氮素利用效率

作物氮素高效利用的生理生态基础重点内容氮素利用效率（NUE)的概念及计算方法主要作物NUE的现状土壤基础供氮力的时空变异及其对NUE的影响提高作物NUE的生理学途径我校资源与环境学院张福锁教授领导的科研小组的研究论文“SignificantAcidificationinMajorChineseCroplands”于2月19日在Science正式发表(2月11日在ScienceExpress上提前刊出与读者见面)。该论文通过深入系统的研究，首次全面报道了自上世纪80年代以来我国主要农田土壤出现显著酸化的现象，并且发现氮肥过量施用是导致农田土壤酸化的最主要原因。http:///show.php?id=0000038773张福锁研究小组论文“SignificantAcidificationinMajorChineseCroplands”在Science发表

土壤酸化（表现为土壤pH值的下降）能够加速营养元素流失、促进铝、锰以及重金属等元素的活化、改变土壤微生物种群及活性、影响作物根系发育和养分吸收、滋生植物病虫害等等，从而对农业生产、生态环境和人类健康构成严重的潜在威胁，对粮食安全和环境安全产生长远影响，是土壤学、生态学和环境科学等领域广泛关注的重大问题。该论文通过对我国主要农田土壤pH值20年的变化研究发现，我国农田土壤pH值平均下降了约0.5个单位，相当于土壤酸量（H+）在原有基础上增加了2.2倍。其中，经济作物体系土壤酸化比粮食作物体系更为严重；即使是过去被认为对酸化不敏感的石灰性土壤，其pH值也同样出现了显著下降的现象。在自然条件下土壤酸化是一个相对缓慢的过程，土壤pH值每下降1个单位通常需要数百年甚至上千年，而我国过去20年来的高投入集约化农业生产大大加速了农田土壤的酸化过程。

通过系统的理论分析，该论文发现氮肥过量施用是我国农田土壤酸化加速的首要原因。在华北冬小麦-夏玉米轮作、华南水稻-小麦轮作等“一年两熟”种植体系中氮肥大量施用每年所产生的酸量（20-30千摩尔/公顷）约占总产酸量的60%；蔬菜大棚等设施农业中过量施氮的年产酸量（约200千摩尔/公顷）占总产酸量的90%。秸秆移出带走的盐基对土壤酸化的贡献（15-20千摩尔/公顷）虽然因农作物种类和生物产量而有所差异，但明显低于氮肥施用的贡献。值得注意的是，长期以来被当作土壤酸化主要原因的酸雨在农田土壤酸化中的贡献并不大，仅为0.5-2.0千摩尔/公顷。由此可见，在保证粮食生产的前提下严格控制氮肥施用量，减少过量施氮，不仅是作物高产高效的需要，而且也是缓解农田土壤酸化的重要途径。目前生产上仍然普遍存在“氮肥越多越高产”的错误观念，过量施氮已成为集约化农业生产体系相当普遍的严重问题。从上世纪80年代以来，我国氮肥用量迅猛增长，到90年代中期我国已成为世界氮肥生产和消费的第一大国，在占世界7%的耕地上消耗了全球35%的氮肥。统计资料显示：1981年至2008年，粮食年产量从3.25亿吨增加到5.29亿吨，增长了63%，而氮肥消费量却从1118万吨增加到3292万吨，增长了近2倍。由此带来不良后果包括：氮肥生产效率不断下降，氮肥损失引起的环境问题日趋严重。过量施用氮肥导致的土壤酸化、温室气体排放和地下水硝酸盐污染等问题已成为全球集约化农业可持续发展的严重威胁。就我国而言，北方一些蔬菜大棚由于长期过量施用氮肥使土壤pH值由原来的7-8降低到4-5，病虫害严重发生，蔬菜品质和产量显著下降，一半以上的氮肥养分进入地下水造成饮用水硝酸盐污染。南方部分红壤的pH值已经降至3-4之间，造成玉米、烟草、茶叶等农作物的大量减产甚至绝收。需要指出的是，这类问题不仅出现在我国，而且也在世界各地的集约化农业生产中普遍存在，氮肥过量施用导致的包括土壤酸化在内的一系列农业与生态环境问题在全球范围引起广泛关注，该论文发现的过量施氮造成农田土壤酸化现象充分揭示了这一重大问题。该课题组及其合作单位的另一研究结果表明，华北平原和太湖流域农田中过量使用氮肥主要通过气体和硝酸盐的形式进入大气和地下水，如果采用科学的养分管理技术可以在降低氮肥用量30-60%的条件下既保证粮食产量又不至造成氮肥污染，实现农业和环境的“双赢”。因此，如何在持续提高作物产量的同时，控制或降低氮肥用量、有效地减少过量氮素对环境的负面影响，已经成为国际农业和生态环境领域所共同面临的重大科学问题。该论文的发表是该科研创新团队立足国家重大问题研究，发表国际一流文章的又一重大成果。该研究小组将以此为契机在集约化农业背景下在农田土壤酸化的风险评估、生态环境效应及其防治对策等方面开展系统深入的研究工作，为实现我国粮食安全与环境协调、实现可持续发展提供理论基础和技术支持。NitrogenFertilizerEfficiency:Theory,Measurement,andPracticeKennethG.CassmanDeptofAgronomyandHorticultureUniversityofNebraskaTemporalVariabilityinNitrogenUseEfficiencyandCropResponseIndexofCereals.G.V.Johnson,W.R.Raun,R.L.WestermanandB.B.Tucker DepartmentofPlantandSoilSciences OklahomaStateUniversityR.A.Olson DepartmentofAgronomy UniversityofNebraska

