EVERGREEN ECOAG 2005 - Soil Nitrogen and Sulfur Dynamics lecture 2-07-06

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Soil Nitrogen and Sulfur DynamicsBiological Importance of Nitrogen and SulfurWhy consider Nitrogen and Sulfur together?Why consider Nitrogen and Sulfur together?Why consider Nitrogen and Sulfur together?Sulfur CycleNitrogen budgeting on a state-wide level, 1000 Mg Pools/Sources of NitrogenNitrogen deficiency verses excessive N fertilizerNitrogen MineralizationAmmonium and Ammonia NH4+ and NH3Nitrification by aerobic bacteria Requires oxygen, carbon source, neutral pH and available water Produces protons = acidificatSoil acidification from long-term use of ammonium containing fertilizersInfluence of soil water and seasonal soil temperatures on nitrification rates and accumulation of soil nitrateWater saturation of soil pores stops aerobic mineralization and enhances anaerobic denitrification Denitrification by heterotrophic, facultative anaerobic or anaerobic bacteria require carbon source and reduced oxygenDenitrification Process Relative production of Nitrogenous gasesReducing denitrification in paddy soils by deep fertilizer placementCan plants use organic N sources? USA Nitrogen input greatly exceeds plant uptake potentialManaging fertilizer application based on available soil nitrate level, Pre-sidedress Nitrate Test (PSNT) for Corn in the MidweSulfur cycle, elemental forms, and transformation reactionsSulfur CycleSulfur deficiency symptomsMajor gains and losses of available soil sulfurSulfur acquisition by plants – airborne, soil organic matter, inorganic sulfate in the subsoilOrganic Sulfur Compounds in the Soil Sulfur Oxidation – produces protons = acidificationDeposition of airborne Sulfur as function of distance from industrial air polluterIndustrial Sulfur Deposition in Eastern USApH dependent adsorption of sulfate to 1:1 clays and oxides reduces cation leachingUnderstanding the big picture Compare and contrast N and S cyclesCalculation of N mineralizationStudy QuestionsSoil Nitrogen and Sulfur DynamicsEcological Agriculture TESC 2-7-06Steve ScheuerellBiological Importance of Nitrogen and Sulfur• Essential elements in amino acids, building blocks of all proteins• Nitrogen – nucleic acids, chlorophyll, carbohydrate utilization, makes up 2-4% plant dry matter• Sulfur – B vitamins, aromatic oils, S-S disulfide bonds affect protein tertiary and quanternary folding structure, makes up 0.15 – 0.45% plant dry matterWhy consider Nitrogen and Sulfur together?Why consider Nitrogen and Sulfur together?• Cycle through soil-plant-animal-atmosphere system• In the surface horizons of most soils, both N and S are largely found in organic forms• Can enter and leave the soil in gaseous forms• Anionic forms (nitrate and sulfate) are subject to leaching from the soil• Transformation and availability are largely functions of soil microorganisms – Mineralization from organic compounds and immobilization into organic compounds (microbial biomass)– Oxidation – reduction reactionsWhy consider Nitrogen and Sulfur together?• Air pollution issues• Sulfur –sulfur dioxide forms sulfuric acid, precipitates as acid rain, pH = 4• Nitrogen – N oxide gases form nitric acid – acid rain– N oxide gases react with VOP’s = ozone smog– NO is greenhouse gas = 300X carbon dioxide–N2O in stratosphere depletes ozone layerNitrogenCycleSulfur CycleNitrogen budgeting on a state-wide level, 1000 MgPools/Sources of Nitrogen• Atmosphere 78% N2, traces of N oxide gases and NH3• Soils range from 0.02 – 0.5% N– Average soil N = 0.15%– Hectare contains 7000 kg N– 95-99% of soil N is in organic compounds• Fertilizers– Based on Urea, Ammonia, and Nitrate– Haber-Bosch process for converting N2 to NH3• High temperature and pressure reaction uses natural gasNitrogen deficiencyversesexcessive N fertilizerNitrogenCycleNitrogen Mineralization• Microbial decomposition of organic matter releases amine compounds• Ammonification• Amines are hydrolyzed to ammonium•R-NH2+ 2H2O OH-+ R-OH + NH4+• Reverse reaction is microbes immobilizing ammonium to build biomassAmmonium and AmmoniaNH4+ and NH3• Environmental conditions favoring loss of NH3–pH > 7– High temperatures– Drying soil• Ammonium fixation by 2:1-type clay mineralsNitrification by aerobic bacteriaRequires oxygen, carbon source, neutral pH and available waterProduces protons = acidification of the soilanion molecule leaches with mass flow of waterNitrate, page 552Urea and ammonium fertilizers cause soil acidificationSoil acidification from long-term use of ammonium containing fertilizersInfluence of soil water and seasonal soil temperatures on nitrification rates and accumulation of soil nitrateWater saturation of soil pores stops aerobic mineralization and enhances anaerobic denitrificationDenitrification by heterotrophic, facultative anaerobic or anaerobic bacteriarequire carbon source and reduced oxygenValence state of nitrogenDenitrification ProcessRelative production of Nitrogenous gasesReducing denitrification in paddy soils by deep fertilizer placementCan plants use organic N sources?• Until recently only believed that plants take up inorganic N – NH4+and NO3-• Soluble Organic Nitrogen (SON)– SON can be at same quantity in soil as inorganic forms of N– Plant uptake mechanisms not well understood– SON can leach out of soil profile, causing pollution problemUSA Nitrogen input greatly exceeds plant uptake potentialNote that this doesn’t estimate losses due to nitrate leaching, denitrification, or soil accumulationManaging fertilizer application based on available soil nitrate level, Pre-sidedress Nitrate Test (PSNT) for Corn in the MidwestSulfur cycle, elemental forms, and transformation reactions• Elemental sulfur – S• Organic sulfur – carbon-based compounds• Sulfides• SulfatesSulfur CycleSulfur deficiency symptomsMajor gains and losses of available soil sulfurSulfur acquisition by plants – airborne, soil organic matter, inorganic sulfate in the subsoilMineralization rate dependson moisture, temperature,aeration, and pH – same factors as for Nitrogenmineralization.Organic Sulfur Compounds in the Soilmicrobes can mineralize SO4directly from estersSulfur Oxidation – produces protons = acidification2Sulfur ReductionPage 584Deposition of airborne Sulfur as function of distance from industrial air polluterIndustrial Sulfur Deposition in Eastern USApH dependent adsorption of sulfate to 1:1 clays and oxidesreduces cation


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EVERGREEN ECOAG 2005 - Soil Nitrogen and Sulfur Dynamics lecture 2-07-06

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