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More Crop Per Drop (2011)

1. Orzolek J K Harper A R Jareff and G L Greaser 2002 Drip irrigation for vegetable production Agricultural Alternatives Pennsylvania State University College of Agricultural Sciences Agricultural Research and Cooperative Extension State College PA USA Luke G 2006 Irrigation scheduling How and why Farm Note 23 1990 Dept of Agriculture and Food Govt of Western Australia p 1 3 Marr C W and D Rogers 1993 Drip irrigation for vegetables MF 1090 Kansas State University Agricultural Experiment Station and Cooperative Extension Service Manhattan KS USA NSW DPI 2004 Water wise on the farm Fact Sheet http www dpi nsw gove au data assets pdf file 0005 164625 soil texture pdf NSW DPI 2008a Water Efficiency Technologies Module 1 Soil Management Notes New South Wales Department of Primary Industries Orange NSW Australia NSW DPI 2008b Water Efficiency Technologies Module 2 Irrigation System Evaluation Pressurized Systems System 8 Drip Trickle Systems Notes New South Wales Department of Primary Industries Orange NSW Australia 82 NSW DPI 2008c Water Efficiency Technologies Module 3 Measurement Scheduling and Benchmarking Notes New South Wales Department of Primary Industries Orange NSW Australia Palada M C S Bhattarai M Roberts N Baxter M Bhattarai R Kimsan S Kan and D L Wu 2008 Increasing on farm water productivity through affordable microirrigation v
2. soil based Plant based method This method is based on the appearance of the plant in response to water stress Wilting is a sign of water stress and some farmers may irrigate when plants start to show signs of wilting In many cases wilting means that the crop is already under water stress Stress will cause plant growth to slow down This will reduce yield and quality of the crop Wilting and signs of plant stress may happen even when there is water in the soil For example some plants roll their leaves or wilt in the middle of a hot windy day Wilting is also a sign of 60 water logging or root diseases This method is not always reliable in monitoring crop water use Weather based method Weather affects crop evapotranspiration Hence measurement of evapotranspiration ET provides estimates of water use by the crop Evapotranspiration is calculated using a reference crop The reference crop is an extensive surface of green grass cover of uniform height actively growing completely shading the ground and not short of water Reference crop evapotranspiration ETo can be found at a local weather station This information indicates how much water the reference crop has used each day The particular crop of interest will be different from the reference crop Soil water based method This method of measurement is based on the amount of water in the soil and calculation of the amount of water needed to refill the readily availab
3. soil water content porosity Field capacity Soil water content after free drainage 24 48 hrs of saturated soil 50 Refill point The water content of the soil below which the plant exhibits some form of stress and a drop in yield it is not constant down the soil profile and the advent of stress might be identified by a drop in daily use water and roots extracting water at greater depth Permanent wilting point Soil water content when plants have extracted much water and wilt but will recover if rewatered Unavailable water Soil water content that is strongly attached to soil particles and aggregates and cannot be extracted by plants Exemplified by water content less than permanent wilting point i e when plants have extracted all of the water they can and do not recover if rewatered SATURATED SOIL Terms describing soil water content Water held in the soil is described by the term water content quantified gravimetric g water g soil and volumetric ml water ml soil basis Terms to describe water content and illustrated in Figure 31 are Gravitational water Water amount held by soil between saturation and field capacity Water holding capacity Water amount held between field capacity and wilting point Plant available water Portion of the water holding capacity that can be used by plant As general rule plant available water is 50 of the water holding capacity From field capacity to the stres
4. stone gravel in the soil Step 6 6 Multiply the thickness of each soil layer by its adjusted RAW value Step 6 7 Add up the RAW for each soil layer to obtain the total root zone RAW 52 Table 6 RAW and Available Water AW values for different soil textures Ramsey 2007 To 20 kPa To 40 kPa To 60 kPa To 100 kPa To 150 kPa Soft crops such as Most fruit crops and table Lucerne most pasture Annual pastures and hardy Available Water AW is vegetables and some grapes Most tropical grapes crops such as crops such as cotton the total water available in tropical fruits fruits maize and soybeaans sorghum and winter the soil cereals Readily Available Water RAW mm m AW mm m EC _ s p _ s J s NENNEN FE wv Clay loam 150 Light clay Tension is O kPa at saturation point The figures are only approximate Except when partial rootzone drying is being practiced on wine grapes should be irrigated before 60 kPa is reached 53 Table 7 Calculating rootzone RAW Example 1 Ramsey 2007 White Radish Daikon is growing in 0 3 m of sandy loam on top of 0 5 m of light clay For a soil pit at this site the calculations would be STEP 1 STEP 2 STEP 3 STEP 4 STEP 5 STEP 6 STEP 7 Identify Determine Identify the Multiply the Add up the Identify Add up the and the soil texture RAW for thickness of each RAW for the RAW in the 0m measure texture of each soil layer soil layer by its each layer effe
5. the drip kit should last 5 to 7 years At the end of each season e Remove sleeves from the far ends of the drip tape e Pour water in bucket to flush out tape and replace sleeves e Store the bucket so that it will not be damaged by rodents e Remove stopper from adapter and rinse filter screen if bucket takes longer than usual to empty Do not remove screen from stopper or rub screen with fingers e Leave drip tapes in place but place a stone over the end of each tape to prevent from blowing away e Protect the tapes from animals CHAPTER 4 Drip Irrigation Scheduling Drip irrigation scheduling Irrigation scheduling is the decision of when and how much water should be applied to vegetable crops in a field The purpose of irrigation scheduling is to determine the exact amount of water to apply to the field and the time for application thereby maximizing irrigation efficiencies Irrigation scheduling saves water and energy Irrigation criteria and scheduling Irrigation criteria are the indicators used to determine the need for irrigation Broner 1993 The most common irrigation criteria are soil moisture content and soil moisture tension The less common types are irrigation scheduling to maximize yield and irrigation scheduling to maximize economic net return The final decision depends on the irrigation criterion strategy and goal Farmers need to define a goal and establish an irrigation criterion and strategy To
6. a mark for sand hour put a mark put a mark for minutes layer for loam layer clay layer Sandy Soil Loam Soil Clay Soil Figure 27 Field soil texturing method with suspension bottle Globe 2005 44 Percent Sand Figure 28 Soil texture triangle NSW DPI 20084 46 Soil texture determination by hand An alternative method for determining soil texture is by the feel method Figure 29 shows the steps involved How the soil feels in the hand and the length of ribbon formed will determine roughly the clay content and the texture as indicated in Table 5 Collect sample Sieve and prepare Add water in handful Knead make ball No Make soil ribbon sample soil ball formation sand measure length to know texture Figure 29 Steps in determining soil texture using the feel method NSW DPI 2008a Table 5 Key to soil texture by feel NSW DPI 2008a Soil texture Sand S Loamy sand LS Ribbon length 5 mm How the soil feels No ball forms Can t be molded sand grains adhere to fingers Clayey sand CS Slight coherence sticky when wet sand grains sticks to fingers discolor fingers little or no organic matter Sandy loam SL Light sandy clay loam Loam L Sandy clay loam SCL Clay loam CL Sandy clay SC Light clay LC Heavy clay HC 15 25 mm 20 25 mm About 25 mm 25 44 mm 40 50 mm 50 75 mm Slight coherence sand grains of medium size can be sheared between thumbs
7. are presented in Table 13 Table 12 Moisture balance sheet for scheduling irrigation in a tomato crop NSW DPI 2008c Crop Tomatoes Soil type Clay Month January Crop coefficient Crop water use Rainfall Effective rain Irrigation application Cumulative soil water deficit K ET_ mm day mm mm d a mm mm ho m os s oo o CO EC zoo s os e s e o s s os rs 9 e E 4 ss os m o e o 8 Effective root depth D 0 55m p 0 4 TAW 180 mm m RAW 0 480 72 mm Net irrigation depth D RAW 0 55 x 72 39 6 40 mm step 6 5 pz Jos feo 0 o po 36 v E A A A A ae Ge IO fas sae 9 9 9 E 8 Jas os 90 29 085 0 3 4 0 85 To calculate effective rainfall during spring summer and autumn periods subtract 5 mm from each of the daily rainfall totals Assume rainfalls of 5 mm or less to be non significant zero for crop water use In winter all the rainfall is assumed to be effective Table 13 Soil water relations and irrigation requirements of various vegetable crops Doorenboos and Peruitt 1992 Preferred soil Amount Preferred cm in Irrigation Critical Irrigation Crop moisture Dredgnr Defects Caused by X Moisture Period i eo Water Deficit 1 Days re EN Comments benefit expansion Cauliflowe
8. bag e Has a 20 liter water storage unit screen filter on off valve sub main pipe and four rows of KB drip lateral drip line 5 meters in length with 44 20 cm long microtube emitters e Can irrigate an area of 20 m Expandable up to 40 m e Provides irrigation for 44 to 88 vegetable plants depending on the crop and spacing 15 Drum Kit Fig 12 Features The irrigated area can be expanded up to 1000 m by using a larger drum placed at an average height of 1 to e A pre assembled kit useful for semi commercial vegetable gardens e The drum kit comprises a 200 liter water storage drum barrel tank or similar container placed at an average height of 1 meter to allow the water to flow by gravity The drum requires a minimum planted area of 100 m e Has five or more rows of lateral drip lines 10 to 20 meters long depending on crop Spacing and shape of the plot 1 5 m 16 ms 200 liter drum di s Y Rc CON Filter 16 mm submain N Microtubes Reducer tee Cap 12mm lateral drip lines Pas Plants 2m e System configuration 16 mm submain with 5 tees 12mm drip lines with 130 microtubes Wetting pattern IDE INDIA Figure 12 A drum kit with drip for semi commercial vegetable production KB Drip Fig 13 A new innovation in low cost drip irrigation Krishak Bandu KB or Farmer s Friend uses lay flat lateral drip lines with a wall thickness of on
