Chinese Soil Research Articles

Soil taxonomy and distribution characteristics of the permafrost region in the Qinghai-Tibet Plateau, China

Understanding the soil taxonomy and distribution characteristics of the permafrost region in the Qinghai-Tibet Plateau (QTP) is very important. On the basis of extensive field surveys and experimental analysis, this study carries out soil taxonomic classification of the permafrost region in the QTP. According to Chinese Soil Taxonomy, the soil of the permafrost region in the QTP can be divided into 6 Orders (Histosols, Aridosols, Gleyosols, Isohumosols, Cambosols, Primosols), 11 Suborders, 19 Groups and 24 Subgroups. Cambosols are the dominant soil type in the permafrost region, followed by Aridosols. From the east to the west of the permafrost region in the QTP, the soil type gradually changes from Cambosols to Aridosols, showing a meridional zonality. The eastern region is dominated by Cambosols, with no obvious latitudinal zonality. From the south to the northwest of the western region, the dominance of Aridosols and Cambosols gradually transited to Aridosols, presenting a latitudinal zonality. The soil in the western region shows a poor vertical zonality, while the distribution of suborders of Cambosols in the eastern region shows a more obvious vertical zonality. The result indicates that precipitation and vegetation are the main factors that influence the zonal distribution of soil. The permafrost in the east has some effect on the vertical soil zonality, but the effect is weakened in the west.

Assessment of soil erosion change and its relationships with land use/cover change in China from the end of the 1980s to 2010

An empirical approach was employed to monitor changes in soil erosion status in China, incorporating landform, slope, vegetation coverage, land use/cover, and expert interpretation of remote sensing images. We built up a National Soil Erosion Database of China (NSED-C) at 1:100,000 scale that contains Chinese soil erosion data for five periods (the end of the 1980s, 1995, 2000, 2005, and 2010), and established the soil erosion situation for China in 2010 and changes in erosion since the end of the 1980s. The results show that water erosion is the most widely distributed erosion type, affecting 56% of the land area of China, followed by wind erosion and freeze–thaw erosion. But the most serious erosion type is wind erosion. Most of the change in soil erosion was concentrated within regions of northern China that have fragile ecosystems, such as the Loess Plateau, Mu Us Sandy Land, Hunshandake Sandy Land, Horqin Sandy Land, Xianghai Wetland and the Tarim River basin. Hilly regions in southern China were also widely affected by differing soil erosion changes. Impacted by some environmental protection measures and economic activities such as reclaim in northern and western China, Grain for Green Project, and planting of fast-growing woods on hills in southern China, two different trends of soil erosion change are identified during the monitoring period: soil erosion in China was getting worse before 2000 after which it has subsequently improved. Nevertheless, a series of environmental protection measures implemented after 2000 did not recover the previous negative impact before, so that the overall soil erosion situation in China in 2010 is worse than at the end of the 1980s.

A comment on “Selenite adsorption and desorption in main Chinese soils with their characteristics and physicochemical properties.” J Soils Sediments 15(5):1150–1158 (2015), doi:10.1007/s11368-015-1085-7

Dear Editors-in-Chief: I would like to point out chemical inconsistency errors in the paper entitled BSelenite adsorption and desorption in main Chinese soils with their characteristics and physicochemical properties^ by Z. Li, N. Man, S. Wang, D. Liang, and J. Liu published in the Journal of Soils and Sediments (2015; 15(5):1150–1158) which invalidate almost the entire paper starting with the title. The authors assert that they were studying Se(IV) not Se(VI) adsorption, yet they prepared their Se solutions from Na2SeO4, clearly a hexavalent Se(VI) salt. Therefore, the authors were, in fact, studying the adsorption of Se(VI). Required corrections start with the title where the word Bselenite^ must be replaced by the word Bselenate^ or Bselenium^ to correctly reflect the chemistry of the Se solutions that were used in the investigation. The authors did not speciate their experimental Se solutions, but instead analyzed for total Se using hydride generation–atomic fluorescence spectrophotometry. If a Se speciation analysis had been carried out, the error in redox state would have become apparent. Throughout the manuscript, the authors compared their Se(VI) adsorption measurements to literature data for Se(IV) adsorption. Such comparisons are clearly invalid, especially since the adsorption behavior of Se(VI) on soils has been shown to be very different from that of Se(VI) by various authors (Neal et al. 1987a, b; Neal and Sposito 1989; Goldberg et al. 2008; Gabos et al. 2014; Goldberg 2014). Several of these investigations were cited by the authors in their current work. While the experimental data of Se(VI) adsorption on Chinese soils is valid and may potentially be publishable, especially given the small number of Se(VI) sorption studies currently in the literature, the title, figure captions, and virtually all discussion in the current publication are invalidated by the mislabeling of the Se species . The cur ren t manuscr ip t i s not va l id . Publication of an erratum will be insufficient to address these issues. The required corrections are so extensive that a new manuscript is warranted, necessitating the retraction of the current publication. The new manuscript must clearly state throughout that selenate Se(VI) adsorption is being investigated. Since the tables and figures in the current paper refer to elemental Se, they can be retained in the corrected submission.

