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Collapsing gully erosion is a specific form of soil erosion that is widely distributed in the hilly granitic region of tropical and subtropical southern China and resulted in extremely rapid water and soil loss. The aim of this study was to investigate the correlations between soil physicochemical and shear properties and the clay mineralogical of different profiles of the non-eroded soils (without soil erosion) and collapsing gully soils in Changting County, Fujian Province, southeastern China. A total of 32 sampling soils collected from four pedons of non-eroded and collapsing gully soils were subjected to conventional soil analyses for physicochemical properties. The soil shear strength of collected soils was measured using a triaxial shear apparatus according to the unconsolidated-undrained (UU) method. The clay mineralogical of different profiles soils was examined with an X-ray diffraction (XRD) analysis. The results showed that non-eroded soils had superior physicochemical characteristics. The cohesive force of the non-eroded soils was generally greater than that of collapsing gully soils. The XRD patterns of the clay fraction indicated that kaolinite, illite, hydroxy-interlayered vermiculite (HIV), and gibbsite were the dominant clay minerals in the studied soils. Pearson’s correlation analysis showed that the cohesive force of the studied soils had significant and positive correlations with CEC, exchangeable Al3+ + H+, Fed, Ald, and Fet; the correlation coefficients (R value) for cohesive force were greater than those of internal friction angle. The stepwise multiple linear regression analyses indicated that exchangeable Al3+ + H+ and Ald were the dominant factors affecting cohesive force. Compared with collapsing gully soils, non-eroded soils had superior physicochemical and shear properties, indicating that non-eroded soils were better able to resist soil erosion. The findings obtained in the present study were of fundamental significance in understanding the correlation between shear strength and the soil physicochemical properties in the non-eroded soils and collapsing gully soils of tropical and subtropical China.

General acid washing is commonly used to treat heavy metal-contaminated soils, but it is sometimes difficult to achieve remediation aims in severely polluted soils. If we expose the surfaces of Fe oxide minerals to reductive dissolution during washing treatment, more of the metals initially adsorbed to these surfaces will be liberated, which may encourage the removal of heavy metals. Initially, the metal extraction capabilities of nine chemical reductants were compared in ten soil samples polluted by Cr, Cu, Zn, and Ni. Sodium dithionite (Na2S2O4) and ferrous sulfate (FeSO4) were screened for subsequent intensive research. In summary, the Na2S2O4 solutions had higher Cr, Cu, and Zn removal rates than either the FeSO4 or acid solution. Application of dissolved organic carbon (DOC) further increased the removal of heavy metals by complexation. About 15%, 86%, 32%, and 52% of the Cr, Cu, Zn, and Ni, respectively, were removed from the representative soil (M-2) by two-stage washing using 0.2 M Na2S2O4 coupled with 1,500 mg L−1 DOC solution at pH 2.0. Meanwhile, most soil fertility was preserved: ammonium nitrogen was increased 3.9 times; the increase in exchangeable potassium was 33%; and the reduction in available P was only 10%.

Understanding rill erosion processes is important in the prediction of soil erosion and the prevention of soil loss. However, limited information is available concerning the impacts of rainfall on rill erosion on steep slopes. Colluvial deposits with steep slopes make up the packed material underlying the collapsing walls in benggang, which collapse due to hydraulic pressure and gravity. They contain loose materials and large amounts of coarse particles. The objectives of this study were to investigate the impacts of rainfall intensity and slope gradient on the rill erosion process, rill development and rill flow dynamic mechanisms on the steep slopes of colluvial deposits. The colluvial soils were subjected to simulated rainfall in a 5-m2 (5-m by 1-m) flume at heavy rainfall intensities (100, 120, and 140 mm h−1) and on five steep slopes (20, 25, 30, 35, and 40°). Rill erosion contributed significantly to colluvial slope erosion; on average, rills accounted for 61% of the soil loss, and the effects of slope gradient were greater than those of the rainfall intensity. After rill development, rill density, rill length, width, and depth all significantly increased. Correspondingly, the soil loss rate sharply raised and irregularly fluctuated. Moreover, the collapse of rill heads or sidewalls tended to increase the relative contribution to rill erosion and rill development. The rill flow was characterized by transitional and subcritical flow regimes. The rill flow velocity was the most sensitive hydraulic parameter, and the unit stream power provided the optimal hydrodynamic parameter to characterize the dynamic mechanisms of rill erosion on colluvial deposits. The collapse of rill heads or sidewalls could result in negative values for critical shear stress, critical stream power, and critical unit stream power of rill erosion, which were −19 Pa, −5.3 N m−1 s−1, and −0.09 m s−1, respectively. These results provide a better understanding of the mechanism of rill erosion on steep slopes.

This study focused on the effects and mechanisms of biochar amendment to Cd-contaminated soil on the uptake and translocation of Cd by rice under flooding conditions. Pot and batch experiments were conducted using Cd-contaminated soil collected from a field near an ore mining area and a cultivar of Oryza sativa ssp. indica. Biochar derived from rice straw under anaerobic conditions at 500 °C for 2 h was mixed with the soil at the rate of 0, 2.5, and 5%. The application of 5% biochar reduced CaCl2-extractable soil Cd by 34% but increased Cd concentration in brown rice by 451%. Biochar amendment decreased water-soluble Fe2+ in soils and formation of Fe plaques on roots and weakened the Fe2+-Cd2+ competition at adsorption sites on the root surface. Biochar increased water-soluble Cd in the soil and consequently Cd uptake by rice roots by releasing water-soluble Cl−. Biochar application also reduced the proportion of cell wall-bound Cd in the root, which caused easier Cd translocation from the cortex to the stele in the root and up to the shoot. Rice straw biochar (with high concentration of water-soluble Cl−) reduced CaCl2-extractable soil Cd but increased Cd concentration in rice under flooding condition.

This study aimed to compare soil physicochemical properties and mineralogical compositions, including the cohesive force and internal friction angle, using direct shear tests with designed water contents and temperatures, between noncollapsible soil and collapsed gullies. Two pedons were collected from Longmen Town (Anxi County, Fujian Province) with severely collapsed gullies that developed from granitic rocks, and another two pedons were collected from metamorphic regions (Gande Town) without soil erosion. The samples were subjected to X-ray diffraction (XRD) analysis, and their soil physicochemical properties were compared. Noncollapsible soils had superior physicochemical characteristics, e.g., these soils contained higher amounts of cations, especially total iron oxides (Fet). Furthermore noncollapsible soils were able to resist shearing due to their greater cohesive force, and the internal friction angle did not differ considerably from that of the collapsed soils. Kaolinite, illite, hydroxy-interlayered vermiculite (HIV) and gibbsite were the dominant clay minerals in the noncollapsible soils. However, in the collapsed soils, kaolinite accounted for > 85% of the total clay mineral composition. The cohesive force and internal friction angle were significantly correlated with sesquioxides of all non-collapsible and collapsed pedons, such as Fed (free Fe-oxides, 0.762**, 0.637**) and total iron (Fet, 0.783**, 0.708**), as well as magnetic susceptibility (0.650**, 0.740**) (P

