氮素利用效率

作物氮素高效利用的生理生態(tài)基礎(chǔ)重點(diǎn)內(nèi)容氮素利用效率（NUE)的概念及計(jì)算方法主要作物NUE的現(xiàn)狀土壤基礎(chǔ)供氮力的時空變異及其對NUE的影響提高作物NUE的生理學(xué)途徑我校資源與環(huán)境學(xué)院張福鎖教授領(lǐng)導(dǎo)的科研小組的研究論文“SignificantAcidificationinMajorChineseCroplands”于2月19日在Science正式發(fā)表(2月11日在ScienceExpress上提前刊出與讀者見面)。該論文通過深入系統(tǒng)的研究，首次全面報(bào)道了自上世紀(jì)80年代以來我國主要農(nóng)田土壤出現(xiàn)顯著酸化的現(xiàn)象，并且發(fā)現(xiàn)氮肥過量施用是導(dǎo)致農(nóng)田土壤酸化的最主要原因。http:///show.php?id=0000038773張福鎖研究小組論文“SignificantAcidificationinMajorChineseCroplands”在Science發(fā)表

土壤酸化（表現(xiàn)為土壤pH值的下降）能夠加速營養(yǎng)元素流失、促進(jìn)鋁、錳以及重金屬等元素的活化、改變土壤微生物種群及活性、影響作物根系發(fā)育和養(yǎng)分吸收、滋生植物病蟲害等等，從而對農(nóng)業(yè)生產(chǎn)、生態(tài)環(huán)境和人類健康構(gòu)成嚴(yán)重的潛在威脅，對糧食安全和環(huán)境安全產(chǎn)生長遠(yuǎn)影響，是土壤學(xué)、生態(tài)學(xué)和環(huán)境科學(xué)等領(lǐng)域廣泛關(guān)注的重大問題。該論文通過對我國主要農(nóng)田土壤pH值20年的變化研究發(fā)現(xiàn)，我國農(nóng)田土壤pH值平均下降了約0.5個單位，相當(dāng)于土壤酸量（H+）在原有基礎(chǔ)上增加了2.2倍。其中，經(jīng)濟(jì)作物體系土壤酸化比糧食作物體系更為嚴(yán)重；即使是過去被認(rèn)為對酸化不敏感的石灰性土壤，其pH值也同樣出現(xiàn)了顯著下降的現(xiàn)象。在自然條件下土壤酸化是一個相對緩慢的過程，土壤pH值每下降1個單位通常需要數(shù)百年甚至上千年，而我國過去20年來的高投入集約化農(nóng)業(yè)生產(chǎn)大大加速了農(nóng)田土壤的酸化過程。

