Biocalcification: the biological accumulation of CaCO3 in rice soils

Lowland rice cultivation can enhance the proliferation of snails resulting in the accumulation of calcium carbonate (CaCO3) in the topsoil. Frank Moormann and Nico Van Breemen, well-known Dutch pedologists, first observed this phenomenon in Central Luzon, Philippines, while visiting the experimental sites of the International Rice Research Institute in the 1970s. H.U. Neue, head of the Soils Department of IRRI at the time, encouraged this writer to investigate the phenomenon. Our research revealed that such biological accumulation of CaCO3 which we named biocalcification, occurs in several rainfed and irrigated rice-growing areas in the Philippines (Asio, 1987; Asio and Badayos, 1998).

The figure below shows the proposed generalized model of biocalcification in rice fields. It consists of two stages. Stage 1 is on the proliferation of snails which is generally dependent upon the calcium content of the soil or irrigation water. Moormann et al. (1976) suggested that calcium, of which some is present in the irrigation water as Ca(HCO3)2, is taken up by the snails and transformed into shells which in turn form the source of the free CaCO3 present in the soil surface. Thus, calcium-rich irrigation waters favor snail proliferation in soils regardless of calcium content and origin. On the other hand, calicum-poor irrigation waters would only promote snail abundance if the soils are rich in calcium like those formed from basic parent materials. In rainfed areas,bunding soils rich in calcium could also enhance snails proilferation or from direct transport of shells from irrigation ditches.

Stage II starts with the accumulation of shells. Dissolution of shells in water normally takes years (CaCO3 is slowly soluble in pure water) particularly in non-acid soils. But in rice soils chemical dissolution of the shells is enahnced by the carbonic acid formed by the reaction between carbon dioxide coming from organic matter decomposition, and water. Moreover, the physical disintegration of the shells is hastened by alternate dry and wet condition which commonly occurs in rice fields, and by field operations particularly puddling. The end result is the accumulation of free CaCO3 and the rise of pH in the soil surface. This condition in turn promotes the proliferation of snails.

Among the soil fertility effects of biocalcification include an increase in the availability of calcium and magnesium but a decrease in the availability of phosphorus and zinc to the rice plant.

References

Asio VB. 1987. Biocalcification and siltation in paddy soils. MSc thesis, UP Los Banos/International Rice Research Institute, Laguna.

Asio VB and Badayos RB. 1998. Biological accumulation of calcium carbonate in some lowland rice soils in the Philippines. The Philippine Agriculturist 81: 176-181.

Moormann FR, Tinsley RL and Van Breemen N. 1976. Notes on a visit to multiple cropping project in Pangasinan. Mimeographed papers (unpublished), IRRI, Laguna, 4pp.

Challenges and opportunities in agriculture

by Dr. Cezar P. Mamaril
Senior Consulting Expert of Philippine Rice Research Institute (PhilRice)

Los Baños, Laguna

I would like to share my thoughts about current challenges and opportunities in agriculture that institutions like Visayas State University (VSU) should be concerned. I could not over emphasize the fact that we are facing the problem of producing sufficient food to feed the ever increasing population of our country. Last census reported that our population is increasing by 2.3 percent, while our food production (particularly rice) is increasing by about 2.5 percent. The minimal growth difference between population and food production is not sufficient to provide the other requirements of small farmers to live a decent life. I hope the current census will show a decline in population growth so that we will have a better breathing space. (If you have not yet been interviewed by the census takers, you better do so otherwise you may not get your ration of rice!). Furthermore, some recent reports show that the per capita rice consumption in the Philippines has been increasing from less than 100 kg/year several years ago to almost 120 kg/year currently which suggest that some people can not afford to purchase other kinds of food besides rice. Yet in developed countries like Japan and Korea, the per capita consumption is decreasing with increasing income. I was told by my younger son who is an Agric. Economist that the Philippines is now the largest rice importer in the world. I read in the newspaper that this year alone, the government will be importing 2.45 million tons of rice. Is this a sign that Filipinos are retrogressing economically while our Asian neighbors are moving forward?

