• Volume 55,Issue 2,2018 Table of Contents
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    • >Reviews and Comments
    • Challenges and Countermeasures for Heavy Metal Pollution Control in Farmlands of China

      2018, 55(2):261-272. DOI: 10.11766/trxb201711240485

      Abstract (5170) HTML (3969) PDF 958.00 K (9576) Comment (0) Favorites

      Abstract:The agricultural soil in China has been widely polluted by heavy metals and the regional contamination is serious. The experience on soil remediation in developed countries is significantly instructive for farmland protection in China. The heavy metal pollution of farmlands in China faces great challenges including spatial heterogeneity of heavy metal accumulation, various enrichment characteristics depending on soil types and crop, soil acidification, loss of soil trace elements, unreasonable development patterns, significant input of heavy metal into soil, poor correlation between the heavy metal concentration in soil and crop plants, inadvisable remediation techniques, and lack of long-term risk control measures. Responses to these problems, we proposed a soil prevention and control system to promote the remediation of contaminated cropland in China, which mainly focused on pollution prevention, and take prior protection as well as risk control as basic course. Based on this system, the soil pollution prevention and control work can be implemented through systematically procedures including soil environment investigation, pollution source control, risk assessment and classification management, and the derivation of soil quality threshold.

    • Effects of Climate Change on Molecular Structure and Stability of Soil Carbon Pool: A General Review

      2018, 55(2):273-282. DOI: 10.11766/trxb201707240324

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      Abstract:Soil generally serves as both sink and source for atmospheric CO2, and plays a crucial role in maintaining carbon balance on the global scale, and mitigating the greenhouse effect. Mechanisms for interaction and combination between climate change and soil carbon pool have long been a hot spot and a hard nut to crack for the academic circle. Although extensive studies have been done on the subject at community-ecosystem, and regional-global scales, little has been reported about mechanisms of the variation of climate factors affecting chemical structure of the soil organic carbon pool (SOC) at the molecular scale. This review summarizes recent works on changes in climate factors and the changes in environmental and ecological factors they trigger and their relationships with molecular structure of the soil organic carbon pool. Climate warming not only changes characteristics of the sources of SOC from plant tissues, and significantly increases the content of cutin, a component of leaf epidermis, but also keeps relatively unchanged or declining the major components of SOC, such as carbohydrate, lignin, suberin and the like. Meanwhile, warming also accelerates decomposition of lignin and some other carbon components, promotes decomposition of aliphatic compounds, cutin and cyclic compounds and enhances soil microbiota in activity, thus leading to accumulation of plant-sourced alkyl-structured and/or microbe-sourced organic matter. Changes in soil hydrological regime also alter characteristics of the functional groups of soil organic carbon. For instance, drainage or drought triggers acceleration of decomposition of organic matter mineralization, thus increasing C=O bonds in soil; and fluctuation of soil water table controls chemical structure of the organic matter by affecting Fe form in the soil. Vegetation succession changes sources of soil organic matter due to difference between plant residues in inherent resistance to decomposition, and consequently alters properties of the soil organic carbon in the end. In the same climate zone, soils covered with various predominant vegetations are often characterized by remarkable differences in molecular structure of soil organic matter. Soil fauna and microorganisms, which are both ecological factors closely related to climate change, also alter properties of the plant residues in soil, promote decomposition of lipids, lignin and saccharides, and form different biomarkers. However, still not much has been done on how soil fauna and microbes alter molecular structure of soil organic matter. Stability of SOC is closely related to molecular structure of soil organic matter. Generally, SOC are more stable in the soil where contents of aromatic and O-alkyl compounds are high. In the soil the youngest fraction of carbon (formed in the past 107 years) usually features more aromatic compounds and low ratios of O-alkyl carbon to aromatic carbon, while the oldest fraction of carbon (over 1000 years) does less compounds and O-alkyl carbon. However, lignin is not so stable as previously expected facing climate warming. In the future, more researches should be done with stresses on special biomarkers and their ecological meaning, effect and mechanism of biota regulating molecular transformation processes of SOC, combined mechanisms of large-scaled environmental/ecological process and transformation of molecular structure of the carbon pool, and techniques to identify and interpret new molecular structures of SOC.

    • >Research Articles
    • Mode of Rotation/Fallow Management in Typical Areas of China and Its Development Strategy

      2018, 55(2):283-292. DOI: 10.11766/trxb201708250387

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      Abstract:[Objective] Currently, researchers all over the country are actively exploring farmland rotation/fallow systems for pilot farms and developing scientific and rational rotation/fallow modes or methods, which is of profound significance to future development of the agriculture in China. [ Methods ] During the period from March to June of 2017, a group of scientists of the Consultation and Research Team for Exploring and Implementing Rotation/Fallow Systems in Pilot Farms investigated the experiments of rotation/fallow systems implemented in areas typical of Jiangsu, Hunan and Hebei Provinces, examined the experiment fields and discussed with local leaders and farmers. Generalization, summarization and analysis were made of the large volumes of data and information obtained during their investigation trips coupled with the data available in the literature. Modes of the rotation/fallow systems and their corresponding technical measures in the three typical areas, i.e. mono-cropping obstacle area ( Jiangsu Province ), heavy metal pollution area ( Hunan Province ) and groundwater funnel area ( Hebei Province ), were summarized and analyzed, too. [ Results ] In Jiangsu, modes, like winter fallow including tillage and sunning, growing winter green manure crops, intercropping with bean crops; and other soil fertility building measures are practiced and advocated, in Hunan. planting new varieties of crops, soil amelioration, scientific irrigation, control of crop uptake of heavy metals and "VPI + n", an innovative pollution control pattern are and in Hebei, seasonal fallow and annual fallow are. Relatively and significantly higher economic, social and ecological benefits are achieved after adoption and implementation of the rotation/fallow modes in the three typical regions. Besides, ”our principles”, “four unifications” and “eight important measures” are brought forth for the rotation/fallow systems in the three typical areas of China. [Conclusion] Different rotation/fallow modes should be adopted site-specifically in different regions and step by step by sort. This paper is expected to be able to provide some practical reference for the pilot experiments and scientific extrapolation of the rotation/fallow system.

    • Design and Application of Soil Map Annotation Auto-configuration System Based on Database-driven Technology

      2018, 55(2):293-303. DOI: 10.11766/trxb201707190119

      Abstract (1701) HTML (722) PDF 2.15 M (2368) Comment (0) Favorites

      Abstract:【Objective】Soil map annotation is an essential component of soil mapping to have a better understanding of soil genesis and distribution. During the Second National Soil Survey sponsored by the Ministry of Agriculture of the People Republic of China in the 1980s, large volumes of soil maps at the county level were plotted in paper using the traditional mapping and annotating method, which is no longer efficient enough for plotting and annotating large-scaled multi-framed soil maps (more than 20 000 standard frames, 1: 50 000 in scale) that contains such huge volumes of soil spatial information. In order to realize automatic and interactive annotation and solution of a series of problems of step judgment in soil mapping, a soil map annotation auto configuration system was built up. 【Method】 The system was developed on ArcEngine 10.1 platform with C# programming language based on database-driven technology. The system solved the problem of annotation overlapping outer-boundaries of soil patches in the map with the help of the over boundary annotation detection method, and realized annotation of the entire map layer and the background layer on the map layer level, using the three-level control method, i.e. layer, grade code and feature object; condition judgment and threshold screening by combining statistics in grade coding and annotations of special features on the feature level. 【Result】In order to evaluate performance of the Soil Map Annotation Auto-configuration System, a standard frame of soil map, F49E010012, of Xinyi, Guangdong, was chosen as an example for adoption of the system, with the 1:50 000 national basic geographic data and the 1:50 000 soil spatial and attribute data of the region as input. The basic geographic information to be annotated in the map includes residential settlements, linear water systems, surface water systems and administrative boundaries, whereas the soil spatial data do soil types and soil profile sites. The spatial data and attribute data were converted into Geodatabase. Analysis of the output volume of annotations shows that a total of 615 annotations were formed out of 2 618 items of feature data, including 2 067 items that already contains annotation names, and that the annotations formed covered only about 30% of all the annotatable feature data. The water systems and soil profile sites rarely annotated were reserved in the annotating process. On the soil map layer, most of the soil codes were reserved as annotation. Residential settlements were too densely clustered to keep the name of each settlement in annotation and only names of the settlements over the township level appeared. In the light of the conditions of the grading code screening module and avoidance analysis module, the volume of annotation was greatly reduced, particularly, the number of residential settlements to avoid overcrowding of the annotations of residential settlements on the map and relief the load of annotation, so as to maintain balance of the map in appearance. Comparison of the two maps shows that the original map had annotations overlapping map boundaries, while the map having processed with the Soil Map Annotation Auto-configuration System did not have such problems. 【Conclusion】Based on the database-driven technique and human-computer interaction, the Soil Map Annotation Auto-configuration System is adopted to rapidly annotate an enormous volume of standard frame soil maps. The system is not only highly flexible, and adoptable to soil maps and other maps varying in scale, but also greatly improving the efficiency and automation degree of data production. All the findings in the study may serve as reference for realizing annotation automatic configuration in soil mapping varying in scale in future.

