Showing papers in "Journal of Soils and Sediments in 2018"

Effects of biochar application in forest ecosystems on soil properties and greenhouse gas emissions: a review

Abstract: Forests play a critical role in terrestrial ecosystem carbon cycling and the mitigation of global climate change. Intensive forest management and global climate change have had negative impacts on the quality of forest soils via soil acidification, reduction of soil organic carbon content, deterioration of soil biological properties, and reduction of soil biodiversity. The role of biochar in improving soil properties and the mitigation of greenhouse gas (GHG) emissions has been extensively documented in agricultural soils, while the effect of biochar application on forest soils remains poorly understood. Here, we review and summarize the available literature on the effects of biochar on soil properties and GHG emissions in forest soils. This review focuses on (1) the effect of biochar application on soil physical, chemical, and microbial properties in forest ecosystems; (2) the effect of biochar application on soil GHG emissions in forest ecosystems; and (3) knowledge gaps concerning the effect of biochar application on biogeochemical and ecological processes in forest soils. Biochar application to forests generally increases soil porosity, soil moisture retention, and aggregate stability while reducing soil bulk density. In addition, it typically enhances soil chemical properties including pH, organic carbon stock, cation exchange capacity, and the concentration of available phosphorous and potassium. Further, biochar application alters microbial community structure in forest soils, while the increase of soil microbial biomass is only a short-term effect of biochar application. Biochar effects on GHG emissions have been shown to be variable as reflected in significantly decreasing soil N2O emissions, increasing soil CH4 uptake, and complex (negative, positive, or negligible) changes of soil CO2 emissions. Moreover, all of the aforementioned effects are biochar-, soil-, and plant-specific. The application of biochars to forest soils generally results in the improvement of soil physical, chemical, and microbial properties while also mitigating soil GHG emissions. Therefore, we propose that the application of biochar in forest soils has considerable advantages, and this is especially true for plantation soils with low fertility.

Effects of metal oxide nanoparticles on soil enzyme activities and bacterial communities in two different soil types

Abstract: With the increased availability of nanoparticle-based products, their releases to soil are undoubtedly inevitable. Among the nanoparticle-based products, potential risks of metal oxide nanoparticles (MO-ENPs) have attracted increasing concerns. However, their effects on soil and soil microorganisms remain largely unknown. In this study, four metal oxide nanoparticles, i.e., zinc oxide nanoparticles (nZnO), titanium dioxide nanoparticles (nTiO2), cerium dioxide nanoparticles (nCeO2), and magnetite nanoparticles (nFe3O4), were enrolled to evaluate their impact on soil enzyme activities (invertase, urease, catalase, and phosphatase) and bacterial communities in two typical soils from northeast China (black soil and saline-alkali soil). The community structure and size were analyzed using pyrosequencing and real-time polymerase chain reaction (RT-PCR). The soils were exposed to metal oxide nanoparticles at 0.5, 1.0, and 2.0 mg g−1 for 15 and 30 days. In general, nZnO had a stronger effect on soil enzymatic activities than nTiO2, nCeO2, and nFe3O4, and saline-alkali soil was more susceptible to metal oxide nanoparticles than black soil. In RT-PCR analysis, a significant decrease (41.66, 36.34, and 47.99%, respectively) on total bacteria population was only observed in saline-alkali soil treated by 0.5, 1.0, and 2.0 mg g−1 nZnO. Meanwhile, pyrosequencing analysis revealed that the samples of saline-alkali soil treated with nZnO showed high variance in their bacterial community composition, e.g., Bacilli, Alphaproteobacteria, and Gammaproteobacteria class. The results suggested that metal oxide nanoparticle incubation could influence soil enzyme activities and change soil bacterial community. Moreover, the soil type was a key component dictating the effect of metal oxide nanoparticles on the bacterial community composition and size. These findings are of great help towards building a comprehensive understanding of the potential environmental risks of metal oxide nanoparticles.

Review of remediation technologies for sediments contaminated by heavy metals

Abstract: Contamination of sediments with heavy metals (HMs) is a worldwide environmental issue, due to the negative ecological effects of HMs. Sediments are an important component of aquatic ecosystems, impacting the transformation and transfer of HMs in the environment. Thus, remediating sediments polluted by HMs is a crucial activity within the full aquatic ecosystem remediation process, and economical, effective, and environmentally friendly remediation techniques are urgently needed. We reviewed the existing literature on sediment remediation techniques and developments in the fields of environmental science and engineering, attempting to provide a better understanding of the advances of remediation techniques and new research directions for sediments contaminated by HMs. This review summarized remediation methods (e.g., physical–chemical strategies, biological strategies, and combined techniques) used to treat sediments contaminated with HMs. This included analyzing the mechanisms associated with biological remediation technologies and their combination with other methods. Then, the review summarized the factors influencing the selection of remediation methods and evaluated the prospects of new emerging remediation methods. Bioimmobilization techniques (e.g., phytostabilization and microorganism immobilization) have received increased attention because of their low remediation cost and environmental compatibility. Furthermore, particular attention has been paid to explore the role of sulfate-reducing bacteria in decreasing heavy metal mobility. The review provides a useful theoretical foundation and technology reference for the remediation of sediment polluted by HMs.

Sugarcane bagasse-derived biochar reduces the cadmium and chromium bioavailability to mash bean and enhances the microbial activity in contaminated soil

Abstract: Remediation of heavy metals by reducing their mobility and bioavailability without removing them from soils is considered to be a cost-effective and an efficient method to address their toxicity for living organisms and soil health. The main objectives of the current study, therefore, were to investigate the potential of sugarcane bagasse biochar in reducing the bioavailability of soil cadmium (Cd) and chromium (Cr) and assessing the impact of biochar application on soil microbial activities and plant growth in metal-contaminated soil. Air-dried soil was artificially spiked with Cd and Cr metals by using Cd(NO3)2 and Cr(NO3)2 solutions. Biochar was homogenously mixed in metal-spiked soil. The experimental spiked soil was categorized as with and without biochar-amended soil. Mash bean crop was used as test plant. After crop harvesting, soil Cd and Cr were extracted by diethylenetriaminepentaacetic acid (DTPA) to estimate the mobility of heavy metals. Furthermore, the plant metal contents, microbial biomass carbon, urease activity, dehydrogenase (DHA) activity, total organic carbon, and plant biomass were determined. The Langmuir adsorption isotherms were studied for Cd and Cr in unamended soil, biochar-amended soil, and biochar only. The electronegative charges of biochar and biochar-amended soil were also measured using the zeta potential. The results show that the application of biochar to Cr- and Cd-contaminated soil significantly reduced their availability by 85 and 63%, respectively. The application of biochar at 15 g kg−1 prominently reduced the extractable Cd contents by 29 and 32% in Cd-contaminated and Cr–Cd-contaminated soils, respectively. The Cr concentration in the plant decreased by 34 and 41% in Cr-contaminated and Cr–Cd-contaminated soil compared with spiked soil without biochar. The Langmuir model achieved the best fit; its isotherm predicted the biochar’s maximum adsorption capacity for Cd (0.42 mg g−1) and Cr (0.35 mg g−1). Biochar incorporation in Cd–Cr-contaminated soil significantly increased the microbial activity and mash bean biomass. Our findings indicate that the addition of sugarcane bagasse-derived biochar significantly reduces the Cd and Cr availability in single and co-contaminated soil. In addition, an increase in the microbial activity and plant growth and a significant reduction in the Cd and Cr uptake by mash bean are possible after biochar addition.

