Actual Acid Sulfate Soil Research Articles

Sebaran Tingkat Kemasaman Tanah dan Potensial Redoks serta Kedalaman Pirit (FeS2) pada Lahan Sulfat Masam di Kecamatan Alalak

Acid sulfate soil has a layer of pyrite, when it is oxidized, can acidify the soil. The presence of pyrite in acid sulfate soils is very diverse and must be known. Not knowing the depth of pyrite can have fatal consequences, because layers of pyrite can be lifted to the surface due to tillage so that it oxidizes. This study aims to determine and map the distribution of pyrite depth, soil pH, and redox potential. Soil samples were determined with an exploratory descriptive method through land surveys and supported by laboratory analysis of pH, Eh and FeS2. The results showed that acidity of acid sulphate soil at all sample points was classified as very acid, Eh was classified as low reduction till oxidation. Based on the results of observations of pyrite depth, 3,492.15 ha (78.1%) was actual acid sulfate soil and 979.13 ha (21.9) was potential acid sulfate soil. So proper management is needed when turning over the soil so that the pyrite is not exposed, applying lime, organic material and regulating the water level so that the groundwater level is not below the depth of the pyrite

Kemasaman Tanah dan Sebaran Senyawa Pirit pada Berbagai Kedalaman Tanah Pasang Surut

Soil acidity (pH) is the main obstacle in tidal swampland. The high soil acidity (pH < 4.0) causes an increase in the solubility of iron (Fe). The high soil acidity affects the balance of chemical reactions in the soil and the availability of nutrients in the soil. The purpose of this study was to determine soil acidity (pH), redox potential (Eh), and soluble Fe at at varying soil depths with different pyrite locations in tidal swampland. This study used a nested design and studied the following factors: 1) Depth of pyrite 0-50 cm layer (actual acid sulfate soil) and 50-100 cm layer (potential acid sulfate soil). 2) Soil depth includes 0-25 cm, 25-50 cm, 50-75 cm, and 75-100 cm. Soil samples were taken at the depth where pyrite was detected, with 3 replicates at each soil depth. This resulted in a total of 24 experimental units. The depth of the nested soil coincided with the depth of the pyrite. The study analyzed the acidity of acid sulphate soil, redox potential, and dissolved Fe at pyrite locations within soil depths of 0-100 cm and 0-25 cm, 25-50 cm, 50-75 cm, and 75-100 cm. The results indicate that there was no significant difference in the measurements between the various soil depths of 0-50 cm and 50-100 cm.

Regional variation in Swedish acid sulfate soil microbial communities is influenced by temperature and geochemistry

AbstractAcid sulfate soils are frequently described as the nastiest soils on Earth, and they pose environmental risks associated with their strong acidity and consequential mobilization of toxic metals present in the soils. Within Sweden, acid sulfate soils have been extensively studied around the northern Baltic coastline and have now been found to occur throughout the area below the maximum Holocene marine limit that stretches for some 2000 km from North to South. This study investigated 20 active acid sulfate soils (field tested pH < 4.0) collected throughout this area that were tested for microbial community composition using 16S rRNA gene amplicons, representing a novel study of microbial communities in ripening zones across a broad regional scale. The microbial community compositions exhibited a north (boreal zone) to south (hemiboreal zone) regional divide, primarily within the oxidized zone (pH < 4.0), to a lesser degree in the transition zone (steep pH gradient), while little differences were observed in the reduced zone (near‐neutral pH). For instance, a higher relative abundance of Ktedonobacteraceae was identified in the northern boreal and Gallionellaceae in the southern hemiboreal oxidized zones. In addition, microbial taxa associated with iron and sulfur oxidation and reduction were identified, such as Acidobacteriaceae, Gallionellaceae and Koribacteraceae that have been previously identified in other acid sulfate soils and acid mine drainage settings. The predominant controls of the microbial community differences were the north–south divide indicative of a strong soil‐temperature effect followed by soil zones suggesting an influence of the soils' pH and/or redox conditions.

An extracellular polysaccharide is involved in the aluminum tolerance of Pullulanibacillus sp. CA42, a newly isolated strain from the Chinese water chestnut growing in an actual acid sulfate soil area in Vietnam.

