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.

     

The effect of biochar loading rates on soil fertility,soil biomass,potential nitrification,and soil community metabolic profiles in three different soils

Purpose

Biochar is increasingly being used as a soil amendment to both increase soil carbon storage and improve soil chemical and biological properties. To better understand the shorter-term (10 months) impacts of biochar on selected soil parameters and biological process in three different textured soils, a wide range of loading rates was applied.

Materials and methods

Biochar derived from eucalypt green waste was mixed at 0, 2.5, 5, 10 % (wt/wt) with a reactive black clay loam (BCL), a non-reactive red loam (RL) and a brown sandy loam (BSL) and placed in pots exposed to the natural elements. After 10 months of incubation, analysis was performed to determine the impacts of the biochar rates on the different soil types. Also, microbial biomass was estimated by the total viable counts (TVC) and DNA extraction. Moreover, potential nitrification rate and community metabolic profiles were assayed to evaluate microbial function and biological process in biochar-amended soils.

Results and discussion

The results showed that biochar additions had a significant impact on NH₄ and NO₃, total C and N, pH, EC, and soil moisture content in both a soil type and loading-dependent manner. In the heavier and reactive BCL, no significant impact was observed on the available P and K levels, or the total exchangeable base cations (TEB) and CEC. However, in the other lighter soils, biochar addition had a significant effect on the exchangeable Al, Ca, Mg, and Na levels and CEC. There was a relatively limited effect on microbial biomass in amended soils; however, biochar additions and its interactions with different soils reduced the potential nitrification at the higher biochar rate in the two lighter soils. Community metabolic profile results showed that the effect of biochar on carbon substrate utilization was both soil type and loading dependent. The BCL and BSL showed reduced rates of substrate utilization as biochar loading levels increased while the opposite occurred for the RL.

Conclusions

This research shows that biochar can improve soil carbon levels and raise pH but varies with soil type. High biochar loading rates may also influence nitrification and the function and activity of microbial community in lighter soils.

     

Sorption and transport of sulfonamides in soils amended with wheat straw-derived biochar: effects of water pH,coexistence copper ion,and dissolved organic matter

Purpose

Sulfonamides are widely used for the prevention and treatment of bacterial infections, hard-degraded contaminants distributed in the environment if they are discharged into the soil and water. Biochar could probably influence the geochemical behavior of ionized antibiotics in the soils.

Materials and methods

To determine the sorption/desorption of three representative sulfonamides (SAs) in soils amended with biochar, we investigated the effects of water pH, Cu²⁺, and dissolved humic acid on the sorption of sulfamethoxazole (SMX), sulfamethazine (SMZ), and sulfadiazine (SD) onto two different soil samples (S1 pH?=?5.13 and S2 pH?=?7.33) amended with wheat straw-derived biochar (size 0.5～0.6 mm).

Results and discussion

Batch experiments showed that the sorption/desorption isotherms of SAs on soil with/without biochar followed the Freundlich model. The biochar had a strong adsorption potential for SMX, SMZ, and SD both in S1 and S2 at low water pH. Except for SMX, the presence of Cu²⁺ inhibited the sorption of SMZ and SD through competing hydrophobic adsorption region in soils. HA suppressed the sorption of three sulfonamides in soil S2 by electrostatic repulsion under alkaline condition. The soil leaching column experiments showed the SA transport in soils, and S1 and S2 amended with biochar (0.5 and 1.0 wt%) brought about 12–20 % increase in SMX, SMZ, and SD retention compared to the untreated soil.

Conclusions

The results indicated that the presence of biochar effectively mitigated the mobility of ionized antibiotics such as SMX, SMZ, and SD in soils, which helps us reconsider the potential risk of antibiotics in the environment.

     

Biochar effects on soil water infiltration and erosion under seal formation conditions: rainfall simulation experiment

Purpose

Soil amendment with biochar can result in decreased bulk density and soil penetration resistance, and increased water-holding capacity. We hypothesized that adding biochar could moderate the reductions in infiltration rates (IR) that occur during high-intensity rainstorms in seal-prone soils, and hence result in reduced runoff and erosion rates. The objectives were to (i) evaluate biochar potential to improve infiltration and control soil erosion, and (ii) investigate the mechanisms by which biochar influences infiltration rate and soil loss.

Materials and methods

Rainfall simulation experiments were conducted on two physicochemically contrasting, agriculturally significant, erosion-prone soils of Israel that are candidates for biochar amendment: (i) non-calcareous loamy sand, and (ii) calcareous loam. Biochar produced from mixed wood sievings from wood chip production at a highest treatment temperature of 620 °C was used as the amendment at concentrations from 0 to 2 wt%.

