Landslides changed the soil characteristics in Leyte, Philippines

By Maria Cristina A. Loreño & V.B. Asio 

Landslide is defined as the downslope movement of soil mass, rocks, and debris. It is one of the most serious environmental hazards in the Philippines. On April 11, 2022, four catastrophic landslides occurred in Leyte due to tropical storm Agaton, which caused the loss of hundreds of human lives (for a detailed explanation of the causes, please see the Soil and Environment blog). Two of the landslides happened in Bunga and Mailhi in Baybay City. Until now, little research has been done on the effects of landslides on soil properties and soil development. Such information is crucial for the rehabilitation of landslide-affected areas. The objective of the study was to evaluate the changes in the morphological, physical, and chemical properties of volcanic soils due to landslides. 

The study was conducted in the Bunga landslide with old soil (Ultisol) and in the Mailhi landslide with young volcanic soil (Andisol). The sites are found on steep volcanic mountain slopes underlain by andesitic pyroclastic rocks. Vegetation in both sites is a mixture of trees, coconuts, and shrubs. Soil profiles were examined and sampled on the upper, middle, and lower portions of the landslides. The soil profiles on the upper slopes were not affected by the landslides and were used as reference (unaffected soil). Soil samples were collected from every soil horizon or layer and analyzed in the laboratory for physical and chemical properties.

 

Results revealed that the landslides changed many soil characteristics crucial to soil use and productivity. In particular, the kind and depth of soil horizons, soil color, abundance of plant roots, and presence of rock fragments were modified by the landslides. The trend was the same for both the old and young soils (Figs. 1&2). In Bunga with old soil, the landslide resulted in more clayey soil but with very irregular distribution with soil depth. In Mailhi, with young soil, the landslide led to the increased sand content in the soil profile (Fig. 3). 

Figure 1. Changes in soil morphology due to landslide in Mailhi, Baybay 

Figure 2. Changes in soil morphology due to landslide in Bunga, Baybay

Figure 3. Changes in the sand, silt, and clay contents with soil depth due to landslides.

As expected, landslides increased the soil's porosity due to the mixing and deposition of soil material. In terms of soil pH, the landslides increased the pH of both the old and young soils due to the mixing of the soil and the deposition of fertile topsoil from the upper slopes (Fig. 4). Landslides tended to decrease the soil organic matter (SOM) in the topsoil but increased it in the subsoils (Fig. 5).

Figure 4. Changes in soil porosity and pH due to landslide.

Figure 5. Changes in soil organic matter content with soil depth due to landslide.

Landslides changed the characteristics of the soils and the degree of soil development. The mixing of the soil made the soil unstable and prone to soil erosion and further slope failure. The landslides also lowered the fertility and potential productivity of the soils. Because of the instability of the soils, a few years should be allowed to pass before the landslide sites are utilized for agriculture, forestry, or other land uses.

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Note: This article is based on the poster presented by the authors at the 12th ASTHRDP Graduate Scholars Conference organized by the DOST-SEI and the National Science Consortium on 12-13 September 2024 at the Dusit Thani Resort Mactan, Lapu-Lapu City, Cebu. We thank the DOST-SEI for the ASTHRDP scholarship to MCAL and Dr. Luz Geneston Asio, and Mr. Kenneth Oraiz, GAC Members, for their valuable comments.

Some notes on the soils in the vegetable landscape of Benguet, Northern Luzon

Soils are formed from the weathering of rocks as influenced by climate, parent rock, topography, living organisms, and time. Among these factors, climate and topography appear to be the dominant factors that have influenced the properties and distribution of soils in Benguet, Northern Luzon. 

Benguet together with Abra, Apayao, Baguio City, Ifugao, Kalinga, and Mountain Province comprise the Cordillera Administrative Region (CAR). Benguet has a mountainous topography consisting of peaks, ridges, and canyons ranging in elevation from about 900m to 2,840m above sea level. 

The highest point of the Philippine highway in Cattubo, Atok, Beneguet

The subtropical highland climate (Cwb based on Köppen climate classification) with annual average highs of 25.3 °C in April and lows of 13.3 °C in January and an average precipitation of 1,829mm (Wikipedia) promotes moderate rock weathering and soil formation rates. The steep slopes on most mountain sides enhances rapid leaching and runoff, the latter results in severe soil erosion on cultivated and bare slopes. 

