Soil Acidity Alkalinity Salinity Why are weak acids buffered but strong acids are not Soil pH is strongly buffered so weak acids get buffered at do not affect soil pH while strong acids do What is pH and how does it relate to H concentration pH is the acidity or alkalinity of level of soil Acid H donor lots of H Base H acceptor little H What are the two forms of soil acidity and which one is measured as soil pH H and H3O and H3O is measured as soil pH What effect does liming have on CEC It raises the pH level of soil to a more alkaline level which will raise CEC How does Al become a source of soil acidity When H comes off of Al clay minerals or hydrous oxides since it is a souluble ion maybe or in the process of hydrolysis How does rainfall acidify soil Causes the following Leaching of anions causes leaching of cations Basic cations mainly Ca2 are lost Acid rain What is base saturation The of bases saturated in the soil See Review Question 100 TEB CEC TEB Total Exchangeable Bases CEC Cation Exchange Capacity What is CaCO3 equivalent CCE The acid neutralizing capacity of a liming material expressed as a percent by weight of pure CaCO3 What are the two essential functions of liming a material To supply a basic cation that will replace exchangeable H or Al More abundant than acidic cations Retained less tightly than acidic cations Supplies H2SO4 and HNO3 Insignificant in Illinois 0 To inactivate the H released into the soil solution Which amendments can be used to acidify soil and how do they differ Elemental sulfur S Most efficient source of acidity Acidification results from microbial activity Requires a few weeks Slower in cold soils Sulfuric acid H2SO4 Fast acting Rough on applicator equipment Aluminum sulfate Al2 SO4 3 Hydrolysis generates acidity Fast acting but expensive Can lead to Al toxicity Ferrous sulfate FeSO4 Hydrolysis generates acidity Supplies Fe as a micronutrient How do saline saline sodic and sodic soils differ Saline White alkali soils Salt crust at surface due to Cl and SO4 Flocculated permeable Salts can be removed by leaching with water Sodic Black alkali soils Dispersed organic matter at the surface High pH due to Displacement of exchangeable Na by H clay Na H OH clay H Na OH Precipitation of Na2CO3 an alkaline buffer Na2CO3 2H2O 2Na 2OH H2CO3 Dispersed impermeable Saline Sodic White salt crust at surface Flocculated permeable Salts cannot be removed by leaching Na2CO3 will dissolve in leaching water 2 of Na Ca and Mg Na will displace exchangeable Ca and Mg Ca and Mg carbonates will precipitate and be flushed out in drainage water A sodic soil will result Soil Organisms Ecology What is the difference between flora and fauna Flora plants nonanimal microbes Fauna animals What kind of organisms are primary producers primary consumers etc What are their metabolic groupings Primary Producers At the base of the food web Mainly vascular plants But also Mosses Algae Lichens and some bacteria Most are capable of photosynthesis CO2 is converted to organic substrates These substrates supply other organisms with Organic C And chemical energy Primary Consumers Animals and microflora that feed on plant tissues Herbivores eat live plants Examples include Nematodes Ants Mice Rabbits Most are considered pests but some do more good than harm Secondary Consumers Soil microflora can feed on primary consumers This group also includes carnivores that consume other animals such as Centipedes Mites Springtails Predatory nematodes Spiders Snails Their grazing can stimulate microbial growth and activity Tertiary consumers Other carnivores prey on secondary consumers Examples include Ants that eat Centipedes Spiders Mites And other insects Robins that pull earthworms from their burrows Predation releases nutrients What kind of organisms are classified as Predators Organisms that is hunting Herbivores Organisms that eats living plants Detritivores Organisms that eat decomposing plant and animal parts as well as feces Bacterivores Organisms that eat bacteria Which two groups of organisms are the main source of soil biomass Fungi and plant roots How do earthworms ants termites nematodes and fungi affect plants Increase soil aeration Increase N cycling Can kill plants if they eat it What is the rhizosphere The rhizosphere is the narrow region of soil that is directly influenced by root secretions and associated soil microorganisms What is the metabolic classification for the most soil bacteria Heterotrophic organism that uses organic carbon for growth rather than fixing carbon from atmosphere How do actinomycetes differ from bacteria and fungi They can decompose more resistant substrates in igneous rocks Biotic Cycling of N S Where does the earth s N occur 98 in the Lithosphere crust as fixed NH4 Vast majority of remaining is in the air and is ultimate source of N for living systems atmosphere 78 N What are the soil forms of N Total content Surface soil 0 06 0 3 N 1200 6000 lb A 6 Subsoil 0 02 N Organic soil up to 3 5 N Organic forms of N 95 of total N in most surface soils Derived from living organisms Inorganic forms of N Typically 2 5 of soil N nitrate N2 dinitrogen N2O nitrous nitrite NO3 ammonium NH3 ammonia NO2 Major forms NH4 oxide What is the difference between symbiotic and nonsymbiotic N2 fixation Symbiotic N2 fixation Legumes Associations with Rhizobium or Bradyrhizobium Fixation occurs in root nodules Amount of N fixed varies widely Fixation reduced by Soil acidity Plant stress NO3 availability Legumes take up soil N Nonsymbiotic N2 fixation Major organisms Photoautotrophs Mainly blue green algae Important in rice paddies Heterotrophs Such as Azotobacter Significance Very limited because of the need for Light Organic C What are the microbial processes known as Mineralization Organic N being changed into NH4 by microbes Immobilization NH4 and NO3 Nitrification A 2 step oxidation Step 1 2NH4 3O2 being changed to 2NO2 O2 being changed to 2NO3 Step 2 2NO2 This is carried out by soil bacteria Denitrification An anaerobic process N gases formed by reduction of NO3 being changed to NO2 NO3 This occurs in waterlogged soil What metabolic groups of soil microbes are responsible for these four processes Bacteria Actinomycetes Fungi What processes lead to gaseous loss of N from soils Denitrification and kinda from nitrification which can lead to denitrifiation How is fertilizer N content expressed being changed into Organic N by microbes being changed to NO to N2O to N2 2H2O 4H 2 82 N