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.

Location of the sampling sites in Cabintan, Ormoc City

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 the 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 a 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.

c. Nitrate and phosphate pollution of the groundwater and the nearby rivers may result from intensive vegetable production. 

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.

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

Anthropocene: The Human Age

Anthropocene is the term coined in 2000 by Paul Crutzen, the Nobel laureate from the Max Planck Institute for Chemistry, Mainz, Germany, to refer to the current geological epoch characterized by the global impact of human activity. The Anthropocene Working Group of the International Commission on Stratigraphy defines it as the present time interval, in which many geologically significant conditions and processes are profoundly altered by human activities (www.quaternary.stratigraphy.org). 

The conditions and processes include changes in: erosion and sediment transport associated with a variety of anthropogenic processes, including colonisation, agriculture, urbanisation and global warming; the chemical composition of the atmosphere, oceans and soils, with significant anthropogenic perturbations of the cycles of elements such as carbon, nitrogen, phosphorus and various metals; environmental conditions generated by these perturbations which include global warming, ocean acidification and spreading oceanic 'dead zones'; the biosphere both on land and in the sea, as a result of habitat loss, predation, species invasions and the physical and chemical changes noted above (www.quaternary.stratigraphy.org) 

According to a recent article in Nature Vol 519 (12 March 2015) by Richard Monastersky, momentum is building to establish a new geological epoch that recognizes humanity’s impact on the planet. But there is fierce debate among scientists whether or not to revise the Geologic Time Scale which is used by millions of people around the world, to accommodate the Anthropocene on top of the Holocene epoch (see scale below).

Source: www.serc.carleton.edu

One focus of the debate is the start of the new epoch. When did it actually began? Recent suggestions include 1610 and 1964. The 1610 suggestion is based on the dip in atmospheric carbon dioxide (measured from Antarctic ice cores) due to forest regeneration of huge areas of abandoned farmlands in Europe. The 1964 proposal is based on the high proportion of radioactive isotopes from the nuclear weapons testing (R. Gonzalez at www.io9com). But the Anthropocene Working Group considers the beginning of the 'Anthropocene' as c. 1800, around the beginning of the Industrial Revolution in Europe.

Once the proposal for an Anthropocene epoch is, after a long process, accepted by the International Union of Geological Sciences, the Quaternary period in the Geologic Time Scale above would consist of three (not anymore two) epochs: Pleistocene (2.6 mya to 12,000 yrs ago), Holocene (12,000 yrs ago to c. 1800) and Anthropocene (c. 1800 to present).

Some notes on the soils and use of fertilizers and pesticides by vegetable farmers in Claveria, Misamis Oriental, Philippines

The gently rolling topography which typifies a large portion of the volcanic landscape in Claveria makes it ideal for intensive large-scale vegetable production. The widely grown vegetables include cabbage, beans, tomato, sweet pepper and eggplant.

The breathtaking volcanic landscape of Claveria, Misamis Oriental

But the strongly weathered soils which range from Oxisols in the lower slopes (about 400 to 600 m above sea level or asl) to Ultisols in the upper slopes (about 600 to 900m asl) are a major constraint to vegetable production in the area. Oxisols (also called Ferralsols) and Ultisols (also called Alisols and Acrisols) are clayey, reddish, acidic and nutrient-poor soils although they generally have good physical properties like good structure and moderate to high porosity. As in other volcanic landscapes, the oldest and most infertile soils (Oxisols) are formed on the older and stable lower slopes.

Dr. Apol & Nelds Gonzaga, Ruby Gabaca, Dr. Steve Harper & myself in front of an Ultisol soil at 920m asl. 

Farmers are apparently aware of the chemical and nutrient limitations inherent in these soils. That is why they apply lime and a variety of chemical and organic fertilizers. Rates of application are, however, not based on soil/plant tissue analysis but on what the farmers perceive as necessary. Thus, the rates appear to be insufficient in the case of lime, but excessive for the chemical fertilizers. This undoubtedly increases the production cost and can lead to more soil and environmental problems like acidification and groundwater pollution, respectively.

Heavy fertilizer application is done starting at planting of vegetables

Pest and diseases are also greatly affecting vegetable production in the Claveria landscape. As a result, farmers practice excessive application of pesticides which poses a serious threat to the health of the farming families, the consumers in urban centers, and the environment in general. The lack of awareness among farmers about the proper application of pesticides can be seen from their improper handling of these hazardous chemicals and from the fact that they just leave the pesticide containers at the farm borders.

It is common for farmers to mix two pesticides with water and spray the cocktail to the vegetables twice a week

The above observations strongly justify the urgent need for research on soil and nutrient management as well as integrated pest management in Claveria.

