Assessing the influence of technosol and biochar amendments combined with <Emphasis Type="Italic">Brassica juncea</Emphasis> L. on the fractionation of Cu,Ni, Pb and Zn in a polluted mine soil

Purpose

Soil metal pollution is a widespread problem around the world and remediation of these soils is difficult. The objective of this study was to investigate the effect of two different strategies on the chemical fractions of metals in a soil of a depleted copper mine: (1) amending with a mixture of a technosol made of wastes and biochar and (2) amending combined with planting vegetation (Brassica juncea).

Materials and methods

A 3-month greenhouse experiment was carried out to evaluate the effects of organic amendments and vegetation on the metal fractionation of Cu, Ni, Pb and Zn in a mine soil of the depleted copper mine at Touro (Spain). We compared the influence of organic amendments alone (technosol?+?biochar) and combined with mustard plants (Brassica juncea L.).

Results and discussion

The results showed that amending with a technosol made of wastes promoted plant growth (from 0.7 to 2.9 g of biomass produced) and reduced the CaCl₂-extractable metal concentration in soil, reduced the mobility factor of Cu from 18.3 to 1.6, Ni from 47.5 to 2.3 and Pb from 17.9 to 2.1, and also reduced the concentration of metals in the mobile soil fractions. It was not possible to grow up Brassica juncea plants in the untreated settling pond soil due to the extremely degraded conditions of that soil. However, the application of the used technosol increased the Pb and Zn pseudototal concentrations in the amended soils.

Conclusions

We conclude that the combination of amending with wastes and planting B. juncea provides little additional benefit for remediating a metal-polluted soil compared with incorporation of wastes alone.

     

Long-term effects of biochar amount on the content and composition of organic matter in soil aggregates under field conditions

Purpose

Soil aggregates play an important role in promoting soil fertility, as well as increasing the sink capacity and stability of soil carbon. In this study, we consider the following research questions:1. Under field conditions, do different dosages of biochar increase the soil aggregation after 3 years of application?2. How does the application of biochar affect the concentration and distribution of soil total organic carbon (TOC) and total nitrogen (TN) in different sizes of aggregates?3. Can the application of biochar alter the composition of organic carbon in soil aggregates?

Materials and methods

Different amounts of biochar (up to 90 t ha^?1) were applied to a calcareous soil in a field experiment in 2009 along with the application of chemical fertilizer annually and the returning of winter wheat and summer maize straws. After 3 years, 0–20-cm soil samples were taken to measure the size distribution of soil water-stable aggregates by wet sieving, the concentrations of TOC and TN in whole aggregates and light or heavy fractions by elemental analysis equipment, and composition of TOC by Fourier transform infrared (FTIR) and pyrolysis-gas chromatography/mass spectrometer (Py–GC/MS).

Results and discussion

(1) The 3 years of biochar application had no significant effects on degree of soil aggregation but reduced the breakage of large soil aggregates (>1000 μm); (2) biochar significantly increased the contents of TOC and TN in soil macro-aggregates (>250 μm), as well as their ratios to total soil amount. Biochar also significantly increased the contents of TOC and TN in light fractions as well as the C/N ratio, which made the soil organic matter more active. The biochar dosage showed a significant positive correlation with organic carbon, total nitrogen, and C/N ratio in light fraction components of aggregates (>250 μm). Biochar mainly affected the organic matter in the heavy fraction components of macro-aggregates; (3) from the Py–GC/MS results, biochar increased the CO₂ content originated from active organic carbon.

Conclusions

Long-term application of biochar improved the stability of soil aggregates, increased the contents of TOC and TN as well as organic carbon and total nitrogen in macro-aggregates, and usually increased the contents of CO₂ originated from active organic carbon in light fractions. The findings were helpful in evaluating the effects of biochar on soil aggregation and organic matter stability.

