Introduction To Irrigation

This power point presentation will give a complete idea of types of irrigation, water requirement of crops, duty, delta, canal revenue etc. This presentation also contain the numerical for complete understanding the concepts.

1. UNIT TWO “INTRODUCTION TO IRRIGATION”

2. What is irrigation? Irrigation is defined as the process of artificially supplying water to soil for raising crops. A crop requires a certain amount of water at some fixed time interval throughout its period of growth. If the water requirement of crop is met by natural rainfall during the growth period, there is no need of irrigation.

3. Nec e s s ity o f Ir r igation. Inadequate rainfall. Non-uniform rainfall. Growing a number of crops during a year. Growing perennial crops. Growing superior crops. Increasing the yield of crops. Insurance against drought.

4. 4 Surface irrigat i on Irrigation Methods S ub -sur f ace irrigation S p rin k l e r irrigat i on Flo o ding method F u r r ow m e t h o d Co n tour farming Wild flo o ding Co n troll e d flooding Free flo o ding Co n tour laterals Bor d er strips Basin flo o ding Check flo o di n g Zig- zag method Drip irrigat i on

5. Factors affecting choice of irrigation method. The s e l e c t i on o f the ir r igat i on m e t hod i s based o n t h e following factors. Soil characteristics of the land to be irrigated. Topography of the area. The available water supply. Type of crop and its requirements. Size of the stream supplying irrigation water. Amount of water required in each irrigation.

6. Surface irrigation method. Surface Irrigation Flooding method Furrow m ethod Contour method Wild f looding Con t r o l l ed flooding Free f looding Conto u r laterals Basin f looding Border Check st r ips flooding Zi g -zag method

7. Surface irrigation method. In surface irrigation methods, the irrigation water is applied by spreading in the form of sheet or small streams on the lands to be irrigated . The surface irrigation is further divided as follows: Flooding method. Furrow method . Contour farming.

8. Surface irrigation methods. All the a bove m e t hods o f the surf a ce ir r i gation are adopted for the perennial irrigation system. The inundation irrigation system adopts only the wild or uncontrolled flooding method of irrigation.

9. Wild flooding method. Wild flooding method is the earliest and the primitive method of application of water to the land. In this method the water is applied by spreading it over the land prior to the application of water, no land preparations is done in the form of border or field ditches. The water is allowed to flow the natural slope of the land.

10. Controlled flooding. In controlled flooding methods irrigation water is applied by spreading it over the land to be irrigated with proper control on the flow of water as well as the quantity of water applied. All the methods of control flooding require prior preparation of the land. The land is properly graded & agricultural fields are divided into small units by levees .

11. Controlled flooding. The various methods of controlled flooding are: Free flooding. Contour laterals. Border strips. Check basins. Basin flooding. Zig-zag method.

12. Free flooding. Free flooding consists of dividing the entire land to be irrigated into small strips by a number of field channels or levees known as laterals. These laterals may be either at right angles to the sides of the field or at right angles to the contour lines .

13. Contour laterals This is a special case of free flooding in which the field channels or laterals are aligned approximately along the contour lines. In this method, irrigation is possible only on side of the laterals.

14. Border strips In this method, the agricultural area is divided into series of long narrow strips known as border strips by levees, i.e. small bunds. This method is suitable when the area is at level with gentle slope.

15. Check flooding In check flooding the crop area is divided into some plots which are relatively leveled by checks or bunds . Water from field channels is allowed to enter to each plot or check basin and the plots are flooded to the required depth.

16. Basin flooding This method is used frequently to irrigate the plantations. It is a special type of check flooding method . Each plant is enclosed by circular channels which is called basin. Basins are connected to small field ditches . Ditches are fed from the main supply channel.

17. Zig-zag method I n this m e thod, the agri c ultural ar e a i s su b - d ivi d e d i n to small plots by low bunds in a zig-zag manner. The wat e r i s sup p l i ed t o the plo t s from the fi e ld cha n nel through the openings. The water flows in a zig-zag way to cover the entire area. When the desired depth is attained, the openings are closed.

18. Furrow method. Furrow irrigation avoids flooding the entire field surface by channeling the flow along the primary direction of the field using ‘furrows,’ ‘grooves’, ‘lines’.

19. Furrow method

20. Contour farming Contour farming is practiced in hilly areas with slopes and with falling contour. The land is divided into series of horizontal strips called terraces. Small bunds are constructed at the end of each terrace to hold water up to equal height.

21. Contour farming

22. Sub-Surface irrigation method. Subsurface drip irrigation (SDI) is the irrigation of crops through buried plastic tubes containing embedded emitters located at regular spacings. The sub surface irrigation method consists of supplying water directly to the root zone of the plants.

