Distribution and fractionation of cadmium in soil aggregates affected by earthworms (<Emphasis Type="Italic">Eisenia fetida</Emphasis>) and manure compost

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.

     

The accumulation and transfer of arsenic and mercury in the soil under a long-term fertilization treatment

Purpose

The North China Plain (NCP) is a strategic grain production base in China with a wild distribution of fertile soils. During the past 20 years, high-input intensive agriculture with excess chemical fertilizer application has sustained high grain yields, but may have resulted in contamination of some elements in farmland. In this study, the accumulation and transfer of arsenic (As) and mercury (Hg) in typical Calcaric Fluvisols with long-term different fertilization practices were investigated.

Materials and methods

Field experiments with seven treatments were launched in 1989, and soil and plant samples were collected and analyzed periodically. The treatments include OM (organic manure), OM?+?NPK (50 % organic manure?+?50 % chemical fertilizer), NPK, NP, PK, NK, and CK (the control experiment with no fertilizer).

Results and discussion

With over 20 years (1989–2009) of cultivation, various extents of As and Hg accumulations were really observed in the soil. The higher As and Hg contents were found in P fertilizers than those in N, K, or OM fertilizers. As a result, the long-term P fertilization slightly promoted Hg accumulations with decreased soil Hg concentrations in the order of NPK?≈?NP?≈?PK?≈?OM?+?NPK?>?OM?>?NK?≈?CK, which was similar to the order of crop yields. At the tillage layer (0–20 cm), Hg accumulation in the soil was enhanced by crop production, due to the highly accumulated Hg in plant roots finally remained in the soil. However, no significant differences of soil As concentrations can be found between treatments with and without P fertilizers probably due to water leaching and plant uptake.

Conclusions

Soil As and Hg were mainly contributed by fertilizers, irrigation, and atmospheric deposition in recent years, but they did not exhibit in significant accumulations in the soil. The contents of As and Hg were not above the critical safe levels of soils for crop production (As, <30 mg kg^?1; Hg, <500 μg kg^?1). Arsenic and Hg tended to move downward in the soil profile and the movement was hindered by clay minerals.

     

Protective mechanism of the soil–plant system with respect to heavy metals

Purpose

The aim of this work was to select and assess the efficiency of different amendments applied to ordinary chernozems artificially contaminated with heavy metals (Zn and Pb).

Materials and methods

The effect of different amendments on ordinary chernozem contaminated with Zn and Pb acetate salts was studied in a long-term 3-year field experiment. Glauconite, chalk, manure, and their combinations were chosen as ameliorating agents. Spring barley (Hordeum sativum) was used as test culture for three successive years. The heavy metal concentration in all the soil samples decomposed by HF?+?HClO₄ was determined by atomic absorption spectrophotometry (AAS). One normal concentration of CH₃COONH₄ at pH 4.8 was used to estimate the actual mobility of metals. The compounds of heavy metals extracted by 1 N HCl are regarded as mobile compounds. The concentration of metals in the plants was determined using the dry combustion in a mixture of HNO₃ and HCl at 450 °C. The content of heavy metals in extracts from soil and plant samples was determined by AAS.

Results and discussion

The content of weakly bound metal compounds increased upon the contamination of the soil with Pb and Zn salts, which led to a low quality of barley grown in these soils. Metal concentrations in the barley grain exceeded the maximum permissible concentrations (MPCs). The content of Zn and Pb in grains was higher than the MPC for at least 3 years after the soil pollution. The application of amendments significantly decreased the mobility of metals, and the simultaneous application of chalk and manure was most significant. The share of weakly bound metal compounds in the contaminated soils decreased to the level typical for the clean soils or even below.

Conclusions

The combined application of chalk and manure to Zn- and Pb-contaminated ordinary chernozems decreased the content of weakly bound metal compounds in the soil and lowered their concentrations in barley plants. The polyfunctional properties of the soil components with respect to their capacity for metal fixation were established. The decrease in the intensity of Zn accumulation in grains of barley shows the presence of a barrier at the root–stalk and stalk–grain interfaces.

