More Yield with Less Water-Techniques to Achieve A Higher Efficiency in Irrigation

More Yield with Less Water-Techniques to Achieve A Higher Efficiency in Irrigation,第1张

Dieter Prinz and AHMalik

Institute of Water Resources Management,Hydraulic and Rural Engineering,University of Karlsruhe,D-76128 Karlsruhe,Germany

1 Introduction

In the Developing World,agriculture counts for about 80% of total water withdrawal(Prinz,2000)Agriculture is under enormous pressure by the other sectors of the economy,as the economic value created per unit water is lowest in agricultureAt the same time,growing populations make it necessary to produce more food and fibre and to ensure that crop yields per unit land continue to riseTherefore,developing countries will have to find ways of growing more food with less waterBut there is not only the problem of water quantity but additionally the one of deteriorating quality of water

There are many modern and traditional or combined technologies available to improve water conservation development(Agarwal,2001,Rijsberman,2001)

There is the need①to define the aim(under given frame work conditions);②to analyze the losses(conveyance,distribution,application aolosses);③to identify the most promising water conservation methods and techniques,and,eventually;④to integrate the various elements within a(soil and)water conservation strategy(Emerson,1998,UNEP,1998)

2 Measures applied in irrigated agriculture

Irrigation water,if in ample supply,reduces considerable the risk of agricultural production and allows yields double as high as the yields which can be obtained from rain-fed agriculture(FAO,2001)Roughly 40% of the food is produced on irrigated land,on 17% of the total cultivated landThe water needed for crops amounts to 1000~3000 m3per ton of cereal harvestedWith other words,it takes one to three tones of water to grow 1kg of rice

As mentioned before,the losses of water have to be covered as well as the measures to increase the efficiency of water use in irrigation

We have to distinguish between recoverable water losses and unrecoverable water losses;the latter ones are those quantities of water lost to the atmosphere,to saline aquifers or to the sea

Recoverable losses include:seepage,surface runoff,operational losses and losses due to deep percolation

Fig1 Water losses within a surface irrigation system in a semi-arid region

The water losses could be(Fig1)

conveyance losses

distribution losses(egcanal evaporation,percolation and operation losses)or

field-ditch losses,

field-application losses which depend on soil,irrigation method and management,

Reduction of conveyance and distribution losses

33%~50% of water diverted for irrigation is lost‘en route’:The conveyance and distribution losses are enormousBy lining the canal system or by conveying the water in pipes,these losses can be significantly reducedIt should be kept in mind,that at least the seepage losses are in most cases recoverable losses;the water might be lifted up from the groundwater layer downstream

Seepage losses occur in unlined main canals,in the canal distribution system and in field ditchesMost of the water is lost in unlined main canalsThe questions which arise here are the following:

What quantities of water are lost

Are these losses easy to recover

What feasible lining methods could be used

How high are the costs of lining and of maintenance

What are the benefits of the saved water

Could the unlined canal be used in the rainy season to recharge an aquifer

Reduction of application losses

Application losses are either surface runoff losses or percolation losses,often summarised as“operational losses”The water applied,should be sufficient to wet the volume of root penetration,but should not go beyondNumerous technical means are available to apply exactly the amount of water needed,but financial and labour problems,in large irrigation schemes also management problems,hinder this

Operational losses depend on:①the chosen distribution system;②the available regulating and mechanical facilities;③the skill and discipline of the operator

3 Crop root zone depth

The active root zone of the crop(if water is not a constraint)depends on:①crop type;②its stage of maturity;③soil conditions(Fig2)

Fig2 The water applied should be sufficient to wet the volume of root penetration(but not more)

Use of efficient irrigation methods

The large differences in water efficiency between the various irrigation methods are quite well known:Traditional surface irrigation generally achieves only around 40% efficiency,sprinkler irrigation can be 70%~80% efficient and drip irrigation might reach over 90% efficiency(Wolf and Stein,1998,Fig3)Modern irrigation technology could in theory save about half of the water presently consumed in irrigation,but technical,economic and socio-cultural factors hinder the transformation of theory into practice

These methods are arranged according to their average efficiency

The surface irrigation techniques are:①basin irrigation,②furrow irrigation and③border irrigation

Fig3 The five basic methods of applying water to the soil

These techniques have one drawback in common:the uneven water application over the irrigated areaWater infiltration is much greater at the top end of the field than the bottom because of the longer opportunity time at the top end and this results in high deep percolation

Surge irrigation(Fig4)has been shown to markedly improve the efficiency of water applicationIt is the practice of intermittently stopping and starting water flows across a field

Fig4 Water percolation in surge and continuous flow

Another method is the sprinkler irrigationLow Energy Precision Application(LEPA)center pivots are one of the most efficient irrigation methods available today because they offer both high water application efficiency and low operating pressureThe water is applied near the ground surface below canopy

Drip/trickle irrigation is characterised by the following:

low flow rate,long duration irrigation,frequent irrigation,water applied near or into the plant's root zone,and low-pressure delivery system shigh investment costs and maintenance demand