Response to the comment by Sabine Goldberg on: Selenite adsorption and desorption in main Chinese soils with their characteristics and physicochemical properties. J Soils Sediments 15(5):1150–1158 (2015), doi: 10.1007/s11368-015-1085-7

Dear Editors-in-Chief We are so sorry that we need to make corrections for an error in our article BSelenite adsorption and desorption in main Chinese soils with their characteristics and physicochemical properties,^ which was published in the Journal of Soils and Sediments (2015; 15(5):1150–1158). We did not realize this error until Sabine Goldberg submitted her letter to the Journal of Soils and Sediments. We checked the paper and found a mistake in the sentence BOne-gram portions of each soil sample placed in 100-mL centrifuge tube were equilibrated with 10mL of 0.01MCaCl2 containing graded levels of Se from 0.15 to 3.14 mg Se/L in the form of Na2SeO4^ in B2.2 Adsorption experiment^ section. Here, we had misspelled Na2SeO3 into Na2SeO4. This was the reason why Sabine Goldberg thought Se(VI) adsorption was studied in the article. In fact, the adsorption behavior of Se(IV) (selenite) was the one studied and analyzed which can be found in the title, the abstract, introduction, and the results part of the paper. As we mentioned in the article, the objectives of this study were to investigate selenite retention of soils and related dominant physicochemical properties in the Se adsorption–desorption process and to provide base knowledge for further implementation of Se supplementation in China. This was a mistake of ours and we regret that we did not find it prior to the publication of our paper. We sincerely apologize to all readers and express our gratitude to Sabine Goldberg. Correction of the mistake would be as follows: BOne-gram portions of each soil sample placed in 100-mL centrifuge tube were equilibrated with 10 mL of 0.01 M CaCl2 containing graded levels of Se from 0.15 to 3.14 mg Se/L in the form of Na2SeO4^ should be replaced by BOne-gram portions of each soil sample placed in 100 mL centrifuge tube were equilibrated with 10 mL of 0.01 M CaCl2 containing graded levels of Se from 0.15 to 3.14 mg Se/L in the form of Na2SeO3.^

Efficient remediation of PAH-metal co-contaminated soil using microbial-plant combination: A greenhouse study

A 2-year greenhouse study was conducted to remediate an actual wastewater-irrigated soil co-contaminated with polycyclic aromatic hydrocarbons (PAHs) and heavy metals (Cd and Zn). The remediation methods included microbial remediation, phytoremediation, and microbe-assisted phytoremediation. The maximum PAH removal (96.4%), PAH mineralization, and metal phytoextraction (36.1% Cd and 12.7% Zn) were obtained by interplanting ryegrass with Seduce alfredii with regular re-inoculation with Microbacterium sp. KL5 and Candida tropicalis C10 in the co-contaminated soil. The plants shoots were harvested at a 4-month interval. After 2 years, the concentrations of 16 individual PAHs were reduced to below the limit of Chinese soil quality standard for agricultural use (grade II, pH 6.5–7.5), and the metal concentrations in ryegrass shoots were below the Chinese national limit for animal feeds (GB13078-2001). The exogenous microbes gradually disappeared with time, and thus a 2-month re-inoculation interval was applied for a purpose to maintain high cell density and activity of the inoculants. KL5 introduction increased soil enzyme activity, plant growth, PAH removal and metal phytoextraction, while C10 promoted soil enzyme activity and removal of high-molecular-weight PAHs. Interplanting with S. alfredii reduced metal concentrations in ryegrass tissues. Ryegrass showed stronger rhizosphere effects than S. alfredii did.