    • Study on Relationship between Soil Calcium Carbonate Content and Inversion Effect Based on Visible Near-infrared Reflectance Spectra

      2018, 55(2):304-312. DOI: 10.11766/trxb201707170240

      Abstract (2044) HTML (1023) PDF 1.61 M (3167) Comment (0) Favorites

      Abstract:【Objective】 Soil visible near-infrared reflectance spectra contains large volumes of information on soil physical and chemical properties, which implies that it is feasible to use soil spectra to invert soil properties quantitatively. Is it the higher the property value, the higher the inversion accuracy? However, at present, it is still unclear how to relate quantitatively effects of inversions to soil property contents. 【Method】 Therefore, this study selected soil calcium carbonate content as the target attribute for exploration of quantitative relationship between spectral inversion effect and calcium carbonate content. A total of 292 soil samples were collected out of the genetic horizons of 69 typical Aridosols profiles in the Heihe River Basin, Northwest China, for analysis of calcium carbonate contents with the gasometric method and acquisition of visible near-infrared reflectance spectra with a Cary5000 spectrophotometer. Based on the characteristics of the distribution of calcium carbonate content in the typical study area, 11 identical sample size subsets (A) and 5 similar dispersion subsets (B) were established with sample size and data dispersion (coefficient of variation) as the criteria for dataset partitioning, and the partial least-squares regression (PLSR) method was used to invert calcium carbonate content from the spectral curves.【Result】 Results show that calcium carbonate in the Aridosols of the Heihe River Basin varied in the range of 4.86 g kg-1 ~ 236.03 g kg-1 in content with an average of 103.07 g kg-1. Soil samples with calcium carbonate content varying in the range of 30 ~ 60 g kg-1 and of 120 ~ 150 g kg-1, were in dominancy, accounting for 21.4% and 32.6% of the total, respectively. As a whole, the soil is high in calcium carbonate content, which is consistent with the characteristics of Aridosols being rich in calcium carbonate. With the PLSR, modeling was performed for prediction of calcium carbonate contents of the soil samples in the 11 A subsets. RPD of the validation set of each subset ranged between 0.92 and 1.04, fluctuating around 1 with no obvious features of variation, which indicates that calcium carbonate content does not have much impact on prediction or inversion of soil calcium carbonate content, using visible near-infrared reflectance spectra. Modeling was also done for prediction of calcium carbonate content in 5 B subgroups, with a similar result. 【Conclusion】 Therefore, soil calcium carbonate content is not the main factor affecting the prediction using spectra, which is inconsistent with the qualitative knowledge the researchers already have in mind. Calcium carbonate can enhance spectral reflectance of visible near-infrared bands, but the effect is not so significantly reflected in using the visible near-infrared spectral reflectance to inverse soil calcium carbonate content. Therefore, it seems unnecessary to divide calcium carbonate samples by content of soil calcium carbonate when using spectra to predict calcium carbonate contents. Whether the conclusion is applicable to other soil properties needs to be further verified, and how to improve accuracy of the prediction of target attribute will be the focal point of the next phase of the study.

    • Inversion of Soil Organic Matter Content in Oasis Typical of Arid Area and Its Influencing Factors

      2018, 55(2):313-324. DOI: 10.11766/trxb201705310236

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      Abstract:【Objective】 Soil organic matter (SOM) content is an important soil index, essential to guiding usage of chemicals in agriculture, and also an important factor affecting regional carbon balance. Scholars have long been interested in the study of soil organic matter and have helped address key environmental, agricultural and social and political issues over the past ten years. It is essential to have simpler, more accurate, more rapid and more inexpensive methods for plotting soil organic matter maps, and moreover, more time-and-cost saving ones.【Method】 Remote sensing data have extensively been used in digital soil mapping, especially in assessing soil organic matter, because the use improves accuracy of the prediction of soil physical parameters to some extent. To explore feasibility of combining the narrow band of hyperspectrum and the wide band of multispectral remote sensing images to realize high-accuracy prediction of soil organic matter (SOM), field data and soil samples were collected in Weigan River Oasis of Kuche in May of 2016 for in-lab analysis of SOM content using the potassium dichromate method; hyperspectral data were in the darkroom with the aid of the ASD Fieldspec3 spectrometer; the first 7 bands of the Landsat 8 OLI remote sensing images of May 30, 2016 were selected and used for atmospheric correction, radiometric correction and fine geometric correction of the images as pretreatment. In addition, the band averaging method was used to fit the measured data of the hyperspectral narrow bands into data of the multispectral wide bands, and then to screen out sensitive spectral parameters; models for assessing soil organic matter were built up, using the partial least squares regression method for test and screening of an optimal model. In the end, spatial distribution of soil organic matter was analyzed, taking into account all soil factors.【Result】Results show that SOM content in the oasis varies in the range of 3.57 ~ 39.22g kg-1. An optimal prediction model was built up based on the 2nd, 5th and 6th bands as independent variables after being subjected to first differential transformation, with determination coefficient R2 of the model dataset being 0.852 and of the validation set being 0.897. On such a basis, the optimal model was applied to multi-spectaral data based prediction of soil organic matter using the Landsat 8 OLI satellite images. Differential transformation significantly improved the correlation of hyperspectrum with soil organic matter content. After the reflectances of the multi-spectral bands were calibrated with the ratio method, determination coefficient R2 of the validation dataset was raised from 0.711 to 0.849. Distribution of soil organic matter was less affected by land use types or soil texture than soil particle composition.【Conclusion】The inversion of SOM indicates that the remote sensing based inversion of SOM fits the actual situation of the study area, displaying good reliability and authenticity. In this study, the findings are the same as and different in places from those of other scholars, so further studies should take into account effects of soil moisture content, salinity, landform and some other factors on soil organic matter content and improve accuracy of the prediction model. All the findings of the study exploring feasibility of combining the hyper-spectral model with remote sensing inversion in predicting soil organic matter in the studied area may serve as scientific basis and technical reference for quick acquisition of SOM information in Arid and semi-arid regions.

    • Hyperspectral Model for Estimation of Soil Potassium Content in Loessal Soil

      2018, 55(2):325-337. DOI: 10.11766/trxb201706040137

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      Abstract:【Objective】Soil is the important carrier of agricultural production, while the potassium in soil is one of the nutrient elements essential for plant growth, so it is very important to quickly and accurately assess soil potassium content in farmland. Conventional soil potassium content determination methods are expensive and time-consuming. The visible and near infrared reflectance spectroscopy (VIS–NIR), which possess the advantages of non-destructive and rapid detection, has been a useful tool for quantitative analysis of soils of numerous attributes. The object of this study is to investigate feasibility to use the visible and near infrared reflectance spectroscopy in estimating soil potassium contents in the Weibei Rainfed Highland. 【Method】A total of 120 loessal soil samples were collected from the farmfields in Qian County of Shaanxi Province for analysis of total potassium (TK) and readily available potassium (AK) contents in lab with conventional chemical methods. Reflectance spectroscopic data of the soil samples were acquired with the SVC HR–1024i spectroradiometer. Three types of pretreatments, including First-order differential of soil spectral reflectance (DSSR), band depth (BD) and First-order differential of band depth (DBD), were adopted to amplify the weak absorption characteristics, eliminate noises in the system and external disturbances. The continuum-removal method was used to extracted band-depths (BD) of the soil reflectance spectra and based on correlation analysis a model was built up for prediction of TK and AK contents in the loessal soil, using the multiple linear regression (MLR) and partial least squares regression (PLSR) methods and validated with independent samples. 【Result】Results show that the multiple linear regression model based on DSSR as independent variable could accurately estimate TK contents while the other multivariate linear regression models could not do TK and AK contents so accurately. Comparison shows that the PLSR models were generally higher than the MLR models in prediction accuracy. The models built up with the PLSR method incorporating the 4 spectral variables, could estimate TK content accurately, specially the PLSR model based on DBD as independent variable, of which coefficient of determination (R2pre) of the validation set was > 0.90, root mean square error of the prediction (RMSEpre) was 0.054, and residual predictive deviation (RPDpre) was 3.310. The PLSR model based on BD followed. However, the PLSR models based on the 4 spectral variables were relatively low in calibration and validation accuracy and only some models could roughly predict AK contents. The PLSR model based on DSSR as independent variable, with RPDprebeing 1.619 and 1.572 was the best for accurate prediction of soil AK contents. 【Conclusion】All the finding in this study demonstrate that the visible and near infrared spectroscopy coupled with MLR and PLSR can be used to predict rapidly and accurately TK content in the loessal soil of the Weibei Rainfed Highland, but only roughly AK contents therein.