Effect of nanoparticles on crops and soil microbial communities

Abstract: 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. 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. 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. 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.

Advances in research on the use of biochar in soil for remediation: a review

Abstract: Soil contamination mainly from human activities remains a major environmental problem in the contemporary world. Significant work has been undertaken to position biochar as a readily-available material useful for the management of contaminants in various environmental media notably soil. Here, we review the increasing research on the use of biochar in soil for the remediation of some organic and inorganic contaminants. Bibliometric analysis was carried out within the past 10 years to determine the increasing trend in research related to biochar in soil for contaminant remediation. Five exemplar contaminants were reviewed in both laboratory and field-based studies. These included two inorganic (i.e., As and Pb) and three organic classes (i.e., sulfamethoxazole, atrazine, and PAHs). The contaminants were selected based on bibliometric data and as representatives of their various contaminant classes. For example, As and Pb are potentially toxic elements (anionic and cationic, respectively), while sulfamethoxazole, atrazine, and PAHs represent antibiotics, herbicides, and hydrocarbons, respectively. The interaction between biochar and contaminants in soil is largely driven by biochar precursor material and pyrolysis temperature as well as some characteristics of the contaminants such as octanol-water partition coefficient (KOW) and polarity. The structural and chemical characteristics of biochar in turn determine the major sorption mechanisms and define biochar’s suitability for contaminant sorption. Based on the reviewed literature, a soil treatment plan is suggested to guide the application of biochar in various soil types (paddy soils, brownfield, and mine soils) at different pH levels (4–5.5) and contaminant concentrations ( 50 mg kg−1). Research on biochar has grown over the years with significant focus on its properties, and how these affect biochar’s ability to immobilize organic and inorganic contaminants in soil. Few of these studies have been field-based. More studies with greater focus on field-based soil remediation are therefore required to fully understand the behavior of biochar under natural circumstances. Other recommendations are made aimed at stimulating future research in areas where significant knowledge gaps exist.

Humic products in agriculture: potential benefits and research challenges—a review

Abstract: Humic products have been used in cropland agriculture for several decades, but lack of widespread credibility has restricted their use to small proportions of farmers. To improve the credibility of humic products, we identify four knowledge gaps and propose pathways of future action to close these gaps. First, while the capacity of humic products to improve plant growth has been proven in greenhouse and growth chambers, more such work is needed in field conditions, especially to determine the modifying effects on humic product efficacy of environmental and management factors, including crop type, annual weather patterns, soil type, and fertility management. Many of the published field studies fail to address any of these factors. Second, full acceptance of humic products by the research community may first require a mechanistic explanation for plant responses to humic products. Some research groups are exploring plant-based mechanisms, but almost entirely in controlled conditions, not in field conditions. Industry often attributes yield responses to enhancement of soil nutrient availability without citing adequate evidence. Microbial-based explanations are also possible. Third, consumer trust in available humic products would be strengthened through industry-wide measures for quality control of humic product production and sale, including standard procedures for measuring their humic and fulvic acid contents and rapid bio-assays for distinguishing effective products from inert frauds. Finally, humic products are widely presumed to promote root growth, which offers the potential to increase soil C inputs and thereby improve soil health. Yet virtually, no such evidence has been presented, in part due to the absence of long-term field trials. Humic product companies in North America have organized a trade association to promote a more knowledge-based industry. To acquire a database that will support these objectives, we propose establishment of a global network of field sites that would measure crop responses to humic products across ranges of humic products, crop types, soil types, and climates. Plant and soil samples would be analyzed by cooperating specialists in advanced laboratories to identify mechanistic processes and benefits to both plant production and soil health. We believe the industry will indeed become more knowledge-based and the credibility of humic products will improve as (i) we learn more about their field efficacy across ranges of field conditions for improving crop yield and soil health, (ii) we gain further insights into possible mechanistic explanations, and (iii) the consumer gains the ability to discern genuine products from fraudulent materials.

Eco-restoration of a mine technosol according to biochar particle size and dose application: study of soil physico-chemical properties and phytostabilization capacities of Salix viminalis

Abstract: 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.

Preface: humic substances in the environment

Abstract: The fate of natural organic matter, and especially humic substances (HSs), has attracted increasing interests of scientists representing various disciplines over recent decades. Among the various organic substances occurring naturally, HSs are the most widespread, being present in soil, water, lake sediments, peat, brown coal, and shales. HSs represent about 25% of the total organic carbon on the earth. These substances represent a class of naturally occurring complex molecular structures, formed by aggregation and assemblage processes through which biomolecules originating from plant and animal residues are progressively transformed via biotic and abiotic pathways. The research of HSs is complex because these organic compounds are bound by, or associated with, soil mineral fractions, and require physical and/or chemical separation from the inorganic components through an extraction procedure, prior to their physico-chemical analysis. The most efficient of these separation procedures implies an extraction with alkali which operatively identifies three HSs fractions, based on their water solubility; they are:

Assessment of bacterial community composition, methanotrophic and nitrogen-cycling bacteria in three soils with different biochar application rates