23. Sub-Surface irrigation method. The favourable conditions for sub surface irrigation: Moderate slope. Uniform topographic condition. Good quality of irrigation water . I m pervi o us su b - soil a t r e a s o n a ble d e pt h . (i.e . 2 - 3 m depth).

24. Sub-Surface irrigation method. The subsurface irrigation methods can be classified as follows: Natural sub-surface irrigation . Artificial sub-surface irrigation.

25. Sprinkler Irrigation Sprinkler irrigation is a method of applying irrigation water which is similar to natural rainfall. Water is distributed through a system of pipes usually by pumping. It is then sprayed into the air through sprinklers so that it breaks up into small water drops which fall to the ground.

26. Sprinkler irrigation

27. Drip Irrigation. Drip irrigation is also known as trickle irrigation . It is one of the latest developed methods of irrigation which is more popular in the regions facing scarcity of water. This method was first introduced in Israel. In India this method is more useful in areas in Gujarat, Maharashtra, Kerala, & Karnataka.

28. Drip irrigation layout and its parts.

29. WATER REQUIREMENT OF CROPS

30. SOIL CLASSIFICATION Sr. No. Name of the soil group Grain size diameter in mm 1 Gravelly Soil 60 to 2 2 Sandy Soil 2 to 0.5 3 Silty Soil 0.5 to 0.002 4 Clayey Soil <0.002

31. Classes of Soil Water Water present in the soil may be classified under three heads: Hygroscopic water: When an oven dried sample is kept open in the atmosphere, it absorbs some amount of water from the atmosphere. This is known as hygroscopic water, and is not capable of movement by the action of gravity or capillary forces . Capillary water : Capillary water is that part, in excess of hygroscopic water, which exists in the pore space of the soil by molecular attraction . Gravitational water : Gravitational water is that part in excess of hygroscopic and capillary water which will move out of the soil if favorable drainage is provided. 12

32. Water Requirement of Crops Factors Affecting Water Requirements: Water Table Depending upon position of water table to ground surface or much below, water requirement may be less or more, respectively . Climate The evaporation loss in hot climate, hence, water requirement will be more and in cold climate water requirement will be less. Type of soil If soil is porous (i.e. sandy) water percolates quickly, retention of water is less, therefore, water requirement is more. But in clayey soil, water requirement is less. Method of Ploughing In deep ploughing , soil can retain water for a longer period and water requirement is less.

33. Intensity of Irrigation Intensity of irrigation means the ratio of area under cultivation to the total cultur a bl e a re a . I f this intensity is m ore, m o re a r e a is under cultivation, hence water requirement is more. Ground slope In steep ground water flows down quickly, finds little time to absorb required amount of water, hence, water requirement is more. For flat slope, water flows slowly, finds enough time for absorption, hence, water requirement is less. Method of application of water In surface flow irrigation, evaporation is more and in sub-surface irrigation, evaporation loss is minimum. Hence, water requirement is more in surface irrigation than sub-surface irrigation .

34. Field C apacity The field capacity of soil is the moisture content after the drainage of gravitational water has become very slow and the moisture content has become relatively stable. This situation usually exists for one to three days after the soil has been thoroughly wetted by rain or irrigation. At field capacity, the large soil pores are filled with air, the micro pores are filled with water and any further drainage is slow. The field capacity is the upper limit of available moisture range in soil moisture and plant relations.

35. Permanent Wilting Point 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. If the natural rain is sufficient and timely so as to satisfy both these requirements, no irrigation water is required for raising that crop.

36. Definitions of some Common Important Terms Crop Period or Base Period The time period that elapses from the instant of its sowing to the instant of its harvesting is called the crop-period. The time between the first watering of a crop at the time of its sowing to its last watering before harvesting is called the Base period. Crop period is slightly more than the base period, but for all practical purposes, they are taken as one and the same thing, and generally expressed in B days.

37. Gross Commanded Area (GCA ) The total area lying between drainage boundaries which can be commanded or irrigated by a canal system or water course is known as gross commanded area. Culturable Commanded Area (CCA) Gross commanded area contains some unfertile barren land, local ponds, villages, graveyards etc which are actually unculturable areas. The gross commanded area minus these unculturable area on which crops can be grown satisfactorily is known as Culturable Commanded Area. CCA = GCA – Unculturable Area

38. Culturable Cultivated Area The area on which crop is grown at a particular time or crop season. Culturable Uncultivated Area The area on which no crop is grown at a particular time or crop season Intensity of Irrigation (I.I) Percentage of CCA that is cultivated in a particular season.

39. Kor depth and Kor period The distribution of water during the base period is not uniform, since crops require maximum water during first watering after the crops have grown a few centimeters. During the subsequent watering the quantity of water needed by crops gradually decreases and is least when crop gains maturity. The first watering is known as kor watering, and the depth applied is known as kor depth. The portion of the base period in which kor watering is needed is known as kor period. While designing the capacity of a channel, kor water must be taken into account since discharge in the canal has to be maximum during this time.

