Effect of Nitrogen Fertilizers on Zinc Accumulation in Fescue

Abstract

This research evaluated effects of nitrogen fertilizers on availability of zinc (Zn) in soils. Two slit loams of the Hadley series (Typic Udifluvents) were used. Zinc sulfate was mixed with the soils to give Zn at 125, 250, 500, or 1,000 mg/kg and incubated for 14 days. Fertilizers (compost, cow manure, urea) were mixed with the soils to supply N at 200 mg/kg. Fourteen days after the fertilizers were mixed with the Zn‐treated soils, soil samples were taken for analysis of plant‐available Zn by extraction with Morgan's solution or water. After the soil samples were taken, fescue (Festuca arundinacea Schreb.) seeds were placed into pots to assess germination, growth, and Zn accumulation. Higher concentrations of Morgan's extractable Zn were detected in soils treated with compost (201 mg/kg) than with calcium nitrate (179 mg/kg), manure (153 mg/kg), or urea (152 mg/kg). However, with water extraction, higher Zn concentrations were detected in soils treated with calcium nitrate (36 mg/kg) with the lowest concentrations being extracted from soils treated with urea (8 mg/kg). Extraction of Zn by Morgan's solution or water increased as the soil‐Zn levels increased. Fescue germinated and grew at all of the soil‐Zn levels. The highest concentration of Zn occurred in plants grown in soils amended with calcium nitrate or urea, and the lowest concentration was in plants grown in soils amended with compost or manure. Fescue grown in soils amended with urea had the largest dry mass, and plants grown with compost or manure had the smallest. Zinc concentration and accumulation for fescue shoots increased as the soil‐Zn levels increased. These results suggest that accumulation of Zn in fescue can be enhanced by selection of nitrogen‐containing fertilizers that affect the solubility of Zn in soils.     

Phytoextraction of Zinc by Indian Mustard and Tall Fescue

Abstract

This experiment evaluated the capacity of two species, Indian mustard (Brassica juncea Czern.) and tall fescue (Festuca arundinacea Schreb.) to extract zinc (Zn) from soils. Also, this experiment focused on using nitrogen (N) fertilizers to increase the phytoextraction of Zn. Two soils of the Hadley series (Typic Udifluvents) were studied. A treatment array of Zn concentrations in soils was supplied as zinc sulfate. Nitrogen was supplied at 200 mg N/kg of soil as calcium nitrate, urea, or compost. Two successive plantings of Indian mustard in the same media were grown until flowering and harvested. Fescue was grown from seeding to a height of 15 cm, harvested, grown again in the same media to a height of 15 cm, and harvested again. After the second harvests of Indian mustard and fescue, soil samples were taken for analysis of extracts with water and with Morgan's solution. Indian mustard was grown with Zn additions ranging from 0 to 100 mg/kg soil. The shoot mass of Indian mustard in both harvests increased to a soil‐Zn level of 25 mg/kg and then decreased. Although growth decreased as the soil‐Zn levels increased beyond 25 mg/kg, Zn concentration and total accumulation increased linearly as the soil‐Zn levels increased. Zinc concentration and accumulation in Indian mustard were highest in soils amended with urea and were lowest in soils with no fertilizer. Fescue was grown with Zn additions ranging from 0 to 1000 mg/kg soil. The shoot mass of fescue increased to a soil‐Zn level of 125 mg/kg (harvest 1) or 250 mg/kg (harvest 2) and then decreased as the soil‐Zn levels increased. Concentration and accumulation of Zn in fescue increased linearly as the soil‐Zn levels increased. Zinc concentration and accumulation were highest in fescue grown in soils amended with urea and lowest in soils with no fertilizer. The highest accumulation of Zn in fescue (3800 mg/pot) occurred at 1000 mg Zn/kg soil. Highest concentrations of soil Zn were extracted with Morgan's solution or water from soils amended with urea, regardless of the species grown in the soils. Lowest concentrations of Zn were extracted from soils with no fertilizer added, regardless of extract or species. In general, if fertilizers (calcium nitrate, urea, or compost) were added to the soils, the pH decreased. Fescue was easy to grow, tolerated much higher soil‐Zn levels than Indian mustard in this research, and could be a species useful for phytoextraction of Zn.     

