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. 

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.

Organic Fertilizers, Organic Plant Growth Regulator, and Organic Plant Supplement as defined in the new Philippine National Standard for Organic Fertilizer

The new Philippine National Standard (PNS) for Organic Fertilizer was published in 2013 by the Bureau of Agriculture and Fisheries Product Standards (BAFPS) of the Department of Agriculture (PNS/BAFPS 40:2013).

According to this new PNS, Organic Fertilizer is “any product in solid or liquid form, of plant (except by-products from petroleum industries) or animal origin that has undergone substantial decomposition that can supply available nutrients to plants with a total Nitrogen (N), Phosphorus (P) and Potassium (K) of five to seven percent (5-7%). This may be enriched by microbial inoculants and naturally occurring minerals but no chemical or inorganic fertilizer material has been added to the finished product to affect the nutrient content.”

Organic Plant Growth Regulator/Promoter is “any compound of organic origin, in liquid or solid form, which in low concentration promotes or modifies physiological process in plants.”

Organic Plant Supplement is “any compound of organic origin in liquid or solid form which in low concentration promotes or modifies physiological processes in plants. Total NPK is not lower than 0.5% and not more than 2.5% (0.5-2.5%) and may contain beneficial microorganisms, micronutrients and plant growth regulators. These plant supplements include, but are not limited to: FPJ (Fermented Plant Juice), FFJ (Fermented Fruit Juice), FAA (Fish Amino Acid), FE (Fish Emulsion), Seaweed Extracts, Vermi Tea, Compost Tea and the like.”

The Technical Working Group which prepared the new/revised PNS was composed of: Dr. Leo P. Caneda, Executive Director, BAFPS (Chair) and the following members: Dr. N.B. Inciong (Professional Regulation Commission), Dr. E.P. Paningbatan Jr (Univ Philippines Los Banos), Dr. E.S. Paterno (UPLB), Dr. P.B. Sanchez (UPLB), Dr. V.C. Cuevas (UPLB), Dr. G.V. Pangga (UPLB), Dr. B.M. Calub (UPLB), Dr. N.E de la Cruz (Central Luzon State University), Dr. V.B. Asio (Visayas State University), Ms. J.B. Lansangan (Fertilizer and Pesticide Authority), Ms. P. Orpia (Bureau of Soil and Water Management), Ms. L.K. Limpin (Organic Certification Center of the Phil), Mr.  A. Aquino (Negros Island Certification Agency), and Mr. P.Belisario (Organic Producers and Traders Association).

History of the soil organic matter conversion factor of 1.72

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

Origin of the conversion factor

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

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

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

Who was Emil Wolff?

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

Prof. Emil Wolff (Source: Hohenheim Univ)

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

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

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

Methane emission from rice fields

Methane (CH4) and carbon dioxide (CO2) are the end products of carbon decomposition in rice fields and other wetlands. Methane, a major greenhouse gas, is the terminal step of the anaerobic breakdown of organic matter in wetland soils. It is exclusively produced by methanogenic bacteria that can metabolize only in the absence of free oxygen and at redox potentials below -150 mV (Neue et al. 1997).

According to the above-cited paper by Dr.H.U. Neue (former Head of the Soils Department at IRRI and later Professor of Soil Chemistry at the University of Halle-Wittenberg, Germany) one of the pioneers in methane research in rice fields, methane is largely produced by transmethylation of acetic acid and to some extent, by the reduction of carbon dioxide in wetland soils.

The rate and pattern of organic matter addition and decomposition also contribute to the rate and pattern of methane production. In rice field, methane production generally increases during the cropping season. Easily degradable soil carbon, plant litter, root exudates, decomposing roots and aquatic biomass that are added to the anaerobic zone of the paddy soil (this is the zone below the thin oxidized or brown soil surface) are the major carbon sources for methane production.

