The Sustainability of Arid Agriculture: Trends and Challenges · 2016-12-05 · The Sustainability of Arid Agriculture: Trends and Challenges Alon Ben-Gal1, Alon Tal2, Noemi Tel-Zur2

The Sustainability of Arid Agriculture: Trends and Challenges

Alon Ben-Gal1, Alon Tal2, Noemi Tel-Zur21 Institute of Soil, Water and Environmental Sciences, Gilat Research Center, Agricultural Research Organization, Israel2 Jacob Blaustein Institutes for Desert Research, Ben Gurion University of the Negev.

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In efforts to provide food and fiber toa growing and developing world, agricultureis challenged to increase productivity.Moving water into arid regions and theintroduction of irrigated agricultureconstitute a key element in any strategyfor increased global production. Aridregions offer large undeveloped land anda climate conducive to plant growth andcan provide high yielding cultivation oncondition that water is available. Thesustainability of arid zone agriculture isquestionable and faced with combinedchallenges of development and protectionof water resources, managing salinity andcreating long-term economically andenvironmentally sound operations. In thisreview we will address strategies to ensurethe sustainability of arid agriculture viafarm and regional management of waterand salinity and the use of appropriate plantand crop sciences with an eye towardsthe agronomic feasibility of the technologiesrequired to overcome the inherent challengesof agriculture in the drylands.

Defining Sustainable Arid-Agriculture

Since the term became fashionable,countless definitions for "sustainable

agriculture" have been proposed (Gold,1999). These can be quite detailed, forexample; the US Congress which definedas sustainable agriculture that can: "satisfyhuman food and fiber needs, enhanceenvironmental quality and the naturalresource base upon which the agriculturaleconomy depends, make the most efficientuse of nonrenewable resources and on-farmresources and integrate, where appropriate,natural biological cycles and controls,sustain the economic viability of farmoperations and enhance the quality of lifefor farmers and society as a whole."(FACTA, 1990) Alternatively, sustainableagriculture has been characterized moresimply, such as the definition put forwardby farmer-philosopher Wendel Berry:"agriculture that does not deplete soils orpeople" (Jackson, 1984). Some argue thatefforts to reach a precise definition areill-advised (Pannell, 1999). As theetymology of "sustainable" can be tracedto the Latin sustinere (sus-, from belowand tenere, to hold) any definition willneed to imply that the yields from suchagricultural activities must be able to last.Frequently, sustainable development isdescribed as having three components:ecological, economic and social. Given the

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limited scope of this article, only the firsttwo elements will be reviewed, even asthere are certain to be critical “ social”aspects to a given local or national strategyfor sustainable desert agriculture.

Discussions about the sustainability ofarid agriculture could of course considerdynamics common to all agriculturalventures. Pest control methods that do notpollute or poison farm workers, fertilizersthat will not contribute to watercontamination and non-erosive tillingpractices, to name a few, are importantcomponents of sustainable agriculturewherever humans work the land. Yet, athorough review of all aspects associatedwith agricultural sustainability is beyondthe scope of a single article. Hence, thisreview of sustainability in arid agricultureshould offer a particular focus on thosechallenges that are unique to this classof drylands. This should begin by clearlyindicating what constitutes "arid lands".

For over fifty years, arid zones havegenerally been defined by versions of "theAridity Index" introduced by Thornthwaite(1948): a ratio relating annual precipitation(P) to annual potential evapotranspiration(ETp), the amount of water lost from nonwater limited soil by plant transpirationand direct evaporation from the ground.According to the UNEP index of aridity,defined as AI = P/Etp-1, arid regions havea P:ETp ration of less than 0.2 and hyperaridregions less than 0.05 (UNEP, 1992). Bythis estimate, the United Nations estimatesthat some 10 million km2 or 7.5% of theplanet are "hyper-arid" lands while some16.2 million or 12.1% of the earth canbe classified as "arid". This generally refersto lands where precipitation does not exceed

300 mm year-1. It is important to emphasizethat the present survey will not includeagriculture in the semi-arid zones, whererainfall can reach 500 mm year-1, and theAI is between 0.20 and 0.50.

The harsh climate in the arid zones givesrise to conditions that are fundamentallydifferent for agriculture than in othertemperate regions, including semi-aridareas; 1) Typically, commercial agriculturemust rely on irrigation; 2) Soil salinityis high and organic content is low; and3) Because biotic activity is not particularlyhigh, these lands are not robust and areconsidered to be especially vulnerableecologically. While archaeological evidenceindicates that domestication of crops, humanagricultural organization and irrigation-based civilizations originated in the then“Fertile Crescent” of Mesopotamia betweensix and eleven thousand years ago, forthe most part, the agriculture of ancientpeoples was not particularly productive inarid regions. Indeed, numerous examplesexist of ancient agriculturally basedcivilizations in the drylands whose lackof attention to the ecological implicationsof their practices eventually led to massivedamage to the soils and water resourcesthat supported them and their ultimatedemise (Diamond, 2005).

Pulitzer prize winner Jared Diamonddescribes the fundamentally unsustainableagriculture of old which essentially sewedthe seeds of its own destruction: "Becauseof low rainfall and hence low primaryproductivity, (proportional to rainfall),regrowth of vegetation could not keep pacewith its destruction, especially in thepresence of overgrazing by abundant goats.With the tree and grass cover removed,

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erosion proceeded and valleys silted up,while irrigation agriculture in thelow-rainfall environment led to saltaccumulation . . . . They committedecological suicide by destroying their ownresource base" (Diamond, 1999).

Key Challenges to Arid Agriculture

During the second half of the twentiethcentury, the demand for arid agriculturalproduction grew as population densities indeserts across the planet rose. Practicesemerged which allowed for dramaticallyexpanded cultivation of these driest of lands.Moreover, the long-growing seasons andthe increased feasibility of long-distanceexport of agricultural produce offeredcertain commercial advantages to farmersin arid lands. The Food and AgriculturalOrganization estimates that while 17% ofthe world’s farmland is irrigated, becauseof the longer growing seasons, itscontribution to overall production may betwice that. (Clemings, 1996) While U.S.irrigated lands only amount to 17% -- theyproduce roughly half the total value ofcrops nationally (Howell, 2001). So whilethe short-term economic feasibility ofagriculture in the drylands is beyondquestion, its sustainability remains unclear.To be agronomically successful andeconomically competitive in the long-run,modern arid agriculture will need to relyon relatively intensive utilization of newtechnologies.

In general the agriculture that emergedduring the past fifty years can largely becategorized as part of the modern"conventional" or "industrial" farming. TheWorld Bank attributes the dramatic 70-90%increase in overall food production to

mechanized approaches and techniques(Gold, 1999). As such, agriculture on aridlands in developed regions also frequentlyinvolved increasingly large farm units andexpensive capital investment, farm equipmentthat efficiently replaces laborers,sophisticated irrigation systems, mono-cultures and extensive utilization of pesticidesand fertilizers.

But despite their remarkable productivity,there were environmental side effects whichraised questions about the sustainability ofmodern agriculture in arid regions. Theseincluded loss of soil fertility due to erosion,compaction, and loss of organic matter.Perhaps of greatest concern was the potentialof irrigation to lead to waterlogging andto the salinization of the soil and surroundingwater resources, or worse yet, their combinedimpact (Kahlown, 2002). Agricultural runoffbecame a leading source of watercontamination in many Western countries.And of course the “mining” of aquifersis by definition unsustainable. From the stateof Gujarat in India to the Ogalala aquiferin the American Middle West, water resourcesbecame depleted in order to meet the growingdemands of agriculture. Pesticides left a tollon human health and in fact led todevelopment of resistance in more than 400insect species (Gold, 1999).These obstaclesmust be overcome if agriculture in arid andsemi-arid lands is to truly be “sustainable” .

There have been many calls by publicinterest groups for a retreat from modernagricultural technologies and theirassociated ecological ills, among them areturn to organic, chemical free, diverse,low impact agriculture (NRDC, 1999). Yet,other perspectives advocated a middle path(Union of Concerned Scientists, 1999).

SUSTAINABILITY OF ARID AGRICULTURE 3

Recognizing the imminence of a food crisis(Brown, 2004) considerable investment hasgone into reducing the impacts of the newtechnologies to create a modern agriculturein the drylands, which both offers the hugeproduction benefits of industrial agriculture,but that also reduces its negativeconsequences. Of particular significance arethe technologies designed to increaseefficient water management and irrigationas well as the introduction of new plantbreeds that are both salt and drought tolerant.Solutions to most of the traditional obstaclesto arid agriculture exist and can be readilyadopted. It also projects those areas wherefuture research can both minimizeenvironmental impacts and contribute togreater agricultural productivity in ariddrylands.