     

Eco-restoration of a mine technosol according to biochar particle size and dose application: study of soil physico-chemical properties and phytostabilization capacities of <Emphasis Type="Italic">Salix viminalis</Emphasis>

Purpose

Anthropic activities induce severe metal(loid)s contamination of many sites, which is a threat to the environment and to public health. Indeed metal(loid)s cannot be degraded, and thus accumulate in soils. Furthermore, they can contaminate surrounding ecosystems through run-off or wind erosion. This study aims to evaluate the phytostabilization capacity of Salix viminalis to remediate As and Pb highly contaminated mine site, in a biochar-assisted phytoremediation context and to assess biochar particle size and dose application effects.

Materials and methods

To achieve this, mesocosm experiments were conducted using the contaminated technosol and four different size fraction of one biochar as amendment, at two application rates (2 and 5%). Non-rooted cuttings of Salix viminalis were planted in the different mixtures. In order to characterize the mixtures, soil pore waters were sampled at the beginning and at the end of the experiment and analyzed for pH, electrical conductivity, and metal(loid) concentrations. After 46 days of Salix growth, roots, stems, and leaves were harvested and weighed, and As and Pb concentrations and distributions were measured.

Results and discussion

Soil fertility improved (acidity decrease, electrical conductivity increase) following biochar addition, whatever the particle size, and the Pb concentration in soil pore water decreased. Salix viminalis did not grow on the non-amended contaminated soil while the biochar amendment permitted its growth, with a better growth with the finest biochars. The metal(loid)s accumulated preferentially in roots.

Conclusions

Fine biochar particles allowed S. viminalis growth on the contaminated soil, allowing this species to be used for technosol phytostabilization.

     

Short-term effects of organo-mineral biochar and organic fertilisers on nitrogen cycling,plant photosynthesis,and nitrogen use efficiency

Purpose

Organo-mineral biochar fertiliser has the potential to replace conventional biochar and organic fertiliser to improve soil quality and increase plant photosynthesis. This study explored mechanisms involved in nitrogen (N) cycling in both soil and ginger plants (Zingiber officinale: Zingiberaceae) following different treatments including organic fertiliser, commercial bamboo biochar fertiliser, and organo-mineral biochar fertiliser.

Materials and methods

Soil received four treatments including (1) commercial organic fertiliser (5 t ha^?1) as the control, (2) commercial bamboo biochar fertiliser (5 t ha^?1), (3) organo-mineral biochar fertiliser at a low rate (3 t ha^?1), and (4) organo-mineral biochar fertiliser at a high rate (7.5 t ha^?1). C and N fractions of soil and plant, and gas exchange measurements were analysed.

Results and discussion

Initially, organo-mineral biochar fertiliser applied at the low rate increased leaf N. Organo-mineral biochar fertiliser applied at the high rate significantly increased N use efficiency (NUE) of the aboveground biomass compared with other treatments and improved photosynthesis compared with the control. There was N fractionation during plant N uptake and assimilation since the ¹⁵N enrichment between the root, leaf, and stem were significantly different from zero; however, treatments did not affect this N fractionation.

Conclusions

Organo-mineral biochar fertiliser has agronomic advantages over inorganic and raw organic (manure-based) N fertiliser because it allows farmer to put high concentrations of nutrients into soil without restricting N availability, N uptake, and plant photosynthesis. We recommend applying the low rate of organo-mineral biochar fertiliser as a substitute for commercial organic fertiliser.

     

Response of CaCl<Subscript>2</Subscript>-extractable heavy metals,polychlorinated biphenyls,and microbial communities to biochar amendment in naturally contaminated soils

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.

     

Distribution and storage of soil organic carbon in a coastal wetland under the pressure of human activities

Purpose

Soil organic carbon (SOC) stock is one of the most important carbon reservoirs on the earth and plays a vital role in the global climate change. However, research on the carbon sequestration and storage of coastal wetland soil is very scarce. Therefore, a study in the coastal wetland was conducted to investigate the SOC distribution, storage, and variation under the influence of human activities.

Materials and methods

Surface soil samples in different seasons and profile soil samples were collected in the Changyi coastal wetland. SOC content, soil physicochemical properties, and sedimentation rate were determined. Organic carbon storage and burial flux were calculated. On the basis of correlation analysis and comparative study, factors affecting the distribution and storage of SOC were investigated.

