Abstract:Soils developed from volcano ejecta in Changbai, Longgang and Kuandian were studied for description of morphological properties of the soils and for determination of pH, organic carbon, phosphate retention, iron-aluminium oxides and volcanic glass. Besides, diagnostic horizons, diagnostic characteristics and taxonomy of the soils were discussed in reference to according to the principles and methods of the “Keys to Chinese Soil Taxonomy (3rd ed) and the “Keys to US Soil Taxonomy (The USA 11th ed)”. Results show that soils developed from volcano ejecta should not necessarily be classified as Andosols. The soil on the top of the volcanic cone, Tianchi of the Changbai mountain is poorly developed and should be classified as Primosols, while the soil at the foot of the cone is well-structured and characterized by volcanic ash and hence should be classified as Andosols. The soils on top of the Qingyi mountain in Kuandian and at the foot of the Longgang maintain all display features of volcanic ash and should be classified as Andosols. The soil at the foot of the Dachuantou maintain in Kuandian falls short of the index of volcanic ash in content of 0.02~2 mm particles, but it displays a clear Cambic horizon, so it should be classified as Cambosols.

Abstract:According to the "Chinese Soil Taxonomy ( 3rd ed) " and " Principles and Criteria for Establishment of Soil Family and Soil Series of Chinese Soil Taxonomy (The trial version) ", the 7 types of salt-affected soils in North Hebei were classified into 7 newly established soil series, under 7 Subgroups, 6 Groups, 6 Suborders and 4 Orders. Results show that referencing comparison between CST and CSGC at the subgroup level did not find that they had any correspondences in CSGC; the classification of some of these soils in CST did not reflect any characteristics of salinity or alkality in their respective higher-level unit, while some amendments had to be made to salt content and position of salt accumulation for classification at the base level, which indicates that the criteria for sorting in the soil taxonomy are stricter and more standard. Besides, issues like diagnostic horizons, diagnostic characteristics and soil analysis methods for classification of salt-affected soils were discussed.

Abstract:To elucidate diagnostic horizon characteristics of the soils derived from loess in subtropical environment on the southern slope of the Qinling Maintains and their significance in soil classification, a soil profile was selected on the first fluvial terrace in Qianfang Village of Yunxuan County, the upper reaches of the Hanjiang River, for investigation of profile structure and analysis of particle-size distribution, magnetic susceptibility, major elements, minerals and mcromorphology. Results show that the soil distributed in the Hanjiang River Valley has an A-AB-Bt₁-Bt₂-BC-C profile structure. The 90～230cm horizon (Bt) of the soil profile is clayey loam in texture and prismatic-bloky and compact in structure, and its structural planes are covered with red brown Fe-Mn clay cutan. Microscopic observation reveals that this horizon is dominated with illuvial clay, mostly in the form of cutan and various shapes of optically oriented fibrous clays, too. Its clay (<2μm) content reaches 18.81%, which is 1.76 times that in the overlying leached layer (10.70%), and 12.57 times that in the underlying parent material layer (7.32%), suggesting that the Bt horizon features an Argic horizon and the diagnostic characteristics of a clay pan and is comparable with the typical Calypani-Udic Argosols in China in argillization degree. Its clay minerals are dominated by illite and some kaolinite. The soil is still at its late decalcification stage of the weathering process, has not yet any significant sign of allitization, and is moderately weathered. The soil can be sorted as Calypani-Udic Argosol.

Abstract:By means of triaxial shearing test in laboratory, effect of the interaction of soil water content and bulk density on soil shearing strength in yellow soil, calcareous purple soil and neutral purple soil was explored. The three types of soils are extensively distributed in the hilly regions of Chongqing. Dynamics of the soil shearing strengths of the three types of soils under wetting-drying alternation were analyzed, using soil samples adjusted to be optimal in soil water content and bulk density specific of the three soils, separately, based on the analysis of effect of soil water content and bulk density on soil shearing strength. Results show that the soil cohesive force first increased and then decreased with the increasing soil water content in all the three soils unchanged in soil bulk density, and it increased with the increasing soil bulk density in the soils the same in soil water content. Internal frictional angle decreased significantly with the increasing soil water content in all the three soils, regardless of bulk density. The interaction of soil water content and bulk density affected soil cohesive force significantly, which increased with increasing soil bulk density in the range of 1.3~1.7 g cm^-3, and would peak when bulk density interacted with a matching soil water content. The interaction did not have much effect on internal frictional angle, which did not vary much when bulk density remained the same, but increased gradually with increasing soil bulk density. In all the three soils, soil cohesive force decreased with increasing number of wetting-drying alternations, and it dropped sharply in the first 2 cycles of wetting and drying and very slowly during the following three cycles, and then leveled off. Internal frictional angle as a whole decreased with increasing number of wetting-drying alternations in all the three soils, however, differences were found between the soils different in soil type. The angle was 24.6°, 22.6° and 19.3° in yellow soil, neutral purple soil and calcareous purple soil, respectively after the fifth cycle of wetting-drying alternation.