9. directly into the sub mainline and the drip tube or tape e Drip lines can be made from tubes or tape Drip tubing has an inner and outer chamber to allow for even water distribution over a range of conditions Most tubing is polyethylene black plastic 4 to 8 mm thickness with holes emitters at intervals of 20 60 cm Drip tape is a low cost alternative to drip tubing t Feeder tube Fa WE EIN iau ee PF Tape connector bi on sin gt ae a A ES ee A BRENT ROWELL Figure 3 Components of a drip irrigation delivery system a sub main connected to tape drip lines by feeder tube and connector b emitter connected to tube drip line c sub mainline connector tape drip line Tape drip line Connectors Many types of connectors can be used to join mainlines sub mains drip tubes and drip tape Fig 4 BRENT ROWELL Figure 4 Various types of drip connectors 10 Filters Filters are essential to the operation of a drip system Screen filters or disc filters are used for well and municipal water Filters remove dirt and solid particles from irrigation water that can clog the drip system Fig 5 Figure 5 a Screen filter unit and main valve b 155 mesh screen filter c disc filter Pressure regulator Pressure regulators are installed in line with the system to regulate water pressure at a given water flow Fig 6 Regulators help prevent surges in water pressure that coul
10. increase Blossom and root growth cracks ee fruit size Blossom end rot tolerate drought low yield Flowering and pod swelling 7096 2 5 5 Fruit sizing gp o Tomato process 2 40 2 5 10 Fruit sizing M 2 20 2 5 21 Fruit amp last 40 days H 50 2 5 5 Fruit expansion o Oo 5096 2 5 7 Fruit expansion 50 2 5 7 Fruit expansion 50 2 5 10 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Root expansion 2 2 Fi 7 4 3 7 2 0 4 7 2 7 0 4 4 4 4 0 5 0 0 5 5 0 5 0 5 0 5 0 0 5 5 5 5 0 40 2 5 21 Fruit expansion 1 ASM Available Soil Moisture Percentage of soil water between field capacity 0 1 bar and permanent wilting point 15 bars 2 Irrigation method a Sprinkler b Big Gun c Trickle drip d Flood 3 Drought tolerance L low M moderate needs irrigation most years H high seldom needs irrigation 4 Depth of rooting of most roots S shallow 30 46 cm M moderate 46 61 cm D deep 61 cm plus 67 NOTES CHAPTER 8 Irrigation Water Quality Irrigation water quality and drip irrigation with recycled water The quality of irrigation water has profound effects on the soil crops and irrigation infrastructure Common soil problems associated with water quality are related to salinity water infiltration rate ion toxicity and long term structural changes in the soil Laboratory determinations and calculations needed to use the gu
11. indication of the percentage of water applied by the irrigation system that is actually available in the right place at the right time The distribution uniformity of the low cost drip system can be assessed by measuring the volume of water over the irrigation period in random catch cans in the field per one emitter CHAPTER 10 Socioeconomic Evaluation of Small scale Drip Irrigation Basic economic evaluaton of small scale drip irrigation To ensure the successful adoption of a farming technology the new technology should perform better than existing farm technology help farmers increase productivity generate substantially higher income and save on capital and or labor costs Farmers are willing to invest in new technology when they feel adequate economic benefits will accrue from using the new technology For successful technology adoption at a community or region wide scale the technology recommended to smallholder farmers should generate extra benefits but should not impose a major risk for crop failure The level of risk associated with a technology is a critical factor governing farmers adoption behavior as excessive risk would deter many potential smallholder farmers from adopting the technology A technology becomes risky when it is a large needs high investment or a lumpy useful for a specific purpose only asset A new technology recommended by extension agents or agriculture service providers is more lik
12. of net return and real net return are estimated separately The parameter net return does not account for opportunity cost of using family labor in cultivation of tomato while the parameter of real net return accounts for the opportunity cost of family labor uses in farming In subsistence economy where rural employment level is also very high calculating net return is acceptable for such enterprise budget analysis but in a place where rural labor market is already tight low unemployment level and where real wage rate is also substantially high specially in peak time of crop season then estimation of parameter like real net return is more appropriate in terms of reflecting the actual investment behavior of an average farmers All other economic parameters derived in Table 17 are self explanatory and the methods derived in estimation of these parameters are also provided under the column remarks Farmers tend to be risk averse because of the uncertainty associated with crop yield which depends on natural and external forces outside of a farmer s control such as the amount of rainfall flooding drought pests and diseases or excessive price fluctuation 79 8 Table 17 Productivity gross returns and economic efficiency of production of tomato under drip and alternate technology 0 1 ha basis Tomato production Tomato production with drip without drip Enter Enterprise A prise B Return 1
13. outlet Follow the arrow for the direction of the flow Tees 16 mm Poly tube roll Easy drip tape roll These connect sub main section and sub mains to laterals These end caps at tached at the distal end of sub main Stops water flow at the end of the drip line 16 mm for the sub main This flat tape used as laterals does not have slits It will be connected to sub mains Microtube 25 cm long Microtubes have an orifice of 0 5 mm for the discharge of water These are inserted through the flat tape at the appropriate spacing for the crop These sharp ended punches are used to make holes to insert microtubes into the flat tape Sleeves are end caps for all flat laterals They can be removed while flushing the system To re join the flat or sub main in case there is a break 23 Component Assembly Figs 17 20 Figure 17 Steps in connecting lateral pipe tube to sub main line tube Figure 19 Inserting microtube emitter to lateral line drip tape Figure 20 Laying out drip lines with inserted drippers i P Figure 18 Laying sub main lines with later als on raised beds 24 Installing a drip kit Step 1 Location and site selection At least 6 8 hours of full sun a day e Away from large trees e As level as possible flat slope e Use a fence to keep out animals Plot size 20 m long x 10 m wide Step 2 Prepare the land by l
14. sensitive at low tensions needs some maintenance and field reading Needs calibration and periodic adjustments since it is only an estimate calculations cumbersome without computer Needs calibration it is only an estimation 39 Measuring soil moisture There are different tools for the measurement of soil moisture based on soil moisture tension The most common are tensiometers Fig 24 26 Although tensiometer moisture readings are accurate they are quite expensive and complex for small farmers to operate A much simpler tool for soil moisture measurement has been developed for practical use in the field The Fullstop Wetting Front Detector FSWD is simple accurate and affordable for small scale growers It does not require wires batteries computer and loggers unlike most other soil moisture sensors The FSWD shows how deep the water has penetrated into the soil after irrigation It also stores a sample of water from the soil so that fertilizer and salt levels can be monitored It can be used to find out if irrigation water is too little or too much assist in management of fertilizer and salts and detection of waterlogging The wetting front detector shows how deep the wetting front has moved in the soil The FSWD is buried in the soil and pops up an indicator flag when a wetting front reaches it With drip irrigation it is possible to see the wetting front on the surface A wet patch develops immediately under the emitt
15. system to drip irrigation can reduce water use by 50 percent or more Crop yields can increase through improved water and fertilizer management under drip irrigation When drip irrigation is used with plastic mulch and raised beds farmers can increase yield and improve the quality of vegetable crops The combined use of drip irrigation plastic mulch and raised beds is known as plasticulture Drip irrigation is not applicable to all farms However when properly managed it can reduce labor and production costs while improving productivity Small scale growers should evaluate the advantages and disadvantages of drip irrigation to determine the benefits for their farms Advantages of drip irrigation e Less water can be used Drip irrigation requires less than half of the water for flood or furrow irrigation and less than three quarters of the water for sprinkler irrigation e Lower operating pressure means reduced energy costs for pumping e Water use efficiency is increased because plants can be supplied with water in precise amounts e Disease pressure may be less because plant leaves remain dry e Water is applied directly to the plant root zone No applications are made between rows or other non productive areas resulting in better weed control and significant water savings e Field practices such as harvesting can continue during irrigation because areas between rows remain dry e Fertilizers can be applied efficiently throu
16. the efficiency of other inputs Simple low cost drip irrigation systems can ensure small scale producers benefit from water resources This 10 chapter manual provides basic step by step procedures for installing simple drip irrigation systems for different crops climates and soils It addresses common problems provides troubleshooting and maintenance tips and offers irrigation scheduling guidelines to avoid under or over irrigation Methods to determine soil types water quality water holding capacity crop coefficient and crop water demand are illustrated The information presented in this guide has been compiled from relevant literature research and development projects and is based on practical field experience This manual is intended as a guide for small scale vegetable producers and as a reference for extension agents to use in training and demonstrations Agricultural input suppliers in rural and peri urban areas may also find it a useful resource to support and promote drip irrigation CHAPTER 1 Introduction to Drip Irrigation What is drip irrigation Drip irrigation which is also known as trickle irrigation or microirrigation is an irrigation method that allows a grower to control the application of water and fertilizer by allowing water to drip slowly near the plant roots through a network of valves pipes tubing and emitters Fig 1 For many crops switching from a conventional flood furrow or sprinkler
