Cropping Pattern Modifications Change Water Resource Demands in the Beijing Metropolitan Area

Available online at www.sciencedirect.comJournal of Integrative Agriculture. ScienceDirect2012, 1(1); 1914-1923November 2012RESEARCH ARTICLECropping Pattern Modifications Change Water Resource Demands in theBeiing Metropolitan AreaHUANG Jing.2, Bradley G Ridoutt, XU Chang -chun, ZHANG Hai-lin! and CHEN Ful1 College of Agriculture and Biotechnology, China Agricultural University, Bejing 100193, P.R.China2 Commonwealth Scientific and Industrial Research Organisation (CSIRO), Sustainable Agriculture Flagship, Victoria 3169, AustraliaAbstractAdequate freshwater supply has become an issue of increasing local and international concern. Reducing water use inagriculture, which is the largest water using sector of the economy, is both important and urgent. The aim of this paperwas to quantify how recent cropping pattern changes have influenced water resources in the great Beijing metropolitanarea, an expanding megacity which also includes rural counties. Crop production affects blue water use through waterconsumption and water pollution, the latter assessed here using a critical dilution method. From 1990 to 2010, the totalblue water used by crop production declined due to a decrease in overall cropped area, initially in response to localgovernment policies favouring urban development. However, the average blue water use per hectare increased from 2 112m3 ha-l yrI in 1990 to 2764 m3 ha-l yr- in 2003, largely as the result of a transition from cereal to vegetable crops, and inparticular an increase in intensively managed plastic and glass covered vegetable production systems. Current policiesaim to conserve agriculural land, in the interests of food security, and to stimulate cereal production systems with higherecosystem services provision. As such, in 2010 the average blue water use was 2 425 m3 ha:l yrl. These results demonstratethat cropping pattern changes in peri urban regions and rural communities surrounding the Beijing metopolitan area canhave a substantial impact on water resources. They also highlight the tradeoffs between food production and urban andindustrial water supply and the need for integrated policy development.Key words: blue water use, water consumption, water pollution, cropping patterm adjustment, peri-urban food productionglobal food security and environmental sustainabilityINTRODUCTION(Vorosmarty et al. 2000; Liu and Savenije 2008;Dominguez-Faus et al. 2009; Qiu et al. 2012). TheFreshwater is a precious resource, essential to humanscale of the problem is such that there is now wide-health and wellbeing as well as the natural environmentspread awareness of the need to urgently reduce the(Koehler 2008). Human activities consume and polluteimpacts of human production systems and consump-large quantities of water and the competition for scarcetion patterns on freshwater resources (Ridoutt andwater resources has become acute in many placesPfister 2010a, b). Since agriculture is, by far, the larg-(UNESCO 2006). Water shortages are being intensi-est water-using sector of the economy (Gleick 2003),fied by population growth, climate change, diet shifts,it must be considered an important part of the solution.and bio-fuel crop expansion, leading to concerns aboutA distinction can be made between consumptive wa-中国煤化工Received 9 May, 2012 Accepted 24 July, 2012MHCNMHGCorrespondence CHEN Fu, Tel: +86-10-62733316, E-mail: chenfiu@cau.cdu.cn◎2012, CAAS Alrights reserved Pubishedby EseverLud.Cropping Pattern Modifications Change Water Resource Demands in the Beijing Metropolitan Area1915ter use, referring to water that is withdrawn from butand Shock 2012). Practices such as installing water-not returned to the local hydrological systemsaving irrigation equipment (e.g., drip and sprinkler ir-(Falkenmark and Lannerstad 2005), and degradativerigation equipment), rainwater harvesting, imigation withwater use, referring to the discharge of emissions torecycled water, and the optimization of fertilizationfreshwater which reduce its quality (Bayart et al. 2010).schedules are measures which have been recommendedTotal water use related to global crop production hasby government agronomists and scholars (Wang andbeen estimated at 7404 billion m3 annually, consistingWang 2005; Ju et al. 2009; Huang et al.2012). Changesof 78% green water (rainwater stored in the soil as soilin cropping patterns are also likely to impact the avail-moisture), 