Abstract:Mr. Hou Kuangchun (1905-1996), also known as Hou Yiru, was among the first group of academicians of the Chinese Academy of Sciences (formerly member of Academia Sinica), a senior fellow of the British Royal Society a national first grade professor of China, a pioneer in soil science in China and also an explorer and founder of the agricultural soil science of China. With the 100th anniversary of Mr Hou birth coming around the corner, to study comprehensively processes, genesis and affecting factors of the formation of Mr. Hou’s academic thought is an event of important theoretical significance, academic value and practical reflection, which will not only help explore and sublime Mr. Hou’s academic life and inner requirements of his thought, but also play an important active role in promoting development of the modern agricultural soil science and strengthening the construction of a benign academic atmosphere. (1) Mr. Hou’s academic career spanned 70 years (1927 to 1996), beginning almost at the same time modern soil science made its debute in China and the development processes of the two were closely related with a high degree of overlapping. Mr. Hou’s academic life can roughly be divided into seven phases, i.e. schooling as a junior, cutting a great figure, struggling in difficulty, ambitious exhibition, downturn, glory days and continuity of thought. Each phase had its own peculiar characteristics in content. (2) On the basis of fully absorbing the advanced research concepts, methods and techniques of the European and American schools of soil science and ex-Soviet Union school of soil science, Mr. Hou founded a China-specific school of soil science, featuring Chinese characteristics in the light of the actual conditions in China. The so-called "Chinese characteristics" were specifically embodied in research concept, research methods and research findings. In the aspect of research concept, Mr. Hou began, as early as in the 1920s and 1930s when he was still in school, to nourish the idea that soil science should serve agricultural; in the aspect of research methods, Mr. Hou advocated summarization and distillation of farmers’ experience in farming production; and in the aspect of research findings, Mr. Hou made a number of representative achievements that suit the specific conditions of the nation, such as propositon of the agricultural soil physiologic conception and the soil fertility bio-thermodynamic theory and development of the technology of natural no-tillage. (3) Mr. Hou’s academic thought is the product of the joint effects of various factors such as social environment, family environment, mentors’ teaching and his own qualities, through decades of accumulation. Tempered by a series of factors, Hou’s academic thought began to take shape, and underwent a course of progressive development from immature to mature, and from fragments to a system.

Abstract:Based on some chapters of the book “Pedodiversity” published by CRC in the US in 2013 and some other related references, a review is presented here of status quo of the study on pedodiversity and challenges it may face in future worldwide, with emphasis on research modes of the study on pedodiversity. Besides, this paper has a few paragraphs devoted to history, progresses major achievements and future challenges of the study. First of all, a brief introduction is made to how the concept of pedodiversity was initiated and connotation of diversity：(1) The exploration of the concept of diversity should proceed from the angle of practicality and the concept should encompass species diversity (or richness) and distribution of individuals of the (evenness or uniformity); From the point of view of methodology, the most popular methods for diversity analysis may be grouped into two general classes: indices of richness and object abundance models. (2) To the knowledge of the authors, the first pedologist who tried to analyze and quantify pedological diversity of a region was a Russian, V. M. Fridland. Regretfully his work did not arouse any attention from his colleagues in the circle. Then at the beginning of the 1990s, Ibáňez and his coworkers adopted the mathematical tools developed by some ecologists in studying soil diversity, created a neologism, “pedodiversity” and then published a number of papers, explaining the main measuring methods used in analyzing soil diversity or pedodiversity, which, as a matter of fact, triggered an expedition to explore theories of and methods for soil diversity theory. Then attempts are made to elaborate objectives and methodology of the pedodiversity analysis, including some fundamental principles, like diversity vs soil classification systems, scale vs sampling intensity. Nowadays, the USDA (United States Department of Agriculture) Soil Taxonomy is being used by pedologists the world over, and at the same time, WRB (the Word Reference Base for Soil Resources), developed jointly by the International Union of Soil Sciences (IUSS) and FAO and later pedologists the world over, has been accepted as a universal soil classification system. In addition, the measurement of pedorichness and pedodiversity depends on methods and scales of soil classification and sampling intensity. And next, analysis is done with emphasis of major models currently used in the research of pedodiversity, such as Willis curve, soil diversity vs biodiversity, abundance distribution models, diversity-area relationships, diversity-time relationships, diversity nested systems, diversity vs pedogenetic processes, diversity vs landscape evolution, etc., of which some are elaborated in detail: (1) Willis curve:The Willis curve has been proved to be able to embody the distribution nature of all biospecies. It originates from the array of taxonomic groups in line with the variation of abundance from the maximum to the minimum, appearing in a concave-shaped curve of frequency distribution. (2) Soil diversity vs biodiversity:Several studies have found strong correlations between pedodiversity and biodiversity under different environments and at different in some regions, and between pedodiversity and landform diversity, too. Furthermore, the relationships of biodiversity of various species groups with lithological diversity and climate diversity have also been demonstrated. (3) Abundance distribution models:The distribution of the numbers of species within an ecological community has long been regarded as a critical aspect in the study of community structure. The most commonly used models include geometric series, logarithmic series, log-normal distribution, "broken stick" (robust) model. Researches show that the same regularities do exist in categorical distribution of soils. (4) Diversity-area relationships:The pedodiversity-area relationship fits a power law and has nothing related to the type and scale of classification. It has been demonstrated that in a given archipelago or other spaces, the power law function value of the index of discontinuours objects index is generally around 0.25. (5) Diversity-time relationships:In a natural area free of human activities, species diversity improves with the time passing on and so does pedodiversity. In the end, as soil is essential to human survival, pedodiversity preservation merits special attention, perhaps more than other natural resources. Nowadays, the pedosphere and many of its soil types are on the edge of extinction as a result of intensive and widespread impact of human activities. Moreover, the impacts on land, soil resources and eco-environment are intensifying more and more significantly with the time going on, and land degradation, industrialized farming and orderless urban sprawl are the main driving forces of changes in and loss of pedodiversity.

Abstract:Phosphorus is a nutrient essential to all living organisms in the soil. Researches have demonstrated that oxygen isotope in phosphate is an important tracer for source and cycling of the phosphate in the ecosystem. This type of researches in based theoretically on the hypothesis that under natural surface temperature and pH conditions, P-O bond in phosphate is quite stable and not likely to get hydrolyzed easily However, in the process of enzyme mediated biological activity, the P-O bond would break, leading to fractionation of oxygen isotopes, which means that oxygen isotope fractionation in phosphate is primarily controlled by biological activity. As phosphate in soil is often very limited in natural abundance and a large quantity of organic matter exists in soil, how to remove the interference of oxygen from other sources in the soil is the key to determination of oxygen isotopes in phosphate that needs several rounds of enrichment, isolation and purification. This paper summarizes the theoretical basis and analytical technique, including methods for extraction and purification and instrumental analysis of soil inorganic P in the study on oxygen isotopes in soil phosphate, reviews recent progresses in the study on application of phosphate oxygen isotopes as tracer ti determining source of the phosphate in soil and cycling of phosphate in the ecosystem, and puts forth methods for extraction of organic phosphate in soil and the use of 18O-labeled and enriched phosphate in the study, which will further help deepen the knowedge about phosphorus transport in soil.

Abstract:Sampling design has long been a key issue of concerns in the study of Soil Geography. How to take samples efficiently is an important problem that investigators or researchers are tackling. As more and more synergic environmental data become easily available, they can also be used to assist designing of sampling so as to improve sampling efficiency. For that end, a multi-grade representative sampling method is developed. Using this method, investigators can catch patterns of soil spatial variability at different scales through designing different representative grades based on the relationship between soil and its environmental covariates. This method has been testified as an effective sampling method in a case study of watershed scale soil mapping. However, the application of this method is very limited, especially for mapping regional soil with more complicated pedogenesis. It is also unknown how it is when comparing with classic sampling methods, such as stratified random sampling. In this paper the multi-grade representative sampling method is compared with the stratified random sampling method in regional scaled soil property mapping, in the following two aspects: 1) designing of sampling sites, and result and accuracy of mapping; and 2) variation of accuracy of mapping with increased number of sampling sites. The case study was laid out in Xuancheng of Anhui Province, China, covering an area of 5900 km2.Seven environmental variables were selected, i.e. parent material (rock), slope gradient, profile curvature, contour curvature, topographic wetness index, annual average precipitation, and annual average temperature. The data of parent rock was used to stratify the study area. For representative sampling, FCM was employed to cluster the environmental variables of each stratum for designing representative sampling sites. Consequently a total of 59 sampling sites featuring three representative grades were defined. For random sampling, the number of sampling sites in each stratum was proportional to its area and also a total of 59 sampling sites were marked out. The two sets of sampling sites were sorted separately into three groups, each consisting of 46, 58 and 59 sites. For representative sampling, the first group of sampling sites was the highest in representativeness grade. The second group was the first group adding the sampling sites with the second highest representative grade. And the third group was the total sample set. For random sampling, the first group of sampling sites was 46 sampling sites picked out randomly from the set. The second group was the first group adding 12 sampling sites randomly drawn from the remaining (59-46) samples. And the third group was the total sample set.Soil surface layer sand content maps were plotted using two different soil mapping methods, i.e. multivariate linear regression and similarity-based mapping. The resultant soil maps were evaluated with independent validation sites and RMSE as evaluation index. Results show: 1) no matter which mapping method was used, in the case of the same sampling size, the representative sampling method was lower than the random sampling method in RMSE and even the former with fewer sampling sites (46) was lower than the latter with more sampling sites (59); 2)with increased number of sampling sites that were lower in representativeness, RMSE displayed a basically declining trend, while in random sampling method, increased number of sampling sites would aggravate the fluctuation of RMSE. It is, therefore, held that the multi-grade representative sampling method is more efficient and stable than the stratified random sampling.

