Understanding Shift in Soil Formation Assessment Answer

Soil Classification

Part 1: Site Characteristics

Vegetation

The soil sample collected from the pit has pastoral vegetation (pasture land) at present. After further evaluation, it was found that originally the land had wetland vegetation. The vegetation in the pastoral land can vary due to a number of influences. The climatic modifications, ecological changes, grazing activity, and releases all cause a shift in the vegetation within pastoral lands. The rich microbial profile of pasture land enhances the growth of multiple grass species for livestock consumption. Pasture lands are rich in minerals essential for promoting crop yield. Certain crops obtained from pasture lands contain a high concentration of nutrients that are necessary for livestock development (Masters et al., 2019).

Surface Soil Condition

The soil surface condition defines the soil capacity, soil functionality in land utilization, soil ecosystem, soil ability to retain biological life promotion activity, and so on. The soil surface is responsible for providing support to the vegetation and comprises of several organic or inorganic substances (Agriculture, 2022). The evaluation of surface soil condition showed that the soil is soft as the soil particles had a coherent consistency which means that the soil particles are aggregated. The soil surface was disrupted easily on the application of pressure of the forefinger. Such type of soil surface possesses higher water retaining capacity. 

Landform Element (20m Radius) 

The soil sample displayed a hill-slope element with a gentle inclination of about 3-10%. Such type of slope element is part of the hills, low hills, or higher landscapes. The hill-slope soil elements can be washed off due to water movements. Since the element was observed to be adjoined to the crest and not to the depression. It was evaluated that the morphology of the soil element is that of an upper slope.

Landform Pattern (300m Radius)

The landform pattern is an important aspect that consists of different landform elements. The landform elements and landform pattern determine the geomorphology and topography of the landform. The characteristics of soil are influenced by the landform patterns or landform elements (Baartman et al., 2018). In the soil sample, the landform patterns showed a low relief of about 30-90m. The modal slope was found to be undulating which means that the landform patterns that the slope had a gentle inclination of around 3-10%. 

Substrate And Parent Material-:

The soil sample had evidence of metamorphic substrate formation from an unidentified metamorphic rock. However, the soil's parent materials are fine grains with an abundance of calcium feldspar along with dark minerals, which classify as basalt. Basalt originates from igneous rocks, which are known to be formed by the solidification of molten mass from volcanic eruptions. The different rock types and rock formation methods in the soil sample imply that the sample has colluvium sedimentation, which means that the soil has been deposited at the hill foot-slope after detachment from the hill-slopes due to landslide, water streams, or simple gravitational influence.

Soil Morphology

A1 horizon- 0-20 cm 

Darker in appearance and comprised of organic matter, which was converted into humus with a loamy soil texture containing 25% clay. The coarse fragments present in the soil sample were basalt of angular shape with a tabular appearance. The boundary for the horizon was clear (20-50 mm) and wavy in topographic appearance, which made the undulations in soil wider rather than deep. The color profile for the horizon fell under 10YR 3/3. The secondary colors or mottles on the horizon were none as per the evaluation. No pedal formation was observed in this soil horizon as the soil was present as a coherent mass. The soil had a weak consistency moist consistency with no segregation. The A1 horizon showed a negative reaction to the acid fizz test and a few roots along with vegetative matter were retrieved in the soil layer.

A3 Horizon- 20-35 cm

The transitional horizon between A and B is present adjacently above the B horizon, the rocks or pebbles were formed from basalt and had a tabular sub-angular shape. A3 horizon had a gradual (50-100 mm) boundary with an irregular shape making the undulations appear deeper than wider. The horizon displayed a color profile of 10YR 4/4 along with medium-sized orange mottles (5-15 mm), which were distinctly visible in around 2-20% abundance. The soil texture in the A3 horizon was clayey with approximately 5-10% clay content. Relatively moist and very weak consistency was observed along with no segregation. The moderate pedal formation was present with peds of about 2-5 mm in size. The soil layer contained some roots and the result of the acid fizz test was negative.

B2 Horizon- 35-30 cm

The horizon had an abundance of clay, iron, aluminum, clay, and other organic matter the soil had a sandy loam texture with 10-20% clay content. No segregation was found and the soil had a very weak but moderately moist consistency. The horizon was darker in color as compared to the horizons above it. The boundary for the B2 horizon was diffused (>100 mm) with a broken or discontinuous appearance. The color of the soil on this horizon was 10YR 5/8 profile. There were about 2-20% coarse brown mottles (>15mm) present on the horizon, which were very prominent in appearance. This horizon showed strong pedal formation with peds in the size range of 5-10 mm. On performing the acid fizz test the results were observed to be negative and basalt coarse fragments with angular shapes were obtained from the B2 horizon in the sample pit.

