Purpose

The aim of this study was to quantify the effect of enhanced agronomic practices on cadmium (Cd) accumulation in the high-biomass energy plant Napier grass (Pennisetum purpureum Schumach).

Materials and methods

Potted-plant experiments were performed to investigate the effects of ammonium fertilizers and chelating agents, alone or in combination, on the growth, accumulation of Cd, and phytoextraction efficiency of P. purpureum on Cd-contaminated soil. The fertilizers included ammonium nitrate, ammonium sulfate, and ammonium chloride. The chelating agents included ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA).

Results and discussion

The addition of ammonium fertilizers and chelating agents generally stimulated growth of P. purpureum, and the shoots accounted for 90.1–94.1% of the total biomass. The concentrations of Cd in different parts of P. purpureum plants were in the order root > leaf > stem. Ammonium chloride alone showed effectiveness in increasing root and shoot Cd concentrations compared to other amendments alone. Both EDTA alone and NTA alone significantly decreased root Cd concentration and increased shoot Cd concentration, while EDTA alone was more efficient on shoot and total Cd accumulation than that by NTA alone. The total accumulation of Cd in P. purpureum ranged from 1.10 to 2.05 mg per plant with 47.3–73.5% of Cd accumulation concentrated in shoots. The results indicate that P. purpureum can remove more Cd through phytoextraction than that by other hyperaccumulators.

Conclusions

Ammonium chloride led to the highest total Cd accumulation. Ammonium chloride applied alone or in combination with either EDTA or NTA resulted in the most effective agronomic approaches for P. purpureum phytoextraction of soil Cd.

Purpose

The subjects of this study were to investigate the remediating potential of the co-cultivation of Pleurotus eryngii and Coprinus comatus on soil that is co-contaminated with heavy metal (cadmium (Cd)) and organic pollutant (endosulfan), and the effects of the co-cultivated mushrooms on soil biochemical indicators, such as laccase enzyme activity and bacterial counts.

Materials and methods

A pot experiment was conducted to investigate the combined bioremediation effects on co-contaminated soil. After the mature fruiting bodies were harvested from each pot, the biomass of mushrooms was recorded. In addition, bacterial counts and laccase enzyme activity in soil were determined. The content of Cd in mushrooms and soil was detected by the flame atomic absorption spectrometry (FAAS), and the variations of Cd fractions in soil were determined following the modified BCR sequential extraction procedure. Besides, the residual endosulfan in soil was detected by gas chromatography-mass spectrometry (GC-MS).

Results and discussion

The results indicated that co-cultivation of P. eryngii and C. comatus exerted the best remediation effect on the co-contaminated soil. The biomass of mushroom in the co-cultivated group (T group) was 1.57–13.20 and 19.75–56.64% higher than the group individually cultivated with P. eryngii (P group) or C. comatus (C group), respectively. The concentrations of Cd in the fruiting bodies of mushrooms were 1.83–3.06, 1.04–2.28, and 0.67–2.60 mg/kg in T, P, and C groups, respectively. Besides, the removal rates of endosulfan in all treatments exceeded 87%. The best bioremediation effect in T group might be caused by the mutual promotion of these two kinds of mushrooms.

Conclusions

The biomass of mushroom, laccase activity, bacterial counts, and Cd content in mushrooms were significantly enhanced, and the dissipation effect of endosulfan was slightly higher in the co-cultivated group than in the individually cultivated groups. In this study, the effect of co-cultivated macro fungi P. eryngii and C. comatus on the remediation of Cd and endosulfan co-contaminated soil was firstly reported, and the results are important for a better understanding of the co-remediation for co-contaminated soil.

Purpose

Biochar can be used to reduce the bioavailability and leachability of heavy metals, as well as organic pollutants in soils through adsorption and other physicochemical reactions. The objective of the study was to determine the response of microbial communities to biochar amendment and its influence on heavy metal mobility and PCBs (PCB52, 44, 101, 149, 118, 153, 138, 180, 170, and 194) concentration in application of biochar as soil amendment.