     

Amendment of sulfate with Se into soils further reduces methylmercury accumulation in rice

Purpose

Both selenium (Se) and sulfate could largely affect methylmercury (MeHg) dynamics and phytoavailability in soil-rice systems, while their combined effects are less understood. Here, we aimed at exploring the potential effects of sulfate on MeHg accumulation in rice in the presence of Se.

Materials and methods

Rice was cultivated in inorganic Hg-spiked soils amended with Se only (selenite/selenate, “Se treatments”) or Se and sulfate (“Se?+?Sulfate treatments”). Soil parameters (e.g., pH and redox potential (Eh)), MeHg concentrations in soils, as well as MeHg or Se accumulation in rice plants were quantified during the rice growth period.

Results and discussion

Soil MeHg concentrations were generally comparable between Se?+?Sulfate and Se treatments. However, MeHg uptake by rice plants in Se?+?Sulfate treatments was 9–31 % lower than those in Se treatments, possibly due to the increased soil pH and formation of iron sulfides, which may reduce MeHg phytoavailability under sulfate amendment. Furthermore, sulfate input enhanced Se accumulation in root (especially in the presence of selenate), which could be responsible for the increased MeHg distribution in root and thus lower MeHg distribution in grain. Consequently, the reduced plant uptake of MeHg together with the decreased MeHg distribution in grain resulted in decline of grain MeHg concentrations in Se?+?Sulfate treatments (8–31 % lower compared to Se treatments).

Conclusions

Our results suggest that sulfate input with Se could further reduce MeHg accumulation in rice, which improved mechanistic understanding of MeHg behaviors in soil-rice systems.

     

Effects of biochar and polyacrylamide on decomposition of soil organic matter and <Superscript>14</Superscript>C-labeled alfalfa residues

Purpose

Various soil conditioners, such as biochar (BC) and anionic polyacrylamide (PAM), improve soil fertility and susceptibility to erosion, and may alter microbial accessibility and decomposition of soil organic matter (SOM) and plant residues. To date, no attempts have been made to study the effects of BC in combination with PAM on the decomposition of soil SOM and plant residues. The objective of this study was to evaluate the effects of BC, PAM, and their combination on the decomposition of SOM and alfalfa residues.

Materials and methods

An 80-day incubation experiment was carried out to investigate the effects of oak wood biochar (BC; 10 Mg ha^?1), PAM (80 kg ha^?1), and their combination (BC?+?PAM) on decomposition of SOM and ¹⁴C-labeled alfalfa (Medicago sativa L.) residues by measuring CO₂ efflux, microbial biomass, and specific respiration activity.

Results and discussion

No conditioner exerted a significant effect on SOM decomposition over the 80 days of incubation. PAM increased cumulative CO₂ efflux at 55–80 days of incubation on average of 6.7 % compared to the soil with plant residue. This was confirmed by the increased MBN and MB¹⁴C at 80 days of incubation in PAM-treated soil with plant residue compared to the control. In contrast, BC and BC?+?PAM decreased plant residue decomposition compared to that in PAM-treated soil and the respective control soil during the 80 days. BC and BC?+?PAM decreased MBC in soil at 2 days of incubation indicated that BC suppressed soil microorganisms and, therefore, decreased the decomposition of plant residue.

Conclusions

The addition of oak wood BC alone or in combination with PAM to soil decreased the decomposition of plant residue.

     

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.

     

Soil nitrogen availability alters rhizodeposition carbon flux into the soil microbial community

Purpose

Soil microorganisms are important in the cycling of plant nutrients. Soil microbial biomass, community structure, and activity are mainly affected by carbon substrate and nutrient availability. The objective was to test if both the overall soil microbial community structure and the community-utilizing plant-derived carbon entering the soil as rhizodeposition were affected by soil carbon (C) and nitrogen (N) availability.

Materials and methods

A ¹³C-CO₂ steady-state labeling experiment was conducted in a ryegrass system. Four soil treatments were established: control, amendment with carboxymethyl cellulose (CMC), amendment with ammonium nitrate (NF), combined CMC and NF. Soil phospholipid fatty acid (PLFA) and ¹³C labeling PLFA were extracted and detected by isotope ratio mass spectrometer.