A novel aluminum-tolerant bacterial strain CA42 was isolated from the aquatic plant Eleocharis dulcis, which grows in a highly acidic swamp in Vietnam. Inoculation with CA42 allowed Oryza sativa to grow in the presence of 300 μM AlCl3 at pH 3.5, and biofilms were observed around the roots. Using 16S rRNA gene sequencing analysis, the strain was identified as Pullulanibacillus sp. CA42. This strain secreted large amounts of an extracellular polysaccharide (CA42 EPS). Results from structural analyses on CA42 EPS, namely methylation analysis and nuclear magnetic resonance (NMR), indicated that the chemical structure of CA42 EPS was a glycogen-like α-glucan. Purified CA42 EPS and the commercially available oyster glycogen adsorbed aluminum ions up to 15-30 μmol/g dry weight. Digestion treatments with α-amylase and pullulanase completely attenuated the aluminum ion-adsorbing activity of purified CA42 EPS and oyster glycogen, suggesting that the glycogen-like structure adsorbed aluminum ions and that its branching structure played an important role in its aluminum adsorbing activity. Furthermore, the aluminum tolerance of CA42 cells was attenuated by pullulanase treatment directly on the live CA42 cells. These results suggest that CA42 EPS adsorbs aluminum ions and is involved in the aluminum tolerance mechanism of Pullulanibacillus sp. CA42. Thus, this strain may be a potential plant growth-promoting bacterium in acidic soils. In addition, this study is the first to report a glycogen-like polysaccharide that adsorbs aluminum ions.

Multi-element features of active acid sulfate soils across the Swedish coastal plains

Acid sulfate soils are sulfide-rich soils with notable associated environmental risks. The low pH of these soils mobilizes metals from the soil minerals, which will lead to both acidification and metal contamination of the surrounding environment. This paper presents the results of a geochemical study of 66 profiles of acid sulfate soils collected from a total of 22 sites (three profiles for each site) on the Swedish coastal plains, which stretch for some 2000 km along the Baltic Sea and Kattegat. The reduced zone at the bottom of the profiles was characterized by pH frequently >6.0, the transition zone (above the reduced zone) by a steep pH gradient from near-neutral to weakly acidic, and the oxidized zone located above the transition zone by highly acidic conditions with a pH minimum <4.0. Each zone in each profile was sampled for geochemical analyses. The aqua regia extractable S concentrations ranged widely in the reduced zone (0.06–7.5%) and were strongly depleted in the oxidized zone (median decrease 69%) from extensive sulfide oxidation and associated severe acidification and sulfate leaching. In addition to S, there were significant losses from the oxidized zone of eight alkali and alkaline earth metals (Ba, Be, Ca, K, Li, Mg, Na, and Sr), four first row transition metals (Co, Mn, Ni, and Zn), three second row transition metals (Cd, Y, and Zr), the rare earth elements (Ce, La, and Yb), and Al, Th, and B. These elements would therefore be expected to be enriched in nearby surface waters, which was supported by hydrogeochemistry data from elsewhere in the boreal zone. Nineteen other chemical elements were not significantly lost from the oxidized zone relative to the reduced zone (Fe, Ti, W, Se, Sc, V, Cu, Cr, P, In, Te, Ag, Sb, Bi, Sn, Mo, U, As, and Pb) and therefore, would not be expected to occur in elevated concentrations in acid sulfate soil affected surface waters, as was supported by literature data from elsewhere in the boreal zone. A hypothesis of more extensive oxidation, acidification, and leaching of the soils in south Sweden (hemiboreal zone) than north Sweden (boreal zone) due to a warmer climate in the former region was rejected based upon pH and multi-element patterns from 9 field sites from the north and 12 field sites from the south. Consequently, the losses were likely primarily controlled by local factors, such as time since drainage and soil development. However, the oxidized zone was significantly thicker in the north (median: 75 cm) than south (median: 40 cm). This suggested that although the proportional losses (i.e., difference in elemental concentrations between the oxidized and reduced zones) were overall not different between the two regions, the total amount of elements lost from the soils will have been larger in the north. Of the elements with no significant losses, several were extracted with 1 M HCl to a larger extent in the oxidized than the reduced zone (Fe, As, Cr, Cu, Mo, Sc, Ti, U, and V). This indicated retention in the acidic environment following release from weathered and/or oxidized soil minerals. These elements, of which several are particularly toxic (As, Cr, and U), may thus be mobilized and leached if the soils geochemical conditions change either naturally or via human activities.