Materials and methods

A pot (macrocosm) incubation experiment was carried out with different biochar amendment (0, 3, and 6 % w/w) for 112 days. The CaCl₂-extractable concentration of metals, microbial activities, and bacterial community were evaluated during the incubation period.

Results and discussion

The concentrations of 0.01 M CaCl₂-extractable metals decreased (p?>?0.05) by 12.7 and 20.5 % for Cu, 5.0 and 15.6 % for Zn, 0.2 and 0.5 % for Pb, and 1.1 and 8.9 % for Cd, in the presence of 3 and 6 % of biochar, respectively, following 1 day of incubation. Meanwhile, the total PCB concentrations decreased from 1.23 mg kg^?1 at 1 day to 0.24 mg kg^?1 at 112 days after 6 % biochar addition, representing a more than 60 % decrease relative to untreated soil. It was also found out that biochar addition increased the biological activities of catalase, phosphatase, and urease activity as compared with the controls at the same time point. Importantly, the Shannon diversity index of bacteria in control soils was 3.41, whereas it was 3.69 and 3.88 in soils treated with 3 and 6 % biochar soil. In particular, an increase in the number of populations with the putative ability to absorb PCB was noted in the biochar-amended soils.

Conclusions

The application of biochar to contaminated soils decreased the concentrations of heavy metals and PCBs. Application of biochar stimulated Proteobacteria and Bacteroides, which may function to absorb soil PCB and alleviate their toxicity.

Purpose

Fruiting vegetables are generally considered to be safer than other vegetables for planting on cadmium (Cd)-contaminated farms. However, the risk of transferring Cd that has accumulated in the stems and leaves of fruiting vegetables is a major issue encountered with the usage of such non-edible parts. The objective of this study was to resolve the contribution of arbuscular mycorrhizal (AM) fungi to the production of low-Cd fruiting vegetables (focusing on the non-edible parts) on Cd-contaminated fields.

Materials and methods

An 8-week pot experiment was conducted to investigate the acquisition and translocation of Cd by cucumber (Cucumis sativus L.) plants on an unsterilized Cd-contaminated (1.6 mg kg^?1) soil in response to inoculation with the AM fungus, Funneliformis caledonium (Fc) or Glomus versiforme (Gv). Mycorrhizal colonization rates of cucumber roots were assessed. Dry biomass and Cd and phosphorus (P) concentrations in the cucumber shoots and roots were all measured. Soil pH, EC, total Cd, phytoavailable (DTPA-extractable) Cd, available P, and acid phosphatase activity were also tested.

Results and discussion

Both Fc and Gv significantly increased (P?<?0.05) root mycorrhizal colonization rates and P acquisition efficiencies, and thus the total P acquisition and biomass of cucumber plants, whereas only Fc significantly increased (P?<?0.05) soil acid phosphatase activity and the available P concentration. Both Fc and Gv significantly increased (P?<?0.05) root to shoot P translocation factors, inducing significantly higher (P?<?0.05) shoot P concentrations and shoot/root biomass ratios. In contrast, both Fc and Gv significantly decreased (P?<?0.05) root and shoot Cd concentrations, resulting in significantly increased (P?<?0.05) P/Cd concentration ratios, whereas only Gv significantly decreased (P?<?0.05) the root Cd acquisition efficiency and increased (P?<?0.05) the root to shoot Cd translocation factor. Additionally, AM fungi also tended to decrease soil total and phytoavailable Cd concentrations by elevating plant total Cd acquisition and soil pH, respectively.

Conclusions

Inoculation with AM fungi increased the P acquisition and biomass of cucumber plants, but decreased plant Cd concentrations by reducing the root Cd acquisition efficiency, and resulted in a tendency toward decreases in soil phytoavailable and total Cd concentrations via increases in soil pH and total Cd acquisition by cucumber plants, respectively. These results demonstrate the potential application of AM fungi for the production of fruiting vegetables with non-edible parts that contain low Cd levels on Cd-contaminated soils.