Abstract: The increased use of biochar as a soil amendment to alleviate the impact of agricultural practices on climate change has been a motivation for many studies to determine the effects of biochar on soil properties, particularly the abundance and activities of soil microbes and related biological processes This study investigates the impact of different application rates of wood-derived biochar on community structure, nitrogen-cycling and methanotrophic bacteria in three soil types Biochar was added at 0, 25, 5 and 10% w/w to black clay loam (BCL, Vertosol), red loam (RL, Dermosol) and brown sandy loam (BSL, Kurosol) soils Soil chemical analysis and 16S rRNA gene amplicon sequencing using the IIlumina Mi-Seq platform were conducted on initial samples and after 10-month incubation The results indicated that the addition of biochar loading levels to the different soils had a significant impact on NH4 and NO3, total C and N, pH, electrical conductivity (EC) and soil moisture content These changes were reflected in significant differences in the bacterial diversity between biochar treatments in the BSL and RL soils, while the BCL soil was more resilient to change Complete ammonia-oxidising (Nitrospira) and nitrite-oxidising bacteria (NOB) were more abundant than standard ammonia-oxidising bacteria (AOB) in all soils Increased biochar loading raised the abundance of nitrifying bacteria in BCL soil while Nitrospira became more abundant in BSL soil Biochar addition affected the abundance of certain N2 fixer groups in a soil-dependent manner Strong positive correlations were observed in Rhizobium (r = 099) and Azospirillum abundance (r = 070) with increased biochar loading rates in BCL Greater biochar loading also significantly increased the relative abundance of methanotrophs, especially in BCL soil The impact of biochar on community structure and nitrogen-cycling bacteria depended on soil types and biochar rates which correlated to the differences in soil properties Overall, the abundance of nitrogen-cycling bacterial groups seemed to be most affected by the changes in soil conditions, including aeration, C/N ratio, nutrients and pH in relation to biochar application in different soils These changes show that short-term biochar loading influences community structure and leads to increases in populations of methanotrophic and nitrifying bacteria

Characterizing natural riparian vegetation for modeling of flow and suspended sediment transport

Abstract: Riparian vegetation imposes a critical control on the transport and deposition of suspended sediment with important implications for water quality and channel maintenance. This paper contributes (1) to hydraulic and morphological modeling by examining the parameterization of natural riparian vegetation (trees, bushes, and grasses) and (2) to the design and management of environmental channels by determining how the properties of natural floodplain plant stands affect the erosion and deposition of suspended sediment. Laboratory and field data were employed for enhancing the physical description of flow–plant–sediment interactions with a consideration of practical applicability. A drag force parameterization that takes into account the flexibility-induced reconfiguration, and the complex structure of foliated plants was validated for small natural trees under laboratory conditions, while the data from a small vegetated compound channel demonstrated the approaches at the field scale. Based on the field data, we identified three key vegetative factors influencing the net deposition and erosion on the floodplain. The significance of these factors was evaluated for vegetative conditions ranging from almost bare soil to sparse willows and dense grasses. Overall, the investigated conditions covered flexible and rigid vegetation with seasonal differences represented by foliated and leafless states. The drag and reconfiguration of woody plants were reliably predicted under leafless and foliated conditions. Subsequently, we present a new easy-to-use methodology for predicting vegetative drag and flow resistance. The methodology is based on a physically solid parameterization for five widely used coefficients or terms (Eqs. (2)–(6)), with the necessary parameter values presented for common riparian species. The methodology was coupled with existing approaches at the field scale, revealing that increasing vegetation density and the associated decreasing flow velocity within vegetation significantly increased net deposition. Further, deposition increased with increasing cross-sectional vegetative blockage and decreasing distance from the suspended sediment replenishment point. Thus, longitudinal advection was the most important mechanism supplying fine sediment to the floodplain, but long continuous plant stands limited deposition. The proposed parameterization (Eqs. (2)–(6)) can be readily implemented into existing hydraulic and morphological models to improve the description of natural vegetation compared to the conventional rigid cylinder representation. The approach is advantageous for evaluating, for example, the effects of both natural succession and management interventions on floodplains. Finally, guidance is provided on how floodplain vegetation can be maintained to manage the erosion and deposition of suspended sediment in environmental channel designs.

A comparative study to evaluate efficiency of EDTA and calcium in alleviating arsenic toxicity to germinating and young Vicia faba L. seedlings

Abstract: This study delineated the effect of calcium (Ca) and ethylenediaminetetraacetic acid (EDTA) addition on arsenic (As) accumulation and physiological attributes of Vicia faba L. Two separate experiments were performed. In the first experiment, V. faba seedlings, grown under hydroponic conditions, were exposed to three levels of As (25, 125 and 250 μM) in the presence and absence of three levels of EDTA (25, 125, 250 μM) and calcium (CaCl2: 1, 5 and 10 mM). The effect of EDTA and Ca on As accumulation and physiological attributes of V. faba was assessed by determining As contents in roots and shoot, chlorophyll contents, H2O2 contents, and lipid peroxidation in young and old leaves. In the second experiment, V. faba seeds were grown in As-contaminated sand culture using the same treatment plan. The accumulation and toxicity of As to V. faba plants increased with increasing As levels in nutrient solution. Arsenic exposure enhanced the production of reactive oxygen species (ROS) in both roots and leaves, which resulted in lipid peroxidation and decreased chlorophyll contents. The presence of both EDTA and Ca, in general, significantly decreased As accumulation by V. faba seedlings, Ca being more effective than EDTA. Both the amendments decreased As-induced reactive oxygen species (ROS) production and lipid peroxidation. In the case of chlorophyll contents, EDTA significantly decreased chlorophyll contents, while Ca significantly increased chlorophyll contents compared to As. The effect of all the treatments was more pronounced in roots than leaves and in young leaves compared to old leaves. It is proposed that EDTA and Ca greatly affect As accumulation and toxicity to V. faba, and the effect varies greatly with their applied levels as well as type and age of plant organs. The germinating seedlings of V. faba may be preferred for risk assessment studies, while transplanting 1-week-old V. faba seedlings to As-contaminated soils can decrease its toxicity.

A meta-analysis and critical evaluation of influencing factors on soil carbon priming following biochar amendment

Abstract: Previous studies have found biochar-induced effects on native soil organic carbon (NSOC) decomposition, with a range of positive, negative and no priming reported. However, many uncertainties still exist regarding which parameters drive the amplitude and the direction of the biochar priming. We conducted a quantitative analysis of 1170 groups of data from 27 incubation studies using boosted regression trees (BRTs). BRT is a machine learning method combining regression trees and a boosting algorithm, which can effectively partition independent influences of various factors on the target variable in the complex ecological processes. The BRT model explained a total of 72.4% of the variation in soil carbon (C) priming following biochar amendment, in which incubation conditions (36.5%) and biochar properties (33.7%) explained a larger proportion than soil properties (29.8%). The predictors that substantially accounted for the explained variation included incubation time (27.1%) and soil moisture (5.0%), biochar C/N ratio (6.2%), nitrogen content (5.5%), pyrolysis time during biochar production (5.1%), biochar pH (4.5%), soil C content (5.2%), sand (4.7%) and clay content (4.1%). In contrast, other incubation conditions (temperature, biochar dose, whether nutrient was added), biochar properties (biochar C, feedstock type, ash content, pyrolysis temperature, whether biochar was activated) and soil properties (nitrogen content, silt content, C/N ratio, pH, land use type) had small contribution (each < 4%). Positive priming occurred within the first 2 years of incubations, with a change to negative priming afterwards. The priming was negative for low N biochar or in high-moisture soils but positive on their reverse sides. The size of negative priming increased with rising biochar C/N ratio, pyrolysis time and soil clay content, but deceased with soil C/N ratio. We determine the critical drivers for biochar effect on native soil organic C cycling, which can help us to better predict soil C sequestration following biochar amendment.

