Abstract:Soybean is an important crop of the agriculture in China, and its position of importance in the human diet structure of the country is irreplaceable in China. Progresses in the research on factors and macro-control obstacles affecting the creation of a soil environment favorable to cultivation of high-yield and quality safe soybeans were collaged in this study. Results based on bibliometric analysis show that in the past 20 years, the hot spots of the researches the world over mainly concentrated on adsorption and transport processes of herbicides in soil-water interface, safety risk of heavy metal pollution in food chain, growth of soybean and pollution toxicology therein, and prevention and control of soil-borne diseases; and more attention was paid to mechanisms of physiological adaption of soybean in response to stress of pollution and diseases rather than to underground soil processes that might affect soybean growth and reduce soybean yield. The researches in China also showed an apparent gap in the field of underground soil environmental processes and micro-ecological effects in soybean producing areas. Under the new situation of the nation adjusting its food security strategy and reforming its agricultural supply lateral structure, it is urgent for the nation to orient follow-up works of the researches around the soybean industry towards tackling the task of combining organically raising grain yields with adopting safe utilization of contaminated cultivated lands, to pay more attention to the expansion of the focus from merely on soil fertility, breeding optimization and yield increase, to on soil safety and micro-ecological health simultaneously while ensuring soybean quality and safety, so as to support high quality green development of the soybean industry, and to unfold researches on construction of a high yield creation system that harmonizes soil health and pollution prevention of the soybean producing areas, and highlights the role of soil environmental protection and function improvement in green production and high-quality development of the soybean industry.

Abstract:Microplastics are almost ubiquitous in the environment. Their pollution of the environment has aroused grave concerns the world over. However, little has been reported in the literature on microplastics in the terrestrial environment, especially in farmland soil, compared with those in the marine and other aquatic environments. Presumably, microplastic pollution may be more serious in the terrestrial environment than in the aquatic environment. This paper is to make a comprehensive and systematic review of research progresses and future directions of the study on microplastics in the terrestrial environment, to introduce status of the pollution, and accumulation and distribution of microplastics in the soil both in China and in other countries as well, to explore their sources in the terrestrial system, including the use of agricultural film, the application of sludge and organic materials as manure, the irrigation with sewage, and surface runoff and to discuss in detail their interactions with other pollutants (heavy metal and organic pollutant), processes of their accumulation, migration, weathering, and degradation in the soil. Moreover, this paper also elaborates ecological effects of microplastics in soil, impacts of microplastics on soil physico-chemical properties, threat of microplastics to animals, plants, and microorganisms living in the soil and potential risks of microplastics to human health via the respiratory exposure and food-chain. In the end, the paper puts forward views and prospects of future researches on microplastics in the soil environment. This paper is expected to be able to provide information and scientific guidance for comprehensive understanding of the presence and future of microplastics in the soil environment.

Abstract:In recent years, plastic pollution has become an environmental issue of global concern. The pollution of microplastic (MPs) in the terrestrial ecosystems, especially in agroecosystems, has attracted increasing attention. Due to their low degradability, MPs accumulate in soil and render damages to soil ecosystems, thus posing health risks for human and animals through food chains. The present paper first introduces sources of MPs in soils, including plastic film mulching, application of sewage sludge and organic manure, irrigation with wastewater, atmospheric deposition, and surface runoff. Then it goes on to elaborate distribution and abundance of MPs in soil environments, particularly in agricultural soils, and discuss migration of MPs in terrestrial environments, with focuses on direct and indirect ecological effects of MPs on soil-plant systems. Current available evidence shows that MPs can directly change soil physio-chemical properties, and affect microorganisms and enzyme activities, soil fauna, seed germination, and root uptake of water and nutrients, and moreover they can be accumulated and translocated upwards, thus causing toxic effects on the plants. MPs can also indirectly affect plants via changing soil properties and interacting with other soil pollutants such as heavy metals. In the end, the paper discusses directions of the research on MPs in soil-plant systems in future. Moreover, this paper is expected to be able to provide a theoretical basis and scientific guidance for better understanding the ecological effects of soil MPs and controlling their potential risks.

Abstract:In recent years, after the issue of microplastics (MPs) pollution in ocean has aroused extensive global concerns, environmental risks associated with MPs in the terrestrial ecosystems are gradually attracting the eyesight of the world environmentalists, and consequently a lot of researches have been done exploring effects of MPs on soil ecological environments with gratifying progresses. This article is trying to make a comprehensive review and summary of recent advances in the research on MPs in the agroecosystem, with focus on MPs in the farmland in relation to their source, environmental behaviors, analysis methodology, impacts on the environment and ecosystem, and directions of future researches. So in the first place, it described the current status of global MP pollution, as well as their concentrations and distribution in agricultural soils, discussed potential sources of MPs and their contributions to MPs accumulation in farmlands, and then introduced sample preparation methods, especially soil sampling strategy and extraction of soil-borne MPs. Furthermore, the paper went on addressing the issues of MPs environmental behaviors in the agricultural ecosystems, such as migration, weathering, interactions with other pollutants and their fates, and the environmental impacts and ecological risks, especially potential challenges to soil health and food security, they might bright about. In the end, the paper listed the current preventive measures for control of MPs contamination with an argument on their potential contributions to prevention of the agricultural MPs pollution. This comprehensive review holds that MPs come into the farmland from multiple sources, with solid plastic wastes, like plastic mulching film, being one of the major contributors. Once entering the soil, under external disturbance or driving forces, including physical, chemical, biological factors, they accumulate, migrate and weather at a varying scale, creating significant ecological impacts on the soil environment, and even on physicochemical properties of the soil, microbial communities, soil biota, and plant growth, thus damaging soil health, and affecting agricultural production and quality of the produce. Besides, MPs pollution, especially that of nanoplastics, is posing a potential threat to human health via the food chain. Plastics in the soil may be fragmented biologically and subjected to slow biodegradation. Considering the ubiquitous distribution, persistence and ecological risks of MPs in the environment, the paper put forth some relevant suggestions for the decision-makers of the country in their efforts to control the problem, while citing as reference the MPs pollution prevention strategies of some other countries.

Abstract:This paper reviewed the development course, research system, as well as technical methods of the researchers on soil environmental criteria in other countries, in combination with synthetical analysis of the status and development needs of the research on soil environmental criteria of China. A "three-step" strategy for development of soil environmental criteria of China was brought up, consisting of 1) to set up a theoretic and methodologic system that suited to the fundamental reality of the country and had a sufficient scientific basis of formulating soil environmental criteria; and to guide relevant personnel to unfold orderly researches on the criteria in light of soil types and their distribution, land use patterns, as well as characteristics of the population and indigenous species in China; 2) to launch a study on values to be suggested for soil environmental criteria for a group of typical pollutants based on the soils types typical of the country, to develop some key laboratories capable of supporting the nation in its development of soil environmental criteria, and gradually to build up and perfect a national fundamental data sharing and application platform for soil environmental criteria; and 3) to form a complete system for research of criteria, with a view to providing scientific support to the development of a soil quality standard system, the prevention and control of soil contamination risks, and the identification and assessment of damages of the soil environment, etc.

