Tetsuhiro Watanabe

Regional trends in the chemical and mineralogical properties of upland soils in humid Asia: With special reference to the WRB classification scheme

Abstract Soils in humid Asia exhibit relatively incipient mineralogical characteristics because of the dominant steep slopes, crust movement and volcanic activity compared with many tropical soils on stable plains. In the present study, the relationship between the mineralogical and chemical properties of these soils was investigated with special reference to the World Reference Base (WRB) classification scheme. A total of 186 upland soil profiles were collected and the chemical and mineralogical properties of the B-horizon soils were analyzed for clay mineral composition, pH(H2O), exchangeable cations, cation exchange capacity (CEC), total C content, particle size distribution and sodium-dithionite-extractable oxides (Fed and Ald). The majority of the soils were acidic. The CEC/clay of the soils derived from sedimentary rocks (excluding limestone) or felsic parent materials showed a clear regional trend, which was usually higher than 24 cmolc kg−1 (corresponding to Alisols if the argic horizon is recognized) under the udic and perudic soil moisture regimes in Indonesia and Japan, whereas it was predominantly lower than 24 cmolc kg−1 (corresponding to Acrisols) under the ustic soil moisture regime in Thailand. In contrast, soils derived from mafic volcanic rocks or limestone were more variable in clay mineral composition, CEC/clay and pH, and were often high in Fed. This trend is in accordance with the clay mineral composition, in that mica and kaolin minerals dominated under the ustic soil moisture regime in Thailand, whereas significant amounts of 1.4 nm minerals formed under the udic and perudic soil moisture regimes in Japan and Indonesia. In conclusion, of the 186 soils studied, only nine and eight soils are classified into Luvisols (or Lixisols) and Cambisols (eutric), respectively, whereas the majority (169 samples) are classified as acid soils, such as Andosols, Podzols, Alisols, Acrisols and Cambisols (dystric). The WRB classification is generally consistent with regional trends in the chemical and mineralogical properties of the soils and successfully describes the distribution patterns of the acid soils in humid Asia using the criteria of CEC/clay = 24 cmolc kg−1.

Spatiotemporal variability in soil salinity and its effects on rice (Oryza sativa L.) production in the north central coastal region of Vietnam

Abstract To better understand the adverse impacts of soil salinization and promote rice (Oryza sativa L.) production in crops from the north central coastal region of Vietnam, the spatiotemporal variability of soil salinity and its effects on rice production were investigated. Experiments were conducted at 19 plots widely distributed in the Quang Phuoc commune, in the Quang Dien district of the province of Thua Thien Hue in the north central coastal region of Vietnam. We determined the elevation of the 19 plots to evaluate the influence of elevation on salt accumulation. Soil samples from the 19 plots were collected in January, May and September 2012 and 2013 to study the spatiotemporal variability of salinity. A soil saturation paste was prepared and used to measure electrical conductivity (ECe). The elevation measurements obtained suggest that the research site could be divided into low- and high-elevation plots, with elevation of the low-elevation plots ranging from –0.52 to 0.07 m and the high-elevation plots from 0.26 to 0.86 m (one of the sampling plot was designated with an elevation of 0 m and the elevations of the remaining 18 plots were measured relative to that). ECe was high at low elevations. In conclusion, although the differences in elevation between the 19 plots were very small (centimeters to decimeters), they still led to large differences in soil salinity levels. In the high-elevation plots, soils were irrigated with freshwater, thus maintaining low ECe levels throughout the year (< 1.0 dS m−1). In contrast, in the low-elevation plots, soils were subject to seawater intrusion, resulting in high ECe levels in all seasons (> 1.9 dS m−1). We recommend several solutions to limit the unfavorable effects of salinity and promote rice production. First, a comprehensive dike system should be constructed along the lagoon to prevent seawater intrusion onto land. Second, it will be necessary to construct adequate drainage facilities in the depressed areas to promote rapid water drainage into canals during and after flooding and irrigation. Third, because ECe was high from May to September, adequate fresh irrigation water should be frequently supplied to lower the ECe during this period.