Purpose

Chlorpyrifos can be effectively adsorbed by drinking water treatment residuals (WTR), ubiquitous and non-hazardous by-products of potable water production. The major metabolite 3,5,6-trichloro-2-pyridinol (TCP) was found to be much more mobile and toxic than its parent chlorpyrifos. To assess the feasibility of WTR amendment for attenuation of chlorpyrifos and TCP pollution, the sorption/desorption and degradation behavior of chlorpyrifos and TCP in WTR-amended agricultural soils was examined in the present study.

Materials and methods

Two representative agricultural soils were sampled from southern and northern China, respectively. The soils were amended with WTR at the rates of 0, 2, 5, and 10 % (w/w). Batch sorption/desorption test were applied to investigate the sorption/desorption characteristics of chlorpyrifos and TCP in WTR-amended soils. The influence of WTR amendment on chlorpyrifos degradation and TCP formation was evaluated using the incubation test, and its effect on the soil bacterial abundance was further studied through DNA extraction and PCR amplification.

Results and discussion

Results showed that WTR amendment (0–10 %, w/w) significantly enhanced the retention capacity of chlorpyrifos and TCP in both soils examined (P < 0.05). Fractionation analyses further demonstrated that the bioavailability of chlorpyrifos was considerably reduced by WTR amendment, resulting in a decreased chlorpyrifos degradation rate. The WTR amendment also significantly reduced the mobility of TCP formed in chlorpyrifos-contaminated soils (P < 0.001). The chlorpyrifos toxicity to soil bacteria community was largely mitigated following WTR amendment, resulting in increased total bacterial abundance.

Conclusions

Results obtained in the present study indicate a great deal of potential for the beneficial reuse of WTR as soil amendments for chlorpyrifos and TCP pollution control.

Purpose

We examined the effects of vermicompost application as a basal fertilizer on the properties of a sandy loam soil used for growing cucumbers under continuous cropping conditions when compared to inorganic or organic fertilizers.

Materials and methods

A commercial cucumber (Cucumis sativus L.) variety was grown on sandy loam soil under four soil amendment conditions: inorganic compound fertilizer (750 kg/ha,), replacement of 150 kg/ha of inorganic compound fertilizer with 3000 kg/ha of organic fertilizer or vermicompost, and untreated control. Experiments were conducted in a greenhouse for 4 years, and continuous planting resulted in seven cucumber crops. The yield and quality of cucumber fruits, basic physical and chemical properties of soil, soil nutrient characteristics, and the soil fungal community structure were measured and evaluated.

Results and discussion

Continuous cucumber cropping decreased soil pH and increased electrical conductivity. However, application of vermicompost significantly improved several soil characteristics and induced a significant change in the rhizosphere soil fungal community compared to the other treatments. Notably, the vermicompost amendments resulted in an increase in the relative abundance of Ascomycota, Chytridiomycota, Sordariomycetes, Eurotiomycetes, and Saccharomycetes, and a decrease in Glomeromycota, Zygomycota, Dothideomycetes, Agaricomycetes, and Incertae sedis. Compared to the organic fertilizer treatment, vermicompost amendment increased the relative abundance of beneficial fungi and decreased those of pathogenic fungi. Cucumber fruit yield decreased yearly under continuous cropping conditions, but both inorganic and organic fertilizer amendments increased yields. Vermicompost amendment maintained higher fruit yield and quality under continuous cropping conditions.

Conclusions

Continuous cropping decreased cucumber yield in a greenhouse, but basic fertilizer amendment reduced this decline. Moreover, basal fertilizer amendment decreased beneficial and pathogenic fungi, and the use of vermicompost amendment in the basic fertilizer had a positive effect on the health of the soil fungal community.

Purpose

Increasing data have shown that biochar amendment can improve soil fertility and crop production, but there is little knowledge about whether biochar amendment can improve water infiltration in saline soils. We hypothesized that biochar amendment could promote water infiltration in saline soil. The aims of this study were to evaluate the effects of biochar amendment on water infiltration and find the suitable amendment rate and particle size of biochar as a saline soil conditioner.

Materials and methods

We measured water infiltration parameters in a coastal saline soil (silty loam) amended with non-sieved biochar at different rates (0.5, 1, 2, 5, and 10%, w/w) or sieved biochar of different particle sizes (≤?0.25 mm, 0.25–1 mm, and 1–2 mm) at 1 and 10% (w/w).