Presently, there is widespread research interest in the development of methods and strategies to reduce methane emission from rice fields and other wetlands. Some early studies have shown that sodium chloride at high concentration inhibits methane formation. Addition of sea water has also been found to inhibit methane formation at low salt concentration because of its sulfate content. Very recently, Dr. Roel R. Suralta and colleagues at Philrice, Nueva Ecija, have demonstrated that iron fertilizer application significantly reduced methane emission from rice field. More importantly, the iron fertilizer application also increased rice yield (Suralta et al., 2011).

References

Neue HU, JL Gaunt, ZP Wang, P Becker-Heidmann, and C Quijano. 1997. Carbon in tropical wetlands. Geoderma 79: 163-185.

Suralta RR, FS Gorospe, CA Asis Jr and K Inubushi. 2011. Effect of iron fertilizer application on the yield and methane emission of paddy rice field. In: Proceedings of the 14th Annual Meeting and Scientific Conference, Philippine Society of Soil Science and Technology (PSSST), VSU, Baybay, Leyte 25-27 May 2011, pp:95-96

Hydrogen peroxide is not a good reagent for the removal of soil organic matter

Organic matter (OM) is the most important cementing agent of soil particles. Soils containing high amount of OM (like the limestone soil from Leyte in the picture below) generally have good aggregation (i.e. the sand, silt and clay particles are glued together by the OM). Removal of OM using chemical reagents is thus an important pretreatment in textural or particle size analysis as well as in the evaluation of soil mineralogy, cation exchange capacity, and surface area.

Soil in Leyte having a dark surface horizon due to OM 

Hydrogen peroxide (H2O2) which was first used in 1923 by G.W. Robinson to destroy soil organic matter, is the most widely used chemical reagent for removing OM in soil laboratories worldwide. However, there have been some scientific reports indicating that it may not be a good reagent for that purpose due to some unwanted effects on the mineral soil particles. In the Philippines, it is not also easy to procure large volumes of hydrogen peroxide since it requires clearance from the Philippine National Police.

Robert Mikutta and colleagues from the Institute of Soil Science and Plant Nutrition of the University of Halle-Wittenberg, Germany in a study published in the Soil Science Society of American Journal, Vol. 69 (2005), compared the performance of the three most accepted reagents for OM removal: hydrogen peroxide, sodium hypochlorite (NaOCl), and disodium peroxodisulfate (Na2S2O8).

The old soil mineralogy lab at the Univ Halle-Wittenberg

They found that: 1) removal of OM from soil is mostly incomplete with efficiency of removal varying with reaction conditions and sample properties; 2) sodium hypochlorite and disodium peroxodisulfate are generally more effective in removing OM compared with hydrogen peroxide; 3) alkaline conditions and additives favoring dispersion and/or decomposition of OM such as sodium pyrophosphate, are crucial for OM removal; and 4) OM removal can be little in soils containing high amounts of clay-sized minerals like Fe oxides, poorly crystalline Fe and Al phases, and expanding clay types.

The authors also found that the use of hydrogen peroxide to remove OM should be avoided for the determination of mineral particle properties since the treatment may promote organic-assisted dissolution of poorly crystalline minerals at low pH, disintegration of expandable clay minerals, and transformation of vermiculite into mica-like products due to ammonium (NH4+) fixation.

Clay collection for mineralogical analysis 

They concluded that sodium hypochlorite and disodium peroxodisulfate are less harmful for soil minerals than hydrogen peroxide; prolonged heating to 40 degrees Celsius during any pretreatment may transform poorly crystalline minerals into more crystalline ones; and sodium hypochlorite can be used at 25 degrees Celsius and can thus prevent heat-induced soil mineral changes.

Simply put: sodium hypochlorite is better than hydrogen peroxide in removing OM from soil samples.

Reference

Mikutta R, Kleber M, Kaiser K and Jahn R. 2005. Organic matter removal from soil using hydrogen peroxide, sodium hypochlorite, and disodium peroxodisulfate. Soil Science Society of America Journal 69: 120-135.