12% blue water (ground- or surface waterability of water resources due to the differences in cropin the form of irmigation) and 10% grey water (pollutantwater requirements (Fasakhodi et al. 2010). Differentdilution water) (Mekonnen and Hoekstra 2011). Thesecrops have different water use characteristics. Forresults highlight the dominance of green water in presentinstance, around 300 m3 of water produces one ton ofcrop production. However, it is blue water consump-vegetables while cereals need about 1 600 m3 of watertion and dilution water use by agriculture which usually(Mekonnen and Hoekstra 2011). This means that theimpact most directly on the availability and quality ofcategories and quantities of crops planted in a regionwater for other parts of the economy and the environ-could influence the total amount of water use for cropment and is therefore the issue of broader concern inproduction. The implication is that regional croppingwater resources management (Seckler et al. 1998;pattern adjustment offers the potential to relieve pres-Shiklomanov 2000; Menzel and Matovelle 2010; Ridouttsure on local water resources and reduce conflict overet al. 2010).the limited water resources.The Beijing metropolitan area covers 16411 km, ofThis paper aims to quantify the historical impact ofwhich 2317 km2 is arable land (BSB 1991-2011). Watercropping patterns on water resources in the Beijingresources in this region are becoming progressivelymetropolitan area and to analyze the possible opportu-scarce, driven by a growing population and a developingnities for alleviating water shortages. The context foreconomy. Beijing's per capita water resources are lessthis research is the on-going adjustment of agriculturalthan 200 m3 (BSB 1991-2011), which is far below thepolicies in China, which means that agricultural pro-internationally recognized threshold of 1 000 m'. Agri-duction patterns are undergoing profound changes.culture is as one of the major water users, accountingHowever, despite the potential of policy changes to havefor around 40% of the total water withdrawal during thesubstantial effects on water resources, in-depth analy-last 10 yr (BSB 1991-2011). Groundwater is the mainsis on this issue is rarely found in literature. This studysource of irrigation and has been significantly over-also has relevance beyond Beijing, as many other largeexploited, with falling water-tables (Wang and Wangcities in China and around the world face similar prob-2005). Declining water tables and depletion of economi-lems of domestic and industrial water scarcity.cally accessible groundwater resources have the poten-tial to cause major social and economic problems. Iraddition, large inputs of synthetic N fertilizer for cropRESULTS AND DISCUSSIONproduction have led to a series of environmental prob-lems including eutrophication of surface waters and ni-Historical cropping patterns and the future trendtrate pollution of groundwater which have effects onhuman health and normal functioning of ecosystems (JuOver the past two decades, the total cropped area inet al.2009). It is imperative to develop sustainable agri-the Beijing region has decreased by almost 50% (Fig. 1).cultural production which can reduce the related nega-In the early 1990s the annual cropped area was abouttive impacts on water resources in Beijing.60x 104 ha yr'. However, between 2000 and 2003 itImproving water and fertilizer management candecreased shacince. etahilized at aroundgreatly reduce the irrigation water consumption and30x10* ha yrYH中国煤化工pped area waswater pollution associated with crop production (Shock largely due tdC N M H Ger, during this◎2012. CAAS. AI rghts reserved Publishedbay EIsevierLtd.1916HUANG Jing et al.0 Other crops口Vegetables (covered)0 Vegetables (open)0 1.0 Other grain crops口Wheat■Maize0一10一0十20一1990 199219941996 199820002002 200420062008 2010YearFig. 