Abstract:In the light of the development of agricultural research, especially soil science, at the current stage of China’s development, the related research achievements on low-yield fields at home and abroad are summarized. The definition, status, negative effects, causes and main limitations of low-yield fields are systematically analyzed. The increasing grain production potential is preliminarily estimated from the improvement of low-yield fields. The “low-yield fields” can be defined as those in which existing limitations cause poor crop growth and thus have 30% lower yields than fields with local high-yields. They have large annual variations in yield under normal tillage cultivation management. The low-yield fields in China are characterized by having large areas, more types of low-yield fields, a relatively concentrated distribution and more apparent yield limitations. The main limitations in low-yield fields include low organic matter and low and unbalanced nutrient concentrations, soil acidification, soil salinization, desertification, soil hardening, soil gleyization, erosion, and severe drought. Finally, further research topics and suggestions, based upon different policies and strategies to support the reclamation of low-yield fields, are proposed.

Abstract:Microbe drives biogeochemical cycling of elements on Earth. Being the fourth most abundant element on earth and the most frequently utilized transition metal in the biosphere, iron (Fe) naturally undergoes active reactions between ferrous and ferric states in circumneutral-pH or acid environment. Due to instability of dissolved Fe(Ⅱ) and adsorptive capability of insoluble Fe(Ⅲ) compounds, active Fe cycling exerts a strong influence on soil geochemistry. Advances in geo-microbiology have transformed our understanding of the edaphic iron cycling from mere physico-chemical reaction to biogeochemical process over the past three decades. Fe ion, undergoing active oxidation-reduction reactions in all life forms, is required asan integral component in cellular processes. And it has been demonstrated that phylogenetically diverse groups of microbes can grow either aerobically or anaerobically using Fe as electron donor or electron acceptor to generate energy from Fe reduction and Fe oxidation in vitro or in vivo. In recent years, significant progresses have been made toward understanding the biochemical mechanisms of microorganisms catalyzing anaerobic reduction of Fe(Ⅲ) in the circumneutral pH environment. Shewanella and Geobacter are the two model organisms commonly used in studyingmechanisms of Fe-reduction, and the use of insoluble ferric oxyhydroxide minerals as terminal electron acceptors in anaerobic respiration through extracellular electron transfer (dissimilatory Fe(Ⅲ) reduction). Comparatively little information is available on mechanisms of Fe(Ⅱ) oxidation at neutral pH conditions. Microaerobic Fe(Ⅱ)-oxidizers, such as Gallionella andLeptothrix, active at circumneutral pH, could compete with O2 in abiotic oxidation of Fe(Ⅱ), forming Fe(Ⅲ) oxide encrustation specific to the oxic-anoxic interface of soil. Fe-oxidizing microbes are not limited to aerobic habitats, but can also oxidize iron under anaerobicconditions using NO3−[nitrate-dependent Fe(Ⅱ)oxidation], or CO2[phototrophic Fe(Ⅱ)oxidation] as the terminal electron acceptor. The microbial Fe(Ⅱ)-Fe(Ⅲ) wheel promotesvarious environmental or ecosystem processes, such as nutrient cycling and contaminant transformation, at the water-soil interphase. It is worthwhile to note that in anaerobic environments, microbial Fe(Ⅲ) reduction is an important pathwayof anaerobic degradation of organic matter. Besides, dissimilatory Fe(Ⅲ) reduction is a key process governing reduction of humic substances, reductive dechlorination and metals reduction. Furthermore, Fe(Ⅲ)-reducing bacteria successfully outcompetemethanogenenic bacteria for H₂ as an energy source, which results in dropping of methane production in soil of high organic matter content. Fe(Ⅱ)-oxidizing microbes have been demonstrated to oxidize both soluble and insoluble Fe(Ⅱ), producing a variety of insoluble Fe(Ⅲ) mineral products. Owing to their high affinity on surface, bacteriogenic iron oxides are ameliorating agents and geochemical barriers for fixing heavy elements, thus generating a major influence on release, transport, immobilization and bioavailability of heavy metals in soil. As a whole, it is apparent that iron biogeochemical cyclingistightly linked to organic matter degradation, denitrification, methane production and metal immobilization, which is one of the most important issues in environmental science.The processes driving iron cycling are not instantaneous, and Fe(Ⅲ) reduction and Fe(Ⅱ) oxidation occur simultaneously in adjacent (micro-scale) locations. Dissimilatory iron-reducing bacteria are found capable of excreting Fe(Ⅲ), resulting in anaerobic reduction of iron oxides in soil. Fe(Ⅱ) species in soils is usually soluble and highly mobile, and able to act as an electron donor for iron oxidizing bacteria. Thus, it is re-oxidized to Fe(Ⅲ), forming secondary iron minerals. So far, it is less understood that the key factors which control Fe-cyclingatcircumneutral pH include local gradients of oxygen, light, nitrate and ferrous iron. And recent researches have demonstrated that environmental organic matter, such as lactate, plays an important role in the transition of Fe(Ⅲ) reduction and Fe(Ⅱ) oxidation. To sum up, in the paper, the authors highlight the process, mechanism and environmental significance of microbe-mediated iron biogeochemical cycling, particularly in circumneutral pH environment that prevailsin soil, and also demonstrate the coupling relationship between iron and other related elements in biogeochemical cycling. Furthermore, the authors discussed key factors controlling shift between Fe(Ⅱ) oxidation and Fe(Ⅲ) reduction. In the end, the authors present their outlook about priority direction of the research on biogeochemical cycling of Fe in soil environment.This review is believed to be conducive to understanding of iron biogeochemical processes in the environment and formation of new strategies for sustainable rational utilization of the soil resources in China.

