Friday, September 29, 2017

Heavy metals in vegetables sold in some cities in the Visayas, Philippines


Every time we buy vegetables in the market, we do not doubt the quality of these farm products. We think they are clean, safe, nutritious and good for our health.

But the worsening environmental pollution due to the overuse and misuse of agricultural chemicals such as pesticides, the improper waste disposal, the manufacturing industry, and the transportation system may be affecting the quality of the food crops we eat everyday. Specifically, heavy metals most of which are toxic to humans at elevated concentrations, are starting to contaminate the vegetables we love to eat.

The scientific principle is simple: a contaminated soil will generally produce contaminated crops.



An interesting and very relevant student research conducted a few years ago revealed such alarming reality. Conducted to determine and compare the Pb, Cu and Zn contents of Alugbati (Basella rubra), Ampalaya (Momordica charantia), Kalabasa (Cucurbita maxima), Kangkong (Ipomoea aquatica), Pechay (Brassica rapa), and Talong (Solanum melongena) sold in markets in the cities of Baybay, Ormoc, and Tacloban (Leyte, Philippines), the study revealed that Ampalaya from Tacloban and Baybay contained excessive levels of Cu and may pose health problems to consumers. 

Likewise, Pechay from Baybay, Ormoc and Tacloban exceeded the safe level for Zn. All vegetable samples collected from the three cities were not contaminated with Pb. Cu and Zn levels varied with crop (vegetable) species and origin (production area). 

The results are very relevant in that they support and confirm the fear among consumers that some food crops sold in the local markets are not safe and may be one of the reasons for the various health problems experienced by many people.

The study was conducted in 2012 by Anna Luisa Ventulan, Christine Gay Cala, and Johannes Reiner Asio, all senior students at VSU Laboratory High School. The research adviser was Luz Geneston Asio of the Central Analytical Services Laboratory, Visayas State University, Baybay City, Leyte.

Tuesday, September 19, 2017

Impact of intensive vegetable production on the organic matter, nitrogen, and phosphorus levels of a volcanic soil (Andisol)


by Niezel Jane D. Estrellanes

Volcanic soils such as Andisols have many unique properties not usually found in soils derived from other parent materials (http:/www.ctahr.hawaii.edu). They are often very young and acidic depending on which type of volcanic materials they come from. They also largely consist of non-crystalline minerals such as allophane and imogolite (Nanzyo et al., 2002) which form strong bonds with organic matter thereby protecting it from decomposition. Andisols are usually light textured and are easy to till. However, they form strong complexes with phosphorus, rendering this element unavailable to plants.

One of the sampling sites in the central volcanic highlands of Ormoc, Philippines
This thesis research, a component of the Australian Center for International Agricultural Research (ACIAR) Soil Project based at the Visayas State University, evaluated the impact of intensive vegetable production on the nitrogen and phosphorus levels of volcanic soils in the central highlands of Leyte specifically in Cabintan, Ormoc City, Philippines. Twelve sampling sites (vegetable farms) including a reference site were chosen for this study. The objective was to find out if the continuous and heavy application of fertilizers for intensive vegetable production have caused the accumulation of nitrogen and phosphorous in Andisols.

Soil samples were taken from the following soil depths 0-20, 20-40, 40-60, 60-80 and 80-100 cm using a soil auger. They were air-dried and passed through 2-mm sieve and analyzed for selected physical and chemical parameters such as pH (H2O, KCl and NaF), available phosphorus and particle size distribution. Enough 2-mm samples were also ground further and allowed to pass through 0.425-mm for organic matter content and total N analysis. 
Soil OM contents of the sampling sites. Sites 2, 4, 6 and 7 have much 
higher values than the reference site 12.
Soil N contents of the sampling sites. Most of the sites have much higher 
N levels than the reference site 12
Soil available P contents of the sampling sites. Reference site (12) has 
much lower P levels compared to all other sites.
Results revealed that majority of the vegetable farms sampled showed higher amounts of organic matter (OM), nitrogen (N), and available phosphorus (P) than the reference site (secondary growth forest). This clearly indicates the impact of the high and continuous application of chemical and organic fertilizers (chicken manure). The very high nitrogen contents of the soils point out to nitrogen pollution which could have serious negative impact on the groundwater quality. The high available phosphorus contents of the soils suggest improvement of the supply of this nutrient to the crops considering the fact that it is the major limiting nutrient to crop production in Andisols.