17. water control systems are poor and access to irrigation water is limited The HED kit allows the user to assemble all parts needed to make an irrigation system Table 2 All of the irrigation accessories are readily available and affordable The kit may be adapted for 5 10 15 or more rows of vegetables depending on the size of vegetable plot The size of the water tank and the length and number of laterals will depend on plot size but in this chapter HED for 100 m is used as an example This irrigation system does not require an electrical power supply as the system works by gravity When a 100 liter bucket or tank of water is raised 1 5 meters above the ground measured from the bucket bottom sufficient pressure is generated to force the water from the bucket through the irrigation tape on the ground Tubes are connected through the bottom or the side of the bucket or tank to the irrigation tape Water drips from the tape into the soil and provides enough moisture for a vegetable garden to feed a family of three to four 22 Table 2 a ee of HED kit IDE India 2007 FIL COMM pM Y HED set The set contains all fittings except the drum and the base Cotton 1 m x 1 m To use as filter from the source to the drum Thin cloth piece Tap and checknuts 1 male threaded adapter in the tap 3 pieces 2 rubber washers 1 female threaded check nut Black PVC with inlet strainer filter screen and Filter screen eat
18. 14 mm is wetted by a dripper with a cylindrical wetting pattern and a radius of 0 2 m the volume of readily available water will be 9 mr x root zone RAW mm mr is the area of a circle where pi rr is equal to 3 14 3 14 x 0 2 x 0 2 x 14 1 8 L plant Radius 0 2 m If there is more than one dripper per plant multiply this by the number of drippers to get the total litres of RAW available to each plant Calculating hours of irrigation Irrigation time can be determined from the volume of water that can be held in the root zone wetted area and the discharge rate of the drippers Irrigation time hours Volume RAW L dripper discharge rate L hour Example 1 Overlapping drippers with a RAW of 63 liters per tree 2 L hr drippers spaced 0 5 meters apart Each plant has access to the full 3 m wetted length between plants 3 m wetted length 0 5 m dripper spacing 6 drippers per plant 6 drippers per plant x 2 L hr drippers 12 L hr plant 63 L RAW plant 12 L hr plant 5 hours and 15 minutes irrigation time Example 2 Non overlapping drippers with a RAW of 1 8 liters per dripper and 8 L hr drippers 1 8 L RAW dripper 8 L hr 0 225 hours 13 5 minutes multiply time in hours by 60 to determine number of minutes Note Using RAW to determine irrigation time will give the maximum time needed to irrigate to refill the RAW If the soil dries out beyond the moisture content that is considered readily available to
19. 5 m long to each side 40 lines Number and Length of Lateral Drip Lines 5 0 m long 10 m long of the sub main 25m long to each side of the sub main 16 mm OD 16 mm OD 32 mm OD 50 mm OD Sub main Outer Diameter and Length 3m 9m 20m 20m Screen Filter Size 12 mm inlet amp outlet 16 mm inlet amp outlet 25 mm inlet amp outlet 32 mm inlet amp outlet Operating Head Height of Tank 1 meter 1 meter 2 meter 2 meter Emitter Flow 2 5 liters hour 2 2 liters hour 2 4 liters hour 2 2 liters hour Water Storage 20 liters 200 liters 1000 liters 2000 liters Price US 3 12 38 60 Vegetable crops Tomato Eggplant Onion Cabbage Rapeseed Paprika Cauliflower Garlic Watermelon Cucumber Lettuce etc Crops l a p The larger systems can be used for short duration fruit crops such as banana and papaya with a few modifications Basic specifications Microtube emitters 0 3 m long 1 2 mm inner diameter emitter spacing 0 30 m intervals KB Drip tape laterals of Linear Low Denisty Polyethylene LLDPE material row spacing at 1m intervals along LLDPE sub mains Prices ex factory Source IDE India 18 16 mm submain reducer tee cap Ju 12 mm lateral 4 plants per outlet gt IDE INDIA Figure 14 A combo kit consisting of cement tank rope pump and irrigation set up for semi commercial production Figure 15 Drawing water from well with a manually
20. 98 Design consideration for vegetable crops drip irrigation system Pp 10 16 In Proceedings of the Seminar on Vegetable Production Using Plasticulture American Society for Horticultural Science Alexandria VA USA Doorenboos J and A S Kassam 1979 Yield response to water Irrigation and Drainage Paper 33 FAO Rome Italy Doorenbos J and W Peruitt 1992 Crop water requirements FAO Irrigation and Drainage Paper No 24 Rev Rome Italy Evans R D K and R E Sneed 1996 Soil water and crop characteristics important to irrigation scheduling North Carolina Cooperative Extension Service Pub No Ag 452 1 Gittinger J P 1982 Economic Analysis of Agricultural Projects Johns Hopkins Univ Press Baltimore MD USA Globe 2005 Soil particle size distribution Lab Guide http classic glove gov fctg soil_fg_particledist pdf Goodwin 2009 How to use tensiometers AgNote No AG 0298 Dept of Primary Industries Victoria Australia p 1 2 IDE International Creating Markets for the Poor 2004 Lakewood Colorado USA IDE India 2004 Manufacturing and assembling manual for affordable micro irrigation technology AMIT International Development Enterprises IDE India New Delhi India International Development Enterprises IDE 2007 Horticulture easy drip kit User Manual 81 IRRI 1991 Basic Procedures for Agro economic Research IRRI Los Banos Laguna Philippines Lamont W J M D
21. A Ay AVRDC Y The World Vegetable Center i lE More Crop Per Drop J T iT L 43 7 E edm 4 n J mm i p zt Using Simple Drip Irrigation Systems for Small scale Vegetable Production Manuel Palada Surya Bhattarai Deng lin Wu Michael Roberts Madhusudan Bhattarai Ros Kimsan David Midmore AVRDC The World Vegetable Center AVRDC The World Vegetable Center is an international nonprofit research institute committed to alleviating poverty and malnutrition in the developing world through the increased production and consumption of nutritious health promoting vegetables AVRDC The World Vegetable Center P O Box 42 Shanhua Tainan 74199 TAIWAN Tel 886 6 583 7801 Fax 886 6 583 0009 Email info worldveg org Web www avrdc org AVRDC Publication 09 723 ISBN 92 9058 1 74 3 Editor Maureen Mecozzi Cover design Chen Ming che Publishing Team Kathy Chen Chen Ming che Vanna Liu Lu Shiu luan 2011 AVRDC The World Vegetable Center Printed in Taiwan c9greative commons This work is licensed under the Creative Commons Attribution ShareAlike 3 0 Unported License To view a copy of this license visit http creativecommons org licenses by sa 3 0 tw or send a letter to Creative Commons 171 Second Street Suite 300 San Francisco CA 94105 USA Suggested citation Palada M Bhattarai S Wu DL Roberts M Bhattarai M Kimsan R Midmore D 2011 More Crop Per Drop Using Simp
22. Crop productivity Kg USSIKg 02 EP AA Kg 3000 USSIkg 3 Variable Cost components Total material costs seeds fertilizers pesticides harvesting bas 0 2 3000 2000 4 150 All materials except labor amp drip sets kets etc 5 1 Dayslcrop 40 70 Family abor 52 Dayslcrop 10 Hof abo 53 Days crop 50 80 Family hired labor 6 US 20 20 wageQ 2 day 62 US 100 Family labor included AAA BEDS UE 7 US 170 4 6 1 72 US 250 4 62 i US Include interest cost y 3100 25 fo uss 275 s Selected economic performance indicators SS 405 200 325 9 enea 13 Total production costperkg USGS ff Brow row o 0 2 0 2 00 70 10 20 310 310 230 3 7 1 8 References Ayers R S and D W Westcott 1985 Water quality for agriculture FAO Irrigation and Drainage Water Rev 1 Food and Agriculture Organization The United Nations Rome Italy Bhattarai S and D Midmore 2009 Oxygation enhances growth gas exchange and salt tolerance of vegetable soybean and cotton in a saline vertisol J Integrative Plant Biology 51 7 675 688 Broner 2005 Irrigation scheduling Crop Series No 4 708 Colorado State University Cooperative Extension Service Fort Collins CO USA Brown M 1982 Farm Budgets From farm income analysis to agricultural project analysis Johns Hopkins Univ Press World Bank Publication Baltimore MD USA Clark G and A G Smajstrla 19
23. DA b M PALADA Figure 26 Soil tensiometer placement in hot pepper drip irrigation field trial plot a and Fullstop Wetting Front Detector on drip irrigated tomato crop b CHAPTER 5 Determining Soil Texture Field determination of soil texture Determination of soil texture is important in irrigation since water holding capacity of the soil depends on soil texture Sandy soils generally have lower water holding capacity than clay soils Therefore irrigation water requirement of crops grown in sandy soils is higher than those grown in clay soils Soil texture can be determined using two methods 1 soil particle separation by suspension and 2 hand feel method Particle separation by suspension Fig 27 shows the separation of soil particle in suspension bottle to determine the amount of sand loam and clay particles Soil sample is placed in a container with clean water The container is shaken for 1 2 minutes After 1 minute the sand particles will settle down while the loam particles settle down after one hour Clay particles finally settle down after one day Determine the soil texture using the soil texture triangle Fig 28 Read the depth of sand silt and clay after settlement in the bottle work out the percentage of these three components and find out the soil texture class by triangulating the formation in the soil texture triangle Clean water Pour soil Settle for 1 minute Settle for an Settle for a day shake 1 2 put
24. a soil is known at any given time the moisture content at any later time can be computed by adding water gains effective rain and or irrigation and subtracting water losses run off deep percolation and crop evapotranspiration ET during the elapsed period Keeping the daily water balance is a simple procedure but it must be completed each day By knowing the daily values for inflow rainfall or irrigation and outflow crop water use the daily balance can be calculated as shown in Table 11 As soon as the accumulated water Variation in Crop Water Use from growing season to growing season Average Crop Water Use N Germination and Emergence Crop Water Use Vegetative Growth Reproduction Seed Set Maturity and Senescence Growing Season p deficit exceeds the value of the net irrigation application depth i e the net amount of irrigation water applied more irrigation water is supplied to maintain optimum soil moisture content for plant growth Three factors determine the amount of water used by crops as follows 1 Crop factor The data on crop rooting depth Table 9 erowth stages and crop coefficient Table 10 are required for the moisture accounting The length of the total growing season and each growth stage of the crop are important when estimating crop water needs The growth of an annual crop can be divided into four stages e Initial establishment from sowing to 10 ground cover e Cro