Mulching is an effective soil conservation practice for permanent gullies in southern China. Knowledge of the sediment characteristics that occur in mulched soils of colluvial deposits could improve the utility of mulching for soil conservation. A rainfall simulation experiment was designed to evaluate the effects of mulch on the runoff, erosion, and particle size distribution of eroded sediments. Straw mulch coverage of 0, 25, 50, 75, and 95% was tested with simulated rainfall. The effective particle size distribution of the sediment was compared with the ultimate particle size distribution to investigate the detachment and transport mechanisms involved in sediment mobilization. Mulching delayed the runoff initiation time and reduced the average runoff rate. Compared with bare soil, the increased mulch coverage decreased the soil loss rate by 13.0 to 90.3%. Moreover, the peak sediment concentration decreased from 80 to 200 g L− 1 under the different mulch coverage conditions. The optimal straw application rate was 1.5 to 3.0 Mg ha− 1 in the permanent gully's deposits. The relationship between instantaneous kinetic energy of rainfall and the proportion of effective clay- and sand-sized particles was well represented using an exponential equation. The effective clay-sized sediments under the different mulch coverage conditions were 2 to 4 times more common than those of the original soil, although there were only 13.9% sand-sized particles in the sediment when the mulch coverage was 95%. The silt-sized sediment was transported as primary particles under the different mulch coverage conditions. The effective to ultimate ratio of silt-sized particles fluctuated around 1. There were depletions of clay and silt in the colluvial deposit soil with mulch cover, and the enrichment ratios of clay and silt were larger than 1 while most of the enrichment ratios for sand were

Information on phosphorus (P) adsorption and its impacts on the redistribution of the P fraction in soil profiles are important for environmental management under intensive agricultural practices. To clarify the dominant factors influencing soil phosphorus adsorption in an Entisol (locally known as purple soil), P adsorption experiments were conducted in Sichuan Basin of southwestern China for cropland and woodland soils with acidic, neutral and calcareous origins throughout their profile. After various doses of P were added during incubation experiments, soil P fractions were also analyzed. The results showed that there were no significant differences in Fe-oxides and P adsorption along the vertical gradients. Agricultural practices and lower pH conditions reduced the P adsorption capacity of purple soils throughout the soil profiles. For acidic and neutral purple soil profiles, the P adsorption capability was mainly influenced by Fe-oxides and soil texture. Ca-bound P and Fe-Al-bound P represented the majority of the total inorganic P of calcareous soils. There was a saturation of adsorption capacity by sesquioxide and a high risk of dissoluble reactive P (NH4Cl-P) being released out of the soil profile in acidic and neutral purple soils after the greatest P addition, indicated by the higher proportions of NH4Cl-P (over 40%) and decreasing Fe-Al-P fraction. P fractions migrated with greater difficulty in calcareous purple soil profiles as Ca-P fraction peaked over 65% when adding a P dose at or greater than 80 g P kg-1, indicating the high potential of P adsorption. The X-Ray Diffraction analysis also verified the formation of brushite. Adaptive management practices should be designed to alleviate P losses for acidic and neutral purple soils.

The objectives of this research were to study the effects of Na2SiO3 application on the uptake, translocation, and accumulation of Pb in rice and to investigate the mechanisms of Pb immobilization by Na2SiO3 in paddy rice soils and rice plants. Pot experiments were conducted using a Cd-Pb-Zn-polluted soil and Oryza sativa L. ssp. indica cv. Donglian 5. L3-edge X-ray absorption spectroscopy was used to identify Pb species in soils and roots. The results showed that the application of Na2SiO3 increased soil pH and available soil Si but decreased DTPA-extractable Pb in the soil. High dose of Na2SiO3 (12.5 g/kg) reduced the Pb level in brown rice as it inhibited Pb transfer from soil to rice grains, especially Pb transfer from the root to the stem. The Pb X-ray absorption near-edge spectroscopic analysis revealed that application of high dose of Na2SiO3 increased Pb-ferrihydrite and PbSiO3 precipitates in the soil and in the root while it reduced Pb-humic acids (Pb-HAs) in the soil and Pb-pectin in the root. The decrease in Pb availability in the soil can be partly attributed to increase the precipitation of PbSiO3 and the association of Pb2+ with Fe oxides in the soil. The inhibition of the root-to-stem translocation of Pb was partially due to the precipitation of PbSiO3 on the root surfaces or inside the roots.

Increasing temperature and nitrogen (N) deposition are major drivers of global change that will influence plant-soil systems. We aimed to understand how plant stoichiometry and nutrient limiting types could change with continued warming and N inputs in subtropical regions. In 2014, the experiments were established in 30 mini-plots (2 × 2 m) with the following treatments: control, high N addition, low N addition, warming, warming + high N addition, and warming + low N addition. We sampled the leaf and root of Cunninghamia lanceolata and soils to assess their elemental and stoichiometric variables and δ15N under all six conditions. Both experimental warming and N fertilization consistently induced an increase in fine-root N, P, and N:P. The N:P ratio of the mature green-leaf and soil was 7.24–11.63 and 4.79–6.56, respectively. On average, C. lanceolata showed higher proportional P resorption, but lower N resorption. The δ15N enrichment factor significantly increased in the warming and N addition treatments. N addition decrease leaf N content, and increased the plant growth, which was due to the effect of the N dilution of C. lanceolata. In subtropical regions, N-limitation affects the growth of C. lanceolata, and the concurrent increase in warming and N fertilization should help relieve N-limiting conditions.

The suitability of an agent for washing heavy metal contaminated soils depends not only on the efficiency of heavy metal removal but also on the persistence of the washing effect, especially for agricultural soil. Redistribution of residual heavy metals in washed soil from inert pools to labile pools can reverse the initial washing effect. In order to study the redistribution of residual Pb in Pb-contaminated soils washed with citric acid (CA), ethylenediaminetetraacetic acid (EDTA), FeCl3, and HCl solutions, washed soils were incubated under both flood and 70% field water capacity (FWC) conditions for 180 days. The Pb availability in CA-, EDTA-, FeCl3-, and HCl-washed soils varied with incubation time. Diethylenetriaminepentaacetic acid (DTPA)-Pb generally increased with incubation time, except in CA-washed soil under flood incubation condition. Pb associated with the exchangeable/acid extractable fraction (F1) increased, whereas Pb in the easily reducible fraction (F2) decreased over time, for all washed soils under flood incubation condition; the changes in the amount of Pb associated with each fraction were much smaller under 70% FWC incubation. The transformation of Pb from F2 to F1 during flood incubation was largely caused by the mobilization of Fe and Mn oxides. The mobility factors (MF) of Pb for samples under flood incubation increased with increasing incubation time while those for samples under 70% FWC incubation changed only slightly, which implies increasing environmental risks of Pb from washed soils that are flooded. Therefore, the redistribution and potential environmental risks posed by heavy metals in washed soils, especially in paddy rice soils, should be taken into account when the suitability of a washing agent is evaluated. In the present study, CA was found to be unsuitable for washing Pb-contaminated agricultural soil, whereas the FeCl3 solution was the most stable washing agent tested, as it had high removal efficiency and low release of Pb after washing.

Mainly located in the Sichuan Basin, known as the ‘Land of Plenty’, purple soils (developed from purple sandstone and shale) have been long noted as highly productive in spite of their rocky texture. However, information on the physicochemical properties (including mineral properties) of purple soils remained obscure for the scientific community. For example, it is not clear what causes the purple color of the soils. In this study, eight soil profiles of the Jiufeng (JF, acidic), Shibao (SB, neutral), and Yanting (YT, calcareous) areas, representing the three most widely distributed purple soils in Sichuan Basin, were individually sampled under both cropland and forestland, and then analyzed using common chemical analysis and conventional X-ray diffraction to clarify the effects of clay mineral and anthropogenic influences on the typical soils. The results show that considerable variability of soil pH and cation-exchange capacity (CEC) exists between soil types (p

The sediment transport capacity (Tc) is an important parameter for analysing and controlling soil erosion processes. However, few studies have investigated the Tc of soils containing gravel (grain sizes of >2 mm) on steep slopes. Colluvial deposits on steep slopes in benggang are composed of loose materials with large amounts of gravel. This study aimed to investigate the effects of gravel content on the Tc of overland flow using colluvial deposits with a range of slope gradients and flow discharges in a nonerodible flume (4 m long, 0.12 m wide and 0.1 m high). The experiments were carried out using six gravel mass contents (0, 10, 20, 30, 40, and 50%), four slope gradients (18, 36, 57, and 84%), and four flow discharges (0. 56, 1.11, 2.22, and 4.44 × 10-3 m2 s−1). The experimental results revealed that the measured Tc increased linearly as the gravel content increased. The effects of the slope gradient, flow discharge and gravel content on Tc were significant (p