In drip irrigation some techniques were developed which are not as efficient as the more costly ones,but which allow even small farmers a very high efficiency egin vegetable cropping:the drip bucket irrigation is such a low cost and relatively efficient technique,applied already on thousands of farms in East Africa(Prinz and Malik,2001)

31 Case study:Growing More Rice with Less Water(China)

Water Efficient Irrigation Techniques

One method to save water in irrigated rice cultivation is the intermittent(submerged)irrigationThis example shows real water saving and increase of productionProduction levels remained stable over the time period in spite of this massive shift of water(see Fig5,Table 1)out of agricultureGrowing more rice with less water improves also the productivity of waterThis was made possible through pol-icy,management,and technological changes(Rijsberman,2001)

Fig5 Water quantities used for domestic,industrial and hydropower purposes increased 10 times during the period 1976 and 1996,with subsequent reduction of water quantities for irrigation

Table 1 Changes in land and land productivity in Zhanghe Irrigation District,China(1966~1998)

Source:Rijsberman 2001

32 Subsurface Irrigation Techniques

321 Pitcher irrigation

Pitcher irrigation or“Pot Irrigation”is a traditional,extreme efficient form of irrigationThe technique is particularly suitable to the irrigation of vegetables(like legumes,beans,water-melons,etc)in home ardens(Fig6)

The clay pots can either be installed independently,iethe water supply is done by the farmers manually,one by one,or interconnected:the water supply is done by using a water reservoir,which can be a tank,a well,etc

322 Surface trickle irrigation

Fig6 Clay pots used for

pitcher irrigation

To reduce deep percolation losses in subsurface irrigation,a trench is dug and a layer of plastic sheets is positioned below the trickler pipe(Fig7)

323 Vertical Pipe Method

A very simple but effective method for ree cultivation is the vertical pipe method:Provided sufficient water storage capacity in the root one is given,a larger quantity of water is applied through the vertical pipe to supply the tree with water for 2~4 weeks(Fig8)

Fig7 Subsurface trickle irrigation with reduced percolation losses

Fig8 Vertical pipe method

The water efficiency depends not only on the method

Wolf and Stein(1998)cite a study made in Israel by Hagan(1994),who found surface irrigation to be 70% water efficient but drip irrigation only 42%~56%

This deviation from generally believed figures is due to differences in the available underlying conditionsFor the farms using surface irrigation,water was in very short supply and therefore it had to be used as efficiently as possibleDrip irrigation on the other hand has been used under conditions of sufficient water to grow crops of high market valueLow cost of water and high market prices did not give any incentive to the farmers to use water efficiently

33 More rational use of irrigation water

331 Supplemental irrigation(SI)

It is the application of small quantities of irrigation water to essentially rain-fed crops in times when the demand can not be covered by rainfall(Oweis,1997)SI is usually practiced usually in the wetter part of the dry areas with 300 to 600 mm annual rainfall in order to improve and stabilise yields(Oweis et al,2001)Supplemental irrigation might be taken from groundwater or from excess water stored during the rainy season

332 Deficit irrigation

Another technique which allows a very high water use efficiency under fully irrigated conditions is deficit irrigationThe deficit irrigation is the distribution of limited amounts of irrigation water to satisfy essential water needs of plantsThe water supply is reduced in less critical periods of water demand by the crop and supply of full amount of water during stress-sensitive periodsA similar technique is the“intermittent submerged irrigation technique”for rice(ISI)This technique has been promoted in China but it is now applied in many rice growing areas world wideUp to 20% of the irrigation water can be saved,if the paddy crop is not grown under submerged conditions through out the main growing season,but only intermittentlyThe phases where submerged conditions are recommended are those“sensitive”stages mentioned earlier

Precondition for deficit irrigation management is the knowledge of the sensitive periods of the crop/the variety in question

333 Aquaculture

Paddy croppingcan be combined with fish raising if certain preconditions are given(Fig9)This allows a multiple use of water and hence water saving per unit produce

Fig9 Combining paddy cropping with fish raising

Case study:Drip Irrigation Systems(DIS)in India

Drip Irrigation Systems in India are being praticised since 1970,being used on a limited scale in Tamil Nadu,Karnataka,Kerala and Maharashtra States,mainly for high value,horticultural crops like coconut,coffee,grape and vegetable production without the benefit of any subsidies from the governmentsAt Rahuri,in Maharashtra State,the use of drip irrigation of pomegranates,grown in gravely soils,resulted in a savings of about 44%(as compared to conventional check basin irrigation systems)with a further water savings of about 14% when compared to un-mulched plots

The capital costs involved are high compared to conventional irrigation systems,but the labor and operational costs are low in IndiaThe net result is that the benefit-cost ratio for DIS is very favourable compared to conventional systems since the payback period for investment very shortThe cost of using drip irrigation system is summarized in the Table 1

With DIS in India,there was an improvement in crop yields and savings in water use of between 18% and 40%Consequently,there was a substantial improvement in the water use efficiency that ranged up to three times that of conventional surface irrigation methods,even with the use of poor quality irrigation waterSee Table 2 for water savings and increased yields achieved using drip irrigation in Indian case

