Slide 1

Rabi H. Mohtar Professor, Agricultural and Biological Engineering Director, Global Engineering Programs February 2, 2009 1Irrigation Principles; Mohtar Slide 2 Planning an Irrigation System You are to plan an irrigation system for a mixed plantation of vegetables, orchards, and forages (4 ha each). The pump is located at the southwest edge of the rectangular field. Select your team and get going! Tasks you need to consider include: 1.Requirements for water; ET; Crop coefficients, etc. 2.Type of irrigation system 3.Irrigation frequency 4.Limitations of selection of irrigation system 5.Design parameters: sizing, spacing, application pattern, 6.Limitations of the design 7.Advantages/disadvantages for each irrigation system 8.Pumping requirement 2Irrigation Principles; Mohtar Slide 3 Irrigation = artificial application of water Can be through subsurface, surface, sprinkler or microirrigation methods of application. Goal is to control soil moisture balance. If: rain < 250 mm irrigation is necessary for crop production 250 - 500 mm limited crop yields possible without irrigation rain > 500 mm can maximize yields with timely irrigation Timing of applications is important. Varies with crop, climatic conditions, stage of plant growth, soil characteristics. 3Irrigation Principles; Mohtar Slide 4 4 Slide 5 5 Slide 6 Benefits/Uses 1. Supply water to root zone 2. Supply pesticides (chemigation); fertilizers and liquid animal manure (fertigation) more efficiently since control timing of release, amount, and to some degree, placement. 3. Misting increases relative humidity around upper portion of plant thereby reducing plant stress, evapotranspiration, temperature. 4. Frost protection. When water freezes it releases latent heat to the air. 5. Control blowing soil. Wet soil is heavier, retains better structure and anchors plants is place. Blowing soil is abrasive to plants. 6. Leach toxic elements from soils. All water contains salts so irrigation adds salts to soil. Evaporation of water from soil surface carries salts to through soil to surface. Allow extra irrigation water just for leaching purposes to dissolve soil salts and flush them away in drainage water. 6Irrigation Principles; Mohtar Slide 7 Benefits/Uses saline soils = contain Ca 2+ and Mg 2+ salts. These reduce available water to plants causing plants to wilt and burn. May show up as white crust on soil surface. sodic soils = contain Na + salts. Sodium damages soil tilth and structure, can lead to formation of hardpans that resist penetration of water and plants roots so get poor plant growth, stunted. 7Irrigation Principles; Mohtar Slide 8 System Planning 1. determine need - estimate crop use vs. rainfall varies with crop, atmospheric conditions (temperature, wind, RH), stage of growth compare evapotranspiration vs. precipitation 2. examine site topography (slope, changes in elevations) soil characteristics (root zone depth, water holding capacity, infiltration rate) 3. availability of water - quantity & quality. Generally groundwater is better quality than surface water. Need well with sufficient pumping capacity if bringing in water through an irrigation canal. 4. economic analysis - compare cost of installing and operating irrigation system vs. expected increase in yields. In Indiana, generally need an increase of the magnitude of 50 bushels of corn per acre per year to justify expense. 8Irrigation Principles; Mohtar Slide 9 Available Water AW = (FC - PWP)D r / 100 AW = available water (mm, in) FC = volumetric field capacity (decimal) PWP = volumetric permanent wilting point (decimal) D r = depth of root zone or depth of soil layer of interest (mm, in) Typical values of FC, PWP, AW are given in a previous handout. 9Irrigation Principles; Mohtar Slide 10 Leaching Requirement extra water applied to dissolve and carry away salts in soil value will be given if needed expressed as a portion of the total irrigation water applied ex. LR = 0.2 and total applied = (1+LR) x soil water deficit Irrigation Requirement IR = [(ET - P e )(1 + LR)] / E a P e = effective rainfall E a = application efficiency ET = u from Blaney-Criddle evapotranspiration equation 10Irrigation Principles; Mohtar Slide 11 Irrigation Efficiencies Conveyance Efficiency: E c = 100 (W d / W i ) W i = water introduced into distribution system W d = water delivered by distribution system Example: A pumping station puts water into a canal at a rate of 50 m 3 /s. After seepage losses and evaporation, water delivered in the canal at the farm is 45 m 3 /s. So E c = 100(45/50) = 90% Application Efficiency: E a = 100 ( W s / W d ) W s = water stored in root zone by irrigation (difference between W s and W d due to surface runoff, drainage, deep percolation, evaporation. Water Use Efficiency: E u = 100 ( W u / W d ) W u = water used beneficially. This includes water used for leaching salts (not included in W s value). 