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# IRRIG PRIN & MGMT AGSM 435

Texas A&M

GPA 3.97

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This 27 page Class Notes was uploaded by Doris Braun on Wednesday October 21, 2015. The Class Notes belongs to AGSM 435 at Texas A&M University taught by James Gilley in Fall. Since its upload, it has received 16 views. For similar materials see /class/225898/agsm-435-texas-a-m-university in Agriculture Education at Texas A&M University.

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Date Created: 10/21/15

CHAPTER 14 MIcRO IRRIGATION Most crops aierad apt able tu ml fulrngatlnn However because the initial mist of these systems is high it is best suited for high valued crops expensive land or where environmental cancems are significant w Xg39 System Types 1 man unowmm an a a m 2 mm av mum Surface dripwater applied slowlythrough srnall emitter openings tothe soil surface also called trickle irrigation 4 HIGH 12 inch dripper spacth dripper spacing a er 3 hours of irrigation mmlilnnl m i own livw mm mm mammalian dmssuillhie lai naan iaiHllAshmg enmin muer aroma in meml mum in iieli Yumle m umlluilc llllsmng innunui pzlh mm passive mmpanmng 9mmquot 39 l Microspraynwater sp39rayed over the soil surface at relatively low pressure also called microsprinkler Bubblera small stream orwager applied 9 rloodthe soil surfac in localized areas Surface Drip The maximum applicationrate for individual emitters is normally less than 3 gallons per hour For porous tubing and other multiple outlet sy e 39 he makimum application rate is approximately05m 15 gpm per 100 foot of tubing Surface Drip Emitter Saturaled 33 ll Accumulation Morslure Conlour Flow Line Bollom 01 am Zone Deep Percolation Surface Drip Advantwes of surface drlp Irrlgatlon over other mlcr o39lrrigatlo39n systems inc u e ease of installation inspection repair and cleaning ofemltters A major advantu e39lsthe aBIIItyto check soil surfaoe wetting patterns and to measure Indlvldu39al emitter dlscharge rates 39 Moislure Conluur Icro Fluw Line typically or 1 9pm gt V gt gt quotEgtggrpiqf RoolZon quot Deep Percolaliun Microspray Microspray systems are used frequently to irrigate trees and other widely spaced agricultural crops These systems are also very common for irrigating turf and landscaping Microspray A major advantage of microspray systems are minimal filtration needs and maintenance requirements are small Like drip microspray systems are sometimes suspended above the soil surface 4 39 Bubbler small str am of water applied to ood the soil surface in localized areal Bubblers With bubbler Irrigation water is applied to the a a much reater than for drlp systems but usually 8398 less than 60 gallons per hour The discha39ge applied at one point normally exceeds the soil39s in ltration rate 81d therd39ore u 5 m earthen dike to control the distribution of water on the soil surface Bubblers Advanages of the bubbler system include quot repair easy visud inspection and low energy requirements compared to other pressurized systems ever largersized laterd lines are normally required to mlnlmlze MES loss a odated Sullece Dup Subsurlece DI ID Emma 1 SUNSHle W D Flow Kim D 03 M 45 dconsiem E Pressure rumorX Head g m 09 an 42 2 A L A A n a T I 7 Is basic ly su e a s m II has been bu ied 0 El 0 V D 0 U 3 6 Radial Distance in Radial immune n Subsurface Drip Subsurface systems are buried at a depth of afew inches to 18 inches or more Shallow systems are installed in planting beds that are maintained over time Deep installations do not require the crops to be placed in the same planting s Subsurface Drip Emmet Roqulrod EQA Pq Whore N I number of emitters d I dopth oflrrlgl on re uired mlttor dllcharge Example 14 1 A tree crop has an irrigauon requirement of03 Inches perday Tree spacing is 15 by 20 teem Iran Irrigltlon ixoo befora penoo ol397 noun por Example 141 Given rl39l uon requirementth 0 wow Are irrig ted A 15 nx 20 n doom i how many eminen are requlr d for uch tree dA N a nigaxion perlod1F 7 hrday Flnd Number of emitters required pernee my Example 141 d A Solution 1 N Example 142 If one spray applicator was installed for the situation described In Example 1A1 now many P q hours would the s tem have to operate each day If each spray outlet applied 40 gallons per hour 2 03 quotI J75 x amp M m Irrigation requirement q 03 Inlday My 12 in tree 113 Are Irrigated A 300 n1 N Emmer discharge q 40 gallhr z Number of emitters per tree n 1 dqy hr am am Irrigation period P N 4 