Abstract:With advanced categories of the Chinese Soil Taxonomy established, focus of the research has been shifted to basic categories in recent years. As one of the major soil orders in the Chinese Soil Taxonomy, Argosols in Henan Province includes some quite different soil types according to the diagnostic criteria. A total of 8 typical soil profiles were selected and their landscape features, morphogenetic descriptions, physical and chemical data were analyzed and their positions in the Chinese Soil Taxonomy defined. Results indicate that the 8 soils could be sorted into 6 soil families, which are Loam mixed calcareous mesic Typic Hapli-Ustic Argosols, Loam mixed nonacid mesic Mottlic Hapli-Udic Argosols, Clay loam mixed mesic Mottlic Calci-Ustic Argosols, Clay loam mixed mesic Typic Calci-Ustic Argosols, Loam mixed calcareous mesic Typic Hapli-Udic Argosols and Loam mixed nonacid mesic Typic Hapli-Udic Argosols. On such a basis and in the light of the rules for soil series division and diagnostic features and structural characteristics of Argosols in Henan, attempts were made to set forth a logic diagram for reference and retrieval of soil series to illustrate the logical processes involved in reference and division of soil series. Through reference, the typical soils, with the 8 soil profiles as representatives, are sorted into 7 soil series, that is, Tangyin Series, Jishui Series, Shengou Series, Shangzhuang Series, Houji Series, Zaolin Series and Shangdian Series.

Abstract:It is of great significance to dynamically simulate development and evolution of soil erosion for the purpose of erosion forecast. Traditionally, most soil erosion models are basically steady-state models that have limitations in real-time simulation of initiation and development of soil erosion. Cellular Automata (CA), with a "from bottom to top" dynamic modeling framework, is capable of simulating spatial-temporal evolutionary processes of the complex geographical system. So, in this paper, rill erosion on loess slope was studied. By means of artificial simulated rainfall and three dimensional laser scanning, how rill erosion started, developed and evolved on a loess slope,15o in gradient, under three intermittent artificial rainfall events were investigated and visualized in graphics. At the same time, the CA-Rill model, already available for simulation of rill erosion process, was used in couple with the NetLogo software, to analyze and compare results of the experiment and the results of model simulation. Results show: (1) The scanning images of the rill erosion processes under the three events of rainfall reveal that the entire course of rill erosion consisted of the following phases in sequence, splash erosion, sheet erosion, drop pit, intermittent rill, continuous rill and rill collapse. Rills developed very rapidly in length, and relatively slowly in width and depth, and soon connected with each other to form a rill network. At the end of the third rainfall event, erosion intensity reached as high as 22.107 kg m^-2, 22.04 times that at the initial stage of rainfall. (2) Results of the CA-Rill simulation indicate that in visualizing evolution of the rill erosion, the model could quite perfectly simulate the entire morphological development of rills and realize visualization of the simulation. (3) Validation of parameter t of the simulated rill erosion under three artificial rainfall events demonstrates that the simulation of mean rill depth of the longest rill, depth of the deepest rill and mean width of the longest rill is not so ideal. However, the effect of the simulation of horizontal rill intensity, length of the longest rill and erosion intensity is quite good.

Abstract:Based on the available soil moisture (ASM) data collected from the 213 sampling sites over a small typical watershed in the hilly region of the Loess Plateau, spatial variability of soil available moisture at the scale of watershed, hillslope and gully and its seasonality (spring, summer and fall) was analyzed separately. Results show that the ASM, no matter at what scale, displays relatively strong spatial variability and ASM in gullies is higher in mean and spatial variability (Standard Deviation and Variation coefficient) than in hillslopes. The ASM also showed higher normality at gully and hillslope scales than at watershed scale. Spatial variability at all the three scales varies with the mean of ASM, and variation coefficient descends exponentially with the increasing mean. ASMs at the watershed and slope scales are closely and positively related to slope aspect, with correlation coefficient being higher than that its correlation with slope and elevation. However, the correlation coefficients of ASM with size of a gully and various landform factors are all low. The spatial variability of available soil moisture exhibits apparent seasonality. The ASM in fall, among the three seasons, is the highest in mean, but the lowest in variability. However, the ASM in summer is just the other way around. At the watershed scale, the ASM in summer is much higher than that in spring and fall in correlation coefficient with elevation, whereas it is in a reverse pattern at the slope scale. Besides, the uncertainty of the sampling of ASM and the estimation errors display a nonlinear descending trend with the increasing number of samples. However, when the number of sampling sites exceeds 20, the effect of increasing the number of samples becomes very limited. The findings presented here are expected to improve the understanding of seasonality of ASM spatial distribution of gully catchment in the Loess Plateau and could help design optimal sampling strategy of soil moisture.

Abstract:In a sand-dune-and-meadow interlaced region typical of Horqin, a total of 240 sampling sites were laid out, covering 9 different types of landforms, i.e., mobile sand dunes, semi-fixed sand dunes, fixed sand dunes, poplar woods in sand dune area, cultivated land in sand dune area, low coverage meadow, high coverage meadow, cultivated land in meadow area, and deserted land, for collection topsoil samples. Physicochemical properties, including the moisture content, dry bulk density, organic matter, and saturated hydraulic conductivity, of the soil samples were determined for analysis of variation of the properties with geomorphic type. These four kinds of pedo-transfer functions, that is Campbell, Cosby, Wosten et al, and Saxton et al, were chosen for use to predict saturated hydraulic conductivity of the surface soils in this region. Results show that the predicted values and the measured values differed quite sharply, with correlation coefficient being less than 0.3, so the precision of the prediction was far from satisfactory for use in this region. On such a basis, soil bulk density, organic matter content, saturated moisture content, average particle size, and particle size standard deviation were used as input variables in combination with principal component analysis and nonlinear regression analysis methods. In this way, new pedo-transfer functions were establishd for prediction of saturated hydraulic conductivity of the surface soil in this region. Results show that the correlation coefficient between predicted and measured values was increased up to 0.661, demonstrating that the new pedo-transfer functions can be applied to prediction of saturated hydraulic conductivity of the surface soil of Horqin sandy land.

Abstract:“Pisha” or soft sandstone, distributed extensively in the region striding over Shanxi Province, Shaanxi Province and Inner Mongolia Autonomous Region, is a kind of sandstone, highly erodible and unfit for vegetation growth. It is also one of the major sources of coarse sediment in the Yellow River. As it contains abundant montmorillonite, this kind of soft sandstone is quite high in water holding capacity. An indoor simulation experiment was carried out on feasibility of using weathered soft sandstone to ameliorate the local soils (Aeolian sandy soil and sandy loess, rather coarse in soil texture) in water holding capacity. The experiment used 3 types of soft sandstones different in color (red, gray and white) in amendment in the ratio of 1:9, 3:7 and 1:1(by weight) separately, to determine effects of the amendment on water retention curve and evaporation process of the local soils. The experiment was conducted in the State Key Laboratory of Soil Erosion and Dryland Farming on Loess Plateau, Institute of Water and Soil Conservation, Chinese Acdemy of Sciences. Three kinds of soft sandstones (Red, Grey, White sandstone) were mixed with aeolian sandy soil and sandy loess, separately, in line with the designed ratios, 1:9, 3:7 and 1:1 (by weight of air-dried soil, m_{soft sandstone} /m_soil), and each had 3 replicates. Original soils were also tested as control. The experiment proceeded under natural conditions. A centrifuger was used to determine soil water retention curve at 12 set rotation rates and the RETC software and van Genuchten model was used to fit the soil water retention curve, and soil evaporation processes were determined through in-lab simulation, using a hard plastic beaker with punched bottom. Before packing soil into the beaker a piece of filter paper was placed on the bottom to prevent the soil from leaking. The beaker was put into a pan with water to wet the soil in a self-suction way through the holes in the bottom for 12 h till the surface of the soil was wet, and then the beaker was put aside for 4 h to drain out gravity water. During the process, the soil was mulched with foam to prevent the water from evaporation loss. The saturated soil column was drained for 4 h to make sure the gravity water out. Weighting method was used to determine evaporation rate. Soil bulk density of the soil in each treatment was controlled as listed in Table 2. Results of the experiment show that (1) weathered soft sandstone was higher than the two local soils in water-holding capacity and amendment of the former improved the latters in water-holding capacity and reduced their water losing rate. White soft sandstone reduced saturated water content of the sandy loess;(2) Soft sandstone, when low in proportion (1:9), improved water supply capacity of the two local soils, but did not have much effect increasing water suction of the soils when specific water capacity of the two soils reached the 10^-2 level, which indicates that the effect of soft sandstone improving the local soils in water holding capacity is not significant, when they are low in suction; (3) Soft sandstone decreased standard evaporation rate of the sandy loess and lowered standard evaporation in the aeolian sand soil, too, but only at the initial stage of the evaporation, and affected reversely in the middle and late periods. The higher the proportion of soft sandstone, the higher the standard evaporation in the Aeolian sand soil. In sandy loess proportion of soft sandstone was not an important factor affecting standard evaporation. The standard evaporation from the mixture of soft sandstone and sandy loess was quite close to that from soft sandstone; (4) In the aeolian sand soil, though addition of red, grey and white soft sandstone increased water loss through evaporation by 11.59%, 10.14% and 0.01%, respectively, it multiplied the eventual moisture content by 4, 2.33 and 1.33 times, respectively, while in the sandy loess, the addition decreased water loss through evaporation by 13.33%, 13.33% and 29.52% and the eventual moisture content, too, by 45.83%, 54.17%, and 66.67%, respectively. The findings may serve as a certain theoretical basis for and a possible technical approach to soil and water conservation and ecological restoration in this soft sandstone region.

Abstract:Information on distribution of heavy metals in various chemical forms in soils may have greater chemical and biological significance than that of just total concentration. The amount of an isotopically exchangeable metal in soil solution, also called E-value, may conceptually best represent the fraction of the metal that is in dynamic equilibrium in the solution phase, and is considered to be a better indicator of availability of the chemically reactive metal to plants. Mercury (Hg) is of great concern in soil because it is phytotoxic to plants through accumulation in plant tissues and detrimental to human health through the food chain. In order to assess its phytotoxicity to vegetables and potential risk to human health, it is very important to have a better knowledge about labile pools of Hg in soils. The aim of this study is to determine the pools of isotopically exchangeable Hg ( E-value) in different soils. E-values of Hg in two typical soils (red soil and fluvo-aquic soil) was measured using the stable isotope ²⁰²Hg dilution technique and E_{1 min}, E_{1 min-24 h min}and E> _{> 24 h} values of Hg in the soils were calculated based on the model of isotopic exchange kinetics (IEK) with an iterative nonlinear regression algorithm. In addition, pools of labile Hg in the soils were also determined with four different single chemical extraction methods and a sequential extraction procedure (modified BCR approach) for comparison. Results show that 24 h after the addition of ²⁰²Hg, equilibrium of ²⁰²Hg/²⁰⁰Hg between soil and solution was established in both soils. The IEK equation was found fitting quite ideally the dynamics of isotope ratios and E_t values of Hg in soils. All the three compartments of E_{1 min}, E_{1 min-24 h min}and E_{> 24 h} in the red soil were markedly higher than those in the fluvo-aquic soil. E _a values, sum of E_{1 min} and E_{1 min-24 h min} and around 38%~60% of total Hg, obtained using the isotope method, were significantly higher than that (10%~15% of total Hg) acquired through extraction with 0.03% TGA-1/15 mol L^-1 Na₂HPO₄ being the highest among the 4 single extraction methods, and than ∑_BCR (20%~27%, sum of acid-extractable, reducible and oxidizable fractions) of the sequential extraction method. It was also found that soil pH had marked influence on E-values of Hg in the two studied soils. Compared with the chemical extraction procedures, the isotope method may yield E _a, which tends to be a bit too higher when used as indictor of content of soil available Hg. It is, probably, related to fixation of the spiked extraneous ²⁰²Hg by the soils and properties of the soil suspensions for E measurement.

Abstract:Quorum sensing, the communication between microorganisms, is mediated by specific diffusible signal molecules. Gram-negative bacteria generally use N-acyl-homoserine lactones (AHLs) as their command language in coordinating their intra- and intercellular population behaviors. AHLs play an important role in controlling diverse physiological processes, including generation of extracellular toxin and enzymes by pathogenic bacteria, formation of biofilm, bioluminescence, biosynthesis of antibiotics, bacteria motility, etc. The authors have found in their recent studies that communication of microbial signals is closely related to microbial degradation of organic pollutant. Therefore, the detection and quantification of AHLs are essential for investigation of quorum sensing in gram-negative bacteria. Currently, there are several AHLs detection methods, including mainly enzyme linked immunosorbent assay (ELISA), biosensor, thin layer chromatography (TLC) and chromatography. In this study, a fast, simple selective method was established for detecting N-acyl-homoserine lactones (AHLs) in soil solution by the GC-MS (gas chromatography-mass spectrometry). The novel method can detect AHLs qualitatively and quantitatively at the same time. Using the full scan mode, seven kinds of AHLs (C₄, C₆, C₇, C₈, C₁₀, C₁₂ and C₁₄-HSL) standards were analyzed by GC-MS. The best results in terms of selectivity and time consumption of the analysis were obtained. Sample injection was done in the split mode (5:1) and pure helium (99.999%) was used as carrier gas at a flow rate of 1 ml min-1. The GC injector temperature was optimized to 290 ℃. The oven temperature program was optimized to start from 100 ℃ to 150 ℃ at a rate of 35 ℃ min^-1 and then to 280 ℃ at a rate of 25 ℃ and maintained for 6 min. Under such optimized conditions, all the 7 kinds of AHLs were well separated within 12 minutes. Furthermore, the mass spectrum of the 7 AHLs exhibited a molecular ion peak [M] ⁺that was unique of each compound, i.e. C₄-HSL (m/z 171)，C₆-HSL(m/z 199)，C₇-HSL(m/z 213)，C₈-HSL(m/z 227)，C₁₀-HSL(m/z 255)，C₁₂-HSL(m/z 283) and C₁₄-HSL(m/z 311). Probably as a result of the McLafferty rearrangement, they generated a common fragment ion m/z 143. As the 7 AHLs all contained abundant m/z 143 ions, the ions could be used as a marker fragment to detect AHLs in unknown samples on mass detector operating in the SIM mode. The detection limits of the seven AHLs (C₄, C₆, C₇, C₈, C₁₀, C₁₂ and C₁₄-HSL) standards were 1.50, 2.00, 1.50, 2.00, 2.00, 2.50, and 2.50 µg l^-1, respectively. The standard curves of all the 7 AHLs displayed nice linear relationships up to 2.0 mg l^-1 and their coefficients of determination were all higher than 0.997. The recovery experiment using ethyl acetate as extracting agent shows that in the solutions with spiking concentrations being 0.5 mg l^-1and 2.0 mg l^-1, recoveries of 6 AHLs (C₆, C₇, C₈, C₁₀, C₁₂ and C₁₄-HSL) varied in the ranges of 76%～85% and 74%～97%, respectively, whereas the recovery of C₄-HSL was relatively low, being about 55% for both spiking concentrations. In 3 soil solutions of Latosolic red soil and Yellow brown soil, different in soil/water ratio, the recoveries of C₄-HSL ranged from 56% to 71% for both spiking concentrations, while the recoveries of the other 6 AHLs were all relatively higher, being in the ranges of 71%～108% and 68%～104% for spiking concentration of 0.5 mg l^-1 and 2.0 mg l^-1, respectively. No significant difference was observed in recovery of each AHL relative to soil solution, indicating that the organic and inorganic compounds in the soil solutions have no influence on extraction of AHLs in soil solutions using ethyl acetate. In addition, significant relationships were observed between the recovery of AHLs in different media and their logP (P stands for partion between normal butanol and water) as well as logS (solubility in water), but no relationship was between the recovery of AHLs and their polarity, showing that the recovery of AHLs were mainly related to their logP values and solubility in water. Therefore, this extracting method coupled with GC-MS can be effectively applied to analysis of AHLs in different soil solutions. Thereafter AHLs concentrations in the soil solutions were determined. It was found that the concentrations of the 7 AHLs varied in the range of 3.8~8.7 µg l^-1and 4.2~9.8 µg l^-1 in the solutions of Latosolic red soil and yellow brown soil, respectively. It could be concluded that AHLs in both aquatic solution and complex media, such as soil solution, can be analyzed using GC-MS coupled with ethyl acetate extraction。

Abstract:Tetracyclines (TCs) is one of the antibiotics most commonly used in animal husbandry nowadays, for it is, cheap and little in side–effect. It is often released into soils through application of animal manure and disposal of pharmaceutical waste and so on, thus not only affecting microbial activities and plant growth, but also interacting with other pollutants existing in the soils, which might eventually lead to eco-toxicity and changes in pollutant characteristics in agricultural soils. In order to explore sorption behavior of oxytetracycline (OTC), a typical TCs, in complex contaminated soil and its effect on desorption of other existing pollutants (especially heavy metals (HMs), such as cadmium, copper, lead and zinc) in three different types of complex contaminated soils, a batch equilibrium experiment was conducted, in line with Guideline No. 106 of the Organization for Economic Co-operation and Development (OECD). Samples of three different types of contaminated soils were collected from three sites different in soil type and were contaminated with HMs-Polycyclic aromatic hydrocarbons (PAHs), HMs, and PAHs. The experiment was designed to have 10 treatments relative to OTC concentration, i.e. 0, 0.01, 0.1, 1.0, 5.0, 10.0, 25.0, 50.0, 100, 200 and 400 mg L^-1. After the addition of OTC, concentrations of cadmium, copper, lead and zinc in the soils were determined. Results show: 1) a threshold value was found with OTC concentration. Around the point, below or above, OTC adsorption characteristics changed in opposite ways. However, all the data in the two ranges of concentration could be well fitted with the Freundlich model and Langmuir model; 2) OTC, varying in the range from 0 to 25 mg L^-1 in concentration, competed for adsorption sites on the surface of the soils with heavy metals and as a result, HMs desorption rate increased with the rising OTC concentration; however, when OTC concentration varied between 25 and 100 mg L^-1, some free HMs ions formed complexes with OTC and got fixed again on the surface of the soils; and when OTC concentration exceeded 100 mg L^-1, HMs desorption rate rose slightly as the addition of a high rate of OTC declined pH of the system. The changes in HMs availability in contaminated soils are mostly attributed to the competition for adsorption and complexation reaction of OTC with HMs, and the change in pH, which upsets the dynamic equilibrium, adsorption or desorption, of the pollutants in the soils. Since HMs desorption rate in solution could, to a certain extent be analogous to its toxicity, it is necessary to study in depth effect of the addition of oxytetracycline, relative to application rate, on desorption of HMs in complex contaminated soils, which is not only conducive to the research on mechanism and toxicity of the complex contamination of antibiotics and heavy metals, but also of a certain significance in guiding maintenance of food security and remediation of complex contaminated soils.

Abstract:Polycyclic aromatic hydrocarbons (PAHs) with highly mutagenic and carcinogenic properties are commonly found in the soil environment. Soil contamination by PAHs has become a major health risk issue. PAHs are widespread and occur at high concentrations (hundreds of mg kg^-1) in soils of many countries. Since natural and xenobiotic PAHs present in soil may be absorbed by plants, PAHs can enter human and animal bodies through the food chain/web. Because of the health hazards of PAHs, understanding the distribution of PAH residues in rhizospheric soils is of crucial importance for risk assessment of PAH-contaminated areas. The distribution of PAHs in the rhizosphere affects their fate in the soil-plant system. After diffusion into rhizosphere soil, root exudates gradually disappear as a result of radial dilution and microbial consumption. Because these root exudates are ready carbon and energy sources to bacteria, a bacterial gradient is observed with a greater number of heterotrophs and PAH-degrading bacteria closest to the roots, which may generate a gradient of PAH degradation between the rhizosphere and bulk soil. Recently, it was reported that the residual concentrations of PAHs showed a rising gradient from the rhizoplane to the loosely adhering soil after 40 and 50 d, and were significantly and negatively correlated with the amount of root exudates in the rhizosphere. This was further supported by an in situ observation that concentrations of 11 EPA-priority PAHs in rhizosphere soils increased with the distance (0~9 mm) from the root surface. However, the documented gradient distributions in rhizosphere soils are overwhelmingly about the total concentrations of PAHs as well as other organic compounds. The International Union of Pure and Applied Chemistry (IUPAC) definition reserves the term of bound residues for the parent compound and its metabolites that cannot be extracted from soil using organic solvents. Bound residues have a direct effect on long-term partitioning behavior, bioavailability, and toxicity of the organic contaminants in soil. The formation of bound residue is considered to act as a soil detoxification process by permanently binding compounds into soil matrices, and the bioavailability of bound residues is the final endpoint for risk assessment and regulatory management of organic chemicals in the soil environment. However, there is little information available on the distribution of their bound residues in the rhizosphere. Therefore investigations were made of rhizospheric gradient distribution of bound-PAH residues (reference to parent compounds) in soils on a field scale. In Moleplant ( Euphorbia lathyris L.) and wood sorrel ( Oxalis corniculata L.) fields of yellow brown earth near a petrochemical plant, rhizosphere soils of the plants were sampled including the rhizoplane, strongly adhering soil, and loosely adhering soil, for analysis of content and gradient distribution of PCBR (Parent compound of bound residue) in the rhizosphere. Results show that PCBRs of the ten EPA-priority PAHs were detected in both the rhizosphere and non-rhizosphere soils, about 3.31 mg kg^-1 in concentration in the latter, much higher than in the former (1.07~1.82 mg kg^-1). The concentration of PCBRs increased with the distance (0~9 mm) from the root surface. It is feasible to use rhizosphere effect (R, in percent) to measure the proportion of the decrement of PCBRs in concentration in the rhizosphere as against that in the non-rhizosphere soil, R decreased with increasing distance from the root. Rof the total PCBRs of PAHs in three continuous layers of rhizosphere reached 45.15%~67.66%. R of two-ringed PAHs was the highest (61.18%~93.50%), while R of four- and five-ringed PAHs the lowest (2.39%~6.31%), which indicates that the PCBRs of PAHs with fewer rings are more liable to transformation in the rhizosphere. R of the PCBRs in the rhizosphere of moleplants was found to be relatively higher than that of wood sorrels, suggesting that the rhizosphere of moleplants was more favorable to transformation of PCBRs. The gradient distribution of PCBRs in the rhizosphere is closely related to that of root exudates, while type of PAHs and rhizosphere environment affect significantly distribution of PCBRs. The findings of this work provide some important information on fate of PAHs in the soil environment and are useful in risk assessment of PAHs-contaminated soils and development of strategies for remediation of contaminated areas.

Abstract:A 3-year stationary field experimentwas carried out to explore soil phosphorus desorption characteristics and their effects on phosphorus concentration in percolating water from fields under the garden bean ( Phaseolus vulgaris)– zucchini ( Lagenaria siceraria)–paddy rice rotation system, as affected by P application rate, and a model and indices for their evaluation as well. Results show that the model the authors designed fit quite wellsoil P desorption process varying with water/soil ratio. With the aid of the model it was feasible to acquire simultaneously P desorption characteristics, like amount of desorbable soil P(Q) and soil solution P concentration (C_li) and its buffer coefficient (b). The concentration of total phosphorus in the percolating water in the field under the vegetable-vegetable-rice rotation was on average only 42.6% of that in the field under vegetable-vegetable rotation. The relationship between Q and concentrationof total P in percolating water in the field fit the dynamic characteristics of “dual rate turning point”. The turning point X₀of soil P loss characterized by Q varied very slightly and averaged to be 24.4 mg kg^-1, no matter the field was under the vegetable-vegetable-rice rotation or vegetable-vegetable rotation. It could, therefore, be concluded that the vegetabe-vegetable-paddy rice rotation system is conducive to reducing the concentration of total P in percolating water, and the dual-rate turning point X₀ of the amount of soil desorbable P may be used as one of the indices to characterize the potential of soil phosphorus leaching loss in vegetable fields.

Abstract:To tackle the problem of water eutrophication of the Nansi Lake along the eastern line of the South-North Water Diversion Project in China, field experiments were carried out on fertilization in farmland under wheat-maize rotation, typical of the region, to explore its effect of controlling S and P loss. In the experiments, market–available fertilizers were used and in-situ lysimeters and surface runoff pools were set up to collect leachate and runoff for lab analysis. Results show that fertilization, regardless of its method, reduced nitrogen and phosphorus loss with water in both crop seasons. The effect varied with fertilization method. NO3--N was the main form of nitrogen lost with runoff water, accounting for 82.7%~86.4% in the maize season and for 94.2% 96.5% in the wheat season, however, it declined slightly in leachate, which suggests that surface runoff is the main route of nitrogen loss. Nitrogen loss during the maize season amounted to 67.0%~71.4% of the total of a year. P loss via surface runoff consisted almost equally of dissolved phosphorus and particulate phosphorus, while P loss via leaching was dominated with dissolved phosphorus, and accounted for a larger proportion of the total. A greater proportion, 54.4% ~ 63.1% of the P loss of a year occurred during the maize growing season. Taking into account both control of N and P loss and crop production of a year, it is advisable to apply decrement controlled-release nitrogen fertilizer or optimize fertilization coupled with straw incorporation for maize season, and optimize fertilization or apply decrement controlled-release nitrogen fertilizer for wheat.

Abstract:Samples of soil and plants were collected from shoal wetlands in the Poyang Lake for indoor simulation of static transfer of phosphorus in a soil-water-plant system to explore laws of the absorption, release and transfer of phosphorus in the soil-water-plant wetland system of the Poyang Lake. Before and after the experiment, transfer of phosphorus relative to form in the system was analyzed. The experiment device was a cylindrical container of polyvinyl chloride, 10cm in inner diameter and 40cm in height, containing a 10cm thick layer of homogeneous sediment. Water lily was planted in the cylinder. The overlaying water in the cylinder was sampled for and analyzed of phosphorus on D3, D6, D9, D16, D23, D28, D35 and D42 after the experiment began (D day). Meanwhile, soil and plant samples were also collected for analysis of phosphorus concentration. At the end of the experiment, fractionation of phosphorus in the surface layer (1～2cm) was performed, and concentrations of Fe-P, Ca-P and Al-P were determined to explore variation of the transfer of phosphorus relative to form. On such a basis, the Freundlich model and Langmuir model were used to perform one-dimension linear regressive analysis of adsorption and desorption of P in the soil sediment of the shoal wetlands in the Poyang Lake. Results show that phosphorus was released continuously from the soil into the water, and mostly absorbed by plants. Before the experiment, phosphorus concentration was found to be 1.0 mg g^-1 in the plants and 2.3 μg mL^-1 in the overlaying-water, and after the experiment it was 2.1 mg g^-1 and 0.062 mg L^-1, respectively. In the initial period of the experiment, phosphorus concentration in the overlaying water decreased from 1.7 to 1.4 mg L^-1, and on D16, it was found to be 0.5 mg L^-1, and then it leveled off from D35 and on. During the first 3 days, phosphorus in the soil decreased quickly, from 25.5 to 11.5 mg kg^-1. As this was only a static experiment, though part of the phosphorus in the soil was released into the overlaying water, the exchange between the soil and the water was very slow. P concentration in the overlaying water as a whole still displayed a decreasing trend. Only the concentration in the water layer close to the surface of the soil increased somewhat. At that time, phosphorus content in the plants kept rising rapidly. Plant roots grew deep into the soil, facilitating phosphorus transfer from the soil into the plants. With the growth of the plant root systems, plants’ demand for P increased. The rising P content in the plant began to level off on D28. The decline of phosphorus content in the overlaying water began to slow down at the mid-later stages of the experiment. At that time, the plants were well developed and phosphorus content in the soil kept almost unchanged, and the phosphorus in the soil-water-plant system reached its equilibrium. Meanwhile, soil phosphorus fractionations before and after the experiment show that the content of Al-P remained almost unchanged, the content of Ca-P increased slightly but the content of Fe-P did by a large margin. The content of Fe-P in the soil was quite high and that of Ca-P and Al-P quite low, either before or after the experiment. Among the three fractions, Al-P was extremely low in content, being 0.020 mg kg^-1 before the experiment and 0.016 mg kg^-1 after the experiment, almost unchanged; the content of Ca-P increased slightly from 0.202 to 0.239 mg kg^-1; and the content of Fe-P increased by a large margin from 0.746 to 0.862 mg kg^-1. Relative to the Freundlich model, the Langmuir model was better in simulating phosphorus adsorption process in wetland soils. The findings of this study may serve as scientific theoretical basis for management of lake pollution and research on environmental effects of pollutant in wetlands.

Abstract:Facility agriculture is an efficient way to solve the problem of food supply in China. However, it tends to lead to deterioration of soil health, such as the occurrence of continuous cropping obstacle, which in turn, triggers decline in yield and quality of the vegetables in facility agriculture. Interplanting is an effective way to avoid continuous cropping obstacle. Numerous reports have been published on positive effects of interplanting of vegetables on vegetable production, but few are available on effect of interplanting of vegetable with edible fungi, let alone papers on its underlying mechanisms, such as soil microbiological mechanism. For this purpose, a tomato-agaricus bisporus interplanting experiment was laid out. Tomato is a thermophilic and photophilic species of plant while agaricus bisporus prefers to grow in dark environment. Therefore the latter can flourish in the shade of the former. From the angle of gas exchange, tomatoes can get more CO₂ for photosynthesis from respiration of agaricus bisporus, while agaricus bisporus can have more O₂ generated from tomato in photosynthesis to decompose cultural media into nutrients available to tomato for growth. It is, therefore, hypothesized that the relationship of mutual benefit between tomato and agaricus bisporus should contribute to improvement of crop yield and soil quality in facility agriculture. In the interplanting experiment, tomato seeds were sown in vermiculite for seedling culture. Thirty days later, the seedlings were transplanted into pots, 2 seedlings each planted in diagonally opposite corners and a ditch was dug in between the two plants for culturing of agaricus bisporus. The experiment was designed to have three treatments, each having three replicates; i.e. Treatment L (control without addition of any mushroom culturing media or inoculation of mushroom spores in the ditch); Treatment LS (mushroom culturing media added, but no mushroom spores inoculated); and Treatment LSA (mushroom culturing media added and mushroom spores inoculated). Biomasses of tomato plants, fresh weight of fruits and nitrate contents therein from different treatments were measured for analysis of effects of the interplanting on yield and equality of the tomato. For the microbial mechanisms, real-time quantitative PCR and PCR-DGGE fingerprinting analyses of targeting soil bacteria and fungi were conducted to determine numbers of copies of 16S and 18S rRNA genes and community compositions. Results show that Treatment LSA significantly increased tomato biomasses (p<0.05) and was the highest in fruit yield, but the lowest in nitrate content in tomato among the treatments. Though the numbers of gene copies of soil bacteria and fungi did not vary much statistically in the soil under the interplanting as compared those in the control, they were the highest in Treatment LSA. The PCR-DGGE fingerprinting profiles reveal that the treatments differed slightly in composition of soil bacterial community, but the PCR-DGGE fingerprinting profiles of the fungal 18S rRNA genes show that Band 4 and Band 6 were obviously lower in intensity in Treatment LSA than in the other two treatments. Cluster analysis indicates that Treatment LSA differed significantly from the other two in soil fungal community composition, that is, in Treatment LSA differentiation occurred in fungal community structure. Moreover, principal component analysis of the changes in soil fungal community structure in different treatments shows that along the X axis (primary principal component), Treatment LSA deviated from the other two and along the Y axis (secondary principal component), Treatment L parted apparently from Treatment LS, indicating that Treatment LSA had some apparent impact on community structure of the dominant soil fungi. By sequencing and constructing phylogenetic tree, it was found that Band 4 and Band 6 that decreased significantly in intensity in the DGGE fingerprinting profiles were affiliated with Fusarium oxysporum and Nigrospora respectively, both of which were documented as pathogens. All in all, the findings suggest that interplanting of tomato with agaricus bisporus may reduce the incidence of some soil borne diseases by inhibiting certain pathogenic microbes, thus contributing to improvement of yield and quality of the crops and soil quality as well.

Abstract:Chinese pine ( Pinus tabulaeformis Carr.) is widely used as a pioneer tree species in the Loess Plateau of Northwest China for windbreak and sand-fixation, soil and water conservation thanks to its high tolerance of cold, drought and soil infertility and its liability of forming ectomycorrhiza. The formation of mycorrhiza has some important influences on soil enzyme activity and soil microbial community in the rhizosphere of the host plant. Rhizosphere refers to the interface between plant roots and soil, and is a complex and dynamic microecosystem developed in the process of plant growth. Study have shown that significant differences exist in rhizospheric soil microbial community between Chinese pines growing in different ecological condition. However, little has been so far reported on effects of the variations of soil properties and microbial distribution caused by the redistribution of soil properties and soil nutrients during the process of rainfall erosion on slope land on soil enzyme and mycorrhizal fungal community in the rhizosphere of pine trees. In order to understand soil enzyme activity and fungal community diversity in the rhizosphere of Chinese pine in the Huanglongshan Forest Farm, the nested PCR-DGGE (denaturing gradient gel electrophoresis) method was used to determine fungal community diversity at different slope positions in the forest farm, and relationships of fungal community diversity with activities of urease, alkaline phosphatase, polyphenoloxidase and hydrogenperoxidase, were investigated in an attempt to provide a theoretical basis for revealing interactions between vegetation, soil microbes and soil enzyme activity. Results show that all the soil enzymes displayed a trend declining down the slope in activity, and from shady slope to sunny slope. As sampling sites along the roadside differed in environment from those in the forest so the enzyme activities therein varied in-between those in the sampling sites located in the forest. Analysis of the samples for Richness, Shannon-Wiener index, Simpson index and Evenness indicates that fungal communities in the pine rhizospheric soils were quite high in similarity, but varied somewhat in Richness (S), Shannon-Wiener index (H), Simpson index (D) and Evenness (E_H), suggesting that the fungi varied with slope position in species, biomass, diversity and functional diversity. The distribution of fungal diversity and the distribution of enzyme activity were quite similar in characteristic except for E_H, both displaying a trend of declining down the slope and from shady slope to sunny slope, and the distributions in the sampling sites alongside roads ranged in-between those in the sampling sites in the forests However, the distribution of soil nutrients in slope land was quite different from that of pine rhizospheric microbial diversity and soil enzyme activity and characterized by losing from the slope and accumulating at the foot of the slope. The distribution of soil enzyme activity on slope is closely related to source and biological properties of soil enzymes, and microtopography and more likely to microecosphere of the rhizospheric microbes. Correlation analysis of fungal richness, soil enzyme activities, soil water content and soil pH shows that positive correlations existed between enzyme activities and fungal diversity (p<0.05), except for that of hydrogenperoxidase; between fungal diversity and soil water content (i>p<0.05); between enzyme activities and soil water content (p<0.05), except for that of polyphenoloxidase; and between the enzymes per se in activity (p<0.05), except for hydrogenperoxidase; but not between soil pH and enzyme activities (p>0.05). All the findings indicate that in semi-arid regions, the higher the water content in the P. tabulaeformis rhizosphere, the higher the abundance of the fungi. Therefore, it can be concluded that soil water content is one of the major factors affecting soil enzyme activities and fungal community diversity in the soil.

Abstract:Tomato (Solanum lycopersicum) is an important economic crop. Bacterial wilt caused by Ralstonia solanacearum is a serious soil-borne disease of Solanaceae crops. Traditional controlling methods, such as cultivation of resistant varieties, crop rotation and use of chemicals, all have certain limitations. Silicon, as beneficial element to plant growth, plays an important role in enhancing plant adaptability to biotic and abiotic stresses. Proteomics is a new branch of science in post-genome era, focusing on proteomics as object to explore the full extent properties of various proteins, and further on pathogenesis, cell model and functional links of diseases at the protein level. In this study, the variety of tomato “Taiwan red cherry” which is susceptible to R. solanacearum was used. The experiment was designed as the following treatments: CK, Treatment Si (Si addition only), Treatment Rs (R. solanacearum inoculation only) and Treatment Si+Rs (Si addition followed by R. solanacearum inoculation), and the technique of iTRAQ (isobaric tags for relative and absolute quantitation) was used to analyze effects of Si addition on resistance of the tomato to R. solanacearum and soil proteome. Results showed that silicon addition significantly reduced disease index of the tomato crop by 19.4%, increased available silicon content in the soil and enhanced resistance of the tomato to R. solanacearum. ITRAQ analysis revealed that out of the 30 soil proteins identified, 29 were differentially expressed (up-regulation ≥1.2 fold and down-regulation ≤0.8 fold); isoelectric point of differentiated proteins varied between 4.1 and 10.7 and relative molecular weight in the range of 9 ~ 392 kDa; and confidence coefficient was ≥95%. Compared with CK, Treatment Si had five proteins up-regulated and nineteen down-regulated and Treatment Rs, five up-regulated and twenty-two down-regulated. Compared with Treatment Si, Treatment Si Rs had eight proteins up-regulated and fourteen down-regulated. Classification based on GO (gene ontology) function shows that of the twenty-nine differentially expressed proteins, 21.88% are involved in metabolic process, 15.63% in cellular process, 12.50% in cell communication, 3.13% in immune system process and another 3.13% in the process of response to stimulus, and classification in light of molecular function reveals that 25.64% are related to structural molecule activity, 25.64% to binding and 20.51% to catalytic activity, the three categories making up a major proportion. Classification according to protein class exposes that nucleic acid binding protein, hydrolase protein and cytoskeletal protein are the three major categories of proteins, accounting for 19.51%, 14.63% and 9.76%, respectively. To better understand effects of Treatment Si Rs and Treatment Rs on soil proteins, further analysis was done of the 22 differentially expressed proteins obtained from Treatments Si Rs/Rs. It was found compared with Treatment Rs, Treatment Si Rs had eight proteins up-regulated by as high as 1.6 folds and fourteen proteins down-regulated by 0.5 fold. All the findings indicate that Si could affect R. solanacearum by altering metabolic and cellular processes in biological process, structural molecule active protein and bindin protein in molecular function, and nucleic acid binding protein and cytoskeletal protein in protein classification. In a word, Si addition can reduce the disease index of tomato bacterial wilt significantly, thus enhancing the plant resistance to the disease. Infection of R. solanacearum down-regulates metabolic-related proteins, influences degradation of misfolded proteins, hinders signal communication and Ca² signal transduction between microorganisms and microorganisms or plants, blocks synthesis of proteins, while Si helps tomato build up its resistance to R. solanacearum infection by affecting soil microbial metabolic capability, regulating expression of resistance and metabolism related proteins, improving signal communication and transduction between microorganisms and between microorganisms and plants, adjusting synthesis of soil proteins and expression of proteins involved in immune system process and stress response and influencing signal transduction of Ca² .

Abstract:Low yield and poor quality of peanut production due to low soil fertility, and environmental pollution as a result of disorderly discharge of animal excretion from large-scale animal farms have become two main problems in the red soil area, of Jiangxi Province. Some researchers have proposed application of animal excretions as organic manure into farmlands and hold that it a win-win solution to the problems. However, some scientists have proved that long-term excessive application of pig manure will bring about heavy metal accumulation in the soil and pollution of groundwater with nitrate; and some others have found that application of pig manure, if low in rate, not only increases labor cost but also has little effect on yield and quality of crops. Hence, how to make use of organic manure properly to optimize crops in yield and quality without any risk of environmental pollution has become a pressing issue. For that a field experiment was carried out at the Yingtan National Agroecosystem Field Experiment Station located in Yujiang County, Jiangxi Province, a subtropical area of China, to tackle this problem. The experiment was designed to have six treatments, i.e. no fertilizer (CK), conventional chemical fertilization (T0), 80% chemical fertilizer N plus 20% manure N (T20), 65% chemical fertilizer N plus 35% manure N (T35), 50% chemical fertilizer N plus 50% manure N (T50), and 35% chemical fertilizer N plus 65% manure N (T65), with a view to exploring effects of application of organic manure, relative to its rate, on physiological characteristics, yield and quality of peanut and further-on an optimal combination of chemical fertilizer with organic manure for peanut production in this area. So this study not only has its important theoretical significance in enriching the physiological study on nutrition and quality of peanut, but also possesses some practical meaning in reducing the waste of organic manure resources and alleviating the potential risk of application of organic manure polluting the environment. Results of the field experiment are encouraging. (1) Combined application of chemical fertilizer with organic manure could significantly enhance the anti-aging enzyme system of peanut leaves. With the rising proportion of organic manure, activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and content of soluble protein increased first and then declined. Peaks were found in Treatment T35, being 38.28%, 9.97%, 8.31% and 12.38%, higher than their respective ones, in Treatment T0. However, the content of malondialdehyde (MDA) displayed a reverse trend, decliing first and then rising with the application rate of organic manure. It was the lowest in Treatment T50, being 5.03% lower than that in Treatment T0. (2) Combined application also had some significant effects on peanut physiological properties. With the rising proportion of organic manure in combination, net photosynthetic rate (Pn), stomatal conductance (Gs) and chlorophyll content Chl(a+b) gradually increased first and then declining with the proportion of organic manure going up (p<0.05), being much higher in Treatments T35 and T50 than in the others. Particularly, in Treatment T35, Pn, Gs, Chl(a b), CAT and SOD in leaves was 8.89%, 10.58%, 18.58%, 8.31% and 38.28% higher than their respective ones in Treatment T0 at the pod setting stage. (3) Combined application had significant effects of improving vegetative growth and yield of peanut. The higher the proportion of organic manure, the better the plant traits. The peanut plants in Treatment T65 ranked first in main stem height and lateral branch length, being 8.01cm and 11.2cm higher or longer than those in Treatment T0, while the plants in Treatment T35 were the highest in pod yield, kernel yield, pods per plant, per hundred kernel weight, being 20.14%, 26.92%, 27.87% and 7.08%, respectively, higher than their respective ones in Treatment T0. (4) Combined application could significantly improve the quality of peanut. Treatment T35 increased contents of fat, protein and soluble sugar in kernels by 3.58%, 5.03% and 12.16%, respectively as compared with Treatment T0. Based on the above-described findings, it can be concluded that on the condition that equivalent N, P, K nutrients are supplied, the application of fertilizer containing 35% of N in the form of organic manure can not only turn large volumes of animal excretions into organic manure,, but also reduce the use of chemical fertilizer and improve the yield, quality and physiological properties of peanut in red soil areas, which means a great augmentation of economic value and social benefit.

