History of the soil organic matter conversion factor of 1.72

Students of soil science are taught that to determine the amount of soil organic matter, soil organic carbon is measured usually by wet oxidation using potassium dichromate (called Walkley-Black method) or in well-equipped laboratories, using CN analyser and then multiplied by a conversion factor of 1.72 or 1.724. Most textbooks and laboratory manuals do not explain how this factor was obtained, so students generally accept the value without any question just like they do with other constants used in natural sciences. 

Origin of the conversion factor

The conversion factor has a very long history and has practically survived the test of time and modern analytical methods. It is about 150 years old. It was based on studies in the 1820s by the famous agricultural chemist, Carl Sprengel of Goettingen University, that organic matter contains 58 percent carbon. But it was another leading agricultural chemistry pioneer, Emil Wolff from Hohenheim, who introduced the value of 1.724 in 1864. Since then this conversion factor has become universal despite the many later studies showing that it is too low for most soils and that a value of 2.0 is more accurate (Pribyl, 2010). When I was doing my masteral thesis at IRRI in the late 1980s, Dr. H.U. Neue, the head of the Soils Department and a leading expert on organic matter of submerged soils, required us to use a factor of 2.0. 

Oldest records of the conversion factor (Source: Pribyl, 2010) 

In an excellent review about this conversion factor, Pribyl (2010) concluded that convenience, authority and tradition rather than strength of evidence are in large part the reason for the widepsread acceptance of the conversion factor until now. However, this may be a controversial conclusion for other soil scientists in some countries. In France for instance, analytical laboratories use the factor of 1.72 or 2.0. The former (i.e. 1.72) is better suited for cultivated horizons while the latter (i.e. 2.0) is more appropriate for forest topsoils (Baize, 1988).

Who was Emil Wolff?

Dr. Emil von Wolff (30 Aug 1818-26 Nov 1896) was a professor of chemistry and agricultural chemistry at the Hohenheim Academy of Agriculture and Forestry in Stuttgart, Germany (since 1967 named University of Hohenheim) from 1853 to 1894. Wolff was one of the agricultural chemistry pioneers who made major contributions to its development and to that of soil science, plant science and animal science. 

Prof. Emil Wolff (Source: Hohenheim Univ)

Emil von Wolff started his studies in medicine at Kiel University in northern Germany but later shifted to natural science which he finished in Berlin. He obtained his PhD in 1843 in Berlin a year after Justus von Liebig published his most important book on agricultural chemistry. This probably infuenced him to focus his teaching and research on soil and plant chemistry as well as on the composition of organic substances including foods. He wrote several books among which were the “Textbook of Agricultural Chemistry (1847)” and “Ash Analysis of Agricultural Products (1877). 

Wolff belonged to the most influential and highly regarded agricultural scientists of the 19th century and had no doubt contributed to the fame of the Hohenheim school. It is thus a fitting tribute that an important street at the heart of the Hohenheim University campus bears his name: Emil-Wolff-Strasse (Emil Wolff street).

References
Baize D. 1988. Soil Science Analyses. John Wiley & Sons, Chichester.
Leisewitz, C. 1910.Wolff, Emil von. In: Allgemeine Deutsche Biographie 55 (1910), S. 115-117 [Onlinefassung]; URL: http://www.deutsche-biographie.de/pnd115599533.html?anchor=adb
Pribyl D.W. 2010. A critical review of the conventional SOC to SOM conversion factor. Geoderma 156: 75-83

The geoecology of the limestone and shale areas in Samar, Philippines

Contributed by

Dr. Ian A. Navarrete
Humboldt Fellow
Soil Science of Tropical and Subtropical Ecosystems
Buesgen Institute
University of Göttingen, Germany

Geoecology, a term coined some 41 years ago by the geomorphologist Carl Troll who was at the time professor at the University of Bonn, Germany, is a broad integrative term to the study of forms and functions of terrestrial geoecosystem (Huggett, 1995). It emphasizes the interdependency and/or inter-relationships of the ecological biosphere with landscape and hence sometimes equated with landscape ecology. For example, the movement and distribution of solutes across soil landscapes are influenced by the geomorphic position in the soil within the landscape thus influencing soil genesis (Sommer and Schlichting, 1997) and vegetation development (Huggett, 1975). 

