Curious facts in Pedology:
1st curiosity
The illustrations below, show a Eutrudalf roadside soil with a typical waving aspect of a argillic horizon, looking like an inclined curtain (Figures 1 and 2).
Figure 1. Typical aspect of a Eutrudalf roadside soil .
Figure 2. Typical aspect of a Eutrudalf roadside soil .
2nd curiosity
The sand fraction is formed predominantly by quartz (that is, silica), but contrarily to it might look like, soils with higher sand contents (or lower clay contents) are those showing lower concentrations of available silicon (Si), and in which, plants might show better response to Si addition, according to Korndörfer research results.
Figure 3 shows the relationship between clay contents and available Si concentrations in the soil.
Figure 3. Relationship between soil clay contents and silicon concentrations.
3rd curiosity
A field test to know whether silt content is high, consists on the observation of how the soil surface looks and feels like: a high silt content gives the soil surface the appearance and feeling of talc (Figure 4). During the texture test, the moist soil mass feels very silky between fingers, like the""wet soap feeling".
Such characteristic can be observed in the typical class of Inceptisol .
Figure 4. Talc looking of a high silt content soil.
4th curiosity
Different soil types may occur at short distances in the landscape. In Figure 5, the proximity between a Hapludalf (light color) and a Hapludox (reddish color) may clearly be observed.
Figure 5. Proximity between an Hapludox and an Hapludalf.
5th curiosity
Did you know that during July, at the Goianésia region (State of Goiás , Brazil), where does not rain for 6 months long, the sugarcane (without irrigation or fertigation) only springs up in a Mollisol , and it does not in an Oxisol?
Figure 6 shows a sugarcane field aspect in a Mollisol , which productivity without irrigation or vinasse application may reach more than 100 t ha -1 (average of 5 cuts), according to Soares results (see Poll 8, production environment A1).
Figure 6. Aspect of a sugarcane field in a Mollisol of the Jalles Machado Farm-industry,
at Goianésia , State of Goiás , Brazil .
Such fact is possible because Mollisol is a naturally high fertility soil, not only in the arable layer (A horizon), but also below this layer (B horizon). Therefore, these are true Eutrophic soils.
However, the main reason for the plant high productivity and longevity cannot be attributed only to the eutrophic character, because plants would not yield that much in an dry eutrophic soil! For instance, an eutrophic Oxisol, contrarily to the Mollisol , is a very dry soil. The sugarcane production in an Oxisol of that same region, without irrigation or vinasse addition, is around 80-84 t ha -1 (average of 5 cuts) (see Poll 8, production environment C2).
Therefore, the favorable differentials attributed exclusively to Mollisol , compared to the Oxisols, are referred to:
• Greater water availability in the A horizon, due to the higher organic matter contents;
• Greater water availability in the B horizon, due to the well-developed block structure;
• In the field, both factors (A horizon organic matter and B horizon structure of Mollisol are responsible for longer water availability in the soil profile.
Alfisol present similar sub surface horizon structure to the Mollisol , and at that same region, allow the growth of sugarcane plants during the drought period. The difference between these two soils is that Alfisol present less organic matter in the A horizon (lighter color) and lower CEC values along the profile.
These are clear evidences of the Pedology relevance as a basic science for the development and management of agriculture projects.
6th curiosity
Soils showing medium or medium-to-high clay textures and mostly coarse sand in the sand fraction, might present “arable layer sealing” and soybean germination damage under conventional tillage system.
This means that, when soybeans are sowed after a favorable rain, but afterwards, a 3-5 day drought is followed, the soil surface become hard causing the "arable layer sealing" (Figure 7). Under such conditions, the soybean seedlings are not able to spring up through the hardened soil surface, causing stand failure and yield losses.
In this case, it is recommended to disrupt this hardened soil layer with adequate implement devices.
Figure 7. Arable layer sealing.
7th curiosity
There is a close and interesting relationship between the native vegetation and the natural soil fertility. According to ANHÊ, soils with high natural fertility are related to tall native trees: aroeira (L. molleoides ), bacuri (Platonia insignis), peroba-rosa (Aspidosperma polyneuron Müll.), pau-d'alho (Gallesia integrifolia), guariroba (Syagrus oleracea Becc.), ipê-roxo (Tabebuia avellanedae), lixa (Curatella americana ), jequitibá (Cariniana strellensis or Cariniana legalis (Mart.) Kuntze ), cedro (Cedrus libani), and jaracatiá ( Jaracatia dodecaphylla A. DC.).
