Improvement of Wheat Water Use Efficiency in Semiarid Area of China

Agricultural Sciences in ChinaVol.2 No.1 35-44January 2003Improvement of Wheat Water Use Efficiencyin Semiarid Area of ChinaDENG Xi-ping'，2,SHAN Lun', KANG Shao-zhong2，Inanaga Shinobu3and Mohanmed Elfatih K Ali3.4(' Institute of Soil and Water Conservation, Chinese Academy of Sciences, Shaanxi 712100，P. R. China;”Northwest Sci- Tech University of Agriculture and Forestry, Shaanxi 712100，P. R. China;3 Arid Land Research Center， Tottori University, Hamasaka 1390， Tottori 680， Japan;“ El-Obeid Research Station, Agricultural Research Corporation, P. O. Bor 429， E-Obeid, Sudan )Abstract: The greatest fear of global climate change is drought since in most areas where wheat is grownwater is the most important factor influencing wheat yield. Average wheat yield throughout the world is only30 - 60% of the attainable yield potential because water shortage is the major factor preventing the realizationof maximum yield. Periods of drought alternating with short periods of available water are common conditionsto influence wheat productivity. Such conditions include variable frequency of dry and wet periods, intensityof drought, rate of drought onset and patterns of soil water deficit and/ or atmospheric water deficit. It is thisdeficit and variable water conditions in semiarid environments that influence wheat productivity variously.This paper reviewed the physiological adaptation and benefits associated with deficit and variable water condi-tions. In addition, it also highlights the compensative effect of limited irrigation and breeding of new varietiesfor high water use efficiency ( WUE) that could improve wheat productivity under water-limited environmentsin the semiarid regions. Considerable potential for further improvement in wheat WUE and productivity insemiarid environments seems to depend on effective conservation of moisture and efficient use of this limitedwater such as soil fertility improvement, conservation tillage, residues and film mulch, rain water harvestingfor limited irrigation, and breeding for water saving varieties. Different crop, soil and water managementstrategies should be adjusted according to the conditions that prevail in various semiarid areas. By combiningsoil and water conservation approaches and adjusting the cropping system by growing drought-tolerant and wa-ter-saving cultivars, increase in wheat WUE and productivity could be achieved.Key words : Semiarid conditions, Dryland wheat, Physiological adaptation, WUE improvementGlobal demand for wheat is growing fasternologies. China has an average wheat yield of 3. 78than gains realized in genetic yield potential. Cur-t ha- higher than the world average. Today， do-rently the gain increase is less than 1% per year inmestic demand for wheat is about 125 millionmost regions1. The largest wheat producingtones.' I o improve total production in China，at-countries of the world are China， United States,tention has been focused on expansion in areas withIndia，Russia， Australia and Canada[2]， wherelow and medium yield in the semiarid regions. Thissemiarid regions occupy the largest area. China hashas required the development and dissemination ofbecome the largest wheat producer in the worldwhe中国煤化工:s that lead to sustain-since the 1980s. Wheat yield has increased byableYHCN M H Gin these areas5396.7% compared with that in the 1950s as a resultPeriods of drought alternating with short peri-of progress in developing wheat production tech-ods of available water are conditions common toDENG Xi p万市数据Professor, Tel: 86- 29 7012437. Fax: 86 29 7012210. E mail: dengxp@ ms. iswc. ac. cn.6DENG Xir ping et almany semiarid areas of the world!4]. Typical semi-integrated with limited water supply in an irriga-arid area in China，for instance， characterized bytion network, as in a water-deficient area, for ex-water shortage and low productivity， has specialample.natural conditions and ecological environment. An-Great WUE potential of wheat production ex-nual precipitation in the area is about 350 -550 mmists in semiarid area, to improve wheat yield, how-and seasonal distribution in spring， summer，auever，biggest challenge is effective conservationtumnandwinteris12-15%，46-65%，20-35%and efficient use of limited water resources. Theand 1 - 3%，respectively. Rainfall, in the form ofobjective of this paper is to viewpoint some benefi-storms，occurs mainly in the period from July tocial effects of wheat response to water deficit andSeptember, characterized by irregular distributionvariable conditions, discuss wheat W UE improve-and intensity-5. Wheat response to this deficit andment and exploit drought- resistant and water- sav-variable water environments is complex and unin-ing potential for improving wheat production insurable, because such conditions can cover variablesemiarid area of China.frequency of drought and wet periods, variable de-Wheat Response to Water Deficitgrees of drought, rate of onset of drought condi-and Variable Conditionstions，and varying patterns of soil water