Gallionella and Sulfuricella populations are dominant during the transition of boreal potential to actual acid sulfate soils

Acid sulfate soils release metal laden, acidic waters that affect the environment, buildings, and human health. In this study, 16S rRNA gene amplicons, metagenomes, and metatranscriptomes all demonstrated distinct microbial communities and activities in the unoxidized potential acid sulfate soil, the overlying transition zone, and uppermost oxidized actual acid sulfate soil. Assembled genomes and mRNA transcripts also suggested abundant oxidized acid sulfate soil populations that aligned within the Gammaproteobacteria and Terracidiphilus. In contrast, potentially acid tolerant or moderately acidophilic iron oxidizing Gallionella and sulfur metabolizing Sulfuricella dominated the transition zone during catalysis of metal sulfide oxidation to form acid sulfate soil. Finally, anaerobic oxidation of methane coupled to nitrate, sulfate, and ferric reduction were suggested to occur in the reduced parent sediments. In conclusion, despite comparable metal sulfide dissolution processes e.g., biomining, Gallionella and Sulfuricella dominated the community and activities during conversion of potential to actual acid sulfate soils.

The potential of organic matter and water management on the alleviation of iron toxicity in rice plants

Iron toxicity in rice plants occurs due to the excessive concentrations of ferrous ions (Fe2+) in the soil solution. The application of organic matter and water management is one way to alleviate iron toxicity in rice plants. This study aimed to determine the potential of organic matter and water management in controlling the solubility of Fe2+ in the soil and its effect on the symptoms of toxicity, growth and yield of rice plants. The research was conducted in the greenhouse of the Indonesian Swampland Agricultural Research Institute from August to December 2020, arranged in a completely randomized design with three factors. The first factor consisted of low Fe2+ concentration (&lt;300 ppm, actual acid sulfate soil (AASS)) and high Fe2+ concentration (&gt;300 ppm, potential acid sulfate soil (PASS)), the second factor consisted of waterlogging without leaching and leaching of once every two weeks, and the third factor consisted of without organic matter amendment and with organic matter amendment of 2.5 ton.ha-1. In comparison to the treatment of without organic matter amendment and leaching, the organic matter and leaching treatment in the AASS reduced the leaf bronzing index by 26.17 % and increased the crop yield by 21.20 %. In the PASS, the organic matter and leaching treatment reduced the leaf bronzing index by 11.74 % and increased the crop yield by 15.72 %. The leaching of once every two weeks and organic matter amendment of 2.5 ton.ha-1 are recommended to alleviate iron toxicity and increase rice productivity in acid sulfate soil.

Acid sulfate soils and their impact on surface water quality on the Swedish west coast

Study regionHalland county, located on the Swedish west coast, with a special focus on the area around Ramsjö canal (Falkenberg municipality). Study focusThis study contributes to the understanding of the development of active acid sulfate soils and environmental consequences of leaching from these soils in an area without previous investigations. Samples taken from different soil profiles in an agricultural area and water samples from the agricultural drainage system were analysed in pH, electrical conductivity, and metal concentrations. To evaluate the on-site situation, the results of the soils sample analysis were compared to the national soil classification system and the water samples to areas in northern Europe affected by acid sulfate soils. New hydrological insights for the regionThe results prove the existence of active acid sulfate soils in a coastal area in Halland. In the study region, acid sulfate soils were discovered in an agricultural area of drained wetland and peatland. Water samples taken from the drainage system and a man-made canal flowing into Kattegat Sea have low pH combined with high electrical conductivity and increased metal concentrations. This is a direct consequence of intensive leaching from the discovered acid sulfate soils in that area. Therefore, this is the first case study proving the existence of acid sulfate soils and highlighting their environmental impact on surface water quality on the Swedish west coast (i.e. outside the Baltic Sea Basin).

Microbial activity of potential and actual acid sulphate soil from Kalimantan Island

Drainage on acid sulphate land causes a change in the type of acid sulfate (AS) soil, from the potential to actual due to pyrite oxidation. The alteration might cause changes in microbial composition and activity. The objective of the study was to compare the microbial activity of two types of acid sulphate (AS) soil, potential AS soil from South Kalimantan and actual AS soil from Central Kalimantan. The microbial activity of both soils was determined by measuring respiration, dehydrogenase, and nitrogenase activity. The presence of culturable soil rhizospheric microorganisms was determined by Total Plate Count methods and their nitrogen fixation function was determined by the ability of culturable rhizospheric soil bacteria to grow in semisolid nitrogen-free medium, as well as, nifH detection. The result of the research revealed that the respiration, dehydrogenase, and nitrogenase activity soil from potential (1.34 mg CO2.kg1 hour−1 and 1.75 nmol C2H4.g−1. hour−1) and actual AS soil (1.23 mg CO2.kg−1. hour−1 and 2.00 nmol C2H4.g−1.day−1) were relatively not different. However, the dehydrogenase activity of actual AS soil (6.29 μg TPF.g−1. hour−1) was higher than that of potential AS soils (3.32 μg TPF.g−1. hour−1). Similarly, the microbial abundance of both soils was not different and the abundance of bacteria was higher than that of fungi. The soils contained nifH genes. In both soils have been detected the presence of microbial abundance and functional microorganisms as a nitrogen fixer, a culturable phosphate solubilizer, or phytohormone producer. However, limiting factors of both soils, i.e., very acidic soil, low nutrient availability, and Al toxicity brought about the low microbial activity.

Dredging and deposition of metal sulfide rich river sediments results in rapid conversion to acid sulfate soil materials

Sediments along the Baltic Sea coast can contain considerable amounts of metal sulfides that if dredged and the spoils deposited such that they are exposed to air, can release high concentrations of acid and toxic metals into recipient water bodies. Two river estuaries in western Finland were dredged from 2013 to 2018 and the dredge spoils were deposited on land previously covered with agricultural limestone to buffer the pH and mitigate acid and metal release. In this study, the geochemistry and 16S rRNA gene amplicon based bacterial communities were investigated over time to explore whether the application of lime prevented a conversion of the dredge spoils into acid producing and metal releasing soil. The pH of the dredge spoils decreased with time indicating metal sulfide oxidation and resulted in elevated sulfate concentrations along with a concomitant release of metals. However, calculations indicated only approximately 5% of the added lime had been dissolved. The bacterial communities decreased in diversity with the lowering of the pH as taxa most similar to extremely acidophilic sulfur, and in some cases iron, oxidizing Acidithiobacillus species became the dominant characterized genus in the deposited dredge spoils as the oxidation front moved deeper. In addition, other taxa characterized as involved in oxidation of iron or sulfur were identified including Gallionella, Sulfuricurvum, and Sulfurimonas. These data suggest there was a rapid conversion of the dredge spoils to severely acidic soil similar to actual acid sulfate soil and that the lime placed on the land prior to deposition of the spoils, and later ploughed into the dry dredge spoils, was insufficient to halt this process. Hence, future dredging and deposition of dredge spoils containing metal sulfides should not only take into account the amount of lime used for buffering but also its grain size and mixing into the soil.

Effect of soil leaching and organic matter on Fe2+ concentration and rice yields in acid sulfate soils

The negative impact of climate change causes extreme weather become unpredictable, leading to flood and drought. In acid sulfate soil, El Nino increases pyrite oxidation which causes sulfate and iron toxicity when flood comes. Iron toxicity in plants is caused by excess concentrations of iron Ferro (Fe2+) in the soil solution. This research aims to determine the effect of leaching and organic matter on Fe2+ concentration, physiological response and yield of rice in acid sulfate soils. The research was conducted in the Indonesian Swampland Agricultural Research Institute (ISARI) Greenhouse from August to December 2020, using a completely randomized design with three factors. The first factor: actual acid sulfate soil (AASS) and potential acid sulfate soil (PASS), the second factor: waterlogging without leaching (-SL) and soil leaching (+SL), and the third factor: without organic matter (OM) and with organic matter (+OM). The results showed that soil leaching and adding organic matter decreased Fe2+ concentration, thereby increasing root length, relative water content, width of stomata, leaf K and Mg content, root-shoot dry weight, number of grain and crop yield. In comparison to the treatment of without leaching and organic matter, the leaching and organic matter treatment in AASS showed the lowest increase in Fe2+concentration from 123.4 to 241.9 ppm and increased yield from 3.13 to 3.80 ton ha−1. Whereas in PASS, the leaching and organic matter treatment showed the highest decrease in Fe2+ concentration from 2,298.7 to 686.6 ppm and increased crop yield from 2.39 to 2.77 ton ha−1.