The microbial ATP concentration in aerobic and anaerobic Chinese soils

Soil adenosine 5′-triphosphate (ATP) is an excellent indicator of soil microbial biomass in moist aerobic soils, having an extracellular half life of less than 1 h. It is measured by the firefly luciferin-luciferase system. Jenkinson and Oades (1979) proposed a method to measure ATP in aerobic soils, with a reagent of Na2HPO4, trichloroacetic acid (TCA) and paraquat, (TCA reagent). Their method has been superseded by an alternative where paraquat is replaced by imidazole, termed the TIP reagent. Both methods give the same results. We found a constant biomass ATP concentration of 7.9 ± 2.24 μmol ATP g−1 biomass C in aerobic soils irrespective of substrate addition and a much lower, and highly variable concentration of 2.83 ± 0.82 in anaerobic soils. Possible reasons are discussed.

A review of soil cadmium contamination in China including a health risk assessment.

Cadmium (Cd) is one of the most serious soil contaminants in China, and it poses an increasing risk to human health as large amounts of Cd are emitted into the environment. However, knowledge about soil Cd concentrations and the human health risks of these concentrations at a national scale is limited. In this study, we conducted a review of 190 articles about soil Cd concentrations during 2001 to 2010. The study involved 146 cities in China, and we quantified the risks to human health according to different regions. The results showed that elevated Cd levels were present compared to the background value of soil in 1990, and the soil Cd concentrations in the Guangxi province exceeded even the class III Soil Environmental Quality standard, which is the limit for the normal growth of plants. The Chinese soil Cd concentrations ranged from 0.003 mg kg(-1) to 9.57 mg kg(-1). The soil Cd concentrations had the following trend: northwest > southwest > south central > east > northeast > north. The sources of soil Cd are mainly from smelting, mining, waste disposal, fertilizer and pesticide application, and vehicle exhaust, etc. but differentiated in various regions. The soil Cd contamination in urban areas was more serious than contamination in the agricultural areas. Currently, there is no significant non-carcinogenic risk in any of the provinces. Regarding the different exposure pathways, the dermal pathway is the primary source of soil Cd exposure, and the risk associated with this pathway is generally hundreds of times higher than the risk for an ingestion pathway. For most of the provinces, the health risk to the urban population was higher than the risk to the rural population. For each population, the carcinogenic risk was less than 10(-6) in most of the provinces, except for the urban population in the Hunan province. If the other exposure pathways are fully considered, then the people in these areas may have a higher carcinogenic risk. This review provides a comprehensive assessment of soil Cd pollution in China, and it identifies policy recommendations for pollution mitigation and environmental management in the relevant regions.

Potential risk of cadmium in a soil-plant system as a result of long-term (10 years) pig manure application

Animal manure may be a primary source of cadmium (Cd) to Chinese farmlands because abnormally high values of Cd were observed in various manures. In this study, we evaluated the potential risk of Cd in soil-plant (maize and soybean) system as a result of the long-term (10 years) application of pig manure (PM). During 10 years, the loading rate of Cd through PM application ranged from 26.33–131.50 g/ha/year, while the crops removal rate of Cd was relatively small in comparison to the quantity of Cd supplied by PM application (1.03–4.36 g/ha/year). The PM ap plication significantly increased total Cd concentration in soil. Although the Cd levels did not exceed the Chinese soil quality criteria (1.0 mg/kg dry matter (DM)), it would only take less than two years to reach this limit at high PM application rate. The same trend was also observed for the Cd concentration in maize and soybean. More seri ously, Cd concentration in grain of soybean was higher than the threshold values for animal and human ingestion (0.2 mg/kg DM). Based on a mass balance calculation, we found that atmospheric deposition was also an important source of Cd in the experimental area (10.27 g/ha/year). Moreover, the application of PM enhanced the leaching loss of Cd, but they were still fairly small (0.34–0.73 g/ha/year).