Results and discussion

Compared with the control, amending non-sieved biochar at 10% significantly decreased water infiltration into the saline soil (P?<?0.05). In contrast, sieved biochar of ≤?0.25 mm significantly improved water infiltration capacity, irrespective of the amendment rate. Sieved biochar of 1–2 mm was less effective to improve soil porosity and when amended at 10%, it even reduced the water infiltration capacity. The Philip model (R²?=?0.983–0.999) had a better goodness-of-fit than the Green-Ampt model (R²?=?0.506–0.923) for simulation of cumulative infiltration.

Conclusions

Amending biochar sieved to a small particle size improved water infiltration capacity of the coastal saline soil compared with non-sieved biochar irrespective of the amendment rate. This study contributes toward improving the hydrological property of coastal saline soil and rationally applying biochar in the field.

Purpose

Irrigation and fertilization can change soil environment, which thereby influence soil microbial metabolic activity (MMA). How to alleviate the adverse effects by taking judicious saline water irrigation and fertilization regimes is mainly concerned in this research.

Materials and methods

Here, we conducted a field orthogonal designed test under different saline water irrigation amount, water salinity, and nitrogen fertilizer application. The metabolic profiles of soil microbial communities were analyzed by using the Biolog method.

Results and discussion

The results demonstrated that irrigation amount and fertilizer application could significantly change MMA while irrigation water salinity had no significant effect on it. Medium irrigation amount (30 mm), least (50 kg ha^?1) or medium (350 kg ha^?1) N fertilizer application, and whatever irrigation water salinity could obtain the optimal MMA. Different utilization rates of carbohydrates, amino acids, carboxylic acids, and polymers by soil microbial communities caused the differences of the effects, and D-galactonic acid γ-lactone, L-arginine, L-asparagine, D-glucosaminic acid, Tween 80, L-threonine, and D-galacturonic acid were the indicator for distinguishing the effects.

Conclusions

The results presented here demonstrated that by regulating irrigation water amount and fertilizer application, the effects of irrigation salinity on MMA could be alleviated, which offered an efficient approach for guiding saline water irrigation.

Purpose

Biochar application has been shown to be effective in improving soil fertility and sequestering soil contaminants. However, the impact of biochar amendments on the environmental fate of pesticides and the bioavailability of pesticides to living organisms in the soil environment is still not fully understood.

Materials and methods

Dissipation of fomesafen and its bioavailability to corn (Zea mays L.) and the earthworm Eisenia fetida in an agricultural soil amended with three different rates of rice hull biochar (0.5, 1, and 2 % (w/w)) under laboratory conditions was investigated.

Results and discussion

Biochar amendment significantly increased the DT₅₀ of fomesafen from 34 days in unamended soil to 160 days in 2 % biochar-amended soil. Furthermore, biochar amendment decreased fomesafen concentration in soil pore water resulting in lower plant uptake of the pesticide. In this case, total plant residue and soil pore water concentrations of fomesafen in 2 % biochar-amended soil decreased to 0.29 % and 0.28–45 % of that in the control, respectively. Similar results were obtained for bioavailability of fomesafen in earthworms, as the earthworm residue and soil pore water concentration of fomesafen in 2 % biochar-amended soil declined to 0.38–45 and 0.47–0.50 % compared to the level of the control, respectively.

Conclusions

As biochar could markedly reduce the concentration of fomesafen in soil pore water and subsequently reduce plant and earthworm uptake of fomesafen from contaminated soil, biochar amendment could be considered an appropriate option for immobilizing fomesafen in soils, protecting nontarget organisms from fomesafen contamination.

Purpose

This study aimed at investigating the rhizosphere effects of Populus euramericana Dorskamp on the mobility of Zn, Pb and Cd in contaminated technosols from a former smelting site.

Materials and methods

A rhizobox experiment was conducted with poplars, where the plant stem cuttings were grown in contaminated technosols for 2 months under glasshouse conditions. After plant growth, rhizosphere and bulk soil pore water (SPW) were sampled together. SPW properties such as pH, dissolved organic carbon (DOC) and total dissolved concentrations of Zn, Pb and Cd were determined. The concentrations of Zn, Pb and Cd in plant organs were also determined.

