Showing papers in "Journal of Soils and Sediments in 2020"

Sediment source fingerprinting: benchmarking recent outputs, remaining challenges and emerging themes

Abstract: This review of sediment source fingerprinting assesses the current state-of-the-art, remaining challenges and emerging themes. It combines inputs from international scientists either with track records in the approach or with expertise relevant to progressing the science. Web of Science and Google Scholar were used to review published papers spanning the period 2013–2019, inclusive, to confirm publication trends in quantities of papers by study area country and the types of tracers used. The most recent (2018–2019, inclusive) papers were also benchmarked using a methodological decision-tree published in 2017. Areas requiring further research and international consensus on methodological detail are reviewed, and these comprise spatial variability in tracers and corresponding sampling implications for end-members, temporal variability in tracers and sampling implications for end-members and target sediment, tracer conservation and knowledge-based pre-selection, the physico-chemical basis for source discrimination and dissemination of fingerprinting results to stakeholders. Emerging themes are also discussed: novel tracers, concentration-dependence for biomarkers, combining sediment fingerprinting and age-dating, applications to sediment-bound pollutants, incorporation of supportive spatial information to augment discrimination and modelling, aeolian sediment source fingerprinting, integration with process-based models and development of open-access software tools for data processing. The popularity of sediment source fingerprinting continues on an upward trend globally, but with this growth comes issues surrounding lack of standardisation and procedural diversity. Nonetheless, the last 2 years have also evidenced growing uptake of critical requirements for robust applications and this review is intended to signpost investigators, both old and new, towards these benchmarks and remaining research challenges for, and emerging options for different applications of, the fingerprinting approach.

Antibiotics in poultry manure and their associated health issues: a systematic review

Abstract: Antibiotics are growing environmental contaminants leading to public health concern. Antibiotics are commonly used as growth promoters and therapeutic agents in poultry feed that are not completely metabolized in the body tissues of chicken, get deposited in meat as parent compounds, and ultimately excreted via poultry droppings into the environment. These antibiotics in the soil result into the creation of antibiotic resistance in bacteria via activation of antibiotic resistance genes (ARGs). The development of ARGs and antibiotic-resistant bacteria (ARB) lead to huge physical and economic losses, as these bacteria cannot be treated with commonly used antibiotics. Moreover, these antibiotics after entering into food chains seriously affect the human immune system, growth, and metabolism of the body. Therefore, to reduce the future health risks of antibiotics, there is a dire need to understand the fate of poultry antibiotics and spread of ARGs in the soil environment. In this manuscript, we reviewed the existing literature about the antibiotics used in the poultry sector, soil contamination through application of poultry manures, and development of ARB in environment. An attempt has been done to present a better understanding of emerging contaminants (ARGs, ARB) in the soil environment and their associated human health effects. In this paper, we summarized the use of antibiotics in the poultry sector, persistence of antibiotics in animal body, and their release into environment. Transfer mechanism of antibiotics and their metabolites to the human body and their fatal effects have been investigated. Developments of ARB and ARGs in the soil due to excessive use of veterinary antibiotics have been highlighted. Poultry antibiotics are causing human health risks by development of ARGs and ARB. Such antibiotic resistance cannot be treated with common antibiotics. Therefore, effective measures are needed to control this emerging problem by improving the efficiency of antibiotics, reducing the spread of resistance genes, and proper monitoring of antibiotics in poultry feed and manure. Manure composting and biochar application are the possible ways to reduce the risk and spread of ARGs in environment due to manure application in agriculture field. The pathways that allow antibiotic, ARGs, and ARB to move through the environment are not fully understood and there is a need for further research to make clear the reservoirs and routes of antibiotic-related contaminants in the ecosystem.

Soil erosion and sediment dynamics in the Anthropocene: a review of human impacts during a period of rapid global environmental change

Abstract: Humanity has been modifying the planet in a measurable way for thousands of years. Recently, this influence has been such that some feel we are in a new geological epoch, the Anthropocene. This review will describe how soil erosion and sediment dynamics have (i) been used to assess the impact of humans on the planet and (ii) affected the global climate and influenced water security. Emphasis is placed on changes since the middle of the twentieth century, as this coincides with what many suggest is the start of the Anthropocene Epoch. The use of sediment archives has been instrumental in our understanding of how environmental systems have developed over time, both naturally and in response to anthropogenic activities. Additional information has come from measurement and monitoring programs, and tracing and fingerprinting studies. In turn, models have been developed that enable forecasting. Some of the main global impacts of enhanced soil erosion and changes in sediment dynamics and sediment composition include: changes in radiative energy balances and impacts on the cryosphere; the global carbon cycle; and greenhouse gas emissions. Impacts on water security include: effects on freshwater biota, including wild salmon populations; fluxes of contaminants, including microplastics; and reservoir and river channel sedimentation, including flooding. Sediment archives and monitoring programs have also been used to document the effect of mitigation measures and environmental policies. Sediment archives enable us to assemble information over a variety of timescales (i.e., 100 to 105 years and longer) and a range of spatial scales (from sub-watershed to continental), in addition to environments ranging from arid to tropical to polar. Often the temporal resolution is better than other paleoenvironmental reconstruction approaches. As such, sedimentary records, when combined with measurement and monitoring approaches and other sources of information, have enabled us to determine changes in atmospheric, terrestrial, and aquatic systems, especially over the last 100 years. While soil erosion and sediment dynamics have provided a wealth of information and greatly enhanced our understanding of the role of humanity in modifying the planet, suggestions are given for further research.

An effective biochar-based slow-release fertilizer for reducing nitrogen loss in paddy fields

Abstract: As a carbon sequestration material, biochar has attracted much attention due to its potential to enhance rice productivity and nitrogen retention in paddy fields. However, little information is available about the impacts of rice straw-derived biochar on coating materials of slow-release fertilizers especially with bentonite, starch, and humic acid. In this study, a biochar-based slow-release fertilizer was developed and evaluated at field scale. An orthogonal experimental design was applied to investigate the blending ratios of biochar, humic acid, and bentonite with three adhesives, and how these influenced N release. The optimum coating combination was 25% biochar, 4% bentonite, and 10% humic acid with modified cornstarch as the adhesive (herein referred to as CF10). The product not only decreased N leaching and runoff losses at the seeding and tillering stages but also supplied more nutrients to the rice at the heading and maturing stages. The SEM and FT-IR observations revealed that an effective dense layer was formed that slowed N release from the granule. Laboratory- and field-scale studies showed that biochar has played a crucial role in developing a slow-release coating for the compound fertilizer based on its structural properties, porosity, and chemical interaction with other coating ingredients. We conclude that biochar-based slow-release fertilizer is a promising alternative N fertilizer for rice production.