Based on the results it can be concluded that:
a. The intensive vegetable production has increased the nutrient status of the Andisol; 

b. The frequent and high rates of fertilizer application for the intensive vegetable production have greatly increased the nitrogen and phosphorus contents of the Andisol soil.


Tuesday, April 18, 2017

Ecological quality, macroinvertebrate communities and diversity in rivers in Leyte, Philippines


Researchers from the Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, Belgium, in collaboration with researchers from the Institute of Tropical Ecology and Environmental Management of Visayas State University in Leyte have published scientific evidence of a strong link between ecological quality and macroinvertebrate communities and diversity in rivers in Leyte.

In a paper published this year (2017) in the prestigious journal Ecological Indicators, Vol. 77 and pages 228-238, Marie Anne Eurie Forio and colleagues assessed the macroinvertebrate communities, diversity, and ecological quality of 85 rivers on Leyte island. Specifically, they evaluated the biological (macroinvertebrates), chemical, physical and hydromorphological characteristics. Canonical Correspondence Analysis (CCA) and multivariable linear regression (LRM) were performed to relate the environmental variables and macroinvertebrates.

Eurie Forio and Daphne Radam during the field sampling in Cabintan, Ormoc
(at the central highlands of Leyte) in 2015
The researchers found several taxa of snails, shrimps, dragonflies, beetles, bugs and caddisflies. Although many sites had good to very good ecological quality and high diversity, about 41% had moderate to very bad ecological quality and low diversity. Based on CCA, the researchers concluded that macroinvertebrate communities were associated with velocity, sediment, conductivity and dissolved oxygen. They also observed that sensitive and tolerant taxa were encountered at high and low flow velocities, respectively. Moreover, LRM indicated that macroinvertebrate diversity and ecological quality were associated with physical (turbidity), chemical (chlorophyll), hydromorphological characteristics (bank slope & pool/riffle class), habitat degradation (gravel/sand quarrying, erosion) and the presence of logs and twigs.

Eurie Forio (lead author) and Prof. Peter Goethals (lead scientist)
This ecological study, the first of its kind (i.e. covering 85 rivers of an entire tropical island) to be conducted in the Philippines, supports the use of invertebrates as indicators of certain environmental conditions and the results of this investigation can serve as a basis to set up dedicated experiments to further prove the causality of these discovered relations. 

The study also revealed that organic pollution, as reflected by biological oxygen demand and chemical oxygen demand, was weakly related to invertebrate composition, diversity and ecological quality. This was linked to the low input in most sites and the relatively short rivers which are closely connected to the marine system. Thus, typical midstream and downstream systems were not encountered and the accumulation of these pollutants along the river is less likely. Although the island encounters intensive natural disturbances (e.g. severe typhoons), the taxa (families) were similar to those in other tropical systems and the effects of the environmental conditions were comparable.

The findings of this collaborative research are relevant and valuable in understanding the ecology of tropical islands. They also provide insights into the effects of environmental conditions on stream invertebrates, which aids in protecting and conserving tropical insular systems.

Reference:


Forio, M.A.E., K. Lock, E.D. Radam, M. Bande, V.B. Asio and P.L.M. Goethals (2017). Assessment and analysis of ecological quality, macroinvertebrate communities and diversity in rivers of a multifunctional tropical island. Ecological Indicators 77 (2017) 228–238

Tuesday, January 3, 2017

Cape Bojeador, Paoay Sand Dunes, Kapurpurawan White Rocks, Bangui Windmills, Pagudpud Resorts, and Cagayan River: Just a few of North Luzon’s wonders worth visiting

A tour around the northern tip of Luzon is really an amazing experience. For those interested in our natural environment, it is a must. This short report describes briefly some of the wonderful places that one can visit starting from Vigan City in the west (1) to Cagayan Valley in the east (10).


