2. Crop water requisacascascacscrements.pptx

zxczxcxc

1. Irrigation Engineering Crop Water Requirements Soil~Water~Plant Relationship 1

2. Objective of Study on Crop Water Requirement: To decide possible Cropping Pattern of area Effective use of available water Plan and design an irrigation project Plan water resource development in an area Assess irrigation requirement of an area Management of water supply from sources 2

3. Crop Water Requirements Crop water requirement (CWR): It is the total amount of water required by the crop in a given period of time for normal growth , under field conditions . It includes; evapotranspiration , water used by crops for metabolic growth, water lost during conveyance and application of water and water required for special operations such as land preparation, tillage and salt leaching etc. It is expressed as the surface depth of water in mm, cm or inches. CWR = Consumptive use (Cu) + Conveyance losses (Wu) + Water required for special operation (Ws) 3

4. Crop Water Requirements Approximate daily water use and total growing season water use in millimetres (mm) for some commonly grown crops in Alberta Source: http://www1.agric.gov.ab.ca/%24department/deptdocs.nsf/all/agdex12726 4

5. The crop water requirement mainly Depends on: the climate: in a sunny and hot climate, crops need more water per day than in a cloudy and cool climate the crop type: crops like maize (Makei) or sugarcane (ganna) need more water than crops like Millet (Bajra) or Sorghum (Jawar) the growth stage of the crop: fully grown crops need more water than crops that have just been planted. Moreover, there are short duration crops, e.g. green peas, with a duration of the total growing season of 90-100 days and longer duration crops, e.g. melons, with a duration of the total growing season of 120-160 days Crop Water Requirements Climatic factor Crop water requirement High Low Sunshine Sunny (no clouds) cloudy (no sun) Temperature hot cool Humidity low (dry) high (humid) Wind speed windy little wind 5

6. Conveyance Losses: These losses take place from diversion structure (barrage) to the field (outlet). Major loss of water in an irrigation channel is due to absorption , seepage or percolation and evaporation . In an earthen channels losses due to seepage are much more than the losses due to evaporation. The absorption losses depend upon the: Type of soil Subsoil water Age of canal Position of Full Supply Level w.r.t to Natural Surface Level Amount of Silt carried by canal Wetted perimeter Crop Water Requirements 6

7. Crop Water Requirements  Irrigation water losses in the field Irrigation water losses in canals 1. Evaporation from the water surface, 2. Deep percolation to soil layers underneath the canals, 3. Seepage through the bunds of the canals, 4. Overtopping the bunds 5. Bund breaks, 6. Runoff in the drain 7. Rat holes in the canal bunds 1. Surface runoff, whereby water ends up in the drain 2. Deep percolation to soil layers below the root zone 7

8. SEEPAGE LOSSES (FPS system): In Pakistan the following formula can be used for obtaining the conveyance losses in earthen channels K= 5 Q 0.0625 K= absorption loss (cusecs) per million square feet of wetted perimeter Q= Discharge in channel ( cusecs ).   According to Lacey Q A =0.0133 L Q 0.5625 Q A = Absorption loss, cusecs L= Length of channel in thousand feet Q= discharge in channel (cusecs) Crop Water Requirements 8 (Ref: Mowafy , 2001) http://www.iwtc.info/2001_pdf/03-3.pdf

9. Other Studies SEEPAGE LOSSES (SI units): [Ref: Garg SK (1999)] Loss = 0.005 (B+D) 2/3 (used in U.P. India) Loss in cumecs per km length , B is width and D is depth of channel in meter Loss = 1.9 Q 1/6 (Used in Indian Punjab) Loss in cumecs per million sq. meter of wetted parameter , Q is flow in cumecs 9

10. Evapotranspiration (ET) and Consumptive use (Cu) Consumptive use (CU): It is the amount of water required by a crop for its vegetated growth to evapotranspiration and building of plant tissues plus evaporation from soils and intercepted precipitation. It is expressed in terms of depth of water DEFINITIONS   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. 10