Abstract:Six field investigation sites in Meihekou City, Jilin Province, which were also covered by the first national water conservancy survey of China for water erosion survey, were chosen as typical research sites in the study on development of gully erosion and its influencing factors in hilly regions with cultivated slope land in Northeast China, using field investigations coupled with geographical information technology (GIS). As results show, (1) in the six investigation units, 142.9 hm²in total area, 93 erosion gullies were found, making up 5 476 m in length, 3.83 km km^-2 in gully density and 4 575 m³ in gross erosion, and accounting for 61.03% of the total valleys in length and 92.35% of the gross erosion of the region; (2) gully erosion was quite severe in the study region, of which Xiaoyang Township, Hongmei Town, Shuangxing Township and Yizuoying Town fell into the category of “Severe” in gully erosion intensity, with gully density reaching 7.12, 4.63, 5.55 and 4.25 km km^-2 respectively, Niuxinding Town and Hailong Town was sorted into the category of “Strong” and “Moderate”, respectively; (3) slope gradient was a critical factor of the development of gully erosion in cultivated slope land and in significant linear relationship with gully density with correlation coefficient being 0.71 (p<0.05). The greatest gully density appeared on a slope with gradient > 8°; (4) with a slope extending on and on, gully density increased first and then gradually decreased, that is, peaking when a slope varied in the range of 200 ~ 299 m in length, and declining gradually when a slope was longer than 500 m; (5) gully density was quite closely related to the length / width ratio, with correlation coefficient being 0.83 (p<0.05) and it decreased with the length / width ratio increasing.

Abstract:To tackle the problems, such as declining soil organic matter content and degrading farmland quality in the black soil region of Jilin Province, soil samples were collected from a 20-year long-term stationary field experiment on fertilization at the Gongzhuling National Black Soil Fertility and Fertilization Efficiency Monitoring Base for analysis of composition and morphological structure of soil humus by means of modern analytical methods, like NMR Spectroscopy and IR Spectroscopy and exploration of their dynamic variation as affected by fertilization method. It was found that fertilization methods had some significant effects on characteristics of soil humus in cultivated layers. In the field experiment, the component of aliphatic structure in soil humic acid (HA) increased significantly in Treatment S+NPK (conventional NPK plus incorporation of corn stalks) and Treatment M NPK R (conventional NPK plus organic manure and crop rotation; the content of oxhydryl in soil HA increased obviously in Treatment M NPK (conventional NPK plus organic manure) the content of free carboxyl increased too in Treatment S NPK; the component of methyl, methylene and methenyl structures in fulvic acid (FA) increased obviously and free carboxyl did too in Treatments S NPK, M NPK and M NPK R; and inorganic carbonate and silicate increased in the FAs exacted from the soil of Treatment NPK, which means long-term application of chemical fertilizer may cause reduction of free FAs and exhaustive utilization of soil may lead to increase in FA of iron- and copper-bounded or complexed form. Obviously, fertilization methods vary in effect on elemental composition of HA and FA in black soil, and nevertheless all of them reduce HA C content and increase HA N content and FA C, FA N and FA H contents and reduce FA O content. Treatments F (fallow) and M NPK R increased soil HA N content the most significantly, while Treatments F and S NPK reduced soil HA C content the most significantly. Compared with CK, Treatment F reduced soil HA H content markedly, while all the other treatments increased the content markedly. F fertilization, regardless of method, reduced of oxidation degree of soil FAs. Obviously Treatments F, M NPK R, M NPK were better than treatment NPK in adjusting C, H, O and N components in soil FAs. It is, therefore, concluded that elemental composition of soil humus can be regulated by using different fertilization methods.