On the other hand, low natural fertility soils are related to the following shrubs and trees: angico-preto (Anadenanthera falcata Benth.Speg .), gabiroba (Campomanesia corymbosa) , macaúba (Acrocomia aculeata (Jacq.) Lodd . ex Martius), faveiro (Dimorphandra mollis Benth.), jatobá (Hymenaea stigonocarpa Mart .) , pequi (Caryocar brasiliense), and ciganinha (Memora peregrina).
8th curiosity
The vegetation expresses the differences in soil types. Figure 6 illustrates this fact, showing plants with and without flowers at neighbor places, very close to each other, in the region of Goianésia (State of Goiás, Brazil). To better understand the situation, soil samplings at both places were collected, and curiously two soil types were found: a Plintic Haplustox where plants had flowers and Aquox where plants did not have flowers.
Plintic Haplustox are usually very dry soils with low available water, contrarily of Aquox that have high water availability due to the proximity to underground water. It is also known that a dry period induces flowering, what might explain the plant flowering in the Plintic Haplustox and not in the Aquox: Plant Physiology and Pedology explaining the interactions in nature!
All crops of economical interest need a period of stress (drought or cold) to induce flowering. For sugarcane, for instance, it is necessary a drought stress period to plant sprouting and flowering and accumulating sugar, what begins during April in the central-south region of Brazil .
In practice, it is not recommended to buy or rent land areas of Plintic Haplustox due to their dryness and shallowness. Aquox shall not also be economically explored, because these soils occur near rivers and streams and represent areas of environmental protection (EPA).
Figure 8. Proximity between plants with flowers in a Plintic Haplustox
and plants without flowers in a Aquox .
9th curiosity
The armadillo (called "Tatu" in Brazil ) burrows by instinctively "knowing" the CEC and clay content!
In Pedology, "Tb" soils show CEC < 27 cmol kg-1 of clay; and "Ta" soils show CEC ≥ 27 cmol kg-1 of clay. All "Tb" soils correspond to Oxisols and part of Inceptisol and are friable or very friable soils (soft soils), since they have not been submitted to compaction.
On the other hand, Vertisols are firms or very firms, that is, they are compact (hard) soils. Therefore, even the armadillo uses its instinctive knowledge to investigate and classify the soil (Figure 9) before "managing" it (burrowing)!
Figure 9. The armadillo.
10th curiosity
Acric is a term originated from the Latin that means "the end". In Pedology, when an Oxisol is termed "acric Oxisol", it means that such a soil reached the end of the weathering process and it is transformed in an oxidic clay fraction. In mineralogy, the oxidic stadium is the last stadium of transformation, beyond the kaolinitic phase. For this reason, the FAO classification uses the Geric adjective to express this soil condition in Pedology (Figure 10).
11th curiosity
Did you know that clayey or very clayey Oxisols show high micro aggregation of the clay fraction, specially if they are acric soils? These clay microaggregates can be as large as or even larger than the sand particles. For this reason, the rainfall or irrigation water drains fast, and this type of Oxisol (very clayey) is compared to the very sandy ones as concerned to the water availability (Figure 10).
Figure 10. Soil microaggregates of an acric soil.
12th curiosity
Did you know that highly fissured soils might suggest high degree of compaction due to their genesis and not to the excessive use of machines or agriculture implements? In this case, subsoiling has no effect, because the high soil compaction or hardness is a consequence of s ubsurface compaction by geological and/or pedogenetical processes (Figure 11).
Figure 11. Fissures observed in a soil with subsurface
compaction due to pedogenetical processes.
13th curiosity
The author, Hélio do Prado, has been working a lot on Soil Surveys and he has done a large number of soil samplings using a manually turned soil auger (handheld device). At each place, soil samplings have been collected until one meter depth. If the manually turned auger perforations could be put together, all along downwards, the author would reach the soil depth of 11,000 meters or 11 kilometers!
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