Review Questions for Hour Exam 1 Introduction What is soil and how is it important Soil is surface layer of earth supporting plant life Dirt soil that is out of place Importance of soil management To control soil erosion and maintain productivity by o Conservation practices o Crop rotation o Avoiding organic matter depletion o Proper nutrient and water management How has soil exploitation led to erosion Mismanagement led to serious erosion in some historical areas and US such as the Dust Bowl When and where did Dust Bowl occur It first occurred in the 1930s at time of economic depression and drought It happened first in eastern and Midwestern states and then in southern plains What were the black blizzards Dust storms that first appeared in 1935 from early March to April 14th known as Black Sunday It caused serious loss of valuable topsoil to East Coast and Atlantic Ocean and also drastic decline in wheat and cattle output Okies and exodusters headed west as a result of this What has been major type of soil erosion in Illinois Erosion has been less obvious in Illinois Damage has been done by water not wind Years of intensive tillage for row cropping converted soils to sediments They are now dredged from Illinois River in Mud to Parks Project Soils and Soil Properties Where does soil occur and what are two principal constituents Soils occur in upper part of Earth s crust It is composed of organic matter such as living organisms biomass organismal remains residues and inorganic materials such as primary materials in original rock and secondary materials by weathering What are five soil forming factors Climate organisms topography parent material time What is solum and how does it differ from regolith Which horizons are included True soil is solum It includes E horizon and contains organic layer plow layer and subsoil O A B Regolith is unconsolidated material above bedrock O A B C Regolith also consists of C horizon How does texture differ from structure Which one is affected by management structure Texture is proportion of particles by size Sand coarse Silt medium Clay fine Structure is how solid particles make an aggregate Structure is affected by management practices How is organic matter content important to soil properties and processes Organic matter has important effects on physical chemical and biological properties interacting Binding soil particles together to make aggregates Water storage and availability Microbial energy source Nutrient supplying matter What is soil solution and where in soil does it occur It is water and dissolved ions molecules and gases It is held within soil pores It is mobile in large pores but immobile in small pores What is soil atmosphere and how does it differ from ambient air It is gases that occupy soil pores not filled with water It differs from air that it has less O2 more CO2 and more humidity than air What is the typical composition of loam surface soil A mixture with equal properties of sand silt and clay What are six functions of soil 1 Medium for plant growth o Plant support o Aeration O2 and CO2 o Supplies water o Insulator for root system o Controls toxicities o Nutrient supply structural nutrients carbon hydrogen oxygen water and CO2 2 Regulator of water supplies 3 Waste recycling system 4 Habitat for soil organisms 5 Engineering medium 6 Atmospheric modifier Which three nutrient elements are not supplied by soil minerals Carbon hydrogen and oxygen What is pedosphere and how is it important Pedosphere soil it important because it is outermost layer of earth where soil forms and life begins How are hue value and chroma represented by Munsell system Hue Munsell color charts Dominant by spectral colors Varies by chart o Red is first o Brown next o Yellow last Value Lightness or darkness of grayscale mask applied to hue Decreases vertically from pure white 10 to pure black 0 Chroma Intense or brightness of hue Increases toward right where the hue is brightest What effect does organic matter have on soil color Organic matter content means dark coatings on mineral surfaces What are size ranges for sand silt and clay Sand 0 05 2 0 mm Silt 0 002 0 05 mm Clay 0 002 mm What is meant by the term loam A mixture with equal properties of sand silt and clay How do textural classes differ in sand silt and clay content Sand Feels gritty Individual particles visible to naked eye Round or angular Composed mainly of quartz SiO2 Very low in specific surface area Does not cohere to form aggregates Low capacity to store water and nutrients No stickiness or plasticity cannot be molded Silt Feels silty like flour Cannot see particles in naked eye Low in specific surface area Limited capacity to store water Highly susceptible to wind and water erosion Limited capacity to store water and nutrients Clay Particles invisible to naked eye Sticky and plastic when wet Hard and cloddy when dry Moderate to high in specific surface area High capacity to store water and nutrients Tiny pores limit water movement and aeration What are different types of soil structure and where do they occur in profile Structureless single grained loose sand or dust Massive very large clods difficult to break Spheroidal o Granular or crumb more porous o Prominent in surface soils under grassland where earthworms have been active o Key role in organic matter o Conductive to plant growth o Greatly affected by soil management Plate like o Horizontal peds or plates o Found in surface and subsurface horizons o Possible origins Soil forming processes most common Parent material water or ice laid Mechanical compaction of clayey soils Block like o Angular sharp edges or sub angular rounded o Usually found in B horizons o Good for drainage aeration and root growth Prism like o Columnar rounded tops or prismatic flat tops o Usually found in B horizons o Most common in arid and semi arid regions What soil properties affect consistence Soil moisture content completely characterized when evaluated for dry moist and wet soil Dry Consistence Rated as loose soft slightly hard hard very hard or extremely hard Increased by clay Decreased by organic matter Important to root penetration and tillage Moist Consistence Rated as loose very friable friable firm very firm or extremely firm Determined at 50 moisture Moist soil fractures more easily than dry soil Wet Consistence Determined by saturation Rated for plasticity and stickiness Both properties increase clay content Soil Formation What is original source