Abstract:Geological and human activities in quite a number of regions of the world are found to have brought about serious arsenic (As) pollution in soil and groundwater, gravely threatening the ecosystems and human health in those regions. In order to effectively control As pollution risk at large scales, it is necessary to accurately evaluate interfacial behaviors of As in different media. Being regulated by chemical and microbiological factors migration and transformation of the element in certain typical environmental interfaces, like that of soil-water and rhizosphere, exhibit the characteristics of drastic changes in species at μm-to-mm-scales. Conventional active sampling techniques, which mostly consist of destructive field sampling and afterwards sample analysis in lab, have proved to be not good enough to meet the demands of the study on interfacial process of the element, such as handling an element varying drastically in species, quantifying the element at trace levels, and time- and labor-saving. In recent years, passive sampling technology, represented by diffusive gradients in thin-films (DGT), diffusive equilibrium in thin-films (DET), in-situ porewater iterative sampler (IPI) and dialysis sampler (Peeper), has emerged, displaying great advantages over the conventional ones in the research. The DGT device is composed of filter membranes, diffusion gel, binding gel and plastic bases/caps used to fix the three layers of membrane/gel. The filter membrane is mainly used to prevent particles in the environment to be tested from entering the device; the diffusion gel to facilitate free diffusion of ions and formation of a diffusion gradient; and the binding gel, chosen according to the purpose of the experiment, to absorb the pollutants to be tested. DET is a sister technique of DGT, omitting the binding gel phase. The IPI sampler consists of hollow fiber membrane sampling tubes and catheters. For sampling, the sampling tube is filled with deionized water in advance, and ions and small molecules in the environment diffuse into the tube. After the diffusion reaches equilibrium, the solution in the sampling tube is directly pumped out for measurement of concentrations of the ions tested. In principle, Peeper is similar to DET and IPI, but lower in spatial resolution for measurement of porewater concentration. These passive sampling techniques have been used to determine in situ of total As and As speciations in water and soil porewater, and their one-dimensional distribution profiles. DGT-measured As concentration in soil has a good correlation with its content in plants, showing that DGT is suitable for the evaluation of As phytoavailability. It turns out in recent years to be an important trend to use these passive samplers to study two-dimensional spatio-temporal distribution of As at the soil/sediment-water interface. DGT has been used to characterize the two-dimensional distribution of As at soil/sediment-water interface and plant rhizosphere in submillimeter high-resolution, so it cherishes great advantages in the study on spatial distribution of As, whereas IPI can sample iteratively with low disturbance, thus being one of the few tools that can be used to study dynamic distribution of As relative to species. These studies elucidate biogeochemical behaviors of As from a microscale perspective. In the end, the paper describes a prospect of the research in future, including:1) taking advantage of the merits of the passive sampling techniques in future studies on dynamic-controlled processes of As uptake by plants; 2) developing novel passive sampling techniques with both the spatial resolution and the temporal resolution of As concentration taken into account; 3) combining the passive sampling techniques with other 2D sampling techniques, such as planar optodes and soil zymography, in comprehensive studies on biogeochemical process of As in soils and sediments; 4) extending the use of passive sampling techniques to the study on processes of As uptake by fauna living in soils and sediments; and 5) building models of As transporting across interfaces based on data of changes in spatiotemporal concentration of As at the interfaces in complex environmental matrix.

Abstract:[Objective] Lou soil is an important agricultural soil that has an apparent cumulic epipedon formed on the top as a result of long-term dung stacking therein in the Guanzhong Region of Shaanxi Province, and its classification has received much attention. In order to explore its pedogenic characteristics and attribution in the soil taxonomy and to establish a perfect representative soil system, a total of 18 typical Lou soil profiles were selected in the region.[Method] Of the 18 soil profiles, natural soil forming factors and morphologies were studied and in reference to the Manual of Field Soil Description and Sampling, soil samples collected for analysis of physicochemical properties in reference to the Soil Survey Laboratory Methods. On such a basis, diagnostic horizons and diagnostic characteristics of the selected soil profiles were determined, and their attributions in the Chinese Soil Taxonomy (CST) at the higher and basic category levels defined.[Result] The selected Lou soil profiles were found to have 2 diagnostic surface horizons (cumulic epipedon, ochric epipedon), 3 diagnostic subsurface horizons (argic horizon, calcic horizon and cambic horizon) and 6 diagnostic characteristics (calcaric property, redox features, mesic soil temperature regimes, ustic soil moisture regimes, cumulic evidence and calcic evidence). Thickness of the cumulic epipedon was the key indicator for determining attribution of the Lou soil at the order level. Of the 18 profiles, 13 were sorted into orthic anthrosols with a corresponding cumulic epipedon diagnostic horizon, 4 into ustic argosols, and 1 into ustic cambosols with a corresponding 20~50cm thick cumulic epipedon. They were attributed to 3 subgroups (Calcic Earth-cumuli-Orthic Anthrosols, Mottlic Earth-cumuli-Orthic Anthrosols and typic Earth-cumuli-Orthic Anthrosols) under Group Orthic Anthrosols, one to Subgroup Cumulic Hapli-Ustic Argosols under Group Ustic Argosols and one to Subgroup Typic Hapli-Ustic Cambosols under Group Ustic Cambosols. According to the criteria for sorting at the soil family and soil series levels in CST, they could be sorting into nine soil families (clay loamy mixed type mesic temperature-Calcic Earth-cumuli-Orthic Anthrosols, etc.) and 18 soil series (Yangling series, etc.). Attributes of the Lou soil profiles in the CST and the Chinese Soil Genetic Classification (CSGC), did not always match, for example, three different soil series (Yangling series, Zhenyuan Series and Linping Series) in the CST corresponding to the same soil species (Red oil soil) in the CSGC. The statistics of 71 Lou soil profiles in relevant literatures shows that the cumulic epipedons in the Lou soils varied in range of 17-97 cm in thickness, and averaged to be 50.07 cm.[Conclusion] Compared with the Chinese Soil Genetic Classification, the Chinese Soil Taxonomy reflects and characterizes more accurately differences between the soils in soil development process and degree. The criterion of 50 cm thick cumulic epipedon is appropriate for classification of Lou at high levels soil. In order to improve the ability and accuracy of classification of prototype soils with cumulic phenomenon, it is suggested that the subgroup of Cumulic-Hapli-Ustic Cambosols under Group Hapli-Ustic Cambosols should be added in the CST.

