NRES 201 Lecture 35 Outline of Last Lecture I The Nitrogen Cycle a Nitrification b Denitrification c Plant Uptake d Ammonium Fixation e Ammonia Volatilization f Leaching of Nitrate Nitrogen Fertilizer Sources Outline of Current Lecture II Comparison of nitrogen and sulfur III Sulfur in plants IV Sulfur in soils V The sulfur cycle VI Sulfur fertilizer sources Current Lecture Similarities between Nitrogen and Sulfur Forms of occurrence as organic and inorganic compounds Presence in soil organic matter in microbial biomass and humus Subject to microbial transformations for production of energy and biomass Behavior as mobile nutrients o N as NO3 o S as SO4 Loss from soil by leaching or volatilization Differences between Nitrogen and Sulfur Elemental occurrence N as a gas and S as a solid Mineralogical occurrence o N does not occur in minerals except as fixed NH4 o S occurs in many minerals such as pyrite and gypsum Biological Fixation Major soil input of N but not S Volatilization from Soil o N as simple inorganic compounds o S as volatile organic compounds Plant demand Much greater for N than for S Fertilizer Status 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 o N is the most important fertilizer nutrient o S fertilizers are seldom applied but may become necessary in the future due to Increase use of S free fertilizers and pesticides Higher crop yields Lower levels of atmospheric S Loss of soil organic matter from Tillage drainage and intensive N fertilization Functions of sulfur in plants Protein and Enzyme Constituent Three amino acids contain S Synthesis of chlorophyll Electron transport Constituent of plant oils especially for mustard and onion families Ester Sulfates The major form of organic S in Agricultural soils and prairie soils Lower content in forest soils Most soil S is organic in no calcareous temperate soils because SO4 leaches and organic S does not Like the N cycle Inorganic S is immobilized Organic S is mineralized Microorganisms transform inorganic S SO4 leaches S volatilizes But there are some differences Such as S and SO4 minerals SO4 can be adsorbed by clay Mineralization produces either S or SO4 Elemental S undergoes microbial transformations And organic forms of S are volatilized Annual addition of atmospheric S Greatly reduced since the 1980s Largest in the northeastern US Smallest in the western US Impact on crop production often beneficial by supplying S Losses of sulfur from soils Through crop removal o Most crops take up somewhat less S than P By leaching and runoff By volatilization volatile loss or organic S compounds from aerobic or anaerobic soils Volatilization of organic sulfur Occurs in either aerobic or anaerobic soils Probably accounts for most gaseous S loss Substantial emissions from manured soils Produces highly offensive odors Sulfur fertilizer sources Elemental S Least expensive S fertilizer Requires a few weeks Slower in cold soil Gypsum Contains 13 19 S A byproduct of coal fired power plants the P fertilizer industry
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