Evaluating tracer selection for catchment sediment fingerprinting

Abstract: Recent sediment fingerprinting research has shown the sensitivity of source apportionment results to data treatments, tracer number, and mixing model type. In light of these developments, there is a need to revisit procedures associated with tracer selection in sediment fingerprinting studies. Here, we evaluate the accuracy and precision of different procedures to select tracers for un-mixing sediment sources. We present a new approach to tracer selection based on identifying and removing tracers that exhibit non-conservative behaviour during sediment transport. This removes tracers on the basis of non-conservative behaviour identified using (1) tracer-particle size relationships and (2) source mixing polygons. We test source apportionment results using six sets of tracers with three different synthetic mixtures comprising one, five, and ten mixture samples. Source tracer data was obtained from an agricultural catchment in northwest England where time-integrated suspended sediment samples were also collected over a 12-month period. Source un-mixing used MixSIAR, a Bayesian mixing model developed for ecological food web studies, which is increasingly being applied in catchment sediment fingerprinting research. We found that the most accurate source apportionment results were achieved by the selection procedure that only removed tracers on the basis of non-conservative behaviour. Furthermore, accuracy and precision were improved with five or ten mixture samples compared to the use of a single mixture sample. Combining this approach with a further step to exclude additional tracers based on source group non-normality reduced accuracy, which supports relaxation of the assumption of source normality in MixSIAR. Source apportionment based on the widely used Kruskal-Wallis H test and discriminant function analysis approach was less accurate and had larger uncertainty that the procedure focused on excluding non-conservative tracers. Source apportionment results are sensitive to tracer selection. Our findings show that prioritising tracer exclusion due to non-conservative behaviour produces more accurate results than selection based on the minimum number of tracers that maximise source discrimination. Future sediment fingerprinting studies should aim to maximise the number of tracers used in source un-mixing constrained only by the need to ensure conservative behaviour. Our procedure provides a quantitative approach for identifying and excluding those non-conservative tracers.

Humic acid and biochar as specific sorbents of pesticides

Abstract: The aim of the research was to compare the effect of two types of organic sorbents—humic acid (HA) and biochar (BC)—in sorption-desorption processes of different polar pesticides, which residues are commonly present in arable soils and are potentially harmful for the environment. It also aims to advance the understanding of behavior of both ionizable and nonionizable pesticides in the presence of BC and HA in soils. Three different classes of pesticides were investigated: carbamates (carbaryl and carbofuran), phenoxyacetic acids (2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA)), and aniline derivatives (metolachlor). Investigated humic acid was extracted by Shnitzer’s method from topsoil horizon of arable Gleyic Phaeozem. Biochar was produced from wheat straw in gasification process at 550 °C, remaining 30 s in the reactor. To obtain the experimental goal structural properties of both sorbents were determined and sorption-desorption experiments conducted. To the investigated organic matter samples (HA or BC), 10 or 15 mg L−1 pesticide solutions in 10 mM CaCl2 were added and the mixtures were shaken for 24 h. Afterwards, the samples were centrifuged and supernatants analyzed by LC-MS/MS for the pesticide content. Analogous experiment was performed for desorption studies (samples refilled with 10 mM CaCl2). Humic acids exhibited strong affinity for the ionic substances, for which high-percentage uptake (74.6 and 67.9% initial dose of 2,4-D and MCPA, respectively) was obtained. Retention of nonionic carbamates on HA was much weaker (35.4% of carbofuran and 10.2% of carbaryl sorbed). Sorption of carbamates to BC was significantly reduced (76.4–84.3%) by the alkaline hydrolysis. Metolachlor was bound comparably strong both by HA (72.9%) and BC (70.2%), although different mechanisms governed its sorption. Noticeable desorption occurred only in the case of 2,4-D bound to HA (over 50%), whereas other studied compounds were released from HA within the range of 4.4–10.8% of the dose sorbed. Oppositely to HA, desorption of all studied pesticides from BC was completely inhibited, except for 2,4-D (3.7% desorbed). Investigated humic acid has high affinity to polar, ionic pesticides of high water solubility, which are sorbed via specific interactions with HA functional groups. Studied biochar, due to its moderately hydrophobic character, preferentially attracts nonionic pesticides of relatively high logP values and low water solubility. Hydrophobic bonding is postulated as a main mechanism of their attraction to BC. Besides sorbent structural properties, pH is the main factor governing sorption equilibria in the studied mixtures.

Bibliometric analysis of insights into soil remediation

Abstract: Environmental pollution is a great concern worldwide. The soil environment, an important compartment for global elemental cycling, has received tremendous research focuses over the past 20 years. This study investigated the current research activities in the field of contaminated soil remediation and determined the trend of research topics. We performed a quantitative bibliometric analysis based on journal articles published within the past 20 years using the Science Citation Index and Social Sciences Citation Index databases on the Web of Science. To further analyze the publication performance and identify the major soil contamination topics, we employed social network analysis and S-curve predictions. Chemosphere and Journal of Hazardous Materials were the most productive journals with a total of 433 and 431 articles from 1996 to 2015 on contaminated soil remediation, respectively. China had the largest amount of publications (n = 1518) and the Chinese Academy of Science was the most prominent institution (n = 475). Keyword analysis further identified the most studied soil pollutants, such as polycyclic aromatic hydrocarbons, crude oil, and heavy metals, in the top five productive countries, including China, USA, Spain, India, and Canada. Moreover, soil remediation technologies, including microbial remediation, phytoremediation, and electrokinetic remediation, were the major technologies receiving increasing interest in the results of the prediction analysis. Our results identified the hotspots and developing trends of contaminated soil remediation studies and provide guidance for future research directions. However, transitions from the laboratory to field implementations are still required. Bibliometric analysis, combined with patent analysis, social network analysis, and S-curve prediction, is a useful tool to provide a quantitative measurement of research activities in the past and present, enabling a prediction on the future study of soil remediation.