Fig 1. Relation of primary forest and grasslands of Samar

During our fieldwork at the Samar Island Natural Park (along the Paranas-Taft road at about 300 m above sea level) in Feb 2012, we observed two typical grassland ecosystems occurring near or far from the primary forests (Fig 1A).

The first type is the grassland that occurs in the lower residual limestone soil or at the margin of the primary forest. The soils in such grassland are younger as indicated by poor soil profile development. The dominant grass is Paspalum conjugatum which in many areas occur in association with Chromolaena odorata. The second type is the grassland in the degraded rolling and hilly areas usually away from primary forests. The soils in these areas are different from the soils in the primary forest on the upper slopes in that they are mature, reddish, and deep (Fig 1B). They appear to have formed from the limestone residue or from the shale (underlying the limestone) that is widely exposed in the rolling areas. The dominant grass is Imperata cylindrica. 

Fig 2. Primary forest soil in Samar

The soils of the primary forest (limestone forest) on the upper and usually steep slopes are generally very thin and are underlain by consolidated limestone rocks (Fig 2). The presence of nutrient-enriched weathering pockets (where deposition of nutrient and decomposition of organic matter take place) of the limestone parent material, and the high annual rainfall explain the lush growth of the forest vegetation. It also partly explains the high tree species diversity of the forest.

(Members of the team: V.B. Asio, Ariel Bolledo, Mark Moreno, Pearl Carnice, Richel Lupos, Forester Elpidio Cabahit Jr. from the Samar Island Natural Park, and myself)

References

Huggett RJ (1975). Soil landscape systems: a model of soil genesis. Geoderma 13: 1-22.
Huggett RJ (1995). Geoecology: An Evolutionary Approach. Routledge, London.
Sommer M, Schlichting E (1997). Archetypes of catenas in respect to matter-a concept for
structuring and grouping catenas. Geoderma 76:1-33.

Ethnopedology: the study of local soil knowledge

“There is a need to integrate science and local knowledge. Both are vital and can be brought together only by participation” emphasized Prof. Dr. Franz Heidhues in his concluding remarks during the International Scientific Conference on Sustainable Land Use and Rural Development in Mountain Areas held at the University of Hohenheim, Germany on 16-18 April 2012. As can be seen from the figure below, scientific knowledge becomes more relevant when it is combined with local knowledge (Barrios and Trejo, 2003).

Precision & relevance of scientific and local knowledge  

Ethnopedology is the study of the local knowledge on soil and land systems of rural populations, from the most traditional to the modern. Ethnopedological research covers a wide diversity of topics centered around four main issues: (1) the formalization of local soil and land knowledge into classification schemes; (2) the comparison of local and technical soil classifications; (3) the analysis of local land evaluation systems; and (4) the assessment of agro-ecological management practices (Barrera-Bassols and Zinck, 2003; Barrios and Trejo, 2003). It encompasses many aspects, including indigenous perceptions and explanations of soil properties and soil processes, soil classifications, soil management, and knowledge of soil–plant interrelationships (Talawar, 1996).

In a recent study conducted in Vietnam and Thailand and presented in the above-mentioned scientific conference in Hohenheim, Dr. Gerhard Clemens and co-workers found, among other things, that: 1) Farmers classify their soils first of all according to soil color; 2) Farmers are able to describe soil properties and features. They also know the local factors affecting their soil; 3) Local soil classification is not consistent but the predominant soils can be efficiently identified using local soil knowledge.

An old farmer sharing some traditional knowledge 

Our own research in the degraded lands of Parasanon, Pinabacdao, Samar showed that the sweetpotato farmers possess a local knowledge system with regards to the nature of the soil and that of their sweetpotato crop. The demographic traits of the farmers clearly differed but they adhered to the same knowledge system regarding the attributes of the soil in their locality and the growth condition of their sweetpotato plants. Using their native dialect, the farmers have a soil classification scheme based on textural characteristics; they have also certain indicators of soil fertility and plant health. Moreover, the farmers know of certain problems concerning their soil or crop but they are not detracted by these because of their experience in finding ways to circumvent the situation (Pardales et al., 2001).

There has been an increasing research interest in local soil knowledge in recent years. This is the result of a greater recognition that the knowledge of people who have been interacting with their soils for a long time can offer many insights about the sustainable management of tropical soils (Barrios and Trejo, 2003).