Effect of Dissolved Organic Matter from Wheat Straw or Swine Manure on the Cu Adsorption in Three Chinese Soils

Batch equilibration experiments were conducted to evaluate the effects of dissolved organic matter (DOM) from wheat straw (DOMw) and swine manure (DOMs) on copper (Cu) adsorption and behavior in Haplic Phaeozems, Haplic Acrisol, and Eutric Fluvisol in China. Results showed that the Cu adsorption isotherms were well fitted with both Langmuir and Freundlich equations. The Cu maximum potential adsorption capacity of the three soils followed the order of Eutric Fluvisol > Haplic Phaeozems > Haplic Acrisol. DOMw and DOMs increased the Cu adsorption capacity in Haplic Phaeozems and Haplic Acrisol, and the promoting role of DOMs on Cu adsorption was obviously higher than that of DOMw. Increasing DOM concentration of DOMw and DOMs promoted the Cu adsorption in Haplic Phaeozems and Haplic Acrisol. However, this promoting effect weakened with increasing DOM concentration. Moreover, DOMw and DOMs inhibited the Cu adsorption in Eutric Fluvisol, and this inhibitory effect significantly increased with increasing DOM concentration. The results may be used to assess the potential environmental contamination of the studied soils and to control the application of organic fertilizers.

Impact of Soil Heavy Metal Pollution on Food Safety in China.

Food safety is a major concern for the Chinese public. This study collected 465 published papers on heavy metal pollution rates (the ratio of the samples exceeding the Grade II limits for Chinese soils, the Soil Environmental Quality Standard-1995) in farmland soil throughout China. The results showed that Cd had the highest pollution rate of 7.75%, followed by Hg, Cu, Ni and Zn, Pb and Cr had the lowest pollution rates at lower than 1%. The total pollution rate in Chinese farmland soil was 10.18%, mainly from Cd, Hg, Cu, and Ni. The human activities of mining and smelting, industry, irrigation by sewage, urban development, and fertilizer application released certain amounts of heavy metals into soil, which resulted in the farmland soil being polluted. Considering the spatial variations of grain production, about 13.86% of grain production was affected due to the heavy metal pollution in farmland soil. These results many provide valuable information for agricultural soil management and protection in China.

Insights into tetrabromobisphenol A adsorption onto soils: Effects of soil components and environmental factors

Concerns regarding tetrabromobisphenol A (TBBPA), the most widely utilized brominated flame retardant in the world, are growing because of the wide application and endocrine-disrupting potential of this compound. To properly assess its environmental impacts, it is important to understand the mobility and fate of TBBPA in soil environments. In this study, the effects of soil components, dissolved organic carbon (DOC) and heavy metal cations on TBBPA adsorption onto two Chinese soils (red soil and black soil) were investigated using batch sorption experiments. The desorption behavior of TBBPA when the two soils are irrigated with eutrophicated river water was also investigated. The results showed that pH greatly affects the adsorptive behavior of TBBPA in soils. Iron oxide minerals and phyllosilicate minerals are both active surfaces for TBBPA sorption, in addition to soil organic matter (SOM). DOC (50mgOCL−1) exhibited a limited effect on TBBPA sorption only under neutral conditions. TBBPA sorption was only minimally affected by the heavy metals (Cu2+, Pb2+ and Cd2+) in the studied pH range. Eutrophicated river water significantly enhanced the desorption of TBBPA from red soil due to the change in soil solution pH. These findings indicate that mobility of TBBPA in soils is mainly associated with soil pH, organic matter and clay fractions: it will be retained by soils or sediments with high organic matter and clay fractions under acidic conditions but becomes mobile under alkaline conditions.

Dustfall Heavy Metal Pollution During Winter in North China.

In order to study heavy metal pollution in dustfall during Winter in North China, forty-four dustfall samples were collected in North China Region from November 2013 to March 2014. Then forty trace elements content were measured for each sample by inductively coupled plasma-mass spectrometry. Finally, the contamination characteristics of the main heavy metals were studied through a multi-method analysis, including variability analysis, Pearson correlation analysis and principal component analysis. Results showed that the relative contents of cadmium (Cd), zinc (Zn), copper (Cu), bismuth (Bi), lead (Pb) exceeded the standards stipulated in Chinese soil elements background values by amazing 4.9 times. In this study, conclusions were drawn that dustfall heavy metal pollution in the region was mainly caused by transport pollution, metallurgy industrial pollution, coal pollution and steel industrial pollution.

Derivation of Soil Ecological Criteria for Copper in Chinese Soils.