The effect of application of organic manures and mineral fertilizers on the state of soil organic matter and nutrients in the long-term field experiment

Abstract: Soil organic matter (SOM) plays an important role in terrestrial ecosystems and agroecosystems. Changes in the agricultural sector in the Czech Republic within the past 25 years have had a negative impact on SOM content and contribute to gradual soil degradation. The aim of this study is to estimate the effect of long-term application of different mineral fertilizers (NPK) and organic manures (manure, cattle slurry) on soil chemical properties (quality of humus, available nutrients, and soil reaction). Soil samples were collected from Luvisol during two selected periods 1994–2003 and 2014–2016 from long-term field experiment carried out in Prague-Ruzyně (Czech Republic). Average annual temperature is 8.5 °C, and annual precipitations are 485 mm. Different fertilization regimes have been applied for 62 years. The crop rotation was as follows: cereals (45%), root crops (33%) and legumes (22%). Soil analysis—soil organic carbon (SOC) was determined by oxidimetric titration method. Short fractionation method for evaluation of humic substance (HS), humic acid (HA) and fulvic acid (FA) content was used. Absorbance of HS in UV-VIS spectral range was measured by Varian Carry 50 Probe UV-VIS spectrometer. Degree of humification (DH) and color index (Q4/6) were calculated from fractional composition data. Soil reaction was measured by potentiometric method. Available nutrients (phosphorus, potassium, magnesium, calcium) were determined by Mehlich II and Mehlich I methods and by ICP-OES. For data analysis, the following are used: exploratory data analysis, ANOVA, and principal component analysis (PCA). PCA analysis differentiated fertilizers into two categories: (1) variant NPK (lower quality of humus)—higher acidity, lower SOC and HS content, predomination of FA, higher DH and lower content of available nutrients; (2) variants with organic manures (higher quality of humus)—lower acidity, higher SOC and HS content, predomination of HA, middle DH, and high content of available nutrients. The main result of presented study is to give a synthesis of effect of different type of fertilizers on a sustainable organic matter management in arable soils, with respect to yields, food security and adaptation to predict climate changes. Long-term application of mineral fertilizers (NPK) without organic matter input can accelerate humus mineralization and soil quality degradation with all negative consequences such as (nitrogen leaching, higher availability of toxic element for plants, slow energy for soil microorganisms etc.). Application of organic fertilizers (manure and cattle slurry) helps to achieve the long-term stable yields while maintaining soil at optimum quality (long-term sustainable management with SOM). Principal component analysis is a useful tool for evaluation of soil quality changes.

Soil pH rather than nutrients drive changes in microbial community following long-term fertilization in acidic Ultisols of southern China

Abstract: Long-term intensive cultivation and heavy fertilization improve the nutritional conditions in acidic Ultisols, but also sharply accelerate soil acidification. However, the impact of such dramatic environmental changes on soil microorganisms is unclear. The aims of this work were to investigate the responses of microbial community composition and metabolic function to long-term fertilization, and to determine the key factors that primarily drive microbial changes in acidic Ultisols. A long-term fertilization experiment under a winter wheat–summer maize rotation was established in 1990 in acidic Ultisols of southern China. Soils were collected from four treatments in June 2014: (1) non-fertilization control (CK); (2) only N fertilization (N); (3) N, P, and K fertilization (NPK); and (4) NPK plus manure (NPKM; 70% of total N obtained from manure). The amount of N used in all N treatments was 300 kg N ha−1 year−1. The soil pH, cation exchange capacity (CEC), soil organic carbon (SOC), total nitrogen (TN), phosphorus (TP) and potassium (TK), available nitrogen (AN), phosphorus (AP), and potassium (AK) were measured. Soil microbial community composition and metabolic function were determined by phospholipid fatty acids analysis (PLFA) and community-level physiological profile (CLPP) method, respectively. Compared with CK, NPKM significantly increased total PLFA biomass and average well color development (AWCD); NPK increased total PLFA biomass by 2.2 times, but its AWCD was not significantly different from CK, indicating that microbial metabolic efficiency in NPK decreased. N decreased total PLFA biomass by 27.9%, while almost completely inhibiting metabolic activity. NPKM maintained microbial functional diversity indexes at similar levels as CK, while NPK and N significantly decreased microbial functional diversity indexes. Redundancy analysis (RDA) revealed that soil microbial community composition and metabolic pattern were more stably maintained by application of manure compared to chemical fertilizers. Soil pH showed the primary effect on microbial community composition, metabolic activity, and functional diversity indexes. This research demonstrated that the negative effects of Ultisol acidification induced by long-term application of chemical N fertilizer on microorganisms overwhelmed the positive effects of soil nutrition improvement. The inhibiting effect of serious acidification on microbial metabolic function was stronger than that on community composition. Microorganisms live in a low active metabolic state to resist serious Ultisols acidification. Therefore, fertilization in acidic Ultisols should be based on the premise of preventing soil further acidification.

Influence of organic and inorganic passivators on Cd and Pb stabilization and microbial biomass in a contaminated paddy soil

Abstract: Soil contamination with heavy metals, such as Cd and Pb, has caused severe health and environmental risks all over the world. Possible eco-friendly solutions for Cd and Pb immobilization were required to reduce its mobility through various cost-effective amendments. A laboratory incubation study was conducted to assess the efficiency of biochar (BC), zeolite (ZE), and rock phosphate (RP) as passivators for the stabilization of Cd and Pb in paddy soil as well as soil microbial biomass. Various extraction techniques were carried out: a sequential extraction procedure, the European Community Bureau of Reference (BCR), toxicity characteristic leaching procedure (TCLP) test, and single extraction with CaCl2. The impact of passivators on soil pH, dissolved organic carbon (DOC), and microbial biomass (carbon, nitrogen, and phosphorus) was examined in the metal contaminated soil. The results showed that the exchangeable portion of Cd in soil was significantly reduced by 34.8, 21.6, and 18.8% with ZE, RP, and BC at a 3% application rate, respectively. A similar tendency of reduction in Pb soluble portion was observed by ZE (9.6%), RP (20%), and BC (21.4%) at a 3% application rate. Moreover, the TCLP leachate of Cd and Pb was apparently reduced by 17 and 30.3% with BC at a 3% application dose, respectively, when compared to the control. Soil pH, nutrients, and microbial biomass C, N, and P were significantly increased with the addition of BC, RP, and ZE passivators. The results showed that the incorporation of BC, ZE, and RP significantly reduced the Cd and Pb mobility in paddy soil as well as enhanced soil nutrients and microbial biomass. Overall, among all the amendments, rice straw derived-BC performed better for Cd and Pb immobilization in paddy soil.