Results and discussion

Rhizosphere SPW pH increased for all studied soils by 0.3 to 0.6 units compared to bulk soils. A significant increase was also observed for DOC concentrations regardless of the soil type or total metal concentrations, which might be attributed to the plant root activity. For all studied soils, the rhizosphere SPW metal concentrations decreased significantly after plant growth compared to bulk soils which might be attributed to the increase in pH and effects of root exudates. Zn, Pb and Cd accumulated in plant organs and the higher metal concentrations were found in plant roots compared to plant shoots.

Conclusions

The restricted transfer of the studied metals to the plant shoots confirms the potential role of this species in the immobilization of these metals. Thus, P. euramericana Dorskamp can be used for phytostabilization of technosols.

Purpose

The study aimed at comparing the effects of different water managements on soil Cd immobilization using palygorskite, which was significant for the selection of reasonable water condition.

Materials and methods

Field experiment was taken to discuss the in situ remediation effects of palygorskite on Cd-polluted paddy soils, under different water managements, using a series of variables, including pH and extractable Cd in soils, plant Cd, enzyme activity, and microorganism number in soils.

Results and discussion

In control group, the pH in continuous flooding was the highest under three water conditions, and compared to conventional irrigation, continuous flooding reduced brown rice Cd by 37.9%, and brown rice Cd in wetting irrigation increased by 31.0%. In palygorskite treated soils, at concentrations of 5, 10, and 15 g kg^?1, brown rice Cd reduced by 16.7, 44.4, and 55.6%; 13.8, 34.5, and 44.8%; and 13.1, 36.8, and 47.3% under continuous flooding, conventional irrigation, and wetting irrigation (p < 0.05), respectively. The enzyme activity and microbial number increased after applying palygorskite to paddy soils.

Conclusions

Continuous flooding was a good candidate as water management for soil Cd stabilization using palygorskite. Rise in soil enzyme activity and microbial number proved that ecological function regained after palygorskite application.

Purpose

In this study, we investigated the effect of biochar (BC) and fungal bacterial co-inoculation (FB) on soil enzymatic activity and immobilization of heavy metals in serpentine soil in Sri Lanka.

Materials and methods

A pot experiment was conducted with tomatoes (Lycopersicon esculentum L.) at 1, 2.5, and 5 % (w/w) BC ratios. Polyphenol oxidase, catalase and dehydrogenase activities were determined by idometric, potassium permanganate oxidisable, and spectrophotometric methods, respectively. Heavy metal concentrations were assessed by 0.01 M CaCl₂ and sequential extraction methods.

Results and discussion

An increase in BC application reduced polyphenol oxidase, dehydrogenase, and catalase activity. The application of FB increased soil dehydrogenase activity, with the maximum activity found in 1 % BC700?+?FB treatment. Moreover, the CaCl₂ extractable metals (Ni, Mn, and Cr) in 5 % BC700 amended soil decreased by 92, 94, and 100 %, respectively, compared to the control. Sequential extraction showed that the exchangeable concentrations of Ni, Mn, and Cr decreased by 55, 70, and 80 % in 5 % BC700, respectively.

Conclusions

Results suggest that the addition of BC to serpentine soil immobilizes heavy metals and decreases soil enzymatic activities. The addition of FB to serpentine soil improves plant growth by mitigating heavy metal toxicity and enhancing soil enzymatic activities.

Purpose

With its high economic benefits, navel orange (Citrus sinensis) has been widely planted and fertilizer has been increasingly applied in the subtropical China in the last 30 years. Comprehensive assessments are needed to explore the long-term fertilization impacts on soil chemical and biological properties in the navel orange orchards.

Materials and methods

Through a large number of soil and leaf samples from the young, middle-aged, and mature navel orange orchards, this study examined the impacts of stand age (corresponding to the fertilization year using compound chemical fertilizer) on seasonal variations in major soil properties and leaf nutrients in the subtropical China.