• This paper reviews progress in the field,focusing on recent developments indesert farming in this context. It isdivided into three sections:

• Challenges associated with providingefficient irrigation while maintaining theintegrity of water sources in the drylands;

• Challenges associated with plantbreeding and introduction of appropriatecrops given land and water conditionsin arid lands;

• The economic dynamics associated withmodern arid-land agriculture.

The resulting picture is a cautiouslyencouraging one, where recent scientificand technological innovations haveimproved the profitability of arid agricultureand ongoing research promises to increasethe yields and standard of living for agrariancommunities in the drylands.

Water Management and Irrigationin Arid Lands

Long term water supply

Given the inherent dynamics of scarcity,the most fundamental question regardingwater management to support agriculturein arid regions involves the sustainabilityof water sources. Traditionally, desertagriculture relied on the harvesting of runofffrom the infrequent storms. Later, groundwater was tapped by wells. More recentlywastewater reuse and desalination offersupplementary sources of water. Each ofthese sources poses its own challenges andquestion marks.

Water harvesting in the drylands canin fact provide substantial quantities ofwater. Israel, for example, has expandedits water supply by some 7% by capturingrainwater and utilizing it for irrigation inarid and semi-arid regions (Tal, 2005). Yet,this supply is inherently given to periodicdroughts and the quality of water may sufferfrom the salinization caused by evaporation.As the mining of ground water is a relativelyrecent phenomenon, its intrinsicun-sustainability is only now beingappreciated. Some 15,000 wells havealready gone dry in the Indian state ofGujarat, with enormous social turbulenceand human desperation (Pearce, 2006). Thesteady disappearance of the Ogallala aquifer,by far the United States’ largest freshwaterresource, is only now beginning to leaveits mark on the farmers across the drylandsof the western section of the country (deVilliers, 2000). A variety of strategies arebeing explored to reduce water usage,including integration of crop and livestock

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systems on rangelands (Allen, 2005) aswell as water conservation and phaseoutof conventional irrigation systems (Postel,1997). Ultimately, it is clear that agriculturethat relies solely on groundwater, mustadjust extraction rates to meet recharge rates,or inevitably face extinction.

The reliability of treated effluents anddesalinated waters is ostensibly greater;however, they pose other problems – bothenvironmental and economic. Water scarcityhas promoted development of wastewaterreuse programs in dry climate regions ofthe world. In Israel, effluents (treatedwastewater) today contribute roughly a fifthof Israel’s total water supply, and a farhigher percentage of the irrigation supplyfor agriculture (Shelef, 2001). There arethree major concerns involved withwastewater reuse: human health, detrimentaleffects to plant growth, and soil andgroundwater degradation. Health concernscan be rectified by treatment levels highenough to insure safe use of the effluent(Carr et al., 2004). Contaminants in effluentinclude relatively high concentrations ofmineral ions including nutrients, salts andspecific ions toxic to plants includingsodium, chloride and boron. Effluent istherefore regarded as both potentiallybeneficial when nutrients can be utilizedfor crop production instead of fertilizersand detrimental due to negative effects ofsalts on plant growth and yields (Pettygroveand Asano, 1985).

Management of effluent for irrigation,first and foremost, means salinitymanagement and increased leachingrequirements. Soil degradation andgroundwater pollution can occur when the

recycled wastewater contains chemical orbiological contaminants not otherwisepresent in the agricultural ecosystem (Salem,1996). In order for effluent to be thedominant water source for irrigation, watermust be treated to a level allowing unlimiteduse on all crops and on all soils accordingto health, agronomic and environmentalstandards together.

Desalination of brackish groundwaterand seawater potentially could providelimitless water for irrigation. The highenergy costs involved and the cost andecological issues surrounding disposal ofconcentrated brines challenge desalinationprojects. Although desalination is today stillregarded as cost-ineffective (Beltrán andKoo-Oshima, 2006), desalination, first fordrinking water and subsequently forirrigation is becoming more and morecommon, starting in water-poor-currency-rich, countries including Kuwait (Hamoda,2001) and Israel (Tal, 2006).

Providing water for plants in an aridenvironment: Climate-driven demand plussalinity management

The water requirement of plants is mainlya function of the local climate. Most ofthe water consumed by a plant movesthrough it passively and evaporates intothe atmosphere via the transpiration process.The same crop in a hot, dry, arid regioncan require 3 to 4 times the quantity ofwater compared to a cooler, more humidregion (Rana and Katerji, 2000). Acultivated crop in an arid-region may welldemonstrate increased growth andproductivity compared to the same cropgrown in a more temperate zone due toadvantageous temperature and radiation, and


the arid zone may allow production inseasons when cultivation is not possiblein the other regions. For example, favorableclimate has contributed to bell pepper yieldsreaching 160 t h-1 in the Negev Desertof Israel, far higher than normal in coolerclimates where such production woulddepend on expensive climate control. Thelong seasons and winter harvest of thepeppers make cultivation of high qualityproduce and export to European marketsprofitable for the Israeli farmers. Suchproduction necessarily requires largeproduction related inputs; specifically ofwater and fertilizers.

Irrigation water necessary to arid zoneagriculture imports and transports dissolvedmineral salts. These salts present a majorobstacle to sustainability. Mineral ions inirrigation water include nutrients, oftenadded by growers as fertilizers in advancedirrigation systems, as well as undesirablesalts. In arid zones, large amounts ofotherwise innocuous minerals locatednaturally in the soil can be mobilized asintensive water application is practiced(Smedema and Shiati, 2002). Plants takeup water and mineral ions selectively. Mostof the undesired soluble salts are left inthe soil as water uptake occurs (Bernstein,1975). Accumulation of these salts in thesoil creates a negative environment for plantgrowth. Root zone salinity is often describedas behaving in an identical manner todrought. Both the decrease in water andthe increase in solute concentration in thesoil cause a decrease in the soil solution’spotential energy. Water flows from highto low potential along a gradient withinthe soil-plant-atmosphere continuum.

Decreased potential in the root zone causesa reduction in this potential gradient andhampers flow from the soil to the plant(Gardner, 1991).

Of course, the greater the waterrequirement of the crop, the greater theabsolute amount of salts left in the soilfollowing uptake. In arid regions this amountcan be compounded by naturally saline soilsand by available irrigation water with highconcentrations of salts. Since salt build upin the root zone is harmful and can becomedetrimental to agriculture, leaching is criticalin irrigation management. Salts leachedfrom the root zone do not disappear however.Leached salts make their way into bothsubsurface and surface water resources;often those utilized for agriculturethemselves.

Overcoming obstacles to irrigation in thedrylands

Irrigation has been “ invented” and“ reinvented” over thousands of years ofhuman history in order to allow deliveryof water and nutrients to plants where andwhen nature failed to provide agriculturallyefficient rainfall. Desert agriculturedepended historically on proximity to riversand later on engineering schemes to bringwater to the fields. Irrigation developmentin the mid-19th century, in the Punjab,the flat and fertile corner in north-westIndia by the British (Clemings, 1996), andthe later during the 20th century in theWestern USA (Rao, 2000; Reisner, 1993),relied on large-scale water movement andstorage in order to open huge areas ofland to agriculture. More recently, waterfrom deep aquifers (up to more than akilometer deep) is pumped locally to feed

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arid agriculture. (Glennon, 2002)Development of desert agriculture was, fora long time, concerned solely with the supplyof necessary inputs and completelyneglected emissions.

A major problem related to salt leachingin arid zones where large quantities of waterare introduced involves the accumulationof salts in the groundwater below the rootzone. Eventually (sometimes very quickly)the saline water tables rise up and intrudesinto the agricultural soil (Beltran, 1999).Even when aquifers are deep or riversdistant, the salts in arid zones eventuallymake their way to water resources andbecome problematic. Salty water tablesinhibiting leaching from the root zone werethe scourge of ancients in Mesopotamia(Jacobson and Adams, 1958; Gelburd,1985). The Babylonians built civilizationswhose food supply depended upon irrigationof vast arid fields with readily availableriver water only to, over time, witness risingsaline water tables, declines in productivityand yields, and eventual inability to supplythe needs of the cities. Stories similar tothis follow us through human history inarid regions and similar results continueto cause losses in modern agriculturalproductivity worldwide. (Christensen,1998).