Vigan City
Vigan is an old city in Ilocos Sur with well-preserved Spanish colonial and Asian architecture. This UNESCO World Heritage site reminds me of some small towns in southern Spain. It is without question the most beautiful old city in the Philippines.


The Paoay Sand Dunes
The sand dunes area appears to be a raised sea bed. First evidence of this is the fact that it is directly adjacent to the sea. Second reason is the presence of shells of marine organisms in many parts of the area. Third, a road cut exposure east of the sand dunes reveals thick sandstones (formed under the sea) which could be the source, through weathering, of the sand particles. The subduction of the Sunda Plate underneath the Philippine Mobile Belt produced the Manila Trench in the South China Sea and has resulted in the uplift of northwest Luzon. Decades of soil mismanagement and the resulting soil erosion have without doubt contributed to the spread of the sand dunes.   


Cape Bojeador
This is the headland at the northwestern tip of Luzon in Burgos, Ilocos Norte. The raised marine terrace is flanked to the east by steep-sided volcanic and greywacke hills and to the west by the turbulent South China Sea. Perched on top of the hill at about 90m asl is the famous Cape Bojeador Lighthouse constructed in 1892 during the Spanish Colonial period.



Kapurpurawan White Rock Formation
The famous white rock formation in Kapurpurawan, Burgos, is actually a raised reef limestone that has been carved by the waves through time. The raised limestone is associated with the uplifting of northwest Luzon as a result of the subduction of the Sunda Plate underneath the Philippine Mobile Belt as has been mentioned above.



Bangui Windmills
Standing 70 m tall on the black sand beach of Bangui, Ilocos Norte, are 20 giant wind turbines (giant fans) facing the South China Sea in the direction of Taiwan. The area is so windy making it ideal for such a modern energy harvesting facility.


Pagudpud Resorts
A large resort and convention center called Hanna’s Beach Resort is found near the northernmost tip of Luzon and hidden from the highway by the mountain range in Balaoi, Pagudpud, Ilocos Norte.  The bay, which has fine white sand, is unique in its location and local geography. A chat with the locals would reveal controversial stories about the real owner of the resort.



Patapat Viaduct
One of the many major infrastructure projects of former President Marcos is the Patapat Viaduct in Pagudpud, Ilocos Norte. The 1.3 km bridge is elevated about 30 meters above the sea and connects the Maharlika Highway from Laoag, Ilocos Norte  to the Cagayan Valley Region. It is now part of the Asian Highway network (AH 26).


Anahaw Plantations
Anahaw or anahau (Livistona rotundifolia) is an erect palm that is widespread in northern Luzon particularly in Claveria, Cagayan. This makes the landscape in this part of Luzon different to the monotonous coconut plantations in the Visayas.


The Cagayan River
The Cagayan River (the Rio Grande de Cagayan) is considered as the second largest river in the Philippines next to the Rio Grande de Mindanao. The mighty river in the Cagayan Valley region traverses the provinces of Nueva Vizcaya, Quirino, Isabela and Cagayan and has a drainage area of about 27,300 square kilometers. The picture below shows the river from the Magapit Bridge in Magapit, Cagayan.


Soil Degradation in Cagayan Valley
Deforestation followed by decades of grazing (pasture) have caused widespread soil degradation in Cagayan Valley. This is clearly observable from Tuguegarao City down to Enrile and Sta Maria, Cagayan where the traveler sees an endless view of denuded and degraded hills and mountains.

Sunday, October 23, 2016

What is soil analysis?

President Rodrigo R. Duterte emphasized the conduct of soil analysis in the country during his first State of the Nation Address (SONA) on July 15, 2016. He said that “we shall also conduct a nationwide soil analysis to determine areas most suitable for rice farming to optimize production with the use of effective soil rehabilitation and fertilization.”