deficitand/ or atmo-spheric water deficit.Wheat drought tolerance is very complex,A possible means of increasing WUE of wheatwith all the mechanisms involved not clearly un-in semiarid area is to manage transpiration so thatderstood. Research on the effects of water deficitsrelatively more water is used during the vegetativeon physiological processes at the molecular levelphase when vapor pressure deficit (VPD) is low,has shown that some enzymatically mediated .and hence transpiration efficiency (TE) is high.processes increase but others decrease[12]. Root/However，based on budgets of soil water and solu-shoot communication is being increasingly studiedble carbohydrates stored in the vegetative organsat the molecular level-13-16- .A crop 's sensitivity to .and available for retranslocation， this option pro-drought varies during different stages of its life cy-vides lower TE than conserving soil water for tran-cle. This provides the possibility to choose the cru-spiration until grain filling when assimilates are di-cial moments for watering the crop-17. Also arected to grain'6]. Yield of water- limited wheat iscrop s response to drought stress and the degree todetermined by crop water use and WUE. The in-which yield is reduced varying across the differentcrease in transpiration efficiency may result bothgrowth stages of the crop, especially those closelyfrom an increase in photosynthetic rate and a de-related to yield formation. The order in whichcrease in stomatal conductance.Wheat underwheat physiological processes are serially affected .drought stress has self regulatory processes for en-by drought seems to be growth， stomatal move-during the adversity. These range from metabolicment，transpiration, photosynthesis and transloca-adaptation to reduced growth. If the drought doestion[18-20].not damage the crop beyond a critical threshold,1.1Drought tolerant mechanism during seedlingthen some physiological compensation will takeestablishmentplace as soon as the water supply is resumed, thusWheat seedling establishment under waterminimizing the impact of the water deficit on cropdefic中国煤化工idely studied(a1. 2]2 andgrowth，WUE and yield[7.8]. Often the highest ef-how:TYHC N M H Gress signals and howficiency in farmland irrigation is achieved withdoes stress affect regulation of gene expressionmoderate，compared with abundant water sup-have resulted in an understanding of these proces-ply-11.Limited irrigation refers to a system ofses at the molecular level-23.24]. In particular, ma-crop mar而高熬据in which dryland cultivation isjor results on hydrolysis in seed germinationImprovement of Wheat Water Use Efficiency in Semiarid Area of China3anabolism during seedling establishment!26]， plu-cannot be overcome by increasing the concentrationmule elongation growth-27] ,proteins and genesof CO2[36]. Although stomatal closure generallyregulated by plant hormonesC28]as well as wateroccurs when plants are exposed to drought， inabsorption mechanism during seedling establish-some cases photosynthesis may be more controlledment under water deficit conditions have all beenby the chloroplast capacity to fix CO2 than by thereported [29,30].increased diffusive resistancelHowever，howFrom an agronomic viewpoint, Whan et al. [31],photosynthesis adapts to drought environments isfor example，suggested that indeterminate culti-not well understood.vars that have early and vigorous seedling estab-In semiarid environments, photosynthesis waslishment accumulated a relatively large amount ofvariable under different soil moisture contentsh8J .biomass by the beginning of the seed filling stage,Under gradually drying soil conditions， wheat ex-and thus were able to remobilize accumulated pho-hibited higher photosynthetic rate than under fasttosynthate in response to declining soil moisture.drying soil conditions. In the former, osmotic ad-Such cultivars were best adapted to drought condi-justment increased to a certain extent while undertions.the latter process it remained constant. OsmoticIt is generally accepted that crops are oftenadjustment allows for maintenance of photosynthe-less tolerant to drought during germination andsis and growth by stomatal adjustment and photo-seedling stage-32.38， a stage that can take severalsynthetic adjustment538. 393The reported evidenceweeks. Deng et al. [19] showed that of all the stagesshowed that under mild and/ or moderate soil waterof active axis extension， germination， plumuledeficit conditions， photosynthetic depression waselongation and emergence of spring wheat， thecaused by stomatal closure or stomatal limitation ,plumule elongation stage is the most sensitive onebut not by biochemical reactions. However, underto water deficit. Therefore， under water deficitsevere soil water deficit conditions， non-stomatalconditions，the maintenance of anabolism and slowfactors including some limiting enzymes could havegrowth were greatly associated with ATP energybeen responsible for the decline in photosyntheticlevel in cells， as seedling establishment involvescapacity40-42]. Midday declines in