The effectiveness of four different washing extractants--HCl, FeCl3, citric acid, and EDTA--in removing Cd, Pb, and Zn from polluted soil was studied. The removal of these metals, their redistribution between fractions, and the potential risks posed by them, in soils washed with the tested extractants, were examined. Although all the rounds of washing removed Cd, Pb, and Zn from soil, the first round removed more metals than subsequent rounds. Each of the four extractants had different effects on the removal of the metals. At the end of the first round of washing, HCl, EDTA, and FeCl3 were the most effective in removing Zn, Pb, and Cd, respectively. Both the single round and five successive rounds of washing with various extractants resulted in significant increases in Pb in the exchangeable/acid extractable fraction. Washing with HCl, EDTA, and FeCl3 significantly reduced potential risks (calculated as the Potential Risk Index, PRI) posed by Cd in washed soil. The first round of washing, using all extractants, increased the risks posed by Pb and Zn. However, five successive rounds of washing with FeCl3 and EDTA reduced the risk posed by Pb, and washing with citric acid and FeCl3 increased the risks posed by Zn. EDTA and HCl were better for reducing Zn risks, and successive washing with EDTA and FeCl3 were more effective in reducing Pb risks than the other extractants. Finally, five successive rounds of washing, with all the extractants, effectively reduced the potential risks posed by Cd. Among the four reagents, EDTA was advised to be the alternative of the washing reagent by significantly reducing the PRI values of Cd, Pb, and Zn.

The relationships between the basic properties and trace elements in soil argillans and corresponding matrix soils were studied by sampling from the B horizons of 26 Alfisols in croplands of the subtropical area in Central China. The soil elements (K, Na, Ca, Mg, Mn, Co, Cu, Cr, Cd, Li, Mo, Ni, Pb, Ti, V, and Zn) were extracted by acid digestion and their contents were measured using inductively coupled plasma optical emission spectrometry (ICP-OES). The mean contents of clay and organic matter in the argillans were approximately 1.1 and 1.3 times greater than those in the matrix soils, respectively. The pH values and the contents of P2O5 and bases (K2O, Na2O, CaO, and MgO) in the argillans were higher than those in the corresponding matrix soils. Cu, Cd, Ti, and V were enriched in the argillans. Correlation coefficients and factor analyses showed that Co, Cu, Li, and Zn were bound with phyllosilicates and manganese oxides (Mn-oxides) in the argillans. Cr and Pb were mainly associated with iron oxides (Fe-oxides), while Ni was bound with Mn-oxides. Cd, Ti, and V were chiefly associated with phyllosilicates, but Cr and Mo were rarely enriched in the argillans. In contrast, in the matrix soils, Co and Zn were associated with organic matter and Fe-oxides, Cr existed in phyllosilicates, and Mo was bound to Fe-oxides. Cd, Ti, and V were associated with organic matter. The results of this study suggest that clays, organic matter, and minerals in the argillans dominate the illuviation of trace elements in Alfisols. Argillans might be the active interfaces of elemental exchange and nutrient supply in cropland soils in Central China.

Background Clay minerals especially organoclays modified by the introduction of organic molecules into the mineral structure show much promise for environmental remediation applications. Application of organic attapulgite (O-APG) and organic montmorillonite (O-MMT) as soil amendments to bind polychlorinated biphenyl (PCB) in contaminated soils and observe PCBs accumulated in the ryegrass shoots and roots was investigated. Results Pot experiments in greenhouse indicated that organoclays could significantly fix the PCB in soils and reduce its contents in ryegrass shoots and roots. Compared with the control, the migration of concentrations of PCB into the environment in contaminated soils is reduced by about 28.5 and 44.1%, and concentrations of PCB in ryegrass roots and shoots were reduced within the range from 57.0 to 63.0% and 49.6 to 56.5%, respectively, through addition of 6% organic attapulgite and montmorillonite. There was a negative correlation between the accumulation of PCB in ryegrass and the amount of organoclay addition. The accumulations of PCB in ryegrass roots were significantly higher than those in the ryegrass shoots. Conclusions The two organoclays had been proved effective as environmental amendments for reducing the mobility and bioavailability of PCB in contaminated soils. The results of this study provided an efficient method for the remediation of PCB contaminated soils.

Rainfall intensity and slope gradient are important factors that affect soil erosion; however, contradictory observations have been made due to different experimental conditions and materials. Colluvial deposits with loose, coarse material and steep slopes are easily erodible, but the erosion mechanism of colluvial deposition remains obscure. This work investigated the effects of heavy and storm rainfall intensity and steep slope gradients on the infiltration, runoff, and soil loss of colluvial soil. The rainfall intensity ranged from 1.00 to 2.33 mm min⁻¹, and the slope gradient ranged from 36 to 84%. The infiltration rates declined sharply in the initial stage, whereas an opposite trend was observed for runoff rates until a steady state was reached after 5 min. Single- and multiple-peak models illustrated the two types of changes for the sediment yield process. The infiltration volume and the coefficient increased with increasing rainfall intensity and decreased with increasing slope, whereas the runoff coefficient decreased with increasing rainfall intensity and increased with increasing slope. Runoff volume and sediment yield increased with increasing rainfall intensity but had a critical slope gradient of 58% and >47%. The sediment concentration increased with increasing rainfall intensity, and first increased and then decreased with increasing slope gradients at rainfall intensities of 1.00 and 1.33 mm min⁻¹ but increased at rainfall intensities of 1.67, 2.00, and 2.33 mm min⁻¹. The findings of this study can be used to clarify the erosion mechanisms in disturbed soils with high coarse particle content.

This study aimed to determine effects of rice straw biochar on Pb sequestration in a soil-rice system. Pot experiments were conducted with rice plants in Pb-contaminated paddy soils that had been amended with 0, 2.5, and 5% (w/w) biochar. Compared to the control treatment, amendment with 5% biochar resulted in 54 and 94% decreases in the acid soluble and CaCl2-extractable Pb, respectively, in soils containing rice plants at the maturity stage. The amount of Fe-plaque on root surfaces and the Pb concentrations of the Fe-plaque were also reduced in biochar amended soils. Furthermore, lead species in rice roots were determined using Pb L3-edge X-ray absorption near edge structure (XANES), and although Pb-ferrihydrite complexes dominated Pb inventories, increasing amounts of organic complexes like Pb-pectins and Pb-cysteine were found in roots from the 5% biochar treatments. Such organic complexes might impede Pb translocation from root to shoot and subsequently reduce Pb accumulation in rice with biochar amendment.

This study examined the change in the speciation of cadmium (Cd) in contaminated rice paddy soils with prolonged submergence. Three Changhua soils (CH1, CH2, and CH3) from central Taiwan and three Taoyuan red soils (TY1, TY2, and TY3) from northern Taiwan with different levels of heavy metal contamination were selected for the study. The Cd, Fe, Mn, soil pH, and Eh in soil solutions were determined as a function of submerging time. During submergence, the Fe and Mn concentration increased, while the SO4 2− concentration decreased. The concentrations of Cd immediately increased in the soil solutions after a short submerging time and then decreased with further submergence. The sequential extraction showed that the exchangeable fraction decreased and the oxide-bound fraction increased after submergence. According to preliminary calculations of the MinteqA2 program, sulfate cannot be reduced to sulfite or sulfide under the soil Eh and pH values observed for the soils after prolonged submergence. Thus, the observed decreases of sulfate concentration may result from sulfate reduction in the micro-environments, which cannot be accounted for by the thermodynamic calculation. The reduction of sulfate to sulfide may subsequently result in the formation of CdS precipitate, which attributes to the decreases of Cd concentrations in the soil solutions after prolonged submergence.