40. Crop Ratio The ratio of area irrigated in Rabi season to that irrigated in Kharif season is known as crop ratio. The crop ratio is so selected that the discharge in the canal during both the seasons may be uniform.

41. Time factor The time factor of a canal is the ratio of the number of days the canal has actually run to the number of days of irrigation period. For example, if the number of days of irrigation period = 12, and the canal has actually run for 5 days, the time factor will be 5/12. (Note: A day has a period of 24 hours (i.e. it includes the night also). Capacity factor This is the ratio of the mean supply discharge to the full supply discharge of a canal.

42. D E LTA The total quantity of water required by the crop for its full growth may be expressed in centimeter (inches) or hectare- metre (Acre-ft) or million cubic meters (million cubic ft). This total depth of water (in cm) required by a crop to come to maturity is called its delta (∆).

43. DUTY OF WATER The duty of water is the relationship between the volume of water and the area of the crop it matures. This volume of water is generally expressed as, “ a unit discharge flowing for a time equal to the base period of the crop, called Base of a duty”. If water flowing at a rate of one cubic metre per second, runs continuously for B days, and matures 200 hectares, then the duty of water for that particular crop will be defined as 200 hectares per cumec to the base of B days. Hence, duty is defined as the area irrigated per cumec of discharge running for base period B. The duty is generally represented by the letter D. Mathematically, D = A / Q

44. Measurements Of Duty Are Taken At Four Points Noted Below: At the head of main canal - known as Gross Quantity . At the head of a branch canal - known as Lateral Quantity. At the outlet of a canal - known as Outlet Factor. At the head of land, to be irrigated - known as Net Quantity.

45. RELATION BETWEEN DUTY, DELTA AND BASE PERIOD L e t , N o w, base period of the crop be B days, and one cumec of water be applied to this crop on the field for B days. volume of water applied to this crop during B days = V = (1 x 60 x 60 x 24 x B ) m 3 = 86,400 B m 3 By definition of duty (D) , one cubic meter supplied for B days matures D hectares of land. :. This quantity of water (V) matures D hectares of land or 10 4 D sq. m of area. Total depth of water applied on this land = Volume/area = 86400 B / 10 4 D = 8.64 B / D metres By definition, this total depth of water is called delta ( ∆ ), ∆ = 8.64 B / D meter ∆ = 864 B / D cm 17 where, ∆ is in cm, B is in day s ; a a te n r d Re D quir i e s m du t t o y f C i r n op h s ectares/cumec.

46. E XA M P L E Find the delta for a crop when its duty is 864 hectares/ cumec on the field. The base period of this crop is 120 days. Solution: In this question, B = 120 days; and D = 864 hectares/ cumec ∆ = 864 B / D cm = 864 x 120 / 864 = 120 cm

47. FACTORS AFFECTING DUTY Methods and systems of irrigation; Mode of applying water to the crops; Methods of cultivation; Time and frequency of tilling; Types of the crop; Base period of the crop; Climatic conditions of the area; Quality of water; Method of assessment; Canal conditions; Character of soil and sub-soil of the canal; 1. 2. 3. 4. 5. 6. 7. 8. 9. 10 . 11 . 12 . 32 Character of soil and su W b a - t s e o r R il eq o u f ire t m h e e nt i o r f r C i ro g p a s tion fields.

48. METHODS OF IMPROVING DUTY Suitable method of applying water to the crops should be used. The land should be properly ploughed and leveled before sowing the crop. The land should be cultivated frequently , since frequent cultivation reduces loss of moisture specially when the ground water is within capillary reach of ground surface.

49. The canals should be lined . This reduces seepage and percolation losses . Also, water can be conveyed quickly, thus reducing, evaporation losses . Parallel canals should be constructed. If there are two canals running side by side, the F.S.L. will be lowered , and the losses will thus be reduced . The idle length of the canal should be reduced. The alignment of the canal either in sandy soil or in fissured rock should be avoided. The canal should be so aligned that the areas to be cultivated are concentrated along it.

50. The source of supply should be such that it gives good quality of water. The rotation of crops must be practiced. Volumetric method of assessment should be used. The farmers must be trained in the proper use of water, so that they apply correct quantity of water at correct timing. The land should be redistributed to the farmers so that they get only as much land as they are capable of managing it.

51. Research stations should be established in various localities to study the soil, the seed and conservation of moisture. The problems concerning the economical use of water should be studied at research stations. The canal administrative staff should be efficient, responsible and honest. The operation of the canal system should be such that the farmers both at the head of the canal as well as at the tail end get water as and when they need it.