11. Evapotranspiration (ET) Evapotranspiration: It is defined as the water transpired by crop plants and the water evaporated from the soil in the crop field and intercepted precipitation by areal parts of plants in any specified time period 11

12. Classification of Consumptive use Daily consumptive use: The amount of water consumptively used during 24-hours. It is usually estimated to record the peak period consumptive use rates to formulate the cropping pattern and to decide the water supply from sources during different periods of cropping. Peak period consumptive use: It is the average daily consumptive use during a few days ( 6 to 10 days ) of highest consumptive use in a season. It occurs when the vegetation is in abundance, temperature is high and the crops are in flowering stage. It is used in the planning of an irrigation system 12 Seasonal consumptive use: It is the amount of water consumptively used by crops during the entire cropping season/period. It is used to evaluate and decide the seasonal water supply to a command area of an irrigation project.

13. Consumptive use (Representative values) Rabi Season (October to March): Crop Consumptive Use (cm) Wheat 37 Gram 30 Barley 30 Potato 60-90 Fodder 40 Oil seed 45 Berseem 70 Kharif Season (April to September): Crop Consumptive Use (cm) Cotton 25-40 Maize 45 Rice 125-150 Annual Crops Sugar Cane 90 13

14. Important terminology on Evapotranspiration Reference crop evapotranspiration ( ETo ): This is the evapotranspiration rate from a reference crop which is not short of water . The reference crop is a hypothetical grass with an assumed crop height of 0.12m , a fixed surface resistance of 70 sm -1  and an albedo of 0.23 .  The reference crop closely resembles an extensive surface of green, well-watered grass of uniform height, actively growing and completely shading the ground . Reference crop evapotranspiration (ETo) 14 Surface resistance describes the resistance of vapour flow through the transpiring crop and evaporating soil surface

15. Actual crop evapotranspiration ( ET c ): It is the rate of evapotranspiration by a particular crop in a given period under prevailing soil water and atmospheric conditions. It refers to the evapotranspiration from a disease free crop growing in a large field under optimal soil conditions with adequate water and fertility and giving full potential production under the given environment. It is usually calculated by multiplying the Crop Coefficient ( Kc ) with ETo , thus: ET c = K c ET o Important terminology on Evapotranspiration Actual crop evapotranspiration (ETc) 15

16. Factors affecting Evapotranspiration Climatic factors: Precipitation , with greater frequency and amount of rainfall, ET becomes higher. Solar radiations , it supplies energy for ET processes. With increasing day length or solar radiation, ET becomes more. Temperature , Temperature of plant and soil rises because of more amount of solar radiation received from the sun and consequently increases ET. Wind speed, ET from soil surface and plants occurs at a higher rate on a windy day. The moist air in the immediate vicinity of a moist soil or leaf surface is swept away by wind and the dry air occupies the space. Relative humidity, ET varies inversely with the atmospheric humidity 16

17. Factors affecting Evapotranspiration Growing season: Length of growing season and the actual date of sowing and maturing are important factors. The growing season of a crop coinciding with the hotter part of the year is expected to increase ET. Crops grown in different seasons have different ET. Crop characteristics: Growth habit, canopy development, leaf area index, plant density, duration and time of year when the growth is made, are important consideration to study the effect of crop characteristics on ET. Soil characteristics: Hydraulic conductivity and water holding capacity of soil affect the ET. Local Irrigation/Agricultural practices: Irrigation frequency, method of irrigation, depth of irrigation, fertilizer application and mulching are the important cultural factors affecting ET. Mulching is covering of soil by rotten vegetable matters 17

18. Crop Coefficient Crop coefficient: It is the ratio b/w the actual crop evapotranspiration to the reference crop evapotranspiration . Kc = ETc / ETo It is determined experimentally for various crops. ETc is determined by Lysimeter and ETo is determined with USWB class A evaporation pan. Kc is different for different crop and for different crop growth stages. It is mainly affected by crop type, soil type and climate of the area. 18