1 Area planted to the principal crops in Beijing (1990-2010). Source: BSB (1991-2011).period, the reduction in cultivation was also influenced low point of 2003. In 2010, the area of maize wasby local government policies intended to reduce agri-15x 10* ha while that of wheat was at 6x10* ha (Fig.1).cultural water use (Huang et al. 2012).The area planted to other grain crops (such as rice andGrains have traditionally been the crops most widelysoybeans) has continued to decline. In particular, rice,planted in the Beijing metropolitan area. In the earlyregarded as a highly water intensive crop by the Beijing1990s cereals (predominantly maize and wheat) weremunicipal government (BMG 2002), is now estimatedplanted on 80% of the cultivated area (Fig. 1). to be less than 300 ha yrl and may disappear altogetherHowever, the proportion of the area planted to grains(Huang et al. 2012).dropped to 68% in 2000 and reached the lowest pointVegetable production has expanded during 1990-of 47% in 2003. The area of maize decreased from2003. The area planted to vegetables has increased22x 104 ha in 1990 to less than 8*104 ha in 2003. Thfrom 7x104 ha yr! in 1990 to 12x104 ha yrl in 2003,decline in the area of wheat was similarly abrupt, towhich was about 40% of the total cropped area (Fig. 1).4x104 ha in 2003, which was only 20% of the areaWith the expanding urban population and increasingcultivated in 1990 (Fig. 1). However, since 2004, thedemand for fresh produce, vegetable production en-Chinese central government carried out the nationwideabled farmers to achieve the greatest economic benefitGrain Subsidy Policy in order to stimulate greater farmerfrom the scarce agricultural land base (Dong and Wuenthusiasm for cereal production to safeguard the2008). However, due to the above-mentioned govern-nation's food security. In addition, the Beijing Munici-ment policies, the area of vegetables decreased afterpal Government adopted a policy known as the Eco-2004 (Fig. 1). From 2007-2010, the average area oflogical Compensation Policy, which sought to stimu-vegetables was around 8x 104 ha yr!. The latest changelate the planting of winter crops (mainly winter wheat)to be observed is the growth in the area of vegetablesto reduce soil loss and dust. Due to the combined ef-grown in plasti中国煤化工Is. To achievefects of these two policies, the area planted to maizethe so-called“YHCNMHGhoutput,highand wheat has increased slowly but gradually since thequality and high efficiency, the area planted to veg-Cropping Pattern Modifications Change Water Resource Demands in the Bejing Metropolian Area1917etables in covered systems has increased from less thanirrigation. Therefore, since the economic cost of agri-1000 ha yrl prior to 1998 to around 4x104 ha in 2010,cultural water is low, determined esentially by the costaccounting for more than half of the total area ofof electricity to pump water, excessive irigation is veryvegetables.often practiced. Vegetables grown in open fields wereAs described above, reducing cropland area hasalso found to have a relatively high consumptive use oflong been used as a policy measure for reducing agri-imgation water of about 293 mm yrI (Table 1). Apartcultural water use in Beijing. As a water scarce region,from vegetables and rice, other crops had much lowerBeijing can externalize its water consumption by im-consumptive use of irrigation water. The main growthporting food, as it has done with rice. However, theperiod of maize, soybeans, starchy root crops, oil cropsstrict implementation of the National Land Use Plan-and cotton is summer when rainfall levels are the high-ning Policy (2006-2020) (GOC 2008) and related lo-est and irrigation requirements are therefore lower.cal government policies (BMG 2009) means thatThe blue water consumption and pollutant dilutionBeijing's cropland area cannot be further reduced.water requirement of the main crops in Beijing are listedAdditionally, from the perspective of both the govern-in Table 2. Rice and vegetables in covered systems hadment and scholars, Beijing must keep a certain amountthe highest blue water consumption among the consid-of cropland to guarantee emergency food supply andered crops due to the high irrigation water consump-to provide ecological services (Huang et al. 2012).tion and the use of irigation on 100% of the croppedTherefore, with constraints on the further reductionarea. In contrast, only 2% of the area planted to maizeof crop land, alternative approaches to water use re-is irigated. Therefore, maize had the lowest blue wa-duction will be required.ter consumption of about 20 m3 ha' yr!. Vegetables inplastic and glass covered systems also had the highestBlue water consumption and pollutant dilutiondilution water requirement because of the high fertilizerwater requirement of cropsapplication rates. Considering blue and dilution watertogether, vegetables in covered systems had the high-The annual average precipitation was 517 mm in theest blue water use. The total blue water use of veg-Beijing metropolitan area during 1990-2010. The con-etables in plastic and glass