Abstract:Soil, as a natural resource essential to human survival, can provide people with food and fiber they need in their daily life and production. In recent years of rapid economic development, people over-exploit the land and apply irrationally fertilizers, thus triggering a series of problems, like land degradation, reduced grain output, food security and so on, which in turn threatens sustainable development of the human society. Therefore, soil amelioration has become a problem attracting extensive concerns and discussions the world over. Corn stalk is a renewable kind of resource, rich in supply and ready for direct use. Northeast China is a major corn producing region of the country and turns out every year large volumes of corn stalk, which unfortunately is either used as cooking fuel or just burnt in the field, thus leading to a great waste of organic resource and pollution of the environment as well. In the case that the soil urgently needs fertilizing and mechanical farming improving, the practice of deep application of corn stalk is recommended to be an important measure to improve soil fertility, increase soil organic matter, and hence to promote agricultural production and guarantee people’s life. Soil organic matter is a key factor of fertile farmland and humic substances are important components of organic matter and considered to be the most abundant organic ingredients of the nature, and they play a critical role in the ecosystem. Humic substances can be classified, according to their solubility, into humic acid (HA), fulvic acid (FA) and humin (Hu). HA is a kind of polymer compound, complex in structure and soluble in base solution, but not in water or acid. HA is also an important extract of humus. From a field of Cinnamon soil fertilized for 3 years in a field experiment base in Xokoumo Village, Fuxin Mongolia Autonomous County, Liaoning Province, soil samples were collected in October 2012. The field experiment was designed to have two treatments, CK (no stalk applied) and CS (stalk applied at a rate of 24 000kg hm^-2). Each treatment had three randomly-selected sampling points, from which soil samples were gathered at 0~20 cm and 20~40 cm for analysis in lab. Water-soluble substances (WSS), humic acid (HA), fulvic acid (FA) and humin (Hu) were extracted using the modified humus component extraction method to explore effects of deep applied corn stalk on content of organic carbon in various humus components in the soil. Solid HA was extracted from the soil as samples for characterization of its structure through elemental composition analysis, differential thermal analysis and infrared spectral analysis. Results show that deep-applied corn stalk helped increase the content of organic carbon in the surface soil and in WSS, HA, FA and Hu therein, by 33.13%, 28.57%, 11.33%, 9.57% and 18.58%, respectively. It raised, somewhat, the content of organic carbon in WSS too, but reduced the content in HA and Hu in the subsurface soil; it lowered the relative contents of WSS, FA and HA in the surface soil to a varying extent, but did not vary much. The relative contents of all of them except WSS in the subsurface soil, to a varying degree; PQ values of the surface and subsurface soils did not vary much; From the perspective of element composition analysis, it is generally held that H/C and O/C are the factors characterizing condensation and oxidation levels of HA. Compared with CK, Treatment CS was relatively lower in H/C of HA in the surface and subsurface soil, indicating that deep-applied corn stalk raises the condensation degree of HA and complicates its molecular structure, and Treatment CS was higher in O/C of HA in the surface soil but lower in the subsurface soil, indicating that the application of corn stalk intensifies HA oxidation in surface soil, but lessens the reaction in the subsurface soil; The differential thermal analysis shows that the high/medium temperature values in exotherm and weight loss of HA in the surface and subsurface soils both went up, indicating that HA increases its aromatic structure and improves its thermal stability relatively; The infrared spectrum analysis shows that deep-applied corn stalk intensified C = O stretching vibration of HA carboxyl, C = C stretching vibration of aroma and C - O stretching vibration of aromatic ester, and moreover, the semi-quantity system analysis reveals that the 2920/1620 value was higher in CS than in CK, indicating that newly formed HA has strong aliphatic nature.

Abstract:Purple soil is an important type of soil resource, occupying an important position in agricultural production in China. The soil column leaching method was used in this experiment to explore effects of nitrogen fertilizer on purple soil surface electrochemical properties relative to type of the fertilizer and on nitrogen balance in the soil-crop system. Results show that compared with the original soil, purple soils in all fertilization treatments increased in surface charge by 0.05 ~ 0.7 cmol kg^-1; the treatments low in nitrogen level (100 and 200 mg kg^-1) displayed an order of Treatments U (Urea) > Treatments AS (ammonium sulfate) > Treatments AN (ammonium nitrate) in , surface charge; while the treatments high in nitrogen level (300 and 400 mg kg^-1) did a different order of Treatments AS > Treatments U > Treatments AN; purple soils in all the treatments increased in specific surface area, particularly in Treatment N1 (100 mg kg^-1 urea) being 78.04% higher than in CK; the effect of urea was much higher than the other two; Treatment L4 (400 mg kg^-1 ammonium sulfate) was the lowest in the effect, being only 0.06% higher; among the treatments the same in N level, Treatment AS was the highest in both surface charge density and electric field strength, while Treatment U the lowest; the effect was apparently higher in treatments low in N level than in treatments high in N level. Obviously, N fertilizers, different in type and application rate, varied in type and concentration of electrolyte, thus leading to change in soil pH and eventually in soil electrochemical properties and hence in soil nutrient holding capacity and nutrient availability. In this experiment, the non-electrolyte system, when low in concentration, can significantly affect the surface electrochemical properties of purple soil, but the effect is obvious only when strong electrolyte is high in concentration.

Abstract:Through in-lab thermostat incubation, investigation was done of changes in content of soil available phosphorus and soil phosphorus desorption kinetics, in vegetable garden soils different in parent material (basalt, granite, and river alluvium) in Guangdong Province, 30 d and 60 d after application of organic fertilizers (composted chicken droppings or commodity organic fertilizer). Results show that after the application of composted chicken manure or commodity organic fertilizer, contents of soil available phosphorus in all the three soils increased, with amplitudes showing composted chicken manure was higher in the effect than commodity organic fertilizer. Phosphorus desorption kinetic curves in all the treatments presented a period of rapid desorption followed by a period of slow desorption before reaching equilibrium. Phosphorus desorption in the soil was not only closely related to its initial available phosphorus content, but also to its parent material and the type of the organic fertilizer it received. Five kinetics equations were used to fit the kinetics curves of phosphorus desorption in the three soils different in parent material. The simplified Elovich equation, the Parabolic diffusion low equation and the Power function equation were better in fitting.

Abstract:Plant residues are an important source of soil organic matter. Decomposition characteristics of plant straws, soil microbial functional diversity and their relationship was studied so as to find some scientific basis for transformation of organic carbon in soil and rational exploitation of land resources. The mesh bag method was used to explore how plant straws decompose in fields of three long-term field experiments and the biolog micro plate technology was adopted to determine soil microbial community diversities in the fields of the three long-term field experiments. Results show that with decomposition going on, residue rate of fresh plant straws did not varied much. The three long-term field experiments were basically similar in this aspect, displaying an order of FB (Fresh bean stalk) > fc (Fresh corn stalk + nitrogen fertilizer) > FC (Fresh corn stalk), but residue rate of oven-dried milled corn stalk differed quite sharply. In terms of soil microbial community activity (average well color development, AWCD), the three long-term experiments followed an order of Vineyard > Peach orchard > Farmland, indicating it was the highest in the vineyard, while diversity index analysis indicates that the farmland did not differ much from the vineyard and peach orchard in all the soil microbial community indices, except for evenness, which did to a significant level. Principal component analysis of the Biolog 31 carbon sources reveals an order of farmland > Peach orchard > vineyard in terms of soil typical dispersion degree, indicating that the farmland was the lowest in microbial community stability and followed by peach orchard and vineyards. Analysis of microbial community structures utilizing the six categories of carbon sources indicates that significant differences existed between the three experiment fields in the utilization of amino acids and saccharides, while none in that of the other four. The three major indices were extremely closely related to soil temperature, soil alkalytic nitrogen and, readily available phosphorus and, stalk decomposition residual rate was negatively related to dominancy of soil microbial communities, regardless of source of the stalk, which, to a certain extent, affected the decomposition rate of straws. In the farmland low in soil microbial activity and stability, stalk residue rate varied quite sharply between the treatments. while in orchards where the soils were relatively high in soil microbial activity and stability, stalk residue rate did slightly between the treatments.