Results and discussion

Soil total nitrogen (N) and mineral N were significantly higher in the middle-aged and mature orchards than in the young orchard. Total phosphorus (P), available P, labile P, slow P, occluded P, weathered mineral P, total exactable P, and residual P generally increased with fertilization years (P?<?0.05), and the increasing percentages for soil P fractions were much higher than those for N variables. The total N and P use efficiencies (plant uptake/soil input) were 20–34 and 10–15 %, respectively. Soil microbial biomass, invertase, urease, and acid phosphatase activities showed significant seasonal variations and decreased with fertilization years. Leaf N concentration significantly decreased with fertilization years, but no difference was found for P.

Conclusions

Soil self-fertilization was impeded, and less fertilizer amount should be applied especially in the older navel orange orchards since N and P accumulations do not increase leaf nutrients but worsen soil biological quality.

Purpose

Copper (Cu) contamination has been increasing in land ecosystems. Biochars (BCs) and arbuscular mycorrhizal fungi (AMF) are known to bind metals, and metallophyte can remove metals from soils. Will BC in combination with AMF contain the Cu uptake by a metallophyte growing in a metal-contaminated soil? The objective of this study was to investigate the effects of BCs on the Cu immobilization and over soil microbial communities in a metal-contaminated soil in the presence of AMF and metallophyte.

Materials and methods

Two BCs were produced from chicken manure (CMB) and oat hull (OHB). A Cu-contaminated sandy soil (338 mg kg^?1) was incubated with CMB and OHB (0, 1, and 5 % w/w) for 2 weeks. Metallophyte Oenothera picensis was grown in pots (500 mL) containing the incubated soils in a controlled greenhouse for 6 months. A number of analyses were conducted after the harvest. These include plant biomass weight, microbial basal respiration, and dehydrogenase activity (DHA), AMF root colonization, spore number, and glomalin production; changes in fungal and bacterial communities, Cu fractions in soil phases, and Cu uptake in plant tissues.

Results and discussion

The BCs increased the soil pH, decreased easily exchangeable fraction of Cu, and increased organic matter and residual fraction of Cu. The BCs provided favorable habitat for microorganisms, thereby increasing basal respiration. The CMB increased DHA by ～62 and ～574 %, respectively, for the low and high doses. Similarly, the OHB increased soil microbial activity by ～68 and ～72 %, respectively, for the low and high doses. AMF root colonization, spore number, and total glomalin-related soil protein (GRSP) production increased by ～3, ～2, and ～3 times, respectively, in soils treated with 1 % OHB. Despite being a metalophyte, O. picensis could not uptake Cu efficiently. Root and shoot Cu concentrations decreased or changed insignificantly in most BC treatments.

Conclusions

The results show that the BCs decreased bioavailable Cu, decreased Cu uptake by O. picensis, improved habitat for microorganisms, and enhanced plant growth in Cu-contaminated soil. This suggests that biochars may be utilized to remediate Cu-contaminated soils.

Purpose

This study aims to investigate the response of a high biomass producer non-hyperaccumulator legume plant species, Dolichos lablab L., to cadmium (Cd) stress for phytoremediation process.

Materials and methods

Three individual experiments were carried out to assess physiological and biochemical parameters to support the use of this plant species as a phytoremediator. The first experiment was carried out in Cd-contaminated soil while the second and third experiments were conducted in sand in which Cd was applied to study biochemical responses. Analysis of mineral nutrition, phytoremediation parameters, antioxidant response, and protein identification by gel-based proteomics were performed.

Results and discussion

Good tolerance to Cd under moderate level of contamination was observed. Mineral nutrition was little affected, and phytoremediation index was satisfactory. Additionally, biochemical responses based on antioxidant enzyme analysis were well responsive in roots, reflecting the capacity of Cd stress attenuation in this organ. A proteomic analysis revealed positive regulation of root proteins involved in carbohydrate, amino acids, nitrogen metabolism, and abiotic/biotic stress response, which together may contribute to create a scenario to overcome Cd-induced stress.

Conclusions

Based on the physiological and biochemical results, we concluded that D. lablab L. is suitable for phytoremediation/phytostabilization purposes.