Table 2 Drip irrigation cost;water savings vincreased yield achieved in India

Source:Saksena 2000

4 Improving water availability

As mentioned earlier,aquifer depletion is a common problem in many dry areas of the worldMany techniques have been developed to artificially recharge aquifers to sustain the water table and to allow further control of pumping water to cover the water needs of humans and cropsOne interesting example of combined basin irrigation with groundwater recharge is reported from Uttar Pradesh Province in India(IWMI,2002)In the monsoon season,surface water is diverted through an unlined canal system to provide farmers with irrigation water for rice cropsAround 60% of the irrigation water applied is used by the plants,most of the remaining 40%filters through the soil to recharge the groundwaterCombined with seepage from unlined canals those“losses”provide farmers with groundwater to irrigate dry season cropsThe research showed,that the water table in the study area,which had been progressively declining,has been raised from an average of 12m below ground level to an average of65m

5 Summary

We need information on crop water requirementsLosses have to be avoided in conveyance,distribution and application of irrigation waterIn larger irrigation schemes the conveyance losses alone sum up 30%~50% of the total water demand

Farmers can apply more efficient irrigation methods like trickle irrigation,subsurface irrigation or pitcher irrigation

Improved application techniques like surge irrigation have also shown a great potential to increase water productivity in irrigation

Further-on,an increase in efficiency in irrigation water can be accomplished by a more rational use of water egin“supplemental irrigation”or“deficit irrigation”

Aside of increasing the efficiency of irrigation water use,there are some other important water conservation methods,eg

selecting best suited crops and cropping methods reducing the losses of stored water and improving water availability

“More yield with less water”can be achieved to a very large extent by applying appropriate methods and techniques in irrigation management

References

[1]Agarwal AIncreasing water harvesting and water conservation is the only way to ensure food securityDown to Earth,Vol 10,No3,June 30,2001

[2]Bastani S“Unterflurbewässerung mittels Kuseh-RohrenEntwicklung eines neuen Bewässerungssystems mit hoher Wassereffizienz und Bewässerungsversuche in Karadj/Iran”Diss,InstfWasserwirtschaft und LandschaftsäkoHeft 26,UnivKiel1998

[3]Beets WCRaising and sustaining productivity of smallholders farming systems in the tropicsAgBe Publishing,Holland1990

[4]Cape JIrrigation Research:Past,present and futureIrrigation Australia,1995,Vol10,30~32

[5]Chritchley W,Reij Cand Turner SDSoil and water conservation in Sub-Saharan Africa:to-wards sustainable production by the rural poorIFAD,Rome and CDCS,Amsterdam1992

[6]Emerson,HConservation,it's the future of waterOn Tap,1998Vol7,Issue 4

[7]FAOCrops and drops:Making the best use of land and waterFood and Agriculture Organisation(FAO),Rome2001

[8]Fatondji D,Martius Cand Vlek,PZai-A traditional technique for land rehabilitation in NigerNewsletter No8,Zentrum für Entwicklungsforschung/Center for Development Research,Universität Bonn,September2001

[9]Hagan HConstraints to high efficiency in irrigation water management in the Jordan ValleyProceedings of the regional seminar,Amman1994

[10]Hudson NWSoil and water conservation in semi-arid areasFood and Agriculture Organisation(FAO) Soil Bulletin,1987,57 pp109~122

[11]IWMIA success story in reversing groundwater declineIWMI Research Update,June 2002IWMI,Colombo,Sri Lanka

[12]Oweis TSupplemental irrigation:A highly efficient water-use practiceICARDA,Aleppo,Syria,1997,16pp

[13]Oweis T,Prinz Dand Hachum,AWater harvesting,indigenous knowledge for the future of the drier environments,ICARDA,Aleppo,Syria,2001,36pp

[14]Prinz DGlobal and European water challenges in the 21st centuryKeynote Speech,3rd Inter-Regional Conference on Environment-Water,“Water Resources Management in the 21st Century”,1-3 June 2000,Budapest/HungaryProceedings,p247~254

[15]Prinz Dand Malik AHWater Conservation in Agriculture,FAO Training Course,Draft Version on CD ROM,FAO,Rom2001

[16]Prinz Dand Wolfer SOpportunities to Ease Water Scarcity(Water Conservation Techniques and Approaches)Proceedings,International Conference on“World Water Resources at the Beginning of the 21stCentury”03-06 June 1998,ParisUNESCO-IHP,Paris1998

[17]Rijsberman FRBalancing water uses,water for food and water for natureThematic Background Paper,International Conference on Freshwater-Bonn 2001International Water Management Institute IWMI,Colombo,Sri Lanka2001

[18]Saksena,RSMinistry of Water Resources,Government of India,New Delhihttp://wwwuneporjp/ietc/Publications/TechPublications/TechPub-8e/dripasp2000

[19]UNEPSourcebook of Alternative Technologies for Freshwater Augmentation Some Asian Countries,UNEP,Paperback,1998,223 pages

[20]Wolff Pand Stein TMWater efficiency and conservation in agriculture-opportunities and limitationsAgriculture+Rural Development;1998vol5;no2;pp17~20

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