Why volcanic ash can fertilise soil: An explanation
Jakarta (ANTARA) - The eruption of Mount Anak Krakatau in the Sunda Strait has drawn significant attention in recent days after volcanic ash spread across several regions. The Geological Agency of the Ministry of Energy and Mineral Resources (ESDM) reported that volcanic ash has been observed spreading across five provinces, namely Banten, parts of West Java, DKI Jakarta, Lampung, and Bengkulu. The distribution of this ash has also impacted flight activities and schooling in several areas.
The continuous eruption episode of Anak Krakatau, which lasted approximately 25 hours, ended on Sunday (6/9), but volcanic activity is still being monitored. Following the end of the continuous eruption, the volcano continues to experience Strombolian eruptions that produce volcanic ash.
Amidst the impacts of ash that can disrupt health and daily activities, there is an interesting aspect regarding volcanic material. In the long term, volcanic ash can play a role in the formation of fertile soil.
So, how can a material that is initially disruptive actually help fertilise the soil?
Volcanic ash is not merely ordinary dust. This material originates from fragments of rock, minerals, and volcanic glass ejected when a volcano erupts.
Its composition can vary depending on the type of volcano and the magma released. However, certain types of volcanic ash can carry mineral elements such as magnesium, calcium, sulphur, potassium, and other elements required by plants. The US Geological Survey (USGS) notes that specific volcanic ash, particularly those derived from basaltic and andesitic materials, can contribute a number of nutrients to the soil.
When these materials undergo weathering and mix with the soil, some of their mineral elements can become a nutrient source for plants.
Freshly fallen volcanic ash is not necessarily immediately fertile. The process requires time. Rainwater, temperature, microbial activity, and chemical processes within the soil gradually help break down the minerals contained in the volcanic material.
Research regarding soil formed from volcanic ash in Indonesia also shows that volcanic material plays an important role in soil development and characteristics. However, the level of fertility still depends on the ash composition and the subsequent soil formation process.
In addition to providing minerals, volcanic ash can also affect the physical properties of the soil. If present in appropriate amounts and mixed with the soil, ash material can help increase the soil’s water retention capacity. The USGS mentions that certain ash deposits can provide a mulching effect, thereby reducing water loss due to evaporation. Coarser-sized material can also assist with soil aeration and drainage.
These conditions can provide a more supportive environment for plant growth.
However, this does not mean that the more ash covers the soil, the more fertile the land becomes. This is a common misconception.
While volcanic ash can indeed assist soil fertility in the long term, large deposits can actually damage crops. Ash that is too thick can bury plants, disrupt the photosynthesis process, hinder air exchange within the soil, and make it difficult for roots to obtain oxygen.
The chemical composition of the ash must also be considered. Some types of ash can increase soil acidity or alter the balance of nutrients. This means the effects of volcanic ash are not always positive and cannot be generalised for all regions.
Fertile volcanic soil is essentially the result of a long process. After eruptive material settles, the rocks and minerals within it undergo weathering. This material then mixes with organic matter from plants and organisms living on the soil surface.
Over a long period, this process produces soil with characteristics that support plant growth. The USGS notes that the weathering and erosion of volcanic material over geological time also play a role in the formation of fertile soil.
This is why several volcanic regions in Indonesia are known to have highly productive agricultural land.
Despite containing minerals, volcanic ash cannot be regarded as an instant fertiliser that immediately makes plants flourish after an eruption. Plants still require nutrients in a balanced composition, including nitrogen. In several studies of surfaces newly covered by volcanic material, nitrogen levels can actually be a limiting factor for initial plant growth. Fertility subsequently increases as organic matter and organism activity enter the ecosystem.
Therefore, the process is more accurately described as the gradual formation and improvement of soil, rather than volcanic ash instantly transforming into fertiliser.