Sewage sludge (SS) is used on sloping land, as a soil amendment, because of its organic matter (OM) and nutrient content. However, the presence of nitrogen (N), in acidic soils amended with sludge, and its transport in runoff can lead to eutrophication of downstream surface water. This study assesses the effects of different application methods on N transport, via runoff from plots amended with SS (0 and 120 Mg ha−1). A lateritic red soil (pH 5.2) was selected for this study, using simulated rainfall conditions. When sludge was broadcasted and mixed with surface soils (BM), the concentrations and mass losses of total N in the mixed sample (MTN), total N in the settled sample (STN), total particulate N (TPN), total suspended N (TSN), total dissolved N (TDN) and NH4+-N, in runoff water, were highest at 1 or 18 d after application. BM treatments showed initial pollution risks to surface waters, which diminished gradually with time. Whereas the concentrations and mass losses of NO3−-N, in all sludge plots, appeared to have a declining trend, after an initial ascent. Hole-application (HA) and broadcast application with hay mulch (BH) treatments prevented N loss effectively, the runoff losses coefficient of MTN increased in the order BM (0.43%) > HA (0.15%) > BH (0.03%). For sludge treatments, N was largely lost in dissolved species, while a large portion of NH4+-N was lost in particulate fraction. Nitrogen (N) losses in runoff were greatly affected by the transformation of sludge N in the soil and the modification of soil properties, induced by sludge amendment. The risk associated with the application of sludge to sloping fields, in areas of acidic soil, is an important research subject that merits further study.

This study investigates the species of Cu and As (enargite) residues present in soils of the Chinkuashih area, northern Taiwan. Two pedons, on the shoulder and footslope along a toposequence, were examined for their metal partitioning and geochemical origins. The bulk soils were analyzed by sequential extraction combined with mineralogical analyses, including X-ray diffraction (XRD) and scanning electron microscopy ∕ energy dispersive spectrometer (SEM ∕ EDS) analyses. Soil pH ranged from 4.23 to 4.91 with low base saturation, and the soils can be classified as fine, mixed, thermic, Typic Kandiudults. Mineralogical study indicated that enargite and pyrite particles mainly coexisted in silt and sand fractions, particularly in lower soil horizons of the footslope, showing high contents of Cu and As. Kaolinite and illite were dominant minerals in clay fractions. The footslope accumulated more total Cu and As than that of shoulder pedon. The sequential extraction experiments resulted in high proportions of Cu remaining in residual fractions, while the most of As was bound in amorphous Fe and Al oxyhydroxide fraction. The risk analyses of Cu and As (enargite) contamination in soils of the Chinkuashih area merits further study.

Purpose Biochar amendments can alter phosphorus (P) availability in soils, though the influencing mechanisms are not yet fully understood. This work investigated the adsorption and desorption of P on ferrihydrite (F, a Fe-oxide widely distributed in surface environments) in order to evaluate the interactions between P and Fe-oxide in the absence or presence of biochar (F or ferrihydrite–biochar (F–B) interaction) in soils.

BACKGROUND: Tea plants are always cultivated in acid soils in hilly regions and their growth can be dependent on to soluble aluminium (Al). The mechanism of Al detoxification and the influence of Al on phenolic compounds (i.e. catechin) in the roots of tea plants has remained obscure. This study aimed to investigate the influence of Al changes on the concentrations of phenolic substances in tea plants through hydroponic experiments. RESULTS: Tea plants were cultivated in nutrient solution containing 1.5 and 2.5 mmol L−1 Al, and these treatments enhanced the growth of new buds and roots. Aluminium stimulated the uptake of Ca, Mg, K and Mn, whereas the uptake of Fe, Cu and Zn was retarded. Moreover, total phenol concentrations in tea plant tissues increased with increasing Al concentrations. In general, catechin concentrations in leaves increased with increasing Al concentrations in the hydroponic experiments. High correlation coefficients were obtained between Al and (−)-ECG (r2 = 0.85, P < 0.01) and between Al and total phenols (r2 = 0.92, P < 0.01). CONCLUSIONS: The Al concentration in tea plants indeed increases catechin concentrations and plays an important role in the growth of tea plants. Copyright © 2011 Society of Chemical Industry

Attapulgite and montmorillonite were utilized to remediate heavy metal polluted red soils in Guixi City, Jiangxi Province, China. The effects of clay minerals on availability, chemical distribution, and biotoxicity of Cu and Zn were evaluated. The results provided a reference for the rational application of clay materials to remediate heavy metal contaminated soils. From the sorption experiment, the maximum adsorbed Cu2+ by attapulgite and montmorillonite was 1501 and 3741 mg/kg, respectively. After polluted red soil was amended with attapulgite or montmorillonite and cultured at 30 and 60 days, soil pH increased significantly compared to the control. An 8% increase in the amount of montmorillonite in soil and 30 days incubation decreased acid exchangeable Cu by 24.7% compared to the control red soil. Acid exchangeable Cu decreased with increasing amounts of attapulgite and montmorillonite, with best remediation effect reached at a dose of 8%. Results also showed that the Cu poisoning effect on earthworms was reduced with the addition of attapulgite and montmorillonite. Montmorillonite showed the best effect, with the addition of a 2% dose the mortality of earthworms decreased from 60% to zero compared to the control. Our results indicated that the bioavailability of Cu in soils was reduced more effectively with the application of montmorillonite than attapulgite.

Contents and properties of heavy elements in iron-manganese cutans and the corresponding matrix soils of three subtropical Chinese soils (Fragiudalf, Ferrudalf, and Hapludult) were investigated to discern the effect of soil-forming factors on the enrichment of heavy elements in the iron-manganese cutans with respect to the matrices. Results showed that the contents of clay, organic matter (OM), bases, and heavy metal elements were higher in the cutans than in the matrices. Cutans in the Fragiudalf had a neutral pH and higher content of OM and bases than those in the other soils. The cutans in the Ferrudalf were acidic, with increased contents of Fe and Mn oxides. The cutans in the Hapludult were more acidic and clayey than the cutans in the Fragiudalf and the Ferrudalf. Moreover, the contents of free Fe oxides and ratios of extractable noncrystalline Fe oxide/free Fe oxide (Feo/Fed) in the cutans of the Hapludult were higher than those in the other cutans. Compared with the corresponding matrices, the contents of heavy-metal elements in cutans of Hapludult increased more than those in other iron-manganese cutans. The varimax orthogonal factor rotation of factor analysis was chosen to make the statistical test a good fit to show the elemental distribution between the cutans and their corresponding matrices. The results revealed that Mn oxides played a leading role in the enrichment of most heavy metals for the cutans in the Fragiudalf. In the Ferrudalf, Fe oxides strengthen the migration process of the metals to the cutans. For the cutans in the Hapludult, the influence of Mn oxides on the enrichment of heavy metals decreased, and the impact of clay and Fe oxides increased with respect to the cutans in other soils. The factors that affected the heavy metals were the least for the cutans of the Ferrudalf compared with those in the cutans of the Fragiudalf and the Hapludult. The transport of heavy metals from the matrix soils to iron-manganese cutans in the three soils was mainly influenced by the different soil-forming environments and soil compositions. Statistical analysis indicated that the soil-forming factors that affected the enrichment of heavy metals in the cutans were more prominent in the Ferrudalf than in the Fragiudalf and the Hapludult.