Abstract:[Objective] Sichuan is an area the most typical of concentrated distribution of purplish soil in China. For this paper, a total of 100 samples were collected from 30 typical purplish soil profiles widely distributed in Sichuan Province for analysis in an attempt to explore quantitative relationships of colorimetric parameters of purplish soil with forms of iron and manganese, and organic matter.[Method] The samples were subjected to color measurement and chemical analysis in the laboratory for determination of Munsell HVC, CIE L*a*b* colorimetric parameters, content of iron and manganese by form (total Fe_t/Mn_t, free form Fe_d/Mn_d, amorphous form Fe_o/Mn_o and organic-bound form Fe_p/Mn_p) and content of organic matter. Correlation analysis and stepwise regression analysis of the data were performed to specify quantitative relationships of colorimetric parameters of the purplish soil with forms of iron and manganese, and organic matter therein.[Result] Results show that organic matter content in the purplish soil is significantly and negatively related only to C, a* and b*, but not related at all to H, V and L*. Content of iron and manganese in the purplish soil is closely related to color of the soil. Fe_t, Fe_o, Fe_p, Mn_t, Mn_d and Mn_o are significantly correlated with colorimetric parameters of the two color systems. Pearson correlations of manganese of all forms, except for organic-bonded form, with colorimetric parameters are higher than those of iron of all forms in coefficient, and so are one-way fitting determination coefficients of manganese of all forms with colorimetric parameters. Determination coefficient R² of stepwise regression fitting of the joint effect of iron, manganese and organic matter on color of the purplish soil varies between 0.46 and 0.54.[Conclusion] Manganese content has an extremely important effect on purplish soil, which is "purple" in color. The soils derived from the purplish parent rocks that are relatively high in manganese content are slightly purple in color. Compared with the effect of iron or manganese alone, the combined effect of iron, manganese and organic matter exhibits a higher degree of regression fit with the two color systems.

Abstract:[Objective] Although large-scale afforestation improves vegetation coverage of the Loess Plateau, it also leads to soil moisture deficit in this region. The emergence of dry soil layers slows down or cuts off the exchange of soil moisture between the upper and lower layers, thus causing deterioration of the soil environment and degradation of the vegetation. As an important part of the slope-gully system on the Loess Plateau, the development and evolution of gullies change the soil moisture on the slope, and the distribution and utilization efficiency of water resources in the catchments. However, so far little has been done on temporal and spatial distribution of soil moisture in gully and its surrounding areas.[Method] In this study, a typical gully in Liudaogou Watershed of Shenmu County was selected as the research object for monitoring soil moisture. In the gully three sample strips were laid out at the bottom (along the centerline), the edge (1 m wide) and the gully bank (20 m wide). Following the direction of the gully, 12 observation points were arranged at the gully bottom from the head to the outlet of the gully, and 7 observation points were set up along the gully edge and bank, separately. At each point, a hole was prepared with an auger to the depth of about 480 cm at the bottom section, and approximately 980 cm at the edge and bank sections for insertion of a neutron tube (CNC503DR) for in-situ observation of soil moisture. Measurement was made at 10 cm intervals along the 0-100 cm soil profile, and at 20 cm intervals when it got below 100 cm. Then soil moisture distribution was characterized and dried soil layers were analyzed and compared, as well as its influencing factors. Soil samples were collected while holes were prepared.[Result] (1) Soil moisture conditions were better at the bottom than at the edge and the bank, and water deficit was the most obvious at the edge. At the bottom section, soil moisture content increased obviously along the gully from the head to the outlet, and higher in the deep layers than in the surface soil layer, of which the 0-10 cm soil layer was the lowest in moisture content. The mean soil moisture content of the 0-480 cm soil profiles was 17.1% at the bottom, 13.5% at the edge and 14.4% at the bank; (2) In the soil layer above 480 cm, the mean soil water storage capacity was 80.54 cm at the bottom, 67.49 cm at the edge and 71.05 cm at the bank; (3) Topography and soil texture were the main factors affecting soil water storage capacity, and soil water storage was positively related to distance from the gully head, soil clay and silt content; (4) Dry soil layers in the gully area mainly appeared at the gully head, with an average thickness of 243 cm, an average initiation depth of 257 cm, and an average water content of 9.5%. The average thickness of the dry soil layers at the bottom, edge and bank was 100 cm, 286 cm and 331 cm, respectively.[Conclusion] The existence of gullies affects distribution of the soil moisture in this area and enhances its variability. Dry soil layers in this region exist stably for long and in case of severe droughts, they are likely to keep on growing. All the findings may serve as a theoretical basis for management of soil moisture resources and evaluation of soil reservoir in this area.

Abstract:[Objective] The technique of heat-pulse dual probe has been widely used for measuring soil thermal parameters and water content. However, being only 2.8 cm long, the conventional dual probes are very limited in monitoring range. Using lengthened probes may improve representativeness of the measurement, but long probes tend to get deflected, causing deviation of the distance between two probes, thus affecting measurement accuracy. Once the probe gets deflected by 1°the measurement of soil thermal diffusivity and volume heat capacity may deviate by 10%. By measuring temperatures at different points of the probe, spacing error caused by the deflection may be corrected with an in-situ spacing correction linear model or non-linear model. The linear model is preferred because it only requires the probe to have two thermistors rather than three thermistors as the non-linear model does, thus making it easier to assemble and lower in cost because it needs less data acquisition interfaces. However, as to which one, linear or non-linear, is more suitable for long probes, more work should be done.[Method] In this study, 10 cm long probes were designed and used, because 1) in measuring heat-pulses in large soil columns, the probe used by the single probe technique is 10 cm; 2) the thermo-TDR probes longer than 10 cm can improve accuracy of the measurement of soil water contents; and 3) the minimum resolution of the distributed optic fibre temperature measurement is about 10 cm. With development of the technique of thermo-TDR and thermo-distributed temperature sensing with heated fiber optics, the use of 10 cm long probes in this study may better embody the advantages of the above-described technique and cherish a bright future in applying the technique. In the indoor soil column experiment, soil thermal properties and water contents were measured with probes that might deflect off in four ways(coplanar extraversion, non-coplanar- extraversion, coplanar-introversion, non-coplanar-introversion), and errors of the measurements resulting from deflection-caused changes in needle spacing were corrected with the linear or the non-linear model, separately.[Result] In using the extended dual probes, the non-linear model performed better in correcting probe spacing in-situ than the linear model (relative error of the former was -8.30 and of the latter 43.90%). Correction with the non-liner model improved accuracy of the measurement of soil volumetric heat capacities and water contents by a large margin, controlling relative errors within 10%. It is worth noting that the main factor affecting the nonlinear model correcting probe spacing is that the corrected spacing acquired by the non-linear model is determined only determined by t_m(the time when the temperature response curve reaches the highest value), while t_m is determined jointly by spacing and soil moisture content. Therefore, it is expected to further improve the accuracy of probe spacing correction in using the non-linear model by modifying t_m value in the nonlinear model to reflect changes in probe spacing and water content.[Conclusion] This study has effectively solved the problem of measurement errors caused by probe deflection of the extended dual thermal pulse probe, and hence provided a theoretical basis for the wide application of the probe. Compared to the linear model, the non-linear one can effectively minimize spacing errors. With the development of thermo-TDR and thermo-distributed temperature sensing with heated fiber optics, the use of 10 cm-long dual probes may embody advantages of the above-described measuring technique and has broad application prospects.

