Abstract:Soil chronosequence is a valuable means in investigating rates and directions of pedogenic evolution. A soil chronosequence consisting of one tract of mudflat and five paddy soils of different rice cultivation ages were selected for this study. Ages of the paddy fields were estimated according to the literature available indicating the time when the polder was built up to reclaim the mudflat into paddy fields. The objectives of this study were to evaluate lithologic discontinuity (LDs) of the parent material in the inter-and intra-profiles of the chronosequence, and to verify relative ages of the fields by making use of various soil attribute parameters. Results show that low variation coefficient was associated with clay-free silt and Ti/Zr ratio of the silt fraction between horizons, suggesting no LDs in the studied profiles, that is to say, the profiles of the chronosequence have developed from a relatively homogeneous parent material.The clay-free silt and Ti/Zr ratio of the silt fraction are the most useful parameters in identifying LDs in this study. In order to establish a well-dated chronosequence, CaCO₃ content, magnetic susceptibility and differentiation degree of free iron oxide in the profiles were used to assess soil relative ages and they were shown as good indicators of soil age and development. However, these parameters in the 500a soil profile have an odd tendency along the sequence, so it should be excluded from the chronosequence when a reliable comparison of soil changes is desired.

Abstract:Surface seals and crusts, formed as a result of aggregate disintegration and compaction during a rain or irrigation event, are higher in shear strengths, greater in bulk density, finer in pore and lower in infiltration rate than the underlying soil. Soil surface strength and micromorphological photos are important indices and direct representations in the research on soil crust. Two soils, Lu Soil and Black Soil, typical of arable soils in China, were used to investigate effects of wetting rates (WR) of (2 (low) or 50 (high) mm h^-1) and cumulative rainfall on crust formation, under simulated rainfall with intensity of 60 mm h^-1. The experiment indicated that the effect of WR was negligible, but that of cumulative rainfall was significant on crust formation of Lu Soil. The crust formation processes of Black Soil were affected mostly by WRs. High WR had much greater effect than the low WR. Disintegration of soil aggregates plus rainfall of high intensity led to formation of crusts of high surface strength. Thus, the relative importance of WR and rain depth depends on stability of soil aggregates. For soils with stable aggregates, the impact of raindrops impact alone is not sufficient to destroy aggregates and form crusts. Fast wetting of dry soil is essential for aggregate breakdown and crust formation. For soils with unstable aggregates, the impact of raindrops is sufficient for seal formation.

Abstract:The sieve-pipette method is a traditional technique for determination of soil particle size distribution (PSD), while the laser diffraction method is a relatively new technology. To explore conversion relationship between the PSDs determined by the two different methods, 265 soil samples from 6 soil orders of the Chinese Soil Taxonomy were determined by the two methods. Results show that the clay content using the laser diffraction method was obviously lower than that using the sieve-pipette method, while the silt content using the former was higher than that using the latter, but the sand content was sometimes higher and sometimes lower with no consistent difference. However, significant relationships were found between the clay, silt and sand contents determined by the two different methods, even for each of the seven fractions of the USDA (United States Department of Agriculture) soil texture classification criteria. Based on the equations for conversion of data between the two methods, thresholds for classifying soil texture in clay, silt and sand were worked out, using the data obtained by the laser diffraction method. The findings demonstrate that data from the laser diffraction method can be directly used to classify soil texture.

Abstract:With the development of the nation, petroleum has become one major energy source. The industry of oil exploitation and refining is expanding steadily, thus leading to occurrence of more and more pollution events mainly due to irrational management, among which, soil pollution by crude oil is especially serious. In order to understand the mechanisms of the pollution, it is necessary to study crude oil infiltration into soil. In this study soil columns were used to determine relationship of advance distance and advance rate of crude oil into soils with time, and residue of the contaminant. Results indicated that in soils the same in texture, advance distance, advance rate and residue of crude oil decreased with the increase of the bulk density of the soils. But into soils the same in bulk density, the same trend was observed with the increase in silt content. The variation of advance distance of crude oil with time can be described by a logarithmic function, and the advance rate by a power function. The findings in the research on crude oil infiltration in soil columns are of some importance to the study on the transport of crude oil in soils.