Effect of humic acid on growth and crop nutrient status of wheat on two different soils

The effect of plant-derived humic acid (PDHA) and coal-derived humic acid (CDHA) on wheat growth was tested on two alkaline calcareous soils in pots. Humic acid derived from plant and coal materials was applied at the rate 0 (control), 50 and 100 kg/ha to wheat in pots carrying two soils viz. clayey loam soil and sandy loam soil separately. Data was collected on plant growth parameters such as spike weight, grain and straw weight, and plant nutrients (macronutrients and micronutrients). Results showed that spike weight increased by 19%, 15%, and 26%, and 11% with application of PDHA at the rate of 50 and 100 mg/kg in clayey loam and sandy loam soil, respectively. Grain yield show an increase of 21% and 11% over control with application of PDHA and CDHA at the rate of 50 mg/kg on both soils, respectively, and 10% and 22% with application of PDHA and CDHA at the rate of 100 mg/kg on both soils.     

Polycyclic aromatic hydrocarbons (PAHs) in rural soils of Dongjiang River Basin: occurrence,source apportionment,and potential human health risk

Purpose

A comprehensive study was conducted to investigate the presence of polycyclic aromatic hydrocarbons (PAHs) in Dongjiang River Basin (DRB) soils and to evaluate their sources and ecological and health risk. In addition, factors affecting the distribution and fate of PAHs in the soils such as emission density, soil organic matter, degradation, etc. were studied.

Materials and methods

Surface soil (0–20 cm) samples from 30 sampling sites in the rural areas of DRB were collected and analyzed for 17 polycyclic aromatic hydrocarbons (16 EPA priority PAHs and perylene). Positive matrix factorization model was used to investigate the source apportionment of these PAHs, and an incremental lifetime cancer risk (ILCR) was used to estimate the integrated lifetime risks of exposure to soil-borne PAHs through direct ingestion, dermal contact, and inhalation collectively.

Results and discussion

The total PAH concentrations in the rural soils in DRB range from 23.5 to 231 μg/kg with a mean concentration of 116 μg/kg. The predominant PAHs in the rural soils were naphthalene, fluoranthene, phenanthrene, and benzo(b)fluoranthene. Cluster analysis was performed to classify the soil PAHs into three clusters, which could be indicative of the soil PAHs with different origins and different properties. Source apportionment results showed that coal, biomass, oil, commercial creosotes, and vehicle contributed 24 %, 24 %, 17 %, 17 %, and 18 % of the total soil PAH burden, respectively. The ILCR results indicated that exposure to these soil-borne PAHs through direct ingestion, dermal contact, and inhalation collectively produces some risk.

Conclusions

PAHs in the soils of the DRB will produce long-term influences on rivers and oceans via soil erosion and river transport. Therefore, PAHs in rural soils of DRB have potential impacts on the water supply and human health risk.     

Arsenic contents and physicochemical properties of agricultural soils from the Red River Delta,Vietnam

Abstract

To evaluate arsenic (As) levels in agricultural soils of the Red River Delta in northern Vietnam, surface (0–5 cm) and subsurface (20–25 cm) soil samples were collected from 18 paddy and six upland fields on both sides of the river. As a reference, forest soils were also sampled at two sites of the upper river basin. The total As contents of approximately 80% of the surface paddy and upland soils exceeded the maximum allowable limit for Vietnamese agricultural soils (12 mg kg^?1). Arsenic contents higher than 35 mg kg^?1 were found in soils from the Hungyen and Hanam provinces, where high As levels in the groundwater have also been reported. Sequential fractionation of As in these soils indicated that the amounts of As in the phosphate-extractable and residual fractions were higher than those in the forest soils. Elevated total As contents were also detected in the surface soil of a paddy field near a fertilizer factory in Hanoi (site P10). The amount of HCl-extractable As in the surface soil at P10 corresponded to 84% of the total As, while the proportion never exceeded 40% at other locations. In the surface soil at P10, most of the As was part of the phosphate-extractable fraction. Significant correlations between the total As contents of the upland soils and their non-crystalline Fe oxide contents (r = 0.652, P ≤ 0.05) and between As levels of paddy soils and their crystalline Fe oxide contents (r = 0.544, P ≤ 0.01) were observed. Overall, the present study indicated that although serious As pollution was not found in the studied area, there were some point pollutions caused by industrial activities, in addition to some non-point pollutions resulting from high As concentrations in the groundwater. In addition, Fe oxides in the soils are important factors affecting the As contents of agricultural soils in the Red River Delta.     