Abstract:[Objective] Loess is loose and porous, and hence contains much air. Soil water vapor movement in the soil is a complex process, in which water and air, two phases of fluids, drives and affects each other in vertical movement in the soil. So it is essential to get to know how dry air flow affects soil water and heat transfer to agricultural production in the Loess Plateau.[Method] To explore effect of soil dry air on soil moisture and heat transfer in an apple orchard of loess on a hill, the STEMMUS model (Simultaneous Transfer of Energy, Mass and Momentum in Unsaturated Soil)was adopted to simulate soil hydrothermal dynamic process. Numerical simulation is a feasible and economical method to reproduce the process.[Result] Results show:(1) the model is a useful tool to well simulate the dynamic process of soil water and heat in the soil. By optimizing the soil hydraulic parameters, in simulation of soil moisture druing the calibration and verification periods, the model varied in the range of 4.7%-30.0% in normalized root mean square error and in the range of 0.83-0.96 in consistency index, while in simulation of soil temperature, it did in the range of 0.1%-9.9% in normalized root mean square and in the range of 0.76-0.99 in consistency index; (2) the simulation using the two-phase coupling STEMMUS model with the dry air mechanism taken into account was more approximate to the measured value than the single-phase STEMMUS model without taking the dry air mechanism into account. After 1 day of rainfall, the increment of soil moisture content in the soil profile of the coupled model was obviously lower than that in the soil profile of the single-phase model. The coupled model was 0.07% in normalized root mean square error, and from 0.93 to 0.97 in consistency index, while the single phase model varied in the range of 0.06%-0.2% normalized root mean square error, and in the range of 0.95-0.96 in consistency index. Considering the existence of pressure infiltration in this area, the coupled model can better reflect the actual soil water movement.[Conclusion] Compared with traditional models, the STEMMUS model can better reflect the actual soil water and heat dynamics in loess by taking soil dry air mechanism into account, which is favorable to designing optimal management strategies for orchards on the Loess Plateau.

Abstract:[Objective] Soil structure is an important factor affecting movement of water, gas and nutrients, root growth, and soil biological activities in the soil. Reasonable tillage is an important farming practice to create soil structure favorable to crop growth. No-tillage has already demonstrated to improve soil structure and soil biodiversity in upland fields. However, so far few studies have reported effect of no-tillage on soil structure of paddy fields. This study was conducted to explore effects of no-tillage on the structure of a paddy soil in a rice-rapeseed rotation system.[Method] Based on a 4-year(2016-2019)tillage field experiment in the Dongting Lake area of North Hunan, effects of rotary tillage (RT) and no-tillage (NT) on soil pore structure of the plough layer (0-25 cm) of a paddy soil were investigated using the X-ray CT imaging technique. Soil aggregate stability was also evaluated using the Le Bissonnais fast wetting method.[Result] The soil organic carbon content of the top soil layer (0-5 cm) in the RT and NT treatments was 34.3 g·kg^-1 and 34.4 g·kg^-1, respectively, which were higher than those of the other soil layers. Compared with the plots under RT, the plots under NT had a slightly lower soil bulk density in the 0-5 cm soil layer (P>0.05), and significantly more>2 mm soil aggregate in the 0-5 cm and 5-10 cm soil layer. Tillage significantly affected soil macroporosity (>25 μm). Compared with the RT treatment, the NT treatment significantly increased soil macroporosity by 78% and 115% in the 0-5 cm and the 5-10 cm soil layer, respectively. Soil pore size distribution was also greatly altered by tillage practices. The NT treatment increased macroporosity of each of the pore size fractions in the 0-5 cm and 5-10 cm soil layers, especially increased the 300-500 μm macropores in the 0-5 cm soil layer and the 25-300 and 300-500 μm macropores in the 5-10 cm soil layer by 70.5%, 82.8% and 167.2%, respectively.[Conclusion] Our findings show that no-tillage in paddy field improves soil aggregate stability and increases macroporosity of the topsoil, which are beneficial to improvement of physical structure of the paddy soil.

Abstract:[Objective] Color of a soil is an important physical indicator characterizing genesis, classification and fertility of the soil. Soils black in color are generally high in organic matter content, but the Shajiang black soil (Calci-Aquic (SCA) Vertisols) in China is a typical soil, dark in color but low in organic matter content. This study aims to establish an effective method for extracting the black color matter from the SCA Vertisols, to explore their compositions and characteristics, so as to expose how organic matter forms and accumulates in the soil. [Methods] In this paper, soil samples were collected from the topsoil layers (0-40 cm) and black soil layers (40-70 cm) of three typical SCA Vertisols of the Huang-Huai-Hai Plain in China and processed with three physical methods, separately, for fractionation by color. The three physical methods includes 1) (HP) to treat prepare the sample with hexametaphosphate (HMP) and have it subjected to oscillation and multi-level sonication; 2) (SC) to treat the sample with sodium carbonate solution and have it subjected to oscillation and multi-level sonication; and 3)(US)to treat the sample with ultrasound only for dispersion. And for fractionation by color, six fractions, that is, POM, White and Light White (white group) and Light Black, Black and Deep black (dark group), were set up. After the soil sample was fractionated, each fraction was analyzed for blackness, organic matter content, particle size distribution and mineral composition with a spectrophotometer, TOC instrument, nano-laser particle size analyzer and X-ray diffractometer separately. [Results] Blackness of the soil had nothing to do with organic matter content, regardless of treatment method, but much with amount of anyone of the dark fractions (Light Black, Black and Deep black). Among the three methods, the HP method got the largest dark fractions, which were significantly related to blackness (P<0.01) of the soil. Particles of organic-inorganic complexes <100 nm amounted to more than 50% of the total dark fractions (TDF), and composed mostly of Fraction DB and B, accounting for over 90%. The content of <100nm organic-inorganic complexes was significantly and positively related to blackness (P<0.01) of the soil, while the content of >100 nm organic-inorganic complexes was negatively related, in all the soil samples, though from different sampling sites. Particles of organic-inorganic complexes <100 nm amounted to 18.4-60.4 g·kg^-1 in the black soil layer, significantly higher than that (2.4-15.2 g·kg^-1) in the topsoil layer in all the three SCA vertisols, and content of organic-inorganic complexes <100 nm in particle size was also significantly and positively related to blackness (R²=0.971) of the soil.[Conclusion] The HP method is the best one for extracting fractionation of SCA Vertisols by color. Soil color depends mainly on content of black nano-organic-inorganic complexes formed out of adsorption of organic matter by smectite in the SCA Vertisols rather than organic matter content, which has relatively less direct impact.