Considerable information on copper (Cu) ecotoxicity as affected by biological species and abiotic properties of soils has been collected from the last decade in the present study. The information on bioavailability/ecotoxicity, species sensitivity and differences in laboratory and field ecotoxicity of Cu in different soils was collated and integrated to derive soil ecological criteria for Cu in Chinese soils, which were expressed as predicted no effect concentrations (PNEC). First, all ecotoxicity data of Cu from bioassays based on Chinese soils were collected and screened with given criteria to compile a database. Second, the compiled data were corrected with leaching and aging factors to minimize the differences between laboratory and field conditions. Before Cu ecotoxicity data were entered into a species sensitivity distribution (SSD), they were normalized with Cu ecotoxicity predictive models to modify the effects of soil properties on Cu ecotoxicity. The PNEC value was set equal to the hazardous concentration for x% of the species (HCx), which could be calculated from the SSD curves, without an additional assessment factor. Finally, predictive models for HCx based on soil properties were developed. The soil properties had a significant effect on the magnitude of HCx, with HC5 varying from 13.1 mg/kg in acidic soils to 51.9 mg/kg in alkaline non-calcareous soils. The two-factor predictive models based on soil pH and cation exchange capacity could predict HCx with determination coefficients (R2) of 0.82–0.91. The three-factor predictive models – that took into account the effect of soil organic carbon – were more accurate than two-factor models, with R2 of 0.85–0.99. The predictive models obtained here could be used to calculate soil-specific criteria. All results obtained here could provide a scientific basis for revision of current Chinese soil environmental quality standards, and the approach adopted in this study could be used as a pragmatic framework for developing soil ecological criteria for other trace elements in soils.

Prediction of soil attributes using the Chinese soil spectral library and standardized spectra recorded at field conditions

Organic matter (OM), total nitrogen (TN), and pH are essential soil properties for assessing the fertility of paddy soils. They can be measured with visible and near infrared (vis–NIR) spectroscopy effectively in the field. However, environmental factors e.g., soil moisture and particle size distribution affect the accuracy of spectroscopic measurement and successful calibration transfer between laboratory and field spectra. Large spectral libraries derived from dried and ground soil samples thus could not be used to predict soil properties using spectra of fresh (non-processed) samples. In this paper, we investigated the possibility of using the Chinese soil spectral library (CSSL) of dry ground soils to predict OM, TN and pH of paddy soils in the Yangtze River Delta using spectra of fresh (non-processed) soil samples measured in situ, after removing the influences of the environmental factors with direct standardization (DS). The locally weighted regression (LWR) model built on the CSSL was then used to predict with the DS-transferred field spectra. The CSSL consists of vis–NIR spectra of over 3993 samples collected local dataset from 19 Chinese provinces. Two hundred and twenty-five soil samples independent from the CSSL (local dataset) were collected from 20 target sites in the Yangtze River Delta, China and their spectra were measured in both field and laboratory conditions. Using DS, a subset of the corresponding field and laboratory spectra from the independent set (designated as the transfer set) was used to derive the DS transfer matrix, which characterized the differences between the field and laboratory spectra. The field spectra of the 225 samples were then transferred to match characteristics of laboratory measured spectra of processed soil samples. The predictions of soil properties were performed on the DS-transferred field spectra using a LWR model derived with the CSSL. Results showed that DS effectively removed the effects of moisture from field spectra, and led to simultaneous improvement in the predictions of pH, OM, and TN to an acceptable level (pH: R2=0.611, root mean square error (RMSE)=0.73 and ratio of performance to inter-quartile range (RPIQ)=2.30; OM: R2=0.641, RMSE=6.82gkg−1 and RPIQ=1.79; TN: R2=0.658, RMSE=0.39gkg−1 and RPIQ=1.81). We recommended the use of DS combined with CSSL models for the efficient prediction of soil pH, OM, and TN simultaneously using field scans of paddy soils.