Distribution of Polycyclic Aromatic Hydrocarbons in Soils of an Arid Urban Ecosystem

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants produced by incomplete combustion sources such as home heating, biomass burning, and vehicle emissions. PAH concentrations in soils are influenced by source inputs and environmental factors that control loss processes and soil retention. Many studies have found higher concentrations of these pollutants in soils within cities of temperate climates that have a centralized urban core. Less is known about the factors regulating PAH abundance in warm, arid urban ecosystems with low population densities but high traffic volumes. The relative importance of sources such as motor vehicle traffic load and aridland ecosystem characteristics, including temperature, silt, and soil organic matter (SOM) were explored as factors regulating PAH concentrations in soils near highways across the metropolitan area of Phoenix, AZ (USA). Highway traffic is high compared with other cities, with an average of 155,000 vehicles/day. Soils contained low but variable amounts of SOM (median 2.8?±?1.8% standard deviation). Across the city, median PAH concentrations in soil were low relative to other cities, 523?±?1,886 ??g/kg, ranging from 67 to 10,117 ??g/kg. Diagnostic ratio analyses confirmed that the source of PAHs is predominantly fuel combustion (i.e., vehicle emissions) rather than petrogenic, biogenic, or other combustion sources (coal, wood burning). However, in a multiple regression analysis including traffic characteristics and soil properties, SOM content was the variable most strongly related to PAH concentrations. Our research suggests that dryland soil characteristics play an important role in the retention of PAH compounds in soils of arid cities.     

Effects of Cement Dust on Soil Chemical Properties in the Calabar Environment,Southeastern Nigeria

Abstract

Some chemical properties of soils around the Calabar Cement Company operational area were studied from three profile pits sited at the crest, upper slope, and middle slope topographic positions. The results showed that the soil pH was moderately to slightly acid (mean 5.8), organic‐matter content was moderate (mean 2.54%), total N (N) content was low (mean 0.04%), and available phosphorus (P) was high (mean 87.43 mg/kg). Exchangeable calcium (Ca) content was moderate to high (3.02 to 7.44 cmol/kg) in the surface soil; most samples had low magnesium (Mg) content (mean 0.25 cmol/kg), medium concentration of exchangeable potassium (K) (mean 0.10 cmol/kg), and medium to high exchangeable sodium (Na) (0.27 to 1.38 cmol/kg). The exchange acidity was low (mean 1.58 cmol/kg), and effective cation exchange capacity (ECEC) had low to medium (2.50 to 15.17 cmol/kg) values. The percentage of base saturation was high with most soils having values greater than 50% (mean 70.8%). The moderate to high content of Ca and the favorable pH in the soils of the study area are uncommon in the coastal plain soils of southern Nigeria; these, therefore, were readily attributable to the continuous deposition of cement dusts on the surface and leaching into deeper horizons.     

矿粮复合区煤累积对土壤团粒结构的影响

为理解煤对土壤结构的影响,以土壤煤累积现象普遍的焦作矿粮复合区为研究区,选取3种不同程度的煤累积土壤(低累积、中累积和高累积)为研究对象,不含煤的土壤为对照,通过测定0—40 cm土层深度范围的水稳性团聚体组成,并采用分形维数(D)、平均重量直径(MWD)、几何平均直径(GMD)和大团聚体破坏率(PAD)作为团粒结构的评价指标,探讨煤累积对土壤团聚体组成与稳定性的影响。结果表明:煤在土壤中累积可以促进水稳性微团聚体向大团聚体转化,降低团聚体的分形维数,提高团聚体稳定性。深层(20—40 cm)土壤水稳性大团聚体含量的增幅高于表层(0—20 cm)土壤。土壤团聚体稳定性随着煤累积程度的增高表现出先增加后降低的趋势。土壤团聚体的稳定性主要取决于>2 mm粒级水稳性团聚体的含量。总体上,煤在土壤中的累积改善了土壤的团粒结构性状。此外,根据本研究结果,研究区长期运煤、堆煤、洗煤和矿井水灌排等活动导致的"黑土"现象并不能视作煤污染。     

Tillage Effects on Particulate and Mineral‐Associated Organic Matter in Two Tropical Brazilian Soils