Steep slopes with young soils are terraced and planted to various vegetables

Most soils in Benguet have developed from diorite, an intermediate plutonic rock, as well as metavolcanics and metasedimentary rocks particularly slate. According to the published literature, the dominant natural vegetation of Benguet was the pine forest type. Compared with broadleaf forests, pine forests have lower soil organic carbon (SOC) contents, smaller labile carbon fractions, and lower amounts of SOC stocks. Moreover, pine forests tend to experience severe water erosion events (Nie et al., 2019. Catena 174: 104-111).

Outcrops of metasedimentary rocks in Atok, Benguet

The high soil erosion rates result in poorly developed and thin soils (Inceptisols). On more stable surfaces such as on summit positions, old soils can be found which may qualify as Ultisols. Regardless of the stage of soil development, most soils are acidic with pH below 5.0 (Laurean et al., 2015. Benguet State University Research Journal 74: 10-34).

Red and old soils on summit positions in the mountains.

Where intensive vegetable production is found, the landscape can be called Anthropocene landscapes due to the considerable soil and landscape modification resulting from human activities such as land use conversion from forest to agriculture, terracing, fertilizer and pesticide application, liming and others.

The beautiful Anthropocene vegetable landscape in Natubling, Buguias, Benguet.

In general, the rates of fertilizer and lime application by the vegetable farmers are not based on recommended rates. This necessitates soil fertility assessment of vegetable farms to be able to determine the appropriate rates of fertilizer and lime application for improved vegetable production. This is one of the objectives of our ACIAR SlAM Project (2020117) on managing heavy metals and soil contaminants in vegetable production led by Dr. Steve Harper of the University of Queensland, Australia.

Our ACIAR Slam Project Team from the Univ Queensland, UPLB, BSU, VSU & USTP

Tropical soils: some important aspects of these less understood soils

Tropical regions occur between the Tropic of Cancer and the Tropic of Capricorn. The tropics include approximately 40% of the land surface and is the largest ecozone of the earth. According to Köppen (1931), the tropics are characterized by an annual mean air temperature above 18°C through­out the whole year. The largest climatic variation is introduced by the variability of precipita­tion, reaching from nearly 0 mm in the Saharan and Atacama Desert to 11,700 mm on Mt. Waialeala in Hawaii (Eswaran et al., 1992).

An Afisol (Luvisol) soil derived from mudstone in Eastern Samar, Philippines

According to Uehara and Gillman  (1981), "tropical soils" is a common name used to identify any soil that occurs in the tropics. They noted that like most common names, the term lacks precision, but it is more readily understood by a larger audience than are the scientific names. In contrast, Sanchez (1976) argued against the use of the term "tropical soils" since it does not accurately reflect the soils in the tropics. 

Selected properties of the major tropical soils (Jahn and Asio, 2006)

The name tropical soils is now globally accepted but these soils have remained poorly understood until now. The following are some important aspects of tropical soils (Jahn and Asio , 2006):

1. The tropics,  the world’s largest ecological zone, have a very high potential for plant growth but with soil limitations in vast areas.
2. About one-third of the soils of the world are tropical soils. The most widespread are Ferralsols, Acrisols, Luvisols, Cambisols, and Arenosols.

3. The large proportion of Cambisols (Inceptisols) and Luvisols (Alfisols) in Southeast Asia re­flects clearly the younger age of land surfaces and therefore the short duration of weathering processes.

4. Some soils occur almost exclu­sively within the tropics. About 90% of the Ferralsols (Oxisols), 80% of the Nitisols (Oxisols/Ultisols), and 60% of the Acrisols (Ultisols) are situated in tropical regions.
5. The major soil limitations or soil constraints  are  low cation exchange capacity, low base saturation (low pH, high Al-saturation) and high P retention. They are most widespread in South America, Africa and Southeast Asia (in decreasing order based on area).
6. Physical constraints like high groundwater table, air deficiency, and low soil depth are of lesser significance but govern special requirements for soil management in specific landscapes.
7. Due to severe chemical limitations, proper management of nutrients is the main challenge for effective land-use systems in the tropics.
8. Internal and external fluxes of nutrients are different among soil types and different among tropical landscapes. These have to be considered in ecological land-use systems.
9. To conserve the stock of organic matter in tropical soils (and to increase it in degraded soils), biomass productivity will be a key point for ecological land-use systems.
10. To enable policy-makers as well as land users to establish sustainable and ecological land use systems in the tropics, more precise soil maps and soil information are needed.