Results and discussion

The average SOC content of the surface soil in June and November was 4.65 and 6.13 g kg^?1, respectively. The distribution of surface SOC content was consistent with the distribution of vegetation and was affected by the soil particle size. In plant-covered area, the relationship between SOC content and depth could be expressed by the power function y?=?ax ^b . The contribution of plants to SOC was only significant in the shallow layer. As for the deep layer, the SOC content was higher in the mudflat. The organic carbon storage in the upper 1 m soil was estimated at 1.795 kg m^?2 in average and the total organic carbon storage of Changyi wetland was estimated at 6.373?×?10⁷ kg. The sedimentation rate was very low and the average organic carbon burial flux of the whole wetland was 17.5 g m^?2 a^?1.

Conclusions

Low sedimentation rate, weak downward migration, and high decomposition rate of organic matter caused by poor hydrological condition were the reasons why the SOC storage in Changyi wetland was low. Under intensive human activities, the Changyi wetland was drying and the organic carbon storage was reducing. Strategies were proposed to be taken urgently to restore the wetland for the long-term benefit.

     

Interactive effects of biochar addition and elevated carbon dioxide concentration on soil carbon and nitrogen pools in mine spoil

Purpose

This study aimed to assess the effects of biochar on improving nitrogen (N) pools in mine spoil and examine the effects of elevated CO₂ on soil carbon (C) storage.

Materials and methods

The experiment consisted of three plant species (Austrostipa ramossissima, Dichelachne micrantha, and Lomandra longifolia) planted in the N-poor mine spoil with application of biochar produced at three temperatures (650, 750, and 850 °C) under both ambient (400 μL L^?1) and elevated (700 μL L^?1) CO₂. We assessed mine spoil total C and N concentrations and stable C and N isotope compositions (δ¹³C and δ¹⁵N), as well as hot water extractable organic C (HWEOC) and total N (HWETN) concentrations.

Results and discussion

Soil total N significantly increased following biochar application across all species. Elevated CO₂ induced soil C loss for A. ramossissima and D. micrantha without biochar application and D. micrantha with the application of biochar produced at 750 °C. In contrast, elevated CO₂ exhibited no significant effect on soil total C for A. littoralis, D. micrantha, or L. longifolia under any other biochar treatments.

Conclusions

Biochar application is a promising means to improve N retention and thus, reduce environmentally harmful N fluxes in mine spoil. However, elevated CO₂ exhibited no significant effects on increasing soil total C, which indicated that mine spoil has limited potential to store rising atmospheric CO₂.

     

Humic substances and aggregate stability in rhizospheric and non-rhizospheric soil

Purpose

The paper describes rhizospheric (Rs) and non-rhizospheric (nRs) soil to demonstrate the zone of the plant root impact on physical and chemical properties of the soil. The effects of the process accompanying the transformations of organic matter into humic substances in the rhizosphere of “common dandelion” Taraxacum officinale have been determined, and the properties of humic acids (HAs) were described. The importance of iron and clay minerals for the formation of a stable and water-resistant soil structure has been emphasized.

Materials and methods

The laboratory analysis involved determination of basic physical and chemical soil properties: texture, pH, cation exchange capacity (CEC), electrical conductivity, and content of total organic carbon (TOC) and dissolved organic carbon (DOC) and quality of humic substances: optical properties of HAs and its separation into hydrophilic (HIL) and hydrophobic (HOB) fractions, speciation of iron, glomalin operationally described as an easily extractable glomalin-related soil protein (EE-GRSP), and soil aggregate stability (SAS) of six size classes of soil aggregates.

Results and discussion

The Rs was reported with a higher TOC and DOC content (measured in the CaCl₂ extracts), however not significantly. The HAs isolated from Rs revealed a significantly higher content of humic substances at its initial decomposition stage, as compared with nRs. A significantly higher concentration of EE-GRSP was noted in the aggregates of the rhizospheric zone (mean 1.14 g kg^?1) than in the aggregates collected from root-free soil (mean 0.94 g kg^?1). There was noted the highest mean share of 1–3 mm soil aggregates in Rs as well as in nRs, respectively 44.4 and 38.3%. The soil material both in Rs and in nRs contained high amounts of exchangeable Ca²⁺, and smectite is the predominant clay mineral. It was favorable for the accumulation of organic carbon and for the formation of good soil physical condition (tilth). Higher but insignificant SAS values were observed for Rs (mean SAS?=?95.6%) than for nRs (mean SAS?=?93.9%).

