UIUC NRES 201 - Biotic Cycling of Nitrogen and Sulfur II (4 pages)

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Biotic Cycling of Nitrogen and Sulfur II



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Biotic Cycling of Nitrogen and Sulfur II

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Lecture number:
34
Pages:
4
Type:
Lecture Note
School:
University of Illinois at Urbana, Champaign
Course:
Nres 201 - Introductory Soils
Edition:
1
Documents in this Packet

Unformatted text preview:

NRES 201 Lecture 34 Outline of Last Lecture I Nitrogen in plants II Natural occurrence of nitrogen III Nitrogen in soils IV The nitrogen cycle a Biological Fixation b Atmospheric Deposition c Mineralization d Immobilization Outline of Current Lecture V The Nitrogen Cycle a Nitrification b Denitrification c Plant Uptake d Ammonium Fixation e Ammonia Volatilization f Leaching of Nitrate VI Nitrogen Fertilizer Sources Current Lecture Nitrification 2 Step Oxidation Step 1 2NH4 3O2 2NO2 2H2O 4H Step 2 2NO2 O2 2NO3 Carried out by soil bacteria Step 1 is due to Nitrosomonas Step 2 is due to Nitrobacter Both groups are chemoautotrophs o C from CO2 o Energy from oxidizable N Opposing effects on plan N availability The downside NO3 is more prone to loss than NH4 through leaching and denitrification The upside Immobilization by soil microbes is reduced by their strong preference for NH4 over NO3 These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Favored by Alkalinity o Optimum pH 8 0 8 5 o Limiting promoted nitrification o Nitrification produces acidity Soil aeration both steps require O2 Adequate Soil Moisture o Field capacity optimal o Some nitrification at the wilting point and also in flooded soils Denitrification An Anaerobic Process N gases formed by reduction of NO3 Occurs in waterlogged soil A bacterial process that involves mostly heterotrophs an can live with or without O2 Favored by o Waterlogging Controls aeration Large losses in ponded areas Very little loss below field capacity o Decomposable organic matter Energy source for denitrifies Not much denitrification in subsoil o Supply of NO3 and NO2 NO2 favored over NO3 High NO3 increases N2O N2 ratio o Warm Temperatures o Alkalinity Like nitrification Acidity increases the N2O N2 ratio Environmental implications o Beneficial effect Less NO3 leaching o Detrimental effect Emission of N2O greenhouse gas that promotes



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