References

Eswaran H., J. Kimble, T. Cook & F.H. Beinroth. 1992. Soil diversity in the tropics: Implications for agricultural development. In: Myths and Science of Soils in the Tropics. SSSA Special Publ. No. 29.

Jahn R. and V.B. Asio. 2006. Climate, geology and soils of the tropics with special reference to Southeast Asia and Leyte (Philippines). In: Proc. 11th International Seminar-Workshop on Tropical Ecology, 21-25 Aug 2006, VSU, Baybay City, Leyte, pp: 23-42.

Köppen W. 1931. Grundriss der Klimakunde. W. de Gruyter & Co., Berlin

Sanchez, P.A. 1976. Properties and Management of Soils in the Tropics. Wiley, New York

Uehara G. and G. Gillman. 1981. The Mineralogy, Chemistry, and Physics of Tropical Soils with Variable Charge Clays. Westview  Press, Boulder Colorado.

Renowned Australian soil scientist visits Visayas State University

Prof. Neal Menzies, professor of soil and environmental science and head of the School of Agriculture and Food Sciences at the prestigious University of Queensland, Australia, visited the Visayas State University (VSU), Leyte, Philippines from September 16-19, 2014. 

The purpose of his visit was to attend, as a collaborating scientist, the meeting of the ACIAR (Australian Center for International Agricultural Research) - funded Soils Project (Soil and Nutrient Management Strategies for Sustainable Vegetable Production in Southern Philippines- SMCN/2012/029) attended by scientists from the Queensland Department of Agriculture, Fisheries and Forestry (Dr. Stephen Harper and Ms. Zara Hall) and partners from the Visayas State University, University of the Philippines Los Banos, Bureau of Soil and Water Management, Landcare Foundation Philippines Incorporated, Misamis Oriental State College of Agriculture and Technology (MOSCAT) and the World Agroforestry Center (ICRAF). 

Prof. Neal Menzies (middle) with the ACIAR Soil Project partners

He also visited the proposed project site in the central highlands of Leyte (740m above sea level) and was able to observe firsthand the soil problems and fertilization practices of the vegetable farmers in the area (among the most important soil problems is related to the very high phosphorus fixing capacity of the young volcanic soils (Andisols) which developed from andesitic Quaternary volcanics). He also visited the different academic and research units of VSU particularly the Department of Agronomy and Soil Science which prides itself as one of the leading soil science departments in the Philippines today.

Prof. Menzies was elected as Vice-President of the International Union of Soil Sciences (IUSS), the global organization of 55,000 soil scientists, from 2006 to 2010. He has also served as Secretary, Vice-President and President of the Queensland Branch of the Australian Society of Soil Science Inc. (ASSSI). He has published more than 200 articles in peer-reviewed scientific journals many of which have received high citations in international publications.

Prof. Menzies with vegetable farmers & project partners in Cabintan, Ormoc, Leyte

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ACIAR Soils Project (SMCN/2012/029): 2014-17

Project Leader: Dr. Stephen Harper, Principal Research Scientist
Queensland Department of Agriculture, Fisheries and Forestry (QDAFF)
Collaborating Scientist: Prof. Neal Menzies, Professor of Soil and Environmental Sciences
University of Queensland, Australia
Project Coordinator (Philippines): Dr. Victor B. Asio, Professor of Soil Science & Geo-ecology
Visayas State University, Baybay City, Leyte, Philippines
Project Partners: Dr. Pearl B. Sanchez (UPLB); Dr. Gina Nilo & Karen Bautista (BSWM),
Dr. Apol Gonzaga & Dr. Nelda Gonzaga (MOSCAT), Dr. Ben Aspera, Emily Garcia & Edwin Sardido (Landcare Foundation Phil Inc), and Dr. Jun Mercado (ICRAF).  

Highly weathered soils from Visayas, Philippines

Weathering is the alteration by chemical, mechanical, and biological processes of rocks and minerals at or near the Earth’s surface, in response to environmental conditions.