Abstract:[Objective] Dynamic data of soil environment can be used as a scientific basis for decision-making in the field of sustainable agriculture and environmental management. Research and development (R&D) of soil monitoring equipment, low in cost, stable in performance and high in precision, is the key to rapid collection of soil data.[Method] Based on the incoPat, a technology innovation information platform, retrievals were made of output of patents on soil environmental monitoring equipment at home and abroad during 2000-2019, for analysis of number of applications, technology composition, regional distribution, major applicants, legal status, etc. of the patents, in an attempt to reveal R & D status, technology development trends and industry-university-research cooperations in the field of soil environmental monitoring equipment in China.[Result] Results indicate that in recent years, the number of patents has been increasing significantly in China. Soil indices being monitored have extended from soil fertility to pollutants and biological ones. Intelligent in-situ monitoring equipment is being developed in combination with emerging technologies such as modern information technology, and integration of qualitative and quantitative is fully considered in the new R&D. At present, most of the patent applicants in this aspect in China are universities and scientific research institutions, participation of enterprises is relatively lower in degree.[Conclusion] Monitoring of soil pollutants and biological indicators have become a focus, and novel technological achievements in the fields of biology and information science are being introduced into the development of soil monitoring equipment. In China, the industry-university-research cooperation in this field needs to be strengthened urgently.

Abstract:[Objective] This work was performed to understand the research status, hot spot and development trend on remediation of heavy metals in agricultural soils all over the world. Meanwhile, it could objectively reflect the academic level and international influence of relevant countries, institutions and scholars, etc. in this field.[Method] We employed the Web of Science core collection database(WoS), together with the analysis tools self-provided by WoS, HistCitecitation analysis software and VOSviewer software to conduct bibliometric analysis of the literatures on immobilization of heavy metals in agricultural soil.The data were retrieved from the literatures published during the period of 1990-2019.[Result] Results showed that a total of 3376 articles related to immobilization/stabilization of heavy metal pollution in farmland soil were retrieved, and the quantity of publications increased steadily year by year worldwide. The top three countries in number of publications are China, the United States and Spain, and China ranks first in volume of publications, accounting for 28.79%.The Chinese Academy of Sciences, Consejo Superior de Investigaciones Cientificas, University of Florida and Zhejiang University are the major paper-publishing institutions, which have remarkable scientific research level and influence in this field. Particularly, Chinese Academy of Sciences has the highest number of publications and citation frequency, publishing 224 articles with total local citation score 1276 times. Major publishers include Environmental Science and Pollution Research, Chemosphere, Science of the Total Environment, Journal of Hazardous Materials, etc. The passivants include mainly sludge, biochar, red mud, compost, phosphate, lime, and etc. And the research on metal immobilization/stabilization in agricultural soils mainly focuses on the bioavailability of heavy metals. Cadmium, lead, copper, zinc and arsenic are the main concerned heavy metals.[Conclusion] This study would help researchers in this field to grasp the development trend and hotspots accurately, and provide important insights and references for future research.

Abstract:[Objective] Microplastic pollution has become a global environmental issue that has caused widespread concern. Coastal zone is a region of land-ocean interaction under the dual impacts of global climate change and human activities. It is also an important sink for microplastics in the environment. However, by far little attention has been paid to long-term weathering characteristics of microplastics in coastal environments. In this study, microplastics of low density polyethylene(LDPE)film, which were commonly found in the coastal environments of the Yellow Sea and the Bohai Sea, were selected as the object for test in exploring long-term weathering characteristics of the microplastics in different coastal environments, including supratidal, intertidal and subtidal zones at the Yellow River Estuary. The aim of this study is to lay down a scientific basis for clarifying fates and effects of microplastics in the coastal environments.[Method] Microplastics of LDPE film were left in the tidal zones for exposure to the coastal environment for 12 and 18 months. At the end of the each exposure period, they were retrieved for analysis of surface morphology, chemical functional groups(carbonyl index)and density with scanning electron microscopy, Fourier transform infrared spectrometry, and pycnometry. Weathering degree of the microplastics was characterized.[Result] Results show that after 18 months of exposure in the field, colonies of microorganisms were observed on the surface of the microplastics in all the zones and so were significant weathering characteristics. The microplastics in the supratidal zone exhibited the highest degree of cracking. Carbonyl groups were also observed on the surface of the microplastics regardless of where they were in, and in terms of carbonyl index of the microplastics, the three zones displayed an order of supratidal zone (0.28-0.81)> intertidal zone (0.18-0.22)> subtidal zone (0.16-0.20). The microplastics did not show much spatio-temporal variation in density. However, having been subjected to ultrasonic cleaning for removal of surface attachments, the microplastics exposed aboveground at the supratidal zone for 18 months were by (0.85±0.02 g·cm^-3) significantly lower than the untreated ones (0.93±0.03 g·cm^-3) in density.[Conclusion] The dynamic changes in morphological characteristics, chemical functional groups (carbonyl index) and density of the microplastics of LDPE film indicate that weathering degree of the microplastics varying with the tidal zone shows a declining order of supratidal zone > intertidal zone > subtidal zone, and the microplastics in the supratidal zone varied sharply with time in weathering characteristics. The microplastics in the coastal environment are subjected to physical, chemical and biological weathering, such as light, friction, chemical oxidation, and biodegradation. Among them, light-triggered photochemical oxidation may contribute the most to the weathering of microplastics. In the future, more attention should be paid to the research on potential environmental effects and fate of microplastics as affected by the complex environmental factors in the coastal environment.