covered system was moresumptive use of irrigation water varied widely betweenthan 7 000 m3 ha:1 yr', which was 8 times as much asthe different crops, from as low as 75 mm yrl for oilof the widely practiced grain crop maize. Vegetablescrops, to as high as 422 mm yr1 for plastic and glassgrown in open fields and rice also had relatively highcovered vegetables and 470 mm yrl for rice (Table 1).blue water use, both exceeding 4000 m3 ha-1 yr'.In the case of plastic and glass covered vegetableVegetables are generally considered as low water-production, the traditional opinion of farmers is thatintensive crops because of their relatively low virtualhigh crop yields will only be attained with surpluswater contents (the ratio of water used for crop pro-Table 1 Crop water requirements and rrigation water consumption in BejingWater requirementEffective rainfalll .Irrigation water requirement2)Irrigation water consumption》Crop”(mmyrI)(mmyr")757470481116156WheatMaize3624918Soybeans22497Sturchy root crops4429865120Oil crops75Cotton32669108Vegetables (open)293Vegetables (covered)0422Forage312中国煤化工144"Calculated by SIMETAW (Snyder et al.2012).21 The dfference of water requirement and efective rainfall.MYHCNMH G"The volume of imrigation water consumed by crops (see the section“Impact of crop production on biue water").。2012, CAAS:AII rghts reserved. Published by EIsovier Ld.1918HUANG Jing et al.duction to the crop yield) compared to grain crops andby the proportion of the crops and cropping systemsother food products (Liu et al. 2007; Liu and Savenijeused. The total annual blue water use averaged 12x10*2008; Mekonnen and Hoekstra 2011). Therefore, in-m3 yrl during 1990-2000. It fell sharply in the periodcreasing vegetable production has been recommended2000 to 2005 to about 7x108 m3 yr', but since then hasas one of the ways to achieve more efficient use ofbeen gradually increasing again.agricultural water (Liu et al. 2007). However, the yieldThis situation can be explained by examining waterof vegetables usually expressed in fresh weight is gen-use on a land area basis (Fig. 2). The average blueerally much higher than that of grain and other cropswater use per hectare of cropped land increased fromwhich is expressed in dry weight. Therefore, although2112 m3 yrlin 1990 to 2442 m3 yrl in 2000, andthe water use associated with vegetable production maypeaked at 2764 m3 yr1 in 2003. This was mainly thebe lower when expressed on a product basis (as ilus-consequence of an increase in the proportion of veg-trated in Table 2), the water use per hectare can beetable production, which had higher total blue watermuch greater. As such, expanding vegetable produc-use. Even though the area of rice decreased sharply,tion might not be a wise choice for reducing regionalthe average blue water use still increased. Since 2004,agricultural water use. Plastic and glass covered sys-the proportion of vegetables decreased, so the averagetems for vegetable production are the most intensiveblue water use per ha also decreased. However, due toagricultural systems in the Beijing region. Generally,the increase of proportion for vegetables in plastic andthere are three or four vegetables planted in a rotationglass covered systems, the blue water use still remainedcycle per year. Compared with the wheat-maize rota-at a high level in 2010 at about 2425 m3 ha' yr', whichtion which is the traditional crop-rotation patterm widelywas an increase of313 m3 ha'l yrl compared with 1990.practiced in Beijing, each hectare of vegetables-rota-tion consumed more blue water and required more di-Implication of improvement measures to alleviatelution water, resulting in a far more negative impact onwater shortagethe availability of water resources. In summary, theincrease in vegetable production, especially vegetablesAccording to the data provided by Beijing Municipalin covered systems, is exerting increased pressure onBureau of Agriculture, the current vegetable self-suffi-the local water and environment in Beijing.ciency is about 31% for the Beijing region. With thegrowing population, the future demand for vegetablesHistorical effects of crop production on blue waterwill almost certainly increase and the area planted tousevegetables in covered systems will also likely increase.The consequence will be additional pressure on BeijingThe change in total annual blue water use by crops waswater resources unless covered vegetable productionnot as great as the change in total annual