emitters per tree Example 142 dz A Solution N Typically main P 7 lllters injection I equipment and 03 m 1 J I 300 1 743 gal mm m P day 12 m We J33 monitoring l quotmm x 43 2 11 located In close he hr emitter control station P 14 hours per day Control Slation Water Su PP Y Chemical Tank 5 Venilizer chlorine pesticides acid Saree n Wake Meier Mainline Malnlme WaletAppllcalur o Flow Contro Lateral OnO Flaw Pressme ManllaIdSubmam Regulalar Auxmary Filler 11 Mainline and Manifolds Actual systems may be different and far more complex than the illustration The mainline carries water from the control station to manifolds which distribute the water to each lateral Normally there are no fixtures along the mainline other than elbows or tees Exam pie 1 A mainline is required to convey 200 gallons per minute a distance of 500 feet from the control station to the microirrigation manifolds What diameter of PVC pipe would you recommend if the friction loss must be less than 1 foot per 100 feet Given Q 200 gpm Pipe length 500 feet Pipe type PVC Pipe friction loss less than 1 W100 ft Example 1 Find Smallest pipe diameter recommended Solution From Table 82 4inch diameter pipe is too small to keep the friction loss below 1 ftl100 ft Fiveinch diameter pipe will have a friction loss of less than 08 ftl100 ft and is therefore the smallest recommended size Q gdnin 4in 5in Ridim1mdlosin 100 150 111 160 126 170 141 1130 157 210 228 81 240 267 95 230 310 110 280 356 126 110 404 E 320 456 1a 340 510 1a 330 567 202 Laterals For widespaced crops like trees emitters may be closely spaced near the tree with no emitters positioned between tree canopies As the trees grow additional emitters may be added Laterals As in Chapter 8 where friction loss and pipe size were determined for various types of irrigation pipe the same procedure can be used for microirrigation laterals In Chapter 8 the HazenWilliam equation was used to calculate friction loss in pipes For smalldiameter smoothwalled pipe used in microirrigation the HazenWilliams equation with a C value of 150 underestimates the friction loss Keller and Bliesner 1990 Laterals They recommend the DarcyWeisbach equation for microirrigation laterals For sim plicity however the HazenWilliams equation as used in Chapter 8 will be used The reader is cautioned that this equation underestimates the friction loss slightly Table 141 Friction loss in feet per 100 feet rorsinaii diameter pipe based u on the HazenWiiiiains equation for pipewitn a 0 factor of 150 adapted from Clark et ai in pre Nominal sizein 05 075 10 15 Inside pipe diameter in 062 082 105 161 Flow rate Q 9 m p Friction loss ftl100 ft 05 05 01 10 11 05 15 25 06 02 20 59 10 05 25 60 15 05 01 50 64 21 06 01 40 142 56 11 01 50 215 55 17 02 60 501 17 24 05 70 m 52 04 80 151 40 05 90 165 50 06 10 197 m 08 15 592 129 16 20 27 25 41 Laterals hm FL h Friction FORMULA where hm friction loss for laterals with uniform Iy spaced and uniformly discharging outlets F multiple outlet reduction factor L lateral length and hf friction loss of a conveyance pipe without outlets Table 83 Multiple uutlet raams fur lam mls with e ally spteadu es the same dis rge Fur oenmrpivuu see mum Nu ul39 Nu ul39 uutJeu F nudes F 1 10 16 0377 2 0694 17 0376 3 038 18 0373 4 030 19 0372 5 061 20 0370 6 063 22 0368 7 0419 24 0366 8 0410 26 0364 9 0402 28 0363 1 0396 30 0362 11 0392 35 0359 12 038 40 0357 13 034 50 0355 14 031 100 0350 15 0379 Mme than 0345 100 F 54 hmnmptmgwtmmmm r m 39 39 Example 2 Determine the smallest diameter polyethylene pipe to be used fora manifold if the flow rate is to be 70 gpm What will the friction loss be for the manifold if the length is 200 feet Given Q70gpm Manifold length 200 ft Find Smallest recommended pipe diameter Friction loss for the manifold Example 2 Solution From Table 82 a 2inch diameter pipe with a flow of 70 gpm will require a water velocity in excess of 5 fps and is therefore not recommended lfa 25inch diameter pipe is available it would satisfy the velocity requirement of 5 fps and the friction head loss would be 242 ft 00 ft or a total of 484 ft of head loss This would probably be considered too high a friction loss for a manifold A 3inch diameter pipe would have a friction head loss of 092 x 2 184 ft Table 82 Example 3 Q gtmm l n ll 2 u a 2 u quotquot quot f quot h quotmnn quotquotquot quot What is the smallest recommended pipe diameter 2 1535 g 3 g g for a polyethylene lateral that is 200 feet long and f m g i 33 3 3 has an emitter outlet spacing of 2 feet Each 5 m m 35 4 D5 