Characterization of phosphorus engineered biochar and its impact on immobilization of Cd and Pb from smelting contaminated soils

Abstract: Biochar has been used as an amendment to immobilize toxic metals (TMs) and increase nutrient content in the contaminated soil. In this study, Ca(H2PO4)2-engineered swine manure biochar (PSMB) and swine manure biochar (SMB) were prepared and investigated to evaluate their effects on the availability of toxic metals (Cd and Pb) and soil nutrient content in Fengxian (FX)- and Kunming (KM)-contaminated soils through incubation experiment. The soil samples were collected at 0–20 cm depth from two contaminated farmlands close to abandoned Pb smelters, which are located in FX and KM. Swine manure was obtained from the rural hog lot in Yangling, China. Each biochar (SMB and PSMB) was mixed with the air-dried soil samples (FX and KM) at a dosage of 1% and 3% w/w, respectively. Then, a portion of 3 kg of the mixture was placed in plastic pots and incubated for 30 days in a greenhouse. After the soil incubation experiment, pot experiments were performed in a greenhouse of Northwest A&F University, Yangling, China. Adding PSMB at a rate of 3% maximally decreased the concentrations of DTPA-extractable Cd (34.02 and 47.73%) and Pb (18.70 and 24.58%) in FX and KM soil. The BCR data revealed that the percentage of acid-soluble Cd and Pb fraction in FX and KM soils remarkably decreased whereas the percentages of residual Cd fraction and reducible Pb fraction in FX and KM soils significantly increased in all the biochar-amended soils compared with control. To confirm these results, a pot experiment was conducted to investigate the effects of amendments on growth and uptake of toxic metals in Chinese cabbage (Brassica rapa L. spp. pekinensis). The results showed that the addition of PSMB3% significantly (P < 0.05) increased the biomass of plants and reduced the absorption of toxic metals in plant. The results revealed that the dry biomass increased and the absorption of toxic metals decreased in plants. All treatments of biochar were beneficial and application of PSMB 3% was most effective in enhancing plant biomass and reducing the accumulation of toxic metals in the plants.

Sustainable reuse of dredged sediments as pavement materials by cement and fly ash stabilization

Abstract: The process of removing sediments from the bottom of dams generates large amounts of dredged sediments, which are considered waste. The purpose of this research was to present the results of testing conducted on dredged sediment stabilized with ordinary Portland cement (OPC) and fly ash (FA) for reuse as pavement materials. The base sediment was high plasticity silt (MH) based on the Unified Soil Classification System (USCS). The experiments in this study consisted of unconfined compression (UC), California bearing ratio (CBR), and resilient modulus (Mr) tests on stabilized dredged sediment. A combination of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) was used to investigate the microstructures of the stabilized specimens. Finally, a simple comparative cost analysis between roads using conventional earthen materials and stabilized dredged sediment was performed. The results showed that the unconfined compressive strength (qu), CBR, and Mr improved the pavement materials from unsuitable to suitable, and a 10% FA content provided the optimal strength enhancement. The SEM images showed that the calcium silicate hydrate (CSH) product, which was formed by hydration and pozzolanic reactions, attached to the clay clusters and filled the pore spaces between clay particles, resulting in a denser sediment structure. The EDX analyses showed that the calcium weight proportion and the silica-aluminum ratio were important factors in improving the strength of the dredged sediment treated with OPC and FA. These EDX results agreed with the qu, CBR, and Mr results. For the studied situation, roads using stabilized sediment were 1.5 times more economical than roads using conventional earthen pavement materials. Dredged sediments treated with OPC and FA can be sustainably reused as pavement materials based on the Department of Highways of Thailand standard, as well as the recommendations of Austroads (2017). Thus, for suitable sediments, reuse in road and pavement construction may be considered with appropriate treatment and conditioning.

Soil and microbial biomass stoichiometry regulate soil organic carbon and nitrogen mineralization in rice-wheat rotation subjected to long-term fertilization

Abstract: Soil microbial biomass (SMB), as the source and sink of soil nutrients, and its stoichiometry play a key role in soil organic carbon (SOC) and nitrogen (N) mineralization. The objective of this study was to investigate the responses of SOC and N mineralization to changes in microbial biomass and SOC, N, and phosphorus (P) stoichiometry resulted from long-term fertilization regimes. Soil was sampled from a rice-wheat rotation system subjected to 37 years of nine fertilization treatments with different nutrient input amounts: control (CK), N alone, N combined with mineral phosphorus (NP), NP plus potassium (NPK), manure alone (M), and M combined with N (MN), NP (MNP), NPK (MNPK), and a higher rate of M with NPK (hMNPK). The sampled soil was incubated for the determination of SOC and N mineralization, C, N, and P stoichiometry of soil and SMB, and associated soil enzymes related to C and N cycling. Relative to the CK and treatments with mineral fertilizers, treatments with manure (M, MN, MNP, MNPK, and hMNPK) significantly increased SOC and N mineralization by 48–78% and 54–97%, respectively. Microbial metabolic quotient (qCO2) decreased by 32–55% in treatments with manure compared to the N and NP treatments, but showed no effect on the qCO2 when compared to the NPK treatment. The leucine amino peptidase (LAP) enzyme showed significant positive correlation with SOC and N mineralization, and negatively related to the qCO2. Significantly negative correlations were also observed between SOC and N mineralization and soil C:P and N:P ratio, as well as microbial biomass SMBC:SMBP and SMBN:SMBP stoichiometry, respectively. However, the availability of N and P had limited effects on the qCO2 after reaching a certain value (0.69–0.72 mg CO2-C g−1 MBC h−1). Lower soil elemental (C:P and N:P) and microbial biomass stoichiometry (SMBC:SMBP and SMBN:SMBP) and increase of LAP resulted from combined application of manure and mineral fertilizers, accelerated SOC, and N mineralization. Mineral nutrient input with manure amendments could be an optimal strategy to meet the microbial stoichiometric demands and enhance nutrient availability for crops in agricultural ecosystems.

Translocation and accumulation of heavy metals in Ocimum basilicum L. plants grown in a mining-contaminated soil

Abstract: The evaluation of the ecotoxicity effects of some heavy metals on the plant growth and metal accumulation in Ocimum basilicum L. cultivated on unpolluted and polluted soils represented the objective of the present study. The basil aromatic herb was evaluated in a laboratory experiment using soil contaminated with Cd, Co, Cr, Cu, Ni, Pb, and Zn, similar to the one from a mining area. The soils and different organs of the basil plants were analyzed, the total contents of the added elements being determined using inductively coupled plasma optical emission spectrometry. The ability of basil plants to accumulate metals from soil and to translocate them in their organs was evaluated by transfer coefficient, translocation factor, enrichment factor, and geo-accumulation index determinations. The basil plants grown in the metal-polluted soil showed stimulation effects comparing with the plants from the control soil. At the end of the exposure period, the plants had a visible increase of biomass and presented inflorescences and the leaves’ green pigment was intensified. The metals gathered differently in plant organs: Cd, Co, Cr, and Pb were accumulated in roots, while Cu, Ni, and Zn in flowers. Cr and Pb exceeded the toxic levels in roots. Also, the heavy metal intake depends on the plant development stages; thus, Cd, Cr, and Pb were accumulated more in mature plant leaves. The Cd and Pb contents were higher than the World Health Organization and European Commission permissible limits. The experimental results revealed that the basil plants exposed to a mixture of heavy metals have the potential to reduce the metal mobility from soil to plants. Translocation process from roots to flowers and to leaves was observed for Cu, Ni, and Zn, emphasizing a competition between metals. The calculated bioaccumulation factors were insignificant, but Cd and Pb concentrations exceeded the legal limits in the mature plants, being restricted for human or animal consumption.