The Murray-Darling river basin inAustralia is a noteworthy modern examplewhere leached salts from agricultural landsreturn to the river and create a problemfor downstream users (Herczeg et al., 1993).Average salinity of River Murray wateris 500% higher at the end of the riverin South Australia compared to river sourcesin Victoria/New South Wales. Due to acombination of continued reductions of river

flow, dryland recharge and leachate fromirrigated agriculture along the river basin,downstream water is predicted to continueits rate of increase of salinity and doubleover the next 100 years (Murray-DarlingBasin Ministerial Council, 1999). Thissalinity increase will lead to agriculturalproductivity decline and infrastructurelosses estimated at over $1 billion.

The FAO (2002) estimated that theproductivity of approximately 20-30 Mhairrigated land has been significantlydecreased by salinity and that salinizationresults in the loss of an additional 0.25-0.5Mha each year globally. Salinization is farfrom being a problem of “developingcountries” . In 1990, 1.4 Mha of irrigatedCalifornia land were assessed as havinga water table within 1.5 m of the surfaceand 1.7 Mha were determined to be salineor sodic (Tanji, 1990). Recent workinvolving regional scale hydro-salinitymodelling questions the sustainability ofirrigated agriculture in the San JoaquinValley, California due to inevitablesalinization of soil and groundwater(Schoups et al., 2005). Approximately 8.8million hectares in Western Australia arethreatened by rising water tables and maybe lost to production by 2050 (NLWRA,2001).

Often, irrigated agriculture in arid zonesrequires systems for drainage watercollection in order to allow long-termleaching. Despite installation of extensivedrainage systems and groundwatermanagement in recent years, some 25%(more than 5 Mha) of the Indus Riverbasin of Pakistan are still estimated to beeffected by salinity and water logging (Tanjiand Keilen, 2002). While drainage collection


may facilitate field-scale salinitymanagement, there remains an issue ofdisposal of the collected saline water.Leachate contains the unwanted salts, excessagricultural inputs including nutrients,herbicides and pesticides, as well asnaturally occurring contaminants that,without irrigation would not have beenmobilized. Proper design of drainagesystems including shallow placement oflaterals have been shown to cause lowerdrainage volumes and salt loading (Ayars,2006). In spite of this, design criteria fordrainage systems in arid lands are far fromstandardized.

California’s experience with agriculturaldrainage water is particularly sobering.Strategies to dispose of the water viaevaporation in wetlands failed miserablyin the late 1970s and early 1980s due tohigh concentrations of selenium that causedfish mortality and bird deformities (Leteyet al., 1986; Presser and Ohlendorf, 1987).The selenium in California does not comefrom the irrigation water itself but is movedfrom the soil where it exists naturally.Demands of zero environmental release ofcontaminated agricultural water waste havebeen established to prevent environmentalcontamination from salts and nutrients.These demands, necessary for long termsustainability, create major challenges toirrigation management today in Californiaand elsewhere.

Approaches to water and salinitymanagement

A variety of strategies have emergedto address the negative phenomenaassociated with salinization due to irrigation.

Leachate collection and disposal: Evenwith low-salt-input irrigation, some excesswater is eventually needed in order tomaintain healthy root zone conditions foragricultural production. Sustainablemanagement must take long termresponsibility for the contaminantstransported in this excess leachate. Drainagewater collection systems and disposalschemes must become integral to desertagriculture to avoid environmentaldegradation. Examples today includeregional interception of saline water beforeit enters the Murray River in Victoria andSouth Australia (Alexander, 1990), largescale off- and on-farm drainage collectionin The Indus River Valley of Pakistan(Aslam and Prathapar, 2006) and inCalifornia where farm scale drainagesystems and local containment and treatmentof the leachate has become more prevalent(Tanji et al., 2002). Common to all ofthese cases is a problem of final disposalof the collected contaminants. Evaporationand water treatment can concentrate theminto brines or solids and thus reduce thevolume of the waste. Sea-ocean disposalis common where practical, but may notprove truly environmentally sound orsustainable, depending on specific chemicalmake-up of the contaminants.

Reduction of leaching: Agricultural rootzone management most often incorporatesa concept of “ leaching fraction” ; thequantity of excess irrigation water neededto maintain a predetermined salinity levelin the soil. Leaching fractions are calculatedbased on: a) desired soil salinity; a functionof presumed relative sensitivity of a givencrop and; b) predicted water consumption

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of the crop based on cover and climateconditions. (Ayars and Westcot, 1985) Themost common of these paradigms fordecision making regarding the amount ofwater needed in order to leach salts donot sufficiently take into consideration soiltype or feedback due to actual plant responseto the saline conditions.

Current work suggests that salt balancecalculations must take into considerationsoil type and that there is substantial “self-regulation” by plants (Dudley et al., 2006;Shani et al., 2007). This suggests over-estimation of the amount of water neededto leach salts since plant water uptake willbe reduced (and therefore leachingincreased) for salty conditions, even withoutadditional applications of water, as wellas under-estimation of the yield-reductioncost from saline irrigation water. Applicationof soil-crop-climate integrated considerationof irrigation management (Dudley, 2006;Shani et al., 2007) could allow effectiveprediction of crop response to managementvariables, more efficient water use, andreduction in leachate.

Reduced inputs: Water use efficiencyhas increased in irrigated agriculture withthe introduction of precision techniquesincluding drip/trickle distribution systems.Adoption of low volume microirrigationsystems (e.g., drip, micro-sprinklers) andautomation increases the average efficiencyto 90% as compared to 64% for furrowirrigation or 75% for sprinklers (Howell,2001). Development of drip irrigationtechnology that allows low flow applicationof water uniformly throughout agriculturalfields and the application of this technologyin agricultural water management has been

a cornerstone in Israel’s progress in wateruse efficiency. The first regulated surfacedripper was patented by Israeli waterengineer Simha Blass in 1959. Modern dripsystems were then developed in and forhyper-arid agriculture through workconducted in Israel’s Arava Valley in the1960s (Goldberg and Schmueli, 1970).

Drip irrigation promotes efficient waterapplication by reducing losses in distributionsystems, by distributing water directly tothe root zone, and by promoting efficientwater and nutrient uptake by locallymaintaining conditions of relatively highwater content. These advantages aresupplemented by a number of otherstrategies also made possible by dripirrigation including distribution of fertilizersdirectly via the irrigation system (Bar Yosef,1999), subsurface application withsubsequent elimination of water loss fromsurface evaporation (Ben-Gal et al., 2004)and high frequency scheduling allowingmatching of water application with planttranspiration demand (Segal et al., 2006).Today, microirrigation accounts for onlysome 1.5% of all irrigation systemsworldwide, but is increasingly importantin the more arid zones of developedcountries. In the USA such systemsincreased from 0.6% of the total in 1979to almost 4% in 1994 (Howell, 2001). Theworld area under microirrigation increasedalmost six- fold during the last 20 yearsfrom 1.1 Mha in 1986 to 6.1 Mha in 2006(Reinders, 2006).

Both issues of water resourceconservation and salinity management canbe approached by reduction. Since waterapplication in quantities greater than theplants’ actual needs is a function of salinity,


reduction of water application whenconditions are saline is impractical forproductive agriculture. Reduction thereforemust concern the salts in the irrigationwater. Use of lower salinity water allowsmore efficient use of water as a greaterpercentage of applied water direct plantconsumption and less to leaching salts.

Today’s policies of providing agriculturewith marginal water contaminated with saltsand nutrients are, in the end, highly non-sustainable. Better sustainability would befound by providing agriculture with thehighest qualities of water; promoting highestproductivity along with the lowestenvironmental consequences. It may wellbe a better strategy to desalinate waterprior to distribution and thus have wellcontained, concentrated salt waste and allowgreater irrigation efficiency, minimal fieldscale leaching, and minimal contaminationwith nutrients, soil contaminants (e.g.,selenium, boron) and various agrochemicalsthan to irrigate copiously to leach saltsand then find solutions for drainage water.

Plant Biodiversity and CropDevelopment

Introduction of sustainable crops in aridlands

Agriculture in arid zones does not dependonly on water saving and the use of moderntechnologies. Competition in markets forconventional grains and produce generallyfavors production in less environmentallystressful areas where energy and input costsare lower. Thus, one option for drylandagriculture is to expand its traditional rangeof crops to new grains, fruits, vegetables

and sources of fiber that offer specificadvantages over agriculture in other zones.