Abstract:Aiming at the complexity and spatial variability of the dynamic soil water and salinity in the saline region of the Lower Yellow River Delta, artificial neural network was introduced for modeling and prediction of soil water and salinity. Influence of the number of neurons in the hidden layer on training and forecasting was discussed for the three-layered network, and Back Propagation Neural Network (BPNN) models were established for modeling contents of water and salinity and their spatial distribution in the surface soil 0~20 cm in depth. Results indicate that the water and salinity in the surface soil was significantly correlated with soil bulk density and groundwater properties across the study area. For surface soil salinity, it is advisable to have the five variables, i.e. longitude and latitude of the site, soil bulk density, and depth and mineralization of groundwater cited as input vectors, while for soil moisture, the four variables, i.e. longitude, latitude, bulk density, and groundwater depth. An excessive number of neurons in the hidden layer would result in overfitting. Considering forecasting precision, the topological structure of the BP network was defined as 5∶8∶1 and 4∶6∶1 for salinity and moisture in the surface soil, respectively. Distribution maps of the observed surface soil water and salinity and their BPNN simulation displayed similarity in spatial pattern, and the BPNN effectively simulated contents of water and salinity and their spatial distribution in the surface soil with high accuracy. The findings of the study can serve as a theoretical basis for analyzing the occurrence, development and evolvement regularities of soil salinization in the Yellow River Delta, and provide a scientific basis for decision-making in regulating soil water and salt regulation and implementing scientific management of saline soils.

Abstract:Soil samples were collected from non-agricultural (forest and shrub lands) and agricultural lands (tea, rice paddy and upland) in Jiangxi Province, China and incubated at 60% water-holding capacity and 30℃. The results showed that the nitrification activity was weak or absent in the studied soils due to be acid (pH 4.2~6.3 with a mean of pH 4.9). The nitrification rate was significantly correlated with mineralization rate of organic N, but not with soil pH if NH₄⁺ was not amended into soils before incubation. In contrast, the nitrification rate was significantly correlated with soil pH if NH₄⁺ was amended into soils before incubation. For majority of the non-agricultural soils (14 of 18 samples), the nitrification rates were smaller than their net mineralization rate. Consequently inorganic N was dominated by ammonium rather than nitrate even after 56-days incubation. Nitrification activity was stimulated by agricultural use, dependent on land use types, with the greatest in upland soils followed by tea and paddy soils. Enhancement of soil pH by liming, application of N fertilizers, and improvement of available P status were the main factors stimulating nitrification activity in agricultural soils. The stimulation effect of agricultural use on nitrification weakens the capacity of humid subtropical soils to retain inorganic N. The NO₃^--N produced through nitrification may threaten the environment by leaching and run-off, particularly when N fertilizers are applied into agricultural soils in seasons with higher temperatures and heavy rainfall.

Abstract:A laboratory incubation experiment was conducted to investigate nitrous oxide (N₂O) emission from an arable Ultisol as affected by antecedent water regime. The soil was maintained either air-dried (Sample D) or submerged (Sample S) for 110 days before the two soil samples were adjusted in soil moisture up to or down to 20%, 40%, 60%, 80% and 100% water holding capacity (WHC), respectively. And then they were incubated with or without 10% (v/v) acetylene for 138 h at 25℃. Results show N₂O emission from Sample S was 2.48 to 6.36 times as much as that from Sample D with soil moisture content ranging from 20% to 80% WHC (p <0.01). When the soil moisture content was adjusted to 100% WHC, N₂O emission from Sample S was only 19 percent of that from Sample D, and N₂O emission from Sample D incubated with acetylene was lower than that without acetylene (p <0.01). The content of nitrate increased after incubation with acetylene. CO₂ emission from Samples S and D increased with the soil moisture content. Heterotrophic nitrification might be present in the tested soil. Antecedent water regime significantly influences N₂O emission, and should hence be considered as a factor in determination of N₂O emission in situ.

Abstract:Plant carbon storage, soil organic carbon storage, daily and seasonal variation of soil respiration rate were measured in 2005 to understand effects of desertification on soil respiration and carbon balance in Horqin sandy grassland. Results show that (1) desertification decreased significantly daily variation of soil respiration rate and daily mean soil respiration rate; as compared with that, in the non-desertified grassland, light, moderate, heavy and severe desertification decreased daily mean soil respiration rate by 6.4%, 12.8%, 33.0% and 39.4%, respectively; (2) it also decreased carbon storage in the grassland by 50.3%, 74.0%, 86.4% and 90.2%, respectively; litter carbon storage, in particular, dropped the most drastically, and was followed by soil organic carbon storage, and plant carbon storage; and (3) it gravely disturbed carbon balance in the grassland; the amount of carbon consumed by soil respiration exceeded the amount of carbon fixed by plant photosynthesis once desertification occurred, thus turning soil organic carbon deposit into reserve carbon source to make up the shortage between carbon consumption and carbon fixation. To promote restoration of the carbon deposit in desertified grassland, it is necessary to intensify management of grassland desertification and reestablish vegetation of the grassland.