Conclusions

The studies confirm the role of common dandelion roots in the process of organic carbon accumulation in rhizospheric zone and a favorable effect on the mechanism of the formation of water-resistant aggregates. Higher values of SAS for the Rs were affected by the content of TOC, DOC, exchangeable Ca²⁺ and the concentration of EE-GRSP, and, less considerably, the content of Fe and clay minerals.

     

Biochar addition drives soil aggregation and carbon sequestration in aggregate fractions from an intensive agricultural system

Purpose

Biochar application is deemed to modify soil properties, but current research has been mostly conducted on the degraded land in tropical regions. Using six consecutive years of biochar field trial, we investigated effects of biochar on soil aggregates, structural stability, and soil organic carbon (SOC) and black C (BC) concentrations in aggregate fractions. The findings have important implications in managing soil structure and SOC sequestration in high fertility soils of the temperate areas.

Materials and methods

The study had four treatments: control; biochar rate at 4.5 (B4.5) and biochar rate at 9.0 t ha^?1 year^?1 (B9.0); and straw return (SR). Soil samples were collected from 0–10-cm layer, and aggregate size distribution was determined with the wet-sieving method. Then, the mean weight diameter (MWD) of aggregates and the aggregate ratio (AR), i.e., the ratio of the >250 μm to the 53–250 μm size were calculated to assess the structural stability. Total SOC and BC concentrations in bulk soil (<2 mm) and separated fractions (i.e., >2000, 250–2000, 53–250, and <53 μm) were measured.

Results and discussion

The B4.5 and B9.0 significantly increased macroaggregate (250–2000 μm) and MWD and AR indices relative to the control. Comparing to the SR, the improvements in soil aggregation under biochar treatments were limited. Additionally, more SOC in larger fractions (>2000, 250–2000, and 53–250 μm) and BC in extracted fractions under biochar soils were observed. These results implied that biochar addition enhanced both native SOC and BC physical protection by aggregation.

Conclusions

Biochar application is effective in mediating soil aggregation, and thus improves both native SOC and BC stabilization in an intensive cropping system of North China.

     

Assessment of heavy metal tolerance in two plant species growing in experimental disturbed polluted urban soil

Purpose

Urban soil, which is strongly influenced by anthropogenic activities, receives a major proportion of trace metal wastes. The aim of this work was to determine heavy metal concentration in (a) soil, to know the degree of the soil pollution; (b) roots and leaves of two plant species, Brassica juncea as an accumulator plant and Solanum lycopersicum as a crop plant; and (c) drainage water, to evaluate the heavy metal mobility.

Materials and methods

The study area is located in Sants, a neighborhood in Barcelona (Catalonia, Spain). Thirty kilograms of two representative soil depths (0–15 and 15–40 cm) was sampled and subsequently mixed. The two studied species were cultivated for 3 weeks in greenhouse conditions, and all pots were irrigated with water weekly to field capacity with a nutrient solution (pH = 6.5). If not otherwise stated, given results are means ± standard deviation of four replicated pots each with a composite sample of 12 individual plants per treatment. X-ray fluorescence (FRX) and diethylenetriaminepentaacetic acid soil extraction (DTPA) were used for total and available metal soil contents, respectively. Weekly cumulative drainage water of each pot was collected in polyethylene bottles and stored at 4 °C until analysis.

Results and discussion

The main pollutants are Cu, Pb, and Zn with topsoil total concentrations of approximately 1355, 2230, and 6239 mg kg^?1, respectively. The same soil elements for available fractions were slightly elevated (9.6, 5.8, and 6.7% of total concentration). The concentrations of Cu, Pb, and Zn in the plants’ leaves are greater in B. juncea than in S. lycopersicum. Furthermore, they are greater in the roots than in leaves. The Pb concentrations in a crop plant exceeded the 0.10 mg kg^?1 limit established for vegetables devoted for food in the European legislation. Unusually elevated concentrations of Pb (over 10 μg L^?1) were detected in the drainage water. These values exceeded the acceptable toxic concentrations in waters, according to the Spanish legislation.