emitter discharges 2 gallons per hour In in 79 3 A 72 6 23 u 25 mm m 2 7U 91 a 1 an m 3 78 9 35 33 m 33 7 25 m L 200 feet 22 l 33 ill i 33 s 2 feet 5 8 7 9 7 3 3 3 9 Emitter discharge 2 gaIIhr 22 48 ll 64 L 154 S l 64 4 l 6 Polyethylene pipe 1819 5 2 535 7 a l Z Find Smallest i e diameter recommended 8 3 l 3 2 i A l n 9 4 n Naminllulxl n 05 075 10 1 Example 3 InIdpIpdumcurun a 032 1 u 161 Solution Number of outlets n 200 ftI2 ft 100 Q n x 2 gallhr Q 200 gallhr 33 gpm hr 9 ftlloo ft for d 05 in Table hr 26 ftlloo ft for d 075 in Table hfm F L hf Equation 1 F 035 Table hrquot 035 200 ft 9 ftlloo ft for d 05 in hrquot 63 ft A 05 in diametertubing is acceptable Tubing of 05 in diameter is the smallest size recommended Flow rat a npm Frlnuonloumnaa n 0 11 25 2 IJ a I 54 o 14 1 41 l 301 4 19 z 2 131 o 1a a 1 191 41 1 quot2 129 2 220 2 1 Title 5 3 Mul ple uniflotan for Ilhrullwllh oqullly Iprud outlet oftho um dllohlrgo For plvob no footnotequot No01 No01 ou oh F unlit F 1 10 10 0377 2 0684 17 0376 3 0520 10 0373 4 0400 10 0372 5 0451 20 0370 0 0 22 0300 7 0419 24 0306 0 0410 20 0 304 9 0402 20 0 303 10 0300 10 0 302 11 0302 35 0 35 12 0300 40 0 357 13 0304 39 14 0301 1W 0 350 15 0370 v39 100 39F 054foMnhr pivot Mthullond gull F050f r Example 4 If microsprayers with a discharge rate of 05 gpm at a spacing of 8 feet were substituted forthe emitters in Example 3 what would be the minimum recommended pipe diameter Given L 200 feet s 8 feet Microspray discharge 05 gpm Polyethylene pipe I i a Smallest recommended pipe diameter Example 4 Solution n 200 ftIS ft 25 Q n x 05 gpm Q 125 gpm h 95 ftllOOftfor d 10 in Table h 12 ftllOOftfor d 15 in Table hfm F L hEquation 141 F 0365 Table hfquot 0365 200 ft 95 ftl100 ft for d 10 in hfquot 69ftford 10 in hfquot 0365 200 ft 1 moo ft for d 15 in hfquot 09ftford 15 in ominlleizl n 05 075 10 15 Inside pip dilmlor n 082 002 105 10 1 FlowrteO 9pm Frinh onlon l100 03 01 11 03 23 00 02 39 10 03 30 15 05 01 34 21 06 01 M 2 30 11 01 215 55 17 02 301 77 24 03 102 32 04 125 131 40 05 as a I n n A I 107 11 03 302 120 10 41 Title 5 3 Mulllple milflour for Ilhrullwllh oqullly Iprull outlet ofth39o um dllohlrgo For Example 4 no No01 No01 oumu F wtlotl F The friction loss for 15 In diameter 1 m 15 9311 polyethylene is acceptable for the entire 2 684 11 0316 3 om a mm lateral The friction loss for 10 in diameter 4 0430 13 0372 5 M51 20 mm pipe is not recommended for the rst a as 22 use portion of the lateral because of excessive Z 31 5535 velocity Table 141 You could repeat 1 33 3 gig these calculations to decide when the 11 0392 55 035 39 12 uquot 40 ME lateral diameter could be reduced from 15 03 so mass to 10 in diameter 14 03 100 0350 15 0179 Meridian 0345 100 F 54foronhr plvohimthuilond gull F SGf Clogging Clogging Clogging of emitters is one of the major concerns for microirrigation Obviously the smaller the orifice or the longer the capillary section the more prone the emitter is to clogging Emitters can be clogged by particles bacterial slimes algae waterborne organisms or precipitation of various chemicals If emitters become clogged water distribution is not uniform and in severe cases crop loss from water stress occurs Clogging problems are frequently site speci c and economical solutions are not always available Emitter Discharge q39 K hx Equation 141 where h is the pressure head In feet at the emitter The emitter discharge coef cient K contains the effects of the cue clent of discharge emitter geometry and the acceleration of gravity The value of x the emitter discharge exponent characterizes the type and ow regime of the emitter I x I x D 20 110 D 10 20 30 Pressure Head Variation A Fliin Compensating x0 o 7 10 30 Ram Pressure X Emltter DIscharge zo F075 Ori cetype emitters are fully turbulent and F05 have an emitter discharge exponent of 05 g m x0 4 539 With long path emitters x 05 for those with E Rated Discharge X0 0 fully turbulent ow and 10 for laminar flow g 9 An x value of less than 05 Indicates an emitter 5 391 Laminar x1 u that compensates for changes In pressure 3 Long Faih FD 75 D Ori ce m TmbuienL x0 5 20 Vortex x0 Emitter Discharge To determine K and x for an emitter the discharge must be measured at two different operating heads h1 and h The x may be determined analytically from 10g qel qu 10g h1 h2 Equation 142 Example 144 Determine the discharge exponent and the discharge coefficient for a vortex emitter M From laboratory measurements q is 075 galIhrwhen h 15 ft q is 10 galIhrwhen h 30 ft Find Discharge exponent x and