Besides inadequate food production, lands suitable for the expansion of food production is declining fast suggesting that time will come when we can no longer increase food production by expansion of area. Likewise, there is also the problem of conversion of agricultural lands for other human activities such as real estate housing projects, industrial activities, game parks like golf courses, etc. It is also unfortunate that most of these areas being converted into other human activities are productive lands mostly irrigated lowland rice areas. Since land is a finite resource, we should properly and efficiently utilize it.

Population also creates pressure on water resources which is quite critical especially in rice growing areas. Forests are also subjected to tremendous pressure with increasing population because of the demand for building materials and for fuel. With increasing deforestation, water resources will also diminish. Likewise, when water resources decrease, the share for agriculture for water will also decrease while domestic and urban needs increase because of increasing population. Thus, food production will be greatly affected especially for lowland rice and could lead to lower yields. It has been observed that not only the surface water resources that is affected by deforestation but also the ground water level. It is doubly serious especially in coastal areas because as the fresh ground water table gets deeper, sea water intrusion takes place to replenish the fresh ground water. Subsequently when ground water which is contaminated with sea water is pumped for irrigation the soil may become saline which is adverse to crops production.

The challenge therefore is how one can proceed to produce sufficient food for an unabated population growth with less land and declining soil productivity and less water resources and climate change. The current scenario looks bleak but we should remain optimistic and be challenged and remain hopeful for Divine intervention. We should put our efforts and minds together to use effectively and efficiently whatever resources are available.

Currently there are technologies being disseminated which are not cost effective because they are highly generalized rather than site specific. Thus most often farmers do not realize the benefits that are claimed to be obtained through these technologies. You may also agree with me that there is no “perfect” or “universal” technology that is appropriate for all sites and conditions. Technologies being generated should define the site characteristics and conditions where such technology is effective. Certain technologies are being disseminated prematurely; i.e. not extensively tested before being released for dissemination under all conditions and crops. What is effective for one crop is not necessarily true for all crops. A more specific example is technologies suitable for upland rice is not necessarily appropriate for irrigated or rainfed lowland rice and yet they are the same crop. A friendly advice to researchers is to define and characterize your experimental sites thoroughly so when you finally will disseminate your findings, you can specify where such technology works or where it does not.

In preparing research programs, it might be wise to involve the different stakeholders, such as the farmers and providers of farm inputs, to insure that there is relevance to the stakeholders’ need and capability and for the eventual adoption of whatever results generated by research. As researchers we often feel that we have better ideas than the farmers to resolve their problems and yet while research results might seem encouraging, farmers are hesitant to adopt these due to other factors that the research failed to consider during the process of conducting the study. I can cite several examples. A technology may produce successfully high yields but it requires high cost of inputs, both materials and manpower, which some farmers does not have the capacity to obtain the inputs. Naturally it is likely that many farmers will not adopt such technology. It might be a good idea to generate a cafeteria of technologies that require different levels of inputs and capabilities from which farmers can choose depending on their financial and technical capacities. Thus, socio-economic characterization of target stakeholders is imperative besides biophysicochemical characterization of the target areas.

There are rice areas where once farmers can grow two seasons of rice a year with reasonable yield but because of declining supply of water resources, the dry season rice crop often fails. Under such situation, crop diversification may be considered wherein during the dry season other crops should be planted. In choosing the alternative crop, however, the crop being introduced should have an economic value equal or better than rice if possible. Crop diversification will also enhance soil productivity. In a rolling landscape, it is possible that the bottom portion of the toposequence will be planted to rice while those in the top and slope portion to upland crops. Integrated crop diversification will likewise reduce economic risks on the part of the farmer.