52. 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 conveyance Efficiency (ηc) It is the ratio of the water delivered into the fields from the outlet point of the channel, to the water pumped into the channel at the starting point. It takes the conveyance or transit losses into account. r c  W f Wat e r divert e d f rom t h e r iv e r or r e se rvoir W W a t e r d e l iv e r e d to the f a rm  

53. Wa t e r d el iver e d to t h e f a r m  D e e p p e rco l a t i o n f f f a R f  Surface runoff ; D f W f W   R  D    s  W f where W Water application Efficiency ( η a ) It is the ratio of the quantity of water stored into the root zone of the crops to the quantity of water delivered into the field. It may also be termed as farm efficiency, as it takes into account the water lost in the farm.   Water stored in the root zone during irrrigation

54. Water storage Efficiency ( η s ) It is the ratio of the water stored in the root zone during irrigation to the water needed in the root zone prior to irrigation ( i.e. field capacity – existing moisture content ). s  W s W n W a t e r n ee d e d in t h e root z o n e p r i or to i r r i g a t i on Water stored in the root zone during irrrigation  

55. Water-use Efficiency ( η u ) It is the ratio of the water beneficially used, including leaching water, to the quantity of water delivered. u  W u W d W a te r d e l i v er e d to t h e farm Water used consumptively  

56. 54 Irrigation Efficiencies (v) Uniformity coefficient or Water distribution Efficiency ( η d ) The effectiveness of irrigation may also be measured by its water distribution efficiency), which is defined below: where d  average depth of water stored during irrigation; . y  a v e r a ge n u m e r i c a l d e v ia ti on i n de p t h o f wate r s t o r e d fr om average depth stored during irrigation   d    y  ; d   100  1

57. 55 Irrigation Efficiencies . cu W d  W  Net amount of water depleted from root zone soil water Norm a l con s u m p t i v e u s e of w a ter Consumptive use Efficiency ,  cu

58. Cropping Seasons

59. Q-1) The base period, intensity of irrigation and duty of various crops under a canal system are given in the table below. Find the reservoir capacity if the canal losses are 20% and the reservoir losses are 12%. Crop Base period (days) Area (hect a re s ) Duty at the field (hectares/cumec) Wheat 1 20 4800 1800 Sugar-cane 3 60 5600 800 Cotton 2 00 2400 1400 Rice 1 20 3200 900 Vegetables 1 20 1400 700

60. Crop Base period B (days) Duty at the field D (ha/cum e c) Delta Δ = (8.64 B)/D A r ea (ha) Volume = (Δ x A) (ha-m) Wheat 1 20 1800 0.576 4 8 2765.0 Sugar-cane 3 60 800 3.890 5 6 21800.0 Cotton 2 00 1400 1.235 2 4 2965.0 Rice 1 20 900 1.152 3 2 3690.0 Vegetables 1 20 700 1.480 1 4 2070.0 T otal 33290 Therefore, capacity of the reservoir = 33290 / (0.8 x 0.88) = 47,300 ha-m

61. Q-2) An irrigation canal has gross commanded area of 80,000 hectares out of which 85% is culturable irrigable. The intensity of irrigation for Kharif season is 30% and for Rabi season is 60%. Find the discharge required at the head of canal if the duty at its head is 800 hectares/cumec for Kharif season and 1700 hectares/cumec for Rabi season. Solution: Gross culturable area = GCA = 80,000 hectares Culturable commanded area = CCA = 0.85 x 80,000 = 68,000 hectares Area under Kharif season = 68,000 x 0.30 = 20,400 hectares Area under Rabi season = 68,000 x 0.60 = 40,800 hectares Water required at the head of the canal in Kharif = Area/duty = 20,400/800 = 25.5 cumecs Water required at the head of the canal in Rabi = Area/duty = 40,800/1700 = 24.0 cumecs Since water requirement in Kharif is more so the canal may be designed to carry a discharge of 25.5 cumecs .

62. Q-3) A watercourse has a culturable commanded area of 2600 hectares, out of which the intensities of irrigation for perennial sugar-cane and rice crops are 20% and 40% respectively. The duty for these crops at the head of watercourse are 750 hectares/cumec and 1800 hectares/cumec respectively. Find the discharge required at the head of watercourse if the peak demand is 20% of the average requirement. Solution: Culturable commanded area = CCA = 2,600 hectares Area under sugar-cane = 2600 x 0.2 = 520 hectares Area under rice = 2600 x 0.4 = 1040 hectares Water required for sugarcane = Area/duty = 520/750 = 0.694 cumecs Water required for rice = Area/duty = 1040/1800 = 0.577 cumecs Since sugar-cane is a perennial crop, it will require water throughout the year. Hence, Watercourse must carry a total discharge = 0.694 + 0.577 = 1.271 cumecs

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