Introduction to soil sciences

# Introduction to soil sciences
### Benjamin Nowak
### VetAgro Sup (Unit 512)
### 2021/09/23 (updated: 2021-09-27)

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# Pedogenesis

### Pedogenesis is the process of soil creation from parent bedrock

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# The 3 steps of [pedogenesis](https://planet-terre.ens-lyon.fr/ressource/formation-sols-climat-tempere.xml)

<table>
 <colgroup>
 <col span="1" style="width: 33%;">
 <col span="1" style="width: 33%;">
 <col span="1" style="width: 33%;">
 </colgroup>
 <tr>
 <th> 1. Weathering</th>
 <th> 2. Enrichment </th>
 <th> 3. Horizonation </th>
 </tr>
 <tr>
 <td> Degradation of parent materials</td>
 <td> Addition of organic matter (required to be defined as soil) </td>
 <td> Vertical differentiation of horizons (from top to bottom) </td>
 </tr>
 <tr>
 <th> <img src="fig/soil/ped1.png" height=250 width=150></img> </th>
 <th> <img src="fig/soil/ped2.png" height=250 width=150></img> </th>
 <th> <img src="fig/soil/ped3.png" height=250 width=150></img> </th>
 </tr>
</table>

.footnote[
[Source] [Dossier INRA "Le sol", Janvier 2009](https://belinra.inrae.fr/index.php?lvl=notice_display&id=20700)
]

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background-image: url(fig/soil/microped.jpg)
background-size: cover
class: center, bottom, inverse

# Two layers of pedogenesis 
### Secondary pedogenesis on a rocky scree

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# Factors influencing pedogenesis
 
- There are **5 main factors** influencing the process of soil creation:
     - Climate (Cl)
     - Organisms (O)
     - Relief (R)
     - Parent material (P)
     - Time (T)
     
- This may be remembered as 'ClORPT' (Hans Jenny, 1941)
     
       $$ Soil=f(Cl,O,R,P,T)$$

- The combination of these different factors gives a multitude of soils.
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# Climate
 
- T° and H2O influence how fast rocks weather: soils develop faster in warm, moist climates and slowest in cold or arid ones.

.footnote[[Latitudinal gradient in soil structure and weathering depth in relation to climate and vegetation (Huston & Wolverton, 2009)](https://www.montana.edu/hansenlab/documents/bio494/hustonWolverton2009.pdf)
]
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# Organisms
.pull-left[
- Living organisms accelerate the weathering of the bedrock, through physical (root penetration...) or chemical (exsudate...) degradation

- They stabilize the soil and limit erosion
]
.pull-right[
  ![](fig/soil/root.jpg)
]
--

- **Mineral particles resulting from the alteration of parental bedrocks need to be enriched in organic matter to define a soil**

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# Organisms

- Soil organic matter is an important carbon pool (~twice bigger that the atmospheric pool)
> The fate of [soil carbon can have a strong influence on climate change](https://www.4p1000.org/), depending on whether carbon is stored or mineralized

.pull-left[
- Soil organic carbon is stabilized by the interaction with mineral particles (clay, limestone...)
]
.pull-right[
- Soil organic carbon is mineralized by the respiration of aerobic organisms...
]

- But there are still many things to discover about [the nature of soil organic carbon](https://www.quantamagazine.org/a-soil-science-revolution-upends-plans-to-fight-climate-change-20210727/)

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background-image: url(fig/soil/slope.jpg)
background-size: cover
class: center, bottom, inverse

# Relief 
### Soil creation of soil only occurs if alteration > erosion

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# Relief
 
- Soils are generally shallow on slopes due to erosion...

- ...whereas deeper soils form at the bottom of a hill because gravity and water move soil particles down the slope.