The Linkuo terrace, situated to the west of the Taipei Basin in NW Taiwan, has thick red soils that have been little studied. This paper aims to interpret the development of these soils through chemical and micromorphological investigations, and relate the soils to their palaeo-environments. The soil samples were air dried, crushed and passed through a 2 mm sieve, and then subjected to conventional soil chemical and physical analyses, together with clay mineralogical and morphological characterization. Pedons I and II were clay with low base saturation (BS), cation-exchange capacity (CEC), and exchangeable cations. The pH of pedons I and II ranged from 3.80 to 5.26. The low magnetic susceptibility of these soils indicates that no magnetite (Fe3O4) or maghemite (γ-Fe2O3) are present. X-ray diffraction patterns of the magnetic clay fraction showed lepidocrocite, goethite and hematite, the amounts of which may relate to water fluctuation in the soil environments. Illite, kaolinite and quartz are major clay minerals in the red soil clay fractions. The micromorphology of all horizons showed a great accumulation of Fe-oxides. The upper horizon showed darkened isotropic Fe-oxide materials, and lower horizon showed a black to reddish dense plasma with soil matrix. The groundmass of the oxic horizon is generally characterized by a homogeneous distribution of the different coarse and fine constituents. The thick (4 m depth) and homogeneous red soils of the Linkuo terrace were developed from fine sediments after the gradual subsidence of the Taipei Basin. Alarge amount of gravel was flushed from the Xindian River before the Taipei Basin subsided. The Linkuo red soils can be classified as mesic, Typic Kandiudox. From the chemical compositions of clay fractions and the red soil features, these red soils can be considered as lateritic red earths or red earths that do not reach the criteria for laterite.

The dynamics of Cs and Sr sorption by soils, especially in the subtropics and tropics, as influenced by soil components are not fully understood. The rates and capacities of Cs and Sr sorption by selected subtropical and tropical soils in Taiwan were investigated to facilitate our understanding of the transformation and dynamics of Cs and Sr in soils developed under highly weathering intensity. The Langmuir isotherms and kinetic rates of Cs and Sr sorption on the Ap1 and Bt1 horizons of the Long-Tan (Lt) and the A and Bt1 horizons of the Kuan-Shan (Kt), Mao-Lin (Tml) and Chi-Lo (Cl) soils were selected for this study. Air-dried soil (2mm) samples were reacted with of 7.5 x 10(-5) to 1.88 x 10(-3)M of CsCl (pH 4.0) or 1.14 x 10(-4) to 2.85 x 10(-3)M of SrCl(2) (pH 4.0) solutions at 25 degrees C. The sorption maximum capacity (q(m)) of Cs by the Ap1 and Bt1 horizons of the Lt soil (62.24 and 70.70 mmol Cs kg(-1) soil) were significantly (p0.05) higher than those by the A and Bt1 horizons of the Kt and Cl soils (26.46 and 27.49 mmol Cs kg(-1) soil in Kt soil and 34.83 and 29.96 mmol Cs kg(-1) soil in Cl soil, respectively), however, the sorption maximum capacity values of the Lt and Tml soils did not show significant differences. The amounts of pyrophosphate extractable Fe (Fe(p)) were correlated significantly with the Cs and Sr sorption capacities (for Cs sorption, r(2)=0.97, p1.0 x 10(-4); for Sr sorption, r(2)=0.82, p2.0 x 10(-3)). The partition coefficient of radiocesium sorbed on soil showed the following order: Cl soilKt soilTml soilLt soil. It was due to clay minerals. The second-order kinetic model was applied to the Cs and Sr sorption data. The rate constant of Cs or Sr sorption on the four soils was substantiality increased with increasing temperature. This is attributable to the availability of more energy for bond breaking and bond formation brought about by the higher temperatures. The rate constant of Cs sorption at 308 K was 1.39-2.09 times higher than that at 278K in the four soils. The activation energy of Cs and Sr sorbed by the four soils ranged from 7.2 to 16.7 kJ mol(-1) and from 15.2 to 22.4 kJ mol(-1), respectively. Therefore, the limiting step of the Cs(+) or Sr(2+) sorption on the soils was diffusion-controlled processes. The reactive components, which are significantly correlated with the Langmuir sorption maxima of Cs and Sr by these soils, substantially influenced their kinetic rates of Cs and Sr sorption. The data indicate that among components of the subtropical and tropical soils studied, short-range ordered sesquioxides especially Al- and Fe-oxides complexed with organics play important roles in influencing their capacity and dynamics of Cs and Sr sorption.

The relationship between organic matter contents and soil aggregates of particle size ranging from >4, 2–4, 1–2, 0.5–1 to 0.25–0.5 mm in three eroded (slightly, moderately and severely) Ultisols in central China was investigated using dry-sieving and wet-sieving methods, as well as chemical analyses. In different eroded Ultisols, the size distribution percentages of >4 and 2–4 mm macroaggregates obtained by dry-sieving method were all higher than that by wet-sieving method by separately between 12.3 and 45.7%, 3.0 and 24.7% , but the percentages of 0.25–0.5, 0.5–1 and 1–2 mm macroaggregates showed opposite trend. Microaggregates ( 0.25 mm water-stable aggregates (WSA) and average of mean weight diameter (MWD) decreased from slightly eroded soil to severely eroded soil by 28.0% and 0.14 mm, respectively. The organic matter (OM) content of macroaggregate fractions from slightly and moderately eroded Ultisols rose with increasing in particle size fractions from 0.25–0.5 to >4 mm, but that of macroaggregates fractions from severely eroded Ultisols decreased with increasing in particle sizes. The percentages of >0.25 mm WSA correlated well with the OM contents of eroded Ultisols ( r 2 = 0.6573, n = 19). The OM contents of macroaggregates in eroded soils showed high correlation with that of the bulk soil, and the correlation coefficients decreased in the order of slightly > moderately > severely eroded Ultisols.

Injection of saline solutions can enhance the effect of electro-osmotic pressure. This study considers the consolidation and stability of foundation soil for building construction. Kaolinite (KGa-1) and Taipei silty clay were subjected to zeta potential (ZP), electro-osmosis and laboratory vane shear tests with injection of saline solutions. The ZP values decrease (i.e., less negative potential) with increased cationic valences and concentrations. The increased electro-osmotic permeability from injecting CaCl2 (1 N, EOC5) solution is about 172% higher than that without injection due to an increase of drained water from the cathode and the resulting increase of undrained shear strength. Average undrained shear strength for injecting CaCl2 solution over a period of 7 days is about 4 to 5 times greater than that without injection during electro-osmosis tests. Electro-osmosis tests with injection of saline solutions reveal that the increase of undrained soil shear strength (ΔSu) is proportional to the ZP tests.

Forest fires can disturb the evolution of plant communities and influence both soil organic matter (SOM) and soil physicochemical properties. The historic vegetation changes and the influences on soil properties and OM induced by fires are still not well known for central Taiwan. This study investig

The goal of this study was to investigate the characteristics of iron–manganese cutans and to observe information of their pedogenic processes and certain environmental condition changes in the pedogenic process of subtropical Chinese soils. The characteristics of micromorphology of iron–manganese cutans and element distribution with linear microprofiles (i.e., the vertical microprofile from cutan to matrix soil) in Fragiudalfs (FRA), Ferrudalfs (FER) and Hapludult (HAP). Cutans and matrix soils were studied by chemical analyses, optical microscopy (OM) and energy dispersive spectroscopy (EDS). The micromorphological structure of iron–manganese cutan was a thin black film with alternating color of red and brown, and about 1 mm thick of soil particles. The structures of cutan materials were denser, and the boundaries between cutans and matrix soils were clear. EDS analyses of cutans and the plasma phase of the matrix soils, showed that the contents of MnO 2 , Fe 2 O 3 and CaO in cutans were higher than those in matrix soils, while the content of SiO 2 showed the opposite trend. From the outer to inner, cutans in Fragiudalfs and Ferrudalfs can be easily fractionated into manganese-rich, iron–manganese-rich and iron-rich regions. But there were only iron–manganese-rich and iron-rich regions in cutans in Hapludult, there was no clear manganese-rich region of belt structure in it. These differences were attributed to soil-forming factors. The formation of belt structure in iron–manganese cutans would probably undergo several great change in landscapes and soil environments. It indicated that the growth of cutans was in environments of alternating wetting and drying. They gradually grew in the oxidation–reduction process on the dry or wet condition of whole bulk soils.