Abstract:Soil detachment is an unavoidable path and important process of slope soil erosion and sediment yield. Precise prediction of the process of soil detachment is of great significance to the consummation of a physical model for soil erosion. A runoff scouring experiment, designed to have a hydraulic flume, of which the slope gradient is adjustable with the range of 8.8% ~ 46.6%, and various flows (0.5 ~2.5 L s^-1) was carried out to study relationships of soil detachment rate with slope, flow, shear stress, stream power and unit stream power on yellow soil slopes in Southwest regions, and difference between yellow soil and loess in soil detachment rate in the case of the same flow rate and typical slope of the regions. Results show that the soil detachment rate of yellow soil in the Southwest region increases with the flow and slope. Multiple regression analysis of the slopes and flows may be used to predict detachment rate of the soil very well (R²=0.9). Stream power and unit stream power both display good power function relationships with soil detachment rate of the yellow soil, with determination coefficient(R²) being 0.83 and 0.79, respectively. However, flow shear stress is not a good factor to predict soil detachment rate (R²=0.18). In Loess, the soil detachment rate is obviously higher than in yellow soil, and the difference between the two soils in soil detachment rate widens with increasing slope scouring flow. Although flow, slope, stream power and unit stream power all can be used to predict soil detachment rate, and their regression equation differ slightly from those in other domestic researches, the coefficients that characterize soil erodibility in the equations differ sharply, which reflects the particularity of the soil erosion process of yellow soil being affected by runoff.

Abstract:The aims of this study were to explore the evolution of pH in topsoils under long-term different fertilization regimes, and further to understand the mechanisms and methods against soil acidification in croplands. We collected historical data on six 18–30 years long-term fertilization experiments in typical Chinese croplands of red soil in Qiyang and Jinxian, purple soil in Chongqing, black soil in Gongzhuling and Harbin with conventional and high fertilization rates, and then analyzed the differences in soil pH and acidification rate among experimental stages (six years each) and treatments, i.e., no-fertilizer control (CK), sole chemical nitrogen fertilizer (N), chemical nitrogen plus phosphorous and potassium fertilizers (NPK) and NPK fertilizers amended with manure (NPKM). Results show that under control, topsoil pHs declined somewhat and acidification rates averaged 0.013 pH a ^-1. Under the N treatment, topsoil pHs of the experiments in Qiyang, Gongzhuling and Harbin with conventional fertilization rate were lowered by 0.32–0.55 units at the initial 6 years and all the experiments by 0.64–1.46 units at the recent 6 years as compared with those under control. Topsoil pHs under the NPK treatment were obviously lower than those under the N treatment over the 1–12 years experimental period. However, topsoil pHs under the NPKM treatment were 0.30–0.53 units higher than those under the NPK treatment, and the two had a similar pH evolution curve. Paired T test between the treatments shows that in terms of soil acidification rate, the treatments followed the order of N > NPK > NPKM ≈ CK. The mean soil acidification rate under the N and NPK treatments was 4.6 and 3.2 times, respectively as high as that under control. Taking well-drained upland or upland-paddy rotation croplands in the humid or semi-humid zone as examples, the processes of soil acidification in the croplands were analyzed. The evolution of pH in topsoils of croplands was characterized as a common response to fertilization, regardless of certain regional differences.

Abstract:A total of 10 groups of field trials on N fertilizer application rate for winter oilseed rape were conducted in the main production areas of Jiangsu and Zhejiang provinces in 2008-2009 and 2009-2010 to explore responses of the crop in seed yield, dry biomass, N uptake and accumulation, and N fertilizer use efficiency, for modeling of appropriate N fertilizer application rate under the current production condition. Results show that the crop responded significantly to N fertilization in seed yield. When 270 kg N hm^-2 was applied, the mean yield was increased by 1 265 kg hm^-2 or 121% over the control (treatment without N fertilization), reaching as high as 2 581 kg hm^-2. Nitrogen fertilization also improved considerably shoot biomass, N uptake and accumulation of the plant. However, excessive N fertilization led to decline in harvest index and N harvest index of the crop, and hence in the N fertilizer use efficiency. The regional mean optimal N fertilizer application rate (RMONR) was 199 kg hm^-2 under current production condition in our study. The use of the average may not only reduce by a large margin the use of N fertilizer, but also ensure a relatively higher regional rapeseed yield level and N fertilizer use efficiency level. Hence, the currently recommended N application rate, N 200 kg hm^-2, is appropriate and may be subject to slight adjustment in light of the specific conditions of a region or field.