Soil nutrients and heavy metal availability under long-term combined application of swine manure and synthetic fertilizers in acidic paddy soil

Abstract: Fertilization is a vital approach to increase the crop yield by enhancing soil fertility, but some of the fertilizer sources such as pig manure contain non-essential toxic heavy metals, which can produce the environmental and public health risk. Therefore, the purpose of this study was to investigate the soil fertility and heavy metal pollution risk under long-term fertilization in acidic paddy soil. Fertilizer treatments that were arranged in randomized complete block design (RCBD) included CK (no fertilization), NK (inorganic nitrogen and potassium fertilization), NPK (inorganic NK and phosphorus fertilization), NPKM1 (70% of NPK and 30% pig manure application), NPKM2 (50% of NPK and 50% of pig manure application), and NPKM3 (30% of NPK and 70% of pig manure application). The rice grain yield and soil nutrient contents were highest under NPKM3 treatment. Long-term addition of manure significantly (P ≤ 0.05) increased soil pH and SOC content compared to the NPK fertilization. Soil available and total Cr, Cd, and Hg contents were highest under NPKM3 treatments, while soil total and available Pb content was significantly (P ≤ 0.05) higher under NPK treatment. Highest ecological risk (IR) was (1904) under NPK treatment and highest pollution load index (PLI) was 1.5 under NPKM3 treatment. Cd concentration in rice grain exceeded the maximum permissible limit of 0.1 mg kg−1 under combined application of manure and inorganic fertilization treatments. Grain Cr, Hg, and Pb contents were within safe limits of their concentration in all treatments. Moreover, biological accumulation coefficients of Cr, Cd, Hg, Pb, Zn, and Cu were highest under NPK treatment. Redundancy analysis (RDA) showed that soil pH and nutrient contents showed significant correlation with heavy metal concentrations in soil. Soil pH showed significant (P ≤ 0.05) positive effect on Cd accumulation in rice grain. Heavy metals in pig manure should be monitored before application to the field to reduce the risk of heavy metal pollution in soil and plant. Furthermore, combined application at the rate of 70% inorganic fertilization and 30% of manure could be better strategy to produce high crop yield with minimum risk of heavy metal contamination in soil and food crops.

Rheological analysis of mud from Port of Hamburg, Germany

Abstract: An innovative way to define navigable fluid mud layers is to make use of their rheological properties, in particular their yield stress. In order to help the development of in situ measurement techniques, it is essential that the key rheological parameters are estimated beforehand. Is there only one yield stress? In which shear rate/shear stress range is yield expected to occur? How is yield stress dependent on depths and locations in the harbor? In order to answer these questions, we investigated the changes in the rheological properties of mud from along the river stream in the Port of Hamburg, Germany, using a recently developed laboratory protocol. In this study, a detailed rheological analysis was carried out on the mud samples collected from different locations and depths of the Port of Hamburg. A variety of rheological tests was performed including: stress sweep tests, flow curves, thixotropic tests, oscillatory amplitude, and frequency sweep tests. The yield stresses of sediments from different locations were significantly dissimilar from each other due to differences in densities and organic matter content. Two yield stresses (termed static and fluidic) were observed for every sample and linearly correlated to each other. The thixotropic studies showed that all mud samples, except from one location, displayed a combination of thixotropic and anti-thixotropic behaviors. The results of frequency sweep tests showed the solid-like character of the sediments within the linear viscoelastic limit. The yield stresses, thixotropy, and moduli of the mud samples increased by going deeper into the sediment bed due to the increase in density of the sediments. This study confirmed the applicability of the recently developed protocol as a fast and reliable tool to measure the yield stresses of sediments from different locations and depths in the Port of Hamburg. The fluid mud layer, in all the locations it was observed, exhibited relatively small yield stress values and weak thixotropic behavior. This confirms that despite the fact that rheology of fluid mud is complex, this layer can be navigable.

Polyphosphate fertilizers increased maize (Zea mays L.) P, Fe, Zn, and Mn uptake by decreasing P fixation and mobilizing microelements in calcareous soil

Abstract: Polyphosphate (Poly-P) is an alternative source of phosphate (P) fertilizer. However, as a condensed P, the effects of different polymerization content of poly-P on crop P nutrition status are often inconsistent. The aims of this study are to explore the transformation of fraction and the fate of poly-P in calcareous soils with ammonium polyphosphate (APP) of different polymerization content as P resource that reveal the effects of different polymerization content of poly-P fertilizer on maize growth (Zea mays L.), soil available P, Fe, Zn, and Mn, and soil inorganic P transformation. A pot experiment was carried out with four treatments: (і) no phosphate fertilizer (control); (іі) mono-ammonium phosphate (MAP); (ііі) APP with averaging polymerization degrees of 3 and poly-P/total-P of 70% (APP-3-70%); (іv) APP with averaging polymerization degrees of 3.8 and poly-P/total-P of 90% (APP-3.8-90%). Concentrations of soil available Fe, Zn, and Mn were determined by inductively coupled plasma-atomic absorption spectroscopy procedure. Soil inorganic P species were determined by sequential extraction method. Compared with the MAP treatment, soil available P, Fe, and Zn concentrations significantly increased by 22.7%, 6.5%, and 16.7% respectively, in the APP-3.8-90% treatment. Soil labile P forms of resin-P, NaHCO3-P and NaOH-P in the APP-3.8-90% treatment were 91.6%, 24.4% and 27.6% higher, respectively, relative to the MAP treatment, while soil HCl-P concentration was decreased by 7.2%, accordingly. Maize seedling total dry weight (shoot plus root) in the APP-3.8-90% treatment was 42.4% higher than in the MAP treatment. In addition, the APP-3.8-90% treatment is more pronounced than the APP-3-70% treatment in increasing soil available P and Fe, Mn, and Zn. Poly-P application exhibited obvious advantages in increasing soil P availability and mobilizing soil micronutrients. Specially, appropriately increasing the polymerization content of poly-P is beneficial to play a better role. Hence, it could be recommended as a promising source of P fertilizer substituting orthophosphate (ortho-P) fertilizers.