19. Crop Coefficient (Kc) Curve 19

20. Methods of estimating Evapotranspiration These methods are classified into three types: Direct methods (for research purpose) Lysimeter method Field experimentation method Soil water depletion method Inflow-outflow method Pan evaporimeter method USWB class-A pan evaporimeter Empirical methods Blaney-criddle method Penman method Modified Penman method Radiation method Penman Monteith equation Ref. Book for the topic: Irrigation Water Management: Principles and Practice By D. K. Majumdar

21. Direct Methods Lysimeter method: Used to measure ET and various components of water balance It is a container (usually 0.5m – 2m in diameter) to separate the root zone soil hydrologicaly from the surrounding soil. Lysimeter are installed in fields having the same crop & same conditions as in the field Measurements of different components of soil water are made for water balance studies. Important measurements are: Water input through direct precipitation (P), Water input through irrigation ( IR n ), Change in soil water content (storage) (  S w ), Water lost or input through surface runoff (R), and Water lost through deep percolation (PW)

22. Direct Methods Lysimeter method: By recording the amount of precipitation that an area receives and the amount lost through the soil, the amount of water lost to evapotranspiration can be calculated.

23. Direct Methods Lysimeter method: The general relationship to estimate ET is : Lysimeters are so constructed that measurements of deep percolation and surface runoff are possible or it is possible to avoid these losses Both weighing and non weighing type lysimeters are used for measurement. For very short period (daily or hourly) estimates of ETc , weighing type lysimeter is used.

24. Pan evaporimeter method USWB class-A pan evaporimeter : There exist a close relationship between the rate of consumptive use by crop and the rate of evaporation from properly located pan evaporimeter . Pan evaporation is the combined effect of all atmospheric factors and is independent of plant and soil factors Crop evapotranspiration rates for various crops may be estimated from the pan evaporation rates multiplied by a factor known as crop factor ( K crop ) which varies with the stages of growth, extent of ground cover with foliage, climate and geographical locations

25. Pan evaporimeter method

26. Pan evaporimeter method It is the most widely used evaporimeter for finding evaporation from the free water surface The Class A Evaporation pan is circular, 120.7 cm in diameter and 25 cm deep. It is made of galvanized iron (22 gauge) with a stilling pan The pan is mounted on a wooden open frame platform which is 15 cm above ground level to facilitate the circulation of air beneath the pan Daily evaporation rate is given by the fall in water level measured in the stilling well by hook gauge Adjustments are made to the evaporation values if rainfall occurs during a period of measurement After measuring the drop in water level each time, water is added to the pan to bring back the water level to original position of pointer tip level

27. Pan evaporimeter method The relationship between potential evaporation from an extensive free surface of water and pan evaporation is given as: K p (Pan Coefficient) is usually taken as 0.7 Crop Evapotranspiration is estimated similarly by multiplying the Crop Factor ( K c ) with Pan Evaporation ( E pan ) 27

28. Crop Coefficient ( K c ) for Pan Evaporation Method [Location Specific !]

29. Empirical methods Blaney Criddle method Penman method Modified Penman method Radiation method Modified Penman Monteith equation by FAO

30. Blaney Criddle Formulae (1950) Simple and is very commonly used (FAO also recommended its use in its I&D Paper-24) Relate temperature and sunshine hours with evaporation Should not be applied for duration shorter than a month Where: CU = Consumptive use (cm/month) or Evapotranspiration k = crop factor determined by experiments for each crop under environment conditions of particular area t= Mean monthly temperature in o C p= Monthly day light hours as %age of annual day light hours In FPS: CU=k.p.t/100 CU in in/month t in o F p in %