Results and discussion

In the non-calcareous loamy sand, 2 % biochar was found to significantly increase final IR (FIR) by 1.7 times, and significantly reduce soil loss by 3.6 times, compared with the 0 % biochar control. These effects persisted throughout a second rainfall simulation, and were attributed to an increase in soil solution Ca and decrease in Na, and a subsequently decreased sodium adsorption ratio (SAR). In the calcareous loam, biochar addition had no significant effect on FIR but did reduce soil loss by 1.3 times. There were no biochar-related chemical changes in the soil solution of the calcareous loam, which corresponds to the lack of biochar impact on FIR. Surface roughness of the calcareous loam increased as a result of accumulation of coarse biochar particles, which is consistent with decreased soil loss.

Conclusions

These results confirm that biochar addition may be a tool for soil conservation in arid and semi-arid zone soils.

     

Dissipation of fomesafen in biochar-amended soil and its availability to corn (<Emphasis Type="Italic">Zea mays</Emphasis> L.) and earthworm (<Emphasis Type="Italic">Eisenia fetida</Emphasis>)

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.

     

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.

     

Salt-affected soils,reclamation, carbon dynamics,and biochar: a review

Purpose

This paper reviews chemical, physical, and biological problems of salt-affected soils and different reclamation methods applied to rehabilitate these soils.

Methods

Methods to increase C stocks in these lands are discussed with a focus on biochar application as a potential new approach to not only to increase the C content but also to improve soil properties. Gaps in research knowledge in this field are then identified.

Results

Given the concern on the continued worldwide expansion of salt-affected lands and the focus on C sequestration processes, this review has evaluated current knowledge on salt-affected soils and their remediation with organic materials and plants. The review of the published literature has highlighted important gaps in knowledge, which limit our current understanding of rehabilitation of salt-affected soils with organic amendments specially biochar and the associated carbon dynamic. Knowledge about application of biochar in salt-affected soils is scant, and to date, most studies have evaluated biochar use only in nonsalt-affected soils.

     

Biochar-induced changes in soil properties affected immobilization/mobilization of metals/metalloids in contaminated soils

Purpose

Remediation of metal contaminated soil with biochar is attracting extensive interest in recent years. Understanding the significance of variable biochar properties and soil types helps elucidating the meticulous roles of biochar in immobilizing/mobilizing metals/metalloids in contaminated soils.

Materials and methods

Six biochars were produced from widely available agricultural wastes (i.e., soybean stover, peanut shells and pine needles) at two pyrolysis temperatures of 300 and 700 °C, respectively. The Pb-, Cu-, and Sb-contaminated shooting range soils and Pb-, Zn-, and As-contaminated agricultural soils were amended with the produced biochars. The mobility of metals/metalloids was assessed by the standard batch leaching test, principal component analysis and speciation modeling.

Results and discussion

The changes in soil properties were correlated to feedstock types and pyrolysis temperatures of biochars based on the principal component analysis. Biochars produced at 300 °C were more efficient in decreasing Pb and Cu mobility (>93 %) in alkaline shooting range soil via surface complexation with carboxyl groups and Fe-/Al-minerals of biochars as well as metal-phosphates precipitation. By contrast, biochars produced at 700 °C outperformed their counterparts in decreasing Pb and Zn mobility (100 %) in acidic agricultural soil by metal-hydroxides precipitation due to biochar-induced pH increase. However, Sb and As mobility in both soils was unfavorably increased by biochar amendment, possibly due to the enhanced electrostatic repulsion and competition with phosphate.

Conclusions

It is noteworthy that the application of biochars is not equally effective in immobilizing metals or mobilizing metalloids in different soils. We should apply biochar to multi-metal contaminated soil with great caution and tailor biochar production for achieving desired outcome and avoiding adverse impact on soil ecosystem.

     

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).

     

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.

     

Sugarcane bagasse biochars impact respiration and greenhouse gas emissions from a latosol

Purpose

A paucity in knowledge remains on the influence of biochar production temperature and the rate of application on greenhouse gas emissions from soil. The objective of this column experiment was to evaluate a biochar thermosequence by doses on CO₂, N₂O, and CH₄ emissions from a latosol following nitrogen fertilizer application following a pre-incubation period.