    • Spatio-temporal Variation of Soil Total Nitrogen in Huangshui River Basin and Its Affecting Factors in the Past 30 Years

      2018, 55(2):338-350. DOI: 10.11766/trxb201705130216

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      Abstract:【Objective】Nitrogen is the most important nutrient for plant growth, and so an important index for evaluation of soil fertility, too. Spatio-temporal variation of soil nitrogen can cause global nitrogen shifting between "source" and "sink", thus affecting nitrogen recycling in the terrestrial ecosystem. The study on spatio-temporal variation of soil total nitrogen (TN) may help effectively reveal relationships between spatio-temporal patterns of soil TN and ecological processes, which is of great significance to sustainable utilization of the soil resources. As in agricultural regions, the soil is subjected to dual influences, natural and artificial, the study on spatio-temporal variation of TN in the soil may help expose more accurately how artificial and natural factors affect the variation and guide rational fertilization and sustainable utilization of the soil in the regions. 【Method】 To that end, analysis was done of the data of the 45 profiles of the second national soil survey in 1985 and the 61 profile of the soil survey in 2015 in the Huangshui River Basin of Qinghai Province, using the classical statistics including descriptive statistics analysis, correlation analysis and variance analysis, and the geostatistics including semi-variance analysis and Ordinary Kriging analysis, for spatio-temporal variations of TN in the 0~15 cm and 15~30 cm soil layers and their influencing factors in the past 30 years. 【Result】Results show that: by excluding abnormalities, the data valid for analysis consisted of 45 items of the 0~15 cm soil layer and 44 items of the 15~30 cm soil layer obtained in 1985 and 61 items of the 0~15 cm soil layer and 58 items of the 15~30 cm soil layer obtained in 2015. From 1985 to 2015, the mean TN content in the 0~15 cm and 15~30 cm soil layers increased from 1.33 g kg-1 to 2.25 g kg-1 and from 1.15 g kg-1 to 2.08 g kg-1, or by 69.2% and 80.87%, respectively, and variation coefficient of the mean soil TN increased from 58.65% to 68.0% and from 65.22% to 67.79%, respectively, which indicates that soil TN content during the period varied at a medium level; Semi-variance analysis shows that the TN data of the two soil layers in 1985 fit the Exponential model, while those of the 0~15 cm soil layer and the 15~30 cm soil layer in 2005 fit the Gaussian model, and the Spherical model, respectively. Nugget coefficients of the TN data of the two soil layers in 1985 were both <25%, exhibiting strong spatial correlations, which indicates that spatial distribution of the soil TN was mainly affected by structural factors such as topography, parent material, temperature and precipitation, while those in 2015, both varied between 25% and 75%, displaying medium spatial autocorrelations, which indicates that spatial distribution of the soil TN during this period was governed by both structural factors and random factors, simultaneously. The change in spatial distribution autocorrelation from strong in 1985 to medium in 2015 suggests that the influences of random factors like human activities on soil TN was strengthening in the region, thus weakening the spatial distribution autocorrelation in recent years; In the past 30 years, soil TN content in the Basin was on a rising trend, demonstrated mainly in the western, northern and central parts of the region while in the southeast part it was on a reverse trend region decreased. A first-falling-and-then-rising trend was found In 1985 along the east-west and north-south directions, and in 2015 a holistically rising one was along the southeast-northwest direction. The graph of spatial distribution of standard deviations of TN contentprediction demonstrates that the predicted spatial distribution map of soil TN based on Ordinary Kriging of the two lots of TN data is good enough to reflect the real situation Natural factors, such as climate, elevation, soil texture, soil type, and so on and artificial factors, like land use, fertilization, planting structure, agricultural mechanization, etc. acted jointly causing sharp spatio-temporal variation of soil TN, and the intervention of human beings in soil nutrients exhibited an increasing trend. 【Conclusion】Considering the high spatio-temporal variability of TN content, it is suggested that a long-term soil TN monitoring system be set up in the Huangshui River Basin, and that partition management of agricultural nitrogen fertilization should be enforced, so as to ensure sustainable development of the agriculture of the whole Basin.

    • Spatio-temporal Distribution of Thermal Diffusivity in Deep Soil in Qinghai-Tibet Plateau

      2018, 55(2):351-359. DOI: 10.11766/trxb201709140273

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      Abstract:【Objective】The Qinghai-Tibet Plateau is an area relatively active in ground-atmosphere interaction, Only through understanding in depth variation of soil thermal diffusivity in the Qinghai-Tibet Plateau, can the surface energy balance on the Plateau be correctly calculated and the impact of the Plateau on global and regional climate change be understood in depth. 【Method】Based on the data of soil temperatures at 0.8 m and 3.2 m deep in soil profiles accumulated in the 39 observation sites in the Qinghai-Tibet Plateau during the years from 1980 to 2001, thermal diffusivity of each observation site was worked out through fitting of the heat conduction convection method coupled with the least square method, and spatio-temporal variation of soil thermal diffusivity figured out. The heat conduction convection method encompasses heat conduction and thermal convection in calculating soil thermal conductivity. The amplitude and phase was obtained through fitting of the measured soil temperatures at the two soil depth with the least squares method, and substituted into the formula to yield soil thermal diffusivities. 【Result】 Results show that from 1980 to 2001, soil thermal diffusivity of the Qinghai - Tibet Plateau appeared to be on a declining trend. It fluctuated quite sharply before the 1990s and less in the 1990s. As affected by climate factors, soil properties and soil moisture content, soil thermal diffusivity vary in spatial distribution. Soil thermal diffusivity in the deep soil in the eastern part of the Qinghai-Tibet Plateau increased from spring to summer and decreased from summer to autumn and from autumn to winter. It peaked in summer up to 8×10-6 m2 s-1 in summer at the junction of Qinghai Province, Sichuan Province and Gansu Province and in winter up to 5.1×10-7 m2 s-1. In the rest of the Plateau, soil thermal diffusivity decreased from spring to summer, increased from summer to autumn and decreased again from autumn to winter, varying in the range of 1.2×10-7 m2 s-1 to 9.2×10-7 m2 s-1. For years the maximum mean monthly value of soil thermal diffusivity was observed in the eastern part of the Qinghai-Tibet Plateau, including Qinghai, Southwest of Gansu and West Sichuan, being 6.4×10-6 m2 s-1, whereas the minimum was in the region of Qilian Mountains, being 1.2×10-7 m2 s-1, and the mean monthly soil thermal diffusivity was relatively high in the central part of the Plateau. As affected by geographical location, soil properties, soil moisture content and number of snow coverage days, the central and eastern parts of the Plateau, to the northeast part of Nagqu, are sorted as alpine frigid humid climate zone, where the soil thermal diffusivity is high due to high precipitation and high soil water content, and the area of the Qilian Mountains is as alpine frigid semi-arid climate zone, where the soil thermal diffusivity is low varying in the range of 1×10-7~4.8×10-7 m2 s-1 because it is a permafrost region low in soil water content. In most parts of the Qinghai-Tibet Plateau, soil thermal diffusivity varies in the magnitude order of 10-7 m2 s-1, and in the central and eastern parts abeing relatively high-valued regions, it does in the magnitude order of 10-6 m2 s-1.【Conclusion】All the findings in this study demonstrate that soil thermal diffusivity varies sharply temporally and spatially, as affected by a complicated variety of factors, which merit further studies.

    • Discussion on the soil pore structure and pore tortuosity-connectivity based on soil air permeability

      2018, 55(2):360-368. DOI: 10.11766/trxb201707070161

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      Abstract:【Objective】The characteristics of soil hydraulic conductivity are used to construct the geometric model of pore parameters, but the variation of hydraulic parameters in field is usually very large and the measurement efficiency is low. Soil air transmission is highly dependent on soil pore structure and acquisition of the air permeability is simple, fast, and efficient, and little damage to soil structure.Using soil air permeability rate to analyze soil structure and pore geometry distribution is becoming the focus of attention.【Method】We use soil air permeability measurement instrument (PL-300) to get the air permeability, and use the centrifuge to get the soil water characteristic curve.We measured the air permeability of undisturbed and disturbed soils under different water contents and different soil bulks, through the two relative air permeability curve fitting bending pore connectivity factor, we discussed the pore structure and pore tortuosity-connectivity.【Result】The results showed that: 1) Pore tortuosity-connectivity increased with air phase saturation increasing,and the increase degree of undisturbed soil is more significant than disturbed soil. When the air saturation is 18%, 32%, 60% and 86% , the relative permeability of the disturbed soil is respectively 50.77%, 51.65%, 50.31%, and 51.02% of the undisturbed soil. The trend curves of relative air permeability and saturation, both of undisturbed and disturbed soil, were basic same, but not coincident. Which means that the degrees of pore tortuosity-connectivity is different, even if the saturation of undisturbed soil and disturbed soil are same. 2) The air permeability of undisturbed soil depended on the existence of macroporosity, while the air permeability of disturbed soil not only depended on the degree of pore connectivity, but also depended on pore tortuosity-connectivity.【Conclusion】Based on the discussion which soil air permeability create the change of soil pore structure make for pore geometry feature differences, in the soil air transmission and pore structure of the related research and the process of application in mathematical model, in addition to the analysis of soil physical basic parameters, should be taken into account the influence of pore size distribution on air permeability under the condition of high moisture content, distinguishing and discussing undisturbed and disturbed soil different bending connectivity factor, in order to further reveal the internal mechanism of soil air transmission to provide the reference.