Highly weathered soils (or strongly weathered soils) are soils that have undergone prolonged and intense weathering under the net leaching environment of the humid tropics. They are commonly found on stable and old geomorphic surfaces underlain by easily weatherable rocks such as ultrabasic and basic rocks as well as by pre-weathered sediments (Beinroth, 1982). These soils are clayey, deep, reddish, acidic, and have low nutrient status. According to Jackson et al. (1948), highly weathered soils are characterized by weathering stages of 10 to 12 wherein the clay fraction is dominated by 1:1 phyllosilicates (kaolinite & halloysite), aluminum oxide (gibbsite), and iron oxides (goethite and hematite). This mineralogical characteristic is also predicted by the “residua hypothesis” of Chesworth (1973) which states that soil composition will with time move towards the residua system composed of SiO2, Al2O3, Fe2O3, and H2O. In the USDA Soil Taxonomy, the highly weathered soils belong to the Ultisols and Oxisols orders. In the World Reference Base, these soils belong to the reference soil groups Alisols, Acrisols, and Ferralsols. These soils possess nutritional problems for crop growth and thus are a problem for agriculture.

(Beinroth, F.H. 1982.Geoderma 27(1982)-1-73; Chesworth, W. 1973. J. Soil Science 24: 69-81; Jackson, M.L. et al. 1948. J. Physical and Colloidal Chemistry 52: 1237-1260).  

Below are photos of the important highly weathered soils from Leyte, Negros and Samar islands in the Visayas. 

This is an Oxisol that formed from ultrabasic rock in Salcedo, Eastern Samar

The widespread red soil (Ultisol) in the volcanic area of Central Negros

An Ultisol on pre-weathered sediments from basalt in Silago, Southern Leyte

An Ultisol formed on pre-weathered sediments from basalt in Biliran, Leyte

The widespread soil from basalt on the lower slopes of Mt. Pangasugan, Baybay, Leyte

Marginal uplands: current research initiatives at VSU

Marginal uplands are hilly or mountainous lands having very low crop productivity due to poor soil quality (degraded soil), limited water availability, and unfavorable socio-economic conditions. They are widespread in Southeast Asia and other parts of the humid tropics (e.g., Agustin and Garrity 1995; Asio et al., 2009). Resource poor-farmers (~ 1.4 billion people) in the developing world are located on these risk-prone marginal environments (Altieri 2002). 

Marginal uplands in Inopacan and Hindang, Leyte

In the Philippines, the poorest households, who are also the most vulnerable and most food insecure, are living and farming on these marginal lands (Roa 2007). The agro-ecological conditions in these areas are typically not suited to intensive production systems due to low-quality soils, hilly slopes, limited access to inputs or markets and extremely diverse and site specific conditions (Asio et al., 2009; Tyler 2004). Crops that can be grown on these marginal lands are often restricted to root crops such as sweet potatoes, beans and other legumes, thereby limiting food supply and diversity in hilly lands.  In addition, farmers often seek seasonal off-farm employment to survive.  Thus, research efforts are urgently needed to enhance food security and alleviate the difficult and risk-prone living conditions of these poor farming households. 

A daughter of a poor farmer living in the marginal upland of Inopacan, Leyte

Two on-going research projects on marginal uplands at VSU are the CHED-funded Philippine Higher Education Research Network (PHERNET) Program on “Enhancing food production and environmental quality in climate change vulnerable marginal uplands of Eastern Visayas” and the NRCP-funded project “Characteristics and nutrient status of degraded upland soils in Samar Island”.

Poor soil quality and low biodiversity characterize marginal uplands

References
Agustin PC and Garrity DP (1995). Historical land use evolution in a tropical acid upland agroecosystem. Agriculture, Ecosystems and Environment 53:83-95.
Altieri MA (2002). Agroecological principles for sustainable agriculture.  In: Agroecological Innovations (N. Uphoff, ed.). Earthscan, London, pp: 40-46.
Asio VB, Jahn R, Perez FO, Navarette IA, and Abit SM Jr (2009). A review of soil degradation in the Philippines. Annals Tropical Research, 31:61-94.
Roa JR (2007). Food security in fragile lands. PhD Dissertation, Wageningen University, Netherlands.
Tyler S (2004). Participatory research for community-based natural resource management in Asia. JIRCAS International Symposium Series 12: 165-169.

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.

Melanterite Soil: 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 travellers. 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 melanterite soil near the Bagacay mining area in Samar island

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. Melanterite is known to be stable only under highly acidic condition. 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).

Photo of the site along the highway in Central Samar where the melanterite soil occurs

The green soil we have examined in Samar developed from mudstone interlayered with coal deposit. The site is not far from an area which was mined for coal and pyrite and thus it 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”.