Abstract

Two Ferralsols (350 and 600 g kg^?1 clay) from the Brazilian Cerrado Region were evaluated for long‐term effects (5 and 8 years) of no tillage on carbon (C) stocks in particulate (>53 µm) and mineral‐associated (<53 µm) soil organic matter (SOM) fractions. Carbon stocks in particulate SOM increased under no tillage compared with conventional tillage, and the rate was higher in the clayey soil (0.62 Mg C ha^?1 yr^?1) than in the sandy clay loam soil (0.31 Mg C ha^?1 yr^?1). In contrast, the mineral‐associated SOM in the top soil layer (0–20 cm) was not affected by tillage system. Sequestration of atmospheric C in tropical no‐tillage soils seems to be due to accumulation of C in labile SOM fractions, with highest rates in clayey soils probably due to physical protection.     

Effect of Coal Combustion By-products on Phosphorus Runoff from a Coastal Plain Soil

Coal combustion by-products can lower soil phosphorus (P) solubility, but few studies have assessed their effect on runoff P. A soil with elevated P content was amended with fluidized bed combustion ash, flue gas desulfurization gypsum, and anthracite refuse ash at rates of 0–40 g kg^?1 soil, and runoff from small plots was monitored over 3 years. In the first year, by-products lowered dissolved P in runoff by up to 47% below the untreated control; however, effects did not persist into the remaining years of the study. Total P losses were not significantly affected by coal combustion by-products, likely because of elevated particulate P losses. Water-extractable P was up to 40% less in treated soils than in untreated soils across the 3 years. Results demonstrate that although coal combustion by-products readily lower P solubility in soils, their impact on P losses in runoff can be undermined by erosional processes.     

Identifying critical limit in soil and plant for determining response of groundnut (Arachis hypogea) to boron application in Madurai soils of Tamil Nadu,India

To establish critical limit in soils and plant, soil samples were collected from twenty; 12, 5 and 3 soil locations of low, medium and high boron (B) status from Madurai district of Tamil Nadu, India for pot culture experiment. Based on the results of pot culture experiment, the critical limit was determined to be 42.7 mg kg^?1 for groundnut plants and 0.39 mg kg^?1 in Madurai soils. Groundnut plants were highly responded to B application in soils below the critical limit whereas soils with B greater than 0.51 mg kg^?1 did not respond. For the confirmation of pot culture results, a field experiment was conducted with different B treatments comprised of soil and foliar applications and results revealed that the pod yield of groundnut increased with increasing levels of B and the soil application of 20 kg ha^?1 as borax has showed significantly higher pod yield in the district.     

淮南煤矿复垦区土壤重金属含量分布及潜在生态风险评价

以淮南矿区煤矸石充填复垦地为研究对象,对该复垦区不同土地利用方式(小麦地、桃林、蔬菜大棚、油菜地)下土壤Cd,Zn,As,Ni,Cu,Pb,Cr,Mn共8种重金属含量进行了分析和评价。结果表明,相对土壤背景值,该复垦区土壤中Zn,Cr,Mn,As污染较为严重相对未复垦区,复垦区土壤中的Zn,Cd,As分别是未复垦区的4.38,2.57和2.20倍,具有明显的累积现象。不同土地利用方式土壤重金属含量差异较大,小麦地和桃林地的Zn,Cd,As含量远大于油菜地和蔬菜大棚,Cr含量则表现为桃林地、蔬菜地远大于小麦地和油菜地,Ni,Cu,Mn,Pb在4种土地利用类型下的差异不显著。土地利用方式、施肥以及受采矿活动的影响程度不同是导致土壤重金属含量差异的主要原因。淮南煤矿复垦土壤中各重金属的生态风险顺序为:Cd>Zn>As>Ni>Cu>Pb>Cr>Mn。Cd的潜在生态风险值最大(89.71),属于强生态风险,其余元素均为轻微风险。不同土地利用方式的风险顺序为:小麦地>桃林地>蔬菜大棚>油菜地。     

Tillage Effects on Soil Quality Indicators and Nematode Abundance in Loessial Soil under Long‐Term No‐Till Production

Abstract: Soil quality indicators and nematode abundance were characterized in a loessial soil under long‐term conservation tillage to evaluate the effects of no‐till, double‐disk, chisel, and moldboard plow treatments. Indicators included soil electrical conductivity (EC), soil texture, soil organic matter (SOM), and total particulate organic matter (tPOM). Nematode abundance was positively correlated with EC, silt content, and total POM and negatively correlated with clay content. Clay content was the main source of variation among soil quality indicators and was negatively correlated with nematode abundance and most indicators. The gain in SOM in the no‐till system amounted to 10887 kg over the 24 years or 454 kg ha^?1 year^?1, about half of this difference (45%) resulting from soil erosion in plowed soils. The balance of gain in SOM with no till (249 kg ha^?1 year^?1) was due to SOM sequestration with no till. No‐till management reduced soil erosion, increased SOM, and enhanced soil physical characteristics.     

