Review Questions for Hour Exam 2 (Fall 2014) Soil Organic Matter - What is soil organic matter and what are its functions? - How does residue decomposition vary with C/N ratio? - How do soil orders vary in organic matter content? - What effect has synthetic N fertilization had on soil organic matter levels in the Morrow Plots? Soil Water - How do polarity and H bonding affect the properties of water? - What causes capillarity? - What affects the height and rate of capillary rise in soils? - How does water flow in relation to potential? - What are the four potentials that determine the energetics of soil water? Which one is most important? - How is soil water classified with respect to saturation, field capacity, the wilting coefficient, the hygroscopic coefficient, and oven‐dryness? - How is gravimetric water content calculated? - What two factors cause infiltration, and how do infiltration rates compare for fine‐ versus coarse‐ textured soils? - What distinguishes saturated from unsaturated flow? - Why and how is water flow restricted in stratified soils? - How does water move by vapor equalization? - How do texture and organic matter con tent affect soil water availability? The Hydrologic Cycle - How has water management changed over time, and what is the major use today? - How is water balance estimated for a watershed? - How do foliar interception and runoff compare for a deciduous forest versus a corn field? - How does cover cropping help to increase soil water storage? - What is water use efficiency, and how does it compare for arid versus humid regions? - How can evaporation and transpiration be controlled? - What are furrow, basin (flood), sprinkler, and drip irrigation? Which is most efficient, and why? - How do surface and subsurface drainage differ? Which is more important in Illinois? - How does soil type determine the agricultural need for tile drainage? - How does subsoil permeability affect tile spacing and depth? Soil Management & Erosion - How does geological erosion differ from human‐accelerated erosion? Which one predominates today? - How does water erosion occur? What is the role of raindrop impact versus runoff? - What are the three types of water erosion? - What factors affect water erosion, and how are they represented in the Universal Soil‐Loss Equation (USLE)? - What factors affect soil erodibility? - How does terracing reduce water erosion? - How do conservation tillage systems reduce water erosion, and which one is most effective? - How does wind erosion occur, and what is the main transporting process? - What factors affect wind erosion, and how can it be controlled? Soil Aeration & Temperature - How are soils aerated? - How and why does soil air differ in composition from ambient air? - What changes occur when a soil is waterlogged? - What is redox potential (Eh), and how does it relate to soil aeration? - How does soil temperature affect aeration status? - How do plants adapt to poor soil aeration? - What are the two fundamental requirements that define a wetland soil? - What are three properties that can be used as hydric soil indicators? - How does frost heaving occur? - How effective is solar radiation for heating the soil? - How is soil heating affected by albedo and aspect? - How do growing plants cool the soil? - How does evaporation cool a wet soil? - What can be done to manage soil temperature? Colloidal Properties - What are the two sources of negative charge on clay minerals? - Classify the following as 1:1, 2:1, or 2:1:1 clay minerals: ‐ Kaolinite ‐ Montmorillonite ‐ Vermiculite ‐ Illite ‐ Chlorite - Is this a 1:1 or 2:1 clay mineral, and where is the isomor2phous substitution? ‐ (Al2‐xMgx)Si4O10(OH)2∙nH2O ‐ Al4Si4O10(OH)8 ‐ [K2‐x(Ca,Mg)x](Si4‐yAly)Al2O10(OH)2∙nH2O ‐ Mgn(H2O)6(Si4‐xAlx)(Al2‐yFey)O10(OH)2∙nHO - Is cation‐exchange capacity (CEC) directly related to unit‐layer charge? - For what kind of soils would hydrous oxides be an important source of CEC? - How is CEC measured? - Which cation is held most tightly to exchange sites? Which is held least tightly? ‐ Ca2+ ‐ Mg2+ ‐ K+ ‐ Na+ ‐ H+ - Which type of soil colloid is highest in CEC? ‐ Clay minerals ‐ Hydrous oxides ‐ Organic matter - Which type of soil colloid is highest in anion‐exchange capacity (AEC)? ‐ Clay minerals ‐ Hydrous oxides ‐ Organic matter - What is the source of positive charge for AEC? - How does soil acidity affect CEC and AEC? - How does soil weathering affect CEC and AEC? - How are nonpolar organic compounds retained in soils?