Recent updates: In the book "Assessment, Restoration and Reclamation of Mining Influenced Soils" edited by Prof. Jaume Bech (University of Barcelona) and his colleagues and published by Academic Press, London, in 2017,  the occurrence of melanterite mineral in some mining-affected soils from Spain and Portugal has been mentioned. This seems to confirm our observation about the green soil in Samar in 2012.

(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 (VBA)).

The origin of the catena concept

The catena concept in soil science comes from the Latin word “catena” which means chain. So it is a chain of soils linked by topography. It also refers to a sequence of soils in different positions in the landscape. It was introduced to the scientific literature by Geoffrey Milne (1898-1942) in a paper entitled “Some suggested units of classification and mapping particularly for East African soils” published in Soil Research-Bodenkundliche Forschung, Supplement to the Proceedings of the International Union of Soil Science Vol. IV No. 3 (1935), pp: 183-198. He noted “the regular repetition of a certain sequence of soil profiles in association with topography” in East Africa which was also observed earlier (in 1911 and 1912) by the German Peter Vageler. Milne wrote that "a distinctive word is needed in referring to this phenomenon" hence, he proposed the word catena.

Ernst Schlichting (1923-1988) who was a professor at the University of Hohenheim in Stuttgart pioneered the approach of considering the soil always as part of the landscape. He proposed that soils in different positions in the catena exchange materials through transport processes and thus could be compared to the transfer processes between horizons in a soil profile. He and his students have shown that the downward transport of solids or solutions may lead to a direct or indirect linkage between catena elements (Sommer and Schlichting, 1997; see above figure). In Schlichting’s view, the genesis of soil can only be understood if its relation to the other soils in the catena is taken into consideration.

Typical catena in the volcanic areas of Leyte, Philippines

Catena is now also widely used in other sciences particularly ecology albeit with a slightly different meaning (e.g. a catena of terrestrial ecosystems).

Earthworms: the most important soil and ecosystem engineers

Earthworms are thought to be the most ancient soil animals having started colonizing terrestrial environments about 600 million years ago (Spain and Lavelle 2001). They are the most predominant soil fauna except in dry and cold climates. Earthworms are semiaquatic animals which extract water continuously from the surrounding soil inorder to maintain their cuticle in a moist state to facilitate gas exchange. Thus moisture status is a major limitation to earthworm activities and distribution.

Spain and Lavelle (2001) reported that since earthworms live in direct and continuous contact with the soil matrix and the soil solution, their presistence, propagation and activity are greatly affected by the chemical (pH, dissolved ions) characteristics of the soil. Based on their sensitivity to soil pH, earthworms are grouped into acidophilic species (able to thrive below pH 6 such as in organic forest litter), neutrophilic species (they prefer soil pH 6 to 7) and basophilic species (prefer basic soils).

Three ecological types of earthworms (Spain and Lavelle, 2001)

a) Epigeics. Earthworm of this type live in the litter layers and thus are effective compost-makers. However, they have no or little effects on soil structure.

b) Anecics. These are earthworms that feed on the surface littler that they mixe with soil but spend most of the time in galleries they create within the soil. They are
also able to translocate considerable amount of leaf-litter into the soil.

c) Endogeics. Earthworms of this type live and feed within the soil. Among the earthworm types, the endogeics are the major agent of soil aggregation.

Effects of earthworms on soil properties

Earthworm burrows are known to have high continuity in both horizontal and vertical directions and thus greatly influences water and air movement in the soil. Earthworms influence the physical and chemical soil properties in many ways by burrowing, casting, feeding and propagating. According to Emmerling et al. (2002) earthworms are the most important ecosystem engineers (organisms that may modify or create their habitat and thus influence availability of resources to other species and soil properties) in arable soil due to their lasting effects on soil physical and biochemical properties.

In an interesting laboratory study to assess the impact of ecologically different earthworm species on soil water characteristics, such as soil tension, water content, and water infiltration rate, Ernst et al. (2009) exposed three earthworm species (Lumbricus rubellus, Aporrectodea caliginosa, Lumbricus terrestris) in soil columns (diameter 30 cm, height 50 cm) for 100 days with a total fresh earthworm biomass of 22.7 ± 0.4 g per column, each in duplicate. Each column was added with 30 g of sieved and rewetted horse manure placed on the soil surface as a food source. Precipitation events (10 mm) were simulated at day 28 and day 64.