Amelioration of actual acid sulfate soils to improve soil chemical properties and rice yields

This study aim was to determine the effectiveness of various types of ameliorant in improving soil chemical properties and rice yields in actual acid sulfate soils. The study was conducted in Tamban Baru Tengah village, Tamban Catur Subdistrict, Kapuas, Central Kalimantan, from April-September 2019. The research design used a Randomized Block Design with treatment (A1) 5 t ha−1 of lime given once at the beginning, (A2) 3 t ha−1 lime + 2 t ha−1 lime given at the rice age of 1 month, (A3) 3 t ha−1 lime + 2 t ha−1 ‘Porre’ organic fertilizer, (A4) 3 t ha−1 lime + 2 t ha−1 rice husk ask. Each treatment was replicated 4 times. Periodic soil observations included pH H2O, EC, SO4 2-, Fe2+ and Al3+, plant height, tillers number, and rice yields were observed. The results showed that the ameliorant treatment was able to reduce concentration of Fe2+ at planting from 6400 ppm to 1000-1500 ppm, SO4 2- from 8000 ppm to 2100 to 4300 ppm, Al3+ from 16.31 cmol(+) kg−1 to 5.2-6.7 cmol(+) kg−1. Lime combined with “Porre” organic fertilizer (A3) gave the highest rice yield (>17% higher than A1). The use of “Porre” organic fertilizer was able to reduce the use of lime in tidal swampland.

Structural analysis of an aluminum-binding capsular polysaccharide produced by Acidocella aluminiidurans strain AL46, an aluminum-tolerant bacterium isolated from plant roots in a highly acidic swamp in actual acid sulfate soil

Acid sulfate soil is found throughout Southeast Asia, and its strong acidity (pH 2–4) is accompanied by various plant growth-inhibiting factors that can reduce crop production. Among these factors, aluminum elution from the soil due to soil acidity strongly inhibits crop growth and is particularly problematic for agricultural production. We previously isolated Acidocella aluminiidurans strain AL46, a highly aluminum-tolerant bacterium, from the rhizospheres of the grass Panicum repens, inhabiting the acid sulfate soil in Vietnam. To elucidate the mechanism underlying the high aluminum tolerance of strain AL46, in the present study, we investigated the aluminum-adsorption ability of strain AL46 surface polysaccharides and confirmed the strong adsorption ability of the capsular polysaccharide (AL46CPS). Based on this finding, we further determined the chemical structure of AL46CPS using 1H and 13C NMR spectroscopy by conducting 2D DQF–COSY, TOCSY, HSQC, HMBC, and NOESY experiments. AL46CPS comprises a trisaccharide repeating unit with the following structure: [→2)-β-d-Rhap-(1 → 3)-α-d-Rhap-(1 → 2)-α-d-Rhap-(1→]n. These findings highlight the potential application of AL46CPS as a new aluminum-adsorbing substance in acidic environments to prevent crop loss.

Limitation and Recommendation for Rice Cultivation on the Problem Soils in the Southern Region of Vietnam

Background: Soil degradation is the factor causing crops yield decline in the Southern region of Vietnam. Since the recommendations for limitation of soil constraints will consult the proper problem soil management. Methods: The soil limitation identified based on soil chemistry, physics and morphology properties, suggested by Sanchez et al (1998 and 2003). Soil data of 28 field experiments were analysed. Result: There were 25 rice soil fertility classes, among those, CC (clay in top and subsoil) and CCs (clay in top and subsoil, saline affected) types occupied in large areas. The major soil limitation for rice cultivation including soils low in % organic carbon (o); high in P fixation and high Fe toxicity potential (i); potential salinity (s-); low available P (p); low pH and high Al (a); actual acid sulphate soils (c, c-) potential acid sulphate soils (f, f-). The leaching soil toxicity, application of N, P, K fertilizers and organic matter were recommended.