Results and discussion

The combined CMC and NF treatment with appropriate C/N ratio (20) significantly enhanced soil microbial biomass C and N, but resulted in lower soil inorganic N concentrations. There was no significant difference in soil PLFA profile pattern between different treatments. In contrast, most of the ¹³C was distributed into PLFAs 18:2ω6,9c, 18:1ω7c, and 18:1ω9c, indicative of fungi and gram-negative bacteria. The inorganic-only treatment was distinct in ¹³C PLFA pattern from the other treatments in the first period of labeling. Factor loadings of individual PLFAs confirmed that gram-positive bacteria had relatively greater plant-derived C contents in the inorganic-only treatment, but fungi were more enriched in the other treatments.

Conclusions

Amendments with CMC can improve N transformation processes, and the ryegrass rhizodeposition carbon flux into the soil microbial community is strongly modified by soil N availability.

     

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.

     

A simple and economic method for simultaneous determination of 11 antibiotics in manure by solid-phase extraction and high-performance liquid chromatography

Purpose

A simple and highly efficient economic method for the analysis of 11 antibacterial drugs including two tetracyclines, three quinolones, four sulfonamides, chloramphenicol and tylosin, in livestock manure, was developed using solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC).

Materials and methods

The analytes were successively extracted by EDTA-McIlvaine solution and organic solvent mixture. The extracts were degreased with n-hexane and cleaned through SPE on a hydrophile-lipophile balance (HLB) cartridge. All compounds were determined on a C18 reverse phase column with gradient elution.

Results and discussion

Recoveries calculated from spiked samples of animal manures ranged from 62.65 to 99.16 % for 11 antibiotics with relative standard deviations of less than 10.0 %. Limits of detection ranged from 0.1 to 1.9 μg kg^?1, and limits of quantification ranged from 0.3 to 5.9 μg kg^?1.

Conclusions

The results show that SPE-HPLC is an inexpensive and practical method for rapid detection of multiple antibiotics in animal manure.

     

Arsenic modulates the composition of anode-respiring bacterial community during dry-wet cycles in paddy soils

Purpose

Bacteria able to extracelluar respiration, which could be enriched in the anode of microbial fuel cells (MFCs), play important roles in dissimilatory iron reduction and arsenic (As) desorption in paddy soils. However, the response of the bacteria to As pollution is unknown.

Materials and methods

Using soil MFCs to investigate the effects of As on anode respiring bacteria (ARB) communities in paddy soils exposed to As stress. The soil MFC performances were evaluated by electrochemical methods. The bacterial community compositions on anodes were studied using Illumina sequencing.

Results and discussion

In wet 1 phase, polarization curves of MFCs showed cathode potentials were enhanced at low As exposure but inhibited at high As exposure. In the meantime, anode potentials increased with As levels. The dry-wet alternation reduced As levels in porewater and their impacts on electrodes microorganisms. Arsenic addition significantly influenced the anode microbial communities. After dry-wet cycles, Deltaproteobacteria dominated in the anode with high As.

Conclusions

The dynamic changes of the communities on cathodes and anodes of soil MFCs in paddy soils with different As addition might be explained by their different mechanisms for As detoxification. These results provide new insights into the microbial evolution in As-contaminated paddy soils.

     

Effect of nanoparticles on crops and soil microbial communities

Purpose

Nanoparticles (NPs) have received increased attention in recent past due to their unique distinct properties. Metal-based NPs are widely used in chemical and allied sector. Most of the research is directed to study the efficiency of NPs in medicine and agriculture. The aim of this review is to explore the possible threats posed by toxicity of various NPs on plants and microbial diversity.

Materials and methods

First, major sources of NPs to the environment were analyzed. The effects of metal-based NPs on the microbiota and plants are presented in this review. The results obtained by the authors during last 12 years of research are used.

Results and discussion

The exposure of soil to nanoparticles causes a decrease in soil microbial biomass and enzymatic activity, which impacts microbial community composition including yeasts, bacteria, fungi, and biological diversity. The effects of NPs on plants result in various types of abnormalities. Nanoparticles can also pose risks to human health.