25. ai and Midmore 2009 Oxygation using aerated water with subsurface drip irrigation improves yield and water use efficiency of vegetable production under saline and non saline soil conditions An inline air injector suitable for home gardening can be operated with the pressure in the drinking water tap Burying the drip tape just a few centimeters below the soil surface increases the utility of drip irrigation by reducing the evaporative loss of soil water and maximizes the benefit of oxygation in a number of crops This also keeps the weed growth down as the surface is dry and offers the opportunity for maximization of infiltration of rain water into the soil profile Table 14 Guideline for interpretations of water quality for irrigation Degree of Restriction on Use Potential Irrigation Problem Slight to Moderate Severe Salinity affects crop water availability ECw 0 7 3 0 or TDS 450 2000 Infiltration affects infiltration rate of water into the soil Evaluate using ECw and SAR together SAR 0 3 and ECw 0 7 0 2 3 6 1 2 0 3 6 12 1 9 0 5 12 20 2 9 1 3 20 40 5 0 2 9 Specific lon Toxicity affects sensitive crops Sodium Na surface irrigation sprinkler irrigation Chloride CI surface irrigation sprinkler irrigation Boron B Trace Elements see Table 21 Miscellaneous Effects affects susceptible crops Nitrogen NO3 Ny Bicarbonate HCO3 over
26. ameter Symbol Unit Usual range in irrigation water SALINITY Salt Content Electrical Conductivity ECw dS m 0 3 dS m or Total Dissolved Solids TDS mg l 0 2000 mg l Cations and Anions Calcium Ca me l 0 20 me l Magnesium Mg me l 0 5 me l Sodium Na me l 0 40 me l Carbonate CO mel 0 1 mell Bicarbonate HCO me l 0 10 me l Chloride CI me l 0 30 me Sulphate SO mel 0 20 mel l NUTRIENTS Nitrate Nitrogen NO N mg l 0 10 mg l Ammonium Nitrogen NH N mg l 0 5 mg l Phosphate Phosphorus PO P mg l 0 2 mg l Potassium K mg l 0 2 mg l MISCELLANEOUS Boron B mg l 0 2 mg l Acid Basicity pH 1 14 6 0 8 5 Sodium Adsorption Ratio SAR me l 0 15 dS m deciSiemen meter in S I units equivalent to 1 mmho cm 1 millimmho centi metre mg l milligram per liter parts per million ppm me l milliequivalent per liter mg l equivalent weight me l in SI units 1 me l 1 millimol liter adjusted for electron charge ems 72 CHAPTER 9 Irrigation System Assessment Irrigation system assessment An Irrigation System Assessment evaluates the irrigation system performance to ensure that it is operated to match the crop soil and climate conditions present Irrigation is scheduled to replace the climate moisture deficit in a manner that does not exceed the crop s ability to utilize the water or the soil s capacity to store the water applied A key objective of an Irrigation System Assessment
27. and fore finger Coherent ball but very sandy to touch dominant sand grains are of medium size and readily visible Coherent ball sand to the touch dominant sand grains are of medium size and readily visible Forms a thick ribbon pliable ball smooth spongy and no obvious sandiness Greasy to touch if organic matter is present Strongly coherent ball sandy to touch medium sand grains visible in a finer matrix Strongly coherent and plastic ball smooth to manipulate Plastic ball sand grains can be seen and felt 5 50 75 mm Plastic smooth feel easily worked molded and rolled in to rod Rod forms a ring without cracking Medium clay MC Smooth plastic ball can be molded into rod without cracking resistance to shearing Smooth very plastic ball firm resistance to shearing mold into rods stiff plasticine Very sticky and strongly coherent Rod forms a ring without cracks gt 50 47 NOTES CHAPTER 6 Determining Soil Water Status Determining soil water status Soil water status Soil moisture level determines the timing of irrigation Soil moisture status can range from dry to saturated Fig 30 Maintaining soil moisture at field capacity during the critical growth period is important for vegetable production REFILL POINT DRY SOIL Figure 30 Soil moisture status and relative crop growth Ramsey 2007 Terms describing soil moisture status Saturation All pores in the soil are filled with water
28. ctive effective gt the soil each layer and crop texture RAW rootzone rootzone O Layer 1 layers Daikon Table 6 sandy O loam column B O 02m 03m Sandy 60 mm m 0 3m X 60 mm m ua loam 18 mm E Layer2 2 LL LL LLI dm 0 3 to 0 8 m Light clay 45 mm m 0 5 m X 45 mm m 0 5m 0 5m 22 5 mm 0 8m Layer 3 i n 12m 0 8to 1 2 m Medium 45 mm m 0 4 m X 45 mm m l 0 4m clay 18 mm The effective rootzone RAW for this example is 40 5 mm 58 5 mm 40 5 mm 94 Calculation of RAW Example 2 A citrus crop growing in a sandy loam soil containing 20 stone with an effective root depth of 0 3 m and a strategy to irrigate at 40 kPa would have the following calculation From table of the RAW for sandy loam at 40 kPa 60 mm m As the soil contains 20 stone we must reduce the RAW by 20 To reduce RAW by 20 multiply by 0 8 Adjusted RAW 60 mm m x 0 8 48 mm m Hence for a rooting depth of 0 3m total Root zone RAW 48mm m x 0 3 m 14 4mm If irrigating with a drip or micro spray system that does not wet the entire cropped area then convert RAW mm to RAW liters Converting RAW mm to liters for drip systems 1 mm depth of water 1 L applied to 1 m Where irrigation water and plant roots are evenly distributed over the whole planting area water storage and plant water use can be measured in mm Where drip irrigation is used the irrigation water and roots are only distributed in a smaller ar
29. d damage the system components ERIC SIMONE Figure 6 Pressure regulators installed side by side allow a greater flow rate Valves or gauges A zone system using valves to open and close various lines can be used to water several fields or sections of fields from one water source Fig 7 A backflow anti siphon valve is a necessity for a system using a well or municipal source if fertilizers or chemicals are to be injected into the line Hand operated gate or ball valves or electric solenoid valves can be used to automate the system using a time clock water need sensor or automatic controller box ERIC SIMONE Figure 7 A fixed pressure gauge 11 Injectors Injectors allow the application of air fertilizer chemicals and maintenance products into the irrigation system Fig 8 It is necessary to use an anti siphoning device also called a backflow prevention device when fertilizer chemicals or any other products are injected into a drip irrigation system This device ensures water always moves from the water source to the field it prevents chemicals or fertilizers from polluting the water source 12 Figure 8 Fertilizer injector with tank I and bucket r containers BRENT ROWELL Controllers Controllers allow the user to monitor how the drip irrigation system performs Fig 9 These controls help ensure the desired amount of water is applied to the crop throughout the growing season Control
30. e example values considerable variations from these values with in each soil textural class may be noted in the field Water holding capacity of the soil varies greatly from 10 60 mm Water holding capacity Field capacity 8kPa refill point approximately 60kPa The quantity of water applied in one irrigation should not exceed the infiltration rate otherwise water will be lost below the root zone and or added to the water table if one exists Dept of Rooting Zone Effective rooting depth is determined by crop type Table 9 and presence of impeding layers of soil to root growth Fig 32 Rooting depth is generally regarded as the zone where roots are easily observed Where root growth is restricted by an impeding chemical and physical barrier the effective rooting depth is the depth to this layer The rooting density decrease with depth as illustrated in Figure 32 Rooting depth must be taken into consideration for irrigation Loamy sand 30 x0 55 16 5 mm Top 1 4 40 Second 1 4 30 Third 1 4 20 Bottom 1 4 10 Sandy loam 40x0 65 26 mm Clay loam 30 x0 65 19 5 mm 16 5 26 19 5 Total RAW _6 gt mm 3 Figure 32 Illustration of the effective root zone a and soil heterogeneity and root distribution in the soil profile b Ramsey 2007 57 Table 9 Maximum rooting depths of irrigated crops in a medium textured soil Evans et al 1996 Rooting depths wen J 4
31. e tap and fill all the easy tape laterals with water Insert the micotube in the hole in the direction of flow of water m a Punch hole in the easy tape laterals at 30 cm spacing with the help of thumb punch 33 34 Step 14 Now the system is installed and ready to use TRITT hal m se Troubleshooting repair and maintenance Clogging Clogging reduces or stops water from dripping through the tape To avoid clogging open the end caps and flush out the particles once a week Fig 21 The dirt in the piping can be sucked out or blown out easily when dry Regular cleaning of the filter and double filtering of water before pouring into the drum minimizes clogging Fig 22 Figure 21 Open end caps to flush out particles that clog the system Figure 22 Removing filter cap to allow cleaning particles from inner mesh 35 Repairing leaks in drip lines Holes in drip tape can be plugged with a small piece of tubing that has been heated with a match or torch and crimped with pliers Fig 23 Enlarge the hole with a nail before inserting plug A round piece of wood also works it swells when wet and makes a tight fit C Figure 23 Heated tubing a crimped with pliers b and inserted or plugged in drip tape hole c 36 Breakage To repair drip tape cut away damaged area and connect the two pieces with a 16 mm joiner provided in the bag End of Season Maintenance With care
32. ea in the field In these cases it is often easier to use liters to describe both the water use and water storage in the plant root zone This also allows simple calculation of irrigation time as the discharge from drip systems is commonly reported in liters hour Calculating liters of water held in the crop root zone The volume of root zone wet by the drip system will depend on the size and shape of the wetting pattern Overlapping drippers Where the drip patterns overlap it can be assumed that a wetted strip or sausage shaped wetted pattern is produced In this case the volume of water held in the soil can be estimated from the width and length of the wetted strip and the root zone Readily Available Water RAW Volume stored L wetted width m x wetted length m x root zone RAW mm For example for a 1 5 m wetted width 3 m crop spacing and root zone RAW of 14 mm the volume of readily available water 1 5x 3x 14 63 Liters RAW per plant Note If the root zone of your crop does not have access to entire wetted strip you need to adjust the dimensions of the wetted area in your calculation This is particularly important in young plantings where roots may have access to only a small portion of the wetted strip Non overlapping drippers Where wetting patterns do not overlap it is necessary to calculate the wetted volume assuming a cylinder sphere or cone shaped wetting pattern For example if a root zone with a RAW of