    • Effect of Gas-Liquid Interfacial Tension on Shrinkage Cracking of Clay as Affected by Wetting-Drying Alternation

      2018, 55(2):369-379. DOI: 10.11766/trxb201708100298

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      Abstract:【Objective】In recent years, disastrous soil pollution incidents have been taking place quite frequently. Surface activating agents were widely used in remediation of polluted soils as it is an effective soil amendment. Addition of surfactants can accelerate remediation processes and improve soil properties, and alter the surface tension of pore water in the soil as well. It has been demonstrated in a number of studies that surface tension of pore water is substantially reduced by adding a small amount of surfactant, and altered, too, by adding some organic compounds, which are often found as residues in wastewater treated and recycled as irrigation water. The three major equations describing characteristic of the interface, i.e. Young equation, Laplace equation and Kelvin equation, are all related to surface tension. So gas-liquid interfacial tension (also surface tension) is the main factor affecting shrinkage cracking of soil, and besides, changes in surface tension are bound to have an important impact on soil-water characteristics of soil. In addition, under actual climate conditions and natural environment, which are often very complicated, soils are generally subjected to several times of drying and wetting alternations, which may cause delay of the soil water characteristic curve, and variation of contact angle is also an important factors causing delay of the curve, while contact angle and surface tension are closely related to each other. It is, therefore, of great theoretical and practical significance to characterize soil shrinkage cracking from the view point of surface tension as affected by wetting and drying alternation to agricultural irrigation as well as environmental protection.【Method】In order to better understand the effect of surface tension on soil shrinkage cracking, an experiment designed to have the soil samples subjected to wetting-drying alternations was carried out, with drying temperature set at 25°C and 60°C.The experiment had three groups of soil samples treated with different solutions, thus being different in surface tension when initially saturated. Changes in soil water content and evolution of surface cracks were monitored in the samples under dehumidification, and even photos were taken for quantitative analysis of fissure development degree (δ) on the surface of the samples using the digital image processing technique. Then comparative analysis was done for relationships of surface tension with δ and changes in water content, and with temporal variation of δ.【Result】Results show that with the drying-wetting alternation going up in frequency, δ of the soil at the end of the experiment increases somewhat, but not large in magnitude; δ is significantly influenced by temperature: the higher the temperature, the earlier the initial fissures appear. When the drying temperature rises from 25°C and 60°C, critical water content at the onset of cracking increases from 38% to 41%, and δ of the soil at the end of the experiment by 20%~40%; when the drying temperature remains the same, with declining surface tension soil fissure development slows down and δ of the soil at the end of the experiment lowered; but it is found that δ of the soils low in surface tension may be higher than that of the soils high in surface tension at the initial stage; when water content is the same, the higher the surface tension, the more the fissure development degree. Regardless of temperature environment, in terms of surface tension and fissure development degree, the three groups of soil samples exhibits an order of samples treated with pure water >samples treated with alcohol solution >samples treated with soap water.【Conclusion】In a word, wetting-drying alternation does have certain influence on development of soil fissures; and temperature is a major faction directly controlling shrinkage cracking of soil; While surface tension is one restraining the processes.

    • Temperature Sensitivity of Iron Redox Processes in Wetland Soil in the Middle and Lower Reaches of the Yellow River

      2018, 55(2):380-389. DOI: 10.11766/trxb201708110352

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      Abstract:【Objective】 As iron reduction and oxidation processes in soil are closely related to bio-availability of heavy metals, degradation of organic pollutants and emission of carbon-containing greenhouse gases, they have aroused increasing concern among scholars. Temperature is a factor that may affect iron redox in soil by influencing activity of ferric reduction and ferrous oxidation bacteria, and bio-availability of substrates. Temperature sensitivity of heterotrophic respiration, which is driven by iron redox processes, has been intensively investigated, but little has been done on temperature sensitivity of iron redox processes in wetland soils. 【Method】So in this paper, soil samples were collected from paddy fields or wetlands in Yuanyang County of Xinxiang City, Henan Province, a major rice production area in the middle and lower reaches of the Yellow River for analysis of temperature sensitivity of iron redox processes in the soil through temperature-controlled anaerobic incubation. Samples of the paddy or wetland soil were prepared into slurry and then incubated anaerobically in darkness or under illumination at a preset temperature, and ferrous in the slurry was analyzed periodically to monitor temperature sensitivity of iron oxides reduction and ferrous oxidation in darkness and under illumination. Air in the headspace of the vials after 3 days of incubation was analyzed for O2 using an optical fiber oxygen detector (PreSens Microx 4, Germany Regensburg), and for CO2 using a gas chromatographer (GC7900, China Shanghai Tianmei) equipped with a TCD detector. Water soluble organic and inorganic carbon in the slurry was measured with a TOC analyzer (TOC-VCPH Japan Shimadzu) after the incubation. 【Results】Results show that temperature varying in the range of 16 oC ~ 31 oC did not have much effect on ferric reduction capacity in the soil samples, but it did increase the maximum rate and rate constant of iron reduction significantly, and advance the peaking time, when increasing from 16 oC to 40 oC. O2 was found accumulating in the headspace after 3 days of anaerobic incubation in light, and the accumulation increased with increasing incubation temperature. Water soluble inorganic carbon and CO2 increased dramatically with rising temperature in slurries under incubation in darkness, but no detectable CO2 and only little WSIC was found in the vial under illuminated incubation. 【Conclusion】 Temperature-sensitivity coefficient of iron reduction increased from 1.18 to 3.05 with rising temperature, but decreased under illumination by 39.0% on average. Temperature insensitivity of ferrous oxidation was observed during incubation in light. Quality and quantity of iron oxides and illumination conditions are supposed to be potential key factors affecting mineralization of organic carbon in wetland soils. All the findings in this paper could be of great significance to further efforts to understand biogeochemical cycle of iron in soil and its relationship with soil respiration.

    • Accumulation Characteristics of Amino Sugars in Salinized Soils of Different Types in the Yellow River Delta

      2018, 55(2):390-398. DOI: 10.11766/trxb201710310503

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      Abstract:【Objective】Soil salinization is one of the most severe agro-ecological problems that brings about widespread influences on ecosystem security and sustainable development of the agriculture, especially in the Yellow River Delta. It has been demonstrated that soil salinization has significant influences, too, on activity and structure of the soil microbial community through changing soil physicochemical properties. Yet, little has been documented about responses of microbial residues to soil salinization and relative contributions of microbial residues different in kind to soil organic matter (SOM) accumulation. As important constituents of microbial cell walls, amino sugars are considered to be a storage pool for immobilized C and N. Additionally, amino sugars are reliable microbial residue biomarkers thanks to their different origins. Muramic acid (MurA), glucosamine (GluN) and galactosamine (GalN) are amino sugars of particular importance, so far identified. MurA originates uniquely from bacteria as a component of peptidoglycan of bacterial cell walls, while GluN is mainly derived from fungal chitin, although bacterial cell walls and exoskeletons of soil invertebrates also make some contribution. GalN constitutes a significant fraction of the total amino sugar pool, but its origin in soil is still under debate. Therefore, amino sugars as unique and powerful microbial residue biomarkers can be used to indicate time-integrated microbial immobilization of extraneous C and N and stabilization of SOM on a relatively long-term scale, which is termed as “memory effect”.【Method】 Here, investigations were made of accumulation characteristics of the three types of amino sugars in the topsoil layers (0~20cm) of two crop fields of salinized soils, different in salinization level, i.e. light-salinized soil (LS) and moderate-salinized soil (MS), in the Yellow River Delta. In addition, relative contributions of fungal and bacterial residues to SOM accumulation and stabilization were explored by calculating ratio of GluN to MurA.【Result】Results show that soil salinization had significant influences on accumulations of total amino sugars and each. Total amino sugar was significantly higher in LS than in MS, but amino sugars of different kinds responded differently in content to salinization because of their specific origin. GluN content was much higher in LS than in MS. Although it is still not clear as to origin of GalN, it was similar to GluN in accumulation characteristics. Coming solely from bacteria, MurA was much higher in MS than in LS. Besides the much lower ratio of GluN to MurA in MS than in LS suggests that the relative contribution of bacterial residue to SOM accumulation was much higher in MS than in LS, and that the dominance of microbial groups shifted from fungi group to bacteria group with increasing soil salinity.【Conclusion】 As a whole, accumulation of fungal and bacterial residues is closely related to soil salinity, thus playing an important role in regulating stabilization and turnover of SOM in salinized soils. All the findings in this study have enriched our knowledge about microbial processes and related mechanisms of SOM transformation in salinized soils.