With increasing cost of farm inputs, we should assist the farmers to utilize these external inputs effectively and efficiently as well as the proper utilization of farm biomass. One reason why chemical fertilizers are claimed to cause soil degradation is because of misuse rather than overuse of fertilizers which could lead to nutrient imbalance. There is increasing evidence of widespread multi nutrient deficiencies in our country especially in areas where crops are constantly applied with chemical fertilizers like rice, corn and sugarcane. This is because most often than not, only NPK fertilizers are applied and in the meantime the native supply of the other essential nutrients are being depleted. It is imperative that proper diagnosis of the nutrient status of soils should be regularly undertaken so that only the limiting nutrient should be applied in proper proportion to the other essential nutrients. Unfortunately the cost of soil analysis is beyond the reach of small farmers plus the fact that there are limited and inaccessible soil laboratories in the country. Therefore, there is a need to develop cheap and simple techniques to diagnose nutrient status of soils. Currently, the available simple diagnostic tools being promoted are the Soil Test Kit (STK), Nutrient Manager, a computer assisted method developed by IRRI, and the Minus One Element Technique (MOET) kit which is designed primarily for lowland rice soils.

Integrated nutrient management strategy may also reduce the cost of external input use especially if one will fully and efficiently utilized farm produced biomass as supplemental source of nutrients. Utilization of on farm biomass should not require special handling of the materials to the extent that additional time and facilities are required for the farmer to process these materials before such can be applied to the soil. Farmers usually are apprehensive to do extra efforts especially if the additional benefit will not significantly compensate the extra effort spent. More efficient and effective ways to utilize these on farm biomass has to be developed rather than the traditional composting and inoculating with decomposing or mineralizing organisms. There should be some means to stimulate the indigenous and heterogeneous soil organisms to decompose and mineralize organic materials rather than utilizing isolated pure strains of organism which will be an added cost to the farmer.

There must be many more opportunities that could enhance agricultural production and help uplift the well being of farmers but I leave them for you to think about. I would like to point out, however that based from my own farm experience, increasing production does not necessarily lead to better livelihood for a small farmer mainly because under our present situation, the middlemen or traders usually earn more than the farmers. Marketing is an important problem that small farmers face. Unless small farmers are organized to be able to dictate the price of their produce, they will never improve their lot. Unfortunately farmers’ cooperative movements in our country do not have a commendable history. These should be one area of interest that the new government should look into. Coincidentally, while preparing my talk, I heard in the radio last Wednesday, that one of the advocacies that the new Secretary of Agriculture Alcala has proposed to President Aquino during his interview for the DA position which impressed the President is the elimination of middlemen by providing opportunities for small farmers to sell their produce directly to the consumers. It will be interesting to see what plans, programs and strategies our new government will pursue to enhanced the well being of our small farmers and fisher folks.

In closing I would like to reiterate that we should remain optimistic that the seemingly bleak scenario of our agricultural sector mentioned earlier can be overcome if we put our acts together and with the guidance of our Almighty God. Moreover, I would like to leave the following quotation from Henry David Thoreau “If one advances confidently in the direction of his dreams, and endeavors to live the life which he has imagined, he will meet a success unexpected in common hours.” Success in any endeavor could be attained through perseverance, determination and hard work.

----------------
*Excerpt of keynote speech delivered during the College of Agriculture Day, Visayas State University, Baybay, Leyte on July 2, 2010.

*Dr. Mamaril is a retired UP Los Banos soil science professor and International Rice Research Institute (IRRI) scientist. He is the son of Mr. Julian Mamaril, the first Superintendent of Visayas Agricultural College (forerunner of Visayas State University) in the early 1960s.

Global warming and our local environmental problems

Global warming is the increase in the average global temperature. It is a real problem now and we are starting to experience its bad effects like the more frequent occurrence of strong typhoons, the warming of seawater resulting in decreased fish catch by fishermen, and the increased amount of rainfall resulting in catastrophic floods and landslides. It is predicted that the tropics where the Philippines is located will be most affected by global warming.

But apart from this global environmental problem, there are also serious local environmental problems that need urgent action. These include deforestation, land degradation, and soil and water pollution. Except for deforestation, these local problems have seldom grabbed the headlines and the endorsement of politicians and popular personalities hence most people are not well aware of the severity of these problems. But they are already threatening our lives and studies have indicated that these environmental problems may have already contributed to the loss of lives or have caused health problems of people.