We have investigated the clay mineralogy of 3 pedons along a toposequence of perhumid forest soils facing a subalpine lake in northeastern Taiwan to gain insight into the individual factors that affect weathering rates. Toposequence of the transect was investigated from summit to footslope and at the lakeshore. The natural drainage of soils varies from well drained to poorly drained. The major minerals in the well-drained soils at the summit site were illite and kaolinite, whereas illite and vermiculite were dominant in the poorly drained soil at the footslope. In the poorly drained soils of the lakeshore site, almost permanent saturation inhibited weathering of minerals, and vermiculite, illite and illite–vermiculite were the dominant minerals. The magnitude of the mean layer charge of vermiculite was estimated by use of the alkylammonium exchange method (nC = 12). The mean layer charge of vermiculite ranged between 0.63 and 0.78 cmolc/(O10(OH)2). The distribution of clay layer charge varied with location and soil depth. Vermiculite in the surface horizons displayed lower mean layer charges, indicating stronger weathering intensity in the surface horizons. Acidification by organic acids may result in the reduction of layer charge in vermiculite, particularly at the surface. Differences in layer charge with landscape position may be due to differences in weathering processes. The drainage condition caused by topography is a critical factor in the transformation and redistribution of clay minerals. High precipitation, combined with surface runoff, enhance the variation of the type and mean layer charge of clay minerals along this toposequence.

The subtropical alpine forest ecosystem is vulnerable to acid rain deposited through the forest soils. Soil pH buffer capacity is a common index and plays an important role in buffering acidification. In this study, the pH buffer capacity of forest soils along an elevation sequence in central Taiwan was investigated and evaluated through conventional titration and mathematical calculation of proton affinity methods. High pH, cation exchangeable capacity, base saturation were observed in the low elevation site. Three phases of pH buffer capacity (pHBC) were proposed and well described the titration curve through linear fitting. The pHBCs showed no significant differences from the titration curves of various pedons and horizons. However, mathematical calculation of proton affinity potentials showed the highest correlation at the lower elevation site with soil pH (r = 0.90⁎⁎), cation exchangeable capacity (CEC) (r = 0.91⁎⁎), base saturation (r = 0.97⁎⁎), and X-ray non-crystalline sesquioxides (r = 0.68⁎⁎). It is important to evaluate the alpine forest soil pH buffer capacity by combining its proton consumption potentials.

This study aimed to investigate the physical and chemical properties of rhizosphere and bulk soils of three tea plants cultivated at two different elevations for direct comparison each cultivar planted in different soil environments. The three tea plants are Camellia sinensis CV Chin-Shin Dahpan (CSD), Camellia sinensis CV Chin-Shin Oolong (CSO), and Camellia sinensis CV TTES, No. 12 (TTE). The two study sites were located at Yangmei (YM), Taiwan Tea Experimental Station, Taoyuan County of northern Taiwan, and the Luku (LK), Fonghuang Tea Experimental Station, National Taiwan University, Nantou County of central Taiwan. Rhizosphere and bulk soils from A horizon (0–15 cm) below tea plants were sampled. The fresh tissues of tea plants were also collected for comparison. The physical and chemical properties, bioavailability of metals (i.e., Al, Fe, Mn, Cu and Zn), and fractionations of metal speciation of the rhizosphere and bulk soils were studied. The low molecular weight organic acids (LMWOAs) of the soil and fresh tissue samples were determined by gas chromatograph (GC), while the organic functional groups were determined by cross polarization magic angle (CPMAS) nuclear magnetic resonance (13C NMR) analysis. In general, the mean value of cation-exchange capacity (CEC), organic carbon, and C/N ratio of the rhizosphere soils were lower than those of the bulk soils. Bioavailability of Al shows that Al concentrations in YM soils were higher than that of LK soils. However, bioavailability of Fe in YM and LK soils showed no significant differences. Bioavailability of both Al and Fe in rhizosphere soils was higher than those in bulk soils. According to sequential multi-step extractions, the amounts of Al and Fe fractions showed the following order: residual (step 8) > metal-organic complexes-bound (steps 3 and 5) > crystalline Fe-oxide-bound (step 7). The LMWOAs concentrations in rhizosphere soils were higher than those in bulk soils. The LMWOAs exudates in soils showed the following order: oxalic > succinic > fumaric > malonic acids. Regression analysis of bioavailability of Al and Fe in YM and LK sites showed linear relationships with total LMWOAs concentrations (R2 > 0.974 to Al; R2 > 0.791 to Fe). The microbial resynthesis of alkyl-C, hemicellulose of acetal-C and aromatic-C rhizosphere soils was higher than that of bulk soils. On the other hand, the lignin of aromatic-C, phenolic-C and carboxyl-C contents of bulk soils were higher than those of rhizosphere soils. The cellulose component of O-alkyl-C contents in fresh roots at the YM site was higher than that at the LK site. From regression analysis, total LMWOAs concentrations showed high correlation with bioavailability of Al and Fe.

All bee‐eaters (Family Meropidae) are cavity nesters, excavating terrestrial burrows in sites ranging from flat ground, to small mounds of soil, steep earthen banks seen in road clearings, eroded cliff faces, and river gorges. However, very little is known concerning the environmental factors that influence nest site selection in bee‐eaters. We addressed abiotic and biotic issues associated with colony site choice in blue‐tailed bee‐eaters (Merops philippinus) nesting on Kinmen Island, off mainland China, from 2000 to 2002. About 89% of the colonies were located on slopes with soils of sandy loam and the other 11% on sandy clay loam. No colony was found on clay loam, which covered 20% of the island. The sandy loam and sandy clay loam had lower soil pressure, density and moisture, which, presumably, were easier for bee‐eaters to excavate and provided better drainage and ventilation for nest cavities. Bee‐eaters avoided placing nest cavities in areas with dense vegetation and abandoned colony sites when the...

Pollution of agricultural lands by heavy metals has become more serious with increasing pollutants emitted from electroplate plants of northern Taiwan. This study aimed to assess the retardation factor (R) and the dispersion coefficient (D) using one-dimensional convective–dispersive model by comparing the breakthrough curve (BTC) and least squares methods. An acrylic column, with an inner diameter of 9 cm and a length of 15 cm, was uniformly packed with soil for metal leaching experiments. An unpolluted surface (0–20 cm) of the Taoyuan red soil was collected for this study. In miscible displacement experiments, a mixture of 4 mg L− 1 CdCl2, 20 mg L− 1 NiCl2, and 60 mg L− 1 ZnCl2 was leached from top of the column and the effluent was collected in increments with the aid of a fraction collector. The retardation factor (R) calculated from the least squares method was close to the R value observed from breakthrough curves. The R value showed the trend: Cd>Zn>Ni, indicating the rate of metals transport in red soils: Ni>Zn>Cd. Their reactivity was assessed within the framework of the hard–soft acid–base principle (HSAB). From sequential extractions, most of the Cd remained in exchangeable fractions, and Ni and Zn were found to exist in residual Fe- or Mn-oxides, and organic matter fractions.