Abstract:[Objective] With accelerated urbanization, industrial development and excessive utilization of agricultural chemicals, the globe has witnessed soils in a number of regions or areas being salinized and polluted with heavy metals simultaneously. At present, heavy metal-polluted salinized soil has become a worldwide environmental problem. Phytoremediation of heavy metal-polluted salinized soil with halophytes demonstrates benign environmental and good economic benefits. However, little can be found in the literature about how to improve the efficiency of soil remediation with halophytes. The present research is to investigate effects of two remediation agents on remediation of heavy metal-polluted salinized soil with halophytes.[Method] A pot experiment was carried out in greenhouse under natural light. Halophyte Suaeda Salsa was selected as the test plant in the experiment. Four types of soils were simulated by amending the soil with sodium chloride and cadmium chloride solutions separately into 1) soil Cd0S0(0 mg·kg^-1Cd and 0 g·kg^-1NaCl); 2)Soil Cd0S4(0 mg·kg^-1Cd and 4 g·kg^-1NaCl); 3)Soil Cd3S0 (3 mg·kg^-1Cd and 0 g·kg^-1NaCl)and 4)Soil Cd3S4(3 mg·kg^-1Cd and 4 g·kg^-1NaCl). The experiment was laid out in a 2×2×3-factor randomized complete block design(0 and 3 mg·kg^-1Cd; 0 and 4 g·kg^-1NaCl; 0 and 4 mmol·kg^-1 ethylene diamine tetraacetic acid (EDTA) and 15 g·kg^-1biochar). The aim of the experiment was to investigate effects of EDTA and biochar on growth, ion balance, and Cd and Na⁺ uptake and accumulation of the Suaeda salsa grown in cadmium-polluted sodium chloride salinized soil.[Result] Results show that dry weight of Suaeda salsa shoot was 115.5%-341.7% higher in Treatment Cd0S4 than in Treatment Cd0S0, but 62.8%-84.4% lower in Treatment Cd3S4 than in Treatment Cd0S4. With application of biochar, total dry weight of the Suaeda salsa increased significantly by 328.6% in Treatment Cd3S0. K⁺/Na⁺, Ca²⁺/Na⁺ and P/Na⁺ ratios in shoot and root of the Suaeda salsa decreased significantly in Treatments Cd0S4 and Cd3S4 as compared to that in Treatment Cd0S0 or Cd3S0. Application of biochar increased significantly P/Na⁺ ratio in shoot and K⁺/Na⁺ and P/Na⁺ ratios in root of the Suaeda salsa in Treatment Cd3S0. Na⁺ concentration in shoot and root of the Suaeda salsa increased significantly by 32.5%-94.5%, while Na⁺ content in shoot and root of the Suaeda salsa decreased significantly by 21.3%-90.9% in Treatment Cd3S4 as compared to that in Treatment Cd0S4. Cd concentration and content in shoot of the Suaeda salsa increased significantly by 135.8%-223.6% and 132.4%-471.5%, respectively, in Treatment Cd3S4 compared to that in Treatment Cd3S0. Application of EDTA and biochar increased significantly Na⁺ concentration by 38.6% and 56.0%, Na⁺ content by 199.6% and 289.3%, and Cd content by 133.4% and 173.4% in shoot of the Suaeda salsa in Treatment Cd3S4, respectively.[Conclusion] Results suggest that applications of EDTA and biochar significantly promote uptake and accumulation of Cd and Na⁺ in shoot of the Suaeda salsa grown in cadmium-polluted sodium chloride salinizd soil and improve efficiency of the phytoremediation of heavy metal-polluted salinized soil. All the findings in the research may provide certain basic data and a scientific basis for remediation of heavy metal-polluted salinized soil.

Abstract:[Objective] In the recent 30 years, rice has been cultivated extensively in China, involving a great variety of soil types, farming systems and fertilization methods. No matter where it is cultivated, soil phosphorus(P)seems to be a major factor limiting rice production due to its strong P adsorption and fixation capacity of the soil colloids in the paddy fields and low phosphate fertilizer utilization rate of the crop, which consequently leads to accumulation of the element in the soil. The objective of this study was to evaluate utilization and balance of P in the five major rice production regions of the country, which may provide certain scientific bases for recommending rational application of phosphate fertilizer by regions.[Method] Based on the long-term field experiments, starting from 1988, in the five major rice growing regions(i.e. Northeast of China(NE), Yangtze River Delta (YRD), Middle Reaches of the Yangtze River (MYR), South of China (SC) and Southwest of China (SW)), which are significantly different in soil and climate, data were cited from a total of 130 paddy soil monitoring sites scattered in the five regions for comparison and summarization. The data included available P content, and P utilization efficiency, P recovery rate, P agronomic efficiency and soil P balance.[Result] Results show significant differences between the regions in soil available P content. SC was the highest (33.71 mg·kg^-1) and SW the lowest (12.49 mg·kg^-1). The average content of soil available P of the country was 21.18 mg kg^-1, and grew at a rate of 0.36 mg·kg^-1·a^-1. Soil available P content increased significantly with the cultivation going on in all the regions, expect in MYR. All the five regions gained in soil phosphate, with SC being the highest in P surplus. The average annual soil phosphate surplus of the country was 35.03 kg·hm^-2 that accounted for 44.16% of the average phosphate fertilizer input. Moreover, a significant positive relationship was observed between soil available P content and the cumulative P surplus (P<0.05). With every 100 kg·hm^-2 increment in average P surplus, soil available P content increased by 0.82 mg·kg^-1. P recovery rate and agronomic efficiency also significantly increased at a varying in rate with the farming going on in all the five regions, and the highest rates were observed in SW, being 35.92% and 69.02 kg·kg^-1, respectively.[Conclusion] Affected by the 30-year long-term fertilization, soil available P content and cumulative P surplus has increased significantly in all the regions with the rice cultivation going on. However, the variation of P recovery rate and P agronomic efficiency differs from region to region. From all the findings in this study, it is concluded that the fertilization system for each region should be modified in the light of the budgeting of soil phosphorus of the respective locality. For example, in Southwest China, more phosphate fertilizer, especially organic fertilizer should be applied to ensure the normal phosphate supply to meet the demand of the rice crop, while in South China, P fertilization should be reduced in rate, but improved in P utilization efficiency, so as to mitigate the risk of P non-point source pollution.

Abstract:[Objective] Studies on accumulation and potential loss risk of soil phosphorus in non-wood forest soils are essential to management of soil phosphorus and control of non-point source P pollution in watersheds. So a research project was carried out in the Xitiaoxi watershed.[Method] In the project, a total of 105 soil samples were collected in the main non-wood forests, such as moso bamboo (Phyllostachys heterocycla (Carr.) Mitford cv. Pubescens Mazel ex H.de leh.), white tea (Camellia sinensis (L.) O. Ktze.), chestnut (Castanea mollissima Bl.) in the watershed for lab analysis of concentrations of water-extractable phosphorus (WEP) and simulated-acid-rain-extractable phosphorus (SARP) and some main soil physico-chemical properties such as total nitrogen (TN), total phosphorus (TP), total potassium (TK), alkalyzable nitrogen (AN), available phosphorus (Bray 1-P), readily available potassium (AK), pH, soil organic carbon (SOC). Acid rain set at 4.75 in pH was simulated and prepared with sulphate acid and nitrate acid. Correlation analysis and regression analysis was performed of the obtained data to determine influences of soil physico-chemical properties on the risk of phosphorus runoff loss and threshold of soil available phosphorus.[Result] In the survey area, soil TP content varied in the range of 0.22-0.73 g·kg^-1 (0.42 g·kg^-1 on average) and Bray 1-P content in the range of 0.93-313.2 mg·kg^-1 (30.87 mg·kg^-1 on average) with coefficient of variation reaching up to 204.7% and the soil samples over 40 mg·kg^-1 and below 5 mg·kg^-1 in Bray-P content accounted for 17.14% and 38.01% of all the analyzed ones, respectively; soil WEP content varied in the range of 0.03-38.15 mg·kg^-1 (2.64 mg·kg^-1 on average) with coefficient of variation reaching up to 267.5%; and soil SARP content varied in the range of 0.03-42.91 mg·kg^-1 (2.86 mg·kg^-1 on average) with coefficient of variation reaching up to 268.6%. It was found that soil WEP and SARP were significantly and positively related to soil organic carbon (SOC) and TP (P<0.01), and negatively to soil pH, with determination coefficient (R²), however, being only 0.266, 0.251, 0.280, 0.262, 0.187 and 0.190, respectively, which indicates that they are relatively not much affected by these soil properties. The relationship between WEP, SARP and Bray 1-P could be described by the piecewise linear regression equation, which was y=0.148 3x-8.601, x>93.63;0.056 9x-0.043, x<93.63. for WEP with R² being 0.992(r=0.996), and y=0.057 1x-0.021 6, x<87.68;0.160-4x 9.079, x>87.68. for SARP with R² being 0.991 (r=0.995). Hence, the thresholds of soil Bray 1-P was reckoned to be 93.63 and 87.68 mg·kg^-1, respectively, based on WEP and SARP and the latter was 5.95 mg·kg^-1 lower than the former.[Conclusion] All the findings in the study demonstrate that both the phenomena of phosphorus deficiency and excessive accumulation exist in the non-wood forest soils of Xitiaoxi watershed. Soil Bray 1-P, TP, organic matter and pH are the main factors affecting the potential risk of phosphorus runoff loss and Bray 1-P is the most significant one. Acid rain enhances the potential risk of phosphorus runoff loss. As the studied region is one that suffers from frequent acid rain, the content of soil available phosphorus should be more strictly controlled.