Agricultural biodiversity based onutilization and development of germplasmresources is a prerequisite to achievinglivelihood security – profitable andnutritional – for farmers in the drylands(Heslop-Harrison, 2002). A combination ofselecting elite cultivars, reducing inputs(fertilizers, pesticides and the mostimportant, water), cultivating extensive landarea and domesticating under-exploited andwild plant species, can promote thedevelopment high value crops which areintrinsically adapted to arid conditions.These include crops for high value nichemarkets like dates and vine-cacti and ascrops with pharmaceutical or cosmeticcharacteristics; like jojoba (Hodgson, 2002).But, how will plant breeders address theneeds of arid lands? Can the existing cropsmeet these needs? What is the contributionof the introduction of new crops? Can weimprove crops by selecting for droughtresistance and hardiness in nutrient-poorsoils?

Man’s first experimentation with plantand animal domestication, initiated byNeolithic man (around 10,000 years ago)during their transition from nomadic hunter-gatherers to life in agrarian societies,signaled the beginning of moderncivilization. Agriculture is believed to havemultiple origins (Diamond, 2002) but largelytook place in regions that at least todayare considered drylands. Domestication,however, implies the cognizant selectionof desired genetic traits and requires theavailability of a variety of genotypes fromwhich to select and suitable agro-technology

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to grow and manage crops. A subsequentconceptual revelation involved therecognition that seeds can be sown toproduce plants when and where desired.The steady trial and error experimentationin plant domestication gave rise to agrarianeconomies that significantly increasedman’s capability to provide food, thus setthe stage for unprecedented populationgrowth. The process of plant domesticationhas evolved to a multidisciplinary science,involving selection of food plants withspecific traits and development ofagro-techniques for their cultivation.Modern agriculture everywhere in thedrylands is strongly influenced by this ever-evolving process.

A negative outcome of plantdomestication, regardless of climaticconditions, is the loss of genetic diversitythrough population bottleneck (crash of thesize of a population), genetic drift (therandom process by which the allelicfrequency in the population changes overtime), and inbreeding (mating between closerelatives). Knowledge about the process ofplant domestication remains very limited;however, it is possible that strong selectionpressure exerted by humans on the wilddiversity changed plant species (Vavilov,1940). Darwin (1859) was the first torecognize the differences betweendomesticated plants created by artificialselection and breeding processes and theirwild ancestors which evolved throughnatural selection.

Domestication, however, implies thecognizant selection of desired genetic traitsand requires the availability of a varietyof genotypes from which to select along

with suitable agro-technologies to grow andmanage crops. Crops in their presentcommercial form bear little resemblanceto their original ancestors. Improved traitssuch as yield, shelf life, resistance to pestsor diseases and fruit quality are used byplant breeders to select the best availablecultivars. While plant breeders have mademajor achievements over the last 50 yearsin developing improved food crops, aprogressive narrowing of the genetic basehas occurred over the generations ofselection, raising concerns about long-termsustainability.

Like our ancient predecessors practicingagriculture, farmers living in arid lands askthe same crucial question: which plant speciesare the most suitable and offer the mostpotential for cultivation and food productionin any given locale? Of an estimated 250,000species of flowering plants existing today,only twelve species are cultivated providing75% of the world’s edible crop production.Sugar cane, maize, wheat and rice comprisethe four most important crops accountingfor half of all food consumed (www.fao.org,2002). A paramount challenge for agriculturalresearchers, therefore, is to introduce,domesticate and develop new crop candidatesby breeding species with high water-useefficiency and greater resistance to adverseconditions, especially drought and salinity.Each crop needs to be evaluated forsustainability and profitability in eachgrowing zone. The recently introduced newcrops developed for arid lands will not replacethe traditional crops needed for consumptionand trade. The newly developed crops havegreat potential, however, as high-value andlow-volume crops for specific niches wherehigh input traditional agriculture isimpractical or otherwise undesirable.


Plant breeding for technologies for drylands

Wild species reflect the rich naturalvariation and are highly heterozygous. Insome cases crossing crops with wildancestors — despite their traditional lowyields and poor nutritional quality – mayenhance crop performance (McCouch,2004). Frequently, inbred progenies derivedfrom these crosses have better performancesthan the better parent (Frey et al., 1975;Tanksley and McCouch, 1997), aphenomenon known as hybrid vigor. Forexample, rice yield was increasesignificantly up to 30%, following twointrogressions from a wild relative (Denget al., 2004). In tomato, introgressions ofthree segments from a wild relative resultedin 50% yield increase (Gur and Zamir,2004). However, cross incompatibilitybetween wild species and cultivated cropsoften generating sterile F1 hybrid, lowfertility of the resulting generations or lowrecombination between the genomes of thetwo species is the major factor that limitswild introgression breeding.

Complex traits, such as fruit size, yieldand stress resistance are influenced bymultiple genes, each segregating accordingto Mendel’s laws, and their expression ismodified by the environment (McCouch,2004). These quantitative trait loci (QTL)are used in plant breeding and can bedetected using molecular markers, orDNA-based markers. Genetic linkage mapsbased on molecular markers are beingdeveloped for a large number of species(http://probe.nalusda.gov). Studies insegregating populations are important forthe localization of genomic regions derivedfrom the wild parent that have the potential

to improve yield, e.g. for wheat (Huanget al., 2003), soybean (Concibido et al.,2003) chickpea (Singh and Ocampo, 1997),and others. The use of introgression lines(ILs) — sets of lines each carrying a singledefined chromosome segment from anexotic genome in an elite geneticbackground – simplified the analysis ofcomplex traits. In tomato, crosses betweenthe drought tolerant wild species Solanumpennellii and the elite inbred variety M82,ILs lines resulted in a population ofsegmental ILs (Eshed and Zamir, 1995).QTL mapping of these lines is based onthe nearly isogenic nature of these linesand any phenotypic difference between M82and an IL is associated with the S. pennelliigenome (Gur and Zamir, 2004).

Marked-assisted selection (MAS) allowsan efficient targeting of desired genes, suchas disease and pest resistance, which allowfor the improved yield of many crops. Inthe context of arid agriculture, identificationof the loci (QTLs) that affect droughttolerance will strongly improve breedingefficiency. MAS is already helping plantbreeders to improve valuable traits and anintensive effort is being made to generatethe necessary resources for mapping droughttolerance (Tuberosa and Salvi, 2006), whichwill generate novel opportunities to droughttolerance breeding programs in a widenumber of species. Moreover, theidentification of these genes will facilitatebetter understanding concerning the natureof drought tolerance and its pathways, suchas the genes involved in abscissic acid(ABA) production, or genes affected byABA itself.

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Grafting is the connection of two piecesof living plant tissue, the rootstock whichprovide the root system and the scion, whichprovide the reproductive part of the plant,so that they will grow as one plant. Thistechnique permits the propagation of elitecultivars and the use of rootstocks, whichare particularly able to withstand poorquality soils (compaction, poor drainage,low moisture, high salt levels) or to toleratepathogens. Grafting is an ancient way ofcloning plants, in particular fruit crops.

In Citrus, the salt-tolerant Cleopatramandarin (Citrus reshni Hort. Ex Tan.)is widely used as a rootstock. Cleopatra’ssalinity tolerance is credited to exclusionof chloride ions by the roots as they takeup water (Moya et al ., 2003). In vegetables,grafting is becoming popular as analternative way to improve stress tolerances.In tomato (Lycopersicon esculentum Mill.),the grafting process itself did not affectfruit yield under non-saline conditions.However, under saline conditions fruit yieldwas found to be significantly higher inplants grafted onto resistant rootstocks(Estan et al., 2005). This strategy, combiningdesirable shoot characteristics with desirableroot qualities, holds potential for improvingperformance of a wide number of cashcrop vegetables growing under aridagricultural conditions.

Despite the complex technologiesapplied to obtain the hybridization betweenelite varieties and wild relatives (as embryorescue, in vitro embryo culture, somatichybridization) worldwide public opinion isoften more accepting of these new varietiesthan genetically modified crops (GMC).For example, hybridization betweencultivated chickpea (Cicer arietinum) and

wild Cicer relatives result in abortion ofthe immature embryo due to post-zygoticbarriers. The successful development ofembryo rescue techniques is a first stepto wide hybridization that will allowchickpea breeders to transfer desirable traitsfrom wild relatives (Clarke et al., 2006).Unfortunately, despite decades of intensiveresearch in this field, we are still a longway from understanding and applyingtechnologies needed to successfully developcommercial forms of drought tolerantvarieties and arid agriculture has not seena meaningful quantum leap in productivitydue to hybridization techniques.