Dissipation and sorption processes of polycyclic aromatic hydrocarbons (PAHs) to organic matter in soils amended by exogenous rich-carbon material

Abstract: The aim of the research was to assess the effect of biochar addition on aging, degradation, and sorption processes of polycyclic aromatic hydrocarbons (PAHs) to soil organic matter. The study was carried out as a sorption experiment in strictly controlled water and air conditions, which allowed for the accurate observation and prediction of PAH behavior in soils. Four soils were fortified with a PAH mixture (Fluorene-Flu, Anthracene-Ant, Phenanthrene-Phe, Pyrene-Pyr, Chrysene-Chry) at 20 mg kg−1 of single-compound concentration level. The experiment was carried out in two trials: soils + 5PAHs amended with biochar and soil + 5PAHs without biochar addition with incubation times of 0, 1, 3, 6, and 9 months. After each interval time, the extractable (E-SOM) and stable organic matter (S-SOM) were measured as well as PAHs determined in two forms: total concentration (PAH-tot) and residual concentration (PAH-rest) after E-SOM extraction. The PAH loss and half-life times were estimated according to pseudo first-order kinetics equation. The amounts of PAH-tot in the soils without biochar decreased by an average of 92%, while in soil with biochar, this was 41% after 9 months of aging. The amount of PAHs-rest bounded with S-SOM after 9 months of incubation varied from 0.9 to 3.5% and 0.2 to 1.3% of the initial PAH concentration, respectively, for soils non-induced and induced by biochar. In soils without biochar, Flu, Ant, Phe, and Pyr exhibited similar T1/2 (43–59 days), but Chry was characterized by a much higher and broader T1/2 than other hydrocarbons (67–280 days). Biochar addition to the soils significantly influenced the half-life changes for all PAHs. The highest changes were noted for Phe (14-fold increase), and the lowest was for Flu (7-fold increase). The addition of exogenous-rich carbon material such as biochar to the soil significantly changes the behavior and sorption potential of PAHs in the soil. Soils enriched with biochar are characterized by a higher persistence of PAHs, longer aging time, and lower affinity for sorption by native organic matter structures. Soils freshly polluted by PAH are mainly sorbed by E-SOM, which significantly increases their accessibility and reduces formation of bound-residues in the soil.

Influence of in-house produced biochars on cracks and retained water during drying-wetting cycles: comparison between conventional plant, animal, and nano-biochars

Abstract: Biochars produced from different feedstocks (such as wood, pig manure) possess varying physical and chemical properties, which have influence on crack and evaporation rate of biochar-amended soil (BAS). Furthermore, influence of compaction state and drying-wetting cycles on evaporation rate and cracking of BAS has not been investigated comprehensively. The objective of this study was to investigate the effects of biochar types, compaction state of BAS, and drying-wetting cycles on crack propagation and retained water (or evaporation rate). An animal and plant feedstock-based biochars were produced in-house from pig manure (PM) and wood (W), respectively. In addition, nano structured chalk and wheat biochar (CWB) were also produced. Soil amended with individual biochars was compacted in petri-glass discs at two densities. Disc specimens were subjected to multiple drying-wetting cycles, and evaporation rate of specimens and crack area were monitored throughout the experimental period (70 days). Images were captured after every 24 h and processed using image processing technique to obtain the crack intensity factor (CIF). The results show that plant-based W BAS showed the high water retention, i.e., low evaporation rate and low CIF. Furthermore, the crack potential of CW BAS was seen to be higher. In dense compacted soil, maximum CIF% can be reduced from 3.9 to 0.4% for W BAS, from 3.9 to 1.7% for PM BAS, and from 3.9 to 1.6% for CW BAS. WB was able to resist cracking more efficiently than other types of biochar. Evaporation was found to be minimal for plant-based W BAS at 10% biochar percentage. Higher biochar content in soil was seen to increase the water retention of BAS significantly. Dense state of BAS at high biochar content (i.e., 10%) was effective in reducing evaporation rate and crack progression.

Biocrusts resist runoff erosion through direct physical protection and indirect modification of soil properties

Abstract: Biological soil crusts (biocrusts) are ubiquitous in arid and semi-arid regions and play many critical roles in soil stabilization and erosion prevention, greatly decreasing soil loss. Although sediments may be completely controlled by well-developed biocrusts, runoff loss is observed. Consequently, it is important to study how biocrusts resist runoff erosion in different developmental stages to evaluate and manage water erosion. In the Loess Plateau Region, we sampled 32 biocrust plots representing eight stages of biocrust development and 5 slope cropland soil plots as bare soil control plots. We then used a rectangular open channel hydraulic flume to test the effects of biocrust development on runoff erosion. As expected, the establishment of biocrusts enhanced soil stability, and accordingly, soil anti-scourability significantly increased with biocrust development. Biocrusts exhibiting more than 36% or 1.22 g dm−2 of moss coverage or biomass fully protected the soil from runoff erosion. Moreover, soil properties, such as soil organic matter, soil cohesion and soil bulk density, were also important in reducing erosion. The findings indicated that biocrusts inhibited runoff erosion through direct physical protection related to biocrust cover and biomass and through the indirect modification of soil properties. In the early biocrust development stage (when moss cover was less than 36%), cyanobacterial biocrust played a primary role in providing resistance to runoff erosion, with resistance being positively related to cyanobacterial biomass (chlorophyll a) and influenced by soil properties. The relationship between soil anti-scourability and moss coverage or biomass can be divided into two stages based on a moss cover or biomass threshold. The capacity of biocrusts to resist runoff erosion was limited when moss cover was below the threshold value. Therefore, the stage corresponding to this level of moss cover should be of concern when estimating, predicting and managing water erosion.

Bibliometric analysis of research on soil health from 1999 to 2018

Abstract: Soil health has been a major focus of research by international scholars because it is an important factor that supports human survival and development. However, few scholars have performed bibliometric analyses of research on soil health. This study investigated the current research status and development characteristics of soil health. We performed a bibliometric analysis of documents on soil health from 1999 to 2018 in the Web of Science Core Collection. The bibliometric analysis tools, CiteSpace and HistCite software, were applied. A total of 1629 documents on soil health in the Web of Science Core Collection were identified. From the research status of soil health, the number of publications will continue to increase. Most of the research institutions examining soil health are located in the USA, and there is little cooperation and communication among countries, neither do research institutions in this field. Each country has its own research labs while lab cooperation within individual countries is relatively close. Most documents on the research of soil health have been published in the journal Applied Soil Ecology. In addition, research directions are expanding from the basic study of soil production, soil health indicators, and soil pollution to the comprehensive study of soil ecosystem. Bibliometric analysis tools, CiteSpace and HistCite software, provide a comprehensive approach for making predictions regarding trends in the field. This method was used in this study to identify the hotspots, frontiers, and future development of soil health to provide guidance for future research.