Abstract:[Objective] As a pollutant element generated from industrial and agricultural activities, cadmium (Cd) has become an intensifying environmental problem throughout the world. In order to investigate effects of arbuscular mycorrhizal fungi (AMF) on green seedling Cd uptake, a pot experiment was conducted.[Method] A total of twelve species of green seedlings were planted in the Cd-contaminated pots, separately, with or without AMF inoculation. Particular attention was given to the seedlings of A. grandiflora. Effects of inoculation with AMF on population of the microbes and AMF community structure in the rhizosphere of A. grandiflora were analyzed using the PLFA and Hiseq techniques.[Result] After six months, the twelve species of seedlings ranged from 0.25 to 2.59 mg·kg^-1 in leaf Cd concentration, and exhibited an order, excluding Ligustrum japonicum ‘Howardii’ and Eurya emarginata (Thunb.) Makino, of Camellia sasanqua Thunb. < Osmanthus fragrans(Thunb.)Lour < Ligustrum quihoui < Ligustrum sinense ‘Variegatum’ < Elaeagnus pungens var. varlegata Rehd. < Distylium buxifolium < Weigela florida cv. Red Prince < Photinia×fraseri Dress < Abelia grandiflora ‘Francis Mason’ < Weigela florida cv. Variegata. The group inoculated with AMF was obviously higher than their respective ones in the control group without AMF inoculation in leaf Cd concentration. Compared with the control of the same plant, A. grandiflora inoculated with AM2 (Glomus mosseae, BGCAM00164) was 147.85% higher in leaf Cd concentration, so A. grandiflora was designated for investigation in ongoing researches. Twelve months after inoculation with AM2, the plant had Cd concentration in its root, stem and leaf increased up to 164.7, 22.86 and 10.57 mg·kg^-1, or 2.64, 2.06 and 1.76 times as high as that in the control, making up a total of 5 078 μg·plant^-1, higher than that of the control, which is only 1 745 μg·plant^-1. Apparently AM2 reduced the translocation factor and fixed more Cd in the root, thus mitigating Cd damage to the plant. The inoculation of AMF increased PLFA biomass of the AMF, but reduced that of the bacteria and fungi in rhizosphere soil. Glomus, Paraglomus and Archaeospora were the phyla of fungi relatively high in richness in all the samples. Glomus accounted for 55% of the total fungal population, and hence the chief dominant group in the rhizosphere of A.grandiflora. In treatments AM2, Glomus increased significantly from 61.8% to 77.4%, while the AMF community, as a whole, decreased in diversity and richness in the rhizosphere soil, whereas in treatments AM1, Paraglomus increased from 13.1% to 17.8%, but Glomus did not change much. Principal component analysis shows that the AMF community was altered by Cd contamination and AMF inoculation in the rhizosphere of A.grandiflora.[Conclusion] Generally speaking, inoculation with Glomus mosseae may improve the efficiency of A. grandiflora phytoremedying Cd contaminated soils. This type of combined remediation technology can expand the scope of phytoremediation of Cd contaminated soils.

Abstract:[Objective] In this comparative study, impacts of soil arbuscular mycorrhizal symbionts on ammonia-oxidizing microbial communities and their response mechanism in moso bamboo (Phyllostachys pubescens) groves different in management intensity were investigated, in an attempt to provide a theoretical basis for scientific and rational application of nitrogen fertilizer in moso bamboo forests and contribution to mitigation of global climate change.[Method] Sample sites of bamboo groves similar in standing condition but different in management intensity, intensive and extensive, were selected for this field experiment, in each site, four 10 m×10 m quadrats or sample plots were set up, and in each sample plot two microcosmic systems were built up with PVC and nylon nets different in mesh number. With the aid of the microcosmic system, mycorrhiza fungal mycelia were separated from the mycorrhizal root system into two compartments:the mycorrhizal chamber (RA) and the mycelial chamber (AH). Once the systems were fixed, they were left in the soil and cultured in situ for 3 months. Soil samples were collected from the microcosmic systems with a soil auger for analysis in the laboratory. The soil samples were prepared into suspensions, (1:2.5=soil:water) for determination of soil pH with a pH meter; Alkali-hydrolyzale nitrogen (AN) was determined with the alkali-hydrolyzed diffusion method; available phosphorus (AP) was extracted with ammonium fluoride and hydrochloric acid solution and determined with a molybdenum-antimony colorimetry; available potassium (AK) was determined with the flame photometric method; soil organic C (SOC) with the potassium dichromate oxidation method; Soil nitrification potential with the aerobic culture method; copy numbers of amoA gene of ammonia-oxidizing archaea and bacteria with the Real-time quantitative PCR; and ammonia-oxidizing microbial community with the high-throughput sequencing technique.[Results] Results show that both intensive management and extensive management reduced significantly soil pH in the mycelial chambers (AH) in the moso bamboo forest, and only intensive management did soil alkali-hydrolyzed nitrogen in the mycelial chamber (AH). No significant difference was found between the two compartments of the same system in nitrification potential, but the soil nitrification potential in the mycorrhizal chamber (RA) in the bamboo forest was significantly higher under intensive management than under extensive management. AOA in the mycorrhizal chamber and mycelium chamber was significantly lower in gene abundance under intensive management than under extensive management, while AOB in the mycelium chambers was significantly decreased in gene abundance regardless of management intensity. Ammonia-oxidizing microbial communities did not vary much in composition or structure in either chamber under either management. However, network analysis shows that the ammonia-oxidizing microorganisms in the bamboo forest under intensive management displayed better interaction and symbiosis relationship, but less competition than those in the bamboo forest under extensive management.[Conclusion] To sum up, AM mycelia significantly reduce soil pH and AN content in intensively managed moso bamboo forests. Intensity of forest management does have significant impacts on nitrification potential, which however does not differ much between the two mycorrhizal compartments. Intensive management has significant effects on gene abundance of AOA and AOB in the AM mycelial compartment. Although management intensity does not have much impact on structure of the ammonia-oxidizing microorganism community in the soil, intensive management does dull nutrient competition among ammonia-oxidizing microorganisms to a certain extent.

