Hiroaki Sumida

Seasonal changes in organic compounds in soil solutions obtained from volcanic ash soils under different land uses

We investigated the organic matter composition in soil solutions as influenced by land use. Undisturbed mineral soils were collected periodically from mineral layers of Andosols under coniferous and deciduous forest, grasslands and upland fields for 1year using soil core samplers. Soil solutions were obtained by centrifugation under -1.55 x 10 6 Pa condition, which equals to 4.2 pF. The dissolved organic carbon (DOC), hexoses, pentoses, phenolic acids and amino acids in soil solutions were determined. The concentrations of DOC under forest and grassland stands were not influenced by precipitation, but were negatively correlated to the yield of soil solution (P<0.01). Temporal variations in concentrations of hexoses were similar to those of DOC at all Fujisawa sites but not at the Tsukui sites. Except for one forest stand, the concentrations of hexoses increased from autumn to winter. Concentrations of pentoses and phenolic acids showed similar seasonal variation in the forests and grasslands, and peaked in autumn and spring. Variations in the concentrations of pentoses corresponded to litter fall and ground grass cutting in forests, drying of grass at grasslands and harvest at upland lields. Although the concentrations of phenolic acids varied with seasons, differences between land uses were not clear. The release of phenolic acids might depend on the variation of the temperature. Correlations between pentoses and phenolic acids and DOC were weak. The concentrations of amino acids were lower than those of other organic compounds at all sites. At the upland fields, the concentrations of amino acids were significantly (P<0.01) correlated with those of hexoses. The composition of dissolved organic matter (DOM) varied throughout the year. Seasonal changes in organic matters in soil solutions depended on yields of soil solution, temperature variations and the timing of litter supply under different land use.

Characteristics of newly isolated ammonia-oxidizing bacteria from acid sulfate soil and the rhizoplane of leucaena grown in that soil

Abstract We isolated four new ammonia-oxidizing bacterial strains from leucaena (Leucaena leucocephala) grown in fields of an acid sulfate soil (ASS) in Thailand; 17SS from the surface soil and 17RS from the rhizoplane of a non-limed plot; 9SS from the surface soil and 9RS from the rhizoplane in a limed plot. The cells of all strains had the typical lobate shape of the genus Nitrosospira (“Nitrosolobus”). The percentage similarity of the 16S rRNA genes of these strains to that of Nitrosospira (“Nitrosolobus”) multiformis ATCC25196T (ATCC25196T) was 99.52% (strains 17SS, 17RS and 9SS) and 99.66% (strain 9RS). These newly isolated bacteria were all identified as Nitrosospira sp. Each strain, especially 17SS isolated from ASS, had higher urease activity than that of ATCC25196T. The o-acetylserine(thiol)lyase activity of 17SS was the highest of all the isolates. At pH 6.0, every isolate and ATCC25196T were able to utilize urea as the sole nitrogen source, in particular, strain 17SS grew best. The isolates from ASS showed higher urea utility than the isolates from the rhizoplane. Strain 17SS tolerated copper at levels up to 6.3 mmol L−1, but ATCC25196 T was inhibited at that concentration.

Hydrothermal treatment of palm oil empty fruit bunches: an investigation of the solid fuel and liquid organic fertilizer applications

ABSTRACT In this study, the investigation of hydrothermal treatment (HTT) of palm oil empty fruit bunches (EFB) on both solid product and liquid residue characteristics was conducted. The effects of HTT were investigated at temperatures of 100, 150, 180 and 220°C with 30 minutes holding time. Hydrochars were characterized by elemental analysis, SEM, ash analysis and TGA, while liquid products were analyzed by micro- and macronutrient analysis, and germination test. The results showed that the HTT treated EFB has an increased carbon content, lowered ash content, and lowered deposition tendency compared to the raw EFB. Moreover, the maximum of 37% of nitrogen, 65% of potassium and less than 10% of phosphorus in EFB were solubilized into the liquid residue which positively correlated with the temperature. The produced liquid was found unsuitable as a fertilizer due to low pH value, low N content, and low germination index, hence needing improvement when applied as fertilizer. These results demonstrated the possibility of employing the HTT for producing solid fuel as well as nutrient cycling in the plantation.