中国主要湖泊和水库营养状况分类结果统计指标贫营养中营养富营养湖泊数量（个）95567占调查湖泊数（％）6.9041.9051.20湖泊面积（km2）5477.8016525.7011029.90占湖泊的总面积（％）16.6050.033.4水库数量（个）101712占调查水库数（％）25.6043.6030.80水库容积（×105m3）37.36546.1073.94占设置库容（％）5.7083.1011.20城郊湖库富营养化的程度较高，如杭州西湖、武汉东湖、南京玄武湖、济南大明湖等城市湖泊和石河子市的蘑菇水库、北京市的官厅水库等已达富营养化程度。大型淡水湖泊的富营养化问题令人十分担忧，五大淡水湖中的太湖、洪泽湖、巢湖等均已达富营养程度，鄱阳湖、洞庭湖目前虽然维持在中营养水平，但湖水磷、氮的含量偏高，处于向富营养的过渡阶段。安徽省巢湖市中庙风景区的巢湖水域出现大面积蓝藻，使湖水呈翠绿色、粘稠状。据巢湖市环保局专家分析，氮磷总量增加导致湖水富营养化，外加适宜的水温，为蓝藻生长提供了有利条件。以往蓝藻暴发期一般在每年的7月至8月。近期天气持续高温，降雨不多，为了防汛巢湖水位被控制得很低，巢湖水体的自净能力减弱，从而导致蓝藻大面积出现。无锡，鼋头渚最佳观湖景点，但蓝藻成祸，游客已经不能与太湖水亲密接触了。