In Taiwan, the average sulfate and nitrate deposited by acid rain as precipitation amount to 50 kg SO42− and 15–50 kg NO3− ha−1 year−1, respectively. The reactions of sulfate and nitrate with forest soils were not fully understood. Thus, we selected two forest pedons, namely the Dystrochrept and Hapludult of the Lien-Hua-Chi watershed in central Taiwan, to study their sorption and desorption of sulfate. Soil samples were leached with simulated acid rain solutions of various acidity and sulfate concentrations to assess their retention of cations and sulfate. The amounts of sorbed-SO42− of two pedons extracted with NaH2PO4 (0.016 M) solutions in the range 0.14–1.09 mmol kg−1 soil were higher than that of native water-soluble sulfate (i.e., extracted with H2O), in the range 0.15–0.41 mmol kg−1 soil. The amounts of native sorbed-SO42− of two pedons correlated significantly with the exchangeable Al (r = 0.91). The sorption of sulfate did not fit well the Langmuir equation. The native sulfate contents of all tested pedons were near the maximum sulfate sorption capacity. The sulfate sorption capacity and the amount of released Al correlated well with increasing acidity of simulated acid rain added. Introducing solutions of various acidity and sulfate concentrations into the leaching solution flowing through the soil column resulted in sharp increases in amount of sulfate and aluminum released in percolates after several pore volumes were replaced. High clay and sesquioxide contents at soil depths of 30–50 cm (Bw horizon) and 50–80 cm (BC) of pedon 1 retained part of the sulfate added serving as the sulfate sink. Released K, Mg and Ca showed two periods of higher leaching pattern, having a trend similar to that the electrical conductivity (EC) pattern. After leaching of simulated acid rain through the soil column, the soil exchangeable cations were decreased. The tested soils possess an acid-buffering capacity in pedon 1. Pedon 1 is composed of high clay and sesquioxide contents and possesses greater buffer capacity than that of pedon 2.

Summary Soils are the central organizer of the terrestrial ecosystem. Their colloidal and particulate constituents, be they minerals, organic matter, and microorganisms, are not separate entities; rather, they are constantly interacting with each other. Interactions of these components control biogeochemical reactions, namely, the formation of short-range-ordered metal oxides, catalysis of humic substance formation, enzymatic stability and activity, mineral transformation, aggregate turnover, biogeochemical cycling of C, N, P, and S, and the fate and transformation of organic and inorganic pollutants. Furthermore, the impacts of mineral–organic matter–microorganism interactions and associated biogeochemical reactions and processes on biodiversity, species composition, and sustainability of the terrestrial ecosystem deserve close attention for years to come. This paper integrates the frontiers of knowledge on this subject matter, which is essential to uncovering the dynamics and mechanisms of terrestrial ecosystem processes and to developing innovative management strategies to sustain ecosystem health on the global scale.

Cesium is an emission element from nuclear energy generation easily transferred to food chain. More evidence has been found that Brassica crops take up pollutants from soils. The objective of this study was to investigate the correlation between soil bioavailability of cesium and low-molecular-weigh

We used the buried-bag in situ incubation technique to quantify net rates of N mineralization and nitrification in a forest ecosystem in northeastern Taiwan. At the near-ridge top site, NH 4 + concentrations in the organic horizon (O horizon; 2–0 cm) ranged from 14.5 to 58.5 mg N kg −1 and NO 3 − varied from 2.5 to 7.8 mg N kg −1 . In the lower part of the watershed, NH 4 + concentrations in the O horizon were between 10.3 and 28.8 mg N kg −1 and NO 3 − varied from 2.6 to 20.1 mg N kg −1 . There were slightly lower soil NH 4 + concentrations during the summer than other seasons. Using the buried-bag technique, we estimated net mineralization rates to vary between 0.02 and 0.28 mg N kg −1 soil per day and net nitrification rates between 0.02 and 0.26 mg N kg −1 soil per day at the upper site. Rates of both processes were lower during the summer and were positively related to soil moisture content. We speculate that differences in soil texture are likely related to the differing pattern in concentrations of inorganic soil N between the two sites. N mineralization was positively correlated with nitrification rate ( r =0.820, P

We used the buried bag incubation method to study temporal patterns of net N mineralization and net nitrification in soils at Ta-Ta-Chia forest in central Taiwan. The site included a grassland zone, (dominant vegetation consists of Yushania niitakayamensis and Miscanthus transmorrisonensis Hayata) and a forest zone (Tsuga chinensis var. formosana and Yushania niitakamensis). In the grassland, soil concentration NH4 + in the organic horizon (0.1–0.2 m) ranged from 1.0 to 12.4 mg N kg−1 soil and that of NO3 − varied from 0.2 to 2.1 mg N kg−1 soil. In the forest zone, NH4 + concentration was between 2.8 and 25.0 mg N kg−1 soil and NO3 −varied from 0.2 to 1.3 mg N kg−1 soil. There were lower soil NH4 + concentrations during the summer than other seasons. Net N mineralization was higher during the summer while net nitrification rates did not show a distinct seasonal pattern. In the grassland, net N mineralization and net nitrification rates were between −0.1 and 0.24 and from −0.04 to 0.04 mg N kg−1 soil day−1, respectively. In the forest zone, net N mineralization rates were between −0.03 and 0.45 mg N kg−1 soil day−1 and net nitrification rates were between −0.01 and 0.03 mg N kg−1 soil day−1. These differences likely result from differing vegetation communities (C3 versus C4 plant type) and soil characteristics.

The objectives of this study were to investigate selected physical and chemical properties, and availability of metals in rhizosphere and bulk soils of Tsuga and Yushania of alpine forests. The pH of rhizosphere soils was lower than bulk soils. Mean CEC, organic carbon, carbon/nitrogen (C/N) ratio, and clay contents in rhizosphere soils were greater than in bulk soils Concentrations of exchangeable potassium (K) and magnesium (Mg) were also greater in rhizosphere soils than in bulk soils. The availability of aluminum (Al), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in rhizospheres was influenced by the ionic species and concentrations, which depend on the pH change and chemical compositions of root exudates.

Many factors affect adsorption phenomena in solid–liquid systems. One of the most important factors is the sorbent/water (S/W) ratio in the system. However, the effect of varying S/W ratios on the adsorption is still unclear. In this study, batch experiments were examined to observe the adsorption of four contaminants (copper, cadmium, Butachlor, and Deltamethrin) in six soils with texture ranging from silty clay to loamy sand and with different S/W ratios. Dimensional analysis was used to assess the relationship between adsorption phenomena and S/W ratio. We have assumed that the total amount of sorbate sorbed in soil is a function of the equilibrium concentration, the volume of sorbate solution, and the sorbent amount in the system. A power function (Freundlich-like) model was obtained from the dimensional analysis. It can describe precisely the adsorption phenomena of different sorbents and sorbates in the moisture regime of paddy soils. Therefore, proper adsorption parameters can be obtained by this power function model regardless of the solids effect, which can then be utilized to describe the fate of solute in soil using solute transport models.

Many methods have been proposed for measuring exchangeable cations and cation exchange capacity (CEC) in soils. Most of these methods are multi-step operations, which are time-consuming and, therefore, not applicable for routine soil tests. Speed and simplicity of operations are necessary. The objective of this study was to develop a one-step soil column leaching method to determine CEC using 0.01 M SrCl2 solution [CEC(SrCl2)]. Measured CEC(SrCl2) values correlate to the conventional CEC [1 M NH4-acetate (NH4OAc, pH 7)] in slightly acidic, alkaline, and neutral pH soils. CEC(SrCl2) was also compared to the effective CEC (ECEC by 0.01 M SrCl2 and pH 7, 1 M NH4OAc solutions (soil column leaching method) in red soils. Here, ECEC(SrCl2) and ECEC(NH4OAc) are the sum of exchangeable K+, Na+, Ca2+, Mg2+, and Al3+ in soil column leachates. The correlation between CEC(SrCl2) versus ECEC(SrCl2), and CEC(SrCl2) versus ECEC(NH4OAc) of seven red soils showed a linear relationship (r2 values being 0.99 and 0.98, respec...