Mercury (II) Adsorption on Three Contrasting Chinese Soils Treated with Two Sources of Dissolved Organic Matter: II. Spectroscopic Characterization

To reveal the influencing mechanism of dissolved organic matter (DOM) on mercury (Hg II) adsorption by black, red, and fluvo-aquic soils in China, Fourier transform infrared (FTIR) spectroscopy, 13C nuclear magnetic resonance (NMR) spectroscopy, and three-dimensional excitation emission matrix (3DEEM) fluorescence spectroscopy were employed to characterize the DOM samples and DOM-Hg complexes. FTIR spectra showed that the complexation of Hg (II) mainly acted on the C=O, COO−, and O-H groups of DOM from swine manure (DOMs) and wheat straw (DOMw). The NMR spectra indicated that the complex reaction of Hg (II) and DOM corresponded with the change in carboxyl C. The NMR results also showed that the dominant C components in DOM were aromatic C, O-alkyl C, alkyl C, and carboxyl C, and that DOMw imposed more influence on Hg (II) adsorption than DOMs, which was consistent with that of FTIR spectroscopy. The 3DEEM showed that DOM contained both aromatic protein-like and fulvic-like substances, and that the protein-like properties of DOMs and UV fulvic-like fluorescence substances of DOMw can better participate in the formation of Hg complexes. This result provides strong direct evidence to elucidate the DOM-Hg (II) binding mechanism, and further interprets the effect mechanism of exogenous DOM on Hg adsorption by soil.

A Feasibility Study on Co-Processing of Soil Contaminated with Heavy Metals in Cement Kilns

The national general survey manifests that the Chinese soil is suffering from serious contamination, mainly arising from heavy metals (HM). Due to the large amount of heavy metal waste, many researchers have performed the feasibility studies on co-processing this kind of waste in cement kilns. In this paper, we review these results from the perspectives of national standards, the crystal structure of clinker, and the volatility of metals in cement kiln system. The crystal structure of clinker mineral offers physical possibility for the solidification of HM atoms. The volatility studies also indicate that most of the metals will not emit from the kiln system. For the incorporated metals in clinker, their release ratio is very low, and the leaching HM atoms can be immediately enclosed by the cement hydration products. Based on these theoretical results, we measured the HM in the raw materials and in the cement product for 1 year in a cement plant. The bag filter dust contained high level of Tl with an average of 219.30 ppm. The other metals were almost solidified by the clinker. With the vaporization of Tl in the raw materials, the circulation pattern causes the accumulation and buildup of Tl in the system. The incorporation capacity of clinker on HM is predicted in this paper, but the incorporation ratio of HM from contaminated soil, the circulation pattern of HM in cement kiln system, and the emission of HM is currently not clear and further work is in progress.

Comparison of phytotoxicity of copper and nickel in soils with different Chinese plant species

Ecological risk assessment of metals in soils is important to develop the critical loads of metals in soils. Phytotoxicity is one of the endpoints for ecological risk assessment of soils contaminated with metals. The sensitivity of eight Chinese plant species (bok choy, mustard, tomato, green chilli, paddy rice, barley, spinach and celery) to copper (Cu) and nickel (Ni) toxicity in two Chinese soils was investigated to assess their potential use for ecological risk assessment in the region. The results showed that bok choy and mustard were the two most sensitive species to Cu and Ni toxicities. Assessment of metal accumulation by the plants demonstrated that bok choy shoot had the highest bioconcentration factor (BCF, the ratio of metal concentration in plant shoots to metal concentration in soil). Given the importance of bok choy to agricultural production in Asia, it is therefore important that these sensitive plant species are included in species sensitivity distributions for ecological risk assessment of Cu and Ni in soils.

Potential of VIS-NIR-SWIR Spectroscopy from the Chinese Soil Spectral Library for Assessment of Nitrogen Fertilization Rates in the Paddy-Rice Region, China

To meet growing food demand with limited land and reduced environmental impact, soil testing and formulated fertilization methods have been widely adopted around the world. However, conventional technology for investigating nitrogen fertilization rates (NFR) is time consuming and expensive. Here, we evaluated the use of visible near-infrared shortwave-infrared (VIS-NIR-SWIR: 400–2500 nm) spectroscopy for the assessment of NFR to provide necessary information for fast, cost-effective and precise fertilization rating. Over 2000 samples were collected from paddy-rice fields in 10 Chinese provinces; samples were added to the Chinese Soil Spectral Library (CSSL). Two kinds of modeling strategies for NFR, quantitative estimation of soil N prior to classification and qualitative by classification, were employed using partial least squares regression (PLSR), locally weighted regression (LWR), and support vector machine discriminant analogy (SVMDA). Overall, both LWR and SVMDA had moderate accuracies with Cohen’s kappa coefficients of 0.47 and 0.48, respectively, while PLSR had fair accuracy (0.37). We conclude that VIS-NIR-SWIR spectroscopy coupled with the CSSL appears to be a viable, rapid means for the assessment of NFR in paddy-rice soil. Based on qualitative classification of soil spectral data only, it is recommended that the SVMDA be adopted for rapid implementation.

