percolated Water (P) 7/25/2014 118 Dr. L. S. Thakur
  119. 119. Water Requirements of Crops Field Experimental Method  Some fields are selected for expt.  The quantity of water is applied in such a way that it is sufficient for satisfactory growth of crops.  There should be no percolation or deep runoff.  If there is any runoff it should be measured and deducted from the total quantity of water applied. 7/25/2014 119 Dr. L. S. Thakur
  120. 120. Water Requirements of Crops Soil Moisture Study  Several plots of land are selected where irrigation water is to be supplied. The soil samples are taken from diff depths at the root zone of the plants before and after irrigation.  Water contents of soil samples are determined by laboratory tests.  Depth of water removed from soil determined by Dr= depth of water removed in m, p = % of water content, w = Sp. Gr. of soil, d= depth of soil in m)  Total quantity of water removed in 30 days period is calculated.  Then a curve of water consumption versus time is prepared which is used to calculate the water consumption for any period. 100 dwp Dr   7/25/2014 120 Dr. L. S. Thakur
  121. 121. Water Requirements of Crops Irrigation Efficiencies  Efficiency is the ratio of the water output to the water input, and is usually expressed as percentage.  Input minus output is nothing but losses, and hence, if losses are more, output is less and, therefore, efficiency is less.  Hence, efficiency is inversely proportional to the losses.  Water is lost in irrigation during various processes and, therefore, there are different kinds of irrigation efficiencies. 7/25/2014 121 Dr. L. S. Thakur
  122. 122. Water Requirements of Crops Efficiency of Irrigation InputWater OutputWater soiltoappliedwatertotalofAmount soilinstoredwaterofAmount IrrigationofEfficiency  Cumec - day  Quantity of water flowing at 1 m3/s in one day. Hectare - metre  Total quantity of water required to fill 1 hectare area with 1 metre depth. 7/25/2014 122 Dr. L. S. Thakur
  123. 123. Water Requirements of Crops Overlap Allowance  Defined as extra quantity of water required to show irrigation for crop overlapping requirements. This percentage is 5 to 10. 100 sq. mt. = 1 are 100 are = 1 hectare 1 hectare = 10000 sq. metre 1 acre = 0.4047 hectare 1 cusec = 0.0283 cumec 1 cumec = 1 m3/sec 1 cumec – day = 8.64 hectare - metre 1 cumec – day = 86400 cubic metre 7/25/2014 123 Dr. L. S. Thakur
  124. 124. Water Requirements of Crops Efficiency of Water-conveyance (ηc)  It is the ratio of amount of water applied to the land to the amount of water supplied from the reservoir.  It may be represented by ηc. where, ηc = Water conveyance efficiency, Wl = amount of water applied to land, and Wr = Water supplied from reservoir. 100         r l c W W  7/25/2014 124 Dr. L. S. Thakur
  125. 125. Water Requirements of Crops Water Application Efficiency (ηa)  Ratio of water stored in root zone of plants to the water applied to the land. where, ηa = water application efficiency, Wz = amount of water stored in root zone, Wl = amount of water applied to land 100 l z a W W  7/25/2014 125 Dr. L. S. Thakur
  126. 126. Water Requirements of Crops Water Use Efficiency (ηu)  Ratio of the amount of water used to the amount of water applied. Denoted by ηu . where, ηu = water efficiency use, Wu = water used, Wl = water applied 100 l u u W W  7/25/2014 126 Dr. L. S. Thakur
  127. 127. Water Requirements of Crops Consumptive Use Efficiency (ηcu )  Ratio of the consumptive use of water to the amount of water depleted from the root zone. where, ηcu = consumptive use efficiency, Cu = consumptive use of water, Wp = amount of water depleted from root zone 100 p u cu W C  7/25/2014 127 Dr. L. S. Thakur
  128. 128. Water Requirements of Crops Standard of Irrigation water Constituent Long Term Use (mg/L) Short Term Use (mg/L) Aluminium 5.0 20.0 Arsenic 0.10 2.0 Beryllium 0.10 0.5 Boron 0.75 2.0 Chromium 0.1 2.0 Cobalt 0.05 5.0 Copper 0.2 5.0 Fluoride 1.0 15.0 Iron 5.0 20.0 Lead 5.0 10.0 Manganese 0.2 10.0 Nickel 0.2 20.0 Zinc 0.2 10.0 7/25/2014 128 Dr. L. S. Thakur
  129. 129. Water Requirements of Crops Measurement of Consumptive Use of Water Direct Measurement Methods Tank and Lysimeter Method Field Experimental Plots Soil Moisture Studies Integration Methods Inflow & Outflow Studies for Large Areas Use of Empirical Formula Penman Method Jensen – Haise method Blaney – Criddle Method Hargreaves Method Thornthwaite Method Hargreaves Class A Pan Evaporation Method 7/25/2014 129 Dr. L. S. Thakur