Soil organic carbon depletion in global Mollisols regions and restoration by management practices: a review

Abstract: Mollisols are the most fertile, high-yielding soils in the world. During the past several decades, Mollisols have lost about 50% of their antecedent organic carbon (C) pool due to soil erosion, degradation, and other unsuitable human activities. Therefore, restoring soil organic C (SOC) to Mollisols via reasonable management is crucial to sustainable development and is important for environmental stability. However, the existing literature on SOC and soil quality has focused on one soil type or on a given region where Mollisols occur, and the degree of SOC depletion and stabilization in Mollisols have not been comprehensively evaluated. Overall, we propose to develop an optimum scheme for managing Mollisols, and we outline specific issues concerning SOC restoration and prevention of SOC depletion. In this review, we identify the uncertainties involved in analyses of SOC in Mollisols as related to management practices. According to the existing literature on SOC in Mollisols at the global scale, we analyzed the results of SOC depletion research to assess management practices and to estimate the C amount stabilized in Mollisols. The review shows that the SOC stocks in Mollisols in North America under cropped systems had 51 ± 4 (equiv. mass) Mg ha−1 in the top 30 cm soil layer. The SOC contents in Northeast China decreased from 52 to 24 g kg−1 (46%) after 150 years of cultivation management. All of the Mollisols regions in the world are facing the challenge of SOC loss, and this trend could have a negative influence on global climate change. Hence, it is very important to take proper measures to maintain and enhance organic C contents in Mollisols. We concluded that reasonable management practices, including no-tillage, manure and compost fertilization, crop straw returning, and mulching cultivation, are the recommended technologies. The C restoration in Mollisols is a truly win-win strategy for ensuring the security of food and soil resources while effectively mitigating global climate change. Thus, more attention should be given to protective management and land use for its impacts on SOC dynamics and soil properties in Mollisols regions.

Assessment of heavy metal pollution in surface sediments of the Montenegrin coast: a 10-year review

Abstract: Heavy metals are among the most common environmental pollutants, which can be introduced into coastal areas from natural and anthropogenic sources, and thereby possibly impact marine organisms and human population. Therefore, the aim of this study was to evaluate the pollution level of Montenegrin coastal sediments by determining the concentrations of 10 metals and metalloids (Fe, Mn, Zn, Cu, Ni, Pb, Cr, Cd, As, and Hg) during one whole decade. Sediment samples were collected from 11 sites along the Montenegrin coast during the 2005–2016 exposure to different levels and sources of anthropogenic impact. The extent of pollution was estimated by determining total element concentrations in the sediment. Mineralized samples were analyzed for Cu, Ni, Fe, Mn, Cr, As, Pb, Zn, Cd, and Hg. Pollution status was evaluated using the contamination factor, pollution load index, and geo-accumulation index, as well as statistical methods, such as Pearson correlation coefficient (r) and cluster analysis (CA). This study showed that concentrations of individual metals at some locations were extremely high. The metal concentrations (in mg kg−1) ranged as follows: Fe 1995–45,498; Mn 135–1139; Zn 10–1596; Cu 3.8–2719; Ni 2.94–267; Pb 0.1–755; Cr 2.5–369; Cd 0.1–5.4; As 0.1–39.1; and Hg 0.01–14.2. The calculated concentration factor and pollution load index indicates enrichment by either natural processes or anthropogenic influences. The geo-accumulation index value (Igeo) showed that one location was strongly or extremely polluted (3.78 < Igeo ≤ 6.15) with Hg in all investigated years, while extreme Igeo values for four bioactive elements, Pb, Cd, Cu, and Zn, were found in only a few single samples. On the basis of the obtained values, it can be concluded that generally higher metal contents were distributed in Boka Kotorska Bay sites, although some extreme values were also recorded at the locations outside of the Bay. Geo-accumulation index and pollution load index showed that the metal levels were high enough to pose risk to the ecosystem.

Effective bioremediation of heavy metal–contaminated landfill soil through bioaugmentation using consortia of fungi

Abstract: Heavy metals’ contamination of soil is a serious concern as far as public health and environmental protection are concerned. As a result of their persistent and toxic properties, heavy metals need to be removed from contaminated environments using an efficient technology. This study is aimed to determine the heavy metals’ (Ni, Pb, and Zn) bioremoval capacity of consortia of filamentous fungi from landfill leachate-contaminated soil. Three different groups of consortia of fungi, namely all isolated fungi, Ascomycota, and Basidiomycota, were employed for the bioremediation of the contaminated soil. A total of thirteen fungal species were used to make up the three consortia. The setup was kept for 100 days during which regular watering was carried out. Soil subsamples were collected at day 20, day 60, and 100 for monitoring of heavy metal concentration, fungal growth, and other physicochemical parameters. Highest tolerance index of 1.0 was recorded towards Ni and Zn concentrations. The maximum metal bioremoval efficiency was observed for soil bioaugmented with the all isolated fungi for Ni and Pb with the removal efficiencies as 52% and 44% respectively. However, 36% was realized as the maximum removal for Zn, and was for Ascomycota consortium-treated soil. The order for the heavy metal removal for Ni and Pb is all isolated fungi > Basidiomycota > Ascomycota, while for Zn is Basidiomycota > all isolated fungi > Ascomycota. Spectra analysis revealed the presence of peaks (1485–1445 cm−1) only in the consortia-treated soil which corresponded to the bending of the C–H bond which signifies the presence of methylene group. Soil treated using bioaugmentation had the best heavy metal removal as compared to that of the control. This suggests the contribution of fungal bioaugmentation in the decontamination of heavy metal–contaminated soil.

Growth of comammox Nitrospira is inhibited by nitrification inhibitors in agricultural soils

Abstract: The discovery of comammox Nitrospira being capable of complete oxidising ammonia to nitrate radically challenged the conventional concept of two-step nitrification. However, the response of comammox Nitrospira to nitrification inhibitors (NIs) and their role in soil nitrification remain largely unknown, which has hindered our ability to predict the efficiency of NIs in agroecosystems. We evaluated the effect of four NIs, 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin), 3,4-dimethylpyrazole phosphate (DMPP), allylthiourea (ATU) and dicyandiamide (DCD) on the growth of comammox Nitrospira, ammonia-oxidising archaea (AOA) and ammonia-oxidising bacteria (AOB) in two pasture and arable soils. The amendment of nitrogen fertiliser significantly increased soil nitrate concentrations over time, indicating a sustaining nitrification activity in both soils. The addition of all the four NIs effectively reduced the production of nitrate in both soils, but to varying degrees during incubation. The abundances of comammox Nitrospira clade A were significantly increased by addition of nitrogen fertilisers and significantly impeded by the four NIs in the pasture soil, but their abundances were only remarkably hindered by nitrapyrin in the arable soil. All the four NIs obviously inhibited the AOB abundances in both soils. Except for DMPP, the other three NIs effectively suppressed the AOA abundances in both soils. We provided new evidence that growth of comammox Nitrospira clade A can be stimulated by nitrogen fertilisers and inhibited by various nitrification inhibitors, suggesting their potential role in nitrification of agricultural soils.