.footnote[ [(a) Slope and (b) soil depth maps (Tagarakis et al. 2018) ](https://link.springer.com/article/10.1007/s11119-017-9519-4)
]

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# Parent materials

- At the Earth's surface, all rocks are subject to alteration

- Soils inherits traits from the parent material from which they formed
  - For example, soils that form from limestone are rich in calcium, with high pH, while soils evolving from granite have low pH

- As they evolve, soils can drift away from these inherited characteristics
  
- The two main types of parent materials are:
  - Magmatic rocks
  - Sedimentary rocks

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# Parent materials

<table>
 <colgroup>
 <col span="1" style="width: 50%;">
 <col span="1" style="width: 50%;">
 </colgroup>
 <tr>
 <th colspan="2"> Magmatic rocks </th>
 </tr>
 <tr>
 <th> Eruptive rocks </th>
 <th> Plutonic rocks </th>
 </tr>
 <tr>
 <td> Rock resulting from a surface solidification of the lava </td>
 <td> Rocks that solidified from a melt at great depth </td>
 </tr>
 <tr>
 <td> Example: Basalt </td>
 <td> Example: Granite </td>
 </tr>
 <tr>
 <th> <img src="fig/soil/basalt.png" height=250 width=250></img> </th>
 <th> <img src="fig/soil/granite.png" height=250 width=250></img> </th>
 </tr>
</table>

---

# Parent materials

<table>
 <colgroup>
 <col span="1" style="width: 50%;">
 <col span="1" style="width: 50%;">
 </colgroup>
 <tr>
 <th colspan="2"> Sedimentary rocks </th>
 </tr>
 <tr>
 <td colspan="2"> Formation at the surface of the earth or oceanic crust by : (i) Erosion, transport then sedimentation (detrital sedimentary rocks) OR (ii) Accumulations or precipitations of biological or physico-chemical origin in the oceans (limestones...) </td>
 </tr>
 <tr>
 <th> Silicates (Mostly SiO2) </td>
 <th> Carbonates (Mostly CaCO3) </td>
 </tr>
 <tr>
 <td> Example: Sandstone </td>
 <td> Example: Limestone </td>
 </tr>
 <tr>
 <th> <img src="fig/soil/grey.jpg" height=200 width=200></img> </th>
 <th> <img src="fig/soil/limestone.jpg" height=100 width=300></img> </th>
 </tr>
</table>

---

# Time
- The process of pedogenesis is slow and the creation of a soil takes several tens to hundreds of thousands of years.

> But if soils seem stable on a human scale, they are in **constant evolution on a geological scale**.

- The following presentation will present **one example of a chronosequence**

- This example will present one possible evolution of a limestone bedrock

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# An example of soil chronosequence

### A sequence of related soils that differ in their degree of profile development because of differences in their age.

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# Soil denominations

.pull-right[
- The names of the soils used in the rest  of the presentation come from the [French pedological reference system](https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers15-05/010063397.pdf)

- This reference system describes the characteristics of soil horizons and soil types

]

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# Rendosol

.pull-left[
 **General profile for** **a 'very young' soil** 
 <img src="fig/soil/rendosol.png" width=80% ></img>
]

.pull-right[
 **Specific profile for a rendosol** 
 **Aca** Horizon A with limestone
 <img src="fig/soil/rendosol_pic.png" width=60% ></img> 
 **Horizon C** Limestone bedrock
]

.footnote[ 

[Picture: jymassenet-foret.fr](http://jymassenet-foret.fr/cours/pedologie/chapitre6-2006.pdf)

]

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# Clay formation

- Weathering of bedrock minerals, such as [feldspar](https://geology.com/minerals/feldspar.shtml), produces clay
> As minerals, **clays are phyllosilicates**, characterized by alternating layers of silica (tetrahedral sheet) and aluminum (octahedral sheet)

- Si sheets are negatively charged and can thus 'store' cations (K+, Na+...) or H2O (because of its polarity)

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# Clay formation

- Soils are differentiated according to their Si:Al ratio

- Due to the retention capacity of the silica sheets, the higher the ratio, the higher the storage capacity of the soil

.center[
<img src="fig/soil/ratio.png" width=70% ></img>
]
- 2:1 clays are more likely to be [expansive](https://coloradogeologicalsurvey.org/hazards/expansive-soil-rock/)