The iron-rich calcareous soil (Typic Rhodustalf) from the Penghu island group represents a volcanic area. The black soils (Typic Haplustert, Vertic Endoaquoll, Typic Hapludolls) are typical of eastern Taiwan. Four A horizons and a pedon from the iron-rich calcareous soil and four pedons from the black soils were studied to analyze soil properties and clay compositions. The objective was to compare the properties of smectites developed from different parent materials. The materials were studied by using conventional X-ray diffraction (XRD) of K- and Mg-saturated clays and involved the alkylam-monium (C = 12) method and the Greene-Kelly test. The mean-layer charge of smectites (0.48–0.52 cmol(c)/O10(OH)2) in the iron-rich calcareous soil was found to be higher than the black soils (0.43–0.48 cmol(c)/O10(OH)2). A smectite of higher charge developed from the basalts. This smectite is enriched in Fe and Mg, and lacks Si, thereby forming beidellite and/or nontronite. In contrast, under high precipitation, elevated temperature, base saturation (e.g., Na, K, Ca, Mg), and about equal wet and dry cycles per year in the black soil environments, smectites developed from the complicated geologic site of eastern Taiwan. These smectites transformed to smectite-kaolinite mixed-layer clay and thus, resulted in lower-charge smectites. The K fixation capacity of the iron-rich calcareous soil was higher than the black soils.

P-sorption isotherms were determined for calcium carbonate (AR grade) and four soils, which contain various amounts of iron oxides and calcium carbonate. The results could be put into the Langmuir equation. The sorption maximum of calcite was 26 mg P kg−1. This result was used to calculate the surface coverage of calcite by sorbed P. The model indicated that only 1 4 to 1 8 of the unit cell surface was able to adsorb phosphate. High-gradient magnetic separation (HGMS) was used to fractionate soil clays into magnetic and tailing fractions. The amount of P-sorption was correlated with the free iron oxide (Fed) contents of the magnetic clay fractions (r = 0.82), but was not significantly correlated with the noncrystalline iron oxide (Feo) contents. Synthetic hematite and the Lin-Kuo alluvial reddish soils were treated at various pH values with 155 mg P g−1. The results of 57Fe Mossbauer spectra of the hematite treated at pH 3 possessed a FeP doublet, which indicated an FeP compound. It was not observed in the Lin-Kuo soils treated with phosphate. Phosphate treated soils were extracted sequentially with 1M NH4Cl (easily soluble P), NaOH/NaCl/citrate-bicarbonate (CB, FeAl-bound P), dithionite-citrate-bicarbonate (DCB, occluded P), and HCl (Ca-bound P). The P-treated soils were incubated with two cycles of wetting to field capacity water ( 1 3 bar) and drying for a 10 day period. The treatments resulted in higher portions FeAl-bound P in Lin-Kou and Tung-Wei soils. Calcareous Nan-Wan and Hou-Liao soils contained more Ca-bound P. Only a small proportion of the added-P was easily soluble and occluded-bound.

Sewage sludge (SS) applied to sloping fields at rates that exceed annual forest nutrient requirements can be a source of phosphorus (P) in runoff. This study investigates the effects of different slopes (18, 27, 36, and 45%) on P in runoff from plots amended with SS (120 Mg ha). Lateritic soil (pH 5.2) was exposed to five simulated rainfalls (90 mm h) on outdoor plots. When sludge was broadcast and mixed with surface soils, the concentrations and loss in runoff of total P in the mixed sample (MTP), total P in the settled sample (STP), total particulate P (TPP), total suspended P (TSP), and total dissolved P (TDP) were highest at 1 or 18 d after application. Initially, pollution risks to surface waters generally increased to different degrees with steeper slopes, and then diminished gradually with dwindling differences between the slopes. The runoff losses coefficient of MTP increased in the order 36 > 45 > 27 > 18%. The initial event (1 and 18 d) accounted for 67.0 to 83.6% of total runoff P losses. Particulate fraction were dominant carriers for P losses, while with the lower slopes there was higher content of P per unit particulate fraction in runoff. Phosphorus losses were greatly affected by the interaction of sludge-soil-runoff and the modification of soil properties induced by sludge amendment. It is recommended to choose lower slopes (

Surface fire could induce heat transferring into the soil, creating a carbonized environment, which may alter the chemical compositions of soil organic matters (SOM). In the study, a surface soil was carbonized at up to 600 °C with limited air to simulate soils experiencing a surface fire, and Cr(VI) removal on the carbonized soils was investigated. NMR and FTIR analyses demonstrated a remarkable change of SOM structures at 300-400 °C. TGA-MS spectra indicated that (e.g. C(2)H(4), CH(3)OH and C(3)H(8)) were the major components in the evolved gases from the pyrolyzed soil. A maximum amount of Cr(VI) removal (ca. 4 mg g(-1) soil) occurred for the 200 °C-carbonized soils, attributed mainly to a significant increase of Cr(VI) reduction by 0.1 M KCl extractable organic carbon (EOC) with abundant carboxylic groups. Nonetheless, the formation of aromatic C upon carbonization of the soil at400 °C may be responsible for Cr(VI) reduction.

This study investigates the species of As and Pb (beudantite) residues present in the seriously contaminated agricultural rice soils of the Guandu Plain. Two pedons in the Guandu Plain agricultural soils, each pedon separated into five horizons (each of 20 cm) were collected for this study. Soil samples were packed into a column for leaching with simulated acid rains. Soil pH ranged from 5.1 to 7.1 with high base saturation. Soils can be classified as clay loam, mixed, thermic, Typic or Umbric Albaqualfs. The XRD analysis indicated the beudantite particles are present in clay fractions, showing high concentrations of As and Pb. This is because of 50-100 years ago irrigation water was introduced from Huang Gang Creek of hot springs containing high concentrations of As and Pb. Only low concentrations of As and Pb can be leached out with simulated acid rains (i.e., pHs 2 and 4), even through 40 pore volumes of leaching experiments. The sequential extraction experiments resulted in the high portions of As and Pb remaining in the amorphous, Fe and Al oxyhydroxides and residual fractions. Thus, the remediation of As and Pb in this agricultural rice paddy soils merits further study.

The carbon isotope analysis [delta13C values] of organic samples can be a useful research in ecological studies because delta13C values are indicative of the plant source. This study investigated the changes in plant communities along the grassland-forest boundary in the alpine forest at Ta-Ta-Chia long term ecological research (LTER) site in central Taiwan using carbon isotope data. The aim of this study was focused on the forest fire affected the change of vegetation community. Four pedons from grassland dominated by Miscanthus transmorrisonensis (pedons 1 and 2), transition zone by Tsuga and Yushania nittakeyamensis (pedon 3), and forest zone by Tsuga and nittakeyamensis (pedon 4) were examined. Soil organic matter (SOM) delta13C values in the upper soil horizon were similar to delta13C values of the overlaying vegetation types. This indicates that the boundary between these plant communities remained the same in the past decades. The delta13C values of the grassland SOM ranged from -19.4 per thousand to -24.1 per thousand, showing decrease with soil depth. This suggests that C4 plants (transmorrisonensis) have replaced C3 plants of Tsuga and nittakeyamensis. The delta13C values of the Tsuga forest area (pedon 4) range from -27.0 per thousand to -23.5 per thousand and showed only slight change with soil depth, implying that C3 plants have remained the major species in the forest.