Study guide questions for Midterm 1 spring 2016 Please bring an appropriate calculator for the exam A simple calculator i e a TI 30 scientific calculator or below which allow you to do common and natural logarithm calculations is needed Scientific calculators without any programming function are accepted You may not use calculators in your cell phone MP3 player tablet etc during exams If you forget an appropriate calculator you will take the exam without calculators If you have any questions about the type of calculators that are accepted or if you want to make sure your calculator is alright to use please ask the instructor Ch4 How do soil scientists define soil color hint three components of color Hue redness or yellowness Chroma intensity or brightness gley low chroma reduced iron bright oxidized iron Value lightness or darkness What are causes of soil colors 1 Organic matter content 2 Water content 3 Presence of oxidized iron and manganese oxides Please explain the relationship between texture of soil particles and surface area What are five soil properties that are influenced by the surface area SA of soil particles 1 Help the water retention 2 Help to weather minerals i e rate of nutrient release is high 3 Help the retention of nutrient and other chemicals 4 Help the particle attraction resulting in aggregation 5 Provides habitats and reactive sites for soil microbes What soil properties behavior are affected by soil separates sand silt and clay How are they affected 1 How many soil textural classes do we have Which class has most class names 12 Can you read a texture triangle REVIEW LAB 2 Know simplified Stokes law Be sure that you can do the calculation see examples on blackboard V kd 2 Define soil structure Can you name four principal shapes of soil structure Soil structure Arrangement of primary soil particles sand silt clay and organic matter Principal shapes spheroidal surface soils plate like surface and subsurface block like b horizon prism like subsoils with high sodium Do we observe all shapes regardless of depth no If not how are they distributed in surface and subsurface soils What factors are influencing the soil aggregation process Physical chemical processes 1 Attraction of clay particles Biological processes 1 Burrowing and molding activity by earthworms and termites 2 Sticky networks of roots and fungal hyphae 3 Secretion of bio adhesive by microbes bacteria and fungi Role of organic matter 1 can bind clay particles enhancing the formation of aggregates 2 Can act as energy substrates for soil organisms Does organic matter carbon affect the formation of soil aggregates Can you explain how Know particle and bulk density calculation Can you also estimate porosity see examples on blackboard Slide 31 What factors affect the bulk density Ms vs Pour space soil texture depth increases with increasing depth Do our soil management practices affect the bulk density If so how do they affect What soil properties affect the soil strength What factors affect the total porosity 2 Name three types of macropore Interped pores form between loosely packed granules or between blocky and prismatic peds Biopores form by organisms worms and roots tubular shape What types of micropore are important for biological activities 1 Mesopores 0 03 0 08 mm retain water well by capillary action 2 Micropores 0 005 0 03 mm found in interapeds retain water that plant can use accommodate most bacteria What are consistence and consistency Consistence The ease with which a soil can be ruptured when force is applied or at various moisture contents Consistency The degree to which a soil resists the deformation when an object is penetrated to soil What are cohesive no cohesive and collapsible soils 1 Cohesive soils Clay content is more than 15 Two distinctive components a inherent electrostatic attraction force between clay particles and the water b frictional resistance to movement between soil particles of all size Strength of cohesive soil dramatically declines if materials are very wet 2 Non cohesive soils usually sandy soils depends on entirely frictional forces If a small amount of water bridges gaps between particles electrostatic attraction of the water for the mineral surfaces will increase the strength but 3 Collapsible soils exhibit the considerable amount of strength at low water content but they lose the strength if they become wet Soils from Southwestern U S They consist of loose dry low density materials cemented loosely packed sand by gypsum CaSO4 and clay When do they collapse When the land surface is saturated at depths greater than those reached by typical rain events Under the addition of excessive loading 3 Ch 7 What are three principal factors of O2 availability 1 Water content 2 Macroporosity 3 O2 consumption by respiring organisms What are two major mechanisms of gas exchange process at the atmosphere soil interface 1 Mass flow Less important in terms of total gas exchange 2 Diffusion The process facilitates gas to move in a direction determined by its own partial pressure How does soil air exchange at the soil atmosphere interface Pores Most of plants require oxygen but some other plants e g rice and mangrove are capable of uptaking O2 from water logged soils They are called hydrophytes What is the concentration of CO2 in air Is the CO2 concentration in soils higher or lower than that in air 0 04 higher 0 1 Name some important soil gases How do they form Methane CH4 and hydrogen sulfide H2S via organic matter decomposition 4 and ethylene C2H4 that is produced by anaerobic soil microbes What are oxidation reduction reactions tendency or potential of e to be transffered from one substance to another Why do we practice coring on turf Please explain the event in terms of oxidationreduction reaction organic matter Soil aeration is important since all aerobic respiration requires oxygen will rot otherwise Coring is one of ways to promote the oxidation of OM as well as improving the drainage Define Eh Eh is concentrations of e in the system Explain the relationship between Eh and O2 content in soils As the soil get s drier both levels rise Understand the relationship between Eh pH and electron acceptors What factors affect soil aeration Drainage of excess water Draining water in macropores facilitates the diffusion of air e g oxygen and CO2 Rates of respiration The concentration of soil O2 and CO2 is affected by respiration by soil microbes and plant roots 5 Soil heterogeneity