**6. Advantages and disadvantages**

People usually use volcanic residual soil as a growing medium for different kinds of plants [60, 61] because the soil has an organic layer and organic minerals [62]. Priddle et al. [63] argued that volcanic soil, especially red soil, is one of the

#### *Tropical Volcanic Residual Soil DOI: http://dx.doi.org/10.5772/intechopen.98285*

most fertile soils in the world as a product of volcanic material. This soil is very suitable for growing root crops such as potatoes and ginger. In some countries, such as Japan and China, volcanic residual soil is a critical resource with significant consequences for sustainable agricultural production and stable economic growth. These countries use this soil as a basis for infrastructure (roads, buildings, etc.) and landfills [64–67].

Because this type of soil is widely used for agriculture, fertilizers for plant fertilization will be intensive. One source said that the use of fertilizers in the West Lampung area was 17,845 tonnes. The subsidized fertilizer consists of urea of 9,365 tons, SP36 1,300 tons, ZA 1,230 tons, NPK (nitrogen, phosphorus and potassium) Fonseka 5,150 tons, and organic 800 tons. (https://www.liputan6.com/bisnis/ read/4464775/alokasi- pupuk-bersubsidi-lampung-barat-tahun-2021-naik accessed on March 03, 2021). Hu et al. [68] and Ramos et al. [69] state that fertilizers in the soil will increase the likelihood of REE forming. The main areas with an increase of REE in the soil are restricted to regions where agriculture is intense. In agricultural areas, the main REE entrance is caused by the application of phosphate fertilizers. These factors form REE in addition to the parent material that forms the soil and the mineralogical content of the soil. REE will form in all types of rock and soil. Soils originated from igneous rocks, schists, and sandstone tend to contain more REE when compared to those originated from other materials. The adsorption of REE in soils is influenced by clay type and content, especially the concentrations of aluminum silicates and iron and manganese oxides. These last ones have the most remarkable adsorption capacity.

Because the soil type in the research area comes from Quaternary volcanic rock, dominant clayey soils, and contains manganese oxide (Despujolsite), we hypothesize that in the soil of the research area, there is an Low Rare Earth Element (LREE) type. One of the benefits of Rare Earth Element (REE) is in the electronics industry. REE will be used as a chemical catalyst for the manufacture of portable electronic device batteries.

On the other hand, volcanic residual soil still has its disadvantages. Iqbal et al. [28] observed that the liquid limit of volcanic residual soil is >50%, while some researchers [70–73] found that liquid limits >40% would decrease the shear strength of the soil and cause landslides (**Figure 9**). Landslides usually occur during the rainy season. Landslide due to soil lack of strength as rainwater infiltration induces positive pore water pressure and reduces the safety factors (FoS).

**Figure 9.** *Landslide event.*

Many residual soils in the tropics exhibit abnormally high internal shear angles, which can be explained by soil particles randomly arranged by weathering [58]. Another reason the residual soil angle has a large enough internal shear angle is iron oxide in the soil. Zhang et al. [23] revealed that iron oxides in residual soils are present due to local enrichment and exist in the form of layers of clay aggregates binding them to coarser aggregations. Zhang et al. [58] stated that iron oxide in residual soil would cause poor compacting properties, but it is an agent to increase cementation and structural strength of the soil. The presence of iron oxide will make the internal friction angle in the soil quite large. The weakness of the bonds (cementation) formed by iron oxide is that when the soil is saturated with water, the cementation can be damaged or destroyed. The event will reduce soil cohesion. If the soil forms a slope, there will be a possibility of landslides.

Darajaat et al. [74] revealed that one of the factors that influence the stability of the volcanic residual soil slope is rainwater with an intensity condition of 10–43 mm/hour and 120–168 hours. This condition will reduce the slope safety factor by 2–30%. Another, Widisaputra et al. [75] simulated the stability of the volcanic residual soil slopes that were affected by earthquakes. The result is that the safety factor of the volcanic residual soil slopes will decrease by 1/3 to ½.

The observations of Iqbal et al. [76] concluded that the volcanic residual soil in the West Lampung area has swelling potential. This potential is due to the volcanic residual soil containing clay minerals such as kaolinite, halloysite, illite, and montmorillonite. The swelling-shrinking features that belong to this type of soil result in cracking, which occurs during the dry season. The fractures that occur would affect the local hydrological conditions. These conditions can impact the stability of slopes, agricultural production, and plantations [77–81]. On the other side, the mechanism of swelling and shrinking of the soil can cause considerable damage to the walls of the buildings [27, 82, 83].

Another thing that is concerned about is the corrosion process of steel. Veleva et al. [84]; Norhazilan et al. [85]; Noor and Al-Moubaraki [86]; Lim et al. [87]; Wasim and Shoaib [88]; Liu et al. [89] revealed that soil composed of silt and clay will have the highest level of corrosion compared to soil composed of rough grains (gravel to sand), this is related to the water content, the corrosion process will be high in soils with high water content. Iqbal et al. [29] stated that the properties of soil engineering (plasticity index, water content, and clay content) impact the corrosion process of steel. Their paper found that the water content had an adequate contribution of 24.79% to the corrosion process. The corrosion process (in this case, the corrosion rate) will increase if 1% of the index plasticity and water content is added.

Since the soil characteristic of the research area is silt and clay, this process should be taken into account when building infrastructure (such as water/gas/oil buried pipelines or building foundations).