As an effect of this presidential pronouncement, many people including professionals from various academic fields have been wondering what soil analysis is. Several readers of this blog suggested that I write about this topic hence, this article.

Soil analysis refers to the measurement of soil physical, chemical, and biological properties. It is done, depending on the type of soil analysis, for the following purposes: 1) to evaluate the origin and formation of the soil; 2) to assess the level of contamination of the soil; 3) to characterize the soil as a habitat of soil organisms; 4) to assess the soil fertility status; and 5) to evaluate the soil’s suitability for certain crops. Soil analysis is generally synonymous with soil testing. The major steps of soil analysis are soil sampling (and field soil examination) and laboratory analysis.

Soil profile examination and sampling to evaluate the origin of the soil
The first type of soil analysis is the most difficult and complex type. It is carried out by soil specialists called pedologists.  It involves detailed field description of the soil using standard procedures such as the Guidelines for Soil Description (4th edition by Jahn et al., 2006) published by FAO, Rome. Soil description is done on newly dug soil pit at least 1.5m deep or fresh road cuts. Collection of soil samples for intensive laboratory analysis is done on every soil layer (soil horizon) down to the bedrock. Laboratory analyses include the physical, chemical and mineralogical properties of the soil. Geochemical analysis of rock samples is also necessary.

The second type is conducted by soil scientists interested in soil pollution or contamination. Soil samples are usually collected in areas where soil contamination is suspected. Soil sampling is done at random or at fixed interval. Only the top soil layer (0-10 or 0-20 cm) is sampled using a soil auger or similar sampling tool. Soil samples are analyzed for their contents of soil pollutants (e.g. heavy metals) and are compared with published threshold values to know if the sample is contaminated or not.
Soil sampling to assess the contamination of Taft River in E. Samar
The third type of soil analysis is conducted to know if the soil is favorable for certain soil organisms of interest (e.g. earthworms). This is popular among soil ecologists. Soil samples are collected usually from the top soil layer and then they are analysed for soil physical and chemical properties. Correlation analysis is then done between the population of the soil organism and the different soil properties to know which among the soil properties influences the population of the organisms.

The fourth type is the most well-known and commonly done type of soil analysis to support crop production. The main purpose is to know if the soil is fertile or not. Specifically, it is performed to assess, using high-tech laboratory equipment,  if the soil contains sufficient amounts of the essential nutrients required by plants (crops) to grow well and produce good yield (grain, tubers). The essential nutrients that the pant takes up from the soil include: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulphur (S), iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), molybdenum (Mo), boron (B), chlorine (Cl) and nickel (Ni). Since N, P and K are required by the plant in largest amounts, these three are usually the nutrients that are of limited supply in the soil. So farmers need to know how much of these nutrients must be applied to the soil through fertilizers. The final result of this type of soil analysis is a fertilizer recommendation.
Soil sampling for fertility evaluation
The fifth and last type of soil analysis is carried out to assess if a certain soil is suitable for crops such as rice, corn, vegetables, fruit trees, and others. This involves field soil examination to know the soil’s texture, structure, drainage, slope and depth using the methods of the first type of soil analysis. The soil samples are analysed for soil chemical properties such as soil pH, organic matter content, nutrient holding capacity as well as the amounts of the major nutrients (similar to the third type of soil analysis). The soil properties are then matched with the ecological requirement of the crop. The final result is a suitability map or table showing the suitable crops for each soil. It also indicates the soil constraints (or problems) if a crop is grown in a soil that is not suitable for that particular crop.

