Coral origin of Indonesian soils determined
By Amie Lynn Shirkie
He’s a long way from where he started, but it looks like Welhelmus Mella’s trip was worthwhile: The PhD student should soon be contributing to the agricultural development of his homeland and adding to the U of S College of Agriculture’s international reputation for excellence in research.
Mella’s doctoral thesis focuses on the genesis and fertility of two types of soils – alfisols and mollisols – on the uplifted coral reef in West Timor, Indonesia. His research could have important implications for Indonesian farmers and agricultural policy-makers.
According to Mella, conventional literature alleges that the soils in that environment may be formed either from the underlying coral rocks, from material transported in through erosion, or from eolian materials such as dust from nearby volcanic islands and deserts. As soil is an important issue to the agricultural industry in Indonesia, Mella wanted to learn more about the origin and quality of these two types of soil.
Alfisol is a typical tropical order of soil, characterized by a high accumulation of clay in the sub-soil and moderate values of base saturation. “Mollisol is similar to Prairie soils,” in that it has a thick top layer containing high levels of organic matter and high base saturation.
In order to study the origins of alfisols and mollisols, Mella examined the mineralogical and chemical properties of the soils, as well as those of the insoluble residue of the coral rocks.
In nature, the coral rocks are mostly dissolved through weathering, and what remains becomes the material of the soil itself. In the lab, Mella dissolved the coral rocks in weak acid to imitate the natural process.
In theory, if conditions are suitable, mollisols can form alfisol through weathering. When Mella compared the insoluble rock material to the properties of the soils, he found that the mineralogical and chemical properties of the residual rock were similar to those of mollisols, but different from those of the alfisol.
Based on these elemental analyses, Mella concluded that alfisols, which are located on gentler slopes, are in a more advanced stage of weathering than mollisols, and are, therefore, considered to be older. Mollisol, which is found on steeper slopes, is constantly renewed by material from upper slopes. According to Mella, as the coral rocks dissolve, they first form mollisols, then with time and weathering they form alfisol.
Mella’s study led him to the conclusion that both alfisol and mollisol are derived from the underlying coral reef material, but there are indications, based on his analysis of the soils and the rock residue, that materials blown in from other areas also contribute to the soil formation.
In studying the fertility of alfisols and mollisols, Mella compared the top 0-20 cm layer of the soils. He concluded that mollisols are more fertile than alfisols, based on the higher organic material content found in mollisol. However, says Mella, as mollisols are thinner and are located on steeper slopes – and therefore more subject to erosion – alfisol is the best soil for agriculture in high weathering environments in tropical climates.
As an interesting side note, Mella also unintentionally discovered how microorganisms are involved in the destruction and dissolution of coral rocks.
Mella completed his BSc in agronomy in Indonesia, and his MSc in soil and crop science at Texas A & M University, before beginning his doctoral studies in soil science at the U of S.
He says he chose the U of S because the College of Agriculture is known worldwide for its high-quality faculty, publications and research, and because he wanted to work with his supervisor, Adjunct Professor Ahmet Mermut.
Mella hopes his research will be of use to agricultural policy-makers in West Timor, and that his findings will form a basis for his future career in soil science. He plans to eventually return to Indonesia to teach and continue his research.
Amie Lynn Shirkie writes graduate student profiles for the College of Graduate Studies & Research.