我国土壤资源的现状及特点 (48).ppt

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1、7.2 Transformation and regulation of soil nitrogen cycle土壤氮素的循环转化与调控Soil nitrogen transformationOrganic nitrogen Ammonium NH4+Ammonification Nitrate NO3-Organic nitrogen NH3N2、NO、N2ONO3-in groundwaterAdsorbed or fixed by clay colloidsImmobilization NitrificationDNRAVolatilization DenitrificationAdso

2、rption or fixationLeaching lossDiagrammatic sketch of soil nitrogen transformation Immobilization Note:DNRA means Dissimilatory Nitrate Reduction to Ammonium Soil nitrogen transformationOrganic nitrogen mineralization Nitrogenous organic compounds were decomposed into ammonium nitrogen under the mic

3、robial activity(divided into two processes).Definition Hydrolysis process Proteinpolypeptide Amino acids,amides,etcPeptide enzymePeptide enzyme Hydrolysisenzyme Ammonification processsoil microbe enzymeRCHNH2COOH+O2 RCH2COOH+NH3+EHydrolysisenzyme Microbial immobilization Soil ammonium and nitrate ni

4、trogen were assimilated into organic forms by soil microbe.Definition:Process:Organicnitrogen Microbial immobilizationAmmoniumNH4+Microbial immobilization Nitrate NO3-Soil nitrogen transformationAmmonium fixation and release,adsorption and desorptionAdsorption of ammonium ions by soil colloids as ex

5、changeable ammonium.Adsorption of ammonium：The exchangeable ammonium desorbed into soil solution.Desorption of ammonium：Ammonium ion can become entrapped or fixed within cavities in the crystal structure of certain 2:1-type clay minerals which transferred into fixed or non-exchangeable ammonium.Fixa

6、tion of ammonium：The release of fixed ammonium under of microorganism,physics and chemistry activities.Ammonium release:Soluble ammoniumExchangeable ammoniumClay mineral fixed ammoniumSoil nitrogen transformationNitrification Nitrification is soil ammonium oxidized into nitrates under the soil micro

7、be activities(Divided into two processes).Definition:Nitrification process:Nitrifying process:nitrite bacteria 2NH43O2 2NO2 2H2O+4H+660 kJ nitrifying bacteria 2NO2O22NO3+167 kJ Soil nitrogen transformationDenitrification Nitrate or nitrite reduced to gaseous nitrogen(molecular nitrogen and nitrogen

8、oxides).Definition:2HNO32HNO2H2N2O2-2H2O4H+-2H204H+N2O+2H2O-4H22NON2+2H+-2H2O+2H+-H2O Occurred in anaerobic condition,such as flooding or compaction inducing soil poor aeration,soil with high pH and C/N ratio.Soil nitrogen transformationVolatilization of ammonium Under neutral or alkaline conditions

9、,the NH4+transferred into NH3 and volatilized from soil.DefinitionProcess NH4 NH3 H OH-Effect factors:Soil nitrogen transformationlSoil pH;lSoil CaCO3 content;lTemperature:showing a positive correlation;l Fertilization depth;lSoil NH4+content.Nitrate reductionNO3 NH4Nitrate leaching lossNO3-N leachi

10、ng with soil water,reached to 5%-10%of the nitrogen application.Anaerobic conditionsNitrate reductaseSoil nitrogen transformationRegulation of soil nitrogenMaintaining soil nitrogen balance:soil organic matter balance is the basis of nitrogen balance.Regulating the C/N ratio,applied organic and inor

11、ganic fertilizer for agricultural production.TimeN assimilation and mineralization a:N mineralizationb:N assimilationa=bC/N=25:1C/N25:125:1aabMineral N assimilatedSupply more mineral NThe relationship between C:N ratio and soil nitrogen surplus during SOM decomposition process Maintaining soil nitro

12、gen balancelIf SOM is relatively rich,we can apply green manure and other fresh organic fertilizer to induce positive priming effect,promoting original organic nitrogen mineralization and turnover.lIf SOM is relatively poor,we can apply crude organic fertilizer rich in lignin to produce negative pri

13、ming effect,increasing the SOM and N accumulation.Regulation of soil nitrogen soil organic matter balance is the basis of nitrogen balance.Using“priming effect”to regulate SOM and nitrogen balance For paddy soil,ammonium nitrogen should be applied to the aerobic horizon or reduction horizon?Why?Impact of flooding and irrigationRegulation of soil nitrogenSchematic diagram of nitrogen denitrification loss in paddy soilThank you