Abstract:A preliminary study was carried out on vertical distributions of selected soil properties and trace metals in typical calcareous fluvo-aquic soil profiles under different land use. Results indicate that in vegetable fields and upland soils, the topsoil (0~15 cm) is higher in organic carbon content, lower in pH and CaCO₃ content than the other layers in the soil profiles, and shows significant Cd accumulation, however, the concentrations of Cd, Pb, Cu and Zn have not yet exceeded the second grade criteria of the National Standard for Soil Environment Quality of China. Totals of some trace elements in the top soils do not vary much between vegetable and upland soils, but the concentration of DTPA-extractable Cd in the topsoil is significantly higher in the former than in the latter. In light of distribution of the trace elements in the profiles, surface accumulation is quite obvious of total Cd and DTPA-extractable Cd, Pb, Cu, and Zn in calcareous fluvo-aquic soil. This phenomenon is significantly related to content of soil organic matter, soil pH and content of soil CaCO₃. Result of cluster analysis shows that it is more advisable to collect mixed multisite soil samples from the surface soil layer (0~15 cm) for soil environment analysis.

Abstract:Concentrations of pollutants will increase if sewage sludge is applied to soil, thus posing a risk to the health of human. An incubation experiment was carried out with results showing that concentrations of EDTA and CaCl₂ extracted Cu and Zn in the sludge-amended soils increased with time and reached to maximum 150 days after the incubation. The average concentration of EDTA-extracted Cu and Zn was 30.0 mg kg^-1 and 30.1 mg k^-1, and increased by 21.4 mg kg^-1 and 26.1 mg kg^-1 over the control, respectively. The average concentration of CaCl₂ extracted Cu and Zn was 0.11 mg kg^-1 and 3.65 mg kg^-1, about 0.10 mg kg^-1 and 3.37 mg kg^-1 higher, respectively, than in the control. Application of sewage sludge into the soil posed a potential risk of heavy metal pollution. Soil type, sludge characteristics and application time should be taken into account simultaneously for reducing the risk of heavy metal pollution of the soil in making agricultural use of sewage sludge.

Abstract:Basic properties and heavy metal contents were investigated of paddy soil next to a typical used electronic device disassembling site in the Yangtze River Delta. Results show that its soil pH varied from 3.8 to 4.4, with an average of 4.1, which was obviously lower than that (pH=6.0) obtained during the Second National Soil Survey of China, demonstrating severe soil acidification. Its Cu and Cd content was 8.6 and 31.0 times as much as that, respectively, of Grade ⅡCriteria of the National Standard for Environment Quality. Its synthetic pollution index reached 32.3, indicating serious pollution. Soil pH is a leading factor influencing soil pollution of heavy metals, because lower pH improves activity of heavy metals. The extraction rate of Cu and Cd with 0.1mol L^-1 HCl was 72.0% and 50.8%, respectively, and their accumulation in the plant of rice was significant, especially in grains, where the content of Cd was 2 times as high as the criterion in the National Hygienic Standards for Grains. Obviously, soil acidification and heavy mental pollution synchronously existed in this farmland, posing potential health risk through the food chain. It is, therefore, essential to take positive measures to control the pollution and remedy the polluted soil.

Abstract:Nanocolloids in three Chinese soils were studied with the aid of atomic force microscopy (AFM), and their mean diameter and polydispersity index (PI) were used as parameter to characterize their particle size and morphology. Nanocolloids of JH-4 soil (from Jiuhua, Jiangsu Province) are mainly composed of clay mineral particles of regular sharp, with a mean diameter of 21.5 nm (n=98) and PI of 1.9. The particles are partially coated with colloidal organic matter. Similarly, nanocolloids of FY-1 soil (from Fuyang, Zhejiang Province) have a mean diameter of 20.3 nm (n=133) and a PI of 2.0 though they are irregular in shape and almost completely coated with colloidal organic matter. In contrast, nanocolloids of DX-9 soil (from Dexin, Jiangxi Province) are much larger in mean diameter being 56.3 nm (n=147), but lower in PI being 1.3, spherical and rod in shape, and less coated by colloidal organic matter. Nanocolloidal morphology varies significantly with pH: declining pH coagulates nanocolloids whereas rising pH disperses them. Adding Cu²⁺ to the nanocolloids also coagulates them. These morphological changes may be related to such properties of the nanocolloids as electrical charge and organic matter content. Knowledge on size and shape of nanocolloids and effects of pH and heavy metal ions on them may help understand the roles of nanocolloids in facilitating movement and transport of metal contaminants in soil and water environment.

Abstract:Soil organic matter plays a key role in global carbon cycling and global climate changing. Relationships between organic matter (SOM) content and soil pH in topsoil of zonal soils of the whole country and six great geographical regions (i.e. Eastern, Southern, Northern, Northeastern, Northwestern and Southwestern China) were studied statistically based on the data of 886 soil profiles of zonal soil types defined during the second national soil survey of China. Results show that SOM content and soil pH varