Abstract:The appearance of soil environmental problems, such as pollution and degradation, has stimulated researches on hydro-ecological simulation, soil resource management, soil carbon and nitrogen monitoring, etc., thus putting forward higher requirements on basic input data, like types and attributes of soils, in accuracy, scale and timing sequence and causing rapid development of the research on soil sampling oriented towards digital soil mapping. In this study, the bibliometric method was applied to quantitatively analyze variation of the researches at home and abroad in distribution of disciplines hotpot during the recent four decades since 1980. Based on collation and review of the literature, summarization was performed of methods widely used nowadays in soil sampling and speculative mapping, and discussions conducted about future trends of the research on sampling designing for digital soil mapping, in an attempt to provide a reference for development of digital soil survey. Results show: (1) Over the last four decades, hotspots of the research on soil sampling have been focused on theories, methods, techniques, means and strategies of soil sampling, soil management and utilization, digital soil mapping, etc., involving disciplines that have developed from a single field of soil science into a transdisciplinary research covering agronomy, engineering, soil science, environmental science and geography, etc., with theories, techniques and means turning from mere application of probability theory into combination of geostationary models, deep learning and knowledge mining, and focuses laid on application in ecological monitoring and protection, precision agriculture and polluted remediation. (2) Soil sampling designing is a process of selecting an appropriate sampling method to meet the specific goal of a soil survey based on certain prior knowledge. According to the purposes of a soil survey and soil sampling history of the surveyed area, soil sampling designs can be divided into four categories, i.e. comprehensive sampling, supplemental sampling, verification sampling and monitoring sampling. In regions lacking historical soil sampling data, comprehensive sampling can be implemented by appointing sampling sites randomly based on the designed sampling method to achieve uniform coverage of their geospatial space, or by laying out sampling sites with reference to environmental factors to realize coverage and optimization of feature spaces, while in regions rich in data,comprehensive sampling may better adopt model-based sampling methods. For supplemental sampling, sampling points should be laid out in locations low in similarity of environmental factors, or high in uncertainty of predictive mapping or both. For validation sampling, independent sampling points should be arranged in line with the sampling design for better validation effect. And monitoring sampling could be designed into spatial sampling and temporal sampling or both with sampling sites laid out based on the design and the model in combination. And (3) soil mapping is a process of realizing point-plane expansion with the aid of mathematical methods or spatial models based on soil-environment relationship and spatial autocorrelation of soil attributes. In soil mapping, cartographers should pay attention to adoption of environmental factors and efficiency of the method utilizing the information of variables of the sampling sites. Hereby, cartographers should choose a corresponding inference model to implement spatial expression of soil information. So studies in future should be oriented towards application and theory, like designing of multi-scale soil sampling, new hypothesis of soil-environment relationship hypothesis and quantification of realistic problems in soil sampling designing.

Abstract:【Objective】It is of great significance to explore genetic characteristics and evolution laws of the soils derived from Pleistocene sediments to the study of geological evolution and ancient climate change and the management of the soil resources. Chongqing is a region dominated by mountains and hills, and hence known as “Mountain City”, where the soil layer is thin, except for the soils derived from Pleistocene sediments, which are often quite thick in soil layer and hence high in land utilization rate, so it is the important agricultural resource of Chongqing. However, so far little has been reported on genetic characteristics and classification of the soils and effects of cultivation on evolution of their properties. Therefore, this paper addressed the issue in an attempt to promote development of quantitative classification of the soils, to provide certain theoretic bases and important ideas for rational utilization of the soils, relative to soil type. 【Method】Field soil surveys were conducted to specify six soil profiles, 3 upland soils and 3 paddy soils, derived from Pleistocene sediments of pebble-mixed yellow clay (PC), yellow clay (YC) and red clay (RC), of which soil morphological characteristics were obtained through investigations of their soil-forming environments. PC and YC (commonly known as old alluvial sediments) are mainly distributed on the high terraces on both sides of the Jialing River and its main tributaries, and RC mainly on the karst plains and some valleys in Xiushan County. Soil samples were collected from the profiles by horizon for analysis of physico-chemical properties. Based on the comparative analysis, genetic characteristics and classification of the soils relative to cultivation mode were discussed, and diagnostic horizons and diagnostic characteristics of the soils were determined, and the soils were attributed and named in CST level by level in the light of the “Chinese Soil Taxonomy (3rd ed.)”. 【Result】The upland soil derived from PC was found to have a lot of gravels but no iron-manganese speckles or stripes, while that derived from YC was found to be in a reverse condition and that derived from RC to have apparent clay deposition right beneath the plow layer. In the profiles of paddy soils derived from PC and YC, organic matter accumulation was obvious in the upper part, while iron oxide accumulation was in the lower part, so the upper part was lower the lower part in chroma. However in the paddy soil derived from RC, migration of iron oxide was not as obvious. The 3 upland soils were sorted into 3 subgroups, i.e. Typic Hapli-Udic Cambosols, Typic Ferri- Udic Cambosols and Red Ferri -Udic Argosols, and further into 3 soil families, i.e. Coarse bone loamy silica non-acid thermic -Typic Hapli-Udic Cambosols，Clay loamy silica mixture non-acid thermic - Typic Ferri-Udic Cambosols and Heavy clayey illitic mixture acid thermic - Red Ferri - Udic Argosols, separately. The 3 paddy soils were sorted into 2 subgroups, i.e. Typic Fe-accumuli- Stagnic Anthrosols and Typic Hapli- Stagnic Anthrosols, and further into 3 soil families, i.e. Clay loamy silica mixture non-acid thermic - Typic Fe-accumuli - Stagnic Anthrosols, Clayey illitic mixture non-acid thermic - Typic Fe - accumuli - Stagnic Anthrosols and Clayey kaolinitic non-acid thermic - Typic Hapli - Stagnic Anthrosols, separately. The six soils formed 6 soil series in total. 【Conclusion】The soils derived from YC have iron-manganese speckles or stripes, which are reflections of paleo-hydrological conditions, but now they are completely free from the influence of groundwater and no longer were the aquic soil moisture regime. The characteristics of sediments and regional climate do have some impact on clay deposition in the upland soils, thus affecting their classification on the soil order level. Long-term paddy cultivation would transform Cambosols and Argosols derived from Pleistocene sediments into Stagnic Anthrosols. Artificial activities, such as field screening, changing slopes into terraces, gathering pebbles et al, would reduce gravel content in the paddy soil derived from PC, which would in turn influence particle-size fractionation of the soil layers controlled by soil family.

Abstract:Steep slopes of Pisha-sandstone are the major sources of silt and coarse sand in the mid-reaches of the Yellow River of China. Revegetation of herbaceous plants on the slopes is one of the most effective measures to control soil erosion thereupon. However, so far little has been reported in the literature about how herbaceous plants influence soil erosion on steep slopes of Pisha-sandstone. 【Objective】This study aimed to quantitatively study effects of herbs on soil erosion on steep slope of Pisha-sandstone and hydraulic mechanism of the erosion. 【Method】 A total of ten artificial slopes (37°) were set up and planted with alfalfa plants different in spacing (2 cm、4 cm、5.6 cm、8 cm ) in Erdos, Inner Mongolia. Plot runoff scouring experiments were carried out with a constant inflow (2 L.min^-1). Runoff and sediment yields on the slopes and variation in hydraulic features of the runoff were monitored and analyzed to explore the mechanism of alfalfa controlling soil erosion. 【Result】 Results show sediment yield on the slopes planted with alfalfa occurred in the initial period of runoff and scouring period, forming a single peak. Sediment yielding rate increased with flow velocity and stream power in a power function, with determination coefficients being 0.94 and 0.68, respectively. The presence of alfalfa decreased runoff volume and changed the flow hydraulics. Flows on the alfalfa covered slopes were in a laminar and subcritical state. Increase in plant spacing resulted in greater flow velocity ( R²=0.90) and stream power ( R²=0.62), but a decrease in flow resistance ( R²=0.87). Stems and roots of alfalfa played an important role in altering flow hydraulics. Before rill formation, stems of the plants hindered the flow of runoff. However, after rill formation, apart from the stems, roots of the plants standing out in the rills inceased resistance to the flows therein. Due to the changes in flow hydraulics and soil erodibility, soil loss on the slopes decreased exponentially with alfalfa coverage ( R²=0.55). However, compared to the alfalfa coverage, plant spacing was more closely related to soil loss ( R²=0.93). 【Conclusion】 Plant spacing may reflect more comprehensively the effect of alalfa as a whole (shoots and roots) on controlling soil erosion of steep slopes of Pisha-sandstone. The study may provide a certain scientific basis for planting herbs on steep slopes of Pisha-sandstone for erosion control.

Abstract:【Objective】 Revegetation of the Loess Plateau, especially since the implementation of large-scaled “Grain for Green” projects, has brought about great changes in land surface coverage and underlying surface (or subsoil layer) of the plateau and altered significantly physical properties (soil structure, porosity, etc.) of the soil. Such dynamic changes in the environment may generate very important impacts on hydrological processes, hydrological fluxes, water balance, and ecosystems at a watershed scale. In recent years, rainfall-infiltration-runoff processes and their mechanisms as affected by global warming have become a hot topic in the field of hydrology. Therefore, the study to explore water storage capacity of and rainwater infiltration processes in soil profile under severe rainstorm may help expose processes and mechanisms of soil hydrology, soil erosion and surface runoff, and hence is of great scientific value to elucidation of processes of runoff generation and convergence and their influencing mechanisms. 【Method】In this paper, a real-time dynamic soil water monitoring system was used to monitor soil moisture layer by layer at 10 cm intervals in 2 m soil profiles in a tract of grassland in a hilly and gully loess region during the “7•26” severe rainstorm event in northern Shaanxi Province. Data of the rainfall event was obtained from the meteorological station of the region. Both rainfall data and soil moisture data were extracted at 1-hour intervals. Based on analysis of the rainfall and soil moisture data, dynamic changes, distribution characteristics and soil water storage capacity of the soil water in the profiles during the severe rainstorm event were acquired. And with the aid of the Horton infiltration model, movement and infiltration processes of the soil moisture wetting front in the grassland profiles were simulated. 【Result】Results show: (1) the response of soil moisture in the profile to the rainfall varied with process of the rainfall and depth of the soil layer. The soil profile could be divided into three layers, i.e. soil moisture quick-changing layer (0~ 60 cm), soil moisture active layer (70~ 140 cm) and soil moisture stable layer (150~ 200 cm), with soil water varying in the range of 15.49~ 16.72 mm, 2.01~13.27 mm and 0.22~ 0.44 mm, respectively; (2) The 0~140 cm soil layer is critical to the soil hydrological process in the profile, with average water storage being 26.49% higher than that of the 150~ 200 cm soil layer. The soil water storage of that layer could reach as high as 225.99 mm, 1.37 times its initial water storage capacity (95.37 mm). Thereinto, the 0~100 cm soil layer is the one with available soil water closely related to its grass cover; (3) In this area, soil infiltration depends on physical properties of the soil. Soil steady infiltration rate decreases with increasing soil bulk density, and the decrease declines in magnitude with risng bulk density, too；and (4) Rainwater infiltration rate on grassland hillslopes (P< 0.01) shows a decreasing trend with the time going. The attenuation is high in rate in the initial period and turns low. The infiltration rate varies exponentially with time. Cumulative infiltration (R²= 0.99, P< 0.01) shows a logarithmic relationship with wetting front movement process (R²= 0.99, P< 0.01) along the time series. The Horton infiltration model is suitable for simulation of the infiltration process (R²= 0.97, P< 0.01) as affected by severe rainstorm. 【Conclusion】During the severe rainstorm event, the mechanism of runoff generation is still dominated by infiltration excess runoff on hillslopes of the region. The increase in infiltration can reduce runoff volume and delay runoff generation to a certain extent, which has a significant impact on the mechanism of runoff generation.

Abstract:【Objective】The study on rules of spatial distribution of soil nutrients is of important significance to regionalized management of soil nutrients and construction of primary farmlands. 【Method】Using the common ordinary Kriging method and cluster analysis method in combination, horizontal and vertical spatial distribution of soil readily available potassium (AK) in the farmlands was studied and characterized in the core region of the Tongnan National Agricultural Science and Technology Park in West Chongqing.【Result】(1) Results show that the AK in the soil layers of 0~20, 20~40 and 40~60 cm averaged to be 111.6, 96.1 and 90.2 mg·kg^-1, in content respectively, and varied in a moderate degree and in the range of medium ~ deficiency in grade;. (2) The AKs in the 0~20 and 20~40 cm soil layers were both negative in global Moran""s I and spatially isolated, while the AK in the 40~60 cm soil layer was positive and spatially agglomerated; (3) Distribution of the AKs in the 0~20 and 20~40 cm soil layer could be best described with the Gaussian model, and in the 40~60 cm soil layer with the spherical model. The AKs in the 0~20 and 40~60 cm soil layers varied spatially mainly with random factors, and in the 20~40 cm soil layer with structural factors and random factors jointly; (4) The 0~20 cm soil layer high in AK concentrated in the center of the study area, while the layer low in AK scattered quite randomly. The AK in the 20~40 and 40~60 cm soil layers followed a similar trend in distribution. The layers high in AK concentrated in the southeast part and the layers low in AK in the northeast part of the studied region. Vertical distribution of the AK appeared to be in three forms, i.e. uniform, low AK declining and high AK declining, which exhibited a decreasing order in area. 【Conclusion】Soil type, topography and land use are the importment factors that have certain impacts that vary in degree either vertically or horizontally on the spatial distribution of AK contents. All the findings of the study may serve as a scientific basis for selection of land consolidation sites, program optimization and regionalized nutrient management of the consolidatedd land in the study area.

Abstract:【Objective】 Heavy metals pollution level in farmland soil is related to quality and safety of the agricultural produce and health of the farmland ecosystems. Spatial distribution and evaluation of heavy metal pollution of the soils has become the focus of concerns all over the world, and attracted wide attentions from the governments and scientists of all the countries. In recent years, the situation of soil heavy metal pollution in farmland in China is getting so serious that it has aroused country-wide concerns. To address the problem, China has promulgated the “Law of the People's Republic of China on Soil Pollution Prevention and Control”, which is an act of long-term realistic significance to regulation, control, and reasonable evaluation of the pollution of heavy metals in soils of China. 【Methods】Jiangning District of Nanjing City, the largest agricultural produce and sideline product logistics center in East China and the second in the country, has rarely been reported about the issue before. It is, therefore, necessary to perform investigations and evaluations of any heavy metal pollution problems in this region. For this study, samples of topsoil (0~20 cm) were collected from 29 pieces of farmland scattered in the region during November and December, 2017 for analysis of soil pH, organic matter and contents of 8 heavy metals, such as arsenic (As), cadmium (Cd) and chromium (Cr), Copper (Cu), mercury (Hg), nickel (Ni), lead (Pb) and zinc (Zn), and heavy metals pollution of the soil was evaluated in line with the newly released “Standards for Soil Environmental Quality and Risk Control of Agricultural Land Soil Pollution (Trial) (GB 15618-2018)” with a view to improving and optimizing the traditional evaluation methods for pollution assessment, and developing a more scientific and reasonable region-specific evaluation method, which combines the technical characteristics and spatial analysis function of GIS, and makes use of the geostatistics method in analyzing spatial distribution characteristics of the heavy metals pollution.【Results】Results show that the soils in the study area varied in the range from acidic to neutral in soil pH, lacked organic matter, and contained 8.27, 0.17, 70.84, 24.74, 0.20, 32.07, 28.48 and 73.57 mg•kg^-1 of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn, respectively, all of which except for As, were higher than their respective background values of the soil environment of the region, but still within the safe ranges specified in the current standards of the nation for agricultural environment quality. So on the whole, the region is not polluted with heavy metals.【Conclusion】In certain areas of the region, soil Cd, Cu and Hg has reached their respective alert threshold, posing pollution risks, which calls for serious attention in agricultural production. The risks are quite high in the southwest and south parts of the region, forming a band in distribution. In that band, Cd, Cr, Cu, Ni and Zn are found to have come from the same source, potentially the Lishui River running through the study area. The upper reaches of the Lishui River is the Qinhuai River flowing through the urban area of Nanjing. Further studies should be done as to specific sources of the risks. Comparison of the methods for evaluating heavy metal pollution in soil shows that the single factor index method is simple, intuitive and highly adoptable to determination of whether a single item of heavy metal in soil has surpassed the criterion in soil survey and to grading of the risk; the comprehensive index method is more scientific and reasonable for comprehensive evaluation of soil heavy metal pollution; The newly promulgated “Standards for Soil Environmental Quality and Risk Control of Agricultural Land Soil Pollution (Trial) (GB 15618-2018)” is aimed at soil pollution assessment of farmland in the light of soil pH and type of land use. The promulgation of the standard is of great significance to comprehensive risk assessment of soil heavy metal pollution of farmland soils, survey and grading of soil pollution and remediation of polluted soils.

Abstract:【Objective】 In order to expose influence of deep vertically rotary tillage (DVRT) technology on aggregate structure, and explore mechanism of the change, in-lab analyses of soil samples were carried out in this study. 【Method】 Soil samples were collected from farmlands of latosolic red soil different in tillage, conventional rotary tillage 20 cm deep (CT20), deep tilling 40 cm deep (DT40), DVRT 20cm deep (FL20) or DVRI 40 cm deep (FL40), were studied by means of aggregate analysis, scanning electron microscopy (SEM), brunauer-emmett-teller (BET) specific surface area analysis and pore size analysis for differences in morphology and structure of the soil before and after tillage and between the treatments of tillage. Changes in nutrient status and physicochemical properties of the latosolic red soil after tillage were analyzed and compared. 【Result】Results show that FL40 increased the content of mechanical stability aggregates, 1~0.25 mm in particle size (P<0.05) and decreased the content of water stability aggregates, >3 mm in particle size (P<0.05) as compared with other tillage methods. Compared with CT20 and DT40, FL (either FL20 or FL40) changed the soil in micro-morphology to have skeletal grains fine, closely arrayed and smooth in surface, and to be higher in soil specific surface area and more extensive in pore distribution. DT40 differed significantly from the other treatments in available nutrient content (P<0.05). 【Conclusion】Compared with CT20 and DT40, FL (either FL20 or FL40) can increase the content of aggregates in latosolic red soil, and changed the micromorphology of latosolic red soil significantly, and FL20 can increase crop yield significantly.

Abstract:【Objective】 It is of great scientific significance to study physical, chemical and biological processes of the migration of colloidal particles in saturated porous media. Therefore, it is essential to determine factors affecting the migration and deposition of colloidal particles in saturated porous media. 【Method】 An in-lab quartz sand column experiment was conducted to study migration behavior of colloidal particles in the sand column. The colloidal particles, were poured into saturated porous media with water solution of a set water head. The experiment was designed to have three levels of particle size of the colloidal particles, three levels of concentration of the colloidal solution and three levels of particle size of the quartz sand in the column.【Result】 Results show that K/K₀ of the media was reduced to an extent that was positively related to concentration and particle size of the colloidal particles in columns treated with colloidal particles the same in particle size. The smaller the size of the colloidal particles with the same concentration, the larger theK/K₀ of the overall column and the AB segment (surface layer) at the end of the experiment, and the smaller the K/K₀ of the lower EG segment (bottom layer), indicating that large particles were more likely to deposit in the surface layer, while small particles were to move to the bottom. As a whole, the particle size effect was not as noticeable as the effect of change in particle concentration. When the colloidal particles migrated through the porous media different in particle size, K/K₀ of each segment of the porous media large in particle size was significantly lower, while it was only low in the surface layer of the column of sands small in particle size. Regression analysis of temporal variation of the overall relative permeability coefficient with other factors shows a quadratic relationship between the two with R2 being greater than 0.92 except in a few cases, which indicates good correlations. However, the correlation was not significant when the porous media were small in particle size. Analysis of velocity variation indicates that the higher the colloidal particles in concentration and particle size and the porous medium in particle size, the faster the decline of flow rate. Comparison between columns treated with colloidal particles different in concentration and in different particle, separately shows that large particles concentrated mostly in the upper part of the sand column, while small particles did in the lower part, which corresponded to the change of the medium in permeability. Qualitative characterization of the columns with a scanning electron microscope displays significant deposition of colloidal particles on the surface of the porous media after the experiment, which further demonstrates that colloidal particles could clog pores of the porous media, thus affecting their permeability. Secondly, the deposition of colloidal particles in the porous media increased K/K₀ under certain conditions, which was related to concentration C₀of the input and diameter ratio d_p /D_p ( d_p stands for colloidal particle size, and D_p for arithmetic average particle size of the quartz sand) of the particles. Phenomena of rising local permeability coefficient would appear when d_p /D_p was higher than 0.018 and C₀was lower than 0.5 g•L^-1. 【Conclusion】 Generally speaking，the colloidal particles migrating in porous media may clog the pores of the media physically, and hence reduce their permeability. Particle size and concentration of the colloidal particles tested and particle size of the porous media are main factors affecting migration and deposition of the colloidal particles in saturated porous media.

Abstract:[Objective]Layered soil is more often encountered than homogeneous soil in nature, and its water movement follows a law different from the latter’s. And infiltration of water, such as atmospheric precipitation and irrigation water, is an important part of the hydrological process in soil, and is also closely related to groundwater replenishment and pollutant transport. Soil initial water content, soil texture and structure and water supply intensity are all factors affecting the process of water infiltration. The purpose of this study is to explore and grasp law of the water infiltration in layered soil and mechanisms of the influencing factors, and provide a theoretical basis for further rationalization of farmland irrigation measures.[Method]The layered soil used in this research, was constructed in line with the soil profile in the field, i.e. a silt loam layer (18cm thick) and a sandy loam layer (24 cm), and out of the consideration of the mechanisms of ponding water relative to depth, soil configuration and initial soil moisture content affecting water transport. In the indoor ponding infiltration experiment of layered soil, wetting front, cumulative infiltration and soil profile pressure head, relative to depth of standing water, was observed. Moreover, hydraulic parameters of the layered soil were determined with a Ku-pF device and the Hydrus-1D software inversion module, separately. Based on these parameters, the Hydrus-1D model was used to simulate and predict water transport under various set conditions. Applicabilities of the soil hydraulic parameters were verified by comparing the simulated data of the two sets of parameters.[Result]Results show that the wetting front turned from nonlinear advance to linear advance and the cumulative infiltration increased with time, while the infiltration rate decreased rapidly in the early stage of the infiltration and then slowly as the infiltration going on, which is mainly due to the change in soil matrix potential gradient. The soil was relatively dry and high in water suction at the initial stage of the infiltration; as the soil increased in water content, the water suction decreased. As affected by the three factors, water transport varied sharply in characteristics in the layered soil. When the ponding water increased in depth and the initial soil water increased in content, both the wetting front advancing rate and the infiltration rate increased, and the pressure water head increased quicklyat each observation point and the soil water unsaturation degree decreased, which indicates that the change in depth of ponding depth has some impact on pressure potential, and the change in initial water content is related to matrix potential and disintegration and compression of soil aggregates. Compared with the soil configuration of silt loam overlying sandy loam, the one of the reverse order was higher in overall wetting front advancing rate, infiltration rate and pressure head variation. (The infiltration rate at the interface of the wetting front in the layered soil was 0.20 and 0.021 cm•min-1, respectively.) In addition, the two types of layered soils differed significantly in variation of the pressure water head in the soil water redistribution process.[Conclusion]All the findings in this study not only help illustrate that appropriate adjustment of the three influencing factors can reduce soil leakage and optimize soil water management in the field, but also further demonstrate that the parameters of the inversions are more adoptable to simulation and prediction of water infiltration characteristics of layered soils under ponding water in indoor experiments.

Abstract:【Objective】The abundant phytoliths in the forest ecosystem can seal part of the organic carbon in the soil, thus forming a stable carbon pool, which plays an important role in maintaining global carbon balance.【Method】Four different types of subtropical woodlots, i.e. bamboo forest, broad-leaved forest, coniferous forest and coniferous- and broad-leaved mixed forest, in the Jinyun Mountain of Chongqing were selected as research objects in this study. Distribution of soil phytolith and phytolith carbon in the 0～20, 20～40, 40～60 and 60～100 cm soil layers under the forests was studied.【Result】Results show that the soil profile (0～100 cm) under the bamboo forest was the highest in content and reserves of organic carbon, content and reserves of phytolith and content and reserves of phytolith carbon. Both organic carbon and phytolith carbon tended to concentrate in the topsoil layer (0～20 cm) in all the four types of forest soils and declined in content with soil depth. In terms of average content of soil phytolith-occluded organic carbon in the 0～100 cm soil profile, the four forest soils exhibites an order of bamboo forest (1.96 g•kg^-1) > coniferous and broad-leaved mixed forest (0.52 g•kg^-1) >coniferous forest (0.33 g•kg^-1) > broad-leaved forest(0.28 g•kg^-1); the soil phytolith and the phytolith-occluded organic carbon in the bamboo forest were the highest, and significantly higher than their respective ones in the other three forests (P<0.05), and the lowest in the broad-leaved forest. Phytolith carbon showed a trend of surface enrichment in all the four forests. Correlation analysis found that phytolith was significantly and closely related to phytolith-occluded organic carbon (P<0.01), but significantly and negatively related to organic carbon in phytoliths (P<0.05). 【Conclusion】Among the four forest types of forests in the Jinyun Mountain, bamboo forests are the highest in content and storage of soil organic carbon, phytolith, phytolith-occluded organic carbon, and hence a good carbon-rich forest type.

Abstract:【Objective】The interactions between ions and charged particles determine microscopic properties of particles, interface reaction processes and interactions between particles. Ion exchange adsorption is an important physicochemical process of the reactions at solid/liquid interfaces. In this study, based on the newly established ion adsorption kinetics model, adsorption kinetics of alkali metal ions on the surface of montmorillonite particles (a surface with permanent charges) was characterized, in an attempt to analyze specificity of the ions in the adsorption process and to provide theoretical support to studies on interactions between ions and charged particle surface. 【Method】Kinetics of the adsorption of alkali metal ions, Li⁺, Na⁺ and K⁺ on the surface of montmorillonite-Cu²⁺ particles was studied with the aid of the constant flow method, relative to ion concentration of the soluttion. Relationship between ion equilibrium adsorption capacity and system activation energy in 1:1 electrolyte (LiNO₃, NaNO₃, KNO₃) solution was established. 【Result】(1) Li⁺, Na⁺ and K⁺ varied sharply in adsorption rate and equilibrium adsorption capacity, in solutions the same in concentration, and in the ions adsorption process, they exhibited apparent ion specificities. Adsorption selectivities of the ions were subject to concentration of the electrolyte, and in solutions, 1×10^-4 mol·L^-1 and 1×10^-3 mol·L^-1 in electrolyte concentration, the metal ions exhibited an order of K⁺ >> Na⁺ > Li⁺ in equilibrium adsorption capacity, while in solutions, 1×10^-2 mol·L^-1 in electrolyte concentration, they did an order of K⁺ >> Li⁺ > Na⁺, which suggests that volume of the ions is a major factor affecting equilibrium adsorption capacity in solutions high in electrolyte concentration. The adsorption processes of Li⁺, Na⁺ and K⁺ appeared to be of first-order kinetics as affeted by weak force. Their desorption processes did too, but with apparent ion specificities; (2) In the same electrolyte system, d (the distance between alkali metal ions and clay mineral surface when the adsorption reaches equilibrium) decreased with increasing electrolyte concentration, exhibiting an order of d_Na >d_Li > d_K in solutions high in electrolyte concentration (1×10^-2 mol·L^-1 ), and an order of d_Li > d_Na > d_K in solutions low in electrolyte concentration (1×10^-4 mol·L^-1 and 1×10^-3 mol·L^-1). Obviously d of K⁺ is always the lowest regardless of electrolyte concentration because it has a layer of softer outer electron cloud around, and hence is much stronger in non-classical polarization than Na⁺ and Li⁺, but for Na⁺ and Li⁺, in solutions high in electrolyte concentration volume might be a main factor affecting ion adsorption processes, thus resulting in d_Na > d_Li , while in solutions low in electrolyte concentration, non-classical polarization would play a leading role, weakening the volume effect, and reversing the order as d_Li > d_Na. Therefore the joint effect of non-classical polarization and volume effect of the ions determines position of the ions in the double electric layer and then equilibrium adsorption capacity, thus leading to differences in surface potential (absolute value), which increases with decreasing electrolyte concentration, exhibiting an order of Li⁺>Na⁺>K⁺ in solutions the same in concentration, which indicates that surface potential is mainly influenced by non-classical polarization; and (3) As the newly established model can be used to predict positions of the ions in the double electric layer, and further to calcuate activation energy of the system. The activation energy decreases with increasing electrolyte concentration, and in solutions regardless of eletrolyte concentration and type of cation, both adsorption saturation and activation energy of cations follow a similar law. 【Conclusion】 The occurrence of ion specificities is caused and determined mainly by activation energy. All the findings in this study demonstrate that the newly established model of cation exchange adsorption is universally applicable to researches on solid/liquid interface reaction.

Abstract:【Objective】Soil colloid is the material foundation of soil fertility and soil ecological function. Agglomeration and dispersion of soil colloids influences a series of microscopic processes and macroscopic phenomena in soil. The purpose of this paper was to compare Hofmeister effects of 2:1-typed montmorillonite and 1:1-typed kaolinite mineral colloids in agglomeration triggered by alkali cations (Li⁺, Na⁺ and K⁺), and analyze sources of the Hofmeister effects. 【Method】To that end, ultrasonic dispersion and centrifugation of soil samples was performed to extract montmorillonite and kaolinite colloids, and dynamic light scattering was to determine separately,effects of Li⁺, Na⁺ and K⁺ on agglomeration of the mineral colloidal particles. And then comparison was made between agglomerations of the mineral colloids in three different alkali solutions in kinetic process and activation energy. 【Result】Results show that the agglomeration varied sharply in rate, critical coagulation concentration and activation energy as affected by Li⁺, Na⁺ or K⁺, demonstrating strong Hofmeister effects. In solutions with electrolyte concentration being 20 mmol•L^-1, the aggregation of montmorillonite colloid triggered by K⁺ reached 66.61 nm•min^-1 in rate, much higher than that triggered by Na⁺ (5.93 nm•min^-1) and by Li⁺ (4.41 nm•min^-1). And in solutions with electrolyte concentration being 30 mmol•L^-1, the agglomeration of kaolinite colloid activated by K⁺ reached 32.43 nm•min^-1 in rate, which was far too much higher than that triggered by Na⁺ (7.28 nm•min^-1) and by Li⁺ (1.90 nm•min^-1). The effect of Hofmeister effects on aggregation rate of montmorillonite and kaolinite colloids varied with the cation in the solution in an order of Li⁺ < Na⁺ < K⁺, its effect on critical coagulation concentration did in an order of K⁺ (montmorillonite 21.8 mmol•L^-1, kaolinite 34.6 mmol•L^-1) < Na⁺ (montmorillonite 57.6 mmol•L^-1, kaolinite 85.8 mmol•L^-1) < Li⁺ (montmorillonite 81.8 mmol•L^-1, kaolinite 113.9 mmol•L^-1), which could be reasonably explained by activation energy needed in agglomeration of colloids. In solutions, 25 mmol•L^-1 in electrolyte concentration for montmorillonite agglomeration activation energy varied with the cation in the solution in an order of Li⁺ (1.97 kT) > Na⁺ (1.43 kT) > K⁺ (0 kT), while for kaolinite it did in the same order (2.94 kT, 1.71 kT and 0.49 kT). All demonstrated that the Hofmeister effects in agglomeration of montmorillonite and kaolinite did vary with the cation in the solution in the order of Li⁺ < Na⁺ < K⁺. A strong external electric field could greatly amplify the difference in deflection of ion outer layer electron cloud, thus producing strong polarization, i.e. non-classical polarization effect. With the ion radius of Li⁺, Na⁺ and K⁺ increasing the power of the central atom binding the outer electron cloud decreased step by step. The deflection of the electron cloud configuration varied in magnitude with the ion in the solution in an order of Li⁺ < Na⁺< K⁺. Additionally, in the solutions with a given concentration of a given ion, montmorillonite needed lower activation energy than kaolinite for agglomeration. Montmorillonite (0.1227 C•m ^-2) was higher than kaolinite (0.0583 C•m ^-2) in surface charge density, and significantly higher too in surface electric field strength in the same system. Therefore, the strong polarizing capability of Li⁺, Na⁺ and K⁺ was more obvious in the montmorillonite colloidal system, and the stronger the polarizing action, the more significantly the surface potential lowered, which led to higher agglomerability of montmorillonite colloids than that of kaolinite colloids. 【Conclusion】All the findings described above demonstrate that the nonclassical polarization of ions in the strong external electric field is the fundamental cause of the Hofmeister effects in agglomeration of charged colloidal particles.

Abstract:【Objective】It is well known that some fine particles of the soil carry charges, which are basically concentrated on soil colloids. The charges on the soil surface account for a series of physical, chemical and physiochemical properties of the soil. Surface potential, surface charge density, surface electric field intensity, specific surface area and surface charge number are important property parameters of soil colloidal particles. The researches on charge properties and interactions of charged surface with ions, electrons and protons are the foci of the study on soil electro-chemistry. Differences in surface charge properties directly affect surface chemical and physicochemical mechanisms of the soil. Therefore, it is of important significance to have accurate understanding of soil surface electrochemical properties to rational utilization of soil resources. However, it is still unclear how soil surface charge properties evolve with vegetation restoration in the Ziwuling area. 【Method】For this study the method of combined analysis of surface properties was applied to measure surface potential and surface charge density of the soils varying in vegetation in the Ziwuling area. This method can be used to get surface potential and surface charge density without the need for the data of specific surface area, thus making easier to measure surface charge properties. Correlation analysis and redundancy analysis were adopted to explore effects of basic physical and chemical properties of the soil on its surface charge properties. 【Results】Results show that with the vegetation evolving in the Ziwuling area, physical and chemical properties of the soil gradually improved; soil bulk density and calcium carbonate content decreased, varying in the range of 1.04~1.27 g•cm^-3and 80.09~149.95 g•kg^-1 and being 1.16 g•cm^-3 and 113.52 g•kg^-1 on average, respectively; contents of organic carbon, total nitrogen and clay increased, varying in the range of 7.12~17.84 g•kg^-1,0.94~1.16 g•kg^-1and 18.26~22.10%, and being 12.19 g•kg^-1,1.24 g•kg^-1 and 20.52% on average, respectively; and surface charge properties of the soil particles in the soil altered too, with surface charge number, specific surface area, and surface charge density increasing, varying in the range of 10.88~19.85 cmol•kg^-1, 40.67~61.71m²•g^-1 and 0.22~0.31c•m^-2, being 16.18 cmol•kg^-1, 54.88m²•g^-1 and 0.28c•m^-2, on average, respectively and surface electric field intensity reaching as high as 10⁸ V•m^-1 in order of magnitude. Soil clay and organic carbon content are the main factors affecting surface charge properties, explaining 62.5% and 27.9% of the changes, respectively. In terms of impact on surface charge properties, soil properties displayed an order of clay > organic carbon > sand > total nitrogen > C/N > silt > calcium carbonate > pH.【Conclusion】The findings of this study have deepened our understanding of the surface charge properties of the soil in the Loess Plateau, and provided a theoretical basis for better explaining the microscopic processes and macroscopic phenomena occurring in the soil with vegetation restoration.

Abstract:【Objective】Acid sulfate soil is a type of soil developed from the parent material of reducing sulfide and is described as “the nastiest soils in the world” because of its strong acidity and poor plant growth. Acid sulfate soils are mainly distributed along the seacoast of tropical and subtropical regions, wherein the climate is though very suitable for growth of most crops, especially rice (Oryza sativa L.) because of their abundant water and heat resources, it is very hard to bring the production potential of rice into full play, due to their poor soil properties, such as acid threats, metal toxicity and nutrient deficiency. Plants, the same in family, but different in species or variety, vary significantly in capability to adapt to stress soils. Although most crop plants cannot grow in acid sulfate soils, some native plants can do very well. The objective of this study is to screen out rice cultivars that are capable to adapt to acid sulfate soils, and further to explore their underlying mechanisms. 【Method】A total of 240 varieties of rice were planted in acid sulfate soil (pH 3.69) in Taishan City, Guangdong Province, China, and were managed as the local farmer do their crops. None met the target of economic yield. However, accidentally two species of wild plants, identified morphologically and molecularly as Eleocharis kuroguwai and Fimbristylis quinquangularis, were found growing flourishingly in the soil. During the rice harvest season, samples of the rice plants, wild plants, and their rhizosphere and non-rhizosphere soils were collected for analysis of soil chemical properties (pH, exchangeable Al, and available Mn) and contents of 10 elements (N, P, K, Ca, Mg, S, Na, Al, Fe, and Mn) in the roots and shoots. 【Result】 It was found that variation of soil chemical properties such as pH, exchangeable Al and available Mn, in rhizosphere could not explain the difference between the two wild plants and the rice plants in tolerance and that Mn toxicity and N deficiency were not the key factors that limited growth of the plants. Instead, the contents of mineral elements in the plant shoots were found to be closely related to the difference between the rice plants and the wild plants in tolerance. The rice plants accumulated more Al and Fe, but less nutrients (P, K, Ca, Mg, and S) in the shoots than the two wild plants. Little difference was observed in contents of most mineral elements in roots between the plants. Moreover, the Al and Fe contents in the shoot of E. kuroguwai were low, which explains its tolerance to Al and Fe toxicity through exclusion mechanism, while the Al and Fe contents in the shoot of F. quinquangularis were high, which explains its resistance to Al and Fe toxicity through internal tolerance mechanism. 【Conclusion】Al toxicity, Fe toxicity and poor nutrient uptake are the main factors leading to poor growth of rice in acid sulfate soils. In contrast, the two wild plants E. kuroguwai and F. quinquangularis can grow well in the soils thanks to their strong ability to resist Al and Fe toxicity and to take up nutrients. Mn toxicity and N deficiency may not be involved in the difference between the rice plants and the wild plants in adaptability to acid sulfate soils. It is, therefore, suggested that to improve Al and Fe tolerance and nutrient uptake are two approaches key to developing crop productivity potential in acid sulfate soils, which can be achieved through soil management and variety breeding.

Abstract:【Objective】Returning straw into soil and applying composted straw and biochar derived from straw are effective ways of increasing soil organic carbon (SOC). 【Method】Samples of saline soil were collected from the Yellow River Delta and incubated for 30 and 180 days in lab in order to study effects of application of straw, compost and biochar on composition and structural characteristics of humic substances in the soil. 【Results】Results show that the practices increased humin (Hu) more than humic acid (HA) and fulvic acid (FA). The content of Hu increased from 5.48 g·kg^-1 increased to 11.20 g·kg^-1、16.66 g·kg^-1 and 20.60 g·kg^-1, after 180 days of incubation. In addition, the content of HA increased to 1.36 g·kg^-1 in the plot applied with compost plus biochar, while in the plot of straw returning, the content of FA decreased from 3.77 g·kg^-1 to 3.32 g·kg^-1, after 30 days of incubation. Positive correlations were observed between the contents of Hu and SOC in the plots incubated for either 30 (R² = 0.84, P< 0.001, n = 10) or 180 (R² = 0.98, P< 0.001, n= 10) days. Organic carbon (OC) increased mainly in Hu, especially in the plot applied with biochar. Both application of compost or returning of straw were conducive to increasing HA and FA, and application of compost plus biochar was more significant in the effect of increasing HA. The content of Hu was mainly affected by the ratio of biochar in the plots applied with biochar plus straw. Application of straw, compost or biochar was in favour of accumulation of aliphaic groups of FA, and good to accumulation of aliphaic groups and carbohydrate in HA at the initial stage in the plots applied with straw or compost, especially with compost. Application of biochar was good to increasing aromatic groups in HA, while application of straw or compost, especially the latter, was to increasing aliphatic groups and polysaccharide at the initial stage of incubation. But afterwards, aliphatic groups deceased, while polysacharide went on increasing with the incubation lasting, regardless of treatment. 【Conclusion】In summary, biochar mainly increases the content of Hu, while compost plus biochar is in favor of increasing HA. However, straw increases the content of FA at the initial incubation stage. The ratio of biochar in the plots of applied with biochar plus straw or compost affects the content of Hu, aromatic functional groups of HA and aliphatic groups of FA.

Abstract:【Objective】Based on a 36-year fertilization experiment in a field of fluvo-aquic soil, effects of fertilization, especially application of organic manure, on organic carbon fractions in the plow layer were studied in an attempt to learn comprehensively how soil carbon changes and explore effects of fertilization on the status of soil organic carbon through analysis and evaluation of soil organic carbon fractions, so as to better master the physico-chemical and biological mechanisms of the changes in soil organic carbon fractions as affected by long-term fertilization and to provide scientific basis for decision-making for fertilization in sustainable development of agriculture. 【Method】 In this study, physical means were used in combination with chemical ones to determine contents of organic carbon, easily oxidized organic carbon, particulate organic carbon and mineral incorporated organic carbon in soils, and effects of fertilization on soil organic carbon fractions were analyzed. To that end the experiment in the study was designed to have 8 treatments, that is, no fertilization (CK), application of N alone (N), application of N and P (NP), application of N, P and K (NPK), application of organic manure (M), application of nitrogen fertilizer plus organic manure (MN), application of nitrogen and phosphorus fertilizers plus organic manure (MNP), and application of nitrogen, phosphorus and potassium fertilizers plus organic manure (MNPK). 【Result】Results show that long-term fertilization significantly improved soil fertility. Application of organic manure was closely related to increase in soil organic carbon, particulate organic carbon and mineral incorporated organic carbon. Fertilization significantly increased the content of easily oxidized organic carbon (EOC) in the soil. The effect was the most significant in Treatment MNPK with an increase up to 72.13% as compared with CK, while EOC content in Treatment MN, MNP and MNPK increased by 23.18%, 12.53% and 25.92%, respectively, as compared with their respective chemical counterparts, Treatment N, NP and NPK. Fertilization (except for N application alone) significantly increased the content of soil particulate organic carbon (POC). The effect was particularly significant in organic manure-amended treatments, whose mean POC content was 92.69% higher than that of the treatments without organic manure. The content of mineral incorporated organic carbon (MOC) in the organic manure amended treatments was 10.06% higher than that in CK,. The proportion of particulate organic carbon (POC/SOC) in Treatment MNPK increased by 13.33%, while the proportion of mineral incorporated organic carbon (MOC/SOC) decreased correspondingly, as compared with those in CK. Application of organic manure significantly enhanced the contribution of increased total organic carbon to MOC, especially Treatment MNPK where the increased total organic carbon and the native total organic carbon formed a ratio of 1:1 in POC and MOC. 【Conclusion】In conclusion, application of organic manure, especially when in combination with balanced nitrogen, phosphorus and potassium fertilizers, is of great significance to improving soil physico-chemical properties, expanding the fractions of organic carbon, and promoting balanced distribution of newly-sequestrated carbon in various carbon fractions. The findings in the study may serve as a theoretical basis for rational fertilization in sandy loam fluvo-aquic soils.

Abstract:【Objective】In view of the fact that hydrosphere pollution caused by nitrogen losses with runoff from paddy fields in South China is increasingly serious, an attempt was made to explore N losing effect and potential risks of straw returning coupled with nitrogen fertilizer application and an optimum synthetic N fertilization rate in addition to full straw return. 【Method】A field experiment was conducted to explore effects of straw incorporation coupled with N fertilizer application varying in rate on rice yield and dynamics of nitrogen in paddy surface water, and to seek for an optimum fertilizer-N application rate in addition to full straw incorporation contributive to crop yield and the environment. 【Result】Results show: (1) Compared with Treatment N2 (application of synthetic N only), Treatment SN2 (Straw return plus N application at a recommended rate, N:P:K = 240:15:60) was significantly or 22.5% higher in rice yield (P <0.05). Besides, compared with Treatment SN0 (Straw incorporation with no N applied), Treatment SN1 (Straw return plus N application at a reduced rate, N:P:K = 180:15:60), SN2 and SN3 (Straw return plus N application at a conventional rate, N:P:K = 300:15:60) was significantly or 50.1%, 60.1% and 40.8%, respectively, higher in rice yield. This study showed that straw return plus N application significantly increased rice yield, but the effect reduced when too much N fertilizer was applied. Full straw return for 4 or more years in a row could replace part of the N fertilizer applied in yield raising effect; (2) TN (total nitrogen) and NH4⁺-N (ammonia nitrogen) in paddy surface water peaked in concentration in 1~2 days after urea application, then declined rapidly to a relatively low level. So the week after urea application was a period full of risks of nitrogen runoff loss. Moreover, compared with Treatment N2, Treatment SN2 reduced TN concentration in paddy surface water during the period after basal and tillering fertilizer application by 2.0% (P >0.05) and 6.1% (P <0.05), respectively. Treatment SNO reached 53.7% and was obviously higher than Treatment N2, SN1, SN2 and SN3, in DON/DTN (dissolved organic nitrogen/dissolved total nitrogen) and dominated with DON in N release. Treatment SN2 was 12 higher than Treatment N2 in DON concentration. All in all, straw return could effectively decrease the concentration of TN in surface water during the earlier rice-growing stage, while increasing the potential of DON loss; and (3) Compared with Treatment SN2 and SN3, Treatment SN1could save fertilizer-N consumption by 25% and 40% and reduce TN loss by 9.6% and 20.8%, respectively, so it’s an optimal mode that takes both yield and environmental benefits into consideration. 【Conclusion】In a word, for the region in the downstreams of the Yangtze River, especially the flood and runoff prone areas, returning straw fully coupled with 180~225 kg∙hm^-2 –N fertilization in paddy fields is recommended as a long-term farming practice. All the findings in this paper may provide a certain scientific basis for future researches on hydrological N losses as affected by straw return

Abstract:【Objective】It is of great scientific significance to explore effects of the practice of subsoiling coupled with fertilization on the fractions of activated organic carbon and nitrogen, and enzyme activities in black soil. 【Method】Based on a 2-year field experiment in Qinggang County, Heilongjiang Province, a black soil region typical of Northeast China, variations of the soil were analyzed in fractions of dissolved organic carbon (DOC), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), particulate organic carbon (POC), particulate organic nitrogen (PON), and readily oxidizable organic carbon (ROC), and in activity of N-acetylglucosaminnidase (NAG), Cellobiohydrolase (CBH), β-glucosidase (BG) and β-xylosidase (BXYL) with treatment in the experiment, which consisted of five treatments, including no-till + chemical fertilizer (T1), subsoiling 25 cm (in depth) + chemical fertilizer (T2), subsoiling 25 cm + chemical fertilizer + organic manure (T3), subsoiling 35 cm + chemical fertilizer (T4), sub-soiling 35 cm + chemical fertilizer+ organic manure (T5) .【Result】Results showed that both subsoiling and fertilization and their interactions significantly affected the contents of soil activated carbon and nitrogen, particularly of POC and PON; Subsoiling (T2 and T4) significantly reduced the contents of soil activated organic carbon and nitrogen components with varying degree relative to depth of subsoiling, T2 was significantly lower than T1 (P<0.05) in POC and PON content; T3 and T5 significantly increased the contents of soil activated organic carbon and nitrogen. T3 was 8.37%, 46.64%, 35.10% and 42.39% (P<0.05) higher than T2 in content of SOC, POC, ROC and PON. Besides, subsoiling improved stability of the soil activated organic carbon and nitrogen components. Compared with T1, subsoiling treatments significantly reduced the ratios of MBC/SOC and POC/SOC in the soil (P<0.05), and subsoiling 35 cm in depth significantly decreased the ratio of PON/TN (P<0.05); T2 and T4 did not differed much from T1 in enzyme activity, whereas T3 significantly increased CBH activity relative to T2. 【Conclusion】To sum up, subsoiling 25 cm in depth combined with application of chemical fertilizer and organic manure can maintain the content of activated organic carbon and nitrogen components in the soil, hence it is recommended to be extrapolate as an effective farming technique to build up black soil farmland and to increase organic matter content in the soil of this area.

Abstract:【Objective】To investigate long- and short-term effect of liming on soil potassium (K) in acidifying red soil, a long-term fertilization field experiment on soil fertility and fertilization effect in red soil was initiated in 1990. 【Method】The long-term field experiment was designe to have treatments, i.e. application of chemical nitrogen and phosphorus fertilizer (NP), application of NP fertilizer plus liming (NPL), application of NPK (NPK), application of NPK plus liming (NPKL), application of NPK half of the designed rate and straw returning to make up the remaining half (NPKS), and application of NPKS plus liming (NPKSL), and four levels of liming (0 Lime, 0.5 Lime, 1Lime and 1.5 Lime). Soil samples were collected from the treatments and packed into cylinders separately for indoor soil column leaching experiment. Potassium ion (K⁺) in leachate and readily available potassium (AK), slow available potassium (SAK) and pH in the 0 ~ 50 cm soil layer were monitored throughout the leaching experiment . 【Result】Four years later after the initiation of the experiment, it was found that liming increased the content of SAK in the soil surface (0~10cm) and subsurface layer (0 ~ 40 cm), by 2.06% ~ 36.39% in Treatment NPKSL, and the content of AK in the 0 ~ 10 cm soil layer and the content of SAK in the 10~20cm and 40~50cm soil layers in Treatment NPL by 27.26% and 28.51%, 22.55%, respectively. In terms of K⁺ accumulation in leachate, the limed treatments displayed an order of NPKSL_E > NPKL_E > NPL_E, when liming was kept at the same level. Liming reduced K⁺ accumulation in leachate in Treatments NPKSL_E and NPKL_Eby 18.10% ~ 57.70% and hence K+ leaching rates, too. Liming increased soil pH in the surface soil layer. In the soil with K surplus, liming reduced K⁺ leaching rate by 11.7% for each 1 000 kg·hm^-2 of lime applied. Apparently liming and fertilization are the main factors that significantly affect the mean leaching rate of K⁺ and K⁺ accumulation in leachate. 【Conclusion】 Obviously liming for a short or a long period of time can always increase soil pH in the surface soil layer, and retard vertical migration of AK in the profile, thus increasing the content of SAK in the lower soil layers. The amount of soil leaching K⁺, cumulative K⁺ leaching and K⁺ leaching rate all increase with rising AK content in the soil and with declining liming rate. Liming rationally can effectively reduce the risk of K leaching loss in acidifying red soil.

Abstract:【Objective】Fertilization is an effective measure to improve soil fertility and increase crop yield in red soil. As important components of a soil ecosystem, soil microorganisms play an essential role in soil fertility formation, organic matter decomposition, and nutrient biogeochemical recycling as well. However, though soil microorganisms are very sensitive to fertilization, limited information is available in the literature about effects of fertilization on the microbial community in upland red soil. The objective of this study is to investigate responses of the bacterial community in upland red soil to long-term fertilization varying in strategy, and to provide a theoretical basis for rational fertilization and sustainable utilization of the red soil in South China.【Method】In this study, a long-term field fertilization experiment (established in 1990) on winter wheat–summer maize rotation at the Qiyang Red Soil Experimental Station of the Chinese Academy of Agricultural Sciences was carried out. The experiment had four treatments, i.e. no fertilizer (CK), only application of chemical nitrogen fertilizer (N), application of chemical nitrogen, phosphorus and potassium fertilizer (NPK), and application of NPK plus manure (NPKM). Except CK, all the treatments received N 300 kg•hm^-2•a^-1, and the N in Treatment NPKM had 30% coming from chemical fertilizer and the rest from manure. Samples of surface soil (0~20 cm) were collected in May 2015 (after wheat was harvested and before maize was planted). The technology of high-throughput sequencing of the V4-V5 16S rRNA gene region were used to determine composition and diversity of the soil bacterial community in the samples, and then to identify key factors affecting the bacterial community in the upland red soil.【Result】Results show: (1) Long-term fertilization significantly changed chemical properties of the upland red soil. Compared with CK, Treatments N and NPK declined significantly or down to 4.02 and 4.15, respectively, in soil pH, while Treatment NPKM increased significantly or up to 5. 99. Both NPK and NPKM significantly improved soil fertility, but the effect of the latter was much better than the former. However, Treatment N only increased soil TN content, which was not conducive to soil fertility; (2) Long-term fertilization affected relative abundance of the soil dominant bacteria at the phylum level. Non-metric multidimensional scaling (NMDS) and similarity analysis (ANOSIM) shows that soil bacterial communities in the treatments varied significantly; (3) Compared with CK, Treatment N was 21.4%~49.4% lower in the four diversity indices (observed species, Chao1 index, phylogenetic diversity and Shannon index), while Treatment NPKM was 7.0%~66.9% higher. Besides, Treatment NPK was 10.3% and 13.0% lower, respectively in phylogenetic diversity and Shannon index; (4) Stepwise regression analysis shows that soil pH was the primary factor determining relative abundance of the dominant soil bacterial phyla and four diversity indices of the soil bacterial community. Furthermore, multivariate regression tree (MRT) analysis shows that soil pH explained 83.1% of the detected variation of the soil bacterial communities between the treatments, and differentiation of the bacterial community was driven by soil pH; and (5) Compared with CK, statistical analysis of metagenomic profiles (STAMP) shows that Treatment N, NPK and NPKM had 11, 14 and 8 treatment-specific bacterial genera, respectively.【Conclusion】In conclusion, the bacterial community in the upland red soil following long-term fertilization is mainly affected by soil pH, and the negative effects of soil acidification induced by long-term fertilization may have far exceeded the positive effects of fertility improvement. Therefore, fertilization in upland red soil should be based on the premise of prevention of soil acidification, and combined application of chemical fertilizer and manure is a suitable fertilization measure.