通過系統(tǒng)的理論分析，該論文發(fā)現(xiàn)氮肥過量施用是我國農(nóng)田土壤酸化加速的首要原因。在華北冬小麥-夏玉米輪作、華南水稻-小麥輪作等“一年兩熟”種植體系中氮肥大量施用每年所產(chǎn)生的酸量（20-30千摩爾/公頃）約占總產(chǎn)酸量的60%；蔬菜大棚等設(shè)施農(nóng)業(yè)中過量施氮的年產(chǎn)酸量（約200千摩爾/公頃）占總產(chǎn)酸量的90%。秸稈移出帶走的鹽基對土壤酸化的貢獻(xiàn)（15-20千摩爾/公頃）雖然因農(nóng)作物種類和生物產(chǎn)量而有所差異，但明顯低于氮肥施用的貢獻(xiàn)。值得注意的是，長期以來被當(dāng)作土壤酸化主要原因的酸雨在農(nóng)田土壤酸化中的貢獻(xiàn)并不大，僅為0.5-2.0千摩爾/公頃。由此可見，在保證糧食生產(chǎn)的前提下嚴(yán)格控制氮肥施用量，減少過量施氮，不僅是作物高產(chǎn)高效的需要，而且也是緩解農(nóng)田土壤酸化的重要途徑。目前生產(chǎn)上仍然普遍存在“氮肥越多越高產(chǎn)”的錯誤觀念，過量施氮已成為集約化農(nóng)業(yè)生產(chǎn)體系相當(dāng)普遍的嚴(yán)重問題。從上世紀(jì)80年代以來，我國氮肥用量迅猛增長，到90年代中期我國已成為世界氮肥生產(chǎn)和消費(fèi)的第一大國，在占世界7%的耕地上消耗了全球35%的氮肥。統(tǒng)計(jì)資料顯示：1981年至2008年，糧食年產(chǎn)量從3.25億噸增加到5.29億噸，增長了63%，而氮肥消費(fèi)量卻從1118萬噸增加到3292萬噸，增長了近2倍。由此帶來不良后果包括：氮肥生產(chǎn)效率不斷下降，氮肥損失引起的環(huán)境問題日趨嚴(yán)重。過量施用氮肥導(dǎo)致的土壤酸化、溫室氣體排放和地下水硝酸鹽污染等問題已成為全球集約化農(nóng)業(yè)可持續(xù)發(fā)展的嚴(yán)重威脅。就我國而言，北方一些蔬菜大棚由于長期過量施用氮肥使土壤pH值由原來的7-8降低到4-5，病蟲害嚴(yán)重發(fā)生，蔬菜品質(zhì)和產(chǎn)量顯著下降，一半以上的氮肥養(yǎng)分進(jìn)入地下水造成飲用水硝酸鹽污染。南方部分紅壤的pH值已經(jīng)降至3-4之間，造成玉米、煙草、茶葉等農(nóng)作物的大量減產(chǎn)甚至絕收。需要指出的是，這類問題不僅出現(xiàn)在我國，而且也在世界各地的集約化農(nóng)業(yè)生產(chǎn)中普遍存在，氮肥過量施用導(dǎo)致的包括土壤酸化在內(nèi)的一系列農(nóng)業(yè)與生態(tài)環(huán)境問題在全球范圍引起廣泛關(guān)注，該論文發(fā)現(xiàn)的過量施氮造成農(nóng)田土壤酸化現(xiàn)象充分揭示了這一重大問題。該課題組及其合作單位的另一研究結(jié)果表明，華北平原和太湖流域農(nóng)田中過量使用氮肥主要通過氣體和硝酸鹽的形式進(jìn)入大氣和地下水，如果采用科學(xué)的養(yǎng)分管理技術(shù)可以在降低氮肥用量30-60%的條件下既保證糧食產(chǎn)量又不至造成氮肥污染，實(shí)現(xiàn)農(nóng)業(yè)和環(huán)境的“雙贏”。因此，如何在持續(xù)提高作物產(chǎn)量的同時，控制或降低氮肥用量、有效地減少過量氮素對環(huán)境的負(fù)面影響，已經(jīng)成為國際農(nóng)業(yè)和生態(tài)環(huán)境領(lǐng)域所共同面臨的重大科學(xué)問題。該論文的發(fā)表是該科研創(chuàng)新團(tuán)隊(duì)立足國家重大問題研究，發(fā)表國際一流文章的又一重大成果。該研究小組將以此為契機(jī)在集約化農(nóng)業(yè)背景下在農(nóng)田土壤酸化的風(fēng)險(xiǎn)評估、生態(tài)環(huán)境效應(yīng)及其防治對策等方面開展系統(tǒng)深入的研究工作，為實(shí)現(xiàn)我國糧食安全與環(huán)境協(xié)調(diào)、實(shí)現(xiàn)可持續(xù)發(fā)展提供理論基礎(chǔ)和技術(shù)支持。NitrogenFertilizerEfficiency:Theory,Measurement,andPracticeKennethG.CassmanDeptofAgronomyandHorticultureUniversityofNebraskaTemporalVariabilityinNitrogenUseEfficiencyandCropResponseIndexofCereals.G.V.Johnson,W.R.Raun,R.L.WestermanandB.B.Tucker DepartmentofPlantandSoilSciences OklahomaStateUniversityR.A.Olson DepartmentofAgronomy UniversityofNebraska

中國主要湖泊和水庫營養(yǎng)狀況分類結(jié)果統(tǒng)計(jì)指標(biāo)貧營養(yǎng)中營養(yǎng)富營養(yǎng)湖泊數(shù)量（個）95567占調(diào)查湖泊數(shù)（％）6.9041.9051.20湖泊面積（km2）5477.8016525.7011029.90占湖泊的總面積（％）16.6050.033.4水庫數(shù)量（個）101712占調(diào)查水庫數(shù)（％）25.6043.6030.80水庫容積（×105m3）37.36546.1073.94占設(shè)置庫容（％）5.7083.1011.20城郊湖庫富營養(yǎng)化的程度較高，如杭州西湖、武漢東湖、南京玄武湖、濟(jì)南大明湖等城市湖泊和石河子市的蘑菇水庫、北京市的官廳水庫等已達(dá)富營養(yǎng)化程度。大型淡水湖泊的富營養(yǎng)化問題令人十分擔(dān)憂，五大淡水湖中的太湖、洪澤湖、巢湖等均已達(dá)富營養(yǎng)程度，鄱陽湖、洞庭湖目前雖然維持在中營養(yǎng)水平，但湖水磷、氮的含量偏高，處于向富營養(yǎng)的過渡階段。安徽省巢湖市中廟風(fēng)景區(qū)的巢湖水域出現(xiàn)大面積藍(lán)藻，使湖水呈翠綠色、粘稠狀。據(jù)巢湖市環(huán)保局專家分析，氮磷總量增加導(dǎo)致湖水富營養(yǎng)化，外加適宜的水溫，為藍(lán)藻生長提供了有利條件。以往藍(lán)藻暴發(fā)期一般在每年的7月至8月。近期天氣持續(xù)高溫，降雨不多，為了防汛巢湖水位被控制得很低，巢湖水體的自凈能力減弱，從而導(dǎo)致藍(lán)藻大面積出現(xiàn)。無錫，黿頭渚最佳觀湖景點(diǎn)，但藍(lán)藻成禍，游客已經(jīng)不能與太湖水親密接觸了。