    • Selenite Adsorption Mechanisms of Goethite and Goethite-Humic Acid Complex

      2018, 55(2):399-410. DOI: 10.11766/trxb201710090405

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      Abstract:【Objective】Selenium (Se) is an essential micronutrient for human and animals. Ingestion of either an inadequate or excessive amount of Se tends to lead to health problems. Bioavailability of Se in soils depends on its forms. Iron oxides and humic acid are important components of soils and may interact with Se through desorption/adsorption. Iron oxides and humic acid in soils are often cemented together forming aggregates, thus significantly affecting translsocation and transformation of nutrient elements and contaminants in the soils. However, in-depth knowledge about the effects of iron oxides-humic acid complex on speciation and bioavailability of Se in soils is still rarely available. 【Method】In this study, goethite-humic acid complex was prepared through a modified co-precipitation procedure for analysis of selenite (Se(IV) adsorption characteristics in aqueous solutions through a series of tests, like pH, Zeta potential and X-ray photoelectron spectrum(XPS) and isothermal adsorption. 【Result】 At the initial pH=4, the adsorption capacity (Qm), as fitted with the Langmuir model, was 0.202 mmol g-1 and 0.159 mmol g-1 for goethite and the complex, respectively. The Langmuir model was suitable for use to describe isotherm adsorption of Se(Ⅳ) for goethite (R2=0.970), while the Freundlich model was for the complex (R2=0.980). As for goethite and the complex, the isoelectric point (IEP) was about 7.0 and less 3.0, and zeta potential at pH=4.0 was 46.6 mV and -40.5 mV, respectively. X-ray photoelectron spectrum (XPS) showed that the electronic binding energy (B.E.) of the Fe2p3/2 on the surface of goethite and the complex was 711.4 eV and 711.5 eV respectively, and the B.E. of the C1s on the complex surface was 284.8 eV. With the initial pH being 4.0, changes in interactions between the samples and Se(Ⅳ) were embodied mainly in the following aspects: (1) pH rose up to 4.4 and 4.2, respectively in the suspensions of goethite and the complex, while surface potential decreased by 39.08 mV in goethite, but increased by 1.8 mV the complex; (2) B.E. of Fe(Ⅲ) dropped by 0.4 eV on the surface of goethite, but remained almost unchanged in adsorbed Se(Ⅳ); (3) B.E. of Fe(Ⅲ) decreased by 0.3 eV on the surface of the complex , but increased by 0.6 eV on adsorbed Se(Ⅳ), and the B.E. of C in C-O bonds rised to 286.5 eV. 【Conclusion】The complex is lower than goethite in Qm of Se(Ⅳ) and affinity for absorbed Se(Ⅳ). But their adsorptions of Se(Ⅳ) occur mainly through the following mechanisms, i.e. surface coordination reaction and hydrogen bonding. The electrostatic attraction would contribute to improve the Qm of Se(Ⅳ) on goethite, while the electrostatic repulsion was the reason that decreased the Qm of Se(Ⅳ) on complex. Moreover, for surface coordination in the complex, bidentate coordination existed between iron hydroxyl groups (≡FeOH) on the surface of the complex and HSeO3-. In addition, the adsorbed Se(Ⅳ) on the surface of the complex interacted with both goethite and humic acid, forming a goethite-Se(Ⅳ)-humic acid ternary system.

    • Effect of Silica Colloids on Adsorption and Migration of Sulfadiazine in Soil Relative to Ionic Intensity

      2018, 55(2):411-421. DOI: 10.11766/trxb201707250183

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      Abstract:【Objective】Colloid is an active component, exsiting extensively in soil, so how it affects adsorption and migration of sulfadiazine in soil is a scientific issue that is worth further exploring.【Method】Taking Neutral Ludox as extraneous colloid, this work quantitatively analyzed effects of ionic intensity(0.001, 0.003, 0.005, 0.010 mol L-1CaCl2)on the adsorption and migration of sulfadiazine in soil, 6.38±0.03 in pH, where colloid and sulfadiazine coexisted through indoor batch experiments and soil column effluent experiments.【Result】Results showed that the colloid inhibited the adsorption of sulfadiazine in the soil when the ion intensity was 0.001 or 0.003 mol L-1, but the effect of the colloid inhibiting sulfadiazine adsorption in the soil with ion intensity being 0.005 or 0.01 0 mol L-1CaCl2 was effected by the initial concentration of sulfadiazine. Freundlich model could well describe the adsorption process of sulfadiazine in the soil with R2 being 0.958~0.997. The breakthrough curve of vertical transport of sulfadiazine in the saturated condition was delayed in all conditions mainly due to the existence of different forms of sulfadiazine. Neutral ion form of sulfadiazine was adsorbed on soil organic matter through hydrophobic interaction and sulfadiazine in negative ion form was adsorbed on the soil through bonding action. When concentration of sulfadiazine was 30 mg L-1, however, in soil higher in ion intensity, the colloid added could inhibit migration of the sulfadiazine due to the dielectric layer was compressed, forming flocculation that absorbed a certain amount of sulfadiazine, while in soil lower in ion intensity, colloid outflowed, entirely or partly, thus impoving sulfadiazine migration.At 0.010 mol L-1 CaCl2in ionic intensity, the outflow of sulfadiazine from the soil column was advanced, the relative concentration of sulfadiazine peaked higher, and the outflow lasted longer without colloid addition. However, once colloid was added, the relative concentration of sulfadiazine peaked low in value and it was hard for sulfadiazine to outflow. At 0.005 mol L-1CaCl2 in ion intensity, the outflow of sulfadiazine was earlier and the relative concentration of sulfadiazine peaked higher than that without colloid addition. At 0.001 mol L-1 CaCl2 in ion intensity, relative concentration of sulfadiazine peaked higher than that without colloid addition, and it was more difficult for sulfadiazineto to get eluted.【Conclusion】Generally speaking, in soils with colloid existing and lower in ion strength, the addition of colloidal inhibits the adsorption of sulfadiazine and hence promotes the migration of sulfadiazine, while in soils higher in ion strength, it promotes the adsorption of sulfadiazine and hence inhibits the migration of sulfadiazine. All the findings in this study may be of some guiding significance for controlling the migration of sulfonamides in soil.

    • Effects of Single-Factor and Combined Contamination of Triclosan and Cadmium on Respiration and Enzyme Activity of Soil

      2018, 55(2):422-431. DOI: 10.11766/trxb201708040345

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      Abstract:【Objective】 Although some studies have been reported on environmental risk assessment of single-factor contamination of triclosan (TCS), a typical pharmaceuticals and personal care products (PPCPs), little has on effects of combined contamination of TCS and cadmium on ecosystems. The aim of this study is to evaluate comprehensively environmental risks of combined contamination of TCS and cadmium in soil ecosystems.【Method】A laboratory incubation experiment was performed and a combined toxic effect prediction model was used to evaluate ecological toxicity of single-factor and/or combined pollution of triclosan and cadmium on soil microbial and enzyme activities involved in soil carbon and nitrogen cycling. The incubation experiment was designed to have four treatments for triclosan contamination, i.e. 0, 1.0, 10.0 and 50.0 mg kg-1 dry soil, two treatments for Cd contamination, i.e. 0 and 10.0 mg kg-1 dry soil, added in the form of CdCl2, three combined contamination treatments, i.e. 1.0/10.0, 10.0/10.0 and 50.0/10.0 mg kg-1 dry soil in triclosan/cadmium, and three controls containing neither cadmium nor triclosan. Each treatment had three replicates. The treated samples were incubated at 25℃ in dark. The soil respiration, protease and sucrose activities were measured on the 7th, 14th, 28th and 56th day of incubation. 【Result】Results show that both the single-factor and combined pollutions of triclosan and cadmium had soil respiration activated, inhibited and then activated again. In the soils under single-factor stress of either Cd or TCS, soil respiration was significantly activated on Day 7 with activation rate being 18.52 %, 25.26%, 27.98% and 18.45% for Cd 10.0 mg kg-1, triclosan 1.0, 10.0 and 50.0 mg kg-1, respectively, and began to be inhibited after 14 days of incubation, and activated again at the end of the incubation (Day 56), with activation rate being 24.16%, 41.84%, 31.56% and 21.41% for Cd 10.0 mg kg-1, triclosan 1.0, 10.0 and 50.0 mg kg-1, respectively, which were significantly different from that in the controls (p<0.05) . Furthermore, the degree of activation seemed to be related with the concentration of triclosan (p<0.05) spiked. In the soils under combined stress of Cd and TCS, regardless of ratio, soil respiration was stimulated on Day 7, with the effect declining with rising TCS concentration; inhibited on Day 14 and Day 28, with the effect declining too, with rising triclosan concentration, and stimulated significantly again at the end of the experiment (Day 56). The contamination of Cd and TCS, either single-factor or combined, stimulated protease activity with the effect declining first and then rising during the process of incubation and peaking on Day 56, with activation rate being 94.5%, 31.8%, 42.1% and 68.2% for Cd 10.0 mg kg-1, triclosan 1.0, 10.0 and 50.0 mg kg-1, respectively, in soils under single-factor stress of cadmium or triclosan, and being 98.0%, 110.3% and 102.7% for TCS/Cd 1.0/10.0, 10.0/10.0, and 50.0/10.0 mg kg-1, respectively, in soils under combined stress. However, the degree of stimulation of protease activity was not significantly positively related to the concentrations of triclosan (p>0.05) in the soil. The contamination of Cd and TCS, either single-factor or combined, inhibited invertase activity during the whole incubation period. The effect peaked up to 81% on Day 14 in soils under single-factor contamination of cadmium, and was negatively related to concentration of TCS in soils under single-factor stress of triclosan, and did not show any dose-effect relationship in soils under combined pollution of Cd and TCS. The joint effects evaluation model shows that compared to single-factor pollution of either triclosan or Cd, the two pollutants in the treatments under combined stress acted jointly on soil respiration, but not always the same way. Their relationship varied with the time, from antagonistic to synergetic and then additive. Their effects on soil protease varied from synergistic to additive and then to synergetic, while their effects on soil invertase activity were mainly synergistic. 【Conclusion】Throughout the entire experiment, the contamination of Cd and TCS, either single-factor or combined, firstly stimulated then inhibited and in the end stimulated again soil respiration, stimulated protease activity, and inhibited the invertase activity. The joint toxic effects of triclosan and cadmium varied with concentration and duration of the exposure. Therefore, it is suggested that in future studies, joint toxic effects of chemical pollutants in biosolids and soil should be taken into account in health risk assessment.