References

Barrios E and MT Trejo. 2003. Geoderma 111: 217-231
Barrera-Bassols N and JA Zinck 2003. Geoderma 111: 171-195
Clemens G, U Schuler, BL Vinh, H Hagel, and K Stahr. 2012. International Scientific Conference on Sustainable land use and Rural Development in Mountainous Areas, University of Hohenheim, Stuttgart, 16-18 April 2012
Heidhues F. 2012. Conclusions. International Scientific Conference on Sustainable land use and Rural Development in Mountainous Areas, University of Hohenheim, Stuttgart, 16-18 April 2012.
Pardales JR, VB Asio, AB Tulin and DM Campilan. 2001. Project Report, UPWARD-CIP, Laguna.
Talawar, S., 1996. Research paper #2.Department of Anthropology, University of Georgia, Athens, USA.

Masaryk University and geology in the beautiful historic city of Brno (Czech Republic)

Brno's city center

If you have the chance to travel to the Czech Republic, you should not forget to include in your itinerary a visit to the city of Brno, the second largest city in the Czech Republic. Located south of Prague (about 2 hours by train), Brno is the historical capital city of Moravia of the South Moravian Region, one of 14 regions of the country.

Brno is among the most beautiful European cities that I have visited. According to Wikipedia, the city has hundreds of historical sights, including one designated a World Heritage Site by UNESCO, and the second largest historic preservation zone in the Czech Republic next to Prague. It is a university city and boasts of several top universities (total student population of about 90,000) one of which is Masaryk University.

Masaryk University

Masaryk University, named in honor of Tomáš Garrigue Masaryk the first president of Czechoslovakia, is the second-largest public university in the Czech Republic and the leading university in Moravia. It has more than 190 departments, institutes and clinics organized into nine faculties. It is commonly regarded as one of the most significant institutions for education and research in the Czech Republic and a respected Central European university. The university is home to RECETOX (Research Center for Toxic Compounds in the Environment), an excellent environmental research center which is highly regarded in Europe.

The city is not only beautiful, it is clean and orderly. The people are of course generally friendly and willing to assist visitors. A walk around the historical city center led me to the impressive St Peter and Paul Cathedral on top of Petrov hill. The hill is built up by metamorphic rocks particularly schist.

Outside the city I have observed limestones, sandstones, and metamorphic (quartzite, schist) outcrops. Most of the soils around Brno appear to be Cambisols, Chernozems, and probably Luvisols in the World Reference Base (WRB) classification system.  

Characteristics and fertility constraints of degraded soils in Leyte, Philippines

Contributed by

Dr. Ian A. Navarrete

Humboldt Fellow

Soil Science of Tropical and Subtropical Ecosystems

Georg-August Univesity Göttingen

Gottingen, Germany

Soil degradation, a process that lowers the capacity of the soil to produce goods or services, is a prevalent agricultural and environmental problem in the Philippines (Asio et al. 2009). However, to date, the nature and characteristics of degraded soils in the Philippines have been poorly understood, in that there have been few studies on this subject (Asio et al. 2009; Navarrete et al. 2009). Although various crop production technologies have been developed for marginal areas these technologies have not been successfully adapted by farmers or have failed to alleviate crop production (Cramb 2001). Cramb further stated that the introduction of unsuitable soil management technologies to farmers has intensified the soil degradation processes occurring in these areas. Thus, knowledge on the characteristics and fertility status of degraded soil is fundamental in planning suitable soil management strategies for crop production purposes. Because the degree of soil degradation immensely varies among sites depending on soil forming factors, soil management strategies must be location specific, every degraded soil has to be evaluated in terms of its properties and constraints.

In our recent study published in the international journal Archives of Agronomy and Soil Science (Navarrete et al. 2012), 60 soil horizon samples were collected from five locations (across an elevation gradient between 97 and 735 m above sea level) at Ormoc, Baybay, Bontoc, Bato and Matalom on the western side of Leyte island, Philippines. The samples were subjected to various physical, chemical and mineralogical analysis. Results revealed that the most important physical constraint in most of the soils evaluated is the high clay content particularly in the soils of Baybay and Bato because it is a problem for cultivation. The strongly acidic and strongly alkaline pH, low available P and, in some cases, low exchangeable K are the chemical constraints. Most of the variations in the physical and chemical constraint of these degraded soils can be explained directly or indirectly by the nature of the parent material, geomorphic position and anthropogenic effect. Soil fertility characteristics are distinct within similar soil types, primarily because they are related to the dominant soil-forming processes (see for example Figure 1 below). Consideration of the soil physical and chemical constraints is essential for the long-term planning of soil management strategies that will lead to sustainable utilization of these problematic soils.