11Irrigation Principles; Mohtar Slide 12 Irrigation Scheduling if water is available, schedule so as to achieve maximum yields if water is limited / expensive then schedule so as to maximize economic return Typically start irrigation when available water = 55% maximum Irrigation Period = number of days over which irrigation cycle must be complete. Equals the time it take for field at FC to reach 55% AW without rainfall occurring ex. root zone depth = 1 m, allowable depletion = 40%AW, AW = 150 mm/ m depth, ave. ET = 8 mm. day IP = [150 mm/m (1m) (0.4)] / 8 mm/day = 7.5 days So can divide up entire area to be irrigated such that repeat irrigation at same site every 7.5 days. 12Irrigation Principles; Mohtar Slide 13 Water Requirements The irrigation requirement for a given system is dependent on a number of factors. Precipitation and evapotranspiration are extremely important in determining the irrigation requirement. IR = irrigation requirement ET = evapotranspiration P = seasonal precipitation E a = application efficiency LR = leaching requirement The methods for calculating evapotranspiration vary (Blaney-Criddle, Penman, Jensen-Haise). All evapotranspiration calculations are based on two overall factors: ET = ET0* Kc ET = actual ET ET 0 = reference ET (climate) K c = crop coefficient 13Irrigation Principles; Mohtar Slide 14 Characteristic Crop Evapotranspiration Curve 14Irrigation Principles; Mohtar Slide 15 Irrigation Systems 1. Subirrigation ("controlled drainage") 2. Surface Irrigation 3. Sprinkler Irrigation 4. Microirrigation 15Irrigation Principles; Mohtar Slide 16 Infiltration in irrigation design 1. Effect on sprinkler lateral length (runoff) 2. Effect on furrow length (efficiency) 16Irrigation Principles; Mohtar Slide 17 Basin Irrigation Most crops are suitable, used often with grasses, row crops, and orchard. Well suited for moderate to low intake rate, 50 mm/h or less. Limitations: need acurate land levelling start and maintained and appropriate ridge height. 17Irrigation Principles; Mohtar Slide 18 Graded Border Field is divided into graded strips by constructing parallel dikes. Open and with no flow at end of border. Flow rate is such that the desired volume of water is applied to the strip in a time equal or slightly less than that needed for the soil to absorb the amount required. Suited for slopes 1 - 0.5% or less. Most crops in soil types. Limitation is cross slopes. Design Involves balancing water, advance and recession curves to achieve equal time of opportunity for intake at any point. 18Irrigation Principles; Mohtar Slide 19 Furrow Irrigation Used with tilled crops planted in rows. Slope limitation < 1% Can go up to 3% in arid region because of erosion at higher intensity. 19Irrigation Principles; Mohtar Slide 20 Furrow Irrigation Parameters that should be available: Intake characteristics of soil Water storage capacity of soil Crops to be grown To be determined: average depth of application length and width maximum flow rate Types: 1. gradient furrows 2. Cut back inflow with open end 3. level impoundment 20Irrigation Principles; Mohtar Slide 21 Sprinkler Irrigation resembles rainfall. High efficiency with good design cut down on pending and runoff by applying water at rate = or less infiltrations Types: 1. periodic move 2. fixed system 3. continuous move Suitable for most crops, but those affected by blight. application rate intake rate uniformity = f (spacing, operating pressure) 21Irrigation Principles; Mohtar Slide 22 Sprinkler Irrigation Uniformity 22Irrigation Principles; Mohtar Slide 23 Sprinkler Spacing depends on: sprinkler - nozzle combination (pressure-flow) operating pressure desired uniformity wind speed use of the system irrigation in frost Wind conditionlateral spray No wind65% effective D 8 Kw/hr60% efficiency D 716 Kw30% efficiency D Sprinkler Irrigation Uniformity 23Irrigation Principles; Mohtar Slide 24 The Hazen-William friction formula: Friction in a pipe: H f = 10.46 (Q/C) 1.85 L/D 4.87 H f = friction loss in ft. Q = flow rate in gpm L = pipe length in ft. D = actual inside pipe diameter in inches C = Hazen-Williams coefficient 24Irrigation Principles; Mohtar Slide 25 Type of pipeC factor Aluminum with couplers120 Aluminum without couplers140 Polyethylene in PVC140 Cast iron100 Copper130 Steel100 The Hazen-William friction formula: 25Irrigation Principles; Mohtar Slide 26 No. of Outlets Factor No. of Outlets Factor No. of Outlets Factor 115.38030.350 2.51210.36540.349 3.43415.35750.348 4.40520.354100.347 Pipe Friction Calculations 26Irrigation Principles; Mohtar Slide 27 Friction Loss Chart for 1/2" Class 315 Pipe (Loss in PSI per 100' of pipe at flows shown) Flow in GPHLoss in PSIFlow in GPHLoss in PSIFlow in GPHLoss in PSI 15.01770.292002.00 200.2880.372202.39 25.04390.462402.82 30.06100.562603.26 35.08120.782803.73 40.10130.903004.26 45.131501.183204.78 50.151701.483405.34 60.221801.653605.97 1. Select the chart that matches (or approximates) your lateral length. 