31. Monthly day light hours as Percent of Annual day light hours for Northern hemisphere Lat. o N Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 8.5 7.66 8.49 8.21 8.50 8.22 8.5 8.49 8.21 8.5 8.22 8.5 10 8.13 8.1 20 7.74 7.66 30 7.3 7.15 34 7.1 6.91 8.36 8.8 9.72 9.7 9.88 9.33 8.36 7.9 7.02 6.92 36 6.99 6.85 8.35 8.85 9.82 9.82 9.99 9.4 8.37 7.85 6.92 6.79 For complete table see book: Irrigation Engineering by Asawa , 1993 (page 39)

32. Consumptive Use Coefficients k Crop Consumptive Use Coeff , k For whole crop period Monthly max. Corn (maize) 0.75-0.85 0.8-1.2 Cotton 0.6-0.7 0.75-1.1 Rice 1-1.1 1.1-1.3 Sugercane 0.85-0.9 0.9-1.0

33. Example: Using Blaney-Criddle method estimate the yearly consumptive use of water for Suger Cane near Lahore (take Lat.=34 o N ) Month Mean Temp o C Crop Coeff. k Sun Shine % Cons. Use cm/month Jan 12.2 0.75 7.1 7.2 Feb 15.25 0.8 6.91 8.2 Mar 15.45 0.85 8.36 10.6 Apr 21.6 0.85 8.8 13.3 May 21.65 0.9 9.72 15.5 June 23.95 0.95 9.7 17.3 July 22.15 1 9.88 17.8 Aug 21.2 1 9.33 16.4 Sep 20 0.95 8.36 13.5 Oct 20.5 0.9 7.9 12.2 Nov 18.75 0.85 7.02 9.8 Dec 13.8 0.75 6.92 7.4 Sum=149.2 Deduct Effective Rain to find irrigation requirements. Compensate for Irrigation Efficiency (in field, and in conveyance) to get the total water required.

34. Blaney Criddle Formulae for Daily Use If needed to be applied for daily use then use: Where: C u = Consumptive use or Evapotranpiration (cm/day) k = crop factor determined by experiments for each crop under environment conditions of particular area t= Mean DAILY temperature in o C p= DAILY day light hours as per cent of annual day light hours

35. Latitude: Months North o Jan Feb Mar Apr May Jun July Aug Sept Oct Nov Dec South o July Aug Sept Oct Nov Dec Jan Feb Mar Apr May June 60 0.15 0.2 0.26 0.32 0.38 0.41 0.4 0.34 0.28 0.22 0.17 0.13 55 0.17 0.21 0.26 0.32 0.36 0.39 0.38 0.33 0.28 0.23 0.18 0.16 50 0.19 0.23 0.27 0.31 0.34 0.36 0.35 0.32 0.28 0.24 0.2 0.18 45 0.2 0.23 0.27 0.3 0.34 0.35 0.34 0.32 0.28 0.24 0.21 0.2 40 0.22 0.24 0.27 0.3 0.32 0.34 0.33 0.31 0.28 0.25 0.22 0.21 35 0.23 0.25 0.27 0.29 0.31 0.32 0.32 0.3 0.28 0.25 0.23 0.22 30 0.24 0.25 0.27 0.29 0.31 0.32 0.31 0.3 0.28 0.26 0.24 0.23 25 0.24 0.26 0.27 0.29 0.3 0.31 0.31 0.29 0.28 0.26 0.25 0.24 20 0.25 0.26 0.27 0.28 0.29 0.3 0.3 0.29 0.28 0.26 0.25 0.25 15 0.26 0.26 0.27 0.28 0.29 0.29 0.29 0.28 0.28 0.27 0.26 0.25 10 0.26 0.27 0.27 0.28 0.28 0.29 0.29 0.28 0.28 0.27 0.26 0.26 5 0.27 0.27 0.27 0.28 0.28 0.28 0.28 0.28 0.28 0.27 0.27 0.27 0.27 0.27 0.27 0.27 0.27 0.27 0.27 0.27 0.27 0.27 0.27 0.27 DAILY day light hours as Percent of Annual day light hours for Northern & Southern hemisphere