Abstract:In order to explore effects of tillage on dynamics of soil water and salt in saline-alkali soils in the Hetao Irrigation District in Inner Mongolia, a micro-plot field experiment, designed to have four treatments, i.e. Treatment T (tillage), Treatment P (plastic mulching), Treatment S (deep burial of straw) and Treatment P S (plastic mulching plus straw burial), was conducted over a whole sunflower growing period. Results show that Treatment P S not only significantly enhanced water storage capacity of the 0~40 cm soil layer, but also continuously preserve soil moisture. Soil water content of the 0~40 cm soil layer was 5.13%, 3.49% and 1.99% higher in Treatment P S than in Treatments T, P and S before sowing, respectively. Compared to Treatment T, P and S, Treatment P S increased water content of the soil layer by 5.01%, 5.87% and 2.70%, respectively, at the early growing period, and by 7.53%, 11.02% and 6.16%, respectively, at the medium growing period. Moreover, Treatment P S displayed significant long-term effect of suppressing and controlling soil salt in the soil layer. Soil salt content was 18.37%, 20.33% and 1.90% lower in Treatment P S than Treatment T, P and S before sowing, respectively, 45.46%, 37.63% and 39.67% lower in the early growing period, 17.89%, 29.77% and 37.22% lower in the middle growing period, and 14.46%, 13.90% and 19.88% in the later growing period, respectively. In addition, Treatment P S significantly reduced salt accumulation per unit volume of soil, showing a significant effect of desalinizing the soil, particularly the plough layer. The above findings suggest that Treatment P S is an optimal option to regulate and optimize the distribution of soil water and salt, and create a suitable soil environment for better growing of sunflower.

Abstract:The Dual Probe Heat Pulse (DPHP) method is an important method to measure specific heat (c), thermal conductivity (λ) and temperature ( T ) of soil. However, there are a number of factors that may cause errors in measurement of bothλλ and c using DPHP, such as soil pores. With finite element method (FEM) simulating DPHP experiments ,three kinds of quartz sands which different in particle size were used to analyze the effect of soil pores on measurement of specific heat with the DPHP method, and the result shows that (1) soil pores caused significant anisotropy of spatial distribution of measured temperatures and led to a relative difference, reaching as high as 23% in c measured between different spots 6mm away from the heater in different directions; (2) the standard deviation of the measurement of the soil thermal properties with DPHP increased with the increasing particle size, which was consistent with the observation during the experiments; and (3) the existence of soil pores led to overestimation of c when the DPHP method was used. In this simulation, the specific heat measured at 6 mm away from the heater was overestimated by about 6%.

Abstract:By means of air oxidation electrochemical real-time monitoring, and X-ray diffraction (XRD), transmission electron microscope (TEM) and solution analysis, synthesis, oxidation and crystallization of hydroxycarbonate green rust GR1(CO₃²⁻) were investigated. At the synthesis stage when pH of the suspension drops to the lowest or the ratio of n(Fe² )/n(Fe_total) in mineral rises to the highest, GR1(CO₃²⁻) is formed completely. At the transformation stage when pH is controlld within the range of 6.5~10 at 25 ℃, with the rising pH, both the transformation rate and oxidation rate of GR1(CO₃²⁻) decreases, with its oxidate turning from lepidocrocite to goethite and magnetite, and the goethite crystallites increasing in size. When temperature of the suspension is controlled within the range of 15~45 ℃, with the rising reaction temperature, the transformation rate of GR1(CO₃²⁻) increases while oxidation rate decreases, with its oxidate turning from lepidocrocite to goethite and magnetite, and the goethite crystallizes increasing in size. When airflow is controlled in the range of 0 ~ 0.1 m³h^-1 at 25 ℃, with the increasing airflow rate, the oxidation rate increases, with its oxidate gradually turning from goethite to lepidocrocite and decreasing in crystallinity. Therefore, oxidation rate is a determining factor in the transformation of GR1(CO₃²⁻) under the influences of pH, temperature and airflow rate. With increasing oxidation rate, oxidate of the reaction turns from magnetite to goethite to lepidocrocite, and decreases in size of the crystallites and in crystallinity.