Materials and methods

Biochar was produced from sugarcane bagasse pyrolyzed at 300, 500, and 700 °C (BC 300, BC 500, and BC 700, respectively). Biochars were added to air-dried latosol columns at rates of 0, 0.5, 1, 2, 5, 10, and 15 % (w/w), and the water content was brought to 95 % of water-filled pore space (WFPS). The emissions from columns were tested on days 1, 3, 7, 15, and 30 following a 30-day pre-incubation.

Results and discussion

All treatments showed a decrease in respiration across the study period. The higher doses of biochar of BC 300 and BC 700 resulted in significantly higher respiration than controls on days 15 and 30. Neither biochar dose nor temperature had a significant effect on CH₄ emissions during the study period. Application of all biochars suppressed the emissions of N₂O at all doses on days 1 and 3, compared to the control. N₂O emissions from higher temperature biochar-amended soil at 2, 5, 10, and 15 % were greater than that from corresponding treatments of lower-temperature biochar-amended soil on days 15 and 30.

Conclusions

Soil respiration and overall greenhouse gas emission from latosol increased with biochar dose and pyrolysis temperature in the 30-day study period due to increasing water retention facilitated by biochar. Careful consideration is needed when applying bagasse biochar as it changes N cycling and soil physical properties.

     

Effect of biochar amendment on water infiltration in a coastal saline soil

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.

     

Effect of rice planting on the nutrient accumulation and transfer in soils under plastic greenhouse vegetable-rice rotation system in southeast China

Purpose

Greenhouse vegetable-rice crop rotations have rapidly expanded in the southeast of China in recent years. However, how rice planting affects nutrient accumulation and transfer in soils during plastic greenhouse vegetable cultivation is still poorly understood. The aim of this research was to characterize the nutrient accumulation and vertical distribution of greenhouse soil under long-term greenhouse vegetable-rice rotation.

Materials and methods

The nutrient accumulation and transfer between greenhouse eggplant-summer rice (GER) and greenhouse eggplant-summer fallow (GEF) without plastic cover in the Changxing city, Zhejiang province of China, were compared. The soil nutrient contents were determined in the surface soil samples collected from both the GER and GEF systems after eggplant harvest and after summer cultivation as well as the soils collected from both systems at different soil depths after summer cultivation. The nitrogen concentration of the surface water and groundwater samples collected during the flooding water time in GER was also measured.

Results and discussion

Both the GER and GEF soils showed obvious accumulation of nutrients at the 0–20-cm soil depth after eggplant harvest. However, compared with the summer fallow without plastic cover in GEF, rice planting in GER sharply reduced the nutrients in soils at the 0–20-cm layer. The NO₃ ^?-N, Olsen-P, and available K in the soil of GER decreased from 25, 159, and 144 to 8, 127, and 120 mg kg^?1, respectively. Nutrient contents in all different soil depths in GER were lower than those in GEF at equivalent soil depths. The nitrogen content of groundwater in GER showed unobvious enhancement during flooding water time.

Conclusions

Rice planting during the summer after greenhouse vegetable cultivation could reduce the nutrient accumulation in soil. Flooding water in summer did not increase nutrient leaching in comparison with fallow without plastic cover during the summer. Thus, rice can be regarded as a suitable catch crop for greenhouse vegetable cultivation.

     

The effects of biochar and hoggery biogas slurry on fluvo-aquic soil physical and hydraulic properties: a field study of four consecutive wheat–maize rotations

Purpose

The degeneration of fluvo-aquic soils due to long-term excessive fertilization is increasing in the Huang-Huai-Hai Plain, China. Products from crop straw and livestock breeding wastewater, biochar, and biogas slurry provide safe and efficient biomass resources for soil quality improvement. We assumed that biochar and biogas slurry could improve soil structure and soil water retention capacity for their special characteristics. The present study aimed to compare the effects of biochar and hoggery biogas slurry treatments on improvements to soil physical properties and water-holding capacity, and their different driving mechanisms.

Materials and methods

This study was based on a field experiment of four consecutive winter wheat–summer maize rotations on the Huang-Huai-Hai Plain, China. Using the principle of equal nitrogen inputs, three treatments were conducted: conventional farming fertilizers, biochar, and hoggery biogas slurry. The differences in indicators such as soil bulk density, total porosity, aggregate structure, saturated hydraulic conductivity, and hydraulic property parameters between different treatments were compared and analyzed. The driving factors generating these differences were also discussed.