Response of corn to chicken dung and rice hull ash application and mycorrhizal fungi inoculation

By Luz Geneston-Asio, Central Analytical Services Lab, VSU, Baybay, Leyte

The use of locally available and cheap organic fertilizers like chicken dung and rice hull ash which have the ability to increase crop yield and at the same time improve soil quality is becoming popular among farmers in many places in the Philippines. In addition, considering that the world demand for corn as food and feed is projected to greatly increase in the coming decades, there is a need to explore the use of such materials for corn production.

We evaluated the growth and yield responses of corn to chicken dung and rice hull ash application a well as to mycorrhizal fungi inoculation. The experiment was laid out in a split-plot in Randomized Complete Block Design consisting of three replications. Vesicular-arbuscular mycorrhizal (VAM) inoculation served as the main plot while application of fertilizer was designated as the subplot. The fertilizer treatments included the following: To-control, T1-inorganic fertilizer (60-60-60 kg/ha N, P205, K20), T2-chicken dung alone (60 kg/ha N), T3-chicken dung (as in T2) + 30 kg/ha rice hull ash. The experimental area had an alluvial clay loam soil with pH of 5.8 and moderate fertility status.

Results showed that VAM inoculation significantly increased the total N but not the total P, K, and Ca contents of the tissue of corn plant. However, VAM inoculation did not significantly affect the grain yield and the agronomic characteristics of corn. In contrast, fertilization using inorganic fertilizer, chicken dung or chicken dung plus rice hull ash enhanced the early tasseling and silking but not emergence and maturity of corn. The application of fertilizers significantly increased plant height as well as the fresh stover yield compared to the control plants.

The inorganic fertilizer, chicken dung, and chicken dung plus rice hull ash significantly increased the number of ears per plant, ear length, number of grains per ear, weight of 1000 seeds, grain yield and harvest index. The use of chicken dung combined with rice hull ash for corn production is a good substitute for the inorganic fertilizer in increasing corn grain yield. (Above photo shows VAM infection in the root of corn from this study).

Reference

Luz Geneston-Asio and Alfredo B. Escasinas. 2006. Response of corn to chicken dung and rice hull ash application and mycorrhizal fungi inoculation. Annals of Tropical Research 26: 23-36

Continuous cultivation does not always decrease soil organic carbon content

It is generally known that continuous cultivation causes a decline in soil organic carbon and nutrient contents. This has been shown by many years of research on upland soils starting with the classic study by Nye and Greenland (1960). Our studies in the volcanic mountain of Leyte, Philippines, have also confirmed this (e.g. Asio et al., 1998; Navarrete and Tsutsuki, 2008).

But a recent paper by Benbi and Brar (2009) published in the international journal Agronomy for Sustainable Development does not support this widely held view. In fact, they showed that intensive cultivation increased soil organic carbon by 38 % after 25 years. These researchers evaluated the impact of intensive cultivation of an irrigated and optimally fertilized rice-wheat system in Punjab, India, and found that intensive cultivation enhanced carbon sequestration due to improved crop productivity, greater belowground C transport to the soil and reduced organic matter decomposition during the wetland rice season.

Results of the study also revealed that the rice-wheat cropping in alkaline soils creates a favourable pH environment by lowering soil pH towards neutrality. During the 25-year period, the soil pH declined from 8.8. to 7.7 which resulted in the improvement in nutrient availability. Continuous application of phosphoric fertilizer led to build-up of soil P and the magnitude of accumulation was proportional to the amount of fertilizer applied.

References

Asio V.B., R Jahn, K. Stahr, and J. Margraf. 1998. In: Soils of Tropical Forest Ecosystems (A. Schulte and D. Ruhiyat, eds.). Springer Verlag, Berlin, pp: 29-36.

Benbi D.K. and J.S. Brar. 2009. A 25-year record of carbon sequestration and soil properties in intensive agriculture. Agron. Sustain. Dev. 29: 257-265.