From the president’s pronouncement, it looks like that he meant the fifth type of soil analysis. Due to the tremendous amount of field and laboratory works, it cannot be done by the Bureau of Soil and Water Management alone. It needs the participation of universities with strong soil science program throughout the country such as Central Luzon State University, University of the Philippines Los Banos, Visayas State University, Central Mindanao State University, and University of Southern Mindanao.
Soil science students at VSU performing laboratory analysis of soil samples
The laboratory step of soil analysis or soil testing is tedious, time-consuming, and costly because the chemicals and apparatus required are very expensive. Although there are some rapid soil test kits available, they are not reliable. Also, the laboratory analysis has to be done according to accepted procedures and by trained personnel. Examples of accepted procedures of laboratory analysis of soils are:

Carter M.R. and E.G. Gregorich (Eds.). 2008. Soil Sampling and Methods of Analysis (2nd ed). CRC Press, Boca Raton.
International Soil Reference and Information Center (ISRIC). 1995. Procedures for Soil Analysis (L.P. Van Reuwijk, Editor). Wageningen, the Netherlands.
Jones J. B. Jr. 2001. Laboratory Guide for Conducting Soil Tests and Plant Analysis. CRC Press, Boca Raton.
Margesin R. and F. Schinner(Eds.). 2005. Manual for Soil Analysis – Monitoring and Assessing Soil Bioremediation. Springer Verlag, Berlin.
Pansu M. and J. Gautheyrou. 2006. Handbook  of Soil Analysis. Mineralogical, Organic  and Inorganic Methods. Springer Verlag, Berlin.
Schlichting E., H.P. Blume and K. Stahr. 1996. Bodenkundliches Praktikum (Soil Science Practicum). Blackwell Wissenschaftsverlag, Berlin.
Sparks D.L., A.L. Page, P.A. Helmke and R.H. Loeppert (Eds.). 1996. Methods of Soil Analysis Part 3—Chemical Methods. Soil Science Society of America, Madison, Wisconsin.
Westerman R.L. (Ed.). 1990. Soil Testing and Plant Analysis (3rd ed). Soil Science Society of America, Madison, Wisconsin.

Thursday, September 15, 2016

Refocusing Agriculture in the Philippines

Refocusing Agriculture: Excerpt from my Convocation Speech at the 45th Founding Anniversary of Visayas State University (VSU)-Alangalang Campus, Leyte, Philippines on 09 Sept 2016.

By V.B. Asio

Your theme “Agrivolution: refocusing farming for food and nutrition security” is very timely and very relevant.

When I was an agriculture student in ViSCA in 1980, the agriculture battle cry was: we need to increase crop yield by increasing the yield per unit area and by cultivating new lands because of rapidly increasing population. Population of the country at the time was only 48 million. The hot research topic was farming system, which slowly became cropping system, then sustainable agriculture or ecological farming, and now organic agriculture. If you examine these farming strategies, they are closely related. But the last, which is organic agriculture, has become very narrow in scope and very impractical in many aspects.
Highly productive alluvial lands in Baybay, Leyte, are threatened by conversion into residential areas 
But where are we now?

Now more than 30 years have passed, with a staggering country’s population of more than 100 million, we still have the same battle cry:  to increase food production by increasing yield per unit area and by opening new lands. This time though, there are a lot more complications. The problem of increasing food production has become more urgent, and very problematic. Let me cite some reasons:

1.       The gap between population increase and food production has greatly widened. Our population has more than doubled but crop yield has not doubled despite the availability of new high yielding varieties, fertilizers and pesticides. For example, average rice yield in 1980 was 2.3 tons/ha. Now it is only 3.8 tons/ha. What is aggravating the problem is that production cost has greatly increased, and the area of our agricultural lands have decreased.

Many of the new high yielding varieties which showed great potential in the experimental stations, have failed to show their yield potential in the actual world-- in farmers’ fields . According to Dr. Francisco of Philrice in an undated paper, the yield gap ranges from 2 t/ha in the wet season, to 3.9t/ha in the dry season. This also partly explains why we cannot find our new high yielding varieties (say, of sweetpotato) in farmers’ farms in Leyte and Samar.

2.       There is increasing soil degradation due to destructive farming practices, resulting in the decline in soil fertility. This is coupled by increasing incidence of pests and diseases. The latter triggers the farmers to over apply pesticides. In our on-going ACIAR-funded soil research, vegetable farmers in the Visayas and some parts of Mindanao just apply any amount of fertilizers without scientific or logical basis. Worse, they over-apply a cocktail of pesticides, 2-3 times a week, endangering the health of the consumers.