Purpose

Biochar has been suggested as a soil conditioner to improve soil fertility and crop productivity while simultaneously mitigate global climate change by storing carbon in the soil. This study investigated the effect of pine (Pinus radiata) biochar application on soil water availability, nitrogen (N) and carbon (C) pools and growth of C3 and C4 plants.

Materials and methods

In a glasshouse pot trial, a pine biochar (untreated) and nutrient-enriched pine biochar were applied to a market garden soil with C3 (Spinacia oleracea L.) and C4 (Amaranthus paniculatus L.) plants at rates of 0, 1.0, 2.0, and 4.0 % (w/w). Plant biomass, soil pH, moisture content, water holding capacity (WHC), hot water extractable organic C (HWEOC), and total N (HWETN), total C and N, and their isotope compositions (δ ¹³C and δ ¹⁵N) of soils and plants were measured at the end of the experimentation.

Results and discussion

The soil moisture content increased while plant biomass decreased with increasing untreated biochar application rates. The addition of nutrient-enriched biochar significantly improved plant biomass in comparison to the untreated biochar addition at most application rates. Biochar application also increased the levels of labile organic C and N pools as indicated by HWEOC and HWETN.

Conclusions

The results suggested that the addition of pine biochar significantly improved soil water availability but not plant growth. The application of nutrient-enriched pine biochar demonstrated that the growth of C3 and C4 plants was governed by biochar nutrient availability rather than its water holding capacity under the pot trial condition.

Purpose

The objectives of this study were (1) to investigate the effects of manure compost and earthworms on Cd mobility in Cd-contaminated soil, (2) to test whether the bioturbation of earthworms reduces the immobilization effect of the manure compost when they are combined, and (3) to explore the distribution of Cd in aggregates formed by earthworms with corresponding fractionation analysis.

Materials and methods

A laboratory experiment was conducted to evaluate the effect of either or both application of manure compost and the earthworms Eisenia fetida into cadmium historically contaminated soil on cadmium mobility. Soil characteristics and metal concentrations in earthworms and soil were measured, and soil aggregates in the mesocosms were separated for Cd fraction analysis based on four steps sequential extraction.

Results and discussion

Manure compost reduced mobile Cd based on CaCl₂ extraction and Toxicity Characteristic Leaching Procedure (TCLP) test by 60–95 and 25–30 %, respectively. However, earthworm application alone increased Cd mobility by 9–15 %. Besides, in the presence of manure compost, earthworms further immobilized cadmium to a slight extent. The interaction effect of manure compost and earthworms combined on Cd immobilization suggested that earthworms promoted the formation of large macroaggregates (>2 mm) and the redistribution of Cd concentration in soil aggregates. Additionally, earthworms reduced carbonate fraction of Cd from 42.3–49.6 to 6.3–19.5 % in different aggregates, respectively. And, residual fraction of Cd increased from 33.9–42.2 to 63.9–77.5 % simultaneously. The results may be due to the thorough mixture of phosphates and organic matter with cadmium during bioturbation on account of the available form of phosphorus, nitrogen, and cadmium changing to the more recalcitrant form.

Conclusions

Manure compost addition increased the soil pH, phosphorus, nitrogen, and organic carbon content, and decreased Cd mobility. The application of earthworms and manure compost combined exhibited higher efficiency for cadmium immobilization, which can be used for Cd remediation due to the redistribution of Cd concentration in soil aggregates and the transformation of soluble Cd to the residual precipitate fraction.

Purpose

This study aimed to evaluate the effect of combination of alkyl polyglucoside (APG) and nitrilotriacetic acid (NTA) on improving the efficiency of phytoremediation for pyrene and lead (Pb) co-contaminated soil by Scirpus triqueter.

Materials and methods

Seedlings of S. triqueter with a similar size and biomass (3 g/pot) were grown on 2-month aged soil contaminated with 184.5 mg kg^?1of pyrene and 454.3 mg kg^?1 of Pb at pH?=?8.3. After growth for 10 days, different doses of APG and NTA were added into the soil. After 60 days, the height of plants, Pb concentrations in plants, and pyrene amounts in soil were determined.