Characteristics of sulfide bearing soil materials in peat extraction areas in N-Finland

Concern has been raised about the potential formation of acid sulfate soils and associated environmental problems related to peat extraction and, thus, peat, sediment and till characteristics of 15 well drained peat extraction fields were investigated in northern and northwestern Finland. The aim was to identify and characterize the occurrence/abundance of potential acid (hypersulfidic) and actual acid sulfate soil materials as well as metals with regards to their depositional environment (marine/non-marine), black schists and soil material properties. Sulfide-bearing marine sediments were commonly found; the highest contents and thickness of sulfide sediments were found in areas <50 m above the current sea level (a.c.s.l.), while the sulfide contents were relatively low in the mineral soil materials (mainly till) in the non-marine areas (>100 m a.c.s.l.). The highest content of sulfides in sediments was typically found just below the peat layer. The sulfides existed mostly as pyrite (up to 3.5 wt% S) but were occasionally also mixed with more reactive metastable sulfide (Fe:S ratio in the order of 1:1), which coincide with high Fe concentrations, indicating that an abundance of Fe2+ can diminish the rate of pyrite formation. Sediments contained very high amounts of potential acidity, but in-field oxidation of the sediments was very limited. Although the sulfur contents were much lower (max 0.3% S), several of the till samples still became acidic (pH < 4) upon oxidation, and contained, thus, some amounts of potential acidity due to a pore buffering capacity. Consequently, during peat extraction most of the acidity is still retained in sediments limiting environmental consequences and, thus, focus should be on appropriate management to prevent oxidation and leaching after peat extraction has been finished. Locally high Mn and Zn concentrations were found in the sediments in black schist areas, indicating that Zn and Mn have migrated with the ground water from the schists to the sediment layers. In several black schist areas, the peat layer contained high amounts of sulfides with a corresponding high potential acidity as well as elevated As, Pb and Zn. This indicates an upward transport of sulfur and some metals (As, Pb and Zn) through capillary rise and/or plant uptake and/or through lateral water transport from surrounding black schist affected soil material. Air pollution, i.e. atmospheric distribution, was most likely a source for high concentrations of Cd, Hg and Sr concentrations in the peat.

Metagenomes and metatranscriptomes from boreal potential and actual acid sulfate soil materials

Natural sulfide rich deposits are common in coastal areas worldwide, including along the Baltic Sea coast. When artificial drainage exposes these deposits to atmospheric oxygen, iron sulfide minerals in the soils are rapidly oxidized. This process turns the potential acid sulfate soils into actual acid sulfate soils and mobilizes large quantities of acidity and leachable toxic metals that cause severe environmental problems. It is known that acidophilic microorganisms living in acid sulfate soils catalyze iron sulfide mineral oxidation. However, only a few studies regarding these communities have been published. In this study, we sampled the oxidized actual acid sulfate soil, the transition zone where oxidation is actively taking place, and the deepest un-oxidized potential acid sulfate soil. Nucleic acids were extracted and 16S rRNA gene amplicons, metagenomes, and metatranscriptomes generated to gain a detailed insight into the communities and their activities. The project will be of great use to microbiologists, environmental biologists, geochemists, and geologists as there is hydrological and geochemical monitoring from the site stretching back for many years.

BIOLEACHING UNTUK MENINGKATKAN PRODUKTIVITAS LAHAN SULFAT MASAM AKTUAL UNTUK TANAMAN PADI

Technology of microbial utilization to accelerate the oxidation of pyrite followed by leaching (bioleaching) has the potential to resolve problems in land management of actual acid sulphate soil. The research aims to obtain a bioleaching technology package that can improve the productivity of the actual acid sulfate soil. The experiment was conducted on tidal swamp land that has soil type of actual acid sulfate at Wana Raya sub-district, district Batola, South Kalimantan, in July - November, 2014. The study was designed by using strip plot with three replications. The treatment consisted of two factors, namely application of an oxidizing microbial pyrite and leaching amount (intensity). The main plot consisted of (P0) without leacing (naturally), (P1) six times leaching , (P2) eight times leaching, and (P3) 12 times leaching. Subplot consisted of (M0) without oxidizing microbial pyrite, (M1) with oxidizing microbial plant used in this study is Inpara 3 of rice variety. Observations were made on soil pH, oxidizing bacteria pyrite, growth of rice plants (plant height and number of tillers) and rice yield. The results showed that the main problem of actual acid sulfate land studied is a high soil acidity (pH of 3.44). Influ-ence of leaching was greater than microbial application on crop yields. Application of the pyrite oxidizing bacterial and leaching eight times gave the best influence on the growth and yield of rice plants.