Assessment of heavy metal pollution in vegetables and relationships with soil heavy metal distribution in Zhejiang province, China.

There are increasing concerns on heavy metal contaminant in soils and vegetables. In this study, we investigated heavy metal pollution in vegetables and the corresponding soils in the main vegetable production regions of Zhejiang province, China. A total of 97 vegetable samples and 202 agricultural soil samples were analyzed for the concentrations of Cd, Pb, As, Hg, and Cr. The average levels of Cd, Pb, and Cr in vegetable samples [Chinese cabbage (Brassica campestris spp. Pekinensis), pakchoi (Brassica chinensis L.), celery (Apium graveolens), tomato (Lycopersicon esculentum), cucumber (Colletotrichum lagenarium), cowpea (Vigna unguiculata), pumpkin (Cucurbita pepo L.), and eggplant (Solanum melongena)] were 0.020, 0.048, and 0.043 mg kg(-1), respectively. The Pb and Cr concentrations in all vegetable samples were below the threshold levels of the Food Quality Standard (0.3 and 0.5 mg kg(-1), respectively), except that two eggplant samples exceeded the threshold levels for Cd concentrations (0.05 mg kg(-1)). As and Hg contents in vegetables were below the detection level (0.005 and 0.002 mg kg(-1), respectively). Soil pollution conditions were assessed in accordance with the Chinese Soil Quality Criterion (GB15618-1995, Grade II); 50 and 68 soil samples from the investigated area exceeded the maximum allowable contents for Cd and Hg, respectively. Simple correlation analysis revealed that there were significantly positive correlations between the metal concentrations in vegetables and the corresponding soils, especially for the leafy and stem vegetables such as pakchoi, cabbage, and celery. Bio-concentration factor values for Cd are higher than those for Pb and Cr, which indicates that Cd is more readily absorbed by vegetables than Pb and Cr. Therefore, more attention should be paid to the possible pollution of heavy metals in vegetables, especially Cd.

Accounting for the effects of water and the environment on proximally sensed vis–NIR soil spectra and their calibrations

SummaryVisible–near infrared (vis–NIR) spectroscopy can be used to estimate soil properties effectively using spectroscopic calibrations derived from data contained in spectroscopic databases. However, these calibrations cannot be used with proximally sensed (field) spectra because the spectra in these databases are recorded in the laboratory and are different to field spectra. Environmental factors, such as the amount of water in the soil, ambient light, temperature and the condition of the soil surface, cause the differences. Here, we investigated the use of direct standardization (DS) to remove those environmental factors from field spectra. We selected 104 sensing (sampling) sites from nine paddy fields in Zhejiang province, China. At each site, vis–NIR spectra were recorded with a portable spectrometer. The soils were also sampled to record their spectra under laboratory conditions and to measure their soil organic matter (SOM) content. The resulting data were divided into training and validation sets. A subset of the corresponding field and laboratory spectra in the training set (the transfer set) was used to derive the DS transfer matrix, which characterizes the differences between the field and laboratory spectra. Using DS, we transferred the field spectra of the validation samples so that they acquired the characteristics of spectra that were measured in the laboratory. A partial least squares regression (PLSR) of SOM on the laboratory spectra of the training set was then used to predict both the original field spectra and the DS‐transferred field spectra. The assessment statistics of the predictions were improved from R2 = 0.25 and RPD = 0.35 to R2 = 0.69 and RPD = 1.61. We also performed independent predictions of SOM on the DS‐transferred field spectra with a PLSR derived using the Chinese soil spectroscopic database (CSSD), which was developed in the laboratory. The R2 and RPD values of these predictions were 0.70 and 1.79, respectively. Predictions of SOM with the DS‐transferred field spectra were more accurate than those treated with external parameter orthogonalisation (EPO), and more accurate than predictions made by spiking. Our results show that DS can effectively account for the effects of water and environmental factors on field spectra and improve predictions of SOM. DS is conceptually straightforward and allows the use of calibrations made with laboratory‐measured spectra to predict soil properties from proximally sensed (field) spectra, without needing to recalibrate the models.