Abstract:Currently sustainable development of the rice cultivation in China is confronted with a series of problems, among which high N fertilization rate and low use efficiency of N fertilizer is one. Pathways of N loss are closely related to transformation processes of the fertilizer after it is applied into the soil. A better knowledge and quantitative description of the transformation processes in paddy soil would help understand how N is lost in the rice-wheat rotation system. For that, a 2-year field experiment was carried out in a paddy field of alkaline paddy soil (Chaohuang Tu, pH=8.3) in Huai’an, North Jiangsu and a paddy field of neutral soil (Huangni Tu, pH=6.2) in Yixing, South Jiangsu to determine crop N recovery rate. At the same time, an in-lab aerobic incubation was conducted to reckon primary N mineralization and nitrification rates in the two paddy soils, using the ¹⁵N isotope dilution method, so as to further explain causes to the difference in N use efficiency between the two soils in the experiment. The field experiment shows that to achieve similar crop yields, the alkaline paddy soil required a higher rate of N fertilizer than the neutral paddy soil, but was lower in fertilizer N use efficacy (FNUE). The incubation experiment shows that, both the gross N mineralization and nitrification rates were higher in Chaohuang Tu than in Huangni Tu, which may be attributed to the higher pH in the former. Higher N mineralization and nitrification rates may lead to temporary accumulation of NO₃⁻-N, which can not be absorbed immediately by plants and then gets lost via a series of pathways. This may be one of the causes that lead to differences in FNUE between the two fields.

Abstract:Using the new high-throughput sequencing technique, study was carried out on responses to elevated CO₂ (e CO₂) of endophytic bacteria at the whole microbial community level in the roots of ZhenXian-96 (ZX-96), YangDao-8 (YD-8), II You-084 (TY-084), and YangLiangYou-6 (YLY-6), commonly used in the FACE experiment in China. Results show that the family of Enterobacteriaceae within the class of γ-proteobacteria was the highest in relative abundance, accounting for 30.8%~59.8% of the whole community. In ZX-96, YD-8, and TY-084，e CO₂ would probably inhibit growth of the microbial groups that are dominant in population (dominant groups) but stimulate growth of those that are less (rare groups). For instance, in rice TY-084, Enterobacteriaceae, Pseudomonadaceae, Xanthomonadaceae, and Aeromonadaceae were the four dominant bacterial groups, of which each exceeded 14.6% in relative abundance, and their total relative abundance declined from 74.8% to 67.2% under e CO₂. On the contrary, the rare groups in the roots, consisting of Sphingobacteriaceae, Comamonadaceae, Flavobacteriaceae, and Oxalobacteraceae, increased from 4.13% to 16.9% in total. Especially the family of Sphingobacteriaceae increased by up to 344 folds, and hence is the microbial group the most sensitive to e CO₂. However, in YLY-6, the responses of endophytic bacteria differed in pattern from those in other varieties of rice. These findings indicate that relative abundance of microbes may probably be an important factor affecting the response of endophytic bacteria in the roots to elevated CO₂, which may be used as certain basis for the study on variation of structure and function of the whole microbial community in response to the global climate change.

Abstract:Illustrating mechanisms of N₂O generation in and emissions of CO₂ and CH₄ from the soil could help us design greenhouse gas mitigation strategies. An experiment was carried out in fields of acid red soil different in land use, i.e. vegetable garden, paddy field, tea garden and forest in Jinjing river region, Changsha, to study effects of application of carbon, nitrogen and nitrification inhibitor on N₂O, CO₂ and CH₄ emissions under constant temperature and soil moisture, using the static incubation-gas chromatograph method. Results show that less N₂O emission was observed from the acid red soil, low in pH, after application of N fertilizer; the addition of glucose stimulated N₂O emission from the soil applied with urea and from soil denitrification. Heterotrophic nitrification might be the main pathway of N₂O generation in acid red soil and nitrification inhibitor Dicyandiamide (DCD) had no significant effect on N₂O reduction in the acid red soil. In terms of total N₂O emission from the soil applied with N and C, the fields different in land use followed the the order of tea garden > vegetable garden > paddy field > forest land. Extraneous organic carbon could significantly stimulate soil CO₂ emission from the four fields, showing an order of tea garden and paddy field > vegetable garden and forest land, but did not have mucheffect on CH₄ emission in all the four fields except paddy field.