Navarrete IA and K Tsutsuki. 2008. Land-use impact on soil carbon, nitrogen, neutral sugar composition and related properties in a degraded Ultisol in Leyte, Philippines. Soil Science and Plant Nutrition 54: 321-331.

Nye P.H. and D.J. Greenland. 1960. The soil under shifting cultivation. Commonwealth Agricultural Bureau, England.

Organic fertilization improves soil fungi population

While organic fertilization is now widely known to improve the general soil quality, more data from field experiments are still needed to support this notion. Cwalina-Ambroziak and Bowszys (2009) carried out a 3-year field experiment to determine the influence of organic fertilization on the community of soil fungi as compared to no fertilization and NPK fertilization only. Findings of the study revealed a significantly higher total number of fungal colony-forming units in soil applied with organic fertilizer than in soil without fertilizer application and the one applied with NPK mineral fertilizers. Moreover, pathogen population was highest in soil without fertilization and lowest in the soil added with organic fertilizer.

The study demonstrated that organic fertilization has a positive influence on the structure of soil fungi communities. This was particularly more observable in the qualitative changes in fungi composition than in the changes in fungi numbers. Results of the study support the findings of other researchers that organic fertilization stimulates the growth of soil microorganisms and that it protects the plants against pathogens of the genus Pythium and Phytophthora.

According to Terekhova (2007) fungal communities represent one of the most important functional and structural components of biological systems. Fungi affect the properties of the soil via the regulation of pedogenic processes; the composition of soil organic matter; the soil structure status; the soil acidity; the soil temperature characteristics; and certainly via the regulation of the functioning of soil microbiota.

References

Cwalina-Ambroziak B. and T. Bowszys. 2009. Changes in fungi communities in organically fertilized soil. Plant Soil Environ 55: 25-32.

Terekhova V.A. 2007. The importance of mycological studies for soil quality control. Eurasian Soil Science 40: 583-587.

Land use change decreases carbon, nitrogen, and sugar contents of tropical soil

Land use change is an important ecological driver in the Philippines and other parts of the tropics. It is the major cause of the widespread occurrence of degraded lands in this humid tropical country.

Navarrete and Tsutsuki (2008) investigated the effects of land use change in Mt. Pangasugan in Leyte. They found that conversion of forest into secondary land uses like mahogany plantation, rainforestation farm (a form of reforestation using native tree species in combination with fruit trees and some shade-loving crops), coffee plantation, and grassland decreased the soil carbon, nitrogen, and non-cellulosic neutral sugar (mainly arabinose and xylose) contents of the soil. Within land-use type, differences in the above-mentioned soil parameters could be attributed to differences in the vegetation cover, past land use, and the succeeding soil management after land use change. Their findings also revealed that the grassland and rainforestation farm (which was also a former grassland) had the lowest non-cellulosic sugar content while the secondary forest had the highest.

Reference
Navarrete IA and K Tsutsuki. 2008. Land-use impact on soil carbon, nitrogen, neutral sugar composition and related properties in a degraded Ultisol in Leyte, Philippines. Soil Science and Plant Nutrition 54: 321-331.

The "home field advantage" in plant litter decomposition

If you collect leaf litter from a Mahogany plantation and put it beaneath Gmelina trees or vice versa, the rate of litter decomposition will not be the same. According to a recent paper by Ayers et al. (2009), leaf litter decomposition is faster beneath the plant species from which the litter had been derived than beneath a different plant species. This is called home-field advantage. The authors observed that home-field advantage is widespread in forest ecosystems and hypothesized that this is due to the specialization of the soil organisms in decomposing litter derived from the plant above it. In other words, soil organisms living beneath the Mahogany trees are specialized in decomposing the leaf litter from this tree species.

Reference: Ayers E et al. (2009). Home-field advantage accelerates leaf litter decomposition in forests. Soil Biology and Biochemistry 41: 606-610.