Distribution and Mobility of Trace Elements in Soils and Vegetation Around the Mining and Smelting Areas of Tharsis, Ríotinto and Huelva, Iberian Pyrite Belt, SW Spain

Trace elements may present an environmental hazard in the vicinity of mining and smelting activities. However, the factors controlling their distribution and transfer within the soil and vegetation systems are not always well defined. Total concentrations of up to 15,195 mg . kg ^–1 As, 6,690 mg . kg^–1 Cu, 24,820 mg . kg^–1 Pb and 9,810 mg . kg^–1 Zn in soils, and 62 mg . kg^–1 As, 1,765 mg . kg^–1 Cu, 280 mg . kg^–1 Pb and 3,460 mg . kg ^–1 Zn in vegetation were measured. However, unusually for smelters and mines of a similar size, the elevated trace element concentrations in soils were found to be restricted to the immediate vicinity of the mines and smelters (maximum 2–3 km). Parent material, prevailing wind direction, and soil physical and chemical characteristics were found to correlate poorly with the restricted trace element distributions in soils. Hypotheses are given for this unusual distribution: (1) the contaminated soils were removed by erosion or (2) mines and smelters released large heavy particles that could not have been transported long distances. Analyses of the accumulation of trace elements in vegetation (median ratios: As 0.06, Cu 0.19, Pb 0.54 and Zn 1.07) and the percentage of total trace elements being DTPA extractable in soils (median percentages: As 0.06%, Cu 15%, Pb 7% and Zn 4%) indicated higher relative trace element mobility in soils with low total concentrations than in soils with elevated concentrations.     

Impact of an Urban Environment on Trace Element Concentrations in Domestically Produced Lettuce (<Emphasis Type="Italic">Lactuca sativa L.</Emphasis>)

Urban horticulture is gaining more and more attention in the context of sustainable food supply. Yet, cities are exposed to (former) industrial activities and traffic, responsible for emission of contaminants. Trace elements were monitored in soils located in the urban environment of Ghent (Belgium) and 84 samples of Lactuca satica L. lettuce grown on it. The effects of cultivation in soil versus trays, neighbouring traffic and washing of the lettuce before consumption were studied. The 0–30 cm top layer of soils appeared heterogenic in composition and enriched in Co, Cd, Ni and Pb within 10 m from the nearest road. Yet, no similar elevated concentrations could be found in the crops, except for As. Besides uptake from the roots, the presence of trace elements in the plants is also caused by the atmospheric deposition of airborne particulate matter on the leaf surface. Correlation analysis and principal component analysis (PCA) revealed that this latter transport pathway might particularly be the case for Pt, Pd and Rh. Concentrations of Cd did not exceed the 0.2 mg kg^?1 (fresh weight) threshold for Cd in leafy vegetables set by the European Commission. Measurements to reduce the health risks include the washing of lettuce, which effectively reduced the number of samples trespassing the maximum Pb level of 0.3 mg kg^?1 (fresh weight). Also, cultivation in trays resulted in a lower As content in the plants. Taking into account a vigilance on crop selection, cultivation substrate and proper washing before consumption are considered essential steps for safe domestic horticulture in urban environments.     