Qualitative and quantitative soil organic matter estimation for sustainable soil management

Abstract: The aims of this paper were to review tools and methods for qualitative and quantitative evaluation of soil organic matter (SOM) coming from diverse egzogenic sources for effective soil management, and to introduce a new approach to predict dynamics of SOM transformations, especially humification, as a key process in the formation of humic substances (HSs). A review of existing literature is presented on tools and methods for qualitative and quantitative assessment of organic matter in soil originating from various sources for reasonable soil management, attempting to provide a better understanding of the advances in organic matter transformations and new research directions for modeling. Diverse tools and methods for qualitative and quantitative evaluation of organic matter in soil coming from diverse sources have been adopted so far to express transformation processes. For the qualitative analysis of SOM and humic acids (HAs), the analytical techniques are applied, e.g., HPSEC, NMR, and ESI-FTICRMS. The quantitative analysis is done through the following parameters: humification index (HI), humification degree (HD), and humification rate (HR). These analyses indicated that because of lack of reliable data from sufficiently long-term experiments, mathematical modeling may be applied as a numerical tool for quantitative estimation and prediction of humification of SOM. The effective soil management should include soil properties as well as different functions: food production, nutrient and water cycling, storage, filtrating, buffering, biological habitat, gene pool, source of raw materials, climate regulations, heritage, platform for man-made structure. The soil utility value should be evaluated through the SOM qualitative and quantitative analysis of organic carbon and total nitrogen. Knowledge about dynamics of SOM transformations is essential, particularly in the context of stability and efficiency of different sources of organic matter applied into soil. A qualitative understanding of SOM dynamics transformations along with modeling for quantitative assessment of HS formation should be used to develop sustainable soil management. The modeling may be considered as a tool for predicting SOM humification dynamics and consequently the formation of HSs from the diverse sources. The existing archival data from a long-term experiment may be used to build and calibrate the reliable mathematical model of SOM humification. Managing of SOM remains a sound basis for maintaining soil in a good condition for optimizing productivity. The development of land management strategies to optimize both the increase of soil organic carbon levels and the recycling of nutrients from SOM needs to be a priority. This should include policy makers and other users as well.

Using laboratory Vis-NIR spectroscopy for monitoring some forest soil properties

Abstract: The development of rapid, accurate, and cost-effective methods to determine forest soil properties such as visible and near infrared (Vis-NIR) spectroscopy is important for sustainable land management. The main objective of this study was to assess the suitability of Vis-NIR spectroscopy coupled with partial least squares regression (PLSR) to determine some forest soil properties such as organic carbon (SOC), total nitrogen (TN), pH, and soil texture (sand, silt, and clay) for a representative forest area in southern Italy. Soil samples (0–20 cm depth) were collected at 267 locations, oven-dried and passed through a 2-mm sieve, and analyzed for some chemical and physical soil properties using conventional laboratory methods. Vis-NIR reflectance of each soil sample was measured in laboratory under artificial light using an ASD FieldSpec IV 350–2500 nm spectroradiometer. Partial least squares regression (PLSR) was used to develop a calibration model for SOC, TN, pH, sand, silt, and clay. Samples were split into a calibration set (187 samples) to develop the models and a validation set (80 samples) to assess the prediction accuracy of the calibration models. Results showed a good agreement between measured and predicted values with high R 2 and low root mean square error (RMSE) values. Model validation using independent data was satisfactory for all the studied soil properties. Finally, findings confirmed that laboratory Vis–NIR spectroscopy has the potential to be a non-destructive and cost-effective tool for rapid determination of many soil properties. The spectral data collected in this study could contribute to build a regional soil spectral library to be used advantageously in support to soil survey in other areas of the Calabria region (southern Italy).

Mixed chelators of EDTA, GLDA, and citric acid as washing agent effectively remove Cd, Zn, Pb, and Cu from soils

Abstract: Soil washing with chelators is a viable treatment alternative for remediating multi-contaminated soils. The aim of this study was to investigate the removal efficiencies of Cd, Zn, Pb, and Cu in alkaline and acid multi-metal-contaminated soils by washing with the mixed chelators (MC). The batch experiments were carried out to evaluate the removal efficiencies of heavy metals in contaminated soils by the MC with different molar ratios of EDTA, GLDA, and citric acid, and evaluated the washing factors, including contact time, pH, MC concentration, and single and multiple washings at the same MC dose, on the removal efficiencies. Results showed that the removal efficiencies for Cd, Zn, Pb, and Cu by the MC (the molar ratio of EDTA, GLDA, and citric acid was 1:1:3) were as much as those of the only EDTA washing from both soil at the same application dose of total chelators; moreover, the application dose of EDTA decreased by 80%. For the alkaline-contaminated soil, the removal efficiencies of Cd, Zn, Pb, and Cu decreased with the increasing of the solution pH, which was opposite to acid-contaminated soil. This was attributed to that the metal-ligand complex could be obviously re-adsorbed on the soil surface sites, particularly in low pH values. The removal efficiencies of Cd, Zn, Pb, and Cu depended on MC concentration. A higher MC concentration led to a more effective removal of Cd, Zn, Pb, and Cu in alkaline-contaminated soil; however, their changes were slightly increased in acid-contaminated soil. At the same dose of MC, single washing with higher MC concentration might be favorable to remove heavy metals, moreover, with much less wastewater generation. The MC (the molar ratio of EDTA, GLDA, and citric acid was 1:1:3) may be a useful, environmentally friendly, and cost-effective chelators to remediate heavily multi-metal-contaminated soil.

Superabsorbent polymers influence soil physical properties and increase potato tuber yield in a dry-farming region

Abstract: Superabsorbent polymers, new water-saving materials and soil conditioners, are used widely in dry-farming agriculture. However, little is known about their effects on the soil physical properties under dry-farming conditions. To elucidate the effects of two SAPs (Wote and microbe) at different doses on the soil bulk density, water status, potato growth, yield, and economic benefit in a dry-farming region, we conducted a 2-year fixed field position experiment in the semiarid drought-prone area of Ningxia, China. The two SAPs were diluted 1:10 (product:soil) and applied at different rates before planting, i.e., Wote SAP 30 kg ha−1, Wote SAP 60 kg ha−1, Wote SAP 90 kg ha−1, microbe SAP 30 kg ha−1, microbe SAP 60 kg ha−1, and microbe SAP 90 kg ha−1. The treatment without SAP was used as the control. The tilth soil bulk density decreased under different SAP doses compared with the control, and the soil total porosity improved greatly, where the Wote SAP treatments had the greatest effects. The soil bulk density (0–60 cm) under Wote SAP 90 kg ha−1 was significantly decreased by 6.4% compared with the control. The Wote SAP treatments had the greatest effects on water conservation during the critical potato growth stage, where the soil water storage (0–100 cm) was significantly higher than the control. The Wote SAP treatments promoted potato growth in the later period, where the plant height and stem diameter were higher than the control. Higher yield and commodity rate improvements were achieved by the application of Wote and microbe SAP compared with the control, where the optimum dose was 60–90 kg ha−1 for Wote SAP. The application of Wote SAP 90 kg ha−1 significantly increased crop water use efficiency compared with no SAP, and the commodity rate was highest with Wote SAP 60 kg ha−1. The mean potato yield, commodity rate, and net income increased significantly using Wote SAP at 60 and 90 kg ha−1, i.e., by 38.2 and 50.5%, 18.5 and 14.1%, and 28.5 and 35.0%, respectively, compared with no SAP. The application of SAPs can decrease soil bulk density and significantly improve soil porosity and soil water conservation capacity, thereby promoting potato growth. The application of Wote SAP 60–90 kg ha−1 significantly increased potato yield and net income in a dry-farming region of Ningxia, China.