Relationship between chemical and mineralogical properties and the rapid response to acid load of soils in humid Asia: Japan, Thailand and Indonesia

Abstract It is essential to determine the relationship between soil chemical and mineralogical properties and soil response to acid load to understand the acid-neutralizing capacity and cation behavior of different ecosystems. For 46 soil samples from a subsurface horizon in humid Asia, that is, Japan, Thailand and Indonesia, exchangeable cations, total bases and oxalate-extractable Al (Alo) were determined, and acid titration was conducted to investigate the rapid soil response to acid load. The acid titration experiment indicated three types of soil response: (1) the release of base cations (particularly Ca and Mg) strongly correlated with exchangeable bases, which dominated the tropical soil samples, (2) the release of Al correlated with Alo content, which dominated the Japanese soil samples, (3) acid and anion adsorption in soil samples with low acid-neutralizing capacity. To gain further information on the source of soil alkalinity, a column experiment with HCl was conducted using eight selected soil samples in which first-order kinetics were assumed to simulate the time-courses of cation release. In the column experiment, the amounts of Ca and Mg released were close to the exchangeable amounts, and Alo dissolved more rapidly than Al in crystalline minerals. The rate constants of cation release were large for Ca and Mg, and small for Al, clearly indicating a difference between the exchange and dissolution reactions. Thus, rapid soil response to acid load differed among the soils. A cation exchange reaction was dominant in the tropical soils. In some tropical soils, Ca and Mg were present in exchangeable forms at a higher ratio in the total amounts and they were considered to be easily utilized by plants, but leached out from the soils. In the Japanese soils, including the Andisols, secondary mineral dissolution was conspicuous, resulting in a large acid-neutralizing capacity. In both the tropical and Japanese soils with low acid-neutralizing capacity, anion adsorption mainly contributed to acid neutralization.

Detection of anaerobic carbon monoxide-oxidizing thermophiles in hydrothermal environments

Carboxydotrophic anaerobic thermophiles have been isolated from various hydrothermal environments and are considered to be important carbon monoxide (CO) scavengers or primary producers. However, the ecological factors that influence the distribution, abundance and CO-oxidizing activities of these bacteria are poorly understood. A previous study detected the carboxydotrophic bacteria Carboxydothermus spp. in a hot spring sample and found that they constituted up to 10% of the total bacterial cells. In this study, we investigated environmental features, potential microbial CO-oxidation activities and the abundance of Carboxydothermus spp. in various hot springs to determine environmental factors that affect CO oxidizers and to see whether Carboxydothermus spp. are common in these environments. We detected potential microbial CO-oxidation activities in samples that showed relatively high values of total organic carbon, total nitrogen, oxidation-reduction potential and soil-water content. The abundance of Carboxydothermus spp. did not correlate with the presence of potential microbial CO-oxidation activities; however, Carboxydothermus spp. were detected in a wide range of environments, suggesting that these bacteria are widely distributed in spite of the relatively low population size. This study implies that thermophilic CO oxidizers occur in a wide range of environments and oxidize CO in somewhat oxidative environments rich in organic matter.

Inhibitory Effect of Soil Micropores and Small Mesopores on Phosphate Extraction From Soils

Abstract Slow release of added phosphate in soils is of fundamental importance for plant nutrition and pollution in aqueous environments. The diffusion of phosphate in micropores and mesopores after desorption from the inside surface of pores is the most likely mechanism for the slow release. There are limited experimental data on the effects of micropores and mesopores, and differences in the effects of these pores among various soil types have not been reported. Phosphate extractability was characterized using the Hedley fractionation method and sequential anion exchange membrane extraction for soils with widely different acid oxalate–extractable Al and Fe (Alo and Feo) contents (1.7–87 g kg−1 of Alo + 1/2Feo). We measured the total specific surface area (SSA), the SSA of micropores and mesopores, and the decrease in SSA after phosphate sorption. The proportion of labile phosphate relative to added phosphate and the rate of phosphate release in sequential extractions were negatively correlated with Alo and Feo and the porosity of the soils (the 0.7- to 4-nm pore SSA relative to the total SSA). The soil samples in which the 0.7- to 4-nm pore SSA decreased with added phosphate showed low proportions of labile phosphate and slow release rates. We demonstrated that phosphate release from soils with high Alo and Feo contents was more difficult because of phosphate sorption into micropores and small mesopores. Availability of fertilizer phosphate might be low in soils with a high porosity, but the effects of aging and competition with organic molecules should be further investigated.