Effects of drying on the release of solutes from acid sulfate soils distributed in the Mekong Delta, Vietnam

Abstract Acids and soluble metal loads resulting from strong acidification preceded by severe drying of acid sulfate soils are fatal soil conditions for agricultural productivity and aquaculture environments. A greater concentration of dissolved Al and Fe after seasonal drought was confirmed in our previous paper using acid sulfate soils in the Mekong Delta. Furthermore, moisture desiccation resulting from land-use change and subsoil excavation for drainage probably promotes soil oxidation followed by acidification. We prepared air-dried soil moisture condition actual acid sulfate soils in the Mekong Delta to evaluate acidification and the release of acids and metals with drying. The pH values of the deepest horizon in the Hydroaquentic Sulfaquepts drastically dropped and greater concentrations of Al and Fe were released with drying. It was a common change from the sulfidic horizon to the sulfuric horizon. A large increase in Al release without a drop in pH after drying was observed in the sulfuric horizons of the Typic Sulfaquept, which developed on the oldest land in the Mekong Delta. Acidification by oxidation of reduced sulfur compounds might be compensated mainly by exchangeable Al and/or by the dissolution of Fe and Al oxides. In contrast, the concentration of Al increased slightly by drying in the sulfuric horizons in the Hydroaquentic Sulfaquept, which developed in the newer delta. The exchangeable basic cations in these soil horizons might still be effective in compensating for the protons produced by the oxidation of pyrite. The difference in the Al released by drying between the two sulfuric horizons might be attributed to the ripeness of the acid sulfate soils. The ripeness of the soil on the older delta might be higher than that on the younger delta. In this study, drying of acid sulfate soils, even in the sulfuric horizon, can promote metal release due to the exchange by protons derived from the oxidation of reduced sulfur compounds. However, further acidification might be compensated by a substantial amount of exchangeable cation and oxide dissolution.

Effects of humic acids on the sorption and bioavailability of pyrene and 1,2-dihydroxynaphthalene

Abstract Sorption of organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) is an important process that controls their mobility and toxicity in soil. The relationship between the chemical properties of various types of humic acids (HAs) and their pyrene (4-ring PAH) sorption ability was investigated in batch experiments. Commercial HAs as well as those obtained from Umbric Andosol, Dystric Cambisol and cow manure compost were used. Additionally, fractionated Aldrich humic acid (AHA), which was obtained by fractional precipitation with ethanol, was evaluated to better understand how its chemical characteristics affect pyrene sorption. The value of the carbon-normalized partition coefficient (Kdoc ×105 L kg-C−1) for pyrene in all commercial HAs was within the expected range in the two soil HAs (0.43–2.69). Correlation analysis indicated that Kdoc values for fractionated AHA series tended to increase with increasing aromaticity (r = 0.82). Subsequently, the effects of various HAs on the toxicity of pyrene and 1,2-dihydroxynaphthalene (DHN), which is one of the major microbial metabolite of PAH such as pyrene, to a test microorganism were examined by spread plate counting by using a solid agar medium. While pyrene (a poorly water-soluble compound) did not inhibit bacterial growth, the inhibitory effect of the water-soluble DHN was apparent at 10 mg L−1. However, the addition of HA at 25 mg-C L−1 mitigated DHN toxicity. Furthermore, the detoxification effect tended to increase with increasing aromatic carbon content of HA (r = 0.94). The observed reduction in toxicity of DHN may be due to its sorption to the aromatic moiety of HA, by which the bioavailability is reduced.

Effect of land developmental process on soil solution chemistry in acid sulfate soils distributed in the Mekong Delta, Vietnam

Abstract Water-soluble ionic substances in acid sulfate soils are likely to be strong controls for crop production and to have impacts on aquatic ecosystems. In dry seasons, in particular, oxidation of the soil surface followed by acidification probably produces lots of acids and soluble metals. To estimate acid and metal loads from acid sulfate soils to aquatic environments, we determined the composition of water-soluble ions from soils distributed in the Mekong Delta, Vietnam. At the end of the dry season, soils were taken from each soil horizon in two soil profiles on the delta under different land developmental processes. Water-soluble ions were extracted using both distilled water and artificially synthesized irrigation water (pH 6.3) adjusted to the same ionic strength and pH as the field canal water. The relationship between extracted basic cations in both extracts showed high linear correlation, indicating a similar extraction mechanism between both extractants. Higher ionic strength in the artificial irrigation water may not have any advantages for extraction by ion exchange and, thus, properties of extracts are likely to depend on the soil properties. The older the soil parent material, the larger the rates of soluble Al and Fe and the lower the pH. Progressive weathering of the soil on the older delta has already discharged greater amounts of bases, probably for compensation of acids, and the soil has started to release exchangeable Al sorbed onto negative-charge colloids and Fe from decomposed oxides. The soil profile of the older delta released relatively greater concentrations of Al with a lower content of base cations, where the annual averaged rice yield was half that of another site. Soluble metals and acids at both sites appear to accumulate in the upper horizons above the low permeable layer, which is probably widely distributed in the Mekong Delta.