Distribution of As and Zn in Soils Affected by the Spill of a Pyrite Mine and Effectiveness of the Remediation Measures

The concentrations of As and Zn in 100 georeferenced soils uniformly distributed throughout the area affected by the spill from the Aznalcóllar mine (April 1998) were analysed at three depths (0–10, 10–30, and 30–50 cm) and on four dates (autumn–winter 1998, 1999, 2001, and 2004). For an estimate of the geochemical background, 30 unaffected soils near the edge of the spill were also analysed at the same depths. The soils were contaminated before the spill and, the accident seriously increased the concentration of As and Zn in the first 10 cm of almost all the affected soils. After the enormous efforts of cleaning up the tailings, around 45% of the soils had a concentration higher than 100 mg As kg^?1 dry soil, and some 35% had a concentration higher than 1,000 mg Zn kg^?1 dry soil. Both As and Zn penetrated between 10 and 30 cm in 25% and 45% of the soils, respectively, but reached 30 cm in only 12% of the soils. The remediation actions, especially the tilling and homogenisation of the uppermost 25 cm of the all soils, caused the As and Zn concentrations to decline in the soils, but this change was not very effective from the standpoint of pollution. Thus, 6 years after the spill, the uppermost 10 cm of 30% of the soils continued to have an As concentration higher than 100 mg As kg^?1, while the Zn concentration diminished considerably on the surface due to its greater mobility, accumulating between 10 and 30 cm in depth, where 20% of the soils continued to register more than 1,000 mg Zn kg^?1 dry soil.     

Effect of soil type on the time-course of changes in sugar beet (Beta vulgaris L.) productivity in Tokachi District,Hokkaido, Japan

Abstract

To clarify the effect of soil type on changes in sugar beet (Beta vulgaris L.) productivity since 1980 in Tokachi District (Hokkaido, Japan), we analyzed yield data from 121 settlements from 1980 to 2002 using maps of parent materials and surface organic matter contents in a geographical information system. The soil types were Brown Lowland soils, Andosols with an alluvial subsoil, Wet Andosols and Andosols. The sugar beet yields were highest in the Andosols and moderate in Andosols with an alluvial subsoil. Yields in Brown Lowland soils in the 1980s were similar to those in Andosols, but decreased below the yields in the Andosols by the 1990s. The yields in Wet Andosols were the lowest in the 1980s, but have been similar to those in Andosols with an alluvial subsoil since 1990. Thus, productivity appears to have varied over time in Brown Lowland soils and Wet Andosols. The correlation coefficients between yields and cumulative daily mean temperature from late April to mid-July since 1990 were highest in the Andosols (r = 0.67), lowest in the Brown Lowland soils (r = 0.50) and intermediate in the other soil types (r = 0.54–0.60). However, the magnitude of the correlation between the yield and the cumulative precipitation since 1990 was lowest in the Andosols (r = –0.22), highest in the Brown Lowland soils (r = –0.58) and intermediate in the other soil types (r = –0.44 to –0.45). These results suggest that the present soil water environment in the Andosols is superior to that in the other soil types.     

Evaluation of Coal Fly Ash-Based Synthetic Aggregates as a Soil Ameliorant for the Low Productive Acidic Red Soil

A potential new way of producing coal fly ash-based granular synthetic aggregates (CSA) using waste coal fly ash (CFA), paper waste, lime, and gypsum and their utilization as a soil ameliorant to improve crop production in low productive acidic red soil in Okinawa, Japan were studied. The red soil was amended with CSA at three different mixing ratios (i.e., CSA/soil—1:1, 1:5, and 1:10) for the cultivation of Brassica rapa var. Pervidis commonly known as Komatsuna, and the physico-chemical parameters of CSA–soil mixtures and plant growth were analyzed. Incorporation of CSA to the red soil improved the physical and chemical properties of the soil such as water holding capacity, hydraulic conductivity, bulk density, pH, exchangeable cation concentration, cation exchange capacity, particle size distribution, soil pH, electrical conductivity, and carbon content. CSA amendment at ratios of 1:1, 1:5, and 1:10 decreased bulk density by 29.39%, 14.28% and 11.11%, respectively, compared to the original red soil. The acidic pH of the red soil (5.12) was increased to 7.13 and 6.37 by CSA/soil ratios of 1:5 and 1:10, respectively. CSA amendment in soil at 1:5 ratio increased water holding capacity, saturated hydraulic conductivity, electrical conductivity, cation exchange capacity, carbon, potassium (K), magnesium (Mg), and calcium (Ca) content by 0.06 kg kg^?1, ten times, 15.95 mS m^?1, 1.76 cmol_c kg^?1, 6.07 g kg^?1, 0.42 g kg^?1, 0.24 g kg^?1, and 3.38 g kg^?1, respectively, in comparison to the original red soil. Heavy metal contents of the CSA–soil mixtures were below the maximum pollutant concentrations suggested by the US Environmental Protection Agency. Moreover, Na, K, Mg, Ca, copper (Cu), and zinc (Zn) contents in the CSA–soil mixtures increased in comparison with the original red soil. CSA amendment in soil at the ratio of 1:5 and 1:10 resulted in an increase in plant height and plant fresh weight by three and 12 times, respectively, and there was increase in N, K, Mg, Ca, Cu, and Zn contents of the shoots. The results suggest that utilization of eccentric CSA as soil amendment agent can be regarded as an effective waste management practice.     