The fact that much of the original or primary forest in most Philippine islands is now gone clearly indicates that we failed in protecting this vital natural resource. No need to cry over spilled milk says the popular expression. What we need to do is to see to it that the forest that remains is protected and the degraded uplands, the product of deforestation and kaingin in previous decades, are rehabilitated especially in critical watersheds across the country. A degraded land has reduced capacity to absorb rain so that much of the water during rainy days flow on the land surface resulting in floods and lowering of the water table (meaning, drying up of wells!). Degraded lands are also infertile and unproductive and thus are a threat to food security. Many of the poorest farmers are also living and farming in these marginal lands.

Soil and water pollution is largely caused by improper disposal of municipal solid wastes, the unregulated use of pesticides and fertilizers by farmers, and mining. Most towns in the country do not have proper dumpsites. Very disturbing is the fact that many municipalities use their mangrove areas (a vital breeding place for marine organisms) as dumpsites for solid municipal wastes. The unregulated use of pesticides and fertilizers by farmers also leads to soil and water pollution. You can easily notice this from the unusual vigorous growth of algae and aquatic plants around rice fields, ponds, rivers, and bays suggesting excess amount of nutrients from fertilizers and other sources. Mining is also a major cause of soil and water pollution. It is very unfortunate that more and more areas are opened to mining. The negative environmental effects of the Bagacay Mine which operated from 1954 to 1992 are still there. Recent major efforts to rehabilitate the site have not been successful.

One last thing: when you drink a glass of water, how do you know that it is not yet contaminated with harmful chemicals?

Photo source:
The global warming figure above was taken from the Renewable Energy Blog
http://www.solarpowerwindenergy.org

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/

The role of mycorrhiza in the mineral nutrition of plants

Mycorrhiza is the association between fungi and the roots of higher plants. The term was introduced by the German scientist A.B. Frank in 1885 (Mengel and Kirkby, 2001). Mycorrhiza is considered as the most widespread association between microorganisms and higher plants. On a global scale, between 86% and 94% of plants are mycorrhizal (Brundrett 2009). All Gymnosperms as well as 83% and 79% of dicotyledonous and monocotyledonous plants, respectively, are mychorrhizal (Marschner 1995). Nonmycorrhizal plants can be found in stressed soil environments (very dry or saline, waterlogged, severely disturbed as in mining areas, infertile) or even in very fertile soils. Mycorrhizas (or mycorrhizae) are absent under all environmental conditions in the Cruciferae and Chenopodiaceae (Marschner, 1995). Generally, in root-fungus association the fungus is strongly or wholly dependent on the higher plant, whereas the plant may or may not benefit from the association. It is not also essential for plant survival except in some plants like orchids. Mycorrhizal associations are therefore either mutualistic, neutral, or parasitic depending on the circumstances although mutualism is the dominant type.

Groups of mycorrhizas

Two mycorrhizal groups according to how the fungal mycelium relates to the root structure:
a) Endomycorrhizas. The fungi live inside the cortical cells of the roots and also grow intercellularly. The best known type is the vesicular-arbuscular mycorrhiza (VAM). This is widespread in cultivated soils.
b) Ectomycorrhizas. This group of mycorrhiza occurs mainly on roots of woody plants and only occasionally on herbaceous and graminaceous perennial plants. Some temperate tree species like beech, oak, spruce and pine cannot survive without ectomycorrhiza (Schachtschabel et al., 1998). They form a sheath or mantle of fungal mycelium over the surface of fine roots. The hyphae penetrate into the intercellular spaces of the root cortex and it extends outward into the soil.