    • Heavy Metal Contents in Eupatorium Adenophorum in Liangshan of Sichuan, and Safeness of Using the Plant as Organic Manure

      2018, 55(2):432-442. DOI: 10.11766/trxb201710240432

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      Abstract:【Objective】Eupatorium adenophorum, an alien perennial plant of Compositae, native of Central America invaded China extensively via Myanmar in the 1940s. The invasive plant is now widespread in farmlands, forests, and pastures in tropical and subtropical areas of Southwest China, such as Yunnan, Guizhou, Guangxi, Sichuan and Tibet, covering as high as about 20% of the total land in certain regions and causing enormous economic loss and serious ecological calamities, because of its strong ability to adapt various environments. Therefore, E. adenophorum is considered to be the most harmful invasive plant in this country. To control overspreading of the invasive plant, prevention in combination with utilization could be one of the most economical and effective ways. It is necessary to point out that E. adenophorum is no good to be used as pulp, building materials, fuel, and animal food because this plant is short of fiber, weak in rupture strength, and low in combustion value, and contains chemicals noxious to animals. However, this harmful plant is rich in organic matter and mineral nutrient, such as nitrogen, phosphorus, potassium, and microelements. Bio-composting of the plant through inoculation of certain specific microbes can kill the reproductive organs of the plant and decompose the chemicals contained in E. adenophorum noxious to animals, microbes, and other plants. Its content of heavy metals is the critical issue for the plant to be used as source of organic manure. 【Method】Samples of E. adenophorum plants, soils, neighboring plants and in-situ bio-composted E. adenophorum plants were collected from 42 E. adenophorum colonies in lands of mining, agriculture, forestry and transportation typical of Liangshan, Sichuan for analysis of contents of Pb, Cd and Cr using an atomic absorption spectrophotometer, and contents of Hg and As using an atomic fluorescence spectrophotometer in order to evaluate safeness of utilizing E. adenophorum as source of organic manure. 【Result】Results show that heavy metals in the plants varied sharply, exhibiting a sequence of Cr (x ̅=14.17 mg kg-1) > Pb (x ̅=4.55 mg kg-1) > Cd ( x ̅=1.47mg kg-1) > As (x ̅=0.167 mg kg-1) > Hg (x ̅=0.021 mg kg-1), and they did too in the soils, with variation coefficient of Hg, Pb, Cr, Cd and As (%) being 99.99, 305.9, 118.7, 266.8 and 51.74 in the soils, and 58.27, 87.75, 121.2, 87.75 and 71.87 in the plants, respectively, which suggests that absorption of heavy metals by E. adenophorum plants is subject to soil environment. Contents of heavy metals in E. adenophorum plants are positively related to total As, DTPA/HCl extractable Pb, DTPA/HCl extractable Cd, and NaHCO3 extractable As in the soils, with correlation coefficient being 0.528, 0.337 6, 0.761 2 and 0.313 7 (n=38~42), respectively. Among the organs of the plant, stem is the lowest in heavy metal content, root the highest in Cr and As content and leaf the highest in Pb, Cd and Hg content. In the plant Cr and As is not so movable as Pb, Cd and Hg, which move easily from roots to leaves. Compared to most of the 12 plants growing near the E. adenophorum colonies, E. adenophorum plants were lower or similar in heavy metal content, accumulation coefficient and mean and maximum content, which indicates that in the nature E. adenophorum behaves similarly like common plants and does not have any special preference in nutrient or heavy metal absorption and doesn’t support the conclusion drawn by scientists in the past that E. adenophorum is a heavy metal accumulator. Furthermore, heavy metals in the composted E. adenophorum, stems and leaves, were obviously lower than the criteria set in the National Standard for Organic Manure (NY525-2012). 【Conclusion】 E. adenophorum is not a heavy metal accumulator. In E. adenophorum infested areas, the utilization of in-situ composted E. adenophorum plants as organic manure does not pose any heavy metal toxication risk and the risk of translocation of heavy metals between regions and generation of siol pollution is very limited. So this technique is worth extrapolating.

    • Effect of Long-term Fertilization on Aggregation Characteristics and Distribution of Potassium Fractions in Red Soil

      2018, 55(2):443-454. DOI: 10.11766/trxb201711050396

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      Abstract:【Objective】Fertilization greatly influences soil structure and nutrients accumulation in soil aggregates. However, it is still unclear how aggregate-associated potassium (K) changes in distribution in red soil. Therefore, effects of long-term fertilization on aggregate composition and fractions of K therein in red soil were investigated based on a long-term fertilization field experiment in the subtropical area of China, in an attempt to provide certain theoretical basis for amelioration of red soil and improvement of K fertilization efficiency in that region. 【Method】 From the long-term fertilization experiment at Qiyang County of Hunan Province, China (since 1990), five treatments were selected, including CK (no fertilizer), NP (application of chemical nitrogen and phosphorus in combination), NPK (application of NP and potassium in combination), NPKM (application of NPK plus pig manure), and NPKS (application of NPK plus return of half of the straw harvested). Undisturbed soil samples were collected separately from the 0~20 cm layers of the five treatment plots in a 26 year-old (1990—2016) field of the experiment after the crop of corn was harvested, for fractionation of soil aggregates and analysis of total K (TK), non-exchangeable K (NEK) and exchangeable K (EK) therein, Then relationships of the K in the aggregates of different fractions with crop K uptake were explored. 【Results】 Results show: (1) Among the treatments, Treatment NPKM was the highest in proportion of aggregates of >2 mm, 1~2 mm and 0.5~1 mm in particle size, but the lowest in proportion of aggregates of 0.053~0.25 mm and <0.053 mm. However, Treatment NPKS did not affect proportions of aggregates of >2 mm, 1~2 mm and 0.5~1 mm. (2) Compared with Treatment NPK, Treatment NPKM was 24.37%~49.04% and 82.02%~176.3%, higher respectively in NEK and EK content in soil aggregates. The contribution rate of the fraction (>0.5 mm) of aggregates to the bulk soil (CRAB) in TK, EK, and NEK increased by 6.25%~31.97%, 5.72%~43.16% and 6.33%~41.98%, respectively, while that of the fraction (<0.25 mm) decreased by 14.37%~21.44%, 17.04%~33.66% and 34.40%~43.84%, respectively in Treatment NPKM. (3) No significant difference was observed between Treatment NPKS and Treatment NPK in EK and NEK content in aggregates of the same fraction and in contribution rate of the EK and NEK in each fraction of aggregates to the total K in CRAB. And (4) Linear regression analysis shows that when the contribution rate of the fractions (>0.25 mm) of aggregates increased by 1%, K uptake of the crop increased by 9.92~11.89 kg hm-2.【Conclusion】 Long-term application of chemical NPK fertilizers and pig manure in combination may significantly improve formation of soil aggregates in upland red soil and hence increases contribution rate of the aggregates to the bulk soil in K and consequently crop uptake of K.