Results and discussion

Combined application of NTA and APG with lower dosage (1 + 1 g kg^?1 soil and 1 + 2 g kg^?1 soil) had no notable negative influence on the growth of S. triqueter. Moreover, significant synergy on Pb accumulation in S. triqueter was achieved with APG and NTA combined application. Besides, the dissipation of pyrene from soil after 60-day planting was increased in APG and NTA treatments when compared with the control treatments. Application of APG alone or combined with NTA had greater effect on enhancing dissipation of pyrene from soil than NTA alone.

Conclusions

This study demonstrated that the remediation of Pb and pyrene co-contaminated soil by S. triqueter can be enhanced by combined application of APG and NTA. Long-term evaluation of this strategy is needed in co-contaminated field sites.

Purpose

This study was aimed to investigate the potential of biochar (BC), a waste byproduct of a bioenegy industry, Sri Lanka, as a soil amendment to immobilize and reduce the phytotoxicity of Cr in tannery waste-polluted soil (TWS).

Materials and methods

The TWS and bioenergy waste BC were characterized for physio-chemical parameters. A pot experiment was conducted by adding three BC application rates, 1, 2.5, and 5 % (w/w) to investigate the immobilizing capacity and bioaccumulation of chromium (Cr) in tomato plants (Lycopersicon esculentum L.). Soils and plants were digested via microwave digestion and analyzed for total Cr. Further, sequential extraction was conducted to assess the fractionation of Cr before and after the application of bioenergy waste BC on TWS.

Results and discussion

The total Cr concentration in TWS was 12,285 mg/kg. The biomass of tomato plants grown in the 5 % BC amendment doubled compared to the biomass in BC-unamended soil. Bioaccumulation of Cr in plants grown in 5 % BC-amended TWS showed a decrease by 97 % compared to that of the BC-unamended soil. The CaCl₂ extractability of Cr indicated that the bioavailability of Cr in the 5 % BC amendment has decreased by 68 % compared to the control. Sequentially extracted Cr in the exchangeable fraction decreased by 98 % in the 5 % BC amendment.

Conclusions

Pore diffusion, and adsorption via π-π electron donor-acceptor interactions were the primary mechanisms to be involved in the Cr retention in BC. Results suggested that the addition of BC to TWS reduces the mobility, bioavailability, and phytotoxicity of Cr in tomato plants.

Purpose

Two contrasting soils receiving long-term application of commercial sewage sludge fertilizers in China were investigated to determine the concentrations of selected nutrients, heavy metals (HMs) and polybrominated diphenyl ethers (PBDEs) present to evaluate the impact of sewage sludge fertilizer on soil fertility and environmental risk.

Materials and methods

Soil samples were collected from Tangshan City, Hebei province and Ningbo City, Zhejiang province and divided into two portions, one of which was air-dried and sieved through 2-, 0.25- and 0.149-mm nylon mesh for determination of nutrients and heavy metals. The other portion was frozen at ?20°C, freeze-dried and sieved through 2-mm nylon mesh for PBDE analysis. The concentrations of nutrients, heavy metals and PBDEs were determined in all samples.

Results and discussion

Concentrations of nutrients and heavy metals in soils amended with low rates of sewage sludge fertilizer (SSF) and conventional fertilizer were compared. After long-term excessive amendment with SSF from Ningbo City (SSF-N), the concentrations of soil total N, P, aqua regia-extractable HMs and DTPA extractable HMs were higher than the control, especially in the arable layer. Moreover, the concentration of aqua regia-extractable Zn (457 mg kg^?1) exceeded the recommended China Environmental Quality Standard for soils (GB15618-1995). All 8 target PBDE congeners were found in fertilizer SSF-N and soil with excessive amendment with SSF-N for 12 years, but the concentrations of 8 different PBDEs in SSF-N-amended soil were not significantly different from control soil.

Conclusions

Both economic and environmental benefits can be obtained by careful application of sewage sludge fertilizer to recycle plant nutrients. Repeated and excessive application rates of sewage sludge fertilizer may pose environmental risk, especially in respect of soil heavy metal and PBDE contamination, and high concentrations of phosphorus may also be environmentally detrimental.