Abstract:Increasing atmospheric nitrogen (N) deposition can significantly change carbon (C) cycling rates and budget in the terrestrial ecosystem, and is generally considered to be an important pathway of missing of the sink. However, the contribution of atmospheric N deposition to C sequestration in the terrestrial ecosystem is controversial. It is, therefore, essential to accurately evaluate the effects of rate and type of N deposition on amount, composition and stability of soil organic carbon (SOC). Stable C isotope natural abundance (or δ¹³C) contains various information concerning C cycling processes, and hence makes it feasible to track SOC in its transfer, transformation and accumulation processes. The technique of Stable ¹³C natural abundance provides a way to characterize the dynamics of SOC with different turnover times. It is hypothesized in this study that N deposition increases biomass of plants and¹³C-depleted plant debris that leads to expansion of the fraction of coarse particle-sized SOC. Meanwhile, increased N deposition promotes activities of soil microbes, and increases emission of ¹³C-depleted CO2, thus leading to decrease in SOC content and accumulation of δ¹³C. Consequently, this study is mainly aimed at determination of the effects of rate and type of N deposition on contents of SOC and its various particle-size fractions in the soil and quantification of relative contributions of the changes in these fractions to the change in total under the condition of N accumulation. Through the above-described researches, it is expected a better in-depth knowledge could be obtained regarding mechanisms of the effects of N deposition on deposit and stability of SOC. For that end a controlled multi-form, low-rate N addition field experiment was conducted at the Haibei Alpine Meadow Ecosystem Research Station in 2007. The experiment was designed to have three types of N fertilizers, NH₄Cl, (NH₄)₄SO₄ and KNO₄, and four N application rates: 0, 10, 20 and 40 kg hm^-2 a^-1, and three replicates for each treatment. Soil samples, 10 in each treatment lot,were collected randomly with augers at 10cm intervals to a depth of 30 cm. A total of 1080 samples were collected in 2011 for determination of content and δ¹³C value of dissolved organic carbon, as well as contents of the three fractions of SOC: macro particle-sized organic carbon (MacroPOC, >250 μm), micro particle-sized organic carbon (MicroPOC, 53~250 μm) and mineral bonded organic carbon (MAOC, <53 μm). It was found that low N input significantly increased the contents of soil MacroPOC and MAOC, while high N input acted reversely; and N input, no matter high or low, decreased the content of MicroPOC. Besides, the effect of nitrate fertilizer was more significant than that of ammonium fertilizer. In short, For the entire soil profile, low N input increased the SOC storage in the 0～30cm soil layer by 4.5%, while medium or high N input decreased it by 5.4% or 8.8%, respectively. In the treatments of low N input, the increment of C consisted mainly of MicroPOC, while in the treatments of high N input, the decrement did mainly of MicroPOC, too. N application for 5 years in a row significantly promoted decomposition of the POC fraction of SOC, thus leading to increase in the proportion of stable fractions of SOC. The above-described findings indicate that N input may affect, increase or decrease, SOC storage in the alpine meadow, with the critical rate being set at 20 kg hm^-2 a^-1 while taking into account the ambient N deposition rate of 10 kg hm^-2 a^-1. Therefore, as long as the exogenous N input level is kept lower than this critical value, it is safe and beneficial to SOM accumulation in the alpine meadow on the Qinghai-Tibetan Plateau in the current period of time. These findings may serve as a theoretical basis for C and N management of alpine meadows in the future. Further study is still needed to explore microbial mechanisms of N input affecting SOC in quality and quantity.

Abstract:Black soil plays a crucial role in food security and sustainable development of the ecology in China. In the past 50 years the content of soil organic matter (SOM) in the black soil in Northeast of China has been decreasing, thus posing a critical problem of how to maintain its productivity, which has become a hot spot in agricultural science. Based on the long-term stationary fertilization field experiment, variation of soil fertility of and fertilizer efficiency in black soil as affected by long-term fertilization was explored and effects of long-term fertilization on content of soil labile organic matter and carbon pool management index were evaluated. This experiment was laid out in 1990 and designed to have 12 treatments, i.e. CK₀, CK, N, NP, NK, PK, NPK, SNPK, MNPK, MNPKW₂, 1.5MNPK and 2MNPK. All the treatments have the same cropping pattern, mono-cropping of maize, except for Treatment MNPKW₂, which follows a maize-maize-soybean rotation system. In 2013, soil samples were collected from the topsoil (0～20cm) layer for analysis of labile soil organic matter. Contents of three fractions of labile organic matter, namely highly labile organic matter (H-LOM), moderately-labile organic matter (M-LOM) and low-labile organic matter (L-LOM) were determined using 33 mmol L^-1, 167 mmol L^-1 and 333 mmol L^-1KMnO₄, respectively. Results show that contents of soil organic matter in all the fertilized treatments increased to a varying extent. Compared with the initial content (23.3 g kg^-1) of soil organic matter (SOM), it increased by 35.6% in Treatment CK₀ , by 10~15% in Treatments N, NP, NK, PK and NPK, the least in increment, by 20% in Treatment SPNK (NPK plus straw incorporation), and by 66.38 %~92.13 % in Treatments MNPK, MNPKW₂, 1.5MNPK and 2MNPK, the most significant increment. The content of H-LOM, M-LOM and L-LOM were 0.94~4.18 g kg^-1, 0.39~5.10 g kg^-1 and 2.45~11.36 g kg^-1, respectively, accounting for 4%~10%, 1.59%~10.28% and 8.71%~27.45% of the total organic matter, respectively. The content of H-LOM, M-LOM and L-LOM in organic fertilizers treatments, were higher than their corresponding ones in the other treatments, and the more the organic manure applied, the higher, the contents of SOM. The contents of the three fractions of SOM were low in mere chemical fertilizers treatments and Treatment CK, and did not vary much between those treatments. However, Treatment CK0 and Treatment MNPK did not differ much in content of H-LOM, M-LOM and L-LOM, suggesting that fallow had a significant SOM increasing effect. Carbon pool management index (CPMI) is an important parameter to characterize status of soil nutrients. Treatment CK0 did not have much improvement in CPMI of LOM), whereas Treatment 2MNPK exceeded 200, the highest among all the treatments. For M-LOM, CPMI was 22.08 in Treatment CK, lower than any other treatments. Compared with Treatment CK, Treatments N, NK, NP, and PK did not improve much in CPMI, but Treatments NPK, SNPK, MNPK, MNPKW₂, 1.5MNPK, 2MNPK and CK0 did quite significantly, with the highest CPMI being 176.64 in Treatment 2MNPK. On the whole, in terms of CPMI, the treatments followed an order of organic fertilizers > fallow land > straw incorporation> mere chemical fertilizers. For organic treatments, the more the organic manure applied, the higher the CPMI. CPMI was higher in Treatment MNPKW₂ than in Treatment MNPK, suggesting that the maize- maize- soybean rotation system is a good way to improve CPMI.