2. Read down the left-hand column to the flow rate that matches, or approximates the flow rate for your lateral. 3. Read across to the column that corresponds to your emitter spacing to get the total friction loss in the lateral. 27Irrigation Principles; Mohtar Slide 28 100' lateral length200' lateral length300' lateral length Flow Rate GPH Emitter Spacing Flow Rate GPH Emitter Spacing Flow Rate GPH Emitter Spacing 5'10'12.5'20'5'10'12.5'20'5'10'12.5'20' PSI 5.015.0165.029.028.0295.044.042 15.043.04515.084.082 0.8315.125.121 25.075.076.077.08425.145.143.14825.215.209.213 Run main up/down the slope and run lateral across the slope. Place emitters above plant on a slope (down hill) Friction Table 28Irrigation Principles; Mohtar Slide 29 Main line and Lateral size factors Uniformity pumping cost maximum velocity V < 3m/sec to prevent cavitation 29Irrigation Principles; Mohtar Slide 30 Pumps and Pumping a. Considerations in Planning a Pumping System 1. Source of water 2. Pumping rate 3. Total dynamic suction head vertical suction lift length and size of suction pipe number and kind of bends foot valve and strainer 4. Total discharge head vertical lift size and length of pipe number and kinds of bends head required at delivery point (sprinkler system) 30Irrigation Principles; Mohtar Slide 31 Total head = total static head + pressure head + friction head + velocity head Total static head = vertical distance that the pump must lift the water Pressure head = pressure required at sprinkler. [ PSI x 2.31 = Head in feet of water]] Friction head, H f = energy loss due to friction in pipe lengths, fittings, bends, valves (see Appendix C) Velocity head = small amount of energy given to the water to get it in motion; usually negligible Pumps and Pumping 31Irrigation Principles; Mohtar Slide 32 Critical Path Concept Longest path that water has to take, assuming all outlets are the same flow. Branching Network: Steps: determine pipe length in critical path calculate friction loss from lateral end and work backward toward the pump add losses, fittings are neglected add or subtract elevation difference Control Components Pressure loss due to: valve filter circuit along elevation line 32Irrigation Principles; Mohtar Slide 33 Pressure Compensation q=ch x flow (q) Pressure (h) x = orifice exponent typically 0.5 range of x = 0, 1 Can orifice flow be independent from h? Is that desirable? Why? Multi-outlet pipe 33Irrigation Principles; Mohtar Slide 34 Example: Determine limiting rate of application, depth of application, and irrigation period. Limiting rate of application (iph) is the rate above which ponding will occur. Depth of application (ft) is the maximum depth of the root zone. Moisture-holding capacity is a soil property and is the difference between FC and PWP (in/ft). Total moisture capacity (in) needed = moisture holding capacity * root depth soil should not be depleted until all moisture is gone. Net application depth (in) = moisture left in soil * total moisture capacity Peak rate of use (in/day) is gross ET per day Irrigation period (d) = net depth of application/rate of water use per day Irrigation Principles; Mohtar34 Slide 35 Example: Determine limiting rate of application, depth of application, and irrigation period. Limiting rate of application (iph)= 1.3 iph (from soil series) Depth of application (ft) = 1.5 ft ( rooting depth) Irrigation period: The moisture holding capacity (in/ft) is 1.5 in/ft (from soils WHC); hence, the total capacity (in) needed is _________ If irrigation is started when the available moisture reaches 55 %, the depth of application (in) is _________ The peak rate of use by potatoes in Northern Indiana (in/day) is_______; hence the irrigation period (days) = _________ Irrigation Principles; Mohtar35 Slide 36 Irrigation Canal Leakage Many of the irrigation canals are tunnels, from up to 20 or 30 feet underground that are leaking large amounts of water. 1. how you know where the leaks were 2. what you should do? Irrigation Principles; Mohtar36