cultivated areasystems can increase water use efficiency and contain(Fig. 2). This was because the total blue water use isnutrient runoff and leaching. Fortunately, vegetablenot only influenced by the total cultivated area but alsoproduction systems are generally amenable to water-Table 2 Blue water consumption and pollutant dilution water requirements of crops grown in BejingBlue waterDilution waterTotal blue water useCrop(m3 ha' yr)(mha'y")(m) ha: yr')(mt)Rice4698305 128778Wheat1392233236Maize2194496572Starchy root crops456398Soy beans1042502914Oil crops549290Cotton10151442中国煤化工2344Vegetables (open)2636.1 697CNMH G6Vegetables (covered)42193197MH6S348I 14035Forage792目2012, CAS. AI ights reserved. Published by Elsevher Lld.Cropping Patterm Modifcations Change Water Resource Demands in the Bejjing Metropolitan Area1919239 Total use-一Avernge use per hectare280014270013-260012.2500+. 24000会2000s190018003十1700160015001990 199219941996 1998 2000 2002 20042006 2008 2010YearFig. 2 The total blue water use and average blue water use per hectare of crop production in Beijing (1990-2010).saving irrigation practices such as drip irrigation andshifting 1 ha of plastic and glass covered vegetablespray irrigation. At present, about 50% of coveredproduction to an open field system would reduce bluesystems for vegetable production in Beijing are low-water use by 3083 m3 yr', based on current technology.tech (BSB 1991-2011). There are no rainwater har-A shift toward wheat or maize cropping would makevesting systems in place and precipitation on the plas-an even greater difference (up to 5000 m3 ha'l yr").tic or glass systems drains into the surrounding land.However, any change of this kind could be counter-To alleviate water shortage in the Beijing region fromproductive and cause a decrease in local food self-food production, the many low-tech covered systemssufficiency. If Beijing grows fewer vegetables, it willshould become“water smart”by harvesting rainwa-need to import more from outside the region. Thister off the roof and stored in farm pond. This watercould simply shift the water shortage burden elsewherewould partly satisfy the water demands of vegetablein China. Moving vegetable production further awayproduction. Water use for vegetable production couldfrom the Beijing market would also lead to greateralso be reduced by measures such as modernizing withenergy use for transportation and storage and couldwater- saving irrigation equipment, recycling the nutri-even result in more wastage. Greater adoption of waterent runoff into the greenhouse and utilizing recycledand nutrient-efficient vegetable production systems inwastewater from the buit environment in a careful waythe Beijing region would appear to be the best solution.(Page et al. 2011). Furthermore, irigation schedulingcould be implemented to enhance water use efficiencyCONCL USIONand reduce nitrogen leaching (Shock and Wang 2011).Future change in cropping patterns away from COV-中国煤化工ered vegetable production could also relieve pressureThis study hMHCNMHGesincroppingon water resources in the Beijing region. For example,patterns the Beijing metropolitan area substantially af-1920HUANG Jing et al.fected the availability of local water resources. Water1993; Cao 2008), varies annually in the Beijing region duesavings associated with a contraction in cropped area wereto numerous factors such as government policies, marketpartly offset by an increase in water use intensity on thedemands for agricultural products and the economic re-turns to the farmers (Dong and Wu 2008). Historical dataremaining agricultural area. This increase in water useon the crop areas from 1990 to 2010, were obtained fromintensity was largely atributed to a transition fom grainthe Beijing Statistics Yearbook (BSB 1991-2011). Cropscrops to vegetables, especially intensive vegetable pro-included grain (rice, wheat, maize, soybeans, and starchyduction in covered systems. Policies designed to increaseroot crops), vegetables (in open field and in plastic andurban water supplies by constraining the agricultural sec-glass covered systems), and others (cotton, oil crops andtor need to take special consideration of the differences inforage). These crops accounted for more than 95% of thetotal annual planted area in Beijing. For this study, soy-blue water impacts associated with each type of croppingbean was classified into the category“grain crops” ac-practiced. If these differences between crops are ignored,cording