33. egetable based technology in Cambodia Proc 2nd International Forum on Water and Food 11 13 November 2008 Addis Ababa Ethiopia 5 p Postel S P Polak F Gonzales and J Keller 2001 Drip irrigation for small farmers A new initiative to alleviate hunger and poverty Water Institute 26 3 13 Qassim A and B Ashcroft 2006 Estimating vegetable crop water use with moisture accounting method Ag Note 1992 Dept of Primary Industries Victoria Australia p 1 4 Ramsey H 2007 Calculating readily available water Farm Note 198 Dept of Agriculture and Food Government of Western Australia p 1 3 Rhoades J D 1977 Potential for using saline agricultural drainage waters for irrigation Proc Water Management for Irrigation and Drainage ASCE Reno Nevada 20 22 July 1977 p 85 116 Simone E R Hochmuth J Breman W Lamont D Treadwell and A Gazula 2008 Drip irrigation systems for small conventional vegetable farms and organic vegetable farms University of Florida IFAS Extension HS 1144 Stirzaker R 2003 When to turn the water off scheduling microirrigation within wetting front detector Irrigation Science 22 177 185 Stirzaker R and J Wilkie 2002 Four lessons from a wetting front detector Paper presented at the Irrigation Australia Conference 21 23 May 2002 Sydney Australia 7 p 83
34. ely to be adopted when farmers are aware of the economic benefits of replacing the old technology or practice Thus an economic assessment of low cost drip technology as illustrated in this chapter is an important aspect of assessing technology performance in the field and validating the technology A technology must also perform well economically make efficient use of resources and promote financial sustainability Wide adoption of low cost drip irrigation technology brings benefits to the community at large in terms of increased crop production and food security increased employment opportunities especially for landless households and lower prices for local produce Increasing 76 cropping intensity and increasing employment at certain critical periods of the year is an important aspect of rural development There are two types of economic benefits that accrue from the adoption of a new technology by a farmer a Farm level benefits Most of the benefits are realized by the farmers adopting the technology for example increased crop productivity increased cropping intensity increased farm income This also includes reduced cost of scarce resources lower cost or less need for hired labor or less need for chemicals or irrigation water b Community or social benefits These benefits include increased employment availability per hectare of land increased availability of employment at critical periods of the year when work is no
35. en content Tensiometers i Soil moisture including vacuum Tensiometers Soil moisture tension tension auge Electrical Electric resistance of Resistance Soil moisture blocks AC bridge resistance blocks soil moisture tension meter Climatic parameters temperature radiation Weather station e Estimation Water budget wind humidity and or available l l of moisture approach expected rainfall weather i l l content depending on model information used to predict ET Modified Atmometer ESEIMate ol Reference ET moisture atmometer gauge content Advantages Easy to use simple can improve accuracy with experience High accuracy Good accuracy instantaneous reading of soil moisture tension Instantaneous reading works over larger range of tensions can be used for remote reading No field work required flexible can forecast irrigation needs in the future with same equipment can schedule many fields Easy to use direct reading of reference ET Table 3 compares the different methods of irrigation scheduling by monitoring soil moisture content or tension The methods described in the table measure or estimate the irrigation criterion Disadvantages Low accuracies field work involved to take samples Labor intensive including field work time gap between sampling and results Labor to read needs maintenance ineffective at tensions above 0 7 atm Affected by soil salinity not
36. er or dripper Digging the soil away under two dripper reveals two columns of wet soil Wetting front detectors are usually used in pairs The first is buried about 1 3 of the way down the active root zone The second is buried about 2 3 of the depth of the active 40 root zone max depth of soil aimed to wet by irrigation Figure 26 illustrates underwatering adequate watering and overwatering scenarios on drip irrigated crops A tensiometer reading scale is shown in Table 4 Table 4 Tensionmeter readings Goodwin 2009 Tensiometer Readings A Too little water d Indicator up B About right A77 indicator up Indicator up C Too much water A If indicator of the shallow detector rarely pops up then water is not moving deep enough to fill most of the root zone More water should be applied B The indicator of the shallow detector should pop up regularly after irrigation The deeper detector should respond during periods of high demand for water C If the indicators of both the shallow and deep detectors regularly pop up then water could be wasted Apply less water or lengthen the period between irrigations Figure 24 Fullstop Wetting Front Detector showing soil moisture status R STIZAKER a b Figure 25 Soil moisture tensiometer a in pairs at two depths b installation on raised bed c placement near the root zone M PALADA 41 42 X ig a M PALA
37. gh the drip system e Irrigation can be done under a wide range of field conditions e Compared to sprinkler irrigation soil erosion and nutrient leaching can be reduced Disadvantages of drip irrigation e Higher initial investment compared to other irrigation methods e Requires regular maintenance and high quality water If emitters are clogged or the tape damaged the tape must be replaced e The water application pattern must match the planting pattern If emitters are not properly spaced root development maybe restricted and plants may die e Drip tubes may be lifted by wind or displaced by animals unless covered with mulch fastened with wire anchor pins or lightly covered with soil e Drip lines can be easily cut or damaged by other farming operations such as tilling transplanting or manual weeding with a hoe Damage to drip tape caused by insects rodents or birds may create large leaks that also require repair e Water filtration is necessary to prevent clogging Components of a drip irrigation system Water Source Control Value Filter Main Pipe Sub main Pipe Lateral Pipe Microtube Emitter Baffle Dripper Vegetable bed 1 2 3 4 5 6 7 8 ABCD Area for Expansion of the small emitter holes e Compared to sprinkler irrigation water distribution in the soil is restricted e Drip tape disposal causes extra cleanup costs after harvest Planning is needed for drip tape disp
38. head sprinkling only 1 5 8 5 pH Normal Range 6 5 8 4 Adapted from University of California Committee of Consultants 1974 ECw means electrical conductivity a measure of the water salinity reported in deciSiemens per meter at 25 C dS m or in units millimhos per centimeter mmho cm Both are equivalent TDS means total dissolved solids reported in milligrams per liter mg l SAR means sodium adsorption ratio SAR is sometimes reported by the symbol RNa See Figure1 for the SAR calculation procedure At a given SAR infiltration rate increases as water salinity increases Evaluate the potential infiltration problem by SAR as modified by ECw Adapted from Rhoades 1977 and Oster and Schroer 1979 For surface irrigation most tree crops and woody plants are sensitive to sodium and chloride use the values shown Most annual crops are not sensitive use the salinity tolerance tables Tables 4 and 5 For chloride tolerance of selected fruit crops see Table 14 With overhead sprinkler irrigation and low humidity 30 percent sodium and chloride may be absorbed through the leaves of sensitive crops NO N means nitrate nitrogen reported in terms of elemental nitrogen NH N and Organic N should be included when wastewater is being tested Source Ayers and Westcott 1985 71 Table 15 Laboratory determinations needed to evaluate common irrigation water quality problems Ayers and Wescott 1985 Water par
39. idelines are given in Tables 14 and 15 Growing trends towards concentrated population in the cities will increase the access for treated waste water in the peri urban area for horticultural crops in the future Wastewater reuse for agriculture and managed landscapes will aid in meeting growing water demands and conserve current potable supplies in many parts of the world Therefore opportunities exist to use alternative water supplies for irrigation such as treated municipal wastewater However wastewaters often contain microbial and chemical contaminants that may affect public health and environmental integrity Wastewater pretreatment strategies and advanced irrigation systems may limit contaminant exposure to crops and humans Subsurface drip irrigation SDI shows promise for safely delivering reclaimed wastewater The closed system of SDI pipes and emitters minimizes the exposure of soil surfaces above ground plant parts and groundwater to reclaimed wastewater The potential for salt and sodic hazard in soils increases with wastewater irrigation but with SDI the total water input and therefore the salt load can also be minimized Beneficial and safe use of reclaimed wastewater for SDI will depend on 70 management strategies that focus on irrigation pretreatment virus monitoring field and crop selection and periodic leaching of salts Optimization of SDI has been further achieved by the latest development of oxygation Bhattar
40. illustrate irrigation scheduling consider a farmer whose goal is to maximize yield Soil moisture content is the irrigation criterion Different levels of soil moisture trigger irrigation For example when soil water content drops below 70 percent of the total available soil moisture irrigation should start Soil moisture content to trigger irrigation depends on the farmer s goal and strategy In this case the goal is to maximize yield Therefore the farmer will try to keep the soil moisture content above the critical level If soil moisture levels fall below this level the yield may be lower than the maximum potential yield Thus irrigation is applied whenever the soil water content level reaches the critical level 38 If the farmer s goal is to maximize net return an economic irrigation criterion is needed such as net return This is the income from the crop less the expenses associated with irrigation lrrigation scheduling enables the farmer to apply the exact amount of water to achieve the goal This increases irrigation efficiency without knowing how much was applied Also water distribution across the field is important to derive the maximum benefits from irrigation scheduling and management Accurate water application prevents over or under irrigation Over irrigation wastes water energy and labor leaches expensive nutrients below the root zone out of reach of plants and reduces soil aeration and crop yields Under irrigati