photosynthesisthe energy- requiring metabolic reactions. Deng etwere mainly induced by severe vapor pressure defi-al. [34] suggested that the mechanism of seedlingcit, and stomatal limitation was suggested as a ma-drought-tolerance seems to involve regulating ATPjor causet43.441.Under natural semiarid conditions,energy level to change the ratio of catabolism tohowever, this decline usually resulted from soilanabolism in such a way that result in the accumu-water deficit that induced a decrease in leaf waterlation of osmotic component and depression of os-potential at midday. Similar results were reportedmotic potential in growing tissue. Under such con-earlier by Sheriff[+5] and Shi et al46]. Deng etditions，the ability of seedling to uptake water isal. [20] reported that both soil water deficit and highincreased and slow seedling growth is maintainedVPD simultaneously induced the midday depres-during water deficit conditions.sion in photosynthesis, indicating that both stoma-1.2 Effect of water deficit on the photosynthetictal and non-stomatal limitations were responsibleparametersfor photosynthetic decline in spring wheat underUnder drought conditions， stomatal closurethe中国煤化工and inhibition of chloroplast activity reduce photo-MYHC N M H Gnditions, the crop issynthesis5351. Stomatal closure increases the resist-able to synthesize abscisic acid (ABA) by its rootance to CO2 diffusion into the leaf. Inhibition of .system. ABA is then transported through the xy-chloroplast activity at low soil water potential de-lem to leaves， causing regulation of several ion .creases the厄熱据ty to fix available CO2，and thischannels in guard cells which trigger stomatal clo-DENG Xir ping et alsurel47.48]. This may be linked to the role of farne-that in wheat evolution from 2 to 6 n，WUE atsylations that have been connected with ABA sig -whole plant level increases with the increase ofnal conduction[49,50]. With regard to chloroplastploidy chromosomes, root size and root/ shoot ratiocapacity to fix CO2，the evidence shows that theof wheat decrease with the increase of ploidy chro-Rubisco holoenzyme is assembled in a catalyticallymosomes under drought and irrigated conditions.inactive form and is activated by Rubisco activaseRoot growth has an adverse redundancy for WUE,(RCA)51.52].and the root redundancy reduces with the increaseDeng et al. [53] indicated that the notable mid-of ploidy chromosomes， which result in the in-day decline in stomatal conductance that was paral-crease of wheat WUE at whole plant level. Theselel to photosynthetic rate depression resulted fromresults suggested that use of genetic breeding tosevere water vapor deficit at midday. The deviationexcavate water-saving potential of wheat is possi-of stomatal conductance between the control andble.soil moisture deficit treatments was closely related2 Compensatory Effect of Limited |r-to the leaf water status that was obviously affectedrigation in Wheatby the prevailing soil moisture deficit. The follow-ing hypothesis was，therefore, proposed: Molecu-Loomis and Connor[5s6]suggested that therelar mechanism of stomatal conductance variationare three strategies available to improve the waterand intercellular CO2 concentration oscillation isuse of crops in dry areas. The first is to maximize .closely linked with ABA reduced stomatal responsecrop evapotranspiration (ET). The second is toand activation status of the enzyme Rubisco affect-maximize crop transpiration as a fraction of totaled by circadian oscillation of RCA.evapotranspiration while the third is to maximize1.3 WUE and root-shoot relations of wheatcrop WUE. Consistent with these strategies andWhile the current interest in research at thewater limited conditions, Deng et al. [1] proposedmolecular level is important， it should accompanythat 200 mm of supplemental water is needed toresearch on water relations at the whole plant lev-achieve the maximum grain yield; 100 mm of sup-el. The success of wheat plant in producing yieldplemental water is necessary to get the greatestdepends primarily on the success of leaves in con-WUE; and 60 mm of supplemental water is indis-trolling water loss and the effectiveness of roots inpensable for the highest irrigated WUE. In semiar-taking up water. Tolerance of dehydration dependsid conditions, the critical water quantum for limit-on characteristics at the molecular level, such ased irrigation of spring wheat is 60 mm.osmotic adjustment, water transduction in tissues, .Many studies[57,58] have looked at the yieldand the manner in which water deficit affects en-losses associated with drought at different stages ofzyme- mediated processes. Clearly， both avoidanceplant development. Villareal et al. [59] showed thatand tolerance of water deficit will contribute tocrown root initiation and anthesis are the two sta-successful wheat production under semiarid condi-ges at which yield losses from drought stress cantions. Avoidance of severe water deficit requiresbe most critical to wheat. Current research60] iscoordination at the whole plant level between theaimed at identifying different plant traits thatcontrol of water loss from transpiring shoots andwould allow wheat varieties to withstand the dif-water absorption through root systems. Withferel中国煤化工Iecur in the developingmethods of gas exchange and carbon-13 stable iso-worlYHCNMHGtope, Zhang and Shan-54] demonstrated that se-Deng et al.I1] showed that， in the Guyuanquence of WUE in modern wheat cultivars is irriga-County of the Ningxia Hui Autonomous Region inted varieties > varieties of both irrigated and dryChina，where the annual precipitation was 450 mmland > d两方数据varieties. Zhang et al. [5] showedand the annual mean temperature was 6. 