Conclusions

The urban soil studied was highly contaminated by Cu, Pb, and Zn, and this pollution is more evident in the topsoil. A great part of these heavy metals was bioavailable for plants. Thus, the two plants (S. lycopersicum and B. juncea) had an ability to transport heavy metals from the roots to the shoots, especially for Zn. Great contents of heavy metals in the drainage water after the irrigation of plants were observed.

     

Enhanced <Emphasis Type="Italic">Scirpus triqueter</Emphasis> phytoremediation of pyrene and lead co-contaminated soil with alkyl polyglucoside and nitrilotriacetic acid combined application

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.

     

Assessing the potential of using biochar in mine rehabilitation under elevated atmospheric CO<Subscript>2</Subscript> concentration

Purpose

Re-establishment of soil nitrogen (N) capital is a priority in mine rehabilitation. We aimed to evaluate the effects of biochar addition on improving mine spoil N pools and the influence of elevated CO₂ concentration on mine rehabilitation.

Materials and methods

We assessed the effects of pinewood biochar, produced at three temperatures (650, 750 and 850 °C, referred as B₆₅₀, B₇₅₀ and B₈₅₀, respectively), on mine spoil total N concentrations with five different plant species, including a tree species (Eucalyptus crebra), N-fixing shrubs (Acacia floribunda and Allocasuarina littoralis) and C₃ and C₄ grasses (Austrodanthonia tenuior and Themeda australis) incubated at ambient (400 μL L^?1) and elevated (700 μL L^?1) atmospheric CO₂ concentrations, as well as the effects of elevated CO₂ on mine rehabilitation.

Results and discussion

Soil total N significantly improved following biochar incorporation under all plant species (P < 0.05) except for T. Australis. E. crebra had the highest soil total N (0.197%, 0.198% and 0.212% for B₆₅₀, B₇₅₀ and B₈₅₀, respectively). Different from the negligible influence of elevated CO₂ on soil properties under the grasses and the N-fixing shrubs, elevated CO₂ significantly increased soil water and hot water extractable organic C (WEOC and HWEOC, respectively) and decreased total C under E. crebra, indicating that the nutrient demands were not met.

Conclusions

Biochar addition showed the potential in mine rehabilitation in terms of improving soil N pool, especially with E. crebra. However, it would be more difficulty to rehabilitate mine spoils in future with the rising atmospheric CO₂ concentration.

     

Competitive sorption of linear alkylbenzene sulfonate (LAS) surfactants and the antibiotics sulfamethoxazole and ciprofloxacin in wastewater-irrigated soils of the Mezquital Valley,Mexico

Purpose

The increasing reuse of wastewater for irrigation introduces surfactants and antibiotics into the environment. How these two kinds of compounds interact with regard to their sorption processes in soil is not clear.

Materials and methods

We performed batch experiments to investigate the sorption of linear alkylbenzene sulfonates (LAS) and its effect on sorption of sulfamethoxazole and ciprofloxacin in irrigated and non-irrigated soils with different organic matter (OM) contents.

Results and discussion

LAS sorption was non-linear in the presence of the antibiotics, and as general trend, it increased with rising OM content of soils. Free LAS was also removed from solution by complexation with Ca²⁺. Dissolved organic compounds released from soils with OM contents ≥18.4 g kg^?1 further reduced LAS sorption. Sorption of sulfamethoxazole was reduced by LAS sorption only in one soil with a small OM content of 9.5 g kg^?1.

Conclusions

The strong sorption of ciprofloxacin is not affected by LAS. Sulfamethoxazole sorption only competes with LAS sorption in organic matter-poor soils. Accumulation of organic matter in soils, for example due to long-term wastewater irrigation, provides extra sorption capacity for LAS and sulfamethoxazole so that competition for sorption sites is reduced.