Quantification and uncertainty of the impact of climate change on river discharge and sediment yield in the Dehbar river basin in Iran

Abstract: The purpose of this study is to identify future changes in weather variables (precipitation and temperature) due to climate change using different general circulation models (GCMs) for different emission scenarios, so as to assess the impact of climate change on river discharge and sediment yield in the Dehbar river basin in Iran. The magnitude and uncertainty of the impact of climate change on river discharge and sediment yield in the Dehbar river basin in Iran is quantified using a calibrated and validated SWAT model with future weather inputs generated using the LARS-WG6 program to downscale the output of five large-scale GCMs for three possible emission scenarios (RCP26, RCP45, and RCP85) and the period 2021–2040. Annual maximum and minimum temperatures are projected to increase by 22–28% and 65–84%, respectively, with a 1-month shift in temperature peak. The future rainfall amounts show both increasing (fall and winter) and decreasing (spring and summer) trends. Future temperature and rainfall patterns are predicted to cause the largest flows to occur a month earlier (February instead of March), an increase in discharge in the “wet” months of fall and winter (up to 137%) and a decrease in the “dry” months of spring and summer (down to − 100%). Sediment yield, which is caused by runoff (also controlling river discharge), has a similar projected trend, with a general decrease in spring and summer (down to − 95%) and an increase in fall and winter (up to 340%). The coefficient of variation of the future monthly, seasonal and annual river discharges and sediment yields are relatively low, revealing a general agreement in projections among the different GCM and RCP scenarios considered. This study highlights the significant negative impact of climate change on the Dehbar river basin, with amplification of river flows and sediment concentrations in the wet season and increased water scarcity in the dry season. Both effects may adversely impact the region’s livelihood (cultivation, fish farming) and land resources.

Response of organic carbon fractions and microbial community composition of soil aggregates to long-term fertilizations in an intensive greenhouse system

Abstract: Soil organic carbon (SOC) content and stability, which are regulated by microbial communities, vary depending on aggregate size. The objectives of this study were to investigate the distribution of the SOC fraction and microbial community composition within soil aggregates when subjected to different fertilization treatments. This study used high-throughput sequencing technology to analyze the soil microbial community distribution in different-sized aggregate fractions [> 2 mm (large macro-aggregates), 2–0.25 mm (small macro-aggregates), and < 0.25 mm (microaggregates)] when they were subjected to different fertilization treatments in a 16-year greenhouse experiment. The three treatments were chemical fertilizer (CF), 50% organic fertilizer + 50% chemical fertilizer (MF), and organic fertilizer (OF). The results showed that the application of organic fertilizer significantly increased the soil organic carbon (SOC), dissolvable organic carbon (DOC), and microbial biomass carbon (MBC) contents and changed microbial community composition in all the different-sized soil aggregates. We observed that OF significantly reduced the relative abundance of bacterial communities in all aggregates and significantly increased the relative abundances of fungal communities in small macro-aggregates. The larger fungal communities in small macro-aggregates could promote soil aggregation and C sequestration. Organic fertilization increased the substrate contents in soil aggregates and enhanced soil aggregation and microbial activity in macro-aggregates, which are critical factors that facilitate C transformation and sequestration. These improvements resulted in significantly improved soil fertility and increased vegetable yield in the greenhouses.

Biochar and organic fertilizer changed the ammonia-oxidizing bacteria and archaea community structure of saline–alkali soil in the North China Plain

Abstract: The application of a large amount of inorganic nitrogen (N) fertilizer resulted in an increasing N loss. It is an effective practice that biochar and organic fertilizer replace part of inorganic nitrogen fertilizer. Thus, it is necessary to identify and compare the effects of biochar and organic fertilizer on ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) community structure in saline–alkali soil. Three treatments in triplicate were included in the field experiment: (1) CK (no biochar and organic fertilizer), (2) biochar at 10.0 t ha−1 year−1 (C), and (3) organic fertilizer at 7.5 t ha−1 year−1 (M). The community structures and diversities of AOB and AOA were investigated by Illumina sequencing analysis of gene encoding ammonia monooxygenase subunit A (amoA) and followed by principal component analysis, least discriminant analysis effect size, and redundancy analysis. Biochar and organic fertilizers did not change the diversity of AOA and reduced the relative abundance of Candidatus-Nitrosoarchaeum in maize season, while only biochar increased the relative abundance of Candidatus-Nitrosotenuis in wheat season. The diversity of AOB was significantly reduced in the M treatment, but was not changed in the C treatment in wheat season. Moreover, the relative abundances of Nitrosomonas (CK, 15.1%; C, 6.8%; M, 3.4%) were decreased in the maize season, and the relative abundances of Nitrosovibrio (CK, 9.8%; C, 16.8%; M, 14.5%) were increased in the wheat season in the C and M treatments, which probably related to the changes in soil pH, soil NH4+–N content, and soil salt content (SSC). The lower soil pH, higher NO3−–N content, and SSC resulted in Nitrosospira (maize season: CK, 42.2%; C, 40.7%; M, 62.0%; wheat season: CK, 46.6%; C, 50.7%; M, 65.4%) becoming the dominant genus in the M treatment. Our results indicated that AOB was more susceptible than AOA to biochar and organic fertilizer. Organic fertilizer has significant effects on the diversities and community structure of AOB than biochar associated with the changing in soil pH, salinity, and mineral N.

Bioremediation of oil-contaminated soil by combination of soil conditioner and microorganism

Abstract: Oil hydrocarbons are widespread pollutants in soil which pose serious threats to ecological environment. Thus, this study carried out the bioremediation of oil-contaminated soil by using the efficient petroleum-degrading bacteria and soil conditioner, to investigate the changes of physicochemical properties of contaminated soil during bioremediation, reveal the relationship among the exogenous degradation strains and indigenous microbe, and finally illuminate the effects of soil conditioner and microbe on the bioremediation of oil-contaminated soil. A PAH-degrading strain named Stenotrophomonas maltophilia was used in this study, which was isolated from an e-waste dismantling area. The soil conditioner in this present study was developed previously by using agricultural wastes, which was in a powdered form and rich in N, P, and K. The simulated experiments were conducted under the control environmental conditions of greenhouse, to study the effects of inoculation and soil conditioner on bioremediation of oil-contaminated soil. Then, the physicochemical properties of soil and the degradation rates of oil were measured at different set times to evaluate the bioremediation effect. Adding 1% soil conditioner could significantly improve the soil conditions and offer microorganism enough N, P, and K, which would promote microbial growth and played a key role on bioremediation of oil-contaminated soil. Although in polluted soil, the microorganism could maintain metabolic activity and use the petroleum as carbon source. The soil indigenous microbe was more easily to adapt to the contaminated surrounding. However, when both of them co-existed in soil, they would restrain each other, and go against the oil decomposition. Thus, making two types of microorganisms work to achieve synergy was the key to gain much better remediation effect. Because the indigenous microbe was good at decomposing low molecular compounds and saturated hydrocarbons, while the oil-degrading strains can effectively decompose high molecular weight aromatics. The soil nutrient and microorganism, including the exogenous oil-degrading strains and the soil indigenous microbe, had an important effect on degradation of petroleum. The addition of soil conditioner, presence of indigenous microbe, and inoculation of oil-degrading strains all were conducive to bioremediation of oil-contaminated site, but the key was to control the proportion and relationship of the three.