5C，aImprovement of Wheat Water Use Efficiency in Semiarid Area of China35single irrigation of 600 m3 ha-' applied at the joint-soil profile or into ground water[64].ing stage ( equivalent to 30% of irrigated volume ofThe nutrients that are found to be most limit-water for a full cropping season with the highesting in the loess hilly region of China are N andyield) yielded up to 75% of the highest yield were .p[5]. Most of the soils in loess region of China arerecorded. This amounted to a 2. 8 kg increase ircalcareous and these soils are particularly distribu-grain yield per cubic meter of water. The optimumted on the eroded hilly tops. The deficiency is real-time for limited irritation in spring wheat was thely a problem of high pH and runfof:5]。. The yieldjointing stage and the water deficit critical periodand WUE increase from added N were observed inand the optimum irrigation time in wheat are not atseveral dryland areas where crops were grown onthe same growth stage. It seems essential to makethe same land for several years-5a distinction between the critical growth stage atLiu et al. [66] indicated that grain yield andwhich yield is greatly reduced by drought and thatWUE of spring wheat were positively correlatedone at which supplemental irrigation results in thewith fertilization, while grain yield was not closelyhighest yield improvement.correlated with planting density. The results sug-3 Effect of Soil Fertillization on Wheatgested that under the necessary fertilizer input of90 kg N and 135 kg P2O3 per hectare the yields ofWUEabout 2 250 kg ha~' and crop WUE of about 10. 25Drought and poor soil fertility are the main re-kg mm-' ha~! could be achieved.strictive factors for the production of drylandZhao[67] reported that the formation of vegeta-wheat in the semiarid and eroded area of China，astive organs and increase in plant was the maina traditional agricultural area, where dryland farm-growth patterns before the booting stage. Betweening has been practiced for 4 000 years, Li and Xi-booting and flowering was the transient stage for Nao-61J demonstrated that the use of a mulch crop to .and C metabolism. Before jointing stage, N metab-cover fields with green manure plants, CrOP resi-olism was vigorous, and C/N ratio is about 0. 65-due, or plastic film protects the soil from moisture1.0. After flowering， C metabolism becomes thloss by evaporation, reduced soil erosion and thus,main process and C/N ratio was just greater thanimproved soil fertility and conserved water. These1.0. Contents of C and N nutrition at different pe-changes resulted in increased wheat yield and WUEriods influenced reproductive organ development.in the low yielding areas examined. Xu[62] showedLiu et al.[68] showed that the number of fertilethat mulching significantly improved water conser-spikelets, kernels per spike and kernel weight in-vation and soil fertility and resulted in large increa-creased with increase in fertilizer level. Crop waterses in wheat yield in dryland areas. When 30 tonesuse at the jointing stage is the most effective onper ha of green manure was used on fallow land,grain yield formation of spring wheat'about 50 mm of water could be conserved, soil or-4Ecophysiological Approaches forganic matter and nutrients simultaneously en-Wheat Yield Improvementhanced, yield increased by 2. 25 tones per ha andWUE increased by 23%.Greater yield per unit rainfall is one of theRainfall variability greatly increases the risk ofmost important challenges in dryland wheat. WUEusing fertilizer in dryland environments. However,repr中国煤化工rain yield per unit ofestimates from farmers’ fields and experimentalwate:MYHC N M H Gth increasing concernstations indicated that the wheat crop usually re-about the availability of water resources in drylandcovered only 30-50% of the nitrogen that farmersagriculture, there is renewed interest in trying toapply every year-The rest was lost, either dis-develop an understanding of how WUE can be im-sipated in万敏据tmosphere or leached down theproved and how farming systems can be modified0DENG Xi-ping et alto be more efficient in water use. Maximizingtion and water use with available technology toWUE may be more suitable in areas where water,control the efficient use of limited water resources.not land, is the most limiting factor-70]. There is aThe effective use of precipitation and optimi-need for accurate understanding that wheat rezation of WUE are