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# Calcisol

.pull-left[
 **General profile for** **a 'young' soil** 
 <img src="fig/soil/calcisol.png" width=120% ></img>
]

.pull-right[
 **Specific profile for a calcisol** 
 **Sca** Horizon S with limestone
 <img src="fig/soil/calcisol_pic.png" width=60% ></img>

]

.footnote[ 

[Picture: jymassenet-foret.fr](http://jymassenet-foret.fr/cours/pedologie/chapitre6-2006.pdf)

]

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# Decarbonation

`$$CaCO_{3} + CO_{2} + H_{2}O ⇄ 2HCO_{3}^{-} + Ca_{2}^{+}$$`
 
- [Rainwaters absorb atmospheric CO2](https://planet-terre.ens-lyon.fr/ressource/co2-et-carbonates.xml), and these rainfalls erodes limestone, which is then transformed into HCO3- and Ca2+.

- The residual solution is leached out at depth

- So the horizons will be decarbonated **from top to bottom**

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# Brunisol

.pull-left[
 **General profile for** **a 'mid-aged' soil** 
 <img src="fig/soil/calcisol.png" width=120% ></img>
]

.pull-right[
 **Specific profile for a brunisol** 
 Horizon S **without** limestone
 <img src="fig/soil/brunisol_pic.png" width=60% ></img>

]

.footnote[ 

[Picture: jymassenet-foret.fr](http://jymassenet-foret.fr/cours/pedologie/chapitre6-2006.pdf)

]

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# First part of the chronosequence

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# Luvisol

.pull-left[
 **General profile for** **an old soil** 
 <img src="fig/soil/luvisol.png" width=90% ></img>
]

.pull-right[
 **Specific profile for a luvisol** 
 **Clay leaching** from **E** to **B(t)** 
 <img src="fig/soil/luvisol_pic.png" width=60% ></img>

]

.footnote[ 

[Picture: Rossignol (2013)](https://www.snhf.org/wp-content/uploads/2018/01/JPRossignol-pedogenese.pdf)

]

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# Water dynamics

- A **B horizon** enriched in clay is called **Bt**

- Bt horizon induce water accumulation, which will intereact with Fe through redox reactions (electron exchanges with oxygen)
.pull-left[
 *Pseudogley with oxidation traces: markers of temporary flooding (O2 after flooding)* 
 <img src="fig/soil/pseudogley.png" width=90% ></img>
]
.pull-right[
 *Gley with reduction traces: markers of permanent flooding (no O2)* 
 <img src="fig/soil/gley.png" width=80% ></img>
]

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# Luvisol redoxic

.pull-left[
 **General profile for** **an old soil** 
 <img src="fig/soil/luvisol.png" width=90% ></img>
]

.pull-right[
 **Profile for a redox luvisol** 
 Temporary flooding in B(tg) 
 <img src="fig/soil/luvisol_redox_pic.png" width=65% ></img>

]

.footnote[ 

[Picture: Rossignol (2013)](https://www.snhf.org/wp-content/uploads/2018/01/JPRossignol-pedogenese.pdf)

]

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# Reductisol

.pull-left[
 **Soil with permanent flooding** 
 <img src="fig/soil/reductisol.png" width=90% ></img>
]

.pull-right[
 **Profile for a reductisol** 
 Characteristic 'blue' color of G 
 <img src="fig/soil/reductisol_pic.png" width=50% ></img>

]

.footnote[ 

[Picture: Legros (2010)](http://www.forum-zones-humides.org/iso_album/atelier-id-zh-pedologie.pdf)

]

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# Continuation of chronosequence
.center[
<img src="fig/soil/chrono2.png" width=100% class="center"></img>
]
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# Soil evolutions

- Given examples represent only few possibilities of soil evolution, there are a large number of alternatives

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# Soil maps

### Examples of available references

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# French soil map

- Available at [Géoportail](https://www.geoportail.gouv.fr/)
]

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# European soil map

.footnote[ 

[Source: [Soil Atlas of Europe](https://esdac.jrc.ec.europa.eu/content/soil-atlas-europe)]

]

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