3.       As if to make matter more difficult for the next generation, the widespread soil degradation is accompanied by the shrinking of our prime agricultural lands because of urbanization. Urbanization is eating fast our rice lands. In many parts of the country, you would see former productive rice lands have become subdivisions, factory sites and shopping malls.

4.       Climate change has entered the picture. It has changed rainfall pattern, temperature fluctuations, and occurrence of typhoons, floods, and drought. Crops are now subject extreme weather conditions. In short, we are in a more challenging and exciting agriculture.

5.       As a result of the over-application of farm inputs, there is also a degradation of the environment. Soil, water and air pollution are very serious in many places.

6.       This has led to the rise of the organic agriculture movement. The Philippine government has enacted the Organic Agriculture Act of 2010. But we know that organic agriculture cannot produce the amount of food required to feed the fast rising population of the country. Organic agriculture cannot feed our more than 100 million population.
So, we are now facing a dilemma:  protect the environment even if the food production is low, or continue the environmentally damaging practices but with a higher food production. This is like the choice between the ocean and the deep blue sea.

7.       The Genetically Modified Organisms (GMO) technology hold great promise for some crops, but are we sure that they are safe? The debate is raging in the international scientific community. Time will tell if GMO crops are really safe to our health and to the environment.

8.       Despite the more than 40 years of designing of agricultural implements, most of our farmers are still practicing manual labor due to a lot of reasons. Have we really looked into why majority of our farmers are not using modern farm implements until now?

9.       What threatens further our agriculture is the decreasing interest in farming among our young generation. It seems everybody wants a happy and easy life. Interest in agricultural science has continued to decline as reflected by the general decline in enrollment in universities and colleges around the country (fortunately, our enrolment in agricultural sciences at the main campus has continued to increase in the last five years).

10.     The mainstream media are partly to blame. Just observe what kind of TV programs are created and promoted. To cite an example, beauty contests are very popular because of the intense media campaign. No wonder many young girls dream to be a beauty queen instead of becoming scientists. The media have failed to create awareness among the youth about the importance of agriculture or about science. And of course, our government institutions too. Much of the blame should go to them.

What should we do? How can we refocus farming or agriculture?

The problem is so serious and so complex. It needs the active participation of all sectors involved. As an academician, I will just focus on the things that we can do in the academe.

1.      There is a need for retooling of those involved in teaching students agriculture. Agricultural science now is different in many aspects from that 30 years ago.
2.       We need to revise and improve our curricula and the courses we are offering.
3.    We need to change our strategy in promoting agriculture. If we still project agriculture using the image of a farmer with the plow and the carabao, we will not gain bright young students to agricultural science.
4.       There is a need for more involvement of our students in OJT in successful and progressive farms.
5.      We need more reliable data on the effects of fertilizers on crop yield. In the last decade, everywhere, there has been a sprouting of all kinds of organic fertilizers whose efficacy have not been scientifically verified. Proponents just cite anecdotal evidence to promote their products. This has led to the erosion in people's confidence in organic fertilizers.
6.     We need to change our strategy in extension. We need to educate more our farmers. How? It is for all of us to think about.

Before I end my talk let me quote Masanobu Fukuoka, a Japanese farmer and philosopher. He said that:

 “The ultimate goal of farming is not the growing of crops, but the cultivation and perfection of human beings.


Thank you for your kind attention. Happy 45th Anniversary to VSU-Alangalang!


Thursday, September 1, 2016

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 about tropical soils (Jahn and Asio , 2006):

  1. The tropics,  the world’s largest ecological zone, have 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.
  1. 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.
  1. 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.
  2. 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).
  3. 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.
  4. Due to severe chemical limitations, proper management of nutrients is the main challenge for effective land use systems in the tropics.
  5. 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.
  6. 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.
  7. 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.