36. Soil-water (moisture) - plant relationship Water is essential to crop plants for their growth and development. Amount of water required by the crops is influenced by the soil type. Soil water plant relationship is a process that requires to be regulated for maximization of yields with a given unit of water. An understanding of this relationship is essential in order that water management principles are applied to various climate, soil and cropping regions of both rain-fed and irrigated lands. To understand this relationship, the concept of soil water/moisture and field capacity is essential. 37

37. Soil water/moisture and field capacity Gravitational moisture : When the water is applied on field, a part of it gets absorbed in the root zone, and the rest flows downwards under the action of gravity, and is called as gravitational moisture . Field Capacity (FC or  fc ) Soil water content when gravity drainage becomes negligible Soil is not saturated but still a very wet condition Traditionally defined as the water content corresponding to a Soil Water Potential of -1/10 to -1/3 bar (tension in soil or pressure below atmospheric pressure) Permanent Wilting Point (WP or  wp ) Soil water content beyond which plants cannot recover from water stress even if placed in humid environment Still some water in the soil but not enough to be of use to plants Traditionally defined as the water content corresponding to -15 bars of Soil Water Potential (tension). 38 If water tension = 1 bar, a plant root must exert a pull (suction) greater than 14.1 psi (101.3 K.Pa ) to get water from the soil.

38. Soil water/moisture and field capacity Field capacity is further divided into two types: 1. Capillary moisture: It is that moisture which is attached to the soil molecules by surface tension against gravitational forces and which can be extracted by crop through capillarity. 2. Hygroscopic moisture: It is that moisture which is attached to the soil molecules by loose chemical bond and it is not available to the plants for use ( adsorption ). Permanent wilting point: It is moisture content of soil at which plant can no longer extract sufficient water for its growth and wilts up. Available moisture: It is the difference in moisture content between field capacity and permanent wilting point. 39

39. Oven dry soil Max. Capillary Cap. (or field capcity) Wilting point (or Coeff.) Air dry soil Saturation point Hygroscopic moisture Capillary moisture Gravitational moisture Moisture (%) 0 (%) Ref. Wikipedia: Field capacity is the amount of soil moisture or water content held in soil after excess water has drained away and the rate of downward movement has materially decreased, which usually takes place within 2–3 days after a rain or irrigation in pervious soils of uniform structure and texture. The physical definition of field capacity (expressed symbolically as θ fc ) is the bulk water content retained in soil at −33 J/kg (or −0.33 bar) of hydraulic head or suction pressure.

40. Soil water content Mass water content (  m)  m = mass water content (fraction) M w = mass of water evaporated, g (  24 hours @ 105 o C) M s = mass of dry soil, g Bulk Density (  b )  b = soil bulk density, g/cm 3 M s = mass of dry soil, g V b = volume of soil sample, cm 3 Typical values: 1.1 - 1.6 g/cm 3 Particle Density (  p )  P = soil particle density, g/cm 3 M s = mass of dry soil, g V s = volume of solids, cm 3 Typical values: 2.6 - 2.7 g/cm 3

41. How to convert moisture content into volume of water in depth units Q: What is water quantity required (in depth units) if soil has a water deficit of 13% (let field capacity is 25% and irrigation is provided when moisture content depletes to 12%), depth of soil is 1.5m, and bulk density of soil is 1.4 g/cc. Ans : dw =0.13*1.5*1.4 = 0.273 m =27.3 cm If cropped area is given, water depth required can be converted into volume.