Conclusions

Increased applications of NPs pose a threat to beneficial microbial communities as well as crops and soils. Thus, it is important to explore whether NPs could compromise crop yield, soil properties, soil organisms, and functional activities of soil.

     

Bioaccumulation and toxicity of lead,influenced by edaphic factors: using earthworms to study the effect of Pb on ecological health

Purpose

Lead (Pb) is a highly studied contaminant with no known biological function that causes harmful adverse effects on ecological and human health. We tried to evaluate how protective the current soil regulatory levels are for Pb towards safeguarding the ecological health. In order to achieve this, our study evaluated the effect of soil texture and pH on the toxicity and availability of lead to earthworms in soils varying in soil properties.

Materials and methods

The earthworm Eisenia fetida was exposed to Pb in three soils with different physico-chemical characteristics. Pb solutions were homogenously mixed with soil to obtain concentrations ranging from 0 to 10,000 mg/kg Pb dry soil. Avoidance behaviour, weight loss and mortality were measured in this study to calculate the EC₅₀ and LC₅₀ values.

Results and discussion

Weight loss and mortality in earthworms due to Pb toxicity were in the following order: acidic > neutral > alkaline soil. The EC₅₀ values resulting in 50% decrease in worm weight over control for Pb in acidic, neutral and alkaline soils were 460, 3606 and 5753 mg/kg soil, respectively. Thus, the acidic soil recorded an EC₅₀ well below the soil guideline value for Pb. Whereas, the LC₅₀ values resulting in 50% mortality in worms over control were 1161, 4648 and 7851 mg/kg, respectively, for acidic, neutral and alkaline soils. The Pb concentrations in earthworms ranged from 0.2 to 740 mg/kg wet weight. Soils with low clay content and acidic to neutral pH values demonstrated an increased Pb toxicity in earthworms compared to the soils with alkaline pH.

Conclusions

The worm weight loss is a more sensitive parameter than the mortality. This study emphasizes that the soil regulatory levels for Pb are not protective of worms in acidic soils. Therefore, care should be taken when using the current regulatory limits to assess and predict the safety of a contaminated site with acidic soils towards the ecological health.

     

Impact of climate and lithology on soil phytolith-occluded carbon accumulation in eastern China

Purpose

Occlusion of carbon (C) within phytoliths, biogenic silica deposited in plant tissues and returned to the soil, is an important mechanism for long-term terrestrial biogeochemical C sequestration and might play a significant role in mitigating climate change.

Materials and methods

Subtropical and tropical soil profiles (to 100 cm depth) developed on granite and basalt were sampled using a mass-balance approach to explore the influence of climate and lithology on soil phytolith-occluded carbon (PhytOC) accumulation.

Results and discussion

Soil PhytOC storage in the subtropics was significantly greater than in the tropics, with the soil profiles developed on granite storing greater PhytOC than soils derived on basalt. Phytolith and PhytOC content decreased with depth in all soil profiles. Phytolith content showed a positive correlation with the soil bio-available silicon in the soil profiles developed on basalt, while a negative correlation was observed in soil profiles developed on granite.

Conclusions

Climate and lithology have a significant impact on soil PhytOC sequestration. The management of forests (e.g., afforestation and reforestation) and external silicon amendments (e.g., basalt powder amendment) in soils, especially those developed on granite, have the potential to enhance PhytOC accumulation in forest ecosystems.

     

An efficient approach towards the bioremediation of copper,cobalt and nickel contaminated field samples

Purpose

The synthetic soil based bioremediation approach as reasonable and sustainable practice at the farming level where desired bioremediation could be established at lower cost.

Materials and methods

Metal-tolerant bacteria from different environmental field samples, (a) a municipal dump site, (b) an agricultural field and (c) sludge of electro-plating industries, were screened and characterized. Bioremediation of metal contaminants through isolated bacteria was compared under two different conditions, synthetic soil and basic minimal media containing copper, cobalt and nickel.