Abstract:A stationary field experiment was conducted in an oasis along the Manas River, which is a typical inland river in the arid region of Northwest China to study effects of reclamation history of deserted salinized farmlands on labile organic carbon composition and aggregate stability of the soils. Results show that soil microbial biomass C (MBC) and soil labile carbon (LOC) decreased somewhat in content in the first years after the reclamation. And then soil organic carbon (SOC), especially MBC and LOC, increased in content and soil water soluble organic carbon (WSOC) and hot-water soluble organic carbon (HWSOC) in content and in proportion as well, in the years that followed. In the 1st, 5th, and 10th year after the reclamation, soil hot-water soluble organic carbon (HWSOC) in the field was 61.04%, 143.5% and 132.4%, respectively, higher than that in the control. After years of continuous cultivation, SOC and soil macroaggregate (＞0.25 mm) increased in content and the latter in stability, too. In the field 10 years old in reclamation history, soil aggregate (＞0.25 mm) accounted for 57.30% and 56.50%, respectively, in the 0~5 cm and 5~10 cm soil layer, but the aggregate index decreased to 43.00%. Correlation analysis shows that the content of soil water-stable aggregate (＞0.25 mm ) was significantly positively related to SOC and HWSOC and the contribution of the latter is significant to maintaining the stability of soil aggregates in salinized oasis farm fields in the arid region.

Abstract:Polycyclic aromatic hydrocarbons (PAHs) are a group of chemicals with potential carcinogenic, teratogenic and mutagenic effects, and are mainly produced out of incomplete combustion of biomass and fossil fuel. Excessive PAHs releasing into the atmosphere may accumulate in the soil through deposition, resulting in soil pollution. Currently the techniques available for bioremediation of PAHs-contaminated soils are mostly based on the degradation function of bacteria, while the potential of fungi in soil remediation is not yet fully understood. Fungi are important components of the soil ecosystem and extremely high in diversity. Quite a number of strains of fungi, mainly Basidiomycete and Ascomycete, are capable of degrading PAHs with their intracellular cytochrome P450 or extracellular ligninolytic enzymes. And some form Mycorrhizal symbiont with plant roots, which may degrade PAHs synergistically. Thanks to the feature of fungi degrading PAHs, they have their unique advantage in reducing the concentration and ecotoxicity of PAHs in soil. In this review, an overall introduction is presented to the diversity of PAHs-degrading fungi, and their PAHs-degrading mechanism, as well as the fungal remediation techniques currently available. In addition, the concerns and problems associated with fungal remediation are discussed and prospect of its development is predicted.

Abstract:Carbohydrates are readily biodegradable substrates, though accounting only for 10%~20% of soil organic matter (SOM), they are considered as an important indicator in the research of SOM and soil properties. Soil carbohydrates, including monosaccharides, disaccharides, polysaccharides and sugar derivatives, are essential components of and energy sources for microorganisms in soil. Polysaccharides are also important binding material for the formation of soil aggregates. Neutral sugar is commonly used to evaluate stability of SOM, while the amino sugar is used to predict C source from microorganisms in SOM. The processes of absorption and conversion of carbohydrates were related to structure of soil microbial community and biomass of soil microorganisms. Monosaccharides and disaccharides are generally assimilated by bacteria firstly, while polysaccharides are hydrolyzed into simple sugars by fungi. Decomposition of SOM is closely related to distribution of carbohydrates in soil fractions as well as their combination with mineral particles. The turnover of SOM, which including microbial, chemical and physical processes, is very complicated, however, all these processes can be boiled down to the dynamical process of carbohydrates partly. The accumulation of carbohydrates in soil is also affected by soil microorganisms, and fungi and G bacteria are much more conducive to the accumulation of carbohydrates. The effects of soil tillage and fertilization on carbohydrates depend on the content of SOM. This paper reviewed the factors that affect the distribution and transformation of carbohydrates and pointed out future direction of the research on soil carbohydrates.

Abstract:Soil organic matter (SOM) plays a vital role in long-term carbon sequestration in forest soil systems. A stable SOM pool consists of various recalcitrant biomacromolecules which mainly come from plants, animals, fungi and bacteria. These plant- or microbe-derived organic matters in the soil have their own source-specific natural biomarkers. A review is presented here of the advancement in the research on application of plant biomarkers to the study on soil carbon recycling in the past two decades, briefing on application of plant biomarkers to determination of plant sources and decomposition degree of SOM, and introducing application of stable isotopes of plant biomarkers to quantitatively estimating cycling time of SOM. Besides, the review also introduces in detail methods for chemical analysis of plant biomarkers in the soil. Therefore, the review may serve as reference for future studies on application of plant biomarkers to researches on SOM in China.

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