Study guide questions for Midterm #1, spring 2016Please 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 tomake sure your calculator is alright to use, please ask the instructor. Ch4How do soil scientists define soil color (hint: three components of color)?Hue- redness or yellownessChroma- intensity or brightness (gley low chroma, reduced iron..bright=oxidized iron)Value- lightness or darknessWhat are causes of soil colors?1. Organic matter content2. Water content3. Presence of oxidized iron and manganese oxidesPlease 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 chemicals4. 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?1How many soil textural classes do we have? Which class has most class names?12Can you read a texture triangle?REVIEW LAB 2Know “simplified Stokes’ law? Be sure that you can do the calculation (see examples on blackboard)V=kd^2Define 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?noIf 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 31What factors affect the bulk density?Ms/vsPour 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?2Name three types of macropore.Interped pores: form between loosely packed granules or between blocky and prismatic pedsBiopores: form by organisms (worms and roots) tubular shapeWhat types of micropore are important for biological activities?1) Mesopores (0.03-0.08 mm): retain water well by capillary action2) Micropores (0.005-0.03 mm): found in interapeds, retain water that plant can use, accommodate most bacteriaWhat 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 attractionof 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. 3Ch 7What are three principal factors of O2 availability?1) Water content2) Macroporosity3) O2 consumption by respiring organismsWhat 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 pressureHow does soil-air exchange at the soil-atmosphere interface? PoresMost 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 “hydrophytesWhat 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 decomposition4and ethylene(C2H4) that is produced by anaerobic soil microbesWhat are oxidation-reduction reactions?tendency or potential of e- to be transffered from one substance to anotherWhy do we practice “coring” on turf? Please explain the event in terms of oxidation-reduction 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 OMas well as improving the drainageDefine EhEh is “concentrations of e-” in the system.Explain the relationship between Eh and O2 content in soils.As the soil get’s drier, both