Bacterial consortia in iron-deposited colonies formed on paddy soil surface under microaerobic conditions

Abstract The present study observed bacterial consortia in iron-deposited colonies formed on the surface of paddy soils. Plow layer soils under reduced condition, which were collected from a paddy field in Japan and paddy fields located at two sites in Mekong Delta, Vietnam, were incubated at 25 and 30°C in test tubes under a nitrogen (N2) atmosphere with sleeve stoppers made from a synthetic rubber. The sleeve stopper enabled the establishment of microaerobic conditions because of gradual diffusion of oxygen (O2) into the tube (29.2 nmol mL−1 day−1). Many colonies were observed on the soil surface in the test tubes after 2–3 weeks of incubation from both Japanese and Vietnam paddy soils. Bright orange and blood red colonies, which had 0.5–1-mm diameters and circular shapes, were observed. Micro X-ray fluorescence analysis of the colonies showed deposition of iron (Fe) in the colonies, indicating bacteria were enriched in the Fe oxidation. Microscopic observation showed acicular, floc and concentric crystal structures of Fe oxides in the colonies. Long- and short-rod bacterial cells mainly existed inside (or interspace) and outside surface of the colonies. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and clone library analysis of bacterial 16S rRNA genes showed that most of the obtained sequences belonged to Betaproteobacteria, in which bacteria related to “Sideroxydans lithotrophicus” and “S. paludicola” in Gallionellales, known as microaerobic, neutrophilic Fe-oxidizers, were predominant. The sequences related to Thiobacillus spp. and Dechloromonas spp., some strains of which are known to be anaerobic, nitrate-dependent neutrophilic Fe-oxidizers, were also obtained. The present study showed proliferation of bacteria related to neutrophilic Fe-oxidizers in paddy soils under microaerobic condition.

Humus composition and physico-chemical properties of humic acids in tropical peat soils under sago palm plantation

Abstract Tropical peatlands in Sarawak are exploited on a large scale for crop plantations. After reclamation of primary forests, large amounts of gaseous and soluble organic compounds could be released from peatlands. These decomposing products are probably related to the composition and properties of peat humus. Furthermore, these properties might be influenced by land use and topography. Peat soils on the surface and beneath the water table were collected from the edge and the center of a peat dome under sago palm plantations located between two tributaries. The content of alkali-soluble carbon in peat soils and the degree of humification of peat were higher on the edge than in the center of the peat dome and in the deeper horizons compared with the surface horizons. A similar trend was also observed for the contents of carboxylic groups and aromatic constituents in humic acids. The opposite trend was observed for the viscosity of humic acids related to molecular weight. These results indicate that the degree of humification of peat progressed at sites located close to tributaries and in deeper horizons. Peat decomposition might presumably be promoted at locations along the tributaries because of the higher microbial activities supported by a higher mineral nutrient supply. Concurrently, the contents of carbohydrates were lower in the surface horizons than in the deep horizons, suggesting that peat decomposition is accelerated on the ground surface after reclamation. Reclamation of primary forests for the establishment of sago plantations has gradually changed the redox conditions and has promoted biodegradation of peat soils.

Effect of decomposition of city refuse compost on the behavior of organic compounds in the particle size fractions

The effects of the decomposition of city refuse compost on the behavior of organic compounds in various soils were investigated. Organic matter derived from city refuse compost was relatively concentrated in the fine particle fraction (< 2 µm) in soil. The rate of decomposition and changes in city refuse compost were affected by the contents of the original humus substances in soil. It is suggested that the application of city refuse compost contributed to the increase of nitrogen compounds and carbohydrates in the fine particle size fraction of the soil. Multiple regressions on total content of nitrogen (T-N) and organic carbon (T-C), which reflect the effect of decomposition of city refuse compost in soil, and some other variables were computed for their relevant characteristics. Increases in the contents of glutamic and aspartic acids were found to be suitable indices for expressing the increase in the content of T-N, whereas the increase in the hexose content in the residual fraction after hot water extraction could be expressed in terms of data related to the increase in the content of T-C.