Transgenic technology for the developmentof pest and salt-resistant crops

Transgenic technology today allows cropimprovement in ways that traditionalbreeding techniques could not. While avariety of ethical and ecological objectionsto transgenic plants have been widelyadvocated (Lacey, 2002), these protestationshave not stopped the steady expansion oftransgenic plant cultivation. Currently 22countries (11 developing countries) growgenetically modified crops (GMCs), with103 Mha planted (53% in USA). The majortransgenic crops are soybean (57%), maize(25%), cotton (13%) and canola (5%)(http://www.isaaa.org).

The majority of modifications have notinvolved the key characteristics requiredfor successful cultivation in arid lands: saltand drought resistance. Rather, herbicidetolerance has been incorporated in majortransgenic crops such as soybean, maize,canola, cotton and alfalfa accounting forsome 68% of the global GMCs. Insect


resistant transgenic crops account for ca.19% of the global GMC’s.

This may have important long-termimplications for the sustainability ofagriculture in the drylands. Despite thegrowth of regulation and the generalcommitment to reducing biocides inagriculture, since the 1960s after thepublication of Silent Spring, sales continuedapace, doubling roughly every ten years.During the past fifty years the number of"active ingredients" of pesticides climbedfrom a few dozen to close to one thousand(NRDC, 1999). Global sales of biocidesby 2000 had reached 30 billion dollarsa year. Although the rate of growth droppedprecipitously during the 1990s, one recentstudy projected expanded demand as anunexpected result of global warming.

As would be expected, developingdryland nations are relatively modestconsumers of pesticides for obviouseconomic reasons. African consumerscomprise less than 6% of the globalagricultural chemical market. But often lessexpensive, more persistent chemicals aresold in these countries where regulationmay be non-existent. It can be expectedthat as countries move up the economicladder, pesticide usage will increase. Forexample, China in 2004 ranked fifty inglobal pesticide usage, but showed a growthrate of 7 to 9% a year – higher eventhan its explosive increase in GNP (NRDC,2005) Hence, pest resistant crops may beable to reverse these trends and keeppesticides of all forms to a minimum inarid agricultural regions.

Beyond the potential contribution tobiocide reduction, what is the expected

impact of GMC research for agriculturein arid lands? The progress that has beenmade in understanding the mechanismsinvolved in drought and salinity toleranceare significant (Huang et al., 2006; Naranjoet al., 2006; Leshem et al., 2006). However,the fact that the challenge involves complex-polygene traits makes the future of GMCresistance to salinity obscure and uncertain.It is surely conceivable that salt toleranttransgenic crops that increase yields in thedrylands will be developed. But the newbreeds, like traditional crops discussedpreviously, can only be sustainable if theyare irrigated with better quality water, sincewater with high salinity irrigation willultimately lead to excessive soil salinizationand lands that will not support even themost robust strains. Assuming an ongoinginvestment in research and developmentin the field, many obstacles that presentlyexist can be overcome, but it is estimatedthat meaningful commercial progress willtake many years.

Introduction of improved new cultivars andplant species as new crops in aridagriculture: Successful examples

To better understand the potential andthe limitations of crop breeding’scontribution to a sustainable agriculture inarid lands, it is well to consider severalexamples of new crop introductions fromrecent years. In particular we will considerthe experience associated with Cicerarietinum L. (chickpea), Cacti species,Simmondsia chinensis (jojoba); and Ziziphusspecies.

Cicer arietinum L. (chickpea): The genusCicer L. comprises of 43 annual andperennial species, 42 wild and one

14 BEN-GAL et al.

cultivated, the chickpea (Cicer arietinumL.). Chickpea has a deep and wide rootsystem, giving it good drought tolerance.It’s a self-pollinated and annual cool seasongrain legume crop grown under rainfallconditions in arid and semi-arid zones ofIndia and Middle Eastern countries, withvery high nutritive value and growingconsumer demands. India produces 66%of the world chickpea production andconsumes all its production domestically.Australia (22%) and Turkey (20%) are themost important exporters to internationalmarkets (FAOStat 5/2006).

Chickpea is affected by a large numberof diseases, the most destructive of whichare fusarium wilt (Fusarium oxysporum)and aschochyta blight (Aschochyta rabiei)(Kameswara Rao et al., 2003). Theutilization of the wild genepool for breedingand improved resistance to diseases ischallenging and difficult (Kameswara Raoet al., 2003). To date, eight annual speciesthat share the same chromosomal numberas the chickpea have been used inintrogression program (Croser et al., 2003).Due to its long-day requirements, mostMediterranean chickpea stocks are relativelylate to flower (Kumar and Abbo, 2001).Incorporation of early flowering alleles intoMediterranean cultivars might assist inreduced crop duration and avoid damageby biotic and abiotic stresses. The relativelysimple inheritance of flowering time opensup new possibilities for breeding highyielding and stable chickpea cultivars forthe semi-arid and arid regions globally(Kumar and Abbo, 2001). Moreover, theleaves typical of most wild Cicer andchickpea cultivars are compound. Leafshape mutations to a simple leaf could

possibly reduce transpiration demand.Genetic solutions that promise improvedcultivation through new breeding linescombine early flowering, changing plantarchitecture (by leaf shape mutations), andAscochyta tolerance suitable for short rainyseasons in semi-arid regions (up to 400mm rainfall) (Bonfil et al., 2006). Traditionalbreeding in chickpea is a good exampleof crop improvement aimed to assistsustainable agriculture under extremeenvironmental conditions.

Cacti species: Cacti are native to Northand South America and the West Indies(Gibson and Noble, 1986). Cacti specieswere introduced to Spain at the end ofthe 15th century and from there spreadthroughout the entire world. They appearin extreme habitats, hot deserts (up to 55ºC),as well as in cool areas with freezingtemperatures and in tropical rain forests.Cacti can grow in poor and marginal soils(Nobel, 1988). These species have a rangeof specific adaptations that make thempromising crops for introduction in aridlands: i.e., spines instead of leaves, succulentshoots, and the crassulacean acidmetabolism (CAM) pathway for CO2fixation. Transpiration and photosynthesistake place during the night while duringthe day the stomata are closed. Thesemechanisms result in higher water useefficiency (Nobel, 1988; 1994). Today, cactiare cultivated as industrial, ornamental,vegetable and fruit crops (Mizrahi et al.,1997).

The best-known cactus fruit crop is theshrub Opuntia ficus-indica, known as cactuspear or prickly pear, also called tuna inLatin America, ficodindia (fig of India)


in Italy, tzabbar in Israel and sabar in Arabcountries. The problems that historicallyhave limited the cultivation of this speciesare its spiny peel, big and hard seeds, andthe short annual period of production(Mizrahi et al., 1997). Out-of-season fruitingcan be induced in sandy soils by nitrogenfertilization (120 kg ha-1) and by removalof flower buds and young cladodes (stems)(Nerd et al., 1991 (B); Nerd and Mizrahi,1994). In Israel’s Arava Valley with 30mm annual rainfall, extreme hightemperatures (up to 47º) and 3500 mmannual pan evaporation, mango is irrigatedwith 2400 mm water per year while pricklypear is irrigated just 400 mm (Mizrahi etal., 1997). The absolute minimum waterrequirement for prickly pear cultivation is200 mm, also an important factor sinceall the cacti are very sensitive to prolongedlack of oxygen in the root zone (Le Houerou,1996). Laboratory and field observationsdemonstrated that O. ficus-indica is sensitiveto salinity as well (Nerd et al., 1991 (A)).

People familiar with this crop consumeand pay high prices for its fruits (Mizrahiet al., 1997). However, a major challengelies in introducing seedless and salineresistant cultivars using breeding effortsrelying on only a few genotypes that exhibitsuch traits. Appropriate research leadingto such modifications should facilitategreater acceptance by new consumers andpotential for farmers in arid zones not yetfamiliar with this crop.

Vine cacti (Hylocereus and Selenicereusgenera) are an interesting group of plantsbearing attractive and exotic fruits. Theseepiphytic species are native to tropicalregions of northern South America, Central

America and Mexico. Flowers are nocturnaland remain open only for a few hourseach day (Nerd et al., 1997). The fruitsare known in Latin America as pitahayaor pitayas, and are juicy, sweet and haveblack small crispy seeds with either aspineless peel (Hylocereus species) or aspiny one (Selenicereus). In the latter case,the spines are large and easily removedupon ripening.

Currently, worldwide interest in vinecacti species is increasing. Some twentycountries, including the United States,cultivate various vine cacti species (Nobeland de la Barrera 2004). In Israel, sincethe 1980s, an intensive program has beenundertaken with the objective of introducingthese species as new exotic fruit crops (Nerdet al., 2002). At first, information aboutthese species was extremely limited andtherefore the initial introduction programwas designed to ensure the developmentof agricultural techniques for profitablecultivation and a breeding programaccompanied by cytological and molecularstudies (Mizrahi and Nerd, 1999).