Contrastive nutrient leaching from two differently textured paddy soils as influenced by biochar addition

Abstract: The aims of the current study were to (1) examine the interactive effects of biochar addition and differently textured soils (clayey and sandy soils) on nutrient leaching and (2) identify potential mechanisms related to the leaching. A repacked soil column experiment was set up to test the effects of five biochar rates added to clayey and sandy soils grown with rice (Oryza sativa L. ssp. japonica) for 3 months. Four leaching events were conducted to measure concentrations of ten elements in the leachate, including calcium (Ca), sodium (Na), potassium (K), magnesium (Mg), aluminum (Al), iron (Fe), manganese (Mn), ammonium nitrogen (NH4+), nitrate nitrogen (NO3−), and phosphorus (P). On the sandy soil, biochar addition linearly and significantly reduced Ca concentration (by 38%), but increased Na (by 92%), K (by 292%), and P (by 411%) concentrations in the leachate, compared to the non-biochar-added soil. In contrast, on the clayey soil, biochar addition showed no obvious effect on the leaching of these elements. Biochar addition significantly reduced leaching of Al, Fe, Mn, and NH4−, but increased leaching of Mg. Mechanisms related to the reduced leaching of NH4−, Ca, Al, Fe, and Mn could be involved in the liming effect and increased nutrient holding capacity by biochar addition, and those responsible for increased leaching of Na, K, and P could be involved in co-addition of these elements with the added biochar. Biochar addition had contrastive effects on nutrient leaching, which was more profound on sandy soil than on clayey soil grown with rice crop.

Source apportionment of soil heavy metals in fluvial islands, Anhui section of the lower Yangtze River: comparison of APCS–MLR and PMF

Abstract: Source apportionment is a crucial step toward reducing heavy metal (HM) pollution within soils. Although comparison of receptor models to apportion sources is well-established in air and water pollution, it has been poorly implemented in evaluations of soil pollution. This study aimed (1) to assess the accumulation of As, Cr, Cu, Ni, Pb, Zn, Cd and Hg in soils of fluvial islands of the lower Yangtze River and (2) to apportion sources in a comparative evaluation of two receptor models, thus providing basic information for rational management of soil pollution in the study area. Soil samples were collected from representative fluvial islands in the Anhui section of the lower Yangtze River, China. A total of 207 topsoil samples (0–20 cm) were collected at a density of 1 sample per 1 km2 and 43 subsoil samples (150–180 cm) were collected at a density of 1 sample per 4 km2. The extent of pollution was estimated by determining total soil HM concentrations and calculating the geoaccumulation index (Igeo). The Local Moran’s index (LMI) was applied to detect the spatial distribution of HMs. Absolute principal component scores-multiple linear regression (APCS–MLR) and positive matrix factorization (PMF) were adopted to apportion the sources of HMs. The mean degree of contamination of the HMs can be ranked as follows: Cd > Hg > Cu > Ni > Cr > Zn > As > Pb. Average HM concentrations in topsoil were consistently higher than those in subsoil, with total HM concentrations varying between fluvial islands. Source apportionments suggested that the particle size effect was the dominant factor (59.3%) in the APCS–MLR model, whereas in the PMF model, calcium minerals played the most important role (50.2%). Concentrations of Cr and Ni were mainly related to the particle size effect, whereas concentrations of As, Cu, Pb and Zn were mainly related to the particle size effect, fixation by calcium minerals and atmospheric deposition from mining activities. The primary source for Cd anomalies was associated with calcium minerals and atmospheric deposition, whereas the accumulation of soil Hg was mainly driven by coal combustion. This study indicated there was no extensive HM contamination in the study area except for Cd. Compared with APCS–MLR, PMF provided an optimal reconstruction of HM concentrations in soils. Thus, the PMF model could be applied to soils for HM pollution management in areas with multiple emission sources.

Effects of freeze-thaw cycles and initial soil moisture content on soil aggregate stability in natural grassland and Chinese pine forest on the Loess Plateau of China

Abstract: Ongoing global warming is decreasing the thickness of snow covers and increasing initial soil moisture content (SMC), which increase the number of freeze-thaw cycles (FTCs) at mid-high latitudes and high elevations, especially at temperate regions. FTCs substantially affect the stability of soil aggregates, which may increase soil erosion. A comprehensive understanding of aggregate stability under different types of vegetation restoration in response to FTCs, however, has not yet been attained. We evaluated the effects of number of FTCs (0, 1, 3, and 9) and initial SMC (40, 60, and 80% field capacity) on aggregate distribution and stability in cropland, natural grassland, and Chinese pine forestland, the three typical types of vegetation on the Loess Plateau in China. The experiment was conducted under simulated conditions in the laboratory using disturbed soil samples. Most aggregate-size fractions and mean weight diameters (MWDs) were significantly (P < 0.05) affected by FTCs, initial SMC, and vegetation types. FTCs significantly decreased MWD by 3.6–18.1% through disrupting larger macro-aggregates, which increased with SMC. Increased SMC increased MWD by 2.0–53.0% through binding soil particles, the effect of which was much larger than the disruptive effects under the freeze-thaw conditions, especially at high SMC. MWD was in the order of cropland < Chinese pine forestland < natural grassland under each freeze-thaw condition. The results indicated that natural vegetation succession was better than Chinese pine forest plantation for resisting seasonal FTCs and that aggregate stability may increase due to increased initial SMC under scenarios of future global warming.