C Horizon- 60 cm

Possessed the residuals of parent rocks and consisted of weathered material. A firm and dry consistency were found in this horizon with no pedogenic segregation. For the C horizon, the boundary was completely diffused (>100 mm). Coarse fragments from basalt rock origination were found with a tabular sub-rounded appearance. For this horizon, the color value was found to be 10YR 4/6. More than 20% of medium-sized grey mottles were strikingly evident in the pit. Strong pedal formations with peds of size 10-20mm were evident in this pit layer. The C horizon gave no reactivity to the acidic fizz test.

Interpretation

The soil sample collected from the pit showed slow permeability (5-10 Ks mm/day). Soil with a slow permeability generally falls in the massive to moderate grade and displays a clayey texture. This type of soil sample is porous in nature, which is observed with the help of a hand lens. Due to the presence of mottles and the root channels in the sample, the drainage observed for the soil was imperfect. Imperfect drainage in soil implies that the soil retained water for weeks making it wet in nature. After completing the order diagnosis criteria it was found that the soil had a clear or abrupt textural B horizon. According to the order diagnostic criteria, the B and A horizons should be separated by an abrupt boundary. The clay content on moving from A horizon to B horizon should be comparatively more. However, in the soil sample tested the clay content in the B horizon was to be normal, which was expected to be higher by approximately 20%. 

Soil Profile Description And Formation Discussion 

PART 2b

The Parent Material Mineralogy, and Dominant Clay Type 

The parent rock and mineralogy of the soil formation material determine most of the soil characteristics. Important features of the soil like vegetation, microbial features, and drainage duration are significantly affected by the parent rock (Wilson, 2019). As per the soil profile observed in the soil pit, it is concluded that the sample has basalt igneous parent rock in soil composition. The origination of igneous basalt rocks is mostly from volcanic eruptions. Basalt rocks are hard in nature and possess low silica content but high iron and magnesium concentration (Raza et al., 2022). Metamorphic rocks are extremely hard and do not undergo weathering effectively. Metamorphic rocks are referred to as recycled rocks. They are often exposed to extreme environmental factors and have imbalanced mineralogy (Guo et al., 2020). The substrate constitution (pebbles, rocks, etc.) for the soil sample obtained was found to be of metamorphic origin.

Effect Of Climate, Rainfall, And Temperature On Soil Formation 

Climatic factors affect the soil formation procedure indirectly by influencing the microbial features of the soil. Temperature and rainfall are major climatic factors that affect the soil formation procedure. The organic composition increases in case of heavy rainfall and an increase in temperature. Higher rainfall also decreases the pH but enhances the basic ion leaching (Gelybó et al., 2018).

Leaching, bleaching, and acidity- In climatic conditions with high temperatures and heavier rainfall the rate of leaching increases due to extreme precipitation. Under warm atmospheric conditions, the soil pH lowers causing soil acidification.

Eluviation or illuviation- Eluviation is the flow of soil content from the upper slopes to the lower horizons. Illuviation is the deposition of the soil flowed down due to eluviation. Higher humidity in the atmosphere increases the eluviation rate and thus enhances illuviation (Li et al., 2019).

Oxidation/reduction due to imperfect drainage- The oxidation and reduction of minerals in soil can be beneficial if the adequate iron gets oxidized which enhances the vegetative properties of the soil. However, excess redox of a single element might lead to other minerals toxicity. 

Wetting/drying cycles and freeze/thaw events- The freezing and thawing of soil leads to the formation of soil aggregates. The soil sample obtained from the soil pit shows the presence of aggregate mass which means that the soil has gone through thawing during the soil formation procedure.

The soil extracted from the soil pit shows that the soil formation procedure for that soil occurred under favorable environmental factors. As the pH, organic matter content, and microbial profile were normal for the soil sample.

Topography, Slope Position, And Water Movement 

The topographic aspects like slope positioning and inclination affect the water movement. Along with the deposition features, soil erosion activity, and the soil topography also defines the nutrient concentrations in the soil. For steeper slopes in this case, the water movement is rapid which also leads to a higher soil run-off rate causing minimal to no vegetation. As the slope inclination decreases it increases the water and soil sustaining capability of the land (Sharma et al., 2022). The soils in the lower slope are rich in nutrients due to the deposition of soil from upper slope regions. The soil studied from the soil pit had a lower slope inclination which enhanced the water retaining activity of the soil in the sample.

Biotic Activity 

The soil formation procedure in our case can be influenced by the biotic activities or the action of microorganisms in the soil sample. Microorganisms and other biological organisms play a vital role in weathering or soil formation as well. The biological activities enhance the weathering process by assisting in the breakdown of parent rocks (Koshila et al., 2019). The major organic composition of the soil, nutrient cycles, and soil biodiversity is regulated by the action of microorganisms during soil formation. Biotic activity is essential in the determination of the vegetative health of the soil (Kooch & Noghre, 2019). The soil with an effective and beneficial biological activity ensures adequate nutrient supply to the soil which enhances the vegetative compatibility of the soil. The vegetative evidence in the soil sample from the field implies that the soil has healthy biotic activity.