41. ion making behavior of a typical farmer in adoption or not use of the new technology production practices in question The process of producing a particular farm commodity is called as farm enterprise hence a detailed component analysis of inputs used and outputs produced while producing a farm community by farm enterprise and expressing these numbers in a more formalized way or in a monetary term is known as Farm Enterprise Budget Analysis For example say production of tomato using the drip technology is considered as an enterprise A and production of tomato without drip technology under furrow irrigation is considered as enterprise B Then when the net return from the farm enterprise A is higher than that of enterprise B then the drip technology is considered as a profitable investment activity or vice versa Basic sets of farm enterprise data needed for analyzing crop production with drip technology enterprise A and with out drip technology enterprise B are derived by 78 e measuring all of the external inputs used by farmers levels of crop yield and valuing all of them in monetary level e listing the level of labor by key activities used in production process separated by family and hired labor use e Constructing the farm budget table to facilitate economic analysis Table 17 The economic analysis of drip is illustrated by a numerical example a hypothetical data and with assumptions on some of the cr
42. is to ensure that water is used efficiently and will meet the crop s water needs while preventing water loss due to surface flow leaching or drift Appropriate irrigation equipment selection and design as well as good management and scheduling will conserve water supplies while supporting crop growth Evapotranspiration ET is the driver that determines how much water is being used by the plant The climate moisture deficit is the difference between the accumulated ET and the effective rainfall ET is used to determine the irrigation system peak flow rate and annual crop water requirement An Irrigation System Assessment can benefit farm productivity enhance protection of the environment as well as benefit the environment by conserving water and preventing nutrient losses For the farm good water management means e Knowing the farm s irrigation requirements and reducing unnecessary water usage e Saving energy by operating the system efficiently e Reducing runoff and leaching of nutrients beyond the plant s rooting depth e Maximizing crop yield 74 To complete an Irrigation Management Plan irrigation systems must be assessed for distribution uniformity DU and application efficiency Once irrigation system performance has been checked and improved if necessary an irrigation schedule can be developed DU is a measurement of the evenness of water application over a field and is expressed as a percentage Application efficiency is an
43. le Drip Irrigation Systems for Small scale Vegetable Production AVRDC The World Vegetable Center Shanhua Taiwan AVRDC Publication No 09 723 83 p Project Partners International Development Enterprises IDE Central Queensland University niversity AUSTRALIA Photos and illustrations courtesy of IDE India IDE Cambodia NSW DPI Australia Surya Bhattarai Madhusudan Bhattarai Manuel Palada Brent Rowell A Susila Deng lin Wu Eric Simone R Stizaker More Crop Per Drop Using Simple Drip Irrigation Systems for Small scale Vegetable Production Manuel Palada Surya Bhattarai Deng lin Wu Michael Roberts Madhusudan Bhattarai Ros Kimsan David Midmore Contents Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 References Introduction to Drip Irrigation Simple Drip Irrigation Systems Installation of a Simple Drip Irrigation System Drip Irrigation Scheduling Determining Soil Texture Determining Soil Water Status Estimating Crop Water Use Irrigation Water Quality Irrigation System Assessment Socioeconomic Evaluation of Small scale Drip Irrigation 22 38 44 50 60 70 74 76 81 Preface By producing vegetables year round small scale growers can increase their incomes and enhance the diets of their families and communities Vegetable crops respond well to irrigation which helps to improve yield and quality and increases
44. le water RAW There are three basic methods for finding the amount of water held in the soil 1 gravimetric 2 volumetric and 3 tension Gravimetric method is done by drying a soil sample in the oven The decrease in unit weight over that of field capacity represents the amount of water loss or used by the crop Volumetric method uses nuclear or electrical methods such as gypsum blocks The effort a plant has to use to extract water held by soil is measured by a tensiometer and expressed in centibars cb or kilo Pascals kPa Each method of measuring the amount of water held in the soil has advantages and disadvantages Select the tool that is best suited for your farm The amount of water required to supplement crop water needs depends on crop type local climate and soil conditions Fig 33 Integrating information calculated by different methods allows one to evaluate plant water relation with respect to soil plant atmosphere continuum This allows growers or irrigation designers to estimate how much water will be required during the cropping season and how best to deliver it to meet the crop s peak demand This approach is most effective when used in conjunction with other scheduling techniques Estimating crop water use by the moisture accounting method The Moisture Accounting Method involves steps to estimate soil moisture content by using weather data It is based on a soil water balance For instance if the moisture content of
45. lers include pressure regulators water meters pressure gauges timers and soil moisture measuring devices BRENT ROWELL Figure 9 I Water meter installed near the field r water meter and timer to control flow of irrigation water CHAPTER 2 Simple Drip Irrigation Systems Some simple drip irrigation systems International Development Enterprises IDE has developed simple affordable low cost drip irrigation systems for smallholder vegetable growers These systems include e Bucket Kit e Family Nutrition Kit e Drum Kit e Customized System e Combo Kit IDE also offers simple low cost water pumps to use with the drip irrigation kits These include several types of wooden and metal treadle pumps Bucket Kit Fig 10 Features e A pre assembled kit to irrigate vegetables in home gardens e Has a 20 liter bucket with one or two rows of lateral drip lines 5 to 10 meters in length depending on the space available e Can irrigate up to 20 square meters e Bucket can be hung from a tree or pole 1 meter high 14 20 25 liters Figure 10 A simple bucket kit for irrigating a small vegetable garden plot of approximately 20 square meters Figure 11 M PALADA Family Nutrition Kit for home gardens The water bucket is replaced by a 20 liter double plastic bag Family Nutrition Kit Fig 11 Features e A variant of the bucket kit it replaces the bucket with a low cost 20 liter double layer plastic
46. ly 0 125 0 25 mm which expand to 16 mm in diameter when filled with water Microtubes are used as emitters to provide uniform water application The cost in India is around US 600 per ha for closely spaced crops The inlet pressure head for the KB Drip system can range from 0 5 to 3 meters KB Drip kits of various sizes are described in Table 1 KB Drip is popular due to its lower cost small package sizes ability to operate at very low pressure ease of installation and use and uniformity of water distribution Features e KB Drip systems can be customized to suit the needs of the farmer crops and field shape e Typically meant for larger areas of 1000 m and upward e By procuring different components of the KB Drip system the kit can be installed using simple rules of thumb e For smallholding up to two hectares farmers can easily plan and lay the system in the field with some support from local fitters Customized systems KB Drip kits can be customized to meet the specific needs of farmers different crops and fields of various shapes and sizes _ M EA Figure 13 KB low cost lay flat drip irrigation system adjustable to different plot and field sizes 17 Table 1 Specifications for various sizes of KB Drip Kits KB Drip Kit KB Drip Kit KB Drip Kit KB Drip Kit Specification EDK 20 EDK 100 EDK 500 EDK 1000 Area Coverage 20 m2 100 m2 500 m2 1000 m2 Microtubes 60 300 1500 3000 4 lines 10 lines 0 lines 12
47. m Do Camts pf Collards e OI Ts A rita mr EN Tomatoes 58 Peanuts Field corn Soybean Asparagus Cantaloupes Sweet corn Egg plant Okra Watermelon Alfalfa CHAPTER 7 Estimating Crop Water Use Estimating crop water use Scheduling irrigation based on crop water use minimizes chances of under or over watering Proper irrigation also ensures crop growth and minimizes leaching of fertilizers beyond the root zone Weather data can be used for estimating crop water requirements and is a handy management tool when it is used in conjunction with scheduling methods Water use is directly proportional to plant growth Plants use water in transpiration They use it in a process known as transpiration The root hairs take water from the soil The water travels through the stem towards the leaves The water evaporates into the air through pores in the surface of the leaves Water is also lost when it evaporates from the soil and other surfaces The combined loss of water through transpiration and evaporation is termed as evapotranspiration Measuring the evapotranspiration will tell you how much water is being used by the crop The amount of water used by the crop will depend upon the type of crop and its stage of growth It will also depend on environmental factors such as sunlight humidity wind speed and temperature Crop water use can be measured using three methods 1 plant based 2 weather based and 3
48. ng etc Sub Total A ETRE US 25 G Subtotal a b NIN D Reduced returns US 175 a change on income brought by the technology G C 175 25 US 150 Note 1 Assume that the drip irrigation set cost US 100 which is then divided into 2 years or four crop seasons two dry season crop year Hence depreciated cost of the drip technology per crop season is USS100 4 USS25 Basic steps to follow to derive the partial budget Specify and estimate all of the cost components that will increase or decrease with adoption of the drip set Specify and estimate all components of additional returns increase or decrease with adoption of the drip technology If the estimated change brought by the technology is positive i e if additional total return is higher than that of additional total cost then the drip set is giving more economic benefits to the farmer than 77 that of the case without use of the drip e Only items that are changed after the adoption of the drip technology are included in the analysis and it is assumed that other factors that are not counted in the analysis remain unchanged after adoption of the drip technology 2 Farm Enterprise Budget Analysis The process of deriving farm enterprise budget table is a little more complicated than that of the partial budget analysis but information generated from farm enterprise budget analysis is more informative Thereby it reflects more accurately the decis