to China's traditional definition.agricultural structure adjustment in response to local mar-ket opportunities and land use pressures has the potentialField data sourceto undermine water policy objectives.For the rapidly urbanized, water scarce region ofDuring 2002-2008,Bejjing, our results suggest that modernization of veg-conducted by us to evaluate farming practices in the Beijingetable production systems should be a priority to re-region (Huang et al.2012). Included in these studies wereduce water consumption and pollution. An alternativerecords of water and fertilizer utilization for the major crops,would be to increase the importation of vegetables fromwhich are compiled in Table 3. Rice is a minor crop in theoutside the Beijing region. However, it is noted thatBeijing region and was not included in these studies.this second strategy requires careful analysis to ensureTherefore, data on typical water and fertilizer use for ricecultivation was obtained by consultation with agronomiststhat it would not simply result in the shifing of envi-familiar with local rice farming practices. Since there areronmental burdens to an adjacent region. An increasemany types of vegetables, we used data for tomato as thisin food imports to Beijing might also have other undes-is widely grown in Beijing in both open field and coveredired outcomes such as an increase in env ironmentalsystems. Similarly, data for sweet potato were used toimpacts from longer transportation distances, increasedrepresent all starchy root crops, groundnut was consid-food waste and a decrease in local food self-sufficiency.ered representative of the various oil crops, and alfalfawas representative of forage crops.These issues are not unique to the Bejjing region. Theurban population centers are growing rapidly across China,Modeling crop water requirementsand indeed most of the developing world. There are now119 cities in China with a population greater than 1 million(ttp://www.stats.gov.cn). As these cities grow, so tooThe average crop water requirements (ET。mm yr ") andeffective rainfall (P . mm yr) were calculated by SIMETAWdo their demands for water resources and food supplies.(Simulation of Evapotranspiration of Applied Water) appi-However, the potential for local food production is itselfcation program which employs the classic Penman-constrained as the agricultural sector faces competitionMonteith equation to estimate ET。(reference crOPfor water from the expanding domestic and industrialevaporation) following the methodology recommended bysectors. Hence the importance of understanding the ef-FAO (Allen et al. 1998). The SIMETAW program was de-fects of cropping patterm change on water resources toveloped by the Califormia Department of Water Resourcesensure that policies related to land use also have a benefi-and the University of California (Snyder el al. 2012) andhas been verified for local crop and soil parameters incial outcome in terms of sustainable water use.Bejing (Song 2009). Climate data for the model, coveringthe period 1990- 2010, were obtained from the China Me-teorological Data Sharing Service System http://cdcma.MATERIALS AND METHODS ,gov.cn). Crops grown in greenbouses have different dy-namics of crop evaporation which SIMETAW model can-not directly estimate. Compared to irrigated crops grownMapping of historical cropping patternsniratinn, nf mvered horticulturalcrops is lowe中国煤化工e demanddinsideThe cropping pattern, also commonly referred to as“cropgreenbousesMHCNMHGtheETinsideacomposition and distribution”by Chinese scholars (Liugreenhouse is about 70-80% ot that computed with cli-●2012, CAAS AI rghts rserved Published by ElseverLud.Cropping Patterm Modifications Change Water Resource Demands in the Bejing Metropolitan Area1921Table 3 Characteristics of the main crops planted in BeijingIrrigation suppliedProportion of the area irigatedN fertilizer rateYieldCropGrowth period(mmy-')"的(kg ha-))(kg ha:1)2)RiceMay-October848 .100659WheatOctober-June217892165350MaizeMay-September5594Soybeans1059482224Starcby root crops16375726 521Oil crops622830CottonApri-October15)43321 049Vegetables (open)February-July409039071 65Vegetables (covered)January-July87735114 600ForagePerennial205532 597)Based on farmers' pratices recorded in previous studies (Huang et al. 2012) and advised by local expert.7)Based on satistial data (BSB 1991-2011).matic parameters observed outside (Chapagain and Orrported farm water use. This is potentially an excessive use2009). In this study, we assumed that the ET of vegetablesof irrigation. As such, for the purpose of estimating im-in the plastic and glass covered systems were 75% of thepacts on water resources, the irrigation water consump-estimated outdoor value. Crop water requirement (ET, mmtion was calculated as the minimum of the modeled iriga-yr') and effective rainfall (P mm yr ) define the irrigationtion requirement (, mm yr') and the irigation water sup-water requirement (I, mm yr') which was calculated as:ply (I, mm yr) multiplied by the blue water depletion rateI,=ETcPe1)(DR %), Equation 2:l.