Enhancement of rice growth and yield in actual acid sulfate soils by potent acid-resistant Rhodopseudomonas palustris strains for producing safe rice

Purple nonsulfur bacteria (PNSB), Rhodopseudomonas palustris strains (TLS06, VNW02, VNW64 and VNS89), were investigated to increase rice growth and grain yield in acid sulfate soils (ASS) with low available phosphorus (Pavail). P-solubilizers were tested in vitro. A 4 × 3 factorial design consisted of PNSB at 5.4 × 104 cells g−1 dry soil weight (mixture of 4 strains, VNW64 singly, or no-PNSB) and P fertilizer levels (0, 30, 45 and 60 kg P2O5 ha−1) that were used with the rice variety OM5451in pots with two types of ASS (Hon Dat and Phung Hiep). The four PNSB mixture had the ability to dissolve insoluble P from variscite and strengite. The combination of mixed culture with 45 P was the most effective, increasing grain yield by 34%. Enhancement of rice growth and yield in both soils corresponded to the maximal levels of Pavail, total P and NH4+, and the lowest levels of Alexch and Fe2+. Soil health with this treatment was significantly improved, with a strong positive correlation between PNSB population and phosphatase activity in both soil types. The combination of PNSB mixture with P fertilizer reduced the amount of chemical fertilizer needed for maximal grain yield, provided safe rice, and maintained soil health.

Utilization of Na-bentonite to Improve pH-buffering Capacity of Acid Sulfate Soils in Natural Gas Transmission Pipeline Rights-of-Way, Thailand

Na-bentonite, non-hazardous material usually uses as a drilling mud in Horizontal Directional Drilling (HDD) technique. Its alkalinity may reduce severe acidic conditions of acid sulfate soils (ASS) in natural gas transmission pipeline Rights-of-Way in Thailand (RoW). This study focused on the effects of Na-bentonite on pH buffering capacity (pHBC) of ASS. Five major acid sulfate soils in RoW were collected and incubated with incremental amounts of 0.4 M Ca(OH)2 and 0.4 M HCl to determine their pHBC. Hydroxyl equivalent alkalinity derived from pHBC curves was used to define the appropriate rate of Na-bentonite. The various soil:Na-bentonite ratios of 1:0.1, 1:0.15, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:1 were prepared to examine their pH change. The results showed that active acid sulfate soils especially in subsoil had very high pHBC and Na-bentonite can increase soil pH to the optimal pH of 6.0, implying that Na-bentonite was beneficial for acid sulfate soils.

Partitioning and potential mobilization of aluminum, arsenic, iron, and heavy metals in tropical active and post-active acid sulfate soils: Influence of long-term paddy rice cultivation

Drainage of potential acid sulfate soils (PASS) for paddy rice cultivation results in the formation of active acid sulfate soils (AASS) and subsequently post-active acid sulfate soils (PAASS). The drainage of PASS causes severe environmental problems including acidification and metal contamination of soil and water resources. This study examined the vertical distribution and partitioning of Al, As, Co, Cu, Fe, Mn, Ni, Pb, and Zn in six tropical acid sulfate soils representing AASS and PAASS under long-term paddy rice cultivation (>145 years). The bulk soil samples were analyzed for total concentrations of Al, As, Co, Cu, Fe, Mn, Ni, Pb, and Zn. The partitioning of these elements was examined by a sequential extraction procedure. Labile Al is higher in ASS which is associated with low soil pH. During drainage, mobilization of As, Cu, and Pb is limited by coprecipitation with (poorly) crystalline Fe oxides minerals in the topsoil and partly oxidized layer of both soil types. These elements are associated with iron (mono) sulfides in unoxidized layer. When PASS are exposed to air, Co, Mn, Ni, and Zn are leached from the soils and are dominantly associated with iron sulfides in the unoxidized sediments. Labile Mn, Ni, and Zn are elevated in the unoxidized layer of PAASS because these elements are leached from the partly oxidized layers and adsorbed onto soil constituents. Cobalt is probably precipitated or adsorbed onto (poorly) crystalline minerals.