49. on stresses the plant through constraints in water availability and causes yield reduction Advantages of irrigation scheduling e Can rotate water among various fields to minimize crop water stress and maximize yields e Reduces cost of water and labor through less irrigation making maximum use of soil moisture storage e Lowers fertilizer costs by holding surface runoff and deep percolation leaching to a minimum e Increases net returns by increasing crop yield and quality e Minimizes waterlogging reduces drainage requirements e Assists in controlling root zone salinity problems e Results in additional returns saved water can be used on noncash crops that otherwise would not be irrigated during water short periods Irrigation Scheduling Methods Irrigation scheduling methods consist of an irrigation criterion that triggers irrigation and an irrigation strategy that determines how much water to apply Irrigation scheduling methods differ by the irrigation criterion or by the method used to estimate or measure this criterion A common and widely used irrigation criterion is soil moisture status Table 3 Methods of irrigation scheduling Broner 1993 Measured Equipment Irrigation MENOR Parameter Needed Criterion Hand feel and Soil moisture content Soil moisture Hand probe appearance of soil by feel content Gravimetric soil Soil moisture content Auger caps Soil moisture moisture sample by taking samples ov
50. oosening the soil mix in sufficient compost 25 26 Step 3 Fix the tap on the drum and tighten it with checknut and gaskets by rotating checknut from inside Do not rotate the tap from outside Step 4 Prepare a platform or wooden stand 1 m high at the center of one side of the plot and fix the drum on the platform or wooden stand Step 5 Take 16 mm polytube coil cut 1 5 meter piece and connect it to the tap Step 6 Connect the filter to the other end of the 1 5 m piece on the ground Step 7 Cut 25 cm piece of 16 mm polytube and connect it back to the filter Connect 16 mm tee to the other end of 25 cm piece 27 Step 8 Cut 1 meter of 16 mm polytube and connect it to 16 mm tee Similarly con nect all other 16 mm Tees total of 10 pieces at 1 meter spacing 28 Step 9 Connect the end cap at end of the 16 mm polytube after last 16 mm tee 29 Step 10 Take easy drip tape roll and connect one end to 16 mm Tee with the help of 16 mm polytube sleeve Pass the tape through the sleeve con nect it to the tee and put the sleeve over it 30 Step 11 Lay easy tape on the ground and cut at 10 m length Similarly con nect all 10 laterals to 16 mm tees 31 Step 12 Cut 3 cm piece of easy tape fold the end of easy tape and insert 3 cm piece to close the end Repeat the procedure for all 10 easy tape later als 32 Step 13 Put the cloth on the tank and fill it with water Open th
51. op production which are as realistic as the data obtained in the context of developing countries in Asia Comparison of some of the economic parameters such as net return real net return and ratio of real return to investment across the alternate investment enterprises provide improved and more realistic information for farm investment decision Major assumptions made while deriving enterprise budget in Table 16 are listed below a Total cost of the small scale drip set is US 100 which is distributed evenly to four crop periods in the period of two years Thus US 100 as a total fixed cost of drip is equally divided into 25 per crop season basis b The cost for application of other input materials is same for tomato production with and without drip technology This includes cost for fertilizers manures pesticides other chemicals post harvest baskets etc except the human labor cost C In practice the drip irrigation would reduce labor time for irrigating a crop hence the total labor use under drip is assumed less than that of the drip technology Nevertheless because of increased yield there would be slightly more number of labor uses for harvesting under the drip technology These factors have been accounted in the data illustrated in Table 17 Quality of the tomato harvested under drip and without drip technology will remain same and they fetch the same market prices In Table 17 on the next page economic parameters
52. operated rope pump M PALADA Combo Kit Components Figs 14 15 Rope pump The pump capacity of a hand rope pump is 2 4 m per hour 10 m depth well enough to irrigate 2000 tomato plants The water outlet of the multipurpose model is high so a water tank can be filled directly Cement tank Instead of a metal drum a cement tank may be used with the advantages of lower cost per liter longer lasting material no corrosion and larger volume 500 to 5000 liters The tank can be constructed with local materials and skills and also can be used for fish production An 800 liter cement tank consists of 100 bricks 1 kg of steel wire 2 bags of cement and 6 bags of sand The tank is round and reinforced with steel wire on the outside of the bricks A simple filter is included in the tank by using PVC caps no valves are needed The height of 1 meter is enough for drip irrigation to function Costs Depending on the local 43 situation the costs for a basic irrigation set is US 70 to 140 including a rope pump for wells o 1 to 40 m deep cement tank ae 800 liters and drip system for xv 120 m 520 tomato plants The ERE irrigated area can be expanded to 0 5 ha depending on well 4 depth number of plants and duration of irrigation 19 Treadle Pump Fig 16 The treadle pump commonly known as a pedal pump is a water lifting device similar in principle to the hand pump A hand pump consists of a
53. osal recycling or reuse A typical drip irrigation system has seven major components IDE INDIA Figure 1 Layout of a typical drip irrigation system Water source The water for irrigation can come from wells streams ponds tanks rain recycled water from wastewater treatment plants or other sources Fig 2 BRENT ROWELL Figure 2 Irrigation water sources l river canal and r pond Delivery system The delivery system of any drip irrigation system Fig 3 consists of e mainline e sub main also called a header e feeder tubes or connectors e drip lines tubes or tape The role of the delivery or distribution system is to convey the water from the source to the field Delivery systems may be above ground easily movable or underground less likely to be damaged Pipes are most commonly made of PVC or polyethylene plastics The size and shape of the distribution system may vary from field to field and from farm to farm e The mainline delivers water from the source pump filtration system etc to the sub mainline The mainline is made of hard plastic and is joined to the sub mainline by a T connector e The sub main delivers water to the drip tubes or drip tapes through feeder tubes or connectors The sub mainline is made of durable polyethylene pipe or hose e Feeder tubes or connectors connect each drip tube or tape to the sub mainline Feeder tubes are made of plastic and can be inserted
54. p This water is held by the soil with increasing strength as the soil dried out Refill point is the point at which the plant has used all water that is readily available Beyond refill point as the soil dries out the plant needs to work a lot harder to extract water placing stress on the crop The difference between field capacity FC and refill point RP is called RAW RAW is water stored in the soil that is easily extracted by the plant Unless trying to stress the crop irrigation should aim to maintain RAW at all times The amount of RAW available to crop will vary with soil type crop rooting depth and irrigation system 51 Steps in identifying readily available water Step 1 Dig a hole Dig a hole within the root zone of your crop Step 2 Identify the effective root zone area where the main mass of roots is found Step 3 Identify different soil layers measure depth and calculate thickness of each layer Step 4 Identify percentage of gravel stone in each layer use a 2 mm sieve and visually estimate Step 5 Identify soil texture s Step 6 Calculate RAW Step 6 1 Identify the depth of the effective root zone Step 6 2 Identify the depth of different soil layers within the effective root zone Step 6 3 Determine the soil texture and stone gravel of each layer Step 6 4 Select the crop water tension group Table 6 and identify the RAW value for each soil texture layer mm 100 mm Step 6 5 Reduce the RAW figure s by
55. p development from 10 to 70 ground cover e Mid season fruit formation including flowering and fruit set or yield formation e late season including ripening and harvest Figure 33 Typical water use curve for most agronomic crops NSW DPI 2008c 61 A crop coefficient K relates crop water use at a particular Table 10 Crop coefficient Kc for various growth stages of development stage to the amount of evapotranspiration selected vegetable crops Doorenboos and Kassam 1979 ET calculated from weather data Table 10 shows the crop coefficient K for selected vegetable crops at various stages At harvest of growth Cabbage 0 41 0 52 0 7 0 8 0 95 1 1 0 9 1 0 0 8 0 95 04 06 06 0 75 10 115 08 09 0 7 0 80 Crop evapotranspiration is calculated using the equation 04 05 07 08 0 95 1 05 0 8 0 9 0 65 0 75 ET K x ET Fig 34 0 3 0 5 0 6 0 7 0 95 1 1 09 10 0 8 0 95 The first crop reading is for high humidity and low wind conditions The second reading is for low humidity and strong wind conditions Source Doorenbos and Kassam 1979 Grass Climate Where ET Crop Evapotranspiration e K Crop Coefficient ET Reference Evapotranspiration diia Temperature Wind Speed Humidity Well watered grass factor Figure 34 Calculating crop evapotranspiration ET Qassim and O iis PS Ashcroft 2006 Well watered crop optimal agronomic conditions 62 Table 11 shows the c
56. r fo fos fe S255 Head development CAE Ricey curd buttoning Growth cracks Avoid droughts during root expansion Moisture deficit can stop growth Cucumber pickles pe e f 2 5 7 Flowering and fruiting we CO CR Pointed and cracked fruit ire eneit drastically reduce yield pide kale BER misshapen fruit B Tough leaves good yield Thin scale Small leaves 66 Good continuous moisture essential to Preferred soil Amount Preferred obe Rooti Crop moisture cm in Irrigation Critical Irrigation o Don Defects Caused by Comments Bars ASM X Moisture Period Method ance 3 4 Water Deficit 1 Days 2 0 70 40 2 5 14 M H LEN Tough pods Irrigation can reduce yield s ee 00 ICH IE ON Shriveled pods blossom end rot Irrigate for increased pod size and yield Potato Irish Regrowth and misshapen roots Ange A OOO development pitiy roots Good soil moisture needed for rapid growth Flowering o Oo 7096 2 5 7 Bulb development 40 2 5 14 Root expansion H 40 2 5 7 Flowering Transplanting flower fruit 0 50 growth 2 5 7 70 2 5 7 After flowering 40 2 5 14 Fruiting 70 2 5 5 Continuous 20 2 5 21 Leaf emergence 50 2 5 14 Root expansion 40 2 5 14 MH LEN CC Mw CC ICO E CC Ce CC CC LEN CN Gauliiem pas Poor pod fill Plants recover from drought but yield is reduced Pointed and misshapen fruit Fruit sizing Irrigation can double or triple yields Good moisture avoid BER and
