GEOG 3018 - Final Exam Questions The following are sample multiple choice questions taking from Kevin Hamdan's sample exam. HarrisonReed published on December 19, 2018 Stacked 1/38 Compared to upland soils, wetland soils would be characterized by an abundance of _____. Methane CO2 NO3- SO42- Fe3+ 2/38 The P factor in the Universal soil-loss equation is concerned with all but one of the following: Contour Tillage Strip-Cropping Soil Erodibility Terraces Vegetative Covers 3/38 Other things being equal, a soil with 30% clay of the ____ type would be expected to have the greatest potassium -fixing capacity. Allophanic 2:1 1:1 Crystalline Iron Oxide 4/38 The swelling/shrinking tendency of some silicate clay minerals is due primarily to _____. the presence of cations attracted by the negative charges on the internal surfaces the movement of water molecules in and out of the interlayers of the crystal varying thickness of the film of water covering the external surface of the particles expansion in the width of the interlayers due to movement of larger ions such as K+ the high Mg2+ contents in the octahedral layers 5/38 In explaining erosion processes to a friend, which of the following would you say aboutaccelerated erosion? It refers to sediment carried by water flowing at ever greater velocity. It involves a much less rapid process than geological erosion. It is greatly enhanced by the splash effect of raindrops impacting bare soil. It is increasing in intensity in the United States, especially in the past 10 years. it removes more nitrogen from the surface soil than calcium. 6/38 The process of ______ releases soluble nitrogen as the result of the breakdown of nitrogen-rich organic compounds. Nitrification Denitrification Symbiosis Volatilization Mineralization 7/38 The great majority of nitrogen (95 to 98%) in soils can be found in the form of _____. Primary Minerals Secondary Minerals Dissolved Cations Dissolved Anions Organic Compounds 8/38 Soils high in organic matter commonly hold more available water than comparable soils with lower organic matter levels. This is most likely due to what characteristics of the high O.M. soils larger micro pore space lower permanent wilting percentage higher field capacity higher capacity of the O.M. to hold water tightly higher clay content 9/38 The electronegative charge on 2:1 type silicate clays is due primarily to _____. ionization of surface OH groups substitution of one metallic atom for another in the crystal structure of the clay extremely small size of the individual colloid particles the effect of pH on the presence of H+ ions in the exchange complex the preponderance of tetrahedral sheets compared to octahedral sheets 10/38 Suppose leaves containing 1000 kg of carbon fell to the forest floor in a humid temperateenvironment. After a year or so, how many kg of that carbon would you expect to remain in the soil as microbial biomass and humus? 10 20 200 400 800 11/38 The following are characteristics of a water molecule. The H to O to H angle is approximately 90 degrees Celsius. The two H atoms are on diametrically opposite ends of the molecule. It has a positive and a negative side. It is attracted to surfaces with negative but not positive charges. It is held in soils by adhesion but not adsorption. 12/38 Which of the following is not a characteristic of soil colloids? very small size high external surfaces electronegative charges ability to exchange ions with the soil solution low water holding capacity 13/38 Which of the following statements is true? Sheet erosion is most obvious from a distance. Gully erosion carries the most sediment away from lands in the United States. Rill erosion is the most serious in forested areas Rill erosion is initiated before water concentrates in small 1-2 cm channels Rill erosion channels can be removed by ordinary cultivation. 14/38 The R factor of the Universal soil-loss equation is concerned with _____. Soil Erodibility Residue Cover on the Soil Terraces Climate Slope Steepness 15/38 Two soil samples, A & B, at different soil moisture levels are placed in contact with each other. Water will more likely move from soil A to soil B if their water potentials, expressed in kPa, are: A=-5; B=+5 A=-5; B=-5 A=-20; B=-10 A=-30; B=-40 A=-100; B=-50 16/38 The opposite process from mineralization is _______. Immobilization Nitrification Denitrification Ammonification None of the Above 17/38 The bulk of gaseous interchange in soils takes place by _____. Mass Flow Partial Pressure of N2 Diffusion Dissolution in Water Respiration 18/38 In order for nitrate to form from soil organic matter, _____ must be present in the soil. Nitrosomonas Nitrobacter Either A or B Both A and B None of the Above 19/38 Conservation tillage systems are said to have all of the following advantages but one overconventional tillage systems its labor and energy requirements are lower it encourages higher microbial population numbers in the soil it involves the use of less toxic weed control practices it reduces soil erosion 20/38 Capillarity in soils _____. involves both adhesion and cohesion is enhanced by the symmetrical nature of the water molecule is independent of the matric potential in soils is not involved in the process of water uptake from soils does not account for unsaturated water movement in soils 21/38 A soil has a maximum potential cation exchange capacity of 30 cmolc/kg and has a 50% acid saturation. If you want to decrease the percentage acid saturation to 10%, how many cmolc of calcium would it take to replace the exchangeable acid cations per kg of soil? Assume all the calcium exchanged with aluminum 30 40 6 12 5 22/38 Some soil colloids exhibit positive charges under highly acid conditions. To what are these charges likely due? protonation of some hydroxy groups by excess H+ ions the adsorption of Al3+ ions on the colloid the release of some OH ions leaving an unsatisfied positive charge on the colloid substitution of lower valent atoms for higher valent atoms in the octahedral sheet increase in the level of H+ ions on the exchange complex 23/38 Which cation would you expect to be mostly tightly held in a soil at pH 4.5? K+ Ca2+ Al3+ Mg2+ Na+ 24/38 Which of the following does not describe aluminum hydroxy ions (such as Al(OH)2+) in the soil? They are more prominent in acid than in neutral soils. They affect the pH of the soil solution through hydrolysis. They block negative sites on some clays thereby reducing the cation exchange capacity. They influence the swelling of some clays by entering into the interlayer spaces. They are commonly applied to help reduce the soil pH for acid-loving plants. 25/38 Which of the following actions would best assure good aeration in a soil? increase the soil temperature add organic residues use a plastic mulch use cover crops, especially legumes remove excess water 26/38 Humus is an important soil colloid. It differs from 2:1 type minerals in all but one of the following characteristics (select the one). structural framework of the particles CEC dependence on soil pH influence of isomorphous substitution capable of adsorbing cations influence on soil aggregate stability 27/38 A well aerated soil is characterized by a relative abundance of _____. Micropores Fe2+ Ions NH4+ Ions NO3- Ions Methane Gas 28/38 The universal soil-loss equation (USLE) suggests that soil erosion loss is a product of all but one of the following factors: Soil Drainage Climate Slope Length Sloped Steepness Vegetative Cover 29/38 The negative charges associated with smectite clay crystals are due mostly to _____. isomorphous substitution of Mg for Al in the octahedral sheet substitution of Al for Mg in the tetrahedral sheet high pH associated with the formation of the mineral substitution of Si for Al in the tetrahedral sheet OH groups on the external surface of the crystal 30/38 Approximately what percentage of the P in surface soils is typically found in organic forms? 0.1 to 0.5% 1 to 5% 5 to 15% 25 to 75% 95 to 98% 31/38 Which of the following best characterizes the field capacity of a soil? maximum capacity of a soil to hold water water content of a soil with water potential of about -10 kPa the total capillary water in a soil a wetted soil prior to the removal of the gravitational water soil with water potential of -1500 kPa 32/38 To avoid a nitrate depression period when it is added to a garden soil, about how many kg of nitrogen must be added to a load of grass clippings that contains 1000 kg of C and 25 kg of N? 15 35 50 75 100 33/38 Ammonium fixation would be expected to be greatest in soils containing a lot of______. Rhizobium bacteria Frankia vermiculite iron oxides both C and D 34/38 Which of the following is not a major factor in determining the soil aeration status? Redox Potential Volume of Macropores Nitrogen Gas Dissolution in Water Respiration 35/38 The very high pH levels found in some arid region soils are most likely due to high levels of exchangeable _____. Al3+ Al(OH)2+ Ca2+ Mg2+ Na+ 36/38 Nearly all organic compounds from which living beings are made have as their backbone, chains or rings of _____ atoms. Aluminum Oxygen Carbon Nitrogen None of the Above 37/38 The process of aerobic respiration is a significant source of which of the following gases? Methane Oxygen Nitrogen Carbon Dioxide Ammonia 38/38 At which of the following soil moisture potentials (expressed as kPa) is the soil water held most tightly? +5 0 -31 -1500 -3100