2: Soil Patterns, Structure, and Texture
- Page ID
- 38733
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Wind and water, gravity and time, people and plants and more change and shape and move the soil, creating patterns and features that range in size from more than 1000 kilometers to less than 2 micrometers. Recognizing and understanding these spatial patterns is vital to more fully understanding and more wisely managing soil physical properties and processes. And, the patterns and structures we can find in soil are fascinating and beautiful. The spatial organization of soil occurs at hierarchical, or nested, levels which we will consider from large to small in the sections below. You can also listen to a podcast-style audio overview of this chapter here (link). This audio overview was generated using an artificial intelligence tool, Google's NotebookLM, and may contain some inaccuracies. It is provided to supplement, not replace, careful reading of the chapter.
- 2.1: Global scale
- Fig. 2‑1 are strongly influenced by the global patterns of climate variables such as temperature and precipitation. In the frigid regions above 60°N latitude, we find large expanses of Gelisols, which are soils with a subsurface layer that remains frozen throughout the year, while the hot and humid equatorial regions of South America and Africa are dominated by Oxisols, the most highly weathered soils on Earth
- 2.2: Basin or watershed scale
- At the scale of a river basin or watershed, typically 10s to 100s of kilometers, the spatial patterns in soil properties can be so large that we fail to recognize them. We may only travel a few kilometers from our home in a typical day, or if we travel farther, we may not take the time to notice the changes in the soil around us.
- 2.3: Hillslope scale
- One level below the watershed scale, we find soil spatial patterns at the hillslope scale, roughly 10s to 100s of meters in size. Erosion and deposition help create many of the spatial patterns at this scale. Classic examples are alluvial fans, which are fan-shaped deposits of water transported sediment at the base of hills or mountains.
- 2.4: Soil profile scale
- Adjacent horizons differ from each other in physical and/or chemical properties, and the specific combination and sequence of horizons in a soil profile influence, and are influenced by, the presence and passage of water, energy, and living organisms. A soil profile of the Tetonka soil series shown in Fig. 2‑6 provides a dramatic example of the stark contrasts which can occur between adjacent horizons.
- 2.5: Soil aggregate scale
- Soil structure and soil aggregates can change over time and are often altered, for better or worse, by human management practices such as tillage, crop planting, or preparing soil for construction projects. Properly-timed tillage practices using suitable implements can improve soil structural conditions near the surface, but these improvements are often temporary
- 2.6: Scale of primary soil particles
- To measure the particle size distribution, we typically disperse, or separate, the soil particles in a liquid to create a suspension using either chemical or physical dispersion methods, or both. Sometimes pre-treatment of the sample is necessary to remove binding agents such as soil organic matter. Once the soil particles are completely dispersed and well-mixed in the suspension,
- 2.7: Terminology
- As you continue to study soil physical properties and processes, you will need to know and use the following key terms related to soil structure and texture: is the volume of pore spaces per unit volume of soil. Porosity has dimensions of volume over volume and may be written as a unitless decimal, as a percentage, or as a decimal with units
- 2.8: Problem set
- Go outside and use texture by feel to find soil from two different textural classes and report the latitude, longitude, and estimated textural class. If you are in the USA, use the SoilWeb app to determine and report the expected soil series for your location. Do not trespass. Use all appropriate safety precautions.
- 2.9: References
- Koven, C.D., et al., A simplified, data-constrained approach to estimate the permafrost carbon–climate feedback. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2015. 373(2054). Schaefer, A. J. and B I. Magi, Land cover dependent relationships between fire and soil moisture.Fire,2019.55 doi:10.3390/fire2040055