Impact of vegetation restoration on soil organic carbon stocks and aggregates in a karst rocky desertification area in Southwest China

Abstract: The objectives of the study were as follows: (a) to determine the response of soil organic carbon (SOC) fractions to vegetation restoration; (b) to examine the contributions of aggregate-associated OC to total soil OC accumulation along vegetation restoration, (c) to identify the factors that affect SOC accumulation along natural vegetation restoration in a karst region in Southwest China. Four vegetation restoration stages, namely, grassland, shrubland, shrub-arbor mixed forestland, and arbor forestland, were compared with cropland (CL). Soil samples were collected at depths of 0–10 cm and separated into five aggregate size fractions. SOC, light fraction OC (LFOC), easily oxidizable OC (EOC), and aggregate-associated OCs were determined for different aggregate sizes and total soil. Natural vegetation restoration increased macroaggregate amount but decreased the fractions of meso- and microaggregates. Vegetation restoration significantly increased total SOC, EOC, and LFOC concentrations and stocks and soil aggregate-associated OC concentrations. The responses of EOC and LFOC in total soil and soil aggregates were more sensitive than those of SOC along with vegetation restoration. Aggregate-associated OC concentrations generally increased with a decrease in aggregate size. Macro- and microaggregate-associated OC stocks increased, but mesoaggregate-associated OC stocks decreased following the conversion of CL to a natural vegetation ecosystem. The increase in SOC stocks was primarily attributed to the macroaggregate-associated OC stocks and their changes. OC concentrations and stocks in total soil and the soil aggregates were significantly positively related to exchangeable calcium content. Vegetation restoration considerably affects the amount of soil aggregates, OC concentrations, and stocks in total soil and soil aggregates. Changes in OC concentrations and stocks can be more pronounced in the liable carbon fraction than in total SOC. The increase in SOC was mostly attributed to OC accumulation in macroaggregates. Exchangeable calcium also affected soil OC accumulation in total soil and soil aggregates.

Tillage practices improve rice yield and soil phosphorus fractions in two typical paddy soils

Abstract: This research was undertaken (I) to evaluate the status of phosphorus fractions in paddy soils in response to different tillage management practices under different rice-based cropping systems and environments in order to better understand phosphorus behavior in paddy soils and (II) to assess the effects of various tillage practices on crop yield in different soil types and climatic conditions. We selected four tillage treatments, i.e., conventional tillage (T1), conventional tillage with straw return (T2), rotary tillage with straw return (T3), and no-tillage with straw return and autumn plowing with straw return (T4) at Ningxiang and Haerbin, respectively. Soil samples were collected from 20 cm depth, and we investigated soil pH, total P, Olsen P, SOM content, phosphatase activities, phosphorus fractions, and grain yield at the two experimental sites. The results showed that the T4 tillage system led to significantly higher soil organic matter (SOM) content, total P, and Olsen P concentrations at both sites compared with T1. Regardless of the tillage system, the average rice grain yield at Haerbin was 50.3% greater than that at Ningxiang. Phosphomonoesterase (AcP) and phosphodiesterase (DP) enzyme activities were significantly higher, by 39.8% and 62.1% and by 40.3% and 54.6%, under T4 compared to under T1 at Haerbin and Ningxiang, respectively. The organic and inorganic fractions of P were significantly affected by the different tillage systems. Labile and moderately labile P pools were 29.3% and 19.2% higher in Ningxiang and 64.7% and 33.8% higher in Haerbin under T4 compared to T1, and the non-labile P pools were 10.6% and 18.5% lower, respectively. The labile and moderately labile organic P fractions and phosphatase activities showed a significant correlation with SOM and total P concentrations in RDA analysis. Variance partitioning analysis (VPA) showed that different soil properties, climate factors, phosphatase activities, and their interactions were responsible for 7.1%, 6.8%, 1.3%, and 53.7%, respectively, of the variation in grain yield. Different tillage management practices revealed varied effects at both sites for grain yield, P fractions, and phosphatase activities. Tillage management and climatic variations could be the driving factors that influence grain yield in northern and southern parts of China.

Effects of contrasting biochars on the leaching of inorganic nitrogen from soil

Abstract: The use of excessive nitrogen (N) fertilizers usually causes soil N leaching, eutrophication, and water pollution. Nevertheless, biochars may play an important role in decreasing N losses from soil to waterways. The objectives of this study were to explore the effect of contrasting biochars on the leaching of key inorganic N species during the N transformation processes in a biochar-amended soil. A column leaching experiment was carried out through a soil treated with 2% (w/w) application rate of dead pig-derived biochar (DPB), ultrasonic-modified dead pig-derived biochar (UPB), or Platanus orientalis branch-derived biochar (POB). The DPB contained 5% N, which was much greater than that in the POB (1% N). The amount of ammonium and nitrate N (NH4+-N and NO3−-N) in the leachate samples from the soil treated with different biochars were collected and analyzed periodically. After 20 weeks of incubation, the cumulative NH4+-N leaching loss from the control treatment was 1.87, 2.00, and 2.07 times greater than that from the POB-, DPB-, and UPB-treated soils (P < 0.05). Biochar application reduced NH4+-N leaching from the soil, likely because of NH4+ ion retention and adsorption on biochar surface areas and pore spaces. The cumulative NO3−-N in the leachate from the biochar-amended soil was significantly lower than that of the untreated control, in the order of POB < UPB = DPB < untreated control. With the application of DPB and UPB, the cumulative inorganic N (especially NO3−-N) leaching loss was significantly higher by up to 50%, compared with the POB treatment (P < 0.05). The suppression of nitrate leaching may be due to microbial N immobilization, resulting from the addition of different biochars. It is apparent that the ultrasonic modification process of DPB caused no further inhibition of inorganic N leaching from the soil via incorporating the UPB. Despite the relatively high N concentration in the DPB, 2% of DPB dosage reduced inorganic N leaching from the amended soil. Therefore, regardless of the biochar N concentrations, biochars could be used to improve N fertilizer use efficiency by reducing N leaching loss from soils.

Prediction of macronutrients in plant leaves using chemometric analysis and wavelength selection

Abstract: Fast and real-time prediction of leaf nutrient concentrations can facilitate decision-making for fertilisation regimes on farms and address issues raised with over-fertilisation. Cacao (Theobroma cacao L.) is an important cash crop and requires nutrient supply to maintain yield. This project aimed to use chemometric analysis and wavelength selection to improve the accuracy of foliar nutrient prediction. We used a visible-near infrared (400–1000 nm) hyperspectral imaging (HSI) system to predict foliar calcium (Ca), potassium (K), phosphorus (P) and nitrogen (N) of cacao trees. Images were captured from 95 leaf samples. Partial least square regression (PLSR) models were developed to predict leaf nutrient concentrations and wavelength selection was undertaken. Using all wavelengths, Ca (R2CV = 0.76, RMSECV = 0.28), K (R2CV = 0.35, RMSECV = 0.46), P (R2CV = 0.75, RMSECV = 0.019) and N (R2CV = 0.73, RMSECV = 0.17) were predicted. Wavelength selection increased the prediction accuracy of Ca (R2CV = 0.79, RMSECV = 0.27) and N (R2CV = 0.74, RMSECV = 0.16), while did not affect prediction accuracy of foliar K (R2CV = 0.35, RMSECV = 0.46) and P (R2CV = 0.75, RMSECV = 0.019). Visible-near infrared HSI has a good potential to predict Ca, P and N concentrations in cacao leaf samples, but K concentrations could not be predicted reliably. Wavelength selection increased the prediction accuracy of foliar Ca and N leading to a reduced number of wavelengths involved in developed models.