Don't panic when your instructor tells you that you need to write an analysis! All he or she wants is for you to take something apart to see HOW it works.
To write an analysis, you need to think about how each part of something contributes to the success of the whole.
Caution! Make sure that you're NOT just summarizing the original article, story, novel, poem, etc. Go beyond simply telling us WHAT you are talking about: describe HOW and WHY its elements function.
Specific Information for Analyzing Literature
Summarizing = WHAT
Analyzing = HOW & WHY
When you think about analysis, try thinking about how you might analyze a car.
- Ask yourself: What do we want the car to do or accomplish?
- Answer: (minivan) “provide transportation for my family”
- Analysis: how does each part of the van achieve this goal?
- Example: gasoline powers the engine
- Answer: (sports car) “speed, agility, and style”
- Analysis: how does each part of the sports car achieve this goal?
- Example: light-weight construction enables speed
Around the globe, many soil classifications systems have been developed to categorize soils into groups based on morphological and/or chemical properties. The most widely-used classification system is the Soil Taxonomy system that was made known by the United States Department of Agriculture (USDA) (Soil Survey Staff 1999). This system is a morphogenetic system that utilizes both quantitative factors and soil genesis themes and assumptions to guide soil groupings (Buol et al. 1997). “Keys to Soil Taxonomy”, a free publication distributed by the USDA, is a great resource for in-depth classification of soils (Soil Survey Staff 2014a). The USDA has also published a free resource titled “Illustrated Guide to Soil Taxonomy” that is similar to “Keys of Soil Taxonomy”, but written for a broader audience (Soil Survey Staff 2014b). Both resources can be found on the USDA website listed in the Soil Resources section of this article.
The Soil Taxonomy system is a hierarchical scheme consisting of 6 classification levels. In order from broadest to narrowest, the levels of classification are: 1) Order, 2) Suborder, 3) Great Group, 4) Subgroup, 5) Family, and 6) Series. Currently, there are 12 soil orders, 65 suborders, 344 great groups, ∼ 18,000 subgroups, and over 23,000 soil series (Bockheim et al. 2014). The distribution of soil orders across the United States is shown in Figure 3. The defining characteristics of the broadest levels of classification are based on soil-forming processes and parent materials, whereas the narrower levels become much more specific and consider the arrangement of horizons, colors, textures, etc. The soil-forming factor “climate” has a predominate role in Soil Taxonomy classification, followed by parent material, and biota; topography and time are not utilized in defining taxa (Bockheim et al. 2014).
Entisols are the ‘youngest’, or most recently formed soils of all the soil orders. Characteristics of Entisols include weak profile development where very little, if any, horizonation can be documented. Entisols sometimes contain a weakly formed A or Ap (plow layer) horizon. These soils can be found on steep slopes with severe erosion, on floodplains that receive alluvial deposits, and any number of scenarios in between.
Another soil order with notably weak profile characteristics is the Inceptisol order. When Soil Taxonomy was first established in 1975, Inceptisols were commonly referred to as the ‘wastebasket soil order’. These soils generally did not fit into the other soil orders at the time. When additional soil orders were introduced, many Inceptisols were reclassified and the ‘wastebasket’ title no longer applies. Inceptisols are somewhere between the stages of no profile development and weak profile development. Inceptisols are commonly found along major rivers and streams due to the weak profile development. Over time, both Entisols and Inceptisols have the potential to develop more horizons, at which time they would likely be reclassified into a different soil order. The features of ‘young’ soils like Entisols and Inceptisols are more heavily influenced by their parent material, whereas ‘old’ soils are more influenced by climate and vegetation factors.
Gelisols are also ‘young’ soils in regard to geologic time and were developed under cold temperatures or frozen conditions. These soils are often associated with permafrost conditions and cryoturbation (frost churning) in places like Canada and Alaska. Permafrost is a perennially frozen soil horizon (SSSA 2008).
Mollisols are commonly referred to as the ‘prairie soil’. These soils were formed primarily under grassy prairies and are characterized by their high organic matter content, dark color, and deep A horizon. The A horizon must be greater than 8 inches in depth and requires at least a 50 % base saturation (at least 50 % of the cation exchange sites are occupied; see Soil Chemistry section for more information). Mollisols are common in the midwestern United States where native prairies once dominated the landscape.
Alfisols, formed under deciduous forests, are also very common in the midwestern United States. Alfisols are generally found in humid regions of the world and often contain an E horizon in the soil profile. These soils must have a base saturation of at least 35 %.