42. Wheat is sown on 1 hectare land, with soil bulk density of 1.2 g/cc. Wheat has root depth of 1.1 m. Soil in this area has field capacity of 23% and wilting point of 10 %. Water is scheduled once available moisture content (AMC) depletes by 80%. Calculate moisture deficit at the time of next irrigation required. Calculate the water depth required. Calculate volume of water required. If losses in field are 15%, what is volume of water required? Example

43. Water Availability Crop Period: It is the time normally in days that a crop takes from the instance of its sowing to harvesting. Base period: It is the time between first watering of crops at the time of its sowing and the last watering of crops before harvesting Delta of crops: Total depth of water required by the crop in unit area during base period. In other words it is the total depth of water required for maturing the crop. Volume of water required by the crop = Delta x Area or Delta ( ft ) = Volume (acre- ft ) / Area (acres) DUTY of irrigation water: It is defined as the number of hectares (or acres) of land irrigated for full growth of a given crop by supply of 1 m 3 /sec (or 1 ft 3 /sec) of water continuously during the entire base period.

44. Indicative Values of the Total Growing Period Crop Total growing period (days) Crop Total growing period (days) Alfalfa 100-365 Melon 120-160 Barley/Oats/ Wheat 120-150 Millet 105-140 Bean, green 75-90 Onion, green 70-95 Bean, dry 95-110 dry 150-210 Citrus 240-365 Pepper 120-210 Cotton 180-195 Rice 90-150 Grain/small 150-165 Sorghum 120-130 Lentil 150-170 Soybean 135-150 Maize, sweet 80-110 Squash 95-120 Maize, grain 125-180 Sunflower 125-130

45. Relationship between Duty, Delta and Base period Let there be a crop of base period B days. Let D hectares of this crop is being irrigated by 1 cumec of water provided for B days (the base period). Now the volume of water applied to this crop during B days @ 1 m 3 /sec = V = V = 1 x (B x 24 x 60 x 60) m 3 = 86400 B m 3 By definition of duty, D, is the Area in hectare (10,000 m 2 ) irrigated by 1 m 3 /sec of water supplied for B days to irrigate D hectares (=D 10 4 m 2 ) of land. Therefore, total depth of water required by crop per unit area ( ∆, Delta)= Volume/Area Delta = ∆ = Volume/Area = 86400B / 10 4 D Hence, Delta = ∆ = 8.64 B / D (for ∆ in meters) Delta = ∆ = 864 B / D (for ∆ in centimeters) Example: find the delta of a crop when its duty is 864 hectare/ cumecs with base period of 120 days.

46. Full Supply Factor or Duty: The term duty is only used for existing or running projects, but in a proposed project it is known as full supply factor , which is duty at head of the canal. Outlet discharge factor or Discharge capacity factor Duty at head of outlet is called outlet discharge factor. Variation of Duty with respect to location: Duty reduces as we move from field to head of canal. Irrigation Intensity: Percentage of culturable area irrigated during a year . Irrigation intensity has increased from approx. 75% at start of canal irrigation in Punjab to about 150% now-a-days. Cropping Intensity/cultivation intensity: It is the %age of area cropped with respect to culturable command area (CCA) in a year. If whole CCA is cropped once in Rabi, and once in kharif, the Cropping intensity is 200%. Cropping Pattern: Cropping Pattern represents the %age area of land under a crop in a season in command of a canal. Water Availability

47. Find the volume of water required if culturable area is 65,000 ha, from the following data. Water losses may be taken as 16%. Problem B=BASE PERIOD D=DUTY Also find Discharge required during Rabi & Kharif ? Total Volume of Water required

48. Questions….?? Thank you

49. Evapotranspiration (ET) and Consumptive use (Cu) Consumptive use: It is the amount of water required by a crop for its vegetated growth to evapotranspiration and building of plant tissues plus evaporation from soils and intercepted precipitation. It is the evapotranspiration plus the water used by plants for metabolic activities which is hardly 1 % of evapotranspiration It is the water required by plants to fulfill the evapotranspiration needs of crops. (FAO) It is the total amount of water used by the plants in transpiration (building of plant tissues etc) and evaporation from adjacent soils or from plant leaves in any specified time period. (S.K. GARG) It is expressed in terms of depth of water 50