=min (r,1,xDRm)(2The above method was applicable for crops underImpact of crop production on blue waterirrigation. For some crops which were partly grown in rain-fed croplands, the average blue water consumption (BWC,Irrigated crop production consumes blue water (surfacem3 har yr) was calculated as the irigation water consump-and groundwater) and can degrade blue water (pollutanttion (I, mm yr") multiplied by the proportion of area irri-dilution water) through emissions of agrichemical. Irriga-gated (IR, %) and 10 (a factor used to convert mm yrl to m'tion water (I, mm yr", Table 3) is partly stored as soilha-! yrl), Equation 3:moisture and consumed through crop evapotranspiration.BWC=IcxIRx. 10(3In this context, consumed means“lost”from the localhydrological system. Part of the supplied irigation isA pollutant dilution water calculation (Chapagain et al.also “lost" to deep drainage and runoff. However, there2006) was also conducted in consideration of the impactsis potential for this water to be reused in another fieldof water quality degradation associated with cropping. Thedownstream or even return to groundwater and be reused.dilution water requirement refers to the volume of freshwa-Huang and Li (2010a) defined the blue water depletionter that is required to assimilate pollutants such as fertiliz-rate (DR. , %) to reflect the proportion of supplied irniga-ers or and other agro-chemicals from agricultural landtion consumed by the target crop. The blue water deple-(Chapagain et al. 2006). The amount of dilution water fortion rates of grain crops (rice, wheat, maize and soybean)growing a crop was calculated as the N fertilizer applica-in the first-order basins in China were also calculatedtion rate per hectare (kg ha:l) multiplied by the leachingusing a bydrological model (Soil and Water Assessmentfraction divided by the permissible concentration (kg m-*).Tool, SWAT) (Arnold et al. 1998) in conjunction withFollowing Hu et al. (201 1), the leaching fraction for cropscrop production and water use statistics (Huang and Liin dry land was 4.35% and that for rice was 2. 19%. The2010b). The blue water depletion rate (72%) of Hai basinstandard recommended by US EPA for nitrate in drinkingwhere Beijing is located was subsequently used as anwater (10 mg LI) was used to calculate the necessary dilu-estimated proportion of irrigation supplied which wastion water volume.consumed by the crops.The total annual volumetric blue water use of crop pro-In some cases, the modeled irrigation water requirementduction was calculated by summing the total blue waterexceeded the consumptive water use determined from re-consumption and pollutant dilution water requirement ofported farm water use (adjusted by 72%). This is mosteach crop multiplied by the respective planted area in alikely an indication that crops were grown with less thanparticular year. In order to ilustrate the impacts of crop-full irigation. The alternative situation also occurred, whereping pattern中国煤化工expressed on athe modeled irigation water requirement was exceeded byper hectare te water use bythe consumptive water requirement determined from re- the total crop,YHC NMH G"●2012, CAAS.AI rghte roeved. Pubishedby Elever Ltd.1922HUANG Jing et al.Acknowledgementssustainability and optimal cropping pattern in farmingThis study was jointly supported by the Special Fund forsystems; a multi-objective fractional goal programmingapproach. Water Resources Management, 24, 4639-Agro-scientific Research in the Public Interest, China4657.(201 103001), the National Basic Research Program of ChinaGleick P H.2003. Water use. Annual Review of Environment(2010CB951500), and also by the CSIRO-Chinese Ministryand Resources, 28, 275-314.of Education Ph D Research Fellowship Program.GOC (The Government of China), 2008. The National LandUse Planning (2006-2020). 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