Results revealed that ecologically different earthworms modify soil water characteristics in different ways. The anecic L. terrestris and the endogeic A. caliginosa showed the tendency to enhance the drying of the topsoil and subsoil. Their intensive and deep burrowing activity seemed to enhance the exchange of water vapor due to a better aeration in the soil. In contrast, the epigeic L. rubellus tended to enhance the storage of soil moisture in the topsoil, which might be linked to lower rates of litter loss from soil surface and thus a thicker litter layer remaining. A. caliginosa led to considerable higher water infiltration rates and faster water discharges in the subsoil, relative to the other species, probably due to a high soil dwelling activity.

Vermiculture

The term "vermiculture" refers to the cultivation of epigeic earthworms grown in an organic matter substrate with no soil. Rearing soil dwelling earthworms undercontrolled conditions requires an understanding of their needs. Many earthworm species can exhibit a degree of plasticity in behavior, so general maintenance does not necessarily require extremely large containers. L. terrestris for example does not need access to a vertical borrow and can be bred in pots which may be only a few cm in depth (Butt, 2009).

References

Butt, KR. 2009. Collection and rearing of earthworms. Workshop Kommission III der DBG, 20-21.03.2009, Trier, Germany

Emmerling, C, M Schlotter, A. Hartmann, and E. Kandeler. 2002. Functional diversity of soil organisms- a review of recent research activities in Germany. JPNSS 165:
408-420.

Ernst G, D Felten, M Vohland, and C Emmerling. 2009. European Journal of Soil Biology 45: 207-213.

Lavelle, P. and A.V. Spain. 2001. Soil Ecology. Kluwer Academic Publishers. Dordrecht, 654p
Photo source:

L. FitzPatrick at http://blog.southtownstar.com/

Relation between properties and age of soils in the Amazon forest

The Amazon Basin is that part of South America drained by the Amazon River and its tributaries. It has a tropical climate with an annual rainfall of 1500-2500mm, and a day temperature of 30-35 degrees Celsius (Wikipedia).

Much of what we now know about tropical soils was derived from many years of research in the Amazon rainforest. It is now widely known that this very important rainforest is growing on largely infertile and highly wethered soils called Ferralsols in the IUSS World Reference Base classification or Oxisols in the USDA Soil Taxonomy (see photo of typical soil profile).

It has been suggested by some ecologists that the efficient nutrient cycling and the periodic dust deposition from Africa explain why the infertile soils are able to support the lush rainforest vegetation.

In the recent issue of the international journal Biogeosciences Discussions, Quesada and colleagues reported the results of their interesting study on the soils in the Amazon Basin. Highlights of their findings are as follows:

1. There were large variations of soil chemical and physical properties across the Amazon Basin. The properties varied, as predicted, along a gradient of pedogenic development or in other words with soil development. Contrary to the popular notion especially among ecologists and foresters, the study showed that the Amazon soils varied from young to old soils (e.g. Gleysols and Cambisols to Alisols, Acrisols and Ferralsols).

2. Nutrient pools increased slightly in concentration from the youngest to the intermediate aged soils after which it declined gradually in the older soils. The lowest values of nutrients were found in the most weathered (or oldest) soils.

3. Soil physical properties were strongly correlated with soil fertility, with favorable physical properties occurring in highly weathered and nutrient depleted soils. The least weathered and more fertile soils had higher incidence of limiting physical properties.

4. Soil phosphorus concentrations varied with the degree of weathering. Higher P concentrations were observed in younger than in older soils which agreed with results of earlier chronosequence studies like that of Walker and Syers (1976).

5. Phosphorus availability in the younger soils was governed by the weathering of the primary and secondary minerals (particularly apatite) which in turn was controlled by soil pH.

Reference

Quesada CA, Lloyd J, Schwarz M and co-workers. 2009. Chemical and physical properties of Amazon forest soil in relation to their genesis. Biogeosciences Discussions 6: 3923-3992.

Soil science is a natural science

Soil science or pedology (pedo is Greek for ground or soil) is a scientific discipline at the meeting point of physical, biological, geological and agricultural sciences. Because soil is a natural body, soil science is a natural science that deals with the study of soil in all its aspects such as genesis, composition, properties, geography, ecology, fertility, degradation and protection. A more specific definition states that soil science is an environmental (or ecological) natural science concerned with the evolution, characterization, function, distribution, management and protection of the soil resource in terrestrial ecosystems.