5月30日，无锡某大型超市内的饮用水被抢购一空。土壤植物动物人体人体必需元素54种，这些元素最终来自土壤。农产品中硝酸盐含量与氮肥施用的关系NO3－NO2－NH＋HNO2R1R2R1R2N－N＝O＋H2ODangerous！施用氮肥可使胡萝卜、卷心菜、马铃薯等硝酸盐含量提高0.5-1.5倍，玉米黑麦草等提高1.3-39倍！硝酸盐积累：叶菜类>根菜类>瓜果类;禾本科牧草>豆科牧草;茎/叶>根>种子.硝酸盐在人体内也可被还原为亚硝酸盐。亚硝酸盐与人体血液作用，形成高铁血红蛋白，从而使血液失去携氧功能，使人缺氧中毒，轻者头昏、心悸、呕吐、口唇青紫，重者神志不清、抽搐、呼吸急促，抢救不及时可危及生命。亚硝酸盐在人体内外与仲胺类作用形成亚硝胺类，它在人体内达到一定剂量时是致癌、致畸、致突变的物质，可严重危害人体健康。氮素利用与全球变化ImprovingNitrogenUseEfficiencyforCerealProductionRaunandJohnson.1999.Agron.J.91:357-363.WorldwideNUE=33%1%change=$234,658,462

NO3-labileorgN

SOILN

NH4+stablehumusNINPUTSBNFfertilizermanuredepositionCROPNUPTAKE

HARVESTLEACHINGnitrate(NO3-)solubleorganicNCROPRESIDUESGASEOUSLOSSESdenitrification(N2O)volatilization(NH3)LeachingDenitrificationNO,N2OFertilizersPlantUptakeNitrification

NO3-NH4+N2+H2ONH3+OH-Harvest+OH-NH3VolatilizationLossofNfromsoil-plantsystemFoundationoftheHumanFoodSupplyMaize,rice,andwheatAccountforthemajorityofallcaloriesinhumandietsReceive56%ofglobalNfertilizeruseLikelytobecomeevenmoreimportantEasilytransportedandstoredHigheryieldsthanothercerealcropsRequirelesscookingenergythanothercropsFeedgrainsforlivestockproductionGrowthinGrainSupply-DemandIncreaseincropareaduringthepast30years

Crop Period Area(106ha)

Maize 1966-69 112 1996-99 140(+25%)Rice 1966-69 129 1996-99 152(+18%)

Wheat 1966-99 220 1996-99 225(+2%)

Totalincrease 1966-99 56x106haKeyElementsofaSustainableGlobalFoodProductionSystemIntensifiedcropproductioninfavorableenvironmentswithgoodsoilsandclimateEvolutionofsubsistenceagriculturetomorestableandproductivesystemsinlessfavorableenvironments(poorsoilsandharshclimate)Preservationofremnantnaturalecosystemsasrefugeforbiodiversityandtoprovideabroadspectrumofenvironmentalservices

FocusonNFertilizerEfficiency

SustainingincreasesincropyieldsdependsonproportionalincreasesincropNuptakeNfertilizerislargestsinglesourceofNinputtocultivatedland,especiallyforthemajorcerealsOnaglobalscale,Nfertilizerrepresents46%oftotalNinputstocropland,andamuchhigherproportionincerealcroppingsystemsCombinedinputsfromorganicNsources(cropresidues,manures,legumes&N-fixers)represent38%oftotalNinputsandhavelittlescopeforasubstantialincreaseNitrogenUseEfficiency(NUE)ofanAgroecosystemBroadestmeasure:yieldperunitNinput(Y/F)Incerealsystems:grainyieldperunitNinputExogenousNinputsFertilizer,manure,wet/drydeposition,NinirrigationwaterEndogenousNinputsBiologicalnitrogenfixation(legumes,soilmicrobes)QuantifyingNFertilizerEfficiency(NUE)NUE:grainyieldperunitofappliedN(Y/F)Physiologicalefficiency

(PE):Dgrainyield/DNuptakefromfertilizerUptakeefficiency

(RE):DNNuptake/DNfertilizerrateAgronomicefficiency

(AE):Dgrainyield/DNfertilizerrateAE=RExPE=(DYG/DNP)x(DNP/DNF)=(DYG/DNF)NUEComponentsofNFertilizerEfficiencyattheField-Level:MaizeinNebraskaFrom:Cassmanetal.,2003.Ann.Rev.ResourcesandEnviron.AE=PE=RE=Measurement/Calculation?Applyingtoomuchfertilizer-N?WhyisNUEsolowforconventionalN-fertilizedproductionsystems?