Abstract:Partial factor productivity (PFP) of fertilizer is an important index reflecting overall effect of soil fertility level and fertilizer application rate. Hence, fertilizer application rate has some impact on partial factor productivity of the fertilizer. Based on the questionnaire distributed to 212 potato farmers in 13 counties and 11 prefectures of Yunnan during 2008~2009, relationship between fertilization rate and PFP of the fertilizer in potato production was explored and fertilization of the farmers was evaluated in rationality. Results indicate that on average, N 285 kg hm^-2, P₂O₅ 149.1 kg hm^-2, and K ₂ O 111.9 kg hm^-2 was applied in potato production and in practice fertilization rate varied in the range of N 30~1 005 kg hm^-2, P₂O₅10.5~735.0 kg hm^-2and K₂ O 7.5~466.5 kg hm^-2, and the PFP of the fertilizers in potato production was 82.3 kg kg^-1, and the PFP of N, P and K fertilizers was 158.7 kg kg^-1, 278.0 kg kg^-1 and 416.3 kg kg^-1, respectively. The application rate of N, P and K was in negative exponential relationship with their respective PFP, and so was the application rate of the fertilizers in all with the total PFP, with correlation coefficient being 0.873^﹡﹡, 0.872^﹡﹡, 0.801^﹡﹡ and 0.805^﹡﹡respectively. When the application rate of N 150~250 kg hm^-2, P₂O₅45~90 kg hm^-2, and K₂ O 90~120 kg hm^-2, was set as the rational range of fertilization rate, only 21.6%, 30.7% and 10.8% of the farmers in the survey were termed rational in N, P and K fertilizer application, respectively, in potato production in Yunnan province.

Abstract:A total of 69 soil profiles typical of the Jianghan Plain were collected, identified and classified in line with the “Keys to Chinese Soil Taxonomy (CST)(3rd ed.)”, and their diagnostic horizons and diagnostic characteristics were determined, and their attributes in the taxonomy defined. They were sorted into 5 Orders, 5 Suborders, 8 Groups and 18 Subgroups. Besides, influences of soil parent material, topography and human activities on attributes, spatial distribution and evolution of the soils were discussed. Results show that the CST system reflects properly relationships of distribution of soil types with spatial variation of its influencing factors, such as parent material, topography and human activities, which has provided some practical examples for further perfecting the soil taxonomy.

Abstract:Chronosequence analysis done of three Hydragric Anthrosols derived from purple sand shale, quaternary red clays and red sandstone, respectively, in hilly regions of South China to explore evolutions of their basic physico-chemical properties. Results show that parent material was the major factor determining sensitivity of clay and SOC to forming processes of the soils and hence apparently evolution of their soil properties. Free ion (Fe_d) was very sensitive to the soil forming processes, and its translocation and transformation was mainly affected by the latter, rather than soil parent material. However silicate iron (Fe_t-Fe_d) was not so sensitive to soil forming processes, and the distribution of total ion (Fe_t) was affected mainly by Fe_d. Loss of clay had some important effects on migration and distribution of soil elements, causing enrichment of SiO₂ and loss of Al₂O₃ in the soils. It must, therefore, be careful in working out some indices to indicate development stages of Hydragric Anthrosols by using the two elements, Al and Si. TiO₂ was relatively stable throughout the soil forming processes and hence could be used to indicate migration rates of other major elements in the paddy soils.

Abstract:In Fengqiu County of Henan Province, topsoil samples were collected from 3 608 sampling sites, of which 3 463 sampling sites were chosen to form a master dataset for soil attribute mapping, while the remaining 145 sampling sites were to form a master verification dataset. Then, through 4%~96% multi-scaled stochastic sampling of the former, 17 subsets were formed for mapping of soil organic matter, soil available phosphate and soil readily available potassium using kriging interpolation, inverse distance weight interpolation (IDW) and Polygon value represented by point value (PRP), respectively. Based on direct map comparison between the computerized mapping subsets and the master mapping dataset, correlation coefficients were obtained to evaluate effects of scaling on soil attribute maps, and further more comparison was made with the multi-scaled mapping evaluated with the verification dataset. In the end, variable coefficient of the multi-subset mapping was used to indicate uncertainty of the expression of multi-scaped mapping and comparison was made of this uncertainty with that of the kriging variance and that of the stochastic simulation. Through the direct map comparison, it was found that the relationship between mapping quality and volume of samples was fractal and the fractal dimension was affected dually by mapping method and spatial variability of soil attributes. In the same conditions, the fractal dimension was the smallest with the kriging method and the largest with the PRP method, and the smallest with soil available potassium and the largest with soil available phosphate. The correlation coefficients and Root mean square error(RMSE) between the measured values and forecasted values in the verification dataset did not show any fractal feature as expected. The uncertainty of single-scale mapping expressed by kriging variance and stochastic simulation was significantly influenced by distribution of the sampling sites and value of the kriging estimation, while the uncertainty of the multi-scale mapping based on direct map comparison reflected more objectively natural variation of soil attributes, among which soil organic matter and soil available potassium showed more obvious laws in variation, while soil available phosphate didn’t .

Abstract:Five soil profiles were selected in typical epikarst spring catchments in Nanchuan District, Chongqing Municipality as objects of the study on rules and controlling factors of the vertical migration of 16 kinds of polycyclic aromatic hydrocarbons (PAHs) in the soils. Soil samples were collected from every soil layers, 10 cm thick each, of the soil profiles for quantitative analysis of the PAHs with gas chromatography-mass spectrometry (GC-MS). Results show that all the 16 PAHs were detected in all the 5 soil profiles, varying in the range of 161~3 285 ng g^-1, and averaging 987 ng g^-1 in concentration. In the soil profile at the Hougou epikarst catchment, high-ring PAHs were in dominancy, while in the soil profile at the paddy field of the Lanhuagou spring catchment and at the Shuifang spring catchment, low-ring PAHs were. However, in the soil profiles in pine forests at the Baishuwan and Lanhuagou spring catchments, high-ring PAHs dominated the 0~2 cm soil layers, but low-ring PAHs did the soil layers below 2 cm. From the contents of PAHs and changes in composition along the profiles, it could be inferred that low-ring PAHs migrate easily. But in soil profiles with a thin surface soil layer, artificial disturbance, like plowing, make it easy for high-ring PAHs to migrate. Among the five soil profiles, only the one in the Shuifang spring catchment witnesses the highest mobility of PAHs. As in karst areas, the surface soil layers are generally thin, PAHs migrate easily, thus polluting epikarst spring water. Multiple regression analysis between the total PAHs and physicochemical properties of the soils shows that total organic carbon (TOC) is the main factor controlling the migration of PAHs in the Hougou, Lanhuagou and Baishuwan spring catchments, while in the Shuifang spring catchment, there is no main factor impacting migration of PAHs.

Abstract:Karst areas at different vegetation restoration stages were studied with slope farmland and artificial forest as control using the approach of substituting the temporal serial with spatial serial. And further through lab analysis using the principle component analysis method, variation of soil anti-erodibility was explored. Results show that the contents of soil organic matter, <0.001 mm clay, >0.25 mm water-stable aggregates and <0.05 mm silty clay and the structural particle index were optimal indicators for evaluating soil anti-erodibility. In terms of comprehensive anti-erodibility index, the lands at different vegetation restoration stages mixture of frutex and meadow thicket > mixture of arbor and frutex > frutex > arbor > artificial Chinese Cryptomeria stand > meadow thicket > slope farmland. Slope farmland was the lowest in soil anti-erodibility in the karst region. During the process of vegetation restoration, soil anti-erodibility improved and then deteriorated with the stage of mixture of frutex and meadow thicket as turning point, suggesting that, the model of mixture of frutex and meadow thicket is appropriate to vegetation restoration in karst regions.

Abstract:Based on vertical one-dimensional water and heat movement in soil under seasonal freezing and thawing, a water-heat coupling model was used to simulate variation of moisture and temperature in soil with surface energy and mass in balance. The simulation took into account the effect of ice and water, at times of freezing, on volumetric heat capacity, heat conduction and hydraulic conductivity and the effect of snow cover on the soil surface as well. The model used the meteorological data collected at the weather stations in the studied area during the three years from Jan. 1, 2008 to Dec. 13, 2010 and was verified with observed data of soil temperature, soil moisture, and depth of freezing. Results show that the simulated and the measured data of soil temperature varied with a root mean square error of 3.65, 1.59, 1.75, 1.35 and 1.64℃ at 0, 0.05, 0.40, 0.80 and 1.60m in depth, respectively. The data of frozen depth was almost identical. And the data of soil moisture differed with a mean error of 3% at all the depths except for the surface, and with a root mean square error (RMSE) of less than 4%. Therefore, it could be concluded that the model presented in this study could be used to simulate water and heat movement within a certain depth of soil under seasonal freezing and thawing. It can also be used to study laws of the variation of soil water-heat in the active layer in the permanent frosted regions. Coupled with the ecological process model it will help improve precision of the frozen soil eco-environment model in simulating soil temperature, soil moisture and depth of freezing.

Abstract:To explore effects of ecosystems on molecular structure of humus (HS) in soil aggregates, soil samples were collected from plots of grass land(GL), cultivated land(CL), and bare land(BL) in a long-term (24 years) field experiment in the black soil region of Northeast China for fractionation of soil aggregates into four particle-size fractions (>2 mm, 2～0.25 mm, 0.25～0.053 mm and <0.053 mm ) with the wet sieving method and further for analysis of structural properties of humic acid (HA) in aggregates with element analysis, infrared spectroscopy (FTIR) and differential thermal analysis (DTA) methods. Results show that the type of an ecosystem has some effects on affects molecular structure of the HA in soil aggregates. The HA in soil aggregates from CL was higher that from GL in O+S content and (O S)/C ratio, which indicates that the HA in soil aggregates from CL is higher than that from GL in oxidation degree. The DTA analysis reveals that the HA in soil aggregates from CL and BL was lower than that from GL in thermal discharge under moderate temperature, but higher in high to moderate heat ratio, suggesting that the former is higher than the latter in aromaticity/aliphaticity ratio. The HA in soil aggregates from GL and CL displays higher peaks than that from BL did at 2 920 and 2 850 cm^-1, representing C-H stretching vibration of asymmetric and symmetric aliphatic (CH₃ and CH₂), and the former was also higher than the latter in aliphatic-C/carboxylic-C(2 920/1 720) and aliphatic-C/aromatic-C(2 920/1 620) ratios. Compared with GL, the ecosystems of CL and BL both increased condensation, oxidation and aromaticity of HA in soil aggregates, thus enhancing stability of the molecular structure of HA in soil aggregates.