Spodosols generally originate from coarse-textured (i.e., increased sand content), acidic parent materials. Spodosols are formed under forest vegetation, especially coniferous forests due to the buildup of pine needles that inherently have high acidic resins. When pine litter decomposes, strongly acidic compounds are leached through the coarse materials, transporting Fe, Al, and humus (Brady and Weil 2007). Thus, an illuvial layer of humus and Fe/Al oxides form. Like the Alfisols, an E horizon is commonly found in Spodosol soil profiles. In many cases, a Spodosol will have a white E horizon on top of a bright red B horizon. Spodosols are associated with loamy or sandy soil conditions and can be found in Wisconsin, Michigan, the northeastern United States, and on the coastal plains of the eastern and southeastern United States.
Aridisols are commonly associated with semi-arid and arid regions. These regions have a low mean annual rainfall. The lack of moisture in the soil affects the soil development and weathering process. Therefore, these soils are primarily affected by physical weathering, not chemical weathering (weathering processes discussed in the Soil Chemistry section). Aridisols are characterized by a high base saturation percentage of ∼ 100 %. These soils can be found throughout the deserts or drier areas of the western United States.
Ultisols can be found in humid and warm regions such as the southeastern United States. Ultisols have a high amount of clay mineral weathering and translocation that leads to a subsurface accumulation of clays (Brady and Weil 2007). They have a base saturation of < 35 % and are naturally less fertile than Alfisols or Mollisols. However, Ultisols respond favorably to nutrient management and are cultivated in many regions of the world. These soils are characterized by a high degree of weathering and are typically more acidic than Alfisols, but less acidic than Spodosols.
Oxisols are the most highly weathered soil order in the U.S. classification system. Oxisols get their name from being oxidized. They are dominated by high clay content and Fe/Al hydrous oxides that typically give the soil a red hue. Oxisols can be found in tropical and sub-tropical regions of the world such as Hawaii, Puerto Rico, South America and Africa. Oxisols are generally formed in wetter environments, but can be found in areas that are presently drier than during the time the soils were formed (Brady and Weil 2007).
Vertisols are soils that lack profile development due to the expansion and contraction of clay-rich soil. These processes cause the soil to mix, which does not allow for clear soil profile development. During dry conditions, the soil shrinks and cracks form that can extend to ∼ 80 cm deep and 2 to 3 cm wide. Vertisols are found in the southern United States in places like southeast Texas and eastern Mississippi where smectite, montmorillonite, and vermiculite clays are present.
The Andisol order was developed in 1990. Previously, these soils were grouped with the Inceptisol order. Andisols are soils of recent origin (young) that are developed from volcanic materials. They are found in Hawaii and the northwestern United States in places like Washington, Idaho, and Oregon.
Histosols are the only organic soil order in the classification system. Histosols are comprised of several different subhorizons within the O horizon and contain at least 20 % organic matter. Histosols occupy a small total area, but are found in various places in the United States and Canada such as Wisconsin, Minnesota, the Florida Everglades, and along the Gulf Coast.
Suborder, Great Group, Subgroup, Family, and Series
Suborders categorize properties associated with a climatic connotation of the soil. Great groups account for the most significant properties of the soil as a whole, including the type and arrangement of soil horizons, temperature regimes, and moisture regimes. Scientists use subgroups to further classify soils by assessing the degree of similarity between particular soils and grouping them accordingly. These are intergrades that reflect transitions to other orders, suborders, or great groups. The family grouping has similar physical, chemical, and mineralogical properties, which often relate to plant growth. A soil series is the lowest level of taxonomy, or the most specific to the soil in question. The soil series classification narrows characteristics of similar soils down to a local level where not only physical, chemical, and mineralogical properties matter, but also management, land-use history, vegetation, topography, and landscape position. Most soil series are named based on the location where the series was first discovered. An example of the taxonomic classification for the Illinois state soil is provided (Table 1).
|Family||Fine-silty, mixed, superactive, mesic Typic Endoaquoll|
Pedologists (scientists who study the origin and composition of soils as a component of natural systems) continue to learn more about soil morphology, chemistry, mineralogy, and biota, thus tighter limits on groupings of soils are being defined. Soil scientists are constantly reevaluating soil taxonomy as technology and science progress. It is important to remember that soils are dynamic, living environments. Soils are ever-changing through both chemical and physical weathering processes and can vary across the landscape, resulting in corresponding changes in soil classification over time.