the The value of x calculated from Equation 142 is dISCharge coef c39ent K used to calculate K from Equation 141 Example 144 Example 144 321mm 59mm x710quEIqu q Khx loghl hz 9 x7 logq am 7 log 75 1 710g75 7 7125 qe 7 loghh2 Iog1530 log501301 h x X 042 1 1 024 so 4 2 Emitter Discharge It is impossible to manufacture any two items exactly alike Very small variations in emitter passage size shape and surface nish can result in variations in discharge The amount of variation also depends on emitter design construction materials and precision during manufacturing Emitter Discharge The coefficient of manufacturing variation for an emitter v is a measure of anticipa variations in the discharge for a sample of new emitters The value of v should be available from the manufacturer If not available it can be determined from the discharge data of a sample set of at least 50 emitters operating at a constant reference pressure by Emitter Discharge MIN qu q22 qi nqn 9a Equation 143 where n number of emitters being e e q discharge rate of an emitter and q average emitter discharge rate Emitter Discharge For an emitter having a v of 006 and a qa of 1 gallon per hour 95 of the emitters will have a discharge rate between 088 and 112 gallons per houn Asa general guide manufacturing variability can be classified in accordance with Table 142 A lower standard is given for linesource tubing because it is difficult to keep both the variation and price low 20 Emitter Discharge Table 142 Classification for manufacturing variation v of emitmrs Solomon 1979 Table 14 3 Characteristics ofvanous types of emlllers Keller and Bhesner 1990 Coefficient of Classi ca m Dnp supra LinHource Emitter Discharge manufacturing Flushing mung emitters tubing type exponent x Variation v ability r r r r r quotOnneennn Excellent vlt 005 v lt 01 Vortexorifice 0 42 0 07 None Average 005 ltV lt 007 01 lt V lt 02 Multiple flexible orifices 0 7 0 05 Continuou Ball amp slottedseat 0 50 0 27 Automatic Marginal 007 lt v lt 011 Compensatingball amp slotted 0 25 0 09 Automatic Poor 011ltv lto15 02ltv lt03 mt Capped orifice Sprayers 0 so 0 05 None Unacceptable 015 lt v 03 lt v Discharge Versus Pressure rrLongrpaLhrwnn S a mb 0 70 0 05 N Flow com pensating emitters prowde som e n e SW1 pm 075 0 06 Manual degree cf flow regulation as pressure changes When x is between 02 and 035 some Compensanng 0 40 0 05 None regulation is possmle and there Is still some Compensanng 0 20 0 06 Automatic Tortuous 0 65 0 02 None fleXIbility for adjusting the discharge rate quotShortrpathnrnn Groove Map 033 002 Amman Compensating emitters are valuable on hilly 51M 0 n 0 w Amman Sites where it is impractical to deSIgn for uniform pressure along the laterals Porous pipe 1 0 0 40 None Twin chamber 0 61 0 17 None 21 Emission U nifo rm ity Emission uniformity can be treated like distribution uniformity DU in Chapter 5 and is a measure of the uniformity of emissions from all the water applicators within the entire microirrigation system Emission Uniformity For field tests EU 100 qmq Equation 144 where EU is the emission uniformity from a eld test qn1 is the average discharge for the lowest onefourth of the eld measured emitter discharges gallons per hour and qa is the average discharge of all the emitters checked in the field gallons per hour Emission Uniformity The efficiency of an irrigation system is the relation between gross irrigation amounts and the net addition of waterto the crop root zone Emission uniformity and the various sources of water loss that occur during the operation of the system are the two components of microirrigation efficiency Emission Uniformity To estimate the distribution uniformity for a proposed design the following formula was developed Karmeli and Keller 1974 V EU100 10 127 q m E0145 quot Qa where DU is design emission uniformity in v is the coefficient of manufacturing variation Table 143 for typical values and n is the number of emitters 22 Emission Uniformity The ratio qquotqu expresses the relationship between the minimum qm and the average q discharges resulting from pressure variations within the system The factor 10 INL J adjusts for the additional nonuniform ity caused by anticipated manufacturing variations between individual emitters Example 147 Determine the distribution uniformity for a microirrigation system designed for an average pressure of 20 psi The system is being designed for spiral long path emitters with automatic flushing The field is flat and the friction loss head is a maximum of 10 feet