Results and discussion

Compared to conventional fertilization, soil bulk density decreased under biochar and hoggery biogas slurry treatments, whereas soil total porosity increased after hoggery biogas slurry treatment. In the 0–20-cm soil layer, biochar treatment increased the content of >2-mm macrosoil aggregates and hoggery biogas slurry treatment increased the content of 0.25–0.5 or 1–2-mm soil aggregates. The soil saturated hydraulic conductivity in the 0–20-cm soil layer did not change significantly with biochar application, but increased with hoggery biogas slurry treatment. The application of biochar and hoggery biogas slurry improved the water-holding capacity, increasing the field capacity by 15.34 and 13.83 %, and the available water content by 16.20 and 25.87 %, respectively, in the 0–20-cm soil layer.

Conclusions

Both biochar and hoggery biogas slurry treatments significantly improved soil structure and water-holding capacity. Biogas slurry treatment significantly increased soil saturated hydraulic conductivity, soil aggregate content, while biochar treatment significantly decreased bulk density and increased total porosity of the soil.

     

The properties and functions of biochars in forest ecosystems

Purpose

The production of large quantities of biochar from natural fires has been a part of human history for millennia, causing CO₂ emissions to the atmosphere and exerting long-term effects on soil processes. Despite its potential importance and recent work reflecting the wide interest in biochar, a general review of our deep understanding of biochar functions within forest soils is currently lacking. Gaps in research knowledge in this field are identified in this paper.

Materials and methods

This paper summarizes recent research to provide a better understanding of the concentrations, distribution, and characteristics of biochar produced from forest wildfire and its influences on soil processes. Perspectives and recommendations for future research on biochar in post-fire forest soils are also discussed.

Results and discussion

The concentration, distribution, and characteristics of biochar produced from forest wildfire largely depend on forest landscapes, regional climates, and mostly its feedstock and fire history, like, its duration and severity. The influences of biochar on soil processes, particularly carbon and nitrogen transformations and cycling, like, nitrification and nitrous oxide emissions reduction (Clough and Condron, J Environ Qual 39:1218–1223, 2010), are also determined mainly by the fire temperature and raw materials. Mechanisms can be attributed to the adsorption of organic compounds and nutrients or changed microenvironment, termed as charsphere, by biochar. We also identify the microbial mechanisms involved in the biochar-containing soils.

     

Effects of biochar addition to estuarine sediments

Purpose

Biochar is a carbon-rich product, able to enhance soil fertility and mitigate CO₂ emissions. While biochar effects on agriculture are becoming known, its impact elsewhere, e.g., on estuarine ecosystems, has yet to be assessed. The main aim of the present study was to determine the effect of biochar on sediment–water retention, CO₂ emissions from sedimentary organic carbon decomposition, sediment pH and electrical conductivity, in aerobic conditions similar to those observed at low tide.

Materials and methods

Sediments from the Mondego Estuary (Portugal) were mixed with pine gasification biochar at different doses (5, 10, 14 %) and immersed in water with different salinity values (15, 25, 30) for 96 h. The influence of biochar on water retention, the residence time of water and CO₂ emissions between ?0.75 and ?1.5 MPa, total organic carbon, pH and electrical conductivity (EC) were determined. Carbon chemical composition and polycyclic aromatic hydrocarbon (PAH) concentrations were determined in sediments and biochar. Differences between biochar treatments after immersion in different water salinities were analysed using the Kruskal–Wallis test.

Results and discussion

Results showed that biochar was able to (a) increase sediment–water content in terms of quantity and residence time, (b) decrease CO₂ emissions, but only with a specific soil–water content and at the highest biochar dose, (c) increase sediment pH at all biochar doses and (d) increase sediment EC at the highest biochar dose. In contrast, the percentage of carbon mineralised was not modified. Biochar carbon was rich in PAHs and less decomposable than sedimentary carbon. The increments observed in sediment pH and EC were unable to change sediment alkaline or saline status according to standard classifications.

Conclusions

Our results suggest that the remarkable water adsorption capacity of biochar–sediment mixtures may be considered the main factor in regulating CO₂ emission rates from sediments, together with high PAH concentrations, which probably restrain the organic matter decomposition process.

     

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.

     

Impacts of continuous excessive fertilization on soil potential nitrification activity and nitrifying microbial community dynamics in greenhouse system

Purpose

Sampling and analysis of greenhouse soils were conducted in Shouguang, China, to study continuous excessive fertilization effect on nitrifying microbial community dynamics in greenhouse environment.

Materials and methods

Potential nitrification activity (PNA), abundance, and structure of nitrifying microbial communities as well as the correlations with soil properties were investigated.