Abstract:Based on repeated sampling in a number of areas, variations of organic carbon (SOC), humus carbon (HC), humic acid carbon (HAC) and fulvic acid carbon (FAC) in the surface (0~10 cm) and sub-surface (10~20 cm) layers of alpine steppes different in state (normal, slightly degraded and severely degraded) in the Northern Tibetan Plateau as well as influences and effects of soil microbial community, microbial biomass carbon (MBC) and cellulolytic enzyme activity (CEA) on SOC, HC and HAC. Results show that the soil in cold and acid alpine environment is very low in HC/SOC ratio, but very high in PQ value (HAC/HC). On the whole, the contents of SOC, HC and HAC and the proportion of HC/SOC in steppes different in state declines to a varying extent with soil depth in profile, while PQ value increases to a certain extent. Relative to normal steppes, the increase in SOC declines slightly and in HC (HAC, FAC) rises dramatically in the surface soil layer, and both drop drastically in the sub-surface soil layer. In terms of contents of SOC, HC and HAC in the 0~20 cm soil layer, a decreasing ordeer of normal steppe ＞ severely degraded steppe ＞ slightly degraded steppe is found, and in terms of HC/SOC ratio and PQ value, a decreasing ordeer of severely degraded steppe ＞ normal steppe ＞ slightly degraded steppe, and of normal steppe ＞ severely degraded steppe ＞ slightly degraded steppe is respectively, which means degradation of a steppe promotes formation and accumulation of SOC and HC (HAC and FAC) in the surface soil layer, and also “stimulates” mineralization of the sub-surface soil layer, and especially decomposition of organic debris in severely degraded steppes. However, quality of the humus is not improved correspondingly along with the increasing degree of soil humification. The highly homogenous distribution MBC, CEA, SOC, HC and their components in the soil affects and decides the above-mentioned process. Steppe degradation is conductive to decomposition and transformation of organic debris in the soil by fungus and actinomycetes, especially in the sub-surface soil layer.

Abstract:It is important for the study on soil carbon sequestration to figure out soil carbon pools and their significant influencing factors in different periods. Based on the data of the second National Soil Survey of Bei’an and Kedong area in the early 1980’s, the data of the soil testing for fertilizer recommendation in 2010, and the data of the analysis of actual supplementary soil samples, soil organic carbon pool and spatio-temporal variation of its density was studied using the soil type-GIS correlation method, meanwhile, impact factors of the spatial variation of soil organic carbon density and variation of their significances in the different periods. Results show that the soil organic carbon density and its decreasing rate in the farmlands in valleys and low-lying plains is higher than that in rolling hill high plains in the study region and the carbon pool in the surface soil layer and the profile decreased at an annual average rate of -0.14 t hm^-2a^-1 and -0.13 t hm^-2a^-1, respectively. The soil carbon stock showed an apparent declining trend. In 1980, soil type (subtype), elevation, pH, and total phosphorus were found to be the main impact factor of the soil organic carbon density in the surface soil layer of the farmlands, while in 2010, soil type (subtype) and soil pH remained, but slope degree replaced elevation and total P as major impact factors.

Abstract:Samples of paddy soil were prepared into slurry with water in different ratio and then incubated anaerobically in dark and under light at a constant temperature for exploration of effects of water content on iron redox and, water soluble carbon content in the soil and, CO₂ and CH₄ emissions from the soil. Results show that water content and illumination are key environmental factors regulating iron redox process and transformation of its coupled carbon. Higher water content accelerated appearance of the peak iron reduction rate in and promoted CH₄ emission from the soil under incubation in dark. In the soil lower than 50% in water content incubated under light, increase in water content stimulated re-oxidation of ferrous iron, while in the soil higher than 50%, a reverse effect was observed. In the soil incubated in dark increased water content increased the content of water soluble inorganic carbon (WSIC), which was significantly and positively related to CH₄ emission. However, in the soil incubated under light, increased water content reduced the content of WSIC with an extent expanding with increasing water content. In the soil with water content ranging from 25% to 200%, light reduced CO₂ and CH₄ emissions by 95.80% and of 96.08%, respectively.