    • Concentration-Dependent Effect of Foliar Spraying of Melatonin on Salt Tolerance of Rice

      2018, 55(2):455-466. DOI: 10.11766/trxb201708150308

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      Abstract:【Objective】 Soil salinization is a soil problem getting more and more serious nowadays, reducing plant growth and affecting agricultural production. The area of salinized rice fields is expanding, what is more, rice (Oryza sativa L.), a main staple food crop of the country is quite sensitive to salt stress. More and more attention has been paid to the study on how to regulate salt tolerance of rice. Melatonin (MT) is an important class of indole compounds widely found in most organisms. More and more studies have found that though very low in content in plants, MT plays a very important role in physiological regulation and enhancement of plants. However, little has been found in literature on application of melatonin to rice. It is, therefore, of great significance to explore concentration-dependent effects of MT on salt tolerance of rice and its physiological mechanism. 【Method】A hydroponics experiment was carried out on effects of foliage spraying of MT to rice on plant height, biomass, root/shoot ratio, absorption and transportation of N, P, K and Na, K/Na ratio and SK,Na (K/Na selectivity ratio). In this study, pass boxes were used for hydroponic cultivation of rice and extraneous MT sprayed. The experiment was designed to have 7 treatments, i.e. (1) Nutrient solution + spraying deionized water (Control); (2) Nutrient solution + 75 mmol L-1 NaCl + spraying deionized water (S75); (3) Nutrient solution + 75 mmol L-1 NaCl + spraying 25 μmol L-1 MT (S75 + MT1); (4) Nutrient solution + 75 mmol L-1 NaCl + spraying 50 μmol L-1 MT (S75 + MT2); (5) Nutrient solution + 75 mmol L-1 NaCl + spraying 100 μmol L-1 MT (S75 + MT3); (6) Nutrient solution +75 mmol L-1 NaCl + spraying 200 μmol L-1 MT (S75 + MT4); (7) Nutrient solution +75 mmol L-1 NaCl + spraying 400 μmol L-1 MT (S75 + MT5). Each treatment had six boxes as duplicate, and solutions in the boxes were replaced every other day during the whole culture period; foliar spraying of deionized water or MT varying in concentrations in line with the treatments, in late afternoon every other day; and samples of plants collected for analysis on D15. 【Result】Results show as follows. (1) MT efficiently increased plant height and biomass (dry weight) of the plants under salt stress and reduced their root/shoot ratio. The effects intensified with rising MT concentration, and peaked in the treatment 200 μmol L-1 MT in spraying rate, which was, 51% and 130% higher than the treatment 75 mmol L-1 in MT spraying rate, respectively, in plant height and biomass. (2) In plants under salt stress, extraneous MT significantly increased N, P and K contents in shoot and root of the seedlings. The effects also peaked in the treatment, 200 μmol L-1 MT in spraying rate. Compared with control, the treatment 75 mmol L-1 NaCl in salt stress was lower in N translocation factor (N-TF), unchanged in P-TF, and higher in K-TF, however, foliar spraying of MT significantly increased all the three indices in plants under salt stress. But with MT spraying rate rising up to 200 and 400 μmol L-1, N-TF increased, P-TF remained almost unchanged, and K-TF decreased significantly. (3) With rising MT spraying rate, Na content in the plants decreased significantly. Under salt stress, seedlings were high in Na-TF, which was not affected by spraying of MT, no matter how much. (4) Spraying of MT significantly increased K/Na in both shoot and root of the seedlings under stress, and the value peaked in the treatment 200 μmol L-1 in MT spraying rate. Spraying of MT increased absorptive SK,Na (ASK,Na) of the plants under salt stress. ASK,Na continued to increase with rising MT spraying rate, and also peaked at 200 μmol L-1 MT. Spraying of MT decreased transport SK,Na (TSK,Na) of the plants under salt stress, especially when the rate reached 200 and 400 μmol L-1. 【Conclusion】 To sum up, foliage spraying of 25 ~ 400 μmol L-1 MT significantly increases NPK uptake, decreases Na accumulation, improves ion homeostasis in rice seedlings under salt stress, and promotes salt tolerance of the rice plants. All the findings demonstrate that foliar spraying of MT at 200 μmol L-1 is the most appropriate practice to improve salt tolerance of rice.

    • Principal Component Regression Technology of Ternary Fertilizer Response Model for Improving Success Rate of Modeling

      2018, 55(2):467-478. DOI: 10.11766/trxb201709140242

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      Abstract:【Objective】There is a large number of non-typical ones of ternary quadratic polynomial models for fertilizing effect (TQPM) used in fertilization practice, severely affecting accuracy and practicality of the fertilizing effect models. In order to improve success rate of modeling for field fertilization experiments, this study was oriented to explore new modeling methods. 【Method】Based on 171 field fertilization experiments of“3414”in design on response of early rice to N, P and K fertilization in Fujian Province, efforts were made to explore methods to diagnose multicollinearity of TQPMs and technology for modeling with principal component regression and effects of their usage. 【Result】Diagnoses of number of conditions of the square matrix(XTX)of the matrix X designed for the “3414”field experiments and variance inflation factors (VIF) of the model parameters shows that TQPMs do have serious multicollinearity, which is mainly caused by the specification of the models per se, and severely restrains application value of the ordinary least squares (OLS). Among the 171 field experiments of early rice response to N, P and K fertilization in Fujian province, ternary typical fertilizing effect models using the OLS regression modeling method accounted for only 27.5% of the total. The proportions of the non-typical typed models, such as no maximum-yield point, unreasonable signs of monomial coefficient or quadratic coefficient, and extrapolation of recommended fertilization rate, reached 36.8%, 14.6% and 5.3%, respectively, of the total using the OLS modeling method. Principal component regression(PCR)extracted 9 unrelated principal components from the designed matrix, thus eliminating the negative effect of multicollinearity. When the first 7 principal components were used in regression modeling, the proportion of ternary typical fertilizing effect models increased up to 43.3% or 1.6 times as high as that using the OLS method. What is more, compared with the OLS modeling method, PCR decreased the proportions of non-typical models with unreasonable coefficient symbols by a large margin from 14.6% to zero, and the proportion of non-typical models with no maximum-yield point from 36.8% to 21.1%, which fully manifested the positive effect of eliminating the hazard of multicollinearity on success rate of modeling. Seven-principal-component regression modeling made use of more than 99.9% of the variance information of the designed experimental matrix X, and all the typical models established by PCR modeling did not differ much from those by OLS modeling in recommending fertilization rate and predicting yields. As principal component regression is a kind of biased estimate, only the experimental designed matrix was taken into account in extracting principal components, but not relationship between each principal component and yield of each corresponding treatment. As affected by regression bias, typical models by OLS regression may occasionally turn into non-typical ones. Therefore, from the aspect of practical application, the use of OLS modeling in combination with modeling based on regression of the first seven principal component, increased the proportion of ternary typical fertilizing effect models up to 55.6%, or 2.0 times as high as that using OLS modeling alone, and was much better than using the PCR alone. 【Conclusion】Principal components regression can eliminate the defect of multicollinearity of the ternary quadratic polynomial fertilizing effect model The use of the ordinary least squares method in combination with the PCR modeling based on the first seven principal components is the optimal modeling strategy that can significantly increase the proportion of of ternary typical fertilizing effect models to predict early rice response to N, P and K fertilization.

    • Response of Nitrification and Nitrifiers to Different Nitrogen Sources in an Alkaline Purple Soil

      2018, 55(2):479-489. DOI: 10.11766/trxb201709130312

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      Abstract:【Objective】Nitrification in soil is a highly sensitive process to pH. Responses of nitrification rates and the community structures of nitrifying microorganisms to different N sources in an alkaline purple soil were studied to elucidate the microbiological mechanisms for nitrification. 【Method】Three different N sources and the blank control were used in the 4-week incubation study. Net nitrification rate was calculated by the differences of nitrate concentrations at day 0 and 28. The amoAgene abundances for ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA) were measured by quantitative PCR before and after the incubation. The relative abundance of nitrite oxidizing bacteria (NOB) was analyzed by binning the sequences of the 16S rRNA gene and the amoAgene into operational taxonomic unit (OTUs) at 97% similarity level. The changes of community structures for AOA, AOB and NOB were studied by high-throughput sequencing method before and after the incubation.【Result】In the 4-week incubation study, compared with blank control (CK), soil nitrification rate was stimulated by application of all three kind of nitrogen sources: ((NH4) 2SO4, NH4Cl and CO(NH2)2). The net nitrification rate for blank control (CK) was 0.86 mg N kg-1 d -1. The highest net nitrification rate was observed for CO(NH2)2treatment (N 3.88 mg kg-1 d -1), which was more than 4-times higher than CK. The addition of NH4Cl and (NH4) 2SO4, showed similar stimulation on nitrification to CO(NH2)2application. The net nitrification for NH4Cl and (NH4) 2SO4were N 3.34 and 3.88 mg kg-1 d-1, respectively. But, NH4Cl also reduced the accumulation of nitrate and inhibited the reduction of ammonium when compared with (NH4) 2SO4, and CO(NH2)2. Along with the accumulation of nitrate, the copies of amoA gene in ammonia oxidizing bacteria (AOB) increased significantly during the first two weeks of incubation (p<0.05). The copy numbers of bacterial amoA genes increased from 0.88×107 g-1soil and 0.85×107 g-1 soil at day-0 to 3.38×107 g-1 soil and 3.55×107 g-1 soil at the day 14 of the incubation, then decreased to 1.46×107 g-1soil and 1.69×107 g-1 soil at the day-28, for (NH4) 2SO4, and CO(NH2)2 treatments respectively. The copy numbers of bacterialamoAgenes were significantly lower in NH4Cl treatment than (NH4) 2SO4, and CO(NH2)2addition at the day 14 (p<0.05). On the other hand, the copies of amoAfor AOA did not change significantly during incubation (p>0.05). Results indicated that nitrification in alkaline purple soil was mainly driven by AOB, but not AOA. Pyrosequencing of the 16S rRNA genes was performed at the whole microbial community level for different treatments and control before and after incubation. Approximately more than 30 000 high-quality 16S rRNA reads were obtained, and targeted reads from putative AOA, AOB and NOB sequences were selected for subsequent analysis. The high-throughput sequencing results further showed that the dominant nitrifying microorganisms were mainly related to Nitrospira, Nitrososmonas and Nitrosospira in the alkaline purple soil. The dominant AOB were classified into Nitrosospira Cluster 3, and the dominant AOA were affiliated with Group 1.1b. Furthermore, the relative abundance of NOB was much higher than that of AOB and AOA, which may imply the presence of Comammox in the studied alkaline purple soil.【Conclusion】Results showed that the nitrification in alkaline purple soil was stimulated by the addition of (NH4) 2SO4, NH4Cl and CO(NH2)2. But NH4Cl also showed a inhibition effect on nitrification when compared with NH4)2SO4, and CO(NH2)2 application. The nitrification process in alkaline purple soil was mainly driven by AOB, but not AOA. The evidences from the high-throughput sequencing results further indicated that the dominant population of ammonia oxidizing bacteria was classified into Nitrosospira Cluster 3 in the alkaline purple soil, and AOA was mainly the Group 1.1b. For NOB, Nitrospira was the dominated species.