critical for promoting wheatsponse to water deficit conditions on real- time. Ityield in dryland farming systems. These can beis possible to combines knowledge of crop adapta-summarized in Fig.Biological ModificationEnvionmental Control _Control Soil and Water Loss,Increase Soil Moisture Storage.Raise Pn/TrCHigh Harvest IndexUse Mulch to Diminish SoilEvaporationIncrease CropImprove Field WaterWUEUse RatioGood DroughtImprove Root Growth to UseResistanceDeeper Soil WaterCollect Run off Water forSelection High WUE↓Supplemental IrigationGenotypesRaise Precipitation Use EfficiencyRealize to High Efficient Use of Limited Waler. ResourcesFig. Comprehensive technical approaches to improve crop production in semiarid regions with eroded environmentsThe deficit and variable water conditions inby construction of high- yield farmlands throughsemiarid environments are the major issues influen-the building of leveled terraces， the utilization ofcing crop growth. Water- saving agricultural prac-harvested rainwater for limited irrigation, the usetices must, therefore， be designed and utilized.of tillage practices that conserves water and soil,Central to such research should be the relationshipthe introduction of drought tolerant varieties andbetween the effect of drought stress on crop physi-the application of manure and fertilizer. Especial-ological processes and the yield formation ability.ly, for the dryland low-yielding wheat area, theIn the southern hilly area of Ningxia Hui Au-wide use of chemical fertilizer has played a majortonomous Region of China，with 450 mm of annualrole on this respect3. 53].Ina 10-year period (1980precipitation，the spring wheat yield was 0. 75 -to 1990)，dryland wheat yield in the area doubled.2.25 t per ha, with water consumption of 280 mm,The major contributing factor to the change waswhich is about 62% of the annual rainfall[18]. Thethe use of chemical fertilizerabove figure show that there is still a considerable .Changes in soil management practice to reducepotential for further improvement in the use ofevaporation from the soil surface have been suc-rainfall received. To raise rainfall utilization rate,cessful in some locationsT71]. It is possible to in-a comprehensive approach including prevention ofcrease WUE bv 25_ to 40% through soil manage-water loss and soil erosion， elimination of topsoilmenMYH中国煤化Iillge. Overall, pre-evaporation，extraction of water stored in deepercipitC N M H G be enhanced throughlayers and the steady heightening of the absorbableadoption of more intensive cropping systems inshare of water by crops must be adopted. In thesemiarid environments and increased plant popula-semiarid Loess Plateau， for instance, the water-tions in more temperate and humid environments.savingdraise the rainfall utilization rateModifying nutrient management practices can in-Improvement of Wheat Water Use Efficiency in Semiarid Area of China4crease WUE by 15 to 25%. WUE can be increasedcritical growth stage at which yield is greatly re-through proper management，and field-scale expe-duced by drought from that one at which supple-riences show that these changes positively affectmental irrigation results in the highest yield im-crop yield7z2].provement.Genetic advances in grain yield under rainfedConsiderable potential for further improve-conditions have been achieved by empirical breed-ment in wheat WUE and productivity in semiariding methods. Progress is slowed， however， byenvironments seems to depend on effective conser-large genotype x season and genotype x location in-vation of moisture and efficient use of this limitedteractions arising from unpredictable rainfall,water such as soil fertility improvement, conserva-which is a feature of drought environments. Ation tillage, residues and film mulch, rain watergood understanding of factors limiting and/or reg-harvesting for limited irrigation, and breeding forulating yield now provides us with an opportunitywater saving varieties.to identify and then select for physiological andDifferent crop， soil and water managementmorphological traits that increase the efficiency ofstrategies should be adjusted according to the con-water use and yield under rainfed conditions'ditions prevailing in various semiarid areas. ByWUE is broader in scope than most agronomiccombining soil and water conservation practices,applications and must be considered on a water-and adjusting cropping system by growing droughtshed，basin， irrigation district， or catchmenttolerant varieties， increases in wheat WUE andscale. The main pathways for enhancing WUE inproductivity could be achieved.limited irrigation are to increase the output per unitof water ( engineering and agronomic managementAcknowledgementsaspects)，reduce losses of water to unusable sinks,This paper was supported by the Major Statereduce water degradation (environmental aspects)，Basic Research Development Program of People'sand reallocate water to higher priority uses ( socie-Republic of China (G1999011708) and the Key La-tal aspects)[741. 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