57. ritical growth stages of crops for determining irrigation water needs 2 Soil factor Total and readily available water Ideally a soil should hold enough water to facilitate plant erowth and have the capability to drain away any excess It is important to understand the way in which water behaves in the soil if irrigation efficiency is to be maximized Total available water TAW readily available water RAW and depletion fraction p are critical to planning an appropriate irrigation schedule To maintain soil moisture at optimum levels it is important to understand that not all of the total available water is used before the next irrigation is applied TAW is lowest in sandy S soils and greatest in heavy clay HCL soil S lt SL lt L lt LCL lt CL lt HCL Generally the RAW is only about 50 TAW 3 Climate factor Water is lost from the soil surface by evaporation and from the crop via transpiration i e in total evapotranspiration ET Water losses through ET are influenced by weather conditions temperature wind solar radiation and relative humidity and are estimated using these factors The crop soil and climate factors can be modified to improve the water use efficiency of vegetable crops The moisture accounting method is illustrated in Table 12 for a tomato crop grown in clay soil As soon as the accumulated deficit exceeds 40 mm a further irrigation is supplied To use the moisture balance sheet complete the follo
58. s increased crop intensity using the drip irrigation technology and increased crop yield and of farm employment and farm income Hence a simple economic assessment using a framework of partial budgeting serves the purpose which is also easy and convenient to gauge economic viability of the technology instantly and with limited need of expertise to carry out such economic analysis Experts from other disciplines can also carry out the partial budget analysis To carry out partial budget analysis we need to know only those changes on cost and benefits of the farm enterprises that are caused by the drip technology i e additional changes brought by the decision of technology adoption or changes at the marginal level of resources uses Here we do not need to analyze change on use of other farm resources brought by the technology than that of the direct impacts of the drip irrigation on crop productivity and farm return including due to cost saving on inputs use lts procedures and methods are illustrated in Table 16 but using some hypothetical data Table 16 Partial budgets to estimate to change on net farm income in a crop season due to adoption of drip technology Positive effects Amount Additional annual return from the drip technology due to increased yield 2 m effects Additional cost incurred by use of the drip tech M US 25 US 125 Reduced cost in use due to the tech of input materials nology labor savi
59. s point it is easy to get the water From the stress point to the permanent wilting point plants find it much harder to draw water from the soil and their growth is stunted Below the permanent wilting point no further water can be removed and the plant dies lt Field capacity RAWC TAWC TAWC lt Stress point Drainage Increasing Saturation difficulty for plants m Permanent wilting point to get water 1 Hygroscopic water from soil M Figure 31 Soil water holding characteristics and terms Luke 2006 Total available water content TAWC Readily available water RAW The amount of water crop roots can utilize per cm of soil depth which greatly varies according to the texture of the soil Table 6 Water available to a crop depends on rooting depth and soil texture soils differ in their ability to hold water and water that can be extracted by plant roots RAW in the root zone of a crop mm is the cumulative total of the depth in cm of each soil layer multiplied by the appropriate RAW value for the soil texture of that layer Table 7 The amount calculated represents water holding capacity of soil in the crops root zone that is the amount of irrigation water mm that it takes to fill the soil profile To schedule irrigation one should know how much water a soil can hold that is available to the crop The soil surrounding a plant s roots store the water it needs to live grow and produce a cro
60. single barrel or cylinder which one has to pump with one s hands the treadle pump has two cylinders and the operator can step on the pedals to lift water One person a man woman or even a child can operate the pump by pressing on two foot pedals or while holding on to a bamboo or wooden frame for support IDE India has developed four models of the pump designed for distinct soil water and income conditions e 3 5 inch pump metal barrels with bamboo treadles e 3 5 inch pump metal barrels with metal treadles e 5 inch pump metal barrels with metal treadles e 5 inch concrete pump PVC barrels with wooden pedals 3 5 inch treadle pumps bamboo or metal treadles e 3 5 inch diameter barrel e Pump weighs approximately 14 kg e Ideal for lifting water from water table depth ranging from 4 5 to 6 meters maximum lift 8 m A IDE INDIA e Water output is approximately 0 8 to 1 25 liters Figure 16 A low cost pump with bamboo treadle that can be used per second for furrow irrigation or to fill the tank for drip irrigation e The lifted water can be stored in the tank for 20 drip irrigation or can be applied to plots in furrow irrigation CHAPTER 3 Installation of a Simple Drip Irrigation System Installing a simple drip irrigation system The Horticulture Easy Drip HED kit is a simple drip irrigation system designed for small scale vegetable production in developing countries where water resources are scarce
61. t available locally reduced produce prices although farmers may lose out on this etc A good economic evaluation of technology adoption should quantify both the farm and community level benefits of the technology It should be noted that assessing community level benefits is demanding and time is needed to realize the full scale of these benefits in the technology adoption process Economic analysis at the farm level provides information about the economic viability of the technology based on the decision making behavior of individual farmers A farm level economic analysis of drip technology can be performed in two ways 1 Partial budget analysis or 2 farm enterprise budget analysis The method a practitioner chooses depends on resources time and economic information available ds Partial budget analysis of the drip technology A partial budget analysis of crop production activities with and without drip technology provides a good snapshot of information on financial viability of the technology in relation to farmers level of investment This sheds light on the scale of economic benefits that accrue to the farmer adopting the drip technology and the effective use of scarce resources scarce capital and labor In the first or second years of adopting small scale drip technology no major change would occur on structure of farm land use changes etc but only such change would occur at the production practices of selected two crop
62. the crop then it will need to irrigate for a longer period 56 Measuring dripper discharge Although manufacturers normally specify the output of the drippers it is best to check the actual discharge as your system may be operating at a different pressure or affected by blockages and wear Discharge can be checked by digging a hole under the dripper and using a container to measure the volume emitted over a known period Randomly check drippers across the irrigation system including drippers close to and farthest from the mainline In this way the uniformity of delivery by the emitters and uniformity of distribution of water across the field can be assessed and required adjustment can be made Infiltration rate IR IR is the measure of speed at which water can move through a soil profile and it is largely related to soil texture and affected by bulk density organic matter surface soil stability and ground cover IR of a soil determines the maximum rate at which irrigation should be applied If irrigation exceeds IR it will result in soil puddling and run off The infiltration rates for different soil types are presented in Table 8 Table 8 Example values of soil water characteristics for various soil textures Ramsey 2007 Soil texture 22 13 12 l E 10 E T Field capacity mm mm Infiltration rate mm h Available water capacity mm mm Permanent wilting point mm mm AWC for 8kPa to 60kPa These ar
63. tpotato Tomato Turnip Watermelon 64 CM HA 63 115 63 95 95 125 63 95 125 160 125 190 83 125 63 95 125 190 190 223 75 90 125 223 63 95 95 125 125 160 125 223 95 125 50 75 63 95 95 125 160 190 160 223 160 190 125 255 160 190 33 63 63 95 45 63 63 125 125 160 63 95 63 95 CRITICAL NEED STAGE establishment and fern development bloom and pod set bloom and pod set establishment and early growth establishment and heading uniform throughout growth establishment vining to first net emergence through establishment establishment and 6 7 leaf stage uniform last mont of growth uniform throughout growth establishment tassel elongation ear development bloom fruit set pod development establishment vining fruit set establishment vining fruit set bloom through fruit set rapid growth to maturity establishment uniform throughout growth uniform throughout growth establishment bulbing to maturity establishment bloom set uniform throughout growth vining bloom tuber initiation 2 4 wks after emergence bloom fruit set and development rapid growth and development uniform throughout growth after each cut if needed uniform throughout growth uniform until 2 3 wks prior to anticipated harvest bloom through harvest uniform throughout growth uniform until 10 14 days prior to anticipated harvest Soil water relationships and irrigation water requirements of various vegetable crops
64. wing steps Decide which crop will be erown e g tomatoes Estimate or measure root depth by digging a hole next to the crop or alternatively use Table 6 Find out the soil type and determine total available water Table 6 Decide on an appropriate depletion fraction p roughly 0 3 0 5 for vegetable crops Calculate readily available water depletion fraction p of total available water Calculate net irrigation application depth mm root depth readily available water Record reference evapotranspiration ET from climate data or calculate it from pan evaporation Multiply ET in mm day column A by the appropriate crop coefficient K value column B to obtain crop water needs Record daily rainfall and estimate effective rainfall mm column D amp E Add up column H for all water deficits since the last irrigation and subtract effective rainfall After an irrigation event the soil is saturated and crop water use is assumed to be zero 63 Table 11 Critical growth stage of crops and crop total water use for determining irrigation water needs Doorenboos and Kassam 1979 CROP Asparagus Bean green Bean pinto Beet table Broccoli Cabbage Cantaloupe Carrot Cauliflower Celery Collards kale Corn sweet Cowpea Cucumber pickle Cucumber slicer Eggplant Garlic Lettuce Mustard green Okra Onion Pepper bell Pepper jalapeno Potato Pumpkin Radish red globe Spinach Squash Swee

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