Abstract:【Objective】The effects of straw returning and biogas liquid replacing chemical fertilizer on the growth of early rice seedlings and paddy soil quality were studied, which provided the theoretical basis for the combination of agriculture and animal husbandry with nutrient recycling. 【Method】The comparative effects of “wheat straw returning to the field combined with chemical fertilizer”(S-CF), “wheat straw returning to the field combined with biogas slurry”(S-BS) and “total fertilizer”(CF) on the growth of rice seedlings, nitrogen and phosphorus accumulation, soil nutrients and microbial communities under the condition of equal amount of nitrogen application were studied in greenhouse experiment. 【Result】The growth of rice seedlings with different fertilization application treatments was obviously promoted, with the extension of treatment time, the promoting effect of fertilization treatment was more significant, among which CF treatment was the best, followed by S-BS treatment. The improvement effects of S-BS and CF on root growth were similar, which were significantly better than those of S-CF and CK. The content of soluble sugar in leaves of rice treated with S-BS was significantly higher than that of other fertilization treatments, and the content of N in leaves of rice treated with S-BS was significantly higher than that of treatment of CF. The total bacteria of CF treatment was significantly higher than that of S-BS treatment, while that of S-BS treatment was significantly higher than that of CK and S-CF treatment. The relative abundance of Proteobacteria treated with CF was significantly higher than that of other treatments. The total amount of fungi in CK and S-CF treatments was significantly higher than that in S-BS and CF treatments, and that in S-BS treatment was the lowest. The relative abundance of soil dominant Ascomycota and Basidiomycota in the CK group was significantly higher than that in other treatments. The relative abundance of Chytridiomycota treated with S-CF was also significantly higher than that of other treatments. Alpha diversity analysis showed that the bacterial richness (Chao1 index) and diversity (Shannon index) of S-CF and S-BS treatments were significantly higher than those of CF treatment and CK, and the richness and diversity of soil fungi treated with S-CF was significantly higher than that of CK, and that of soil fungi treated with CF was the lowest. 【Conclusion】 Under the treatment of straw and biogas liquid as a short-term substitute for chemical fertilizer, the growth of rice plant is lower than that of the whole chemical fertilizer treatment. However, the effects of straw, biogas liquid and chemical fertilizer on the growth of rice seedlings were still very obvious, especially the total substitution chemical fertilizer treatment of straw returning to the field and irrigation with biogas liquid. The soil quality, bacterial richness and diversity of straw and biogas treatment were significantly improved even under short-term application conditions.

Abstract:【Objective】In poverty-stricken areas of China, potato is a dominant crop that may help promote food production and get rid of poverty. Due to a limited farming area and intensive potato production therein, mono-cropping is prevailing in those areas. However, long-term mono-cropping may reduce soil microbial community diversity and disturb the balance of soil nutrients in ratio, thus affecting crop growth and yield. Although a large number of studies have demonstrated that rotation is an effective practice to alleviate the impact of mono-cropping on the soil, so far little has been reported on how the rotation of potato with quinoa or maize influences microenvironment of the rhizospheric soil of potato and interactions between soil and the root system. So this study was going to investigate influences of the rotation of potato with quinoa or maize on soil quality and potato growth and its mechanism, so as to provide a theoretical support to remove the obstacle of mono-cropping in agriculture and build a better rotation model for those areas.【Method】In the study, an experiment designed to have three treatments, i.e. Treatment M (mono-cropping), Treatment L (rotation with quinoa), and Treatment Y (rotation with maize), was carried out to explore influences of the above three planting patterns on soil properites and root physiology, root development and plant growth of potato.【Result】Results show: (1) Rotation potato with quinoa or maize reduced soil pH in potato rhizosphere significantly, increased the contents of organic matter, alkalyzable nitrogen and available phosphorus, enhanced activities of soil enzymes, decreased fungi population, increased the number of soil bacteria and actinomycetes, and the ratio of bacteria and fungi (B/F), and improved soil properties and promoted potato growth, which was enbodied to some extent in plant height, stem diameter, shoot dry weight, root dry weight and yield of potato tuber; (2) Rotation of potato with quinoa or maize increased the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in potato root system, decreased the producing rate of O₂^.-and the content of malondialdehyde (MDA), increased the content of osmosis regulating substances. All the findings indicated that the rotation relieved all the stresses of mono-cropping on potato plants; and (3) Rotation of potato with quinoa or maize also increased the total length, surface area, volume, mean diameter and tip number of potato roots significantly. In general, rotation of potato with quinoa or maize promoted the growth and development of potato roots, which corresponded to the improvement of physical, chemical and biological properties of the soil and the development of the shoots of potato as well. 【Conclusion】 Rotation of potatio with quinoa or maize can improve physical, chemica and biological properties of the soil to some extent, enhance antioxidant capacity and osmosis regulating ability of the roots of potato, reduce membrane lipid peroxidation degree, promote growth and development of the roots of potato. These effects of the rotation are also enbodied in increases in plant height, stem diameter and tuber weight. Comparison between the two rotation patterns shows that the rotation of potato with maize is better than that with quinoa in alleviating the adverse impacts of mono-cropping.

Abstract:In order to fully understand contents and degrees of the various ancient human activities in the Yangshao culture period, soil samples were collected from different functional areas (housing foundation, living quarters, urn coffin, pottery kiln) and soil profile not disturbed by ancient human activities (natural profile in short) in the Yangshao Village site for analysis of chromaticity, magnetic susceptibility, particle size composition, free iron, total mineral content and soil micromorphology. By comparing the findings with the natural profile data, it was learnt how much ancient human activities affected the soil. Results show that among the four functional areas, the housing foundation area is the highest in clay content and P content and relatively higher in CaO content and had various ingredients added into the lime layer as the analysis of soil micromorphology indicates; the living quarters is the highest in content of carbon dust content, which exists along a certain direction; the urn-coffin area is the highest in χ_fd, and the highest in content of free iron and ionization degree of the iron; and the pottery kiln area is the highest in χ_lf relatively higher in content of P and has soil that had been calcinated under high temperature ion as analysis of micromorphology indicates. The conclusion shows that, ancient people chose on purpose clay and calcium carbonate sand to pave the ground. Long term residence produced a large amount of phosphorus. Ancient people cooked food, producing a lot of carbon dust in the living area. After burial of the dead with urn, decaying of the corpses facilitated growth of animals and microorganisms, which in turn helped formation of soil fine particles and soil development. In calcinating pots, they might probably used domestic waste as fuel.

Abstract:In order to resolve the problem of low efficiency of the measurement of soil cation exchangeable capacity (CEC) with the traditional glass rod stirring method, an experiment was designed to stir suspensions with a magnetic stirrer instead of glass rod. Parallel tests different in controlled condition were carried out in different labs to determine CEC of soils different in clay content with the magnetic stirring method for comparison between the tests in accuracy, operability, stability and applicability of the measurements with the method.Results show that the magnetic stirring method was not lower or even magnetic stirring method higher than the glass rod stirring method in accuracy and precision of the CEC measurement. What was obtained with the former was highly in consistency with the values of the certified reference materials. When stirring of the suspension went on over 1 min at no less than 850 r?min^-1, duration and speed of the stirring did not have much effect on soil CEC determination, and neither the labs where the tests were conducted. No significant difference was found between labs in CEC measurement. Compared with the traditional glass rod stirring method, the magnetic stirring method has such merits as simple in operation and high in efficiency, stability and precision, when used to measure soil CEC, and is highly suitable for use to determine soil CEC of large batches of soil samples.