Ulrich’s soil acidification hypothesis on forest decline

In 1979, Bernhard Ulrich was the first researcher to discover the connection between air pollution and the forest decline or dieback (Waldsterben) in Germany. He hypothesized that acid rain results in soil acidification which in turn causes the forest dieback phenomenon. According to his soil acidification hypothesis, as soil becomes more acidic there is a release of aluminum that damages the roots of the trees. This leads to the following effects: reduction in uptake and transport of some cations, reduction in root respiration, damage to fine feeder roots and root morphology, and reduction in elasticity of the cell walls. The discovery was first published by Ulrich and co-workers in "Deposition von Luftverunreinigungen und ihre Auswirkungen in Waldökosystemen im Solling." Schriften Forstl. Fak. Univ. Goettigen 58, Sauerländer Verlag, Frankfurt a.M., 291pp. 

Photo source: www.museumplatkow.de

In 1986, Ulrich put forward his 8 theses on soil acidification which appeared in the Journal of Plant Nutrition and Soil Science 149: 702-717 (1986) as follows:

1. Rocks contain only bases and no acid precursors. Therefore, with the exception of sulfide containing rocks, soils cannot acidify as a result of atmospheric rock weathering.

2. A consumption of protons in rocks and soils results in a decrease of their acid neutralizing capacity and can result in the buildup of a base neutralizing capacity.

3. Weak acids (carbonic acid) lead in geological times to the depletion of bases without a larger accumulation of labile cation acids. Strong acids (HNO3, organic acids, H2SO4) can lead within a few decades to soil acidification.

4. The acid input caused by the natural emission of SO2 and NOx can be buffered by silicate weathering even in soils low in silicates.

5. The cause of soil impoverishment and soil acidification is a decoupling of the ion cycle in the ecosystem.

6. Acid deposition in forest ecosystems which persists over decades leads to acidification.

7. Formation and deposition of strong acids with conservative anions (SO4, NO3) shifts soil chemistry into the Al or Al/Fe buffer range up to a great soil depth.

8. In the long run, soil acidification by acid deposition results in the retraction of the root system of acid tolerant tree species from the mineral soil, and in water acidification.

Bernhard Ulrich was professor of forest soil science and forest nutrition at the University of Goettingen, Germany, from 1965 until his retirement in 1991. He obtained his PhD in agricultural science from the University of Hohenheim, Stuttgart, in 1953 based on a dissertation on the rapid determination of soil cation sorption capacity. He was widely recognized as the leading expert of soil acidification and forest ecosystem research.

The arsenic contamination in rice

Arsenic (As) is a heavy metal that is well-known as a poison and a carcinogen. Its average concentration in the soil ranges from 5 to 6 mg/kg which is generally related to rock type and industrial activity.

Arsenic contamination of paddy soils is widespread and elevated arsenic levels in rice grains is now a hot issue in many parts of the world. Martha Rose Shulman wrote in the New York Times (15 April 2013) that “it is clear that the levels of inorganic arsenic in rice and rice products are high, and that we and especially children, babies and pregnant women should limit our intake of rice and rice products.”

According to Bogdan and Schenk (2012) in their recent study published in the highly respected Journal of Plant Nutrition and Soil Science (Wiley-VCH Verlag GmbH), flooded rice may contain high arsenic concentration compared to other grain crops. In fact, aside from arsenic-contaminated drinking water, rice is the largest food dietary source of inorganic arsenic. This is because the reducing environment in flooded rice fields causes the dissolution of arsenic and thus increases its availability to the rice plant. Meharg (2004) added that under paddy field conditions, inorganic arsenic introduced into the soil is inter-converted between the reduced inorganic species arsenite (the dominant type) and the oxidized species arsenate. Moreover, arsenite is taken up into the root by the highly efficient Si pathway and arsenate can be taken up via the phosphate transport system.

Bogdan and Schenk (2012) observed among other things that continuous arsenic supply in the soil resulted in a doubling of arsenic concentration in rice shoot and grains. They also found that arsenic was mobilized from the root and shoot to the rice grains where it accumulated.

References
Bogdan K. and M.K. Schenk. 2012. Arsenic mobilization in rice (Oryza sativa) and its accumulation in the grains. J. Plant Nutr. Soil Sci. 175: 135-141.
Meharg A.A. 2004. Arsenic in rice-understanding a new disaster for South-East Asia. Trends in Plant Science 9: 415-417.

Environmental pollution: the case of Xenobiotics

Xenobiotics are chemical substances that are foreign to the biological system. They include naturally occurring compounds, drugs, and environmental agents (Mondofacto online medical dictionary at www.mondofacto.com). The classes of xenobiotics include pesticides, polyaromatic hydrocarbons (PAHs), polychlorinated aromatics, solvents, hydrocarbons, and others (surfactants, silicones, and plastics).