     

Fractionation of copper and uranium in organic and conventional vineyard soils and adjacent stream sediments studied by sequential extraction

Purpose

Particularly in organic viticulture, copper compounds are intentionally released into the environment as fungicide, whereas uranium originates from conventional phosphate fertilization. Both activities contribute to the metal contamination in wine-growing areas. This pilot study aimed to better understand how soil properties influence the presence and environmental fate of copper and uranium with respect to viticultural management.

Materials and methods

We characterized metal binding forms, i.e., their association with different soil constituents, in organically and conventionally cultivated vineyard soils and adjacent upstream and downstream sediments. The available metal fraction and the fractions associated with manganese oxides, organic matter, iron oxides, and total contents were extracted sequentially.

Results and discussion

Total soil copper ranged from 200 to 1600 mg kg^?1 with higher contents in topsoil than subsoil. The majority of copper (42–82%) was bound to soil organic matter. In all fractions, copper contents were up to 2-fold higher in organic than in conventional vineyards, whereas the sediment concentrations were independent of the adjacent viticultural management. A net increase of copper in downstream sediments was found only when water-extractable organic carbon (WEOC) in an adjacent vineyard was elevated. With 11 ± 1 mg kg^?1, total uranium was 25% higher in conventional than in organic vineyard soils. Its affinity to iron or WEOC potentially rendered uranium mobile leading to a substantial discharge to downstream sediments.

Conclusions

Translocation of copper and uranium from vineyards into adjacent stream sediments may rather be attributed to WEOC and iron contents than the viticultural management. Follow-up studies should scrutinize the processes driving metal availability and transport as well as their interaction at the aquatic–terrestrial interface.

     

Positive effects of apple branch biochar on wheat yield only appear at a low application rate,regardless of nitrogen and water conditions

Purpose

The agriculture industry is under intense pressure to produce more food with a lower environmental impact, while also mitigating climate change. Biochar has the potential to improve food security while improving soil fertility and sequestering carbon. The aim of our research was to evaluate the effects of apple branch biochar on wheat yield and soil nutrients under different nitrogen (N) and water conditions.

Materials and methods

Durum wheat was grown for nearly 6 months in pots with silt clay soil supplemented with apple branch biochar. The biochar was applied at five rates (0, 1, 2, 4, and 6% w/w; B0, B1, B2, B3, and B4), and N fertilizer was applied at three rates (0, 0.2, and 0.4 g kg^?1; N0, N1, and N2). From the jointing to maturation stages, the soil water content was controlled at two rates to simulate sufficient water and drought conditions (75 and 45% of field capacity; W1 and W2). After harvest, we investigated grain yield and soil nutrient status.

Results and discussion

The application of biochar alone had a positive effect on wheat production and soil nutrients, especially under sufficient water conditions. Compared with the addition of N fertilizer alone, the addition of biochar at B1 and B2 combined with N fertilizer under sufficient water conditions increased the crop yield by 7.40 to 12.00%, whereas this was not the case under drought stress. Furthermore, regardless of water conditions, compared with N fertilizer application alone, a high rate of biochar application (B3 and B4) led to a significant decrease in the grain yield of approximately 6.25–21.83%. Biochar had strong effects on soil nutrients, with NO₃^? and available phosphorus contents and the C:N ratio exerting the greatest effects on wheat yield.

Conclusions

The effects of biochar on wheat production and soil nutrients varied with the biochar application rate, N fertilizer application rate, and water conditions. Drought stress weakened or offset the positive effect of biochar on crop production, especially under the high-N level (N2) conditions. The optimum application combination was 1% (or possibly even less) apple branch biochar (B1) and moderate N fertilizer (N1).

     

Biochar nutrient availability rather than its water holding capacity governs the growth of both C3 and C4 plants

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.

     

Organic matter transformation and porosity development in non-reclaimed mining soils of different ages and vegetation covers: a field study of soils of the zinc and lead ore area in SE Poland

Purpose

Plant residue decomposition, porosity status and biological activity in heavily polluted with Zn, Pb and Cd post-mining soils were investigated in relation to natural soil in the area. The study was carried out on soils from different ages and vegetation cover. This work aimed at studying the influence of heavy metal concentration on the humus layer formation with the help of micromorphological methods.

Materials and methods

Soil samples were collected from 5 sites situated in the Zn and Pb mining area and from one site located in the vicinity but unchanged by mining works. In each site, a representative area of about 100 m² was selected and soil samples from 5 randomly selected plots were taken from surface and subsurface layers. Chemical, micromorphological and biological analyses were conducted in order to evaluate humus transformations occurring in studied soils and to establish the main factors affecting these processes. In images taken from thin sections, we separated and measured areas covered by decomposed organic matter, plant residues and pores.

Results and discussion

Mine soils had similar pH soil values (6.7–7.1); only one natural soil was moderately acid (pH = 5.6). The soils differed in SOM content, from 30.84 to 168 g kg^?1. Mine soils were contaminated with heavy metals up to 10,980 mg Zn, 5436 mg Pb and 95.2 mg Cd·kg^?1. The largest amount of the medium-sized and large plant residues (18.4 and 20.5%) were found in post-mining soil covered with xerothermic flora typical of metalliferous areas. The lowest amount of small residues was found in post-mining forest soil. The diversified accumulation of plant residues reflected the organic matter decomposition ratio varying from 1.64 (post-mining soil 15% covered with calamine flora) to 62.7% (natural soil covered with forest). In the natural soil, rounded pores prevailed, while in post-mining soils, planar pores dominated. Invertase activity ranged from 1.64 to 154.2 mg of inverted sugar, and carbon of microbial biomass ranged from 5.94 to 731.2 μg g^?1. Both characteristics were related to the amount of organic matter regardless of the heavy-metal pollution.

Conclusions

The results showed that a decomposition ratio was lower in mining soils than in the natural soil, and large plant residues were accumulated in surface layers. Microbial activity was more influenced by plant cover density and diversity than by heavy metal concentration. The evolution in the organic matter form and pore shapes with the soil age and the vegetation cover was observed.

     

Taxon-specific responses of soil microbial communities to different soil priming effects induced by addition of plant residues and their biochars

Purpose

This work investigated changes in priming effects and the taxonomy of soil microbial communities after being amended with plant feedstock and its corresponding biochar.

Materials and methods

A soil incubation was conducted for 180 days to monitor the mineralization and evolution of soil-primed C after addition of maize and its biochar pyrolysed at 450 °C. Responses of individual microbial taxa were identified and compared using the next-generation sequencing method.

Results and discussion

Cumulative CO₂ showed similar trends but different magnitudes in soil supplied with feedstock and its biochar. Feedstock addition resulted in a positive priming effect of 1999 mg C kg^?1 soil (+253.7 %) while biochar gave negative primed C of ?872.1 mg C kg^?1 soil (?254.3 %). Linear relationships between mineralized material and mineralized soil C were detected. Most priming occurred in the first 15 days, indicating co-metabolism. Differences in priming may be explained by differences in properties of plant material, especially the water-extractable organic C. Predominant phyla were affiliated to Acidobacteria, Actinobacteria, Chloroflexi, Gemmatimonadetes, Firmicutes, Planctomycetes, Proteobacteria, Verrucomicrobia, Ascomycota, Basidiomycota, Blastocladiomycota, Chytridiomycota, Zygomycota, Euryarchaeota, and Thaumarchaeota during decomposition. Cluster analysis resulted in separate phylogenetic grouping of feedstock and biochar. Bacteria (Acidobacteria, Firmicutes, Gemmatimonadetes, Planctomycetes), fungi (Ascomycota), and archaea (Euryarchaeota) were closely correlated to primed soil C (R ²?=??0.98, ?0.99, 0.84, 0.81, 0.91, and 0.91, respectively).

Conclusions

Quality of plant materials (especially labile C) shifted microbial community (specific microbial taxa) responses, resulting in a distinctive priming intensity, giving a better understanding of the functional role of soil microbial community as an important driver of priming effect.

     

Effects of temperature on soil organic carbon fractions contents,aggregate stability and structural characteristics of humic substances in a Mollisol

Purpose

Under a global warming scenario, understanding the response of soil organic carbon fractions and aggregate stability to temperature increases is important not only for better understanding and maintaining relevant ecosystem services like soil fertility and crop productivity, but also for understanding key environmental processes intimately related with the maintenance of other regulatory ecosystem services like global climate change mitigation through carbon sequestration. An increase in temperature would accelerate the mineralization of soil organic carbon. However, the properties of organic carbon remained in soil after mineralization is not well known.

Materials and methods

Mollisol was collected at 0–20-cm depth from maize (Zea mays L.) field in Northeast China. A 180-day incubation experiment was conducted at three different temperatures (10, 30, and 50 °C) under constant soil moisture (60 % water holding capacity). Soil samples were assayed for total organic carbon (TOC), water-soluble organic carbon (WSOC), easily oxidizable organic carbon (EOC), humic fractions carbon, aggregate-associated carbon, and water stability of aggregates. Elemental analysis and solid-state ¹³C nuclear magnetic resonance spectroscopy were used to characterize humic acid and humin fractions.

Results and discussion

The contents of soil TOC, EOC, humic fractions carbon, and aggregate-associated carbon decreased with the increase in temperature. The proportion of 2–0.25-mm macroaggregate and the mean weight diameter (MWD) of aggregates also decreased. The C, H, N, S, alkyl C, and O-alkyl C contents of humic acid and humin decreased, whereas the O, aromatic C, and carbonyl C contents increased. The H/C, aliphatic C/aromatic C, and O-alkyl C/aromatic C ratios in humic acid and humin fractions decreased.

Conclusions

The increase in temperature has a negative impact on soil organic carbon content, soil aggregation, and aggregate stability. Moreover, humic acid and humin molecules become less aliphatic and more decomposed with the increase in temperature.

     

Toxic potential of different types of sewage sludge as fertiliser in agriculture: ecotoxicological effects on aquatic,sediment and soil indicator species

Purpose

Treated and processed sewage sludges (biosolids) generated during the treatment of wastewater usually contain substantial concentrations of nutrients, especially phosphorus, which is essential for plant growth. Sewage sludge therefore can be used as an alternative fertiliser in agriculture. But since sewage sludge could also contain pollutants, analysis and ecotoxicological tests on affected soil and stream water organisms are necessary in order to guarantee its harmless use.

Materials and methods

Three test species were chosen to cover the environmental compartments, water, sediment and soil. The following test species and parameters were applied to evaluate the acute effects of three sewage sludge samples: Lemna minor (growth inhibition, discolouration and colony breakup), Gammarus fossarum (mortality, behaviour) and Eisenia fetida (avoidance behaviour). Chemical assessment included nutrients, organic pollutants and heavy metals.

Results and discussion

The assessment of a non-dewatered sludge (S1) sample resulted in an inhibition of growth of L. minor starting from 0.6 g total solid (TS)?l^?1 after 7 days (EC₅₀ 1.2 g TS l^?1). G. fossarum displayed significantly decreased movement activity at 0.5 and 1.2 g TS l^?1 sludge concentration during an exposure time of 2 days, leading to decreased survival after 4 days of exposure in 0.5 g TS l^?1 (LC₅₀ 0.5 g TS l^?1). After 2 days, E. fetida exhibited an increased avoidance behaviour of contaminated soil from 0.2 g TS kg^?1 sewage sludge (EC₅₀ 0.4 g TS kg^?1). The dewatered sludge samples (S2 and S3) had a lower toxic effect on the test organisms. G. fossarum was the most sensitive test species in the applied test setups. The realistic application amounts of the tested sewage sludge samples of approximately 6.0 g TS kg^?1 (maximum allowed application amount of sewage sludge) and approximately 3 g TS kg^?1 (maximum agronomical relevant application amount) in worst case studies are higher than the analysed EC₅₀/LC₅₀ values of S1 and of the LC₅₀ (G. fossarum) of S2 and S3.

Conclusions

All three tested sewage sludge samples have to be classified as toxic at high concentration levels under laboratory conditions. Realistic output quantities of S1 will negatively influence soil invertebrates and freshwater organisms (plants and crustacean), whereas the dewatered sludge samples will most likely not have any acute toxic effect on the test organisms in the field. Test with environmental samples should be conducted in order to support this hypothesis.