CalculatingSystemEfficiencies

Foraparticularsystem:SystemOutputSystemInputX100=%EfficiencyCalculatingNUECropuseoffertilizer-N:Harvested-NFertilizer-NX100=%NitrogenUseEfficiency(NUE)Harvested-NFertilizer-NX100=%NUECalculatingNUECorrectionfornon-fertilizercontributions:Harvested-N1-Harvested-N0

Fertilizer-N1

X100=NUEHarvested-N1-Harvested-N0

Fertilizer-N1

X100=NUEReliabilityofNUEcalculations?IsmineralizedNoverestimatedfromNuptakeforNO?ContinualcropremovalstimulatesmineralizationinNO.Fertilizeradditionsstimulatemicrobialactivity,causing‘primingeffect’.IsmineralizedNoverestimatedfromN-uptakeforNO?

NO3-labileorgN

SOILN

NH4+stablehumusNINPUTSBNFfertilizermanuredepositionCROPNUPTAKE

HARVESTLEACHINGnitrate(NO3-)solubleorganicNCROPRESIDUESGASEOUSLOSSESdenitrification(N2O)volatilization(NH3)NRateGrainUptakeNfromFertNfromSoilNUEDiffNUE15N032.8

032.8

2350.02.747.375124557.14.352.854106763.68.055.546129090.59.680.96411112105.413.891.66512ReliabilityofNUEcalculations?Calculationsforasingleyearmaybemisleading.Annualvariationsinmineralizedsoil-Nmaybelarge.Annualvariationsincropresponsetofertilizer-Nmaybelarge.InfluenceofyearonNUEwinterwheatreceiving90kgN/ha.SomeconclusionsaboutNUEforwinterwheat.Whencorrectedformineralized-N,NUEstilldecreaseswithincreasingfertilizerinput.Long-termaverageNUEfordrylandwheatrangesfromabout50%atlowNinputto30%athighestinput.WhatiscurrentstatusofNfertilizerefficiency?Estimatesneededfrom‘on-farm’measurementsPaucityofreliabledatafromthemajorcerealcroppingsystemsMeasurementsfromsmallresearchplotstendoverestimatecurrentefficienciesbyalargemarginAvailabledataindicatelowNfertilizeruptakeefficiencyVerylowforriceLowformaizedespiteimprovementsinrecentyearsLowtohighonwheatdependingoncroppingsystemandyieldlevelsNitrogenfertilizeruptakeefficiency(RE)ofmaize,rice,andwheatbasedonon-farmmeasurements.FromCassmanetal.,2002,AMBIO.

Crop Region Number Nfertilizer(kgha-1) RE(%ofapplied)(rotation) mean(+/-SD) mean(+/-SD) Maize USA 55 103(85) 37(30)(maize-soybean)Rice Asia* 179** 117(39) 31(18)(rice-rice) 179*** 112(28) 40(18)Wheat India 23+ 145(31) 18(11)(rice-wheat) 21++ 123(30) 49(10)*SixAsiancountries.**Farmers’practices.***Field-specificmanagement.+Low-yieldyear(1997,2.3Mgha-1).++High-yieldyear(1998,4.8Mgha-1).

AresubstantialincreasesinNfertilizerefficiencypossibleascropyieldscontinuetoincrease?Theanswerdependson:DetailedunderstandingofthebiophysicalcontrolsonNefficiencyandusingthisknowledgetodevelopimprovedcropandsoilmanagementsystemsIsourunderstandinguptothetask,andwhatarethehighestresearchpriorities?TheHolyGrail:

CongruencebetweenNsupplyanddemandPlantsacquireNfromthe‘available’inorganicsoilNpool(NH4+andNO3-)ThepotentialforNlossesviaalllosspathwaysisproportionaltotheamountofNintheavailableNpoolatanypointintimeOptimizingyieldandNuseefficiencydependsonmatchingthesizeoftheavailableNpoolto‘immediate’cropdemand,withoutexcessordeficiency,throughoutthecropgrowthperiod

AchievingcongruencebetweenNdemandandsupplydependsonpredictionof:CropNdemandPhysiologicalrequirements(grainNconcentration,C4vsC3photosynthesis)Yieldlevel(climatexmanagementxgenotype)TheNsupplyfromindigenoussoilresourcesNmineralizationfromsoilorganicmatterandcropresiduesNinputsfrombiologicalNfixation,atmosphereandirrigationThetimingandamountofappliedNfertilizerTightlyconservedrelationshipbetweenplantbiomassyieldandNcontentwhenNistheonlylimitinggrowthfactor:Greenwoodetal,Ann.Bot.1990RelationshipbetweengrainyieldandNaccumulationinabovegroundbiomassfromon-farmexperiments:Maize(n=470,0.115),rice(n=1658,0.081)FromCassmanetal.,2002,AMBIOLittlescopeforimprovingNefficiencyfromgeneticimprovementTightlyconservedrelationshipbetweenbiomassyieldandNuptakerequirementsgiveslittleopportunityforgeneticengineeringConvertingC3plantstoC4photosynthesis?NuptakeefficiencybycroprootsystemsisnotalimitingfactorunderfavorablegrowthconditionsAchievingcongruencebetweenNdemandandsupplydependsonpredictionof:CropNdemandPhysiologicalrequirements(grainNconcentration,C4vsC3photosynthesis)Yieldlevel(climatexmanagementxgenotype)TheNsupplyfromindigenoussoilresourcesNmineralizationfromsoilorganicmatterandcropresiduesNinputsfrombiologicalNfixation,atmosphereandirrigationThetimingandamountofappliedNfertilizerFactorsControllingtheIndigenous

SoilNSupplyRateofNmineralizationfromsoilorganicmatter,recycledcropresiduesContributionsfromappliedmanureandNfertilizerAmountofNlossesfromleaching,volatilization,anddenitrificationAllhavehighdegreeofspatialandtemporalvariationDynamicNatureoftheIndigenousSupplyMakesPredictionDifficultSmallfractionoftotalsoilNstocksTypicallyrepresentsonly1-5%oftotalNHighlysensitivetotemperatureandmoistureregime(irrigation,rainfall)Affectedbyamountandqualityofincorporatedcropresidues,tillagepracticesModifiedfromOlketal.,1999,NutrientCyclinginAgroecosystems

Unfertilizedyieldisvariableovertime.Controlplotyieldofwinterwheat(Lahoma,OK):y=-15.78x+1910C.V.=30.4%7451974

Fertilizedyieldisvariableovertime.Maximumyieldofwinterwheat(Lahoma,OK)Y=23.95x+2581C.V.=20.5%30453088Arefertilizedandunfertilizedwheatyieldsrelated?28个试验年不同氮素水平下小麦产量（Ymax/YN0=1.9)AchievingcongruencebetweenNdemandandsupplydependsonpredictionof:CropNdemandPhysiologicalrequirements(grainNconcentration,C4vsC3photosynthesis)Yieldlevel(climatexmanagementxgenotype)TheNsupplyfromindigenoussoilresourcesNmineralizationfromsoilorganicmatterandcropresiduesNinputsfrombiologicalNfixation,atmosphereandirrigationThetimingandamountofappliedNfertilizerMethodstoimprovetimingandrateofNfertilizerinbalancewithNdemandandNsupplyIn-seasonsoiltestingforavailableNand/orplanttissuetestingforNstatusRelativelyexpensiveandrequiresaccesstopublicorcommerciallabservicesCropandsoilsimulationmodelsNonerigorouslyvalidatedacrosssoiltypes,environments,croppingsystems,yearsNon-destructivemeasurementofcropNstatusChlorophyllmeter,remotesensing(NDVI)OptimizingyieldandNuseefficiencydependsonmatchingthesizeoftheavailableNpoolto‘immediate’cropdemand,withoutexcessordeficiency,throughoutthecropgrowthperiod黑黄当地栽培方式：行株距6×5寸N肥前后比8:2精确定量栽培方式:行株距9×5寸N肥前后比5.5:4.5当地栽培方式：行株距6×5寸N肥前后比8:2精确定量栽培方式:行株距9×5寸N肥前后比5.5:4.5黑黄