Role of mycorrhizas in the mineral nutrition of host plants

Mycorrhizas are very important in the uptake of nutrients such as P, N, K, Cu, Zn and Ca by plants especially in soils low in these nutrients. Since P is the most limiting nutrient in tropical soils, mycorrhizas are vital for improving P nutrition particularly for cultivated plants. External hyphae can absorb and translocate P to the host from soil outside the root depletion zone. The thin mycorrhizal hyphae (2-4 μm in diameter) are able to penetrate soil pores not accessible to the root hairs which are about five times larger than the hyphae (Kirkby and Mengel, 2001). For example, studies have shown that the heavily mycorrhizal root of cassava enables it to grow well in phosphate-deficient soils where other crops fail (Wild, 1993). Also, a long-term study at the National Abaca Research Center at VSU (Armecin and Geneston-Asio, 2004) has provided the first clear evidence that abaca plant (Musa textilis) is mycorrhizal although colonization was relatively low (18-22%). In alkaline soils, mycorrhiza can prevent iron and manganese deficiencies. Mycorrhizas are also known to protect the plant from soil borne pathogens.

Recently, Lambers et al. (2010) reported that terrestrial plants (except epiphytes, parasites and carnivorous species) acquire most mineral nutrients from the soil primarily via two pathways: 1) direct absorption through the roots, and 2) indirect absorption through symbiotic mycorrhizal fungi. The majority of plants can take up phosphorus via both pathways but depend primarily on mycorrhizal fungi to acquire phosphorus.

References

Armecin RB and LG Asio. 2004. Effects of vesicular-arbuscular mycorrhizal fungi inoculation on Abaca (Musa textilis). Unpublished research report. NARC, VSU, Baybay, Leyte.
Brundrett, M. 2009. Plant and Soil 320: 37-77.
Lambers H, MC Brundrett MC, JA Raven and SD Hopper. 2010. Plant and Soil 334:11-31.
Marschner, H. 1995. Mineral Nutrition of Higher Plants. 2nd ed., Academic Press, London.
Mengel, K. and E.A. Kirkby. 2001. Principles of Plant Nutrition (5thed.). Kluwer Academic Publishers, Dordrecht, 849pp.
Schactschabel P., H.P. Blume, G. Brümmer, K.H. Hartge and U. Schwertmann. 1998. Lehrbuch der Bodenkunde (14th ed.). Ferdinand Enke Verlag, Stuttgart, 494pp.
Wild, A 1993. Soils and the Environment. Cambridge University Press, Cambridge, 287pp.

Photo Sources:
1. G. Quinn at http://www.finegardening.com/
2. Nathan Brandt, Iowa State University Extension News at http://www.extension.iostate.edu/

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 excursion to Southern Leyte, Philippines with Prof. R Jahn

On 09 April 2010, we organized a soil excursion to Southern Leyte for selected graduate students pursuing MSc degree in Soil Science at the Department of Agronomy and Soil Science of Visayas State University in Baybay, Leyte. The main objective of the activity was to observe the important soils of the province.

Prof. Dr. Reinhold Jahn of Martin Luther University (Germany), former Chairman of the Soil Geography Commission of the International Union of Soil Sciences (IUSS), served as the resource person. The participants included Grace Enojada, Marilou Sarong, Katrina Piamonte, Deejay Maranguit, Glenn Largo, and Raffy Rodrigo.

The group first focused on the young soils in the alluvial plains which are generally used for lowland rice production. Prof. Jahn discussed the important features of paddy (rice) soils particularly gleying, mottling, and the occurrence of plow pan.

During his recent fieldwork in the Banaue rice terraces in northern Luzon, Prof. Jahn noted that plow pan is generally absent in the rice terraces since puddling is not part of the normal cultural management practices there. Puddling is the process of destroying the structure of rice soil by cultivating it when it is wet in order to homogenize the soil and to produce a watertight soil paste to hold water on the soil surface.

In the mountainous portion of Southern Leyte, highly weathered soils (Ultisols) that developed from basalt and other igneous rocks are widespread. The group examined a Ultisol soil profile that was very deep and heavy clay, and which showed the occurrence of mottles and exfoliation weathering of rock in the lower portion of the profile. Ultisols are acidic, clayey, and have generally low nutrient status. They are the most widespread soils in the Philippines.

The group also found a very beautiful soil profile of a Ultisol near the town of Silago. It formed from two parent materials (bisequm) and clearly showed lithologic discontinuity (i.e. the heterogeneity of the parent rock material).