Early commercial cacti developmentstudies revealed that the species are sensitiveto high irradiation and low temperatures(less than 3°C). Consequently, in Israelthe vine cacti are cultivated under shade-netsor in greenhouses and protected againstcold (Raveh et al., 1993). Due to the lackof natural pollinators (nocturnal animals)and the self-incompatibility of severalgenotypes, manual pollination is routinelyperformed (Weiss et al., 1994; Nerd andMizrahi, 1997). In addition, a long-termpollen storage protocol was developed inorder to insure a constant supply of

16 BEN-GAL et al.

compatible pollen and to guarantee highyields (Metz et al., 2000). Fruit growth,ripening process and optimum harvestingtime were studied for each species (Nerdet al., 1999).

The vine-cacti genotypes introducedto Israel came from the wild and the Israelibreeding program performed at Ben GurionUniversity has focused on improving fruittraits. Successful reciprocal interploidycrosses were performed between diploidHylocereus species and the tetraploid S.megalanthus (Lichtenzveig et al., 2000;Tel-Zur et al., 2004). The fruits of thetriploid hybrids combine the taste qualityof S. megalanthus and the attractiveappearance of H. polyrhizus (Tel-Zur etal., 2004). Moreover, some of the newvine-cacti hybrids show classical "hybridvigor", i.e. heterosis. This is evident fromtheir growth and development under extremedesert conditions, including hightemperatures, low relative humidity and longdrought periods. The successful introductionreflects a combination of hybridity (i.e.,the fusion of parental genomes and suchresulting phenomena as enzymemultiplicity) and genome doubling, whichitself can result in epigenetic or epistaticeffects. The triploid hybrids are fertile, witha relative high per cent of viable seeds.The number of seeds per fruit is stronglydependent on the pollen donor (Tel-Zuret al., 2005). Currently, the breedingprogram is comprised of F2 and firstbackcrosses (BC1) hybrids, which havestarted to flower and show promisingpreliminary results (Tel-Zur, unpublisheddata).

Simmondsia chinensis (jojoba):Simmondsia chinensis (jojoba) is a perennial

dioeciously evergreen shrub endemic to theSonora desert (California, Arizona andMexico). The jojoba is naturally adaptedto extreme high and low temperatures anddry climates. The annual water requirementfor an adult jojoba plantation was foundto be between 500 and 600 mm (Benzioniand Nerd, 1985). Jojoba seeds contain40-60% liquid wax with a high meltingpoint, similar in nature to sperm-whale oil(Yermanos and Ducan, 1976). In the past,Native Americans used jojoba wax forcooking, hair care, and for many therapeutictreatments. Today the wax and its derivativeshave a wide range of potential uses inpolish, cosmetics, pharmaceuticals,lubricants, gear additives, and anti-foamingindustries (US National Research Council,1985; Wisniak, 1987). Attempts to cultivatejojoba began in the late 1960s (Benzioni,1995). Large plantations of jojoba havesince been planted in USA, Mexico, Brazil,Australia, Sudan and Israel (Nimir andAli-Dinar, 1991). In Israel, the introductionof jojoba as a new crop was made possiblethrough field trials designed to optimizehorticultural practices, and via a breedingprogram to maximize yield and otherdesirable traits, such as seed wax content(Benzioni, 1995). The majority of femalejojoba plants bear only one flower budon every second node. However, superiorclones with high female density (whoseinflorescences consist of about 3-10 flowerinstead the usual single female flower)having high yield potential, have beenidentified and selected for development(Benzioni et al., 1999).

Jojoba clones also differ in their chillingdemands (Ferriere et al., 1989; Benzioniet al., 1992). They have a wide variation


in their resistance to environmentalconditions at the time of pollination,affecting fruit set as well as diversity intheir flowering patterns, wax content andcomposition and seed dry weight (Benzioniet al., 1999). Yields collected in selectedgenotypes ranged between 1.53 to 3.35 kgdw plant-1 in 6-year-old plants (Benzioniet al., 1999), illustrating the range of geneticvariability among genotypes. Jojoba grownin the southern, arid regions of Israel ismechanically harvested and watered by dripirrigation. The jojoba wax produced in Israelis exported, mainly for the cosmeticindustry. In 2000, 130.3 tons were exportedat US $10 per kg (http://ienica.csl.gov.uk/reports/israel.pdf). Due to the optimizedhorticultural technologies and the eliteclones selected, jojoba cultivation in Israelis largely considered successful andprofitable.

Ziziphus species: Z. mauritiana is animportant fruit crop in India, Z. jujube isalso indigenous in China, and Z.spina-christi is endemic to the Middle East.Similar to vine cacti, Ziziphus species canserve as a model for development,exemplifying the approach required forproducing new arid zone crops, based onhigh market value with intrinsic adaptationto high stress conditions. Ziziphus fruitsare consumed fresh or dried, and the treesare also used for soil conservation, livestockfodder, hardwood, fuel, high qualitycharcoal, and hedges. Leaves are employedin many traditional medicines. Furthermore,the fruits have a higher content of calcium,phosphorus, iron, Vitamin A and C thanapples and citrus, and they are rich inphenols, compounds with high antioxidant

activity (Jawanda and Bal, 1978; Machuwetiet al., 2005).

Z. mauritiana (Ber) represents anunexploited fruit crop in the Middle East,especially in Israel, with long-term highcommercial potential due to a very lowinput, and a high output. Ber was shownto be well adapted to drought conditions(150-200 mm annual rainfall), saline water(3.5 dS m-1) and soil, and extremetemperatures (-6 to 45ºC in the arid regionsof The Negev Highlands and The SouthernDead Sea in Israel). Chovatia et al. (1993)reported that under arid conditions in India,Ber cultivars yielded an average of 4-18t ha-1 annually and exhibited significantdifferences in fruit weights, ranging from4.6-30.9 g. In Israel, productivity at anexperimental orchard at Neot Hakikar, justsouth of the Dead Sea for a mixture ofsix cultivars averaged 35-40 t ha-1 annually.Fruit weights ranged from 30-50 g (E. Zeiri,personal communication). This orchard wasirrigated with 7,000 m3 ha-1 annually withsaline water. By way of comparison, dates,the most important fruit crop in the aridregions of the Middle East, require annually25,000 m3 ha-1 annually and yield 15-20t ha-1. Indeed, under the prevailing extremeclimatic and edaphic conditions, the treesplanted and grown at Neot Hakikar for12 years did not show any phenotypicsymptoms of stress, which emphasizes theirincredible tolerance of extreme growthconditions. Ber has great potential as anew fruit crop in arid regions, however,more research is needed to improve theknowledge and technology for itsproduction. In Israel, research and selectionof improved genotypes is still in its earlystages (N. Tel-Zur, unpublished data), while

18 BEN-GAL et al.

the traits for selection are fruit size, lowaroma (unpleasant for unfamiliarconsumers) and yield. Additional researchshould accelerate the rate of introductionand commercialization of this species toregional and international marketplace.

Economic Sustainability

Towards cost-effectiveness for aridagriculture

Just as sustainability requires thatfarming practices not be ecologically andhydrologically destructive, agriculture willnot be sustainable if it loses money. Fromthe perspective of economic strategy,farmers in arid lands can take advantageof the warm, protracted, growing seasonsand new salt-resistant strains to attain acompetitive advantage over other regions’agriculture. Several exotic fruit species thatthrive in the drylands are bringing excellentprices in world markets. Recent pricesthroughout Europe for the vine-cacti fruit,for example often exceed seven euros kg-1,a particularly high return for farmers inIsrael who are now producing upward of25 t ha-1 of the fruit with minimal waterdemands (25 to 80 m3 t-1) (Mizrahi, 2007).

But, for the most part, arid agricultureis in an economically disadvantagedposition. In addition to the problem of waterscarcity, water quality is a factor inundermining the competitiveness of aridagriculture. Salinity and other minerals inthe water and soil limit the range of cropoptions and reduce yields. Internationalmarkets ultimately drive the economicviability of crops, and they often pushfarmers to make decisions that makeeconomic sense in the short-term, but are

unsustainable in the long-run, due todegradation of water and soil resources.