Abstract:To investigate effect of sequence of sulfate addition on adsorption of Cu²⁺ by soils, samples of variable charge soils (Ali-Haplic Acrisol from Jinxian, Rhodic from Xuwen and Hyper-Rhodic from Kunming), constant charge soils (Haplic Luvisol from Nanjing and Brown soil from Weihai), geothite and kaolinite were used in the experiment. All the samples, except kaolinite, were treated with electrodialysis. Copper ion was spiked at a rate of 1 cmol L^-1, and sulfate at a rate of 0.1 cmol L^-1 and 1 cmol L^-1, separately. The experiment was designed to have three treatments in sequence, that is, Treatment 1: addition of copper nitrate, stand, vibration and addition of sulfate; Treatment 2: addition of copper sulfate and nitrate the same time, stand and vibration; and Treatment 3: addition of sulfate, stand, vibration and addition of copper nitration. All the samples were treated to keep copper ions and sulfate the same in concentration in the suspensions before vibration in the end. Soil pH of the samples was measured with glass electrodes, and copper ions measured with Atomic Adsorption Spectrometry. Results show that the effect of sequence of sulfate addition on Cu² adsorption by soils varied from soil to soil different in surface charge properties. For constant charge soils, the sequence of sulfate addition did not have much effect on Cu² adsorption. On the other hand, among the three treatments, when pH was kept the same, variable charge soils, kaolinite and goethite in Treatment 2 were the highest in Cu² adsorption rate. For Ali-Haplic Acrisol, the samples in Treatment 3 were higher than those in Treatment 1 in Cu² adsorption rate. For Hyper-Rhodic Ferrasol, Rhodic Ferrasol, kaolinite and geothite, the effect was just the opposite to that on Ali-Haplic Acrisol when they were under the same condition. No matter on what samples, application rate of sulfate did not have any effect on the order of the treatments in Cu² adsorption rate, and a similar phenomenon was observed when Hyper-Rhodic Ferrasol was deprived some of its organic matter. It is generally accepted that anions may affect soil adsorption of coexisting cations in three ways: (1) ion strength; (2) specific adsorption; (3) ion pairing. As in the end, the anions and cations in the suspension are the same in type and concentration, the effect of ion strength on Cu² adsorption should not have any difference. Although specific adsorption of sulfate will lead to release of hydroxyl, thus altering Cu² adsorption electrochemical properties of the suspension, the comparison of the treatments in was done under the condition that the suspensions were the same in pH. In this experiment, the only factor causing differences between the soils in Cu² adsorption might be the complexing reaction of sulfate and copper ions with soil surface. After careful consideration of the findings in the experiment and the differences in surface electrochemical properties between the soils used in the experiment, it can be concluded that the causes of the differences between the soils in Cu² adsorption should be the complexing reaction of copper ions and sulfate with soil sulfate, and the difference between variable charge soils and constant charge soils in surface charge properties.

Abstract:Artemisia annua L., widely distributed in Southwest China, is the sole plant source of artemisinin. To understand the mechanism of resistance to desert about this medicinal plants for higher yield and quality of artemisinin, researches were done to study nutrients and microorganisms in soils where wild A. annuagrew. Results show that the soils at different sample sites varied greatly in organic matter, nutrients, pH, enzyme activity and population of microbes, suggesting that A. annua is tolerable to either high or low soil fertility and hence highly adaptable to a variety of habitats. In soil analysis, 24 kinds of phospholipid fatty acids (PLFAs), biomarkers of soil microbes, were detected with a gas chromatograph-mass spectrometer (GC-MS), including 19 kinds of PLFAs with 11~19 carbons (C), biomarkers of bacteria, 10Me18:0, biomarker of actinomyces, 18:2ω6,9, 18:1ω9c and 18:1ω9t, biomarkers of fungi, and 20:0, biomarker of nematode. And in terms of total amount of PLFAs, the sequence of bacteria > actinomyces> fungi was found. In the rhizosphere of A. annua, pH was obviously lower than in the bulk soil, but contents of organic matter, alkalystic N, available P, readily available K, microbial C and N, and FLFAs, activities of sucrase, urease and phosphatase, and indexes of diversity and homogeneity of microbial colonies were just the otherwise. Rhizosphere microorganisms were closly involved in transformation of N and P in the soils. In addition, total PLFAs in soil microbes were significantly and positively related to plant biomass and yields of artemisic acid and artemisinin, and so were soil microbial biomass C and N to yield of artemisinin, The study provides evidence that it was suitable for growth of various species of microorganisms, high density and enzyme activities in rhizosphere soil of wild A. annua, so effectiveness of the soil nutrient improved was beneficial to the wild A. annua adapted to different soil conditions and that the existence of soil microorganisms significantly affects growth and contents of effective component of wild A. annua .

Abstract:A pot experiment was conducted to study effects of two kinds of herbicides, varying in dosage, on bio-characteristics of paddy soil and nutrients absorption and accumulation of succeeding crops. Results show that the application of either bensulfuron-methyl•butachlor or quinclorac in paddy soil decreased the dry matter weight of Chinese milk vetch, and the higher the application rate, the less the dry matter accumulated. Low doses of bensulfuron-methyl•butachlor significantly decreased N accumulation in Chinese milk vetch, while low doses of quinclorac decreased not only N, also K accumulation in the plant. And high doses of either of the two herbicides decreased N, P and K accumulation in the plant. The application of either bensulfuron-methyl•butachlor or quinclorac, regardless of dosage, decreased the availability of soil N and K. Low doses of quinclorac did not affect much available P content in the soil, while high doses of the herbicide did significantly decrease the availability of soil P. Low doses of bensulfuron-methyl•butachlor did not have much influence on the activities of catalase, sucrase and urease in the soil, while low doses of quinclorac inhibited markedly the activities of catalase. High doses of either of the herbicides did not affect much the activity of sucrase, but did inhibit those of catalase and urease. Furthermore, the application of bensulfuron-methyl•butachlor, either high or low in dosage, increased the amount of bacteria, and while that of quinclorac acted just reversely. The application of either of the herbicides at either high or low rate, decreased the amount of actinomyce, but did not cause much change in that. It is, therefore, quite clear that, the application of quinclorac in paddy field is more harmful to the paddy soil environment and the growth of Chinese milk vetch than bensulfuron-methyl•butachlor.