  130. 130. Water Requirements of Crops Methods of Measuring Irrigation Water a) Direct method: Collect water in a contained of known volume e.g. bucket. Measure the time required for water from an irrigation source e.g. siphon to fill the bucket. Flow rate = Volume/time m3/hr or L/s etc. Weirs: Weirs are regular notches over which water flows. They are used to regulate floods through rivers, overflow dams and open channels. Weirs can be sharp or broad crested; made from concrete timber, or metal and can be of cross-section rectangular, trapezoidal or triangular. Sharp crested rectangular or triangular sections are commonly used on the farm. 7/25/2014 130 Dr. L. S. Thakur
  131. 131. Water Requirements of Crops The discharge through a weir is usually expressed as: Q = C L Hm where Q is the discharge, C is the coefficient dependent on the nature of weir crest and approach conditions, L is the length of crest, H is the head on the crest and m is an exponent depending on weir opening. Weirs should be calibrated to determine these parameters before use eg. for trapezoidal weirs(Cipoletti weir), Q = 0.0186 L H1.5 Q is discharge in L/s, L, H are in cm 7/25/2014 131 Dr. L. S. Thakur
  132. 132. Water Requirements of Crops The discharge through a weir is usually expressed as: Q = C x L x H x m where Q is the discharge, C is the coefficient dependent on the nature of weir crest and approach conditions, L is the length of crest, H is the head on the crest and m is an exponent depending on weir opening. 7/25/2014 132 Dr. L. S. Thakur
  133. 133. Water Requirements of Crops Weirs should be calibrated to determine these parameters before use eg. for trapezoidal weirs(Cipoletti weir), Q = 0.0186 L H1.5 where, Q is discharge in L/s, L, H are in cm. 7/25/2014 133 Dr. L. S. Thakur
  134. 134. Water Requirements of Crops Orifices: An orifice is an opening in the wall of a tank containing water. The orifice can be circular, rectangular, triangular or any other shape. The discharge through an orifice is given by: Q = C A 2 g h Where Q is the discharge rate; C is the coefficient of discharge (0.6 - 0.8); A is the area of the orifice; g is the acceleration due to gravity and h is the head of water over an orifice. 7/25/2014 134 Dr. L. S. Thakur
  135. 135. Water Requirements of Crops Flumes: Hydraulic flumes are artificial open channels or sections of natural channels. Two major types of hydraulic flumes are Parshall or Trapezoidal ones. Flumes need to be calibrated after construction before use. 7/25/2014 135 Dr. L. S. Thakur
  136. 136. Water Requirements of Crops For streams, use gauging. A current meter is used to measure velocity at 0.2 and 0.8 Depth or at only 0.6 depth. Measure areas of all sections using trapezoidal areas. Q = ai x vi 7/25/2014 136 Dr. L. S. Thakur
  137. 137. Water Requirements of Crops Using Floats: A floating object is put in water and observe the time it takes the float e.g. a cork to go from one marked area to another. Assuming the float travels D meters in t secs  Velocity of water at surface = ( D/t ) m/s  Average velocity of flow = 0.8 (D/t)  Flow rate, Q = Cross sectional area of flow x velocity. 7/25/2014 137 Dr. L. S. Thakur
  138. 138. Water Requirements of Crops b) Integration Method: total area of interest divided into sub plots as per crop growing or subdivided under crop, natural vegetation, water ponds, bare land. The consumptive use then calculated as sum of all according to requirement of each. Where, dw1 = consumptive uses of water for crop, dw2 = consumptive use of water for natural vegetation, dw3 = evaporation from the water surface, dw4 = evaporation from barren land. Once the value is obtained it can be expressed in terms of depth of water by dividing by the total area. 44332211 ..... AdAdAdAdAd wwwww  7/25/2014 138 Dr. L. S. Thakur
  139. 139. Water Requirements of Crops c) Inflow & Outflow Studies: found for the total area using the expression Where, U = consumptive use of water in hect-m, I = total inflow during 12 months, P = yearly precipitation on area, Gs = Ground water storage of area at beginning of year, Ge = Ground water storage of area at end of year, R = yearly outflow of the area. All values in hect – m.     RGGPIU es  7/25/2014 139 Dr. L. S. Thakur

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