Soil Fertility Status and Its Determining Factors in Tanzania

The pedogenetic conditions in Tanzania vary widely. In particular, the country has a wide variety of parent materials of soils because of the presence of volcanic mountains, the Great Rift Valley, and several plains and mountains with different elevations (hence, different temperatures). In addition, the amount and seasonal distribution pattern of the annual precipitation vary, from less than 500 mm to more than 2500 mm. The potential land use and agricultural production differ greatly among regions, due to the presence of different soils. There have been several reports on the distribution patterns of soils and their physicochemical and mineralogical properties. According to a review of the history of soil surveys in Tanzania by Msanya et al. (2002), the major soil types described in the country are Ferric, Chromic, and Eutric Cambisols (39.7%); followed by Rhodic and Haplic Ferralsols (13.4%) and Humic and Ferric Acrisols (9.6%). To obtain basic information on soil mineralogy, Araki et al. (1998) investigated soil samples collected from regions at different altitudes in the Southern Highland and reported that the cation exchange capacity (CEC) per unit amount of clay content showed a negative correlation with elevation, which was accompanied by clay mineralogical transformation from mica to kaolinite. The authors suggested that soil formation on different planation surfaces is mainly controlled by the geological time factor whereby the lower surfaces are formed at the expense of the higher surfaces. Szilas et al. (2005) analyzed the mineralogy of well-drained upland soil samples collected from important agricultural areas in different ecological zones in the sub-humid and humid areas of Tanzania. They concluded that all soils were severely weathered and had limited but variable capacities to hold and release nutrients in plant-available form and to sustain low-input subsistence agriculture. Generally, there seems to be a consensus that the soils in Tanzania and the neighboring countries are not very fertile. The relevance of soil organic carbon management and appropriate fallowing systems such as agroforestry have been pointed out since as critical for sustaining agricultural production (Kimaro et al., 2008; Nandwa, 2001). In the present study, the regional trend in soil fertility with respect to the soil mineralogical and chemical properties was investigated. Soil properties were correlated with different

Could Soil Acidity Enhance Sequestration of Organic Carbon in Soils

On the basis of field and laboratory measurements of the dynamics of soil organic matter (SOM) in Japan, Thailand, Indonesia, Kazakhstan, and Ukraine having different soil pH levels, we postulate that soil acidity plays an important role in the accumulation of SOM through two processes. Firstly, the amount of potentially mineralizable C (C 0) in the acid soils of Kalimantan or light-fraction C in the Japanese acid soils often increased drastically. Hence, it seems that high soil acidity can enhance the accumulation of organic materials in surface soils by decreasing the soil microbial activities for SOM decomposition. Secondly, field measurements of C flux in various soils under forest showed that the internal leaching of dissolved organic carbon (DOC) from litter layers or surface soils increased under low pH conditions, typically for Humods in Japan and Udults in Kalimantan. This indicates a downward movement of DOC in acid soils that increases the tendency of the subsoils to accumulate SOM as organo-mineral complexes. It is concluded that high soil acidity can enhance the storage level of soil organic materials in the form of readily mineralizable organic materials in the surface soils and by organo-mineral complexes formed in subsoils as a result of accelerated leaching of DOC from the O horizon.