Abstract:A field experiment was conducted at Jiangtang Agricultural Experiment Station，Jinhua City, Zhejiang Province, China to explore effects of incorporation of Chinese milk vetch coupled with application of chemical fertilizer on nutrient uptake, nutrient use efficiency, and yield of single-cropping late rice and hence to determine optimal application rate of chemical fertilizer in addition to incorporation of Chinese milk vetch at the rate of 45 t hm^-2 fresh grass (GM₄₅). The experiment consisted of 7 treatments: CK (no fertilizers and no Chinese milk vetch), CF (conventional chemical fertilizer rate), GM₄₅, GM₄₅+20�, GM₄₅ 40�, GM₄₅ 60� and GM₄₅ 80�. Results of the 2 year (2011-2012) field experiment show that among all the GM₄₅ treatments, Treatment GM₄₅ 80� was the highest in total N, P, and K uptake by rice, but Treatment GM₄₅ 40�, the highest in N, P, and K uptake by grain, and the internal nutrient use efficiency decreased with increasing chemical fertilizer application rate. However, treatment GM₄₅ 40� was the highest in both NPK agronomic use efficiency and grain yield. From the angle of improving fertilizer use efficiency and reducing environmental risk, in addition to incorporation of 45 t hm^-2 of fresh Chinese milk vetch produced in other fields, N 80.6 kg hm^-2, P₂O₅21.5kg hm^-2 and K₂O 43.3 kg hm^-2 are recommended. Compared with treatment CK, treatment CF and treatments (GM₄₅, GM₄₅ 20�, GM₄₅ 40�, GM₄₅ 60� and GM₄₅ 80�) increased grain yield by 13.7% and 8.5%～17.4%, respectively. In the cropping system of Chinese milk vetch – single-cropping late rice, incorporation of 45 t hm^-2 fresh Chinese milk vetch will not result in the seedling.

Abstract:Based on previous studies on soil polarization of mono-species coniferous forests, an incubation-for-decomposition experiment was conducted of mixtures of soil samples collected from humus layers of Platycladus orientalis, Pinus tabulaeformis and Larix principis-rupprechtii forests in the semi-humid loess hilly region of Shaanxi with litters of seven species of forage grass to explore effects of forage litters remedying pure coniferous forest soils and hence to accumulate scientific data for selection of suitable soil-remedying species of forage grass. Results show that in the pure P. orientalis forest soil, all the litters displayed significant effects mitigating the negative polarization of readily available K, and the litters of Medicago sativa, Leapedeza bicolor, Astragalus adsurgens, Vicia villosa and Melilotus officinalis had similar effects on the activity of protease; in the pure P. tabulaeformis forest soil, all the litters had such similar effects on alkalytic N, those of V. villosa, M. sativa and Melilotus officinalis had on available P, and only the litter of M. sativa had on the activity of sucrase; and in the pure L. principis-rupprechtii forest soil, the litters of L. bicolor and Onobrychis viciaefolia had such similar effects on alkalytic N, the litters of M. sativa, O. viciaefolia, Coronilla varia and V. villosa had on available P, all the litters except those of M. sativa and V. villosa had on organic matter content, and all the litters except that of M. sativa had on the activity of phosphatase. Integrated PCA (principal component analysis) shows that in the pure P. orientalis forest, the litters of A. adsurgens, C. varia, L. bicolor and V. villosa had better comprehansive remediation effects on the soil, in the pure Pinus tabulaeformis forest, the litters of M. sativa, C. varia and M. officinalis had, and in the pure L. principis-rupprechtii forest, the litters of M. sativa, M. officinalis and O. viciaefoli had.

Abstract:With the aid of the Moran’s I index and GIS geostatistic interpolation methods, spatial autocorrelation and spatial distribution of organic carbon density (SOCD) in forest soils of Zhejiang Province were studied and effects of factors affecting SOCD were analyzed using the linear-regression equation. Results show that SOCD in the 0~30 cm layer of the forest soils of Zhejiang Province was 71.2 t hm^-2, on average, lower than the country’s. The overall Moran’s I of the SOCD in Zhejiang Province was 0.176, demonstrating significant spatial autocorrelation. SOCD in the forest soils of Zhejiang Province displayed in distribution a gradient declining from southwest to northeast and three parallel belts. Significantly positive relationships were found of SOCD with dominant tree species, slope position, slope aspect, age group, altitude, shrub coverage, shrubs average height and average age, and a significantly negative relationship was found with herb coverage. SOCD in the 0~30 cm soil layer was not much affected by herb average height. All these influencing factors explained 14.9% of the variation of SOCD.

Abstract:Biochar, as a soil conditioner, can significantly improve soil fertility. But few data are available about impacts of biochar on salt leaching in saline soil. In this experiment, different rates (0%, 2%, 5%, 10%, w/w) of biochar prepared out of mushroom residues were added into surface soil layer (0~20 cm) of sulfate saline soil columns, separately, collected from Hetao, Inner Mongolia. Deionized water was added into the soil columns to form leaching and eluents from the columns were collected and analyzed for electrical conductivity (EC) and contents of some major salt ions, with a view to exploring effect of biochar on leaching of salts and ions from saline soil. Results show that eluents from biochar-amended columns appeared 5~36 days earlier than that from the control column, and the higher the biochar application rate, the earlier the eluent, the shorter the time for EC declining below 5 mS cm^-1. It could be shortened by 41~100 days. Biochar addition at a rate of 2% was the best desalination of the surface soil, reducing salt content by 34.25% as compared to CK. It is obvious now that addition of biochar can shorten the time of desalinization the soil and improve soil desalinization efficiency as well. However, no significant difference was observed between the effects of biochar leaching different salt ions in sequence and rate of leaching.