It is not just myopia, but lack of capitalthat can contribute to inappropriate cropselection and irrigation systems. Forexample, the massive cotton plantations,with their long-growing seasons andprodigious water needs established aroundthe Aral Sea region combined withconventional irrigation practices andinappropriate drainage to emerge as a majorfactor in exacerbating salinization andcontributing to the newly-created aridwasteland. It has been argued thatreasonably simple changes, such as a shiftto wheat and maize along with improvedirrigation and drainage systems would bothbe able to reverse present trends andultimately prove to be cost-effective (Cai,2001). This sort of transformation towardssustainability is not, however, without costs.To cover the annualized investment of 299million dollars, the authors recommendeda salt tax to be paid by farmers.

The economic capability of farmers toinvest in appropriate technologies is a criticalfactor to consider in crafting a strategyfor sustainable agriculture. One of the keyarguments raised by advocates against thedissemination of genetically modified cropsin developing countries has nothing to dowith ecology, but rather involves economicand social concerns. Subsistence and evenmodestly successful small farmers may notbe able to afford the new generation ofseeds developed at some expense by multi-national corporations. As the new seedsincreasingly become an essential economiccommodity, indigent farmers are squeezedout of the market, and replaced by agri-business operations (Shiva, 2001).


In some circumstances, the problem isnot lack of capital but excessive, recklesslyrendered capital invested in waterinfrastructure that can exacerbate problemsassociated with arid agriculture. Givenagriculture’s role in national cultures andconcerns for food security, promotion ofagriculture in the desert frequently defieseconomic logic. Since it began constructionin 1991 Libya has spent roughly 30 billiondollars to transport 600,000 acre feet ofmillion-year old fossil water 1000 km acrossthe desert to irrigate fields on arid landsnear the Mediterranean coast (Pearce, 2006).Colonial Kadaffi’s “man-made river” isonly the most extreme of numerousexamples of water transport projects thatwill never past muster with any cost-benefitanalysis. During the 1950s, some 80% ofall Israeli budgeting for infrastructure wentfor a National Water Carrier that todaybrings relatively saline water from the Seaof Galilee to the drylands in the south(Galnoor, 1980).

With such prodigious subsidies, it islittle wonder that farmers in some aridlands can be prosperous despite their owneconomically dubious practices. Yet, in thelong run, if agriculture is to remainsustainable and to compete in internationaland domestic markets, arid farming willrequire pragmatic “ cost-effective” decisionrules. This is especially true in developingcountries where the local economies donot have the ability to subsidize anagriculture sector. A full accounting of thecosts, including both negative and positiveexternalities, is important when consideringa sustainable agricultural strategy for a givenregion.

The economics of irrigation

While many types of crops can flourishunassisted in rainy climates, agriculture inthe drylands typically requires extensiveinvestment in irrigation infrastructure aswell as ongoing outlays for maintenanceand energy. For example, in the arid regionsof Syria, the relative portion of irrigationin overall production costs reached 52-60%for cotton, 34-51% for wheat, 35% forfava beans, and 20% for vegetables (Gület al., 2005). These involved inefficientfurrow systems, so that the predominantcomponent of irrigation costs only involvedthe fuels for water pumps, rather than pipesor drip systems. The high percentage ofirrigation expenses are to some extent afunction of the low-value crops. In dryregions of Spain, however, Garrido et al.(2006) reported that water extraction costsconstitute only a tiny fraction of localproduce.

Frequently, domestic irrigation policiesfollow their own, arcane, logic. SaudiArabian wheat production, literally fueledby the government’s energy glut, is anextreme case in point. The 141,732 tonsproduced there in 1980 grew ten-fold to1,800,000 tons by the year 2000, due toan increase of 600,000 to 1,620,000 haof irrigated lands (FAO, 2007). But it isthe most expensive wheat in the world.Most dryland nations lack the oil reservesand capital to subsidize field crops. Theaforementioned analysis in Syria, forexample also showed that as fuel pricesrose (or as the 80% subsidies on fuelswere removed) cotton and wheat quicklybecame losing propositions for localfarmers.

20 BEN-GAL et al.

Rainwater harvesting in the drylands,offers a relatively ancient and low-capitalwater management technique in deserts.Harvesting has been proven to be acost-effective source of agricultural waterin a variety of contexts. A recent studyin Turkmenistan, evaluated the costs andbenefits of “takyrs” -- the traditional slightlysloping dense clay surfaces which act asnatural catchment areas. Some 250-350million m3 of water are collected each yearin a variety of traditional reservoirs, evenas today much of the water is unutilized.In assessing their feasibility, researchersmonetized the reservoirs’ construction,maintenance and operational expenses(Fleskens et al., 2007). Benefits wereprimarily based on increased fodderproduction. With an average life expectancyof the facilities set at 30 years, the beneficialvalues of the system far exceeded the costsof producing alternative water sources forthese drylands. This cost-benefit ratioincreased dramatically when wheatcultivation replaced reserve fodder cropsin the irrigated zone (Gintzburger et al.,2005).

In Israel, a rain-harvesting and effluentdistribution reservoir system has beenestablished during the past decade involvinga system of over 190 reservoirs, almostall for arid and semi-arid agriculturalirrigation. The initiative has increased thenational supply of water, but the costs ofreservoirs are relatively high, withconstruction of a typical reservoir(producing 0.5 to 2 million m3 of waterevery year) costing from one to five milliondollars. No economic evaluation of theinitiative has yet been undertaken, butclearly the cost-benefit ratio will be

dependent on the life expectancy of thereservoirs which is unknown and of courseon the discount rate selected (Tal et al.,2005).

Drip irrigation offers the mostenvironmentally sustainable irrigationstrategy. When considering the agronomicadvantages of drip irrigation systems, itis initially difficult to understand why lessthan 2% of irrigated lands world-wide haveadopted them. The answer, of course iseconomic. The initial outlays for a dripirrigation system have not increasedmeaningfully during the past decade,ranging from $2,000 to $3,000 ha-1 fororchards in arid and semi-arid regions. Thisprice includes the entire irrigation system,including pumps and computer systems.With a ten-year life expectancy, theinvestment is easily returned, especially forhigh value-added fruit and vegetable crops(Netafim, 2007; Postel, 1997). Yet, farmers,particularly in developing drylands,frequently do not have the resources tomake such a substantial capital investment,even if it will improve their long-termcompetitiveness. This is also true inwealthier nations. For example, when dripand furrow irrigation were compared inarid areas of Wyoming for the raising ofsugarbeets, the returns were $2310 versus$2080, respectively. The larger the areaconverted to drip irrigation, the shorter the“payback time” but at best, drip systemcosts were covered after a period of sevenyears (Sharmasarkar, 2001).

If an analysis is only based on a modesttime-horizon, economic assessment will notnecessarily produce the environmentallyoptimal solution. As interest rates rise,


sustainable irrigation practices may notalways beat conventional irrigation methodswhen the sole criterion for comparisoninvolves short-term increased yields. Butwhen the environmental advantagesproduced by efficient irrigation, and theassociated savings incurred by preventingproduction losses are integrated into thecalculations, it makes for a far morecompelling equation. One recent analysisof water logging in the India Tungabhadraproject, for example revealed that the lostproduction value caused by soil degradationfrom inappropriate irrigation was at least14.5% of the system’s productive potential,and that the sub-optimal distribution losseswere almost three times more (Janmaat,2004).

Water logging is among theenvironmental woes that economists arequick to attribute to inappropriate waterpricing, or what is deemed as aneconomically irrational policy (Wichelns,1999). Ironically, it is often water subsidieswhich push farmers to retain inefficientand environmentally destructive irrigationpractices (Hellegers, 2006). InvestorRichard Sandor’s often quoted adagecharacterizes the dynamic well: “Whennature is free, it becomes an ‘all you caneat buffet.’ And I don’t know anyone whodoesn’t overeat at an all you can eat buffet”(Daily, 2002). When farmers in arid landsface the real costs of water, the economiccommon sense of efficient irrigation systemsbecomes irresistible. Israeli farmers, afterbeing confronted with higher and lesssubsidized water prices, expeditiouslyconverted their operations to drip irrigationsystems without any command and controlprescriptions (Tal, 2006).