5月30日，無錫某大型超市內(nèi)的飲用水被搶購一空。土壤植物動物人體人體必需元素54種，這些元素最終來自土壤。農(nóng)產(chǎn)品中硝酸鹽含量與氮肥施用的關(guān)系NO3－NO2－NH＋HNO2R1R2R1R2N－N＝O＋H2ODangerous！施用氮肥可使胡蘿卜、卷心菜、馬鈴薯等硝酸鹽含量提高0.5-1.5倍，玉米黑麥草等提高1.3-39倍！硝酸鹽積累：葉菜類>根菜類>瓜果類;禾本科牧草>豆科牧草;莖/葉>根>種子.硝酸鹽在人體內(nèi)也可被還原為亞硝酸鹽。亞硝酸鹽與人體血液作用，形成高鐵血紅蛋白，從而使血液失去攜氧功能，使人缺氧中毒，輕者頭昏、心悸、嘔吐、口唇青紫，重者神志不清、抽搐、呼吸急促，搶救不及時可危及生命。亞硝酸鹽在人體內(nèi)外與仲胺類作用形成亞硝胺類，它在人體內(nèi)達(dá)到一定劑量時是致癌、致畸、致突變的物質(zhì)，可嚴(yán)重危害人體健康。氮素利用與全球變化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‘a(chǎn)vailable’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個試驗(yàn)?zāi)瓴煌厮较滦←湲a(chǎn)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黑黃當(dāng)?shù)卦耘喾绞剑盒兄昃?×5寸N肥前后比8:2精確定量栽培方式:行株距9×5寸N肥前后比5.5:4.5當(dāng)?shù)卦耘喾绞剑盒兄昃?×5寸N肥前后比8:2精確定量栽培方式:行株距9×5寸N肥前后比5.5:4.5黑黃

到了無效分蘗期至拔節(jié)期，即N-n+1（或N-n+2）葉齡期至N-n+3葉齡期，為了有效控制無效分蘗和第一節(jié)間伸長，群體葉色必須“落黃”，頂4葉要淡于頂3葉（頂4﹤頂3，群體才能被有效控制，高峰苗少，通風(fēng)透光條件好，碳素積累充足，為施氮肥攻大穗制造良好的條件。此期群體葉色若不能正常落黃，必然造成中期旺長，帶來中后期生長一系列的不良后果。高產(chǎn)田旺長田頂4葉頂3葉頂4葉頂3葉<>圖

N-n葉期RSPAD與成穗率的關(guān)系再生稻超高產(chǎn)實(shí)踐，2007福建尤溪高產(chǎn)水稻籽粒產(chǎn)量的80-90%以上來源于抽穗后的光合產(chǎn)物，這個比例占得越多，籽粒產(chǎn)量也愈高。說明高產(chǎn)的獲得是靠建造抽穗至成熟期的高光效群體。其關(guān)鍵之一是把群體的封行期控制在葉齡余數(shù)為0的孕穗期。

高產(chǎn)田旺長田再生稻超高產(chǎn)實(shí)踐，2007福建尤溪當(dāng)?shù)卦耘喾绞剑盒兄昃?×5寸N肥前后比8:2精確定量栽培方式:行株距9×5寸N肥前后比5.5:4.5頭季稻-成熟期再生稻超高產(chǎn)實(shí)踐，2007福建尤溪當(dāng)?shù)卦耘喾绞剑盒兄昃?×5寸N肥前后比8:2精確定量栽培方式:行株距9×4寸N肥前后比5.5:4.5再生稻-成熟期再生稻超高產(chǎn)實(shí)踐，2007福建尤溪一塊田施肥能獲得的最高產(chǎn)量主要由當(dāng)?shù)毓?、溫、水資源特點(diǎn)決定。在特定地區(qū)內(nèi)，影響不同田塊之間產(chǎn)量差異的因素有哪些？土地肥沃和貧瘠在本質(zhì)上是什么？有人認(rèn)為多施有機(jī)肥能改善土壤質(zhì)地，進(jìn)而容易實(shí)現(xiàn)高產(chǎn)，你認(rèn)為這種說法有何局限性？傳統(tǒng)栽培多限于經(jīng)驗(yàn)，比如說肥田少施點(diǎn)肥、瘦田多施點(diǎn)肥。你認(rèn)為肥田和瘦田應(yīng)如何施肥才能獲得最大產(chǎn)量或最高肥料利用效率？一塊田不施肥能獲得400kg產(chǎn)量，施肥后能獲得的最高產(chǎn)量是多少？如何協(xié)調(diào)產(chǎn)量和肥料利用效率？思考題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