Results and discussion

The pollutants arising from industrial effluents are imparting a huge negative impact on agricultural land. Microbes are predominant in heavy metal-contaminated sites, which signifies as a potential opportunity for the researchers towards bioremediation. Three bacterial species showed high metal tolerance; 16S ribosomal DNA (rDNA) analysis revealed that the organisms were Proteus vulgaris strain, Stenotrophomonas sp. and Bacillus thuringiensis. Percentage removal of metals was also analysed under different concentrations and pH.

Conclusions

The current tested methods are helpful in streamlining the natural compliance of fragile elements and its uptake into the microbial system under in vitro and in situ conditions.

     

Impact of fertilization on soil polyphenol dynamics and carbon accumulation in a tea plantation,Southern China

Purpose

The strong role that soil polyphenols play in soil organic matter (SOM) formation affects soil carbon sequestration. N deposition, which comes from man-made fertilizer, influences plant growth and soil biochemical properties therefore greatly regulates soil polyphenol metabolism. The objective of this experiment was to understand the effect of fertilizer form and rate on soil polyphenol dynamics as well as to understand the potential relationship between soil phenols and C accumulation.

Materials and methods

Urea, rapeseed cake, and chicken manure, respectively, referred as N, B, and F in the text, were applied at three rates (low N, medium N, and high N, referred as 1, 2, and 3 in the text, respectively); plots without fertilization were set as control (CK, for short). Seasonal dynamics of soil total polyphenol (Tp) and bound polyphenol (Bp) concentrations were monitored. Polyphenol oxidase (PPO), peroxidase (POD), and soil fluorescein diacetate (FDA) hydrolysis activities, all factors relevant to polyphenol metabolism, were measured simultaneously. The relationship between soil polyphenols and soil C concentration was also determined.

Results and discussion

N-fertilization altered the seasonal change pattern and the accumulation level of soil Tp and Bp, which possibly resulted from the enhancement of soil microbial activities and the change of soil nutrient status. Positive linear correlation was observed between soil Tp and TC (total C) contents, which means fertilization could influence C accumulation through affecting the metabolism of soil polyphenols. Soil chemical characteristics and enzyme activities that relate to soil polyphenol metabolism were influenced by fertilization as well. Mitigated TC increment was observed in most fertilization treatments mainly due to the increased SOM decomposition rate.

Conclusions

Our findings reveal the important role of soil phenols played in C accumulation in a tea plantation due to the significant, positive linear relationship between soil Tp and TC. Long-term studies, combined with soil microorganism community structure, soil humification, and tea leaf litter decomposition experiments, are necessary for fully understanding the role that polyphenols play in soil C cycle.

     

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.

     

Dynamics of soil labile carbon and nitrogen pools in riparian zone of Wyaralong Dam in Southeast Queensland,Australia

Purpose

Soil labile carbon (C) and nitrogen (N) pools are considered to be sensitive indicators of changes in soil C and N pools. In this study, we examined possible factors affecting spatial and seasonal variations in soil labile C and N pools in the riparian zones in Southeast Queensland, Australia.

Materials and methods

Soil and sediment samples were collected from two sites in the riparian areas. The spatial and seasonal variabilities of soil moisture, hot-water extractable organic C and total N (HWEOC and HWETN), microbial biomass C and N (MBC and MBN), and the relationships among them were examined.

Results and discussion

Soil labile C and N pools decreased along the transects in both soil depths of the two soil types, with the peak or bottom of values detected between upland slope and the riparian zone. Other factors rather than soil moisture were more important in regulating seasonal changes of soil HWEOC and HWETN except the dry-rewetting influence in November 2013. Soil moisture played a significant role in the seasonal variations of MBC and MBN. Soil labile C (HWEOC and MBC) and N (HWETN and MBN) pools at Site 1 (S₁; heavy texture), which were significantly higher than those at Site 2 (S₂; light texture).

Conclusions

Soil moisture would be an important driving factor for the spatial and seasonal distributions of soil labile C and N pools. Our study highlighted the importance of riparian zones as the hot spot of soil C and N dynamics, especially at the onset of rewetting dry soil in subtropical Australia.

     

Role of woody biochar and fungal-bacterial co-inoculation on enzyme activity and metal immobilization in serpentine soil

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.

     

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.