Geological Periods And Contribution Of Chemical And Physical Weathering 

Time is another important feature that influences soil formation and determines the overall soil characteristics. The influence of time on our soil sample is observed in the development of vegetative properties, microbial actions, topographic formations, and parent rock breakdown (Emadi et al., 2020). The soil attains necessary aspects with time as weathering is a slow and long process. The geological period along with chemical (molecular structures of parent rocks, and chemicals released from rocks) and physical (heat, water, ice, and temperature); weathering factors all contribute to the soil characteristics formation (Kalsev & Toor, 2018).

References

Masters, D. G., Norman, H. C., & Thomas, D. T. (2019). Minerals in pastures—are we meeting the needs of livestock?.  Crop and Pasture Science ,  70 (12), 1184-1195. https://doi.org/10.1071/CP18546

(Agriculture Victoria). (2022). What is Soil? https://agriculture.vic.gov.au/farm-management/soil/what-is-soil

Baartman, J. E., Temme, A. J., & Saco, P. M. (2018). The effect of landform variation on vegetation patterning and related sediment dynamics.  Earth Surface Processes and Landforms,  43 (10), 2121-2135. https://doi.org/10.1002/esp.4377 

Raza, A., Glatz, G., Gholami, R., Mahmoud, M., & Alafnan, S. (2022). Carbon mineralization and geological storage of CO2 in basalt: Mechanisms and technical challenges.  Earth-Science Reviews,  229, 104036. https://doi.org/10.1016/j.earscirev.2022.104036 

Wilson, M. J. (2019). The importance of parent material in soil classification: A review in a historical context.  Catena ,  182 , 104131. https://doi.org/10.1016/j.catena.2019.104131 

Guo, R., Hu, X., Garzanti, E., Lai, W., Yan, B., & Mark, C. (2020). How faithfully do the geochronological and geochemical signatures of detrital zircon, titanite, rutile, and monazite record magmatic and metamorphic events? A case study from the Himalayas and Tibet.  Earth-Science Reviews,  201 , 103082. https://doi.org/10.1016/j.earscirev.2020.103082 

Gelybó, G., Tóth, E., Farkas, C., Horel, Á., Kása, I., & Bakacsi, Z. (2018). Potential impacts of climate change on soil properties.  Agrokémia és Talajtan ,  67 (1), 121-141. https://doi.org/10.1556/0088.2018.67.1.9 

Sharma, S., Singh, P., Chauhan, S., & Choudhary, O. P. (2022). Landscape position and slope aspects impact soil organic carbon pool and biological indicators of a fragile ecosystem in a high-altitude cold arid region.  Journal of Soil Science and Plant Nutrition , 1-21. https://doi.org/10.1007/s42729-022-00831-x 

Kooch, Y., & Noghre, N. (2020). The effect of shrubland and grassland vegetation types on soil fauna and flora activities in a mountainous semi-arid landscape of Iran.  Science of the Total Environment ,  703 , 135497. https://doi.org/10.1016/j.scitotenv.2019.135497 

Koshila Ravi, R., Anusuya, S., Balachandar, M., & Muthukumar, T. (2019). Microbial interactions in soil formation and nutrient cycling. In  Mycorrhizosphere and pedogenesis  (pp. 363-382), Singapore: Springer Publications 

Kalev, S. D., & Toor, G. S. (2018). The composition of soils and sediments. In  Green Chemistry  (pp. 339-357). US: Elsevier. 

Emadi, M., Taghizadeh-Mehrjardi, R., Cherati, A., Danesh, M., Mosavi, A., & Scholten, T. (2020). Predicting and mapping of soil organic carbon using machine learning algorithms in Northern Iran.  Remote Sensing,  12 (14), 2234. https://doi.org/10.3390/rs12142234 

Li, X., Peng, T., Ma, Z., Li, M., Feng, Z., Guo, B., & Li, J. (2019). Late Miocene–Pliocene climate evolution was recorded by the red clay cover on the Xiaoshuizi planation surface, NE Tibetan Plateau.  The Climate of the Past ,  15 (2), 405-421. 

Masters, D. G., Norman, H. C., & Thomas, D. T. (2019). Minerals in pastures—are we meeting the needs of livestock?.  Crop and Pasture Science ,  70 (12), 1184-1195. https://doi.org/10.1071/CP18546

(Agriculture Victoria). (2022). What is Soil? https://agriculture.vic.gov.au/farm-management/soil/what-is-soil

Baartman, J. E., Temme, A. J., & Saco, P. M. (2018). The effect of landform variation on vegetation patterning and related sediment dynamics.  Earth Surface Processes and Landforms,  43 (10), 2121-2135. https://doi.org/10.1002/esp.4377

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