The costs of alternative sources of waterfor desert agriculture

Kuwait was among the pioneers indesalination technology, with much of thesteady growth in demand for water by localmunicipal and agricultural needs met byfive major desalination plants that utilizea multi-stage flash distillation process(Hamoda, 2001). The extremely high energyrequirements made the cost of waterproduction for agriculture in most othernations prohibitively expensive. Twodecades after the Kuwaiti venture intodesalination, the precipitous drop in pricefor desalinized water already has begunto change the economic calculus for aridagriculture in Israel. Israel’s new reverseosmosis desalinization facilities, opened inJanuary 2006 can produce a cubic meterof water (1000 liters) for 52 cents (Tal,2006). During its first year of operation,much of its waters were actually consumed(at subsidized rates) by Israeli agriculturaloperations. While the very low salinity ofthe water was welcomed by local farmers,the very low levels of calcium and completeabsence of magnesium in this ideal drinkingwater can actually cause damage to manycrops (Yermiyahu, 2007). A recent surveyamong Israeli farmers reports that only athird believed that water at the newdesalinized price was reasonable for aprofit-making farm and relatively fewreported a willingness to cultivate additionalhigh value-added crops if they could beguaranteed high quality desalinized waterat that price (Rassas, 2007). But desalinizedbrackish water can now be produced at30 cents per m3 which is very close tomarket rates.

22 BEN-GAL et al.

Wastewater reuse offers anotherpromising source of water for desertagriculture. Like the rest of the world,urbanization in the drylands continues apaceand the reuse of effluents by farmerscontributes to solving a potentiallyproblematic environmental problem. InKuwait, economic analysis suggests thatthe additional treatment required to bringeffluents to a level acceptable for reuseby agriculture would only increase theoverall costs of existing sewage treatmentby 30% (Hamoda, 2001). If, however,wastewater reuse is part of a water supplypolicy for arid agriculture, there is alwaysthe risk that the treated sewage will beused regardless of whether it meets adequatetreatment standards. This has often beenthe case in India (Prinz, 2000) withpredictable implications for public healthand long-term hydrological contamination.

Israel presently recycles 72% of itssewage, the vast majority of which providesirrigation for arid farms (Tal, 2006). Yet,present treatment level standards, based onnon-arid European treatment criteria havebeen ruled inadequate. In arid regions, formost of the year, there is inadequate flowin streams to dilute effluents (Inbar, 2002).Accordingly, the government recentlyapproved the phase-in of a much tougherset of treatment standards that essentiallyrequire tertiary treatment. A cost-benefitanalysis conducted by consultants for thegovernment showed that while the upgradein sewage treatment levels would cost 230million dollars, it was an investment witha high benefit/cost ratio, producing anaverage benefit at least three times thecost per cubic meter of upgraded treatedwastewater. The additional expense

associated with the upgrade per cubic meterwas estimated at 10-15¢/m, while theaverage benefit ranged from 40-55¢/m(Lavee, 2003). Benefits were calculatedbased on the ability of farmers to expandthe range of profitable crops beyond thosewhich are approved for irrigation withsecondarily-treated wastewater. Additionalbenefits to farmers included those associatedwith the reduction in wear and tear onirrigation equipment and the reducednitrogen in the water.

A review by Lawhon and Schwartz(2006), as well as an economic analysisdone on behalf of the farm lobby (Rosenthal,2005) found that the benefits expected fromwastewater recycling following tertiarytreatment were highly overstated due tothe assumption that farmers currently usingwastewater would be able to upgrade tohigh-value crops. This assumption wasargued to be flawed due to the additionalinvestments and knowledge necessary tosubstitute crops. Additionally, neithereconomic analysis attempted to quantifythe benefit to the environment as a resultof cleaner wastewater, the main motivationfor the higher standard in the first place.Despite the debate over the economicconsequences of the upgrade, the Israeligovernment eventually approved the newstandard, which will be implementedgradually in order to give farmers and localauthorities’ time to adjust to the costs ofimproved sewage treatment.

The economic equation justifyingsustainable agriculture ultimately should beinformed by the truism that it is invariablymore cost-effective to prevent theagricultural damage associated with


unsustainable farming then to try to remedycontamination after the fact. There areexceptions. For example, the drainageassociated with remediating water loggingin India produced an intensification of landuse on formerly fallow lands, a shift toremunerative crops and increased cropyields that made restoration effortscost-effective (Datta et al., 2000). But othercases show a far less sanguine economicpicture. While the vast majority ofAustralian farmers have begun to adapttheir practices to the pervasive salinizationof their soils, less than half believe thatthe investment has produced any benefitat all (Kington and Pannel, 2001).

Given market conditions, preventativepractices may not be perceived as profitablewithout government intervention to ensurethat externalities of salinizing practices areinternalized by local farmers. Pannel (2001)reported that such a measure, the conversionof annual crops to perennial trees inAustralia, is typically not sufficientlyprofitable, especially when interest ratesare high. The off-site benefits, to thenon-agricultural sector of such conversions,of course change the equation completely.This is one of the critical areas that decisionmakers should consider when formulatingpublic policy about dryland agriculture. Ithas long been recognized that the full benefitof agricultural production involving“positive externalities” to the non-farmingsectors (the tourism dividend from sceniccountry sides, the water quality benefits,etc.) are often higher than the market valueof the crops themselves (Fleisher and Tsur,2000). Yet, rarely do decision makersinclude these benefits in their agriculturalcalculations. In any event, the Australian

experience suggests that along withprevention efforts, adaptation of saltresistant plants by farmers will ultimatelybe ineluctable -- if farmers can afford them(Pannel, 2001).

Towards the Future

The most important challenge for afarmer in the drylands involves selectingthe crop that is most appropriate andprofitable for specific local conditions andan irrigation system that can maintainproductivity in the long-run. Economicconsiderations are unavoidable. Farmersmust choose crops that are able to returnthe costs of the associated inputs: water,irrigation infrastructure, energy and labor.These expenses can be especially high inarid lands.

These decisions are increasinglycomplex, not only because of the advancesin agricultural technologies, but due to therapidly evolving environmental reality.There is little doubt that global warmingposes a new challenge for agriculturalresearchers focusing on the desert. Recently,the US Department of Agriculture estimateda 32-ton drop in global wheat harvests– roughly half of the entire US wheat harvest.The precipitous decline is attributed to hightemperatures (Brown, 2005). Scientists willhave to scramble to produce crops for aridlands that can adapt to such changingclimatic conditions.

The associated energy situation and risein fossil fuels prices has already begunto affect the dynamics of arid agriculture.Among the crops that may be consideredby dryland nations in their agriculturalproduction scheme are those grains fromwhich fuels can be produced. Given the

24 BEN-GAL et al.

inherent limitations on production in thedeserts, this appears to be a less than optimalimpulse. Put more specifically, theproduction of ethanol from corn shouldnot be part of a long-term agriculturalstrategy for the drylands. As agriculturalpundit Lester Brown points out, the grainrequired to fill a 25-gallon SUV gas tankwith ethanol, for instance, could feed oneperson for a year (Brown, 2006). Recentdemonstrations over the four-fold rise inthe price of tortillas in Mexico are amongthe first symptoms of these changingdynamics.

Agriculture in arid lands will succeedwhen it best exploits the desert’s naturaladvantages. These include long hours ofsunshine, long and multiple growing seasonsand in some case the low number of pestsand diseases. Innovation in agronomictreatments such as drip irrigation,fertigation, and high level of mechanizationare likely to build on these relativeadvantages or at least even the playingfield, creating competitive conditions forfarmers in arid lands. Because of the constantneed for innovation, one of the keys tosustainable and successful agriculture inarid lands lies in a close and constantcooperation between researchers andfarmers. High yields and excellent cropquality can be achieved in arid areas butthey require ongoing monitoring andscientific research.

For example, the role of new crops inincreasing farmers profit has frequently beendemonstrated. Totally new products, suchas exotic fruits and vegetables, create anew niche for farmers in the drylands.Though technical and scientific difficultieshave limited the introduction and

domestication of many “underexploited”species, detailed studies that bringcomprehensive research and analysis abouteach species in a variety of climatic andgeographical locations should beundertaken. This will require expandedresearch funding in these substantive areas.

Ultimately, the history of agriculture indesert lands has not been a happy one.Many of the seemingly prosperousagricultural civilizations disappearedunceremoniously due to unsustainablepractices. During the twentieth century,agricultural communities in arid regionscollapsed due to environmental blunders.Today’s improved technology and scientificunderstanding about the ecological andhydrological conditions in arid lands offerthe hope of lasting prosperity for agriculturaloperations in the drylands. Yet, to besustainable, farmers will need to be ableto invest in appropriate water managementtechnologies and remain nimble and cleverin their introduction of optimal crop typesonto lands that are not naturally hospitable.While there is a strong basis for optimismin a review of the developments ofagriculture in arid lands, this must bebalanced with an equally powerful measureof humility and caution.

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The Sustainability of Arid Agriculture: Trends and Challenges · 2016-12-05 · The Sustainability of Arid Agriculture: Trends and Challenges Alon Ben-Gal1, Alon Tal2, Noemi Tel-Zur2