Evaluation of the possibilities of using humic acids obtained from lignite in the production of commercial fertilizers

Abstract: Technological progress and high market demand contributed to a significant interest in the production of fertilizers based on humic acids. The aim of this study was to evaluate the possibilities of using humic acids obtained from lignite in the production of new commercial products. For this purpose, it is necessary to determine the quality standard requirements for such material. Properties of humic acids depend on source of origin as well as method of its extraction. The humic acids were extracted from polish deposit of lignite–Sieniawa Lubuska by alkaline extraction using for this purpose six kinds of extractants: 0.1 M NaOH and 0.25 M NaOH, 0.1 M KOH and 0.25 M KOH, and 0.1 M Na4P2O7 and 0.25 M Na4P2O7. The humic samples were used in solid powder form and characterized by UV-Vis spectroscopy, 13C NMR spectroscopy, fluorescence spectroscopy, and thermal analysis. The determining factor influencing a degree of humic acids extraction from lignite and their structure is type of extractant. The largest efficiency of extraction (about 50%) was obtained with the use of NaOH solutions. All examined humic acids were generally characterized by simple and heterogeneous molecularly structure with low molecular weight and low aromatic polycondensation. Therefore, it can be concluded that humic acids extracted with NaOH and KOH solutions are less condensed than those extracted with Na4P2O7 solutions. It can suggest that humic acids obtained from lignite using solutions of Na4P2O7 are characterized by a low transformation degree and greater amount of carboxyl groups. Low rank coal can be successfully used in agriculture as a rich source of humic acids. Reagent used in their extraction, apart from high efficiency should have a neutral impact on their structure. Studies on the physicochemical properties of humic acids can be helpful in predicting behaviors of such fertilizer components in the environment and in inventing new products taking the principles of sustainable development into consideration.

Distribution and risk assessment of heavy metals in overlying water, porewater, and sediments of Yongding River in a coal mine brownfield

Abstract: Heavy metals from coal mines migrate into rivers and cause a severe impact on the health of local residents utilizing these rivers as a water source. However, current studies on coal mine brownfields have yet to thoroughly investigate river-associated heavy metals produced by coal mining. Therefore, this study aims to explore the distribution and risk assessment of heavy metals, namely Cr, Cu, Mn, Ni, Pb, and Zn, in overlying water, porewater, and sediments of the Yongding River, China. Overlying water, porewater, and sediments were sampled at 11 sites along the Yongding River. Heavy metal concentrations were determined through ICP-MS, and sediments were subjected to a three-step sequential extraction procedure to verify the behavior of heavy metals through principal component analysis (PCA). Sediments were separated into seven size fractions (< 4, 4–8, 8–16, 16–75, 75–150, 150–250, and 250–840 μm) with sedimentation method based on Stokes’ law. The characteristics of heavy metal distribution in different particle sizes were also explored using the Tucker 3 method. Interstitial water criteria toxic units (IWCTUs) were used to assess porewater heavy metal pollution. Risk assessment code (RAC), sediment quality guidelines (SQGs), and pollution load index (PLI) were applied to evaluate the ecological risk of heavy metals in sediments. Heavy metal concentrations increase in the following sequence: overlying water < porewater < sediment. Lead and Zn in porewater are higher than the criteria maximum concentrations (CMCs). The IWCTUs of Pb and Zn indicate their possible risk of toxicity. Principal component analysis reveals that Mn in sediments is preferentially associated with the exchangeable fraction, Cu and Zn are mainly associated with the reducible fraction, and Cr, Ni, and Pb are strongly related to the residual fractions. Heavy metals in sediments mainly accumulate in the fine fractions (< 4, 4–8, and 8–16 μm). Nickel, Pb, and Zn in sediments occasionally cause adverse biological effects. Overall, PLIs of sediments at sites 1, 4, and 10 in the Yongding River show moderate pollution due to Cr, Cu, Mn, Ni, Pb, and Zn. Different heavy metals possess unique partition coefficients between overlying water and sediments because these metals exhibit various properties and mobility. The chemical fractions of heavy metals also confirm the partition coefficients. Heavy metals in fine sediment fractions also enhance their migration and occasionally cause severe biological effects. Therefore, drinking water security in these areas should be ensured.

Spatial distribution and source apportionment of the heavy metals in the agricultural soil in a regional scale

Abstract: Understanding the spatial distribution and sources of soil heavy metals (HMs) in a large city helps prevent and control soil pollution. This study aimed to investigate the spatial patterns of soil HMs and identify their main sources in a regional scale. A total of 110 topsoil samples were collected from Tai’an City, China. Cd, Cr, Cu, Hg, Ni, Pb, and Zn concentrations in each soil sample were determined. Geostatistics, geographic information system (GIS), and positive matrix factorization (PMF) were used to explore the spatial distribution of seven soil HMs and to reveal the main sources of soil HMs in Tai’an City, respectively. Soil Cd, Cr, Pb, and Zn generally showed slight pollution levels in the study area. However, soil Hg and Cu contents reached moderate to heavy pollution levels in some areas. Soil Hg content increased from north to south across the city, and the highest Hg concentration was detected in Ningyang County. Soil Cd, Cu, and Zn distributions exhibited a similar pattern, and their contents increased from west to east; the highest Cd, Cu, and Zn concentrations were found in Xintai County. The highest soil Ni concentration was obtained in the northeast of Feicheng and Xintai counties. PMF analysis revealed the following four potential sources of agricultural soil HMs in Tai’an City: industrial and mining activities, agricultural activities, residential living activities, and business activities. Soil Hg mainly originated from residential living activities, which accounted for 75.3% of the total source. The main sources of soil Ni were residential living activities, agricultural activities, and industrial and mining activities, which account for 38.2, 27.50, and 25.1% of the total source, respectively. Soil Cu was mainly produced by agricultural activities (36.6%), followed by residential living activities (29.8%) and industrial and mining activities (25.8%). PMF combined with GIS could be effectively applied to determine the main sources of HMs in agricultural soils in a regional scale.