到了无效分蘖期至拔节期，即N-n+1（或N-n+2）叶龄期至N-n+3叶龄期，为了有效控制无效分蘖和第一节间伸长，群体叶色必须“落黄”，顶4叶要淡于顶3叶（顶4﹤顶3，群体才能被有效控制，高峰苗少，通风透光条件好，碳素积累充足，为施氮肥攻大穗制造良好的条件。此期群体叶色若不能正常落黄，必然造成中期旺长，带来中后期生长一系列的不良后果。高产田旺长田顶4叶顶3叶顶4叶顶3叶<>图

N-n叶期RSPAD与成穗率的关系再生稻超高产实践，2007福建尤溪高产水稻籽粒产量的80-90%以上来源于抽穗后的光合产物，这个比例占得越多，籽粒产量也愈高。说明高产的获得是靠建造抽穗至成熟期的高光效群体。其关键之一是把群体的封行期控制在叶龄余数为0的孕穗期。

高产田旺长田再生稻超高产实践，2007福建尤溪当地栽培方式：行株距6×5寸N肥前后比8:2精确定量栽培方式:行株距9×5寸N肥前后比5.5:4.5头季稻-成熟期再生稻超高产实践，2007福建尤溪当地栽培方式：行株距6×5寸N肥前后比8:2精确定量栽培方式:行株距9×4寸N肥前后比5.5:4.5再生稻-成熟期再生稻超高产实践，2007福建尤溪一块田施肥能获得的最高产量主要由当地光、温、水资源特点决定。在特定地区内，影响不同田块之间产量差异的因素有哪些？土地肥沃和贫瘠在本质上是什么？有人认为多施有机肥能改善土壤质地，进而容易实现高产，你认为这种说法有何局限性？传统栽培多限于经验，比如说肥田少施点肥、瘦田多施点肥。你认为肥田和瘦田应如何施肥才能获得最大产量或最高肥料利用效率？一块田不施肥能获得400kg产量，施肥后能获得的最高产量是多少？如何协调产量和肥料利用效率？思考题CenturyNModuleNUEIncreasedsoilNsupply(A—A’);IncreasedsoilNsupplyandyieldpotential(A—B’);Increasedsoilyieldpotential(A—B).Carbonsequestration,whichincreasessoilorganicmattercontent,resultsingreatersoilNsupplycapacity,whichinturnreducesNfertilizerrequirementsandresultsinhighernitrogenuseefficiency.From:Cassmanetal.,2003.Ann.Rev.ResourcesandEnviron.

TakeHomeMessageHighfertilizerNefficiencycanbeachievedathighyieldlevelsandhighratesofNfertilizerapplicationonlywhenappliedNfertilizeriscongruentwithcropNdemandandtheindigenousNsupplyMatchesin-seasonpatternofcropNdemandMatchesspatialvariabilitywithinlargeproductionfields(mechanizedagriculture)Matchesfield-specificrequirementsinsmallproductionfields(labor-intensiveagriculture)PrecisionAgricultureExactimplementationofallmanagementoperationsuniformlyappliedtoasinglefieldSite-specificmanagementwithinafieldtoaccountforspatialvariationinsoilandpestsVariety/hybridselection;tillage;plantingdate,densityandrowspacing;nutrientamount,formulation,andplacement,integratedpestmanag