Xenobiotics levels in soils are generally low (less than 100 ppm) unless they are concentrated by application as in the case of pesticides, by spills or by waste disposal. They can occur in soils in solid, dissolved, and gaseous phases and all undergo microbial and abiotic (chemical) transformations (Logan, 2000).

Photo source: www.cleanwaterfund.com

Pesticides are the most important xenobiotic pollutants because of their widespread use in agriculture. In many developing countries, the unregulated use of pesticides by poor farmers contributes not only to environmental pollution but to health problems as well.

In the soil, pesticides can be temporarily fixed through adsorption by soil particles. The persistence or decomposition of pesticides in the soil is influenced by soil moisture, organic matter content, redox potential, soil acidity, soil temperature, texture, adsorption potential, and clay minerals (Schactschabel et al., 1998; Sonon and Schwab, 2004).

References

Logan, T.J. 2000. Soils and environmental quality. In: Handbook of Soil Science (M.E. Sumner, ed.). CRC Press, Boca Raton, pp: G155-G169.

Schactschabel P., H.P. Blume, G. Brümmer, K.H. Hartge and U. Schwertmann. 1998. Lehrbuch der Bodenkunde (14th ed.). Ferdinand Enke Verlag, Stuttgart.

Sonon, L.S. and P.A. Scwab. 2004. Transport and persistence of nitrate, atrazine, and alachlor in large intact soil columns under two levels of moisture contents. Soil Science 169: 541-553.

How does mining affect the environment?

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

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

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

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

References

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

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

Soil pollution and human health

People living in areas with fertile soils are better nourished than those living in degraded soils due to the higher quantity and quality of food in the former than the latter. Likewise, people living in polluted environments are more exposed to the ill effects of pollutants. The paths of environmental contaminants leading to humans are the following (Logan, 2000):

a) Soilàcropàhuman

b) Soilàlivestockàhuman

c) Soilàcropàlivestockàhuman

d) Soilàsurface watersàfishàhuman

e) Soilàgroundwateràhuman

f) Soilàairàhuman

g) Soilàhuman

The pathways a to e are indirect links between soil and human health and are relatively well-known. The pathways f and g are direct links and are little known and understood.

Direct links between soils and human health is geophagy

Humans ingest soil either involuntarily or deliberately. For the involuntary ingestion, every person ingests at least small quantities of soil. This is because any soil adhering to the skin of fingers may be inadvertently taken in by hand-to-mouth activity. This is especially true for children who like to play outdoors and for people working outside buildings or in the fields. Soil is also an important constituent of household dust and many foods such as fruits, vegetables and tubers crops usually contain some soil particles especially in poor countries. It is estimated that an average adult ingests soil at a rate of 10 mg per day.

Geophagy is the deliberate ingestion of soil by humans and animals. It is practiced by different peoples in all continents but is most common in the tropics particularly in Africa. This phenomenon was already known in the ancient world but the first detailed scientific report about it was written by the great German naturalist and founder of geography Alexander von Humboldt during his expedition of 1799-1804 to South America. Von Humboldt observed that eating soil was practiced by the indigenous Ottomac people in the Orinoco in Venezuela. The reasons for geophagy are still being debated until now but are known to vary from place to place. These include: soil as famine food to appease the pangs of hunger, as medicine and therapeutic (recent research has shown that clay adsorbs and detoxifies toxins and has antimicrobial action), cravings and good taste especially for pregnant women, as source of mineral nutrients to correct deficiencies, and an abnormal appetite for non-food substances. But excessive soil intake can lead to death of an individual due to the toxic effects of some mineral elements like Fe. This is likely to happen if the soil is contaminated with pollutants. Ingesting soil can also cause ingestion of eggs of parasitic worms and other disease-causing organisms (Abrahams, 2002; Dominy et al., 2004).

Another direct link between soil and human health occurs through inhalation. People inhale soil dusts inside their houses and by just walking in the street. The amount of inhaled dusts under normal conditions is generally low and thus is not harmful. But very dusty environments can cause lung problems. Also inhalation of even small amounts of the fibrous dust of serpentine and amphibole minerals commercially called asbestos is dangerous in that it can cause diseases and even cancer.

References

Abrahams, P.W. 2002. Soils: their implications to human health. The Science of the Total Environment 291: 1-32.

Dominy N.J., E. Davoust, and M. Minekus. 2004. Adaptive function of soil consumption: an in vitro study modeling the human stomach and small intestine. Journal of Experimental Biology 207: 319-324.

Logan, T.J. 2000. Soils and environmental quality. In: Handbook of Soil Science (M.E. Sumner, ed.). CRC Press, Boca Raton, pp: G155-G169.