Distribution of anthropogenic lead estimated by Pb isotopic composition in the upper layers of soil from a mixed forest at Dinghushan, southern China

Purpose

The heavy metal lead (Pb) is toxic to living organisms. Forest soils are important sinks for heavy metals generated by human activities. The forest at Dinghushan of southern China has experienced long-term exposure to atmospheric pollutants from the Pearl River Delta (PRD). The objectives of this research were (a) to determine the vertical and temporal distribution of Pb in the forest soil at Dinghushan, (b) to determine whether dilute acid extraction could be used to identify anthropogenic sources of Pb in forest soil, and (c) to determine the main anthropogenic contributors to soil Pb.

Materials and methods

Lead concentrations and isotopes were measured in two sets of forest soil samples. One set consisted of archived samples from 0 to 20 cm depth collected annually from 1997 to 2010. The other set was collected throughout three profiles sampled at 5-cm intervals to the bedrock (85 cm depth) in 2011. The soil samples were air-dried, ground, and passed through a 100-mesh polyethylene sieve. Lead in the samples was digested with concentrated acid (HNO₃?+?HClO₄, 4:1?v/v) or extracted with dilute acid (1 M HCl with a soil/solution ratio of 1:10) and was measured with an inductively coupled plasma mass spectrometer.

Results and discussion

Concentrations of Pb obtained both by total digestion and dilute acid extraction decreased with soil depth in the profile samples and increased over time in the archived ones. Soils at 0–20 cm depth had Pb concentrations of more than twice of the local soil background value. In all soil samples, the ^206/207Pb ratios was lower and the ^206/204Pb, ^207/204Pb, and ^208/204Pb ratios were higher with the dilute acid extraction than with the strong-acid digestion, indicating that dilute acid extraction could be used to distinguish between anthropogenic and geogenic Pb. Comparison of the Pb isotope ratios in the samples with those in the main pollutants from the PRD indicated that coal combustion and industrial emission were the main contributors to the forest soil Pb at Dinghushan.

Conclusions

The forest soil (0–20 cm depth) at Dinghushan was contaminated by Pb. Dilute acid extraction could be used to identify anthropogenic Pb sources. From 1997 to 2010, the main contributors of anthropogenic Pb to the forest soil at Dinghushan were coal combustion and industrial emission. Measures that control Pb emission from coal combustion and industrial activity, changes in coal consumption, and re-adjustments of industry development in the PRD should reduce Pb contamination of forest soil.     

Burn Effects on Soil Aggregate Stability and Water Repellency of Two Soil Types from East and North Tunisia

To date, evidence of the potential effects of burning practices on soil properties in Tunisia is limited. In order to address this issue, we carried out laboratory investigations of the effects of burning on soil aggregate stability (AS) and water repellency (WR) of a clayey and a sandy loam Fluvisol soils. The treatments included low (100°C, LT), medium (300°C, MT) and high (600°C, HT), heating temperatures. Unburned (0°C, UB) soil samples were used as a control. Two breakdown mechanisms, fast wetting (FW) and mechanical breakdown (MB), were used for the measurement of AS. The latter is expressed by calculating the mean weight diameter (MWD). The water drop penetration time (WDPT) was used to evaluate the soil WR. The results showed that the unburned clayey and sandy loam soils are poorly aggregated. The HT and MT treatments significantly (p < 0.05) increased MWD of both soils, compared to UB samples, following the FW stability test. A lesser increase of MWD was observed with the MB test. The LT treatment did not significantly (p < 0.05) affect the soils AS. For the unburned clayey soil, the FW and MB tests gave significantly (p < 0.05) different MWDs . In contrast, the unburned sandy loam soil had similar MWDs under both tests. As for water repellency, the sandy loam soil was initially wettable and the clayey soil slightly water repellent. Burning treatments did not affect the sandy loam soil behavior but caused a decrease of clayey soil WR.