    • Effect of Organic Manure on Nematodes in Rhizosphere Soil of Soybean Under Continuous Cropping

      2018, 55(2):490-502. DOI: 10.11766/trxb201705090101

      Abstract (2430) HTML (917) PDF 1.68 M (3636) Comment (0) Favorites

      Abstract:【Objective】Studies so far made at home and abroad on soil nematodes are found mostly concentrated on nematodes in bulk soil or non-rhizosphere soil, with relatively less focus on those in rhizosphere soils, let alone on phytophagous nematodes in rhizosphere soils. Therefore, the purpose of this experiment was designed to explore effects of organic manures, prepared mainly out of different agricultural wastes, i.e. pig dung, crop stalks, mushroom residue, forage grass, chicken dropping and fulvic acid bio-manure, on soil nematodes in rhizosphere soil of soybean under a continuous cropping system. Soybean nematodes disease is a disastrous one to soybean production, seriously affecting growth and yield of the crop. 【Method】 By comparing organic manures of different nature in effect on number of nematodes and structure of the nematode community, a method to prevent nematode disease in continuous cropping of soybean was proposed here in the paper. Six different organic materials were selected for comparison and analysis of the two treatments to compare the difference of the rhizosphere soil nematodes. Soil samples were collected from plots applied with different organic manure in the experiment for isolation of nematodes with the shallow disk method and counting of the nematodes under an anatomical lens. Then from each lot, about 100 nematodes were sampled out for identification till genus under an optical microscope. 【Result】 Results show that cp values of the dominant genera and key species in the study were 3, indicating that the nematodes were high in breeding ability and disturbance resistance; after 7 years of continuous cropping of soybean, relative abundance of the omnivorous / predatory nematodes among the trophic groups of soil nematode in the rhizosphere decreased significantly, while that of the plant parasitic nematodes in the rhizosphere increased significantly and that of bacterivores and fungivores increased slightly; the number of nematodes in the rhizosphere of soybean of continuous cropping was significantly higher than in the rhizosphere of soybean of non-continuous cropping; compared with application of chemical fertilizer, application of organic manure retarded growth of plant parasitic nematodes in number. In terms of the effect, the organic manures displayed an order of pig dung > crop stalks > mushroom residue > forage grass > chicken dropping > fulvic acid bio-manure > CK (chemical fertilizer), compared with non-continuous cropping respectively increased by 6.48%, 15.34%, 15.98%, 18.51%, 24.35%, 26.33% and 27.4%. With the continuous cropping going on, the proportion of bacterial nematodes expanded obviously and the expansion was inhibited by application of organic manure and so was the proportion of fungal-feeding nematodes and that of plant parasitic nematodes, though varying in extent. The effect of organic manure was higher than that of chemical fertilizer. In the plots treated with organic manure, plant parasitic nematodes dominated the nematodes community, accounting for more than 50%, while omnivorous nematodes and predatory nematodes were on a decreasing trend. Obviously, application of organic manure has an effect of keeping balance of the soil nematode community.. The ecological index of nematodes was significantly improved by organic manure as compared with CK .【Conclusion】The response of soil nematode to fertilizers depends on quality and nutrient content of the crop and fertilizer or manure; Dominant trophic groups, dominant species and key genera of soil nematodes are effective indicators of health of the agricultural soil and degree of soybean nematodes diseases in the soybean fields.

    • Desiccation and Nutrient Status of the Soil in Apple Orchards in Hilly-Gully Region of the Loess Plateau

      2018, 55(2):503-514. DOI: 10.11766/trxb201707280168

      Abstract (1893) HTML (1009) PDF 1.30 M (3437) Comment (0) Favorites

      Abstract:【Objective】Mizhi County is a hill-gully region, typical of the Loess Plateau, where drought and shortage in water supply is a major factor restraining sustainable and healthy development of apple orchards. At the same time, soil fertility or nutrient status is another affecting tree growth and fruit yield and quality. Therefore, it is essential to study variations of water regime and nutrient status in the soil profiles of apple orchards different in cultivation history, and hence to explore mechanism of soil desiccation leading to nutrient imbalance, in an attempt to provide certain theoretic basis for scientific management of soil water and nutrients, soil building and rational fertilization in apple orchards in hill-gully regions of the Loess Plateau.【Method】Distribution of soil water content in soil profiles, 1000 cm in depth and nutrient contents, including soil organic matter, total nitrogen, total phosphorus, alkaline nitrogen, available phosphorus and readily available potassium, in the 0~300 cm soil layer of the profiles in the apple orchards, 7, 10, 18, 25, 30 and 41 years old, were determined; soil desiccation degrees and soil nutrient status along the soil profiles were evaluated for analysis of their relationships with cultivation history of the orchards and depth of the soil layer, and relationship between soil water content and soil nutrient contents in the 60~300 cm soil layers of the apple orchards relative to cultivation history. 【Result】Results show that the soils of the orchards, regardless of cultivation history, all suffered severe or intense desiccation. Mean soil water content of the 0~1 000 cm soil layer increased first, then decreased and then slightly turned upwards again with age of the orchards. The content of organic matter, total nitrogen and alkaline nitrogen in the 0~300 cm soil layers of the orchards, regardless of age, was less than 6 g kg-1、0.5 g kg-1and 30 mg kg-1, respectively, all falling down to the level of extreme deficiency, whilst the contents of total phosphorous and available phosphorous varied in the range of 5.4~6.5 g kg-1 and 4.56~11.86 mg kg-1, respectively, both being on the level of moderate or minor deficiency; and the content of available potassium was 71.98~119.68 mg kg-1or moderate in nutrient availability level. In the orchards of young apple trees, soil water content was closely related to soil organic matter, total nitrogen and alkaline nitrogen contents, whereas in the orchards of apple trees in the full bearing period and in the decline phase, it was not, which indicates that in the former the soil water regime was well preserved and in the latter the soil water environment deteriorated, with severe or intense soil desiccation occurring in deep soil layers. 【Conclusion】It is, therefore, suggested that besides positive water conservation measures proper to orchards different in age, improvement be made in fertilization, by paying more attention to application of organic manure and nitrogen fertilizer, increasing the application rate of phosphorous fertilizer properly and reducing or even stopping application of potassium fertilizer. Compared with the issue of nutrient imbalance caused by soil drought, the one of soil desiccation should have aroused more concern in the region.

    • >Research Notes
    • Effect of Continuous Paddy-upland Crop Rotation on Bacterial Community Structure in Cold Waterlogged Paddy Soil

      2018, 55(2):515-525. DOI: 10.11766/trxb201705110209

      Abstract (2317) HTML (1002) PDF 1.71 M (3614) Comment (0) Favorites

      Abstract:A paddy-upland crop rotation field experiment, consisting of 5 treatments, i.e. fallow-rice (CK), rape-rice (R-R), corn-rice (C-R), milk vetch-rice (M-R) and bean-rice (B-R), was conducted to investigate effects of the rotation modes on bacterial community structure in cold waterlogged paddy soil, using the high-throughput sequencing technique, and relationship between soil physicochemical properties and bacterial community structure as well. Results show that compared with CK, paddy-upland rotation significantly increased rice yield by 18%~44%, but decreased richness of the soil bacterial community in most cases. However, the rotation did not affect much bacterial diversity. Proteobacteria and Acidobacteira were dominant bacterial groups in all the soil samples, and Proteobacteria was the highest in relative abundance. Compared with CK, rotation significantly increased relative abundances of Acidobacteria, Actinobacteria, Nitrospirae, Bradyrhizobium and Nitrosospira and various bacterial groups involved in carbon and nitrogen recycling. Cluster analysis shows that CK and M-R belonged to a group, B-R, C-R and R-R to the other group in terms of soil bacterial community. Redundancy analysis demonstrates that soil total phosphorous, available phosphorous and pH were the main factors affecting soil bacterial community structure.

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