Effects of seasonal rainfall and water table movement on the soil solution composition of tropical peatland

ABSTRACT Understanding the composition of the soil solution of tropical peatlands is important because it directly affects nutrient availability and environmental degradation. The objectives of this study were to investigate temporal fluctuations in the soil solution composition in tropical peatlands in West Kalimantan and Riau, Indonesia and identify the factors controlling these fluctuations. In each site, we established four study plots consisting of three plots under oil palm (Elaeis guineensis Jacq.) plantation and one plot under uncultivated land as the control. Triplicate soil solution samples were collected at 50 and 200 cm depths, fortnightly. During the drought, the pH at 50 cm was low (3.7–4.0), which was influenced by oxidation reactions such as organic acids and NO3− generations. The pH at a depth of 200 cm was high (5.9–6.8), due to reduction reactions such as denitrification. High cation concentrations at both depths would result from organic matter decomposition and the limited downward movement of water. Rewetting the West Kalimantan peatland caused a sharp decrease in pH and ionic concentrations at 50 and 200 cm depths, because of the transportation of ions from the upper acidified layer. However, the lower rainfall levels in Riau than West Kalimantan resulted in a gradual decrease in pH and Ca2+ concentration. The higher pH levels and ion concentrations in West Kalimantan than in Riau would be influenced by the enhanced microbial activity due to water supply from the risen water table in this site. This study showed that seasonal rainfall and water table movement were the main factors controlling the fluctuations in the chemical composition of soil solutions.

Fractionation of phosphorus in soils with different geological and soil physicochemical properties in southern Tanzania

ABSTRACT Soil phosphorus (P) forms have been practically defined as chemically fractionated pools. A knowledge of the abundance and diversity of P forms in soil, and the factors affecting them, will lead to better soil management. However, little is known about the differences in P forms among soils with different geological properties in tropical Africa. The aim of this study was to investigate the P forms in soils with different physicochemical properties formed under different geological conditions in southern Tanzania and to identify the factors affecting the P forms in these soils. In total, 37 surface soil samples were collected from three geological groups; the plutonic (mainly granite) rock (PL) group, the sedimentary and metamorphic rock (SM) group, and the volcanic ash (V) group. Soil P was sequentially extracted by NH4Cl, NH4F, NaHCO3, NaOH + NaCl, and HCl, and inorganic (Pi) and organic P (Po) in each fraction were determined. The lowest total P was in the PL group (average, 360 mg P kg-1) because of the high sand content. Iron (Fe)-P (NaOH-Pi) was the major form in this group, accounting for 8.4% of total P. In the SM group (average total P, 860 mg P kg-1), Fe-P was the major form in most, accounting for 7.8% of total P. Soils in the SM group occasionally had high calcium (Ca)-P due to application of chemical fertilizer at the collection site. The V group had the highest total P (average, 1600 mg P kg-1) and its major P form was Ca-P, which was possibly derived from primary minerals (i.e., apatite), accounting for 14% of total P. In addition, the high oxalate-extractable Al possibly caused the accumulation of Al-P in the V group. Oxalate-extractable Fe generally increased with increasing Fe-Pi, while oxalate-extractable Al increased with increasing organic P and Al-Pi in soils in all three geological groups. These results demonstrate that the soil P forms differ greatly among sites in southern Tanzania with different geological conditions and associated soil properties.

Soil properties that determine the mortality and growth of Haloxylon aphyllum in the Aral region, Kazakhstan

Abstract Black saxaul (Haloxylon aphyllum) is a native tree species tolerant of aridity and salinity. It is planted to alleviate environmental damage due to the formation of the Aralkum desert and improve vegetation of the Aral Sea region. To investigate the environmental factors that determine seedling mortality and growth after rooting, we focused on soil properties and topographic factors in a study plot. We found that a hard clay layer that was low in hydraulic conductivity underlay accumulated sandy sediments at different depths. The soil in low seedling mortality areas was consistently sandy and low in salinity from the surface to a depth of 100 cm. In areas of high seedling mortality (75–100%), soils with a high content of silt and clay, with high salinity were detected within 100 cm depths. This suggests that accumulated sand sediment over a depth of 100 cm is required for root development. Plant height was positively correlated with depth of the hard clay layer. Significant relationships with plant height were also detected in chemical and physical properties at 80–100 cm such as electric conductivity (ECe), sodium adsorption ratio (SAR), and sand ratio. However, these properties had no significant relationship at 0–20 cm or with the relative elevation of the plot, suggesting that the subsequent growth of seedlings depends more on the sub-soil environment than on-surface conditions. The assessment of sub-soil condition is recommended to make site selection for reforestation much more reliable.