Abstract:Soil organic carbon (SOC) plays an important role in maintaining carbon pools in terrestrial ecosystems. Any of its subtle changes may cause great changes in the environment we live in. Therefore, dynamics of soil organic carbon mineralization is an issue of great significance in global climate change, because SOC mineralization plays a critical role in regulating CO₂ concentration in the atmosphere. There are a number of factors, such as soil temperature, soil structure, soil moisture, characteristics of soil micro-organisms and microbial communities, as well as quality and quantity of the substrate, that affect mineralization of SOC. However, human activities are the factor that may generate direct impact on the above-listed factors affecting SOC mineralization. In China, especially in South China where there are rich forest resources, silvicultural activities have a history of over 1 000 years. Although traditional silvicultural activities, such as clear-cutting and burning, are easier and faster, they cause a substantial loss and redistribution of soil organic carbon, while only trunks are harvested, leaving logging residues in the field can increase SOC content in the soil. Studies have been reported all over the world on SOC mineralization in forest soils, but little has been done on impact of silvicultural activities on SOC mineralization, especially at the early stage of silvicultural activities. This research project is oriented to explore effects of management of logging residues on soil organic carbon mineralization at the early stage of the silvicultural activities. The Chenda Town Forestry Farm in Fujian Province, Southeast China, was selected for this project. The farm had a tract of 36-year-old secondary Castanopsis carlesii forest, which was divided into three plots. Clear-cutting was done in Plots 1 and 2 with logging residues burnt in Plot 1 and left intact in Plot 2, and Plot 3 still had trees standing as Control (without clear-cutting). Soil samples were collected from the plots for incubation to determine mineralization of SOC. The first sampling occurred 6 months after burning of logging residues and the second did 18 months after burning. The incubation of soil samples lasted two months, each time. Though the two incubation experiments, results show that: 1, Management of logging residue managements had a significant impact on soil organic carbon mineralization, mainly through altering quality and quantity of the substrate. 2, After two incubations, Plot 1 was obviously lower than Plot 2 and Plot 3 in cumulative SOC mineralization in all soil layers; however, after the first incubation, Plot 2 was significantly lower than Plot 3 in cumulative SOC mineralization in all the soil layers, while after the second incubation, Plot 2 was much higher than Plot 3 in cumulative SOC mineralization in the 10~20 cm and 20~40 cm soil layers. And what is more, in Plot 2, the cumulative SOC mineralization after the second incubation was much higher than that after the first incubation or 57.0%, 112.0% and 49.9% higher in the 0~10, 10~20 and 20~40cm soil layers, respectively. However, there were no such variations in Plot 1 and Plot 3. 3, After both the first and second incubations, Plot 1 was 6.0% and 1.9%, respectively, lower than Plot 3 in organic carbon content in the 0~10cm soil layer, but Plot 2 was 15.6% and 25.0% higher, respectively, than Plot 3. In Plot 2, the contents of dissolvable organic carbon and microbial biomass carbon in all the soil layers were significantly higher after the second incubation than after the first incubation, while in Plot 1 they were in an opposite way. 4, Cumulative SOC mineralization was in significantly liner relationships with the initial contents of organic carbon, dissolvable organic carbon and microbial biomass carbon (p < 0.05), indicating that the latter three are the major factors affecting the former. 5, It can be concluded that the management of keeping logging residues in the field after clear-cutting is superior to that of burning the residues in many aspects at the early stage of silvicultural activities, for instance, it can raise quality and quantity of the substrate, and also raise the soil organic carbon stock.

Abstract:Stable isotope tracer techniques, especially the use of carbon and nitrogen stable isotopes have been extensively applied in agricultural chemistry, geochemistry, and environmental chemistry. Calibration of mass spectrometers for precision in analysis of carbon and nitrogen isotope ratios are directly related to the reliability of the tracer experiments. Currently, as reference materials enriched in carbon and nitrogen stable isotopes are not readily available for calibration, it is advisable to verify accuracy of the instruments and comparability of their analyses through comparison between laboratories in carbon and nitrogen isotope ratio detection capability. For that, in 2013, a total of 14 testing laboratories and a total of 17 sets of equipment all over the country were invited to participate in the comparison sponsored by the Institute of Soil Science, Chinese Academy of Sciences. Agricultural, ecological and environmental samples were used in the test for comparison. The institute also prepared a variety of test samples, including carbon and nitrogen-containing chemical fertilizers, soils and plant samples. For analysis of stable isotopes, samples natural in isotope abundance and different in isotope enrichment level were also prepared. Besides solid samples, there were 3 kinds of N₂O and CO₂ gas samples different in isotope abundance for analysis. The Z score method was used to measure reliability of the analysis in each laboratory. In this paper, comparisons between the 14 laboratories were summarized in 2013.

Abstract:Soil thickness generally refers to thickness of a solum or thickness of the effective soil layer, so it can intuitively express soil properties. On the basis of the work the predecessors have done in light of the definition of solum thickness and relevant criteria for partitioning solum thickness, the authors clarify the concept of solum from the perspective of pedogenesis and put forward some concrete soil thickness partitioning methods specific to soils different in soil type and in land use, while taking into account their own long-term field survey experience. Based on the newly proposed criteria for soil thickness partitioning, 16 soil profiles collected recently in the fields in Anhui, Hubei, Shandong, Qinghai, Gansu, Inner Mongolia and some other provinces were used as cases for soil thickness partitioning. The work may serve as reference for future researches on soil thickness in China.

Abstract:To explore differences between soil in open-field without salt accumulation and soil in greenhouse with salt accumulation in acidification, simulation of soil acidification and salt leaching was conducted of the soils for analysis of changes in soil acidity caused by salt leaching. Results showed that salt leaching lowered electric conductivity (EC), available Ca (A-Ca), exchangeable acid (EA), effective cation exchange capacity (CEC) and active manganese (Ac-Mn) significantly, had little effect on or increased active aluminium (Ac-Al) and iron (Ac-Fe), base saturation percentage (BSP) and pH significantly. The EA, Ac-Al and Ac-Fe increased significantly, while the Ac-Mn and CEC decreased significantly with a decrease in pH of soil with and without salt accumulation. Moreover, when a certain amount of EA appeared, BSP declined significantly with lowering pH. All these indicated that acidifications in the two soils are the same in nature, but when an equal amount of acid was added into the two soil, acidification of the plow layer of the soil with salt accumulated in greenhouse was accelerated, bringing about more severe acid damage and making the soil liable to have salt accumulation. It is, therefore, suggested that in managing soil acidification in greenhouses, it is essential to avoid introduction of more salt so as to prevent aggravation of salt damage.

Abstract:A total of 292 field experiments were laid out and conducted in different regions of Sichuan Province during the period of 2005-2009 to study effect of nitrogen (N) fertilization on rice relative to region, and further to specify features of the crop absorbing N and to lay down scientific basis for recommendation of N fertilization for rice. Results show that N application significantly increased rice yield by 22.4% in the Chengdu Plain (CP), by 33.7% in the hilly region of Central Sichuan (HCS), by 38.9% in the mountainous areas around the Sichuan basin (MAS) and by 33.1% in the mountainous area of Southwest Sichuan (MSWS), which shows that yield response of rice to N application varied with the region due to sharp differences between the regions in landform, climate and soil fertility, and hence in N absorption and utilization rate of the crop. N application increased N absorption per 100 kg grain by 0.19 kg. When N absorption of the crop reached 281.8 kg hm^-2, yield of the crop could be as high as 10.0 t hm^-2 in MSWS. In terms of average N recovery rate (REN) CP was the lowest (32.2%) and MAS the highest (36.7%). Agronomic efficiencies (AEN) of the regions varied from 11.5 to 14.4 kg kg^-1. Difference in landform between the regions is the major factor explaining the difference between the crops in different regions in N recovery rate. The findings of the study suggest that rational recommendation of N fertilization rate in light of landform of a region should be an effective way to improve N use efficiency of rice cultivation in Sichuan Province.

Abstract:Samples of undisturbed soil core were collected, 3 each, from a shrub patch and a grass patch in a tract of degraded sandy grassland encroached by shrub, Caragana microphylla Lam, in Taibus Banner of Inner Mongolia. Analysis of soil porosity is based on CT scanning and Fiji software. we analyze the pore parameters (such as porosity & equivalent diameter) with matlab based on 2D section images in every slice, and obtain trends of variations of pore parameters with depth. In additon, we can realize 3-D visualization of pores network with Fiji and qualitative description of soil pore distribution. Results show that shrub encroachment affected soil porosity and pore structure significantly. As a result, the soil in the shrub patch was much higher than that in the grass patch in total number of soil pores, number of macrospores (>1 000 μm), total porosity, macroporosity, and mean of equivalent pore diameter, and especially in mean macroporosity, the former was 3 times as high as the latter. In the grass patch, macropores were distributed mainly in the 0~50 mm soil layer, while in the shrub patch, they were found throughout the 0~400 mm soil layer, which is closely related to the well-developed root system of the shrubs.