Figure 1. Plots of the first and second principal components (PC) extracted from the principal component analysis (PCA) of all selected properties. (a) distribution of soil samples and soil types (b) distribution of soil properties

References

Asio VB, Jahn R, Perez FO, Navarrete IA, Abit SM, Jr. 2009. A review of soil degradation in the Philippines. Annals Tropical Research 31: 69-94.

Cramb RA (ed). 2001. Soil conservation technologies for smallholder farming systems in the Philippine uplands: a socioeconomic evaluation, ACIAR, Australia.

Navarrete IA, Tsutsuki K, Asio VB, Kondo R. 2009. Characteristics and formation of rain forest soils derived from late Quaternary basaltic rocks in Leyte, Philippines. Environmental Geology 58: 1257-1268.

Navarrete IA, Tsutsuki K, Asio VB. 2012. Characteristics and fertility constraints of degraded soils in Leyte, Philippines. Archives of Agronomy and Soil Science. DOI /10.1080/03650340.2012.663908

How does mining affect the environment?

The major impact of mining on the environment is mainly due to the physical damage of the landscape and the production of large volume of harmful wastes. In general, only a small fraction of the ore is valuable, the remaining large part is waste (tailings). For example, in the Cu mining industry, only about a kilogram of the metal is extracted from one-half ton rock. (Ore is an economic term for a rock from which a mineral can be extracted profitably).

The figure above summarizes the environmental impact of mining and smelting. It shows that mining and smelting produce solid, liquid and gaseous wastes/contaminants. These cause serious environmental damage once they are discharged to the land (terrestrial ecosystem) and bodies of water (aquatic ecosystems) or when they are emitted into ambient air. In particular, they cause soil and water acidification, air, water, soil and plant contamination by trace elements, deterioration of soil biology and fertility, and soil erosion.

Studies have shown that trace metals remain in the soil for a long time ranging from hundreds to thousands of years. Cd, Ni, and Zn have a relatively shorter residence time in the soil than Pb and Cr which may remain for several thousand years. This simply means that it is not easy and cheap to rehabilitate an abandoned mining site. In fact, the physical destruction of the landscape can be irreparable. And more importantly, the health risk of the contaminants that have already entered the food chain can remain for a long time.

Photo: Manicani island, Eastern Samar. Source: www.nickelore.blogspot.com (Feb 2, 2012)

References

Skinner B.J., S.C. Porter, and J. Park. 2004. Dynamic Earth. An introduction to Physical Geology. John Wiley and Sons, NJ.

Dudka S. And D.C. Adriano. 1997. Environmental impacts of metal ore mining and processing: a review. Journal of Envi. Quality 26: 590-602.

A green soil in the highlands of Samar

A soil at the heart of Samar, the third largest island of the Philippine archipelago, and along the Paranas-Taft road at about 300 m above sea level (within the Samar Island Natural Park) easily catches the attention of travelers. This is because it is unique: it is green in color. As far as I know, no soil with such color has yet been reported in the scientific literature.

The dominant green color is probably due to the abundance of the secondary mineral called melanterite, a hydrated iron sulphate mineral (FeSO4.7H2O) formed from the decomposition of pyrite or other iron minerals due to the action of surface waters. It is commonly found in mines as a post-mining formation on mine walls, in sulfidic sedimentary and metamorphic rocks as well as in coal and lignite deposits. It indicates the possible presence of sulfuric acid and should not be handled with bare hands or inhaled (www.mindat.org).

The green soil developed from mudstone interlayered with coal deposit. The site is not far from an area which was mined for coal and pyrite and thus appears to satisfy the environmental conditions favorable for melanterite occurrence.

We had the chance to examine the soil during our fieldwork in Samar on 2-3 Feb 2012 as part of my graduate course in pedology (Soil Science 212). We plan to conduct a detailed pedological and geochemical study on this soil in the near future. For easy reference, I suggest to call it “Samar melanterite soil”.

(Members of the team: Ariel Bolledo, Mark Moreno, Pearl Carnice, Richel Lupos, Dr. Ian Navarrete (Humboldt Research Fellow), Forester Elpidio Cabahit Jr. from the Samar Island Natural Park, and myself)