Abstract:[Objective] Cation exchange capacity of clays is an important index for determining diagnostic horizons and diagnostic characteristics in the Chinese Soil Taxonomy (3rd edition) and the United States Soil Taxonomy. However, some studies have shown that the values of CEC₇ particles predicted using models are often higher than their corresponding measured ones, thus leading to misjudgment of taxon at high taxonomic levels. With the zonal soil in Jiangxi Province taken as the main object, this study aimed to optimize the current CEC prediction model to alleviate the impacts of its error factors, to build up a new model, based on main error factors, for predicting CEC₇ of clay particles, so as to improve prediction accuracy and to provide reliable data support for retrieval in the soil taxonomy.[Method] To that end, an idea of how to optimize the current model was put forward, suspicious error factors were screened out based on the previous researches and collated with those in the current model for correlation analysis, and error law in the current model was explored. Then soil samples were classified in line with the law to improve the model in prediction accuracy. Main error factors in each classification sample were searched out and got involved in modeling. Eventually, the optimized model for soil classification was established.[Result] By comparing the value estimated with the current model with the measured one, it is found that the former is generally higher than the latter. Previous studies have shown that soil organic matter, silt CEC₇, soil pH and soil free iron oxide content are factors affecting CEC of the fine soil in the B layer of weathered soil. Correlation analysis was performed of the factors with the error, and indicated that organic matter and silt CEC₇ were the main ones causing errors. Studies found that in predicting soils higher or lower than 6 g·kg^-1 in organic content, errors varied in dispersion. Therefore, in this study, all soil samples were sorted into two groups, high and low in organic matter content for modeling. For the group high in organic matter, errors were ultra-significantly related to soil organic matter content (R²=0.402, n=23). Considering that organic matter may get bonded with clay particles, the group of samples high in organic matter content were further sorted in three subgroups, i.e. "clay soil samples", "clay loam soil samples", and "loam soil samples" and a model was set up for each of the three subgroups. In the subgroup low in organic matter content, errors were ultra-significantly related to CEC₇ of silt (R²=0.675, n=23), so a direct model was obtained for soil samples low in organic matter. Considering that CEC₇ is not easy to be measured, soil pH, annual mean temperature (Tem℃) and Latitude (Lat) were selected and used in modeling for predicting silt CEC₇, and consequently an indirect model based on environmental factors was established for soil samples low in organic matter. Through the accuracy evaluation of the models, it is found that optimization of the models has brought predicted values closer to measured values, and the models for all subgroups of soil samples are good in accuracy. Optimization of the models has raised retrieval of iron-rich soils from 20% to 93.3% in accuracy.[Conclusion] Based on the above findings, it is found that modeling by content of soil organic matter is reasonable. By analyzing sources of the errors with the current model and following the optimization formula, models for predicting cation exchange capacity of clay particles are established by content of soil organic matter with higher accuracy. The models may provide reliable data support for retrieval in the soil taxonomy.

Abstract:The Sanjiang Plain is located in the northern part of the mid-temperate zone of China. In recent years, climate warming and cultivated land use have been changing significantly. So it is of great significance in protecting food security and stability to analyze responses of cultivated land use to regional climate change. As cultivated land is a kind of artificial vegetation, its NDVI value reflects certain crop information, like growth and yield. Therefore, by analyzing impacts of climate factors on cultivated land NDVI, information relevant to response of regional cultivated land use to climate change can be obtained.[Objective] Based on the data of cultivated land use, ten-day climatic data, and ten-day normalized difference vegetation indexes (NDVI) of the Sanjiang Plain during the farming period (May~September) of the years from 2000 to 2015, temporal changes in climatic factors and spatial variation of NDVI of the cultivated land were obtained through analysis and furthermore, information about delayed response of cultivated land NDVI to regional climate change was acquired.[Method] In this research, methods, like variation coefficient analysis, trend coefficient analysis and time-delay cross correlation analysis were adopted.[Result] Results show:(1)The interannual variability of temperature was more stable than that of precipitation during the farming period of the Sanjiang Plain, while the intermonthly variabilities of the two tended to be more regular; (2)The cultivated land NDVI did vary much between years, with the vegetation coverage being the highest in September; spatial variation of the cultivated land NDVI during the 16 years exhibited a trend of being low-unstable-increasing in value, representative in the western part of the region and being high-stable-decreasing in value, representative in the eastern part; (3)Maximum unbiased correlation coefficients of the ten-day NDVIs and ten-day mean temperatures of the cultivated land varied mostly in the range between 0.931 and 0.992, and delayed response was observed for 2 ten-day periods. Maximum unbiased correlation coefficients of the ten-day NDVI and ten-day precipitation of the cultivated land varied in the range between 0.778 and 0.927, and delayed response was observed for 1 ten-day period only. The cultivated land NDVI of the Sanjiang Plain, except for Fuyuan County, Raohe County and Tongjiang City, responded more slowly to air temperature than to precipitation. The cultivated land NDVI responded quite slowly to regional climate change in Jiamusi City and Shuangyashan City, while it did rather quickly in Mishan City, Baoqing County, and Hulin City. Moreover, it responded faster to change in air temperature and slower to change in precipitation in Fuyuan County and Muling City; and (4) The maximum unbiased correlation coefficients of dry land ten-day NDVI and ten-day mean temperature were both 0.942, and that of the paddy field's was 0.962. Delayed response of NDVI to mean temperature in dry land was observed for 2.026 ten-day periods, and that in paddy field for 1.633 ten-day period. The mean maximum unbiased correlation coefficient between ten-day NDVI and ten-day precipitation was 0.809 in dry land, and 0.765 in paddy field, and the mean time lag of NDVI to precipitation was 1.323 ten-day period in dry land, and 1.045 ten-day periods in paddy field.[Conclusion] Change in regional temperature impacts cultivated land NDVI more than change in precipitation does. The lag of NDVI responding to air temperature of cultivated land is longer than that to precipitation in most counties. Temperature is a major factor affecting regional paddy field NDVI; the lag of dry land NDVI responding to regional climate change is longer than that of paddy field's. The findings in the research may provide a scientific basis for guiding farming production of the region to cope with climate change and ensure food security.