Urban soil resources of medium-sized cities in Poland: a comparative case study of Toruń and Zielona Góra

Abstract: Despite the many studies of urban soils, a comparative analysis for cities of a similar size has not yet been conducted. Thus, the aim of this review paper was to compare the soil distribution patterns in the area of two medium-sized Polish cities (Torun and Zielona Gora). The authors attempted to answer the question of how natural and technogenic factors contributed to the transformation of urban soils and what the similarities and differences are between these two studied cities. First, both the natural and the human-related (including historical) factors influencing the soil formation in the studied cities were analysed. Then, a comparison of the degree of transformation of the urban soil environment was presented. The data obtained by the authors during nearly two decades of research (over 200 soil profiles) were used. Intensive development of the built-up areas in Torun brought heavy and long-term transformations of soils, which demonstrate the typical properties of Urbic Technosols, Ekranic Technosols and other technogenic soils. Zielona Gora showed a similar state of soil transformation over a considerably smaller area. Currently, the differences in the soil properties in many built up areas have been blurred, despite the habitat and historical base. The similarities of the soil properties concerned, in particular, a high content of skeletal remains (from a few to over 30%), elevated pH (in KCl) values (even above 8.0) and the artificial soil horizons formation. Both cities struggle with similar problems regarding the changes in the land use within the areas covered by these soils. It was found that, despite the significant habitat and historical differences between the two studied cities, most of the urban soils, especially Urbic Technosols, Ekranic Technosols and Regosols (Relocatic and Technic), are characterised by similar morphology and properties. The most important differences are the time and scale of the area transformation, which influence the extent of Technosols and Anthrosols within the city borders. The most distinct differences concern the natural and slightly transformed soils, which are the results of various soil-forming factors.

Prediction of soil and water conservation structure impacts on runoff and erosion processes using SWAT model in the northern Ethiopian highlands

Abstract: Land degradation due to soil erosion is a serious threat to the highlands of Ethiopia. Various soil and water conservation (SWC) strategies have been in use to tackle soil erosion. However, the effectiveness of SWC measures on runoff dynamics and sediment load in terms of their medium- and short-term effects has not been sufficiently studied. A study was conducted in 2011 to 2015 in the Gumara-Maksegnit watershed to study the impacts of SWC structures on runoff and soil erosion processes using the soil and water analysis tool (SWAT) model. The study was conducted in two adjacent watersheds where in one of the watersheds, SWC structures were constructed (treated watershed (TW)) in 2011, while the other watershed was a reference watershed without SWC structures (untreated watershed (UW)). For both watersheds, separate SWAT and SWAT-CUP (SWAT calibration and uncertainty procedure) projects were set up for daily runoff and sediment yield. The SWAT-CUP program was applied to optimize the parameters of the SWAT using daily observed runoff and sediment yield data. The runoff simulations indicated that SWAT can reproduce the hydrological regime for both watersheds. The daily runoff calibration (2011–2013) results for the TW and UW showed good correlation between the predicted and the observed data (R 2 = 0.78 for the TW and R 2 = 0.77 for the UW). The validation (2014–2015) results also showed good correlation with R 2 values of 0.72 and 0.70 for the TW and UW, respectively. However, sediment yield calibration and validation results showed modest correlation between the predicted and observed sediment yields with R 2 values of 0.65 and 0.69 for the TW and UW for the calibration and R 2 values of 0.55 and 0.65 for the TW and UW for the validation, respectively. The model results indicated that SWC structures considerably reduced soil loss by as much as 25–38% in the TW. The study demonstrated that SWAT performed well for both watersheds and can be a potential instrument for upscaling and assessing the impact of SWC structures on sediment loads in the highlands of Ethiopia.

Labile organic carbon fractions and carbon pool management index in a 3-year field study with biochar amendment

Abstract: The aims of this research were to (i) systematically investigate the soil organic carbon (SOC) and labile SOC fraction dynamics over a period of 3 years under biochar amendment, (ii) reveal the relations of labile SOC fractions to SOC, and (iii) evaluate the sensitivity of SOC to biochar added at different rates by determining C pool management index (CPMI). The SOC, labile SOC fractions, and the CPMI in the 0–20-cm layer were analyzed via a 3-year field experiment of maize. Four biochar treatments were studied, with application rates of 0, 15.75, 31.5, and 47.25 t ha−1 (CK, BC1, BC2, and BC3, respectively). Biochar was applied manually before sowing only in the first year of this experiment; an equal mineral NPK fertilizer was applied to each treatment annually. The average data of this 3-year field study demonstrated that biochar incorporation significantly increased SOC, particulate organic carbon (POC), easily oxidizable carbon (EOC), light fraction organic carbon (LFOC), and microbial biomass carbon (MBC) by 31.75–83.62, 92.72–323.30, 29.90–51.55, 194.30–437.37, and 31.13–93.12%, respectively, compared to the control; their concentrations increased with increasing biochar addition rates, except for MBC. In addition, EOC, POC, and LFOC were significantly positively related with SOC. Compared to the control, the DOC contents were reduced after biochar addition, but the specific reasons for this finding need to be further studied. Biochar incorporation could not only significantly improve the soil quality via increasing the soil organic C fractions, but also increase C sequestration rates in the long term by increasing the non-labile C pool (NLC). The CPMI could be used as a representative index in evaluating the impacts of biochar on SOC content and soil quality.

Biochar and biochar with N fertilizer as a potential tool for improving soil sorption of nutrients

Abstract: Biochar usually has a large specific surface area, and due to this, it increases the sorption capacity of the soil where it was applied. The objectives of this study were to (i) quantify the effects of biochar and biochar in combination with N fertilizer on the soil sorption parameters and (ii) quantify the effects of soil organic matter on the sorption parameters after application of biochar with and without N fertilizer. The experiment was established on Haplic Luvisol at the locality of Dolna Malanta (Slovakia) in 2014. The soil samples were collected once a month from the depth 0–0.2 m during 2014 to 2016. The field experiment included three rates of biochar application (B0 = no biochar, B10 = biochar at the rate of 10 t ha−1, B20 = biochar at the rate of 20 t ha−1) and three levels of N fertilization (N0 = no nitrogen, N40 = nitrogen at the rate of 40 kg ha−1, N80 = nitrogen at the rate of 80 kg ha−1). Overall, the decrease of the average values of hydrolytic acidity due to biochar and biochar combined with N fertilization resulted on average in an increase of sum of basic cation (SBC), cation exchange capacity (CEC), and sorption capacity of soil organic matter (CECSOM) in all treatments. However, this effect was the most intensive in B10N40. Despite the fact that the average values of sorption parameters improved, its dynamics during the investigated period were different. A significant decrease in CEC was observed from 2014 to 2016 in all treatments, except B0N0 and B10N0. A stable trend in CECSOM was observed only in B10N40. Humic substances and humic acids had a statistically significant positive effect on the SBC, CEC, and CECSOM only in B20N0 treatment. Negative correlations between the above mentioned parameters were observed in B10N80 treatment. We conclude that the application of biochar and biochar combined with N fertilization had a positive influence on sorption parameters. However, its effects on SBC, CEC, and CECSOM decreased over time after its application.