The system is being designed for 2 emitters per plant and the average design emission rate is 10 gallons per hour Example 147 Given ha 20 psi x 231 ftlpsi 462 ft x 075 and v 006 from Table 143 q 10 galIhr Ahf change in pressure due to friction loss 10 ft h9 change in pressure due to elevation 0 n 2 Example 147 Find The distribution uniformity DU for this design Solution q KhX Equation 143 V EU100 107127 q m Eq147 391 qa q 1 K o056 h 412 1772 23 Example 147 qmKhn hmhPhehf4601O mwn qquot 0056 3675 qn 082 gallhr 03906 E 100107 05082 100 EU10010 7127 J5 EU 78 Management The success of any irrigation system particularly microirrigation depends on management Irrigating by small quantities frequently is quite different from sprinkler and surface irrigation methods where larger less frequent applications are normal With microirrigation precise information on crop water requirements is required to determine the appropriate irrigation amount Wetted Area The percent of the surface area wetted PW by microirrigation systems compared to the entire cropped area depends on the volume and rate of discharge at each application point the spacing of water applicators and soil type No best or minimumwetted area percentage has been found but systems having high PW values provide more stored water which is a valuable advantage in the event of system failure Wetted Area A reasonable design objective for widely spaced crops such as vines bushes and trees is to wet between onethird and two thirds of the soil surface dedicated to each plant In regions that receive considerable supplemental rainfall values of Pquot less than onethird are acceptable for fi netextured soils 24 Wetted Area Maintaining Pquot below twothirds for widely spaced crops maintains dry strips for cultural practiCes In closelyspaced row crops with the laterals in every or every other crop row PW approaches full coverage Salinity Microirrigation has potential advantages where the soil or irrigation water is saline The principal advantage is that with microirrigation the water content of the root zone is maintained high and nearly constant As a result the salt concentration of the soil solution is low and steady and thereby not creating as much salt stress as a system where the soil dries between irrigations with congruent signi cant increases in salt concentration Water Requirements The plant canopies of young or widelyspaced crops shade only a portion of the soil surface area and intercept only a portion ofthe incoming solar radiation Conventional estimates of water requirements of young crops assume a portion of the applied water will be lost to nonbeneficial consumptive use Water Requirements This loss is through evaporation from the wetted soil surface or through transpiration from undesirable vegetation Most microirrigation systems reduce evaporation losses to a minimum so transpiration by the crop accounts for practically all of the water consumed 25 Water Requirements Many commercial systems operate daily or every other day The operational time for a microirrigation system should not exceed 20 hours per day In case of repair or maintenance requirements time is required to catch up This is particularly critical during periods of peak crop water use Water Requirements For example if you wish to drip irrigate a field of tomatoes and the rows are 3 feet apart you might place a lateral along each crop row or midway between adjacent rows If you placed a lateral in every row and the irrigation requirement was 021 inches per day you wanted to irrigate 1 hour per day and you chose an emitterwith a discharge of 2 gallons per hour then Equation A could be used Water Requirements P 61 A 1 hrlday 2 gallhrIO27 inlday CONVERT UNITS A 12 ft2 or an emitter spacing of4 ft Water Requirements To determine the area to be irrigated by each emitter solve Equation A for the AREA Setting N to 1 to determine the area each emitter would irrigate gives A 1 hrlday 2 gallhr I 027 inlday 12 ftz Thus if a lateral was placed in each crop row the spacing between emitters should be 4 feet If one lateral served two crop rows emitter spacing would need to be 2 feet 26 Water Requirements Irrigation scheduling involves two primary decisions when to irrigate timing and how much to apply amount Microirrigation inherently implies frequent irrigations Depending on the system and the sophistication of the controls irrigation frequency can be from once in several days to multiple times every day 27

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