Results and discussion

Short-term excessive fertilization increased soil nutrient contents and the diversity of nitrifying microbial communities under greenhouse cultivation. However, the abundance and diversity of nitrifying communities decreased greatly due to the increase of soil acidity and salinity after 14 years of high fertilization in greenhouse. There was a significant positive correlation between soil PNA and the abundance of ammonia-oxidizing bacteria (AOB) but not that of ammonia-oxidizing archaea (AOA) in topsoil (0–20 cm) when pH ≥7. Soil PNA and AOB were strongly influenced by soil pH. The groups of Nitrososphaeraceae, Nitrosomonadaceae, and Nitrospiraceae were predominant in the AOA, AOB, and nitrite-oxidizing bacteria (NOB) communities, respectively. Nitrifying community structure was significantly correlated with soil electrical salinity (EC), organic carbon (OC), and nitrate nitrogen (NO₃ ^?–N) content by redundancy analysis (RDA).

Conclusions

Nitrification was predominated by AOB in greenhouse topsoil with high fertilizer loads. Soil salinity, OC, NO₃ ^?–N content, and pH affected by continuous excessive fertilization were the major edaphic factors in shaping nitrifying community structure in greenhouse soils.

     

Build-up of carbon fractions in technosol-biochar amended partially reclaimed mine soil grown with <Emphasis Type="Italic">Brassica juncea</Emphasis>

Purpose

Soil organic carbon (SOC) and its labile fractions are strong determinants of physical, chemical and biological properties. The objective of the present work was to evaluate the effects of organic amendments (technosol made of wastes and biochar) and Brassica juncea L. on the soil C fractions in a reclaimed mine soil.

Materials and methods

The studied soil was from a former copper mine that was subsequently partially reclaimed with vegetation and wastes. A greenhouse experiment was carried out to amend the mine soil with different proportions of technosol and biochar mixture and planting B. juncea. B. juncea plants can tolerate high levels of metals and can produce a large amount of biomass in relatively short periods of time.

Results and discussion

The results showed that with the addition of biochar and wastes, soil pH increased from 2.7 to 6.18, SOC from undetectable to 105 g kg^?1 and soil total nitrogen (TN) from undetectable to 11.4 g kg^?1. Amending with wastes and biochar also increased dissolved organic carbon (DOC) from undetectable to 5.82 g kg^?1, carbon in the free organic matter (FOM) from undetectable to 30.42 g kg^?1, FAP (carbon in fulvic acids removed with phosphoric acid) from undetectable to 24.14 g kg^?1 and also increased the humification ratio, the humification index, the polymerisation rate and the organic carbon in the humified fractions (humic acids, fulvic acids and humin). Soils amended and vegetated with B. juncea showed lower FOM values and higher humification index values than the soils amended only with biochar and wastes.

Conclusions

This study concludes that the combined addition of wastes and biochar has a greater potential for both increasing and improving organic carbon fractions in mine soils. The authors recommend the application of biochar and technosol made of wastes as a soil amendment combined with B. juncea on soils that are deficient in organic matter, since they increased all of the SOC fractions in the studied copper mine soil.

     

Measuring the bioavailability of polychlorinated biphenyls to earthworms in soil enriched with biochar or activated carbon using triolein-embedded cellulose acetate membrane

Purpose

Polychlorinated biphenyls (PCBs) are persistent soil contaminants that resist biodegradation and present serious risks to living organisms. The presence of biochar in soils can lower the availability of PCBs to biota. In this study, the effect of biochar enrichment in soils on bioaccumulation of PCBs was investigated.

Materials and methods

We applied two types of biochar including pine needle biochar (PC) and wheat straw biochar (WC), and an activated carbon (AC) to soil (2 % w/w) and employed two alternative methods to quantified rates of bioaccumulation: a living bioassay (using earthworm, Eisenia fetida, as a model organism) and a triolein-embedded cellulose acetate membrane (TECAM).

Results and discussion

Our results show that the application of biochar or AC greatly reduced the uptake of PCBs (particularly less-chlorinated PCBs) by earthworms (the reduction in total PCBs concentration was up to 40.0 and 49.0 % for PC and WC treatments, while 71.6 % for AC application). We found that the bioaccumulation factors (BAFs) for PCBs in the earthworms in biochar/AC-enriched soils were strongly correlated with O:C ratio of the biochar/AC (R ²?=?0.998, p?<?0.05). We observed that BAFs increased at log K _OW below 6.3 and decreased at log K _OW values greater than 6.3. We demonstrated that the concentration of PCBs in TECAM membranes were positively correlated with the concentration of PCBs earthworms in soil.

Conclusions

TECAM offers an efficient and cost-effective method for predicting the bioavailability of PCBs in field-contaminated soils undergoing sorbent-based remediation.