Soil Acidity, Alkalinity, & SalinityWhy 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 • More abundant than acidic cations • Retained less tightly than acidic cations- Acid rain • Supplies H2SO4 and HNO3 • Insignificant in Illinois What is % base saturation?The % of bases saturated in the soil (See Review Question)100*(TEB/CEC)TEB= Total Exchangeable BasesCEC= 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 AlTo inactivate the H+ released into the soil solution Which amendments can be used to acidify soil, and how do they differ?Elemental sulfur (S 0 ) Most efficient source of acidityAcidification results from microbial activityRequires a few weeksSlower in cold soils Sulfuric acid (H2SO4)Fast-actingRough on applicator equipment Aluminum sulfate [Al2(SO4)3]Hydrolysis generates acidityFast-acting but expensiveCan lead to Al toxicity Ferrous sulfate (FeSO4)Hydrolysis generates aciditySupplies Fe as a micronutrient How do saline, saline/sodic, and sodic soils differ?SalineWhite alkali soilsSalt crust at surface due to Cl – and SO42- of Na, Ca, and MgFlocculated, permeableSalts can be removed by leaching with water SodicBlack alkali soilsDispersed organic matter at the surfaceHigh pH due to:- Displacement of exchangeable Na+ by H+clay-Na + H+ + OH- clay-H + Na+ + OH-- Precipitation of Na2CO3, an alkaline bufferNa2CO3 + 2H2O 2Na+ + 2OH- + H2CO3Dispersed, impermeable Saline/SodicWhite salt crust at surfaceFlocculated, permeableSalts cannot be removed by leaching- Na2CO3 will dissolve in leaching water- 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 & EcologyWhat is the difference between flora and fauna?Flora: plants + nonanimal microbesFauna: animals What kind of organisms are primary producers, primary consumers, etc.? What are their metabolic groupings?Primary ProducersAt the base of the food webMainly vascular plantsBut also: Mosses, Algae, Lichens, and some bacteriaMost are capable of photosynthesisCO2 is converted to organic substratesThese substrates supply other organisms with:- Organic C- And chemical energy Primary ConsumersAnimals and microflora that feed on plant tissuesHerbivores eat live plants- Examples include: Nematodes, Ants, Mice, Rabbits- Most are considered pests but some do more good than harm Secondary ConsumersSoil microflora can feed on primary consumersThis group also includes carnivores that consume other animals, such as: Centipedes, Mites, Springtails, Predatory nematodes, Spiders, SnailsTheir grazing can stimulate microbial growth and activity Tertiary consumersOther carnivores prey on secondary consumersExamples include:- Ants that eat: Centipedes, Spiders, Mites, And other insects- Robins that pull earthworms from their burrowsPredation 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.Biotic Cycling of N & SWhere does the earth’s N occur?98% in the Lithosphere (crust) as fixed NH4+ in igneous rocks.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 contentSurface soil: 0.06-0.3% N (1200-6000 lb/A-6”)Subsoil: <0.02% NOrganic soil: up to 3.5% N Organic forms of N>95% of total N in most surface soilsDerived from living organisms Inorganic forms of NTypically 2-5% of soil NMajor formsNH4+(ammonium), NH3(ammonia), NO2-(nitrite), NO3-(nitrate), N2 dinitrogen, N2O nitrous oxide What is the difference between symbiotic and nonsymbiotic N2 fixation?Symbiotic N2 fixation---Legumes---Associations with Rhizobium or BradyrhizobiumFixation occurs in root nodulesAmount of N fixed varies widelyFixation reduced by: Soil acidity, Plant stress, NO3- availabilityLegumes take up soil N Nonsymbiotic N2 fixation---Major organisms---Photoautotrophs- Mainly blue-green algae- Important in rice paddiesHeterotrophs- 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- being changed into Organic N by microbes-Nitrification:A 2-step oxidationStep 1: 2NH4+ + 3O2 being changed to 2NO2- + 2H2O + 4H+Step 2: 2NO2- + O2 being changed to 2NO3-This is carried out by soil bacteria. -Denitrification:An anaerobic processN gases formed by reduction of NO3-NO3- being changed to NO2- being changed to NO to N2O to N2This occurs in waterlogged soil What metabolic groups of soil microbes are responsible