NRSM 211N Fall 2024 Exam 3 Study Guide PDF

**Note: Exam 3 will cover all material presented in lecture from 10/24 -- 11/7, textbooks chapters 8 & 9, and the article assigned on 11/7 (Bowman et al. 2008 on Canvas). The exam will consist of a mix of multiple choice and/or true/false and short answer questions. There will also be another extra...

**Note: Exam 3 will cover all material presented in lecture from 10/24 -- 11/7, textbooks chapters 8 & 9, and the article assigned on 11/7 (Bowman et al. 2008 on Canvas). The exam will consist of a mix of multiple choice and/or true/false and short answer questions. There will also be another extra credit question.** **[Soil Colloids & Chemistry]** What is a soil "colloid"? What are the general properties of soil colloids, and how do those properties influence their behavior? How are soil colloids formed? What are the major types and how are they similar/different (e.g., crystallin versus non-crystalline) [Layered Silicate clays:] What are layered silicate clays? What is their general composition? What are the different structure sand types (2:1, 1:1, etc), and how are the different types of clays different with respect to surface area, charge, expansion, etc. (e.g., kaolinite, smectite, vermiculite, etc.). How are these various clay types similar, and how are they different? How do variations in clay structure and composition affect properties (expandability, nutrients). Be familiar with the general structure, types, and properties of the different layered silicate clays (vermiculite, smectite, fine-grained mica, chlorite, kaolinite) What is an octahedral sheet? Tetrahedral sheet? (what are these, and how do they vary between types of clay?) Why are some clays expansive, and some not? For example, what properties of different clay minerals influence their overall negative charge and surface area? What is a micelle, and why do clay micelles generally have net negative charge? What causes the charges to develop? [Isomorphous substitution:] What is it, and how does it influence clay properties? What is substituting for what, and how/why does this occur? What are aluminum and iron oxides and how do they form? How do their properties vary from the 2:1 and 1:1 clay minerals above? [Non-crystalline colloids] What are the general types and properties of non-crystallin colloids (e.g., amorphous clays and organic matter) General distribution of clays by soil type and by soil horizon: If you wanted to find soil high in kaolinite, where would you go? Smectite? Vermiculite? How do colloids affect soil properties: variations in clay minerals can have important practical implications for soil uses. Be able to explain how variations among particles may influence the use of soil as: a building substrate, a good garden soil, etc. [Cation Exchange Capacity:] What is the definition of cation exchange capacity (What does it refer to?) How do cations interact with clay minerals? That is, how do soils retain soil cations? What is an "outer sphere complex"? What principles govern cation exchange? What is meant by the following and how do they work: Reversibility, mass action (Ratio law), charge equivalence, cation selectivity, complementary cation effect. How do plants "remove" cations from soil exchange sites and how does this work? [Effects of soil type on CEC:] Consider how CEC can be predicted based on different soil types/textures. As a function of weathering, how would you expect CEC to change? **[Soil Acidity:]** What is acidity, and what is the definition of an acid as it relates to soil? What is pH, what does it measure, and why is high acidity = low pH? What is the difference between concentration and pH? What are some of the common acids and bases in the earth system and what is their origin? What are the most common acids in soils? What is the relationship between soil respiration, ecosystem productivity and weathering, and what is the reason that for this relationship? What are the three pools of acidity on soils? That is, what are active, exchangeable and reserve acidity and how do they influence soil pH? Be sure to understand the role of each of these in soil buffering capacity, and how buffering capacity changes from soil to soil. What are the sources of acids and bases in the earth system? In soils? How does nitrogen cycling contribute to soil acidity? Sulfur cycling? Plant cation exchange? Aluminum? Why/how do acid inputs to ecosystems generally contribute to cation losses? What is "buffering capacity" and how does it work in soils? What is the definition of a buffer? What factors influence buffering capacity? What is meant by the term "base saturation," and how is it calculated? What are some ways that increases in acidity affect plant processes? In other words, how could acidic inputs to soils affect them in ways that are important or detrimental to plants? What is the relationship between acid inputs and cation exchange (and available cations) in soil? What are some of the observed effects of increases in soil acidity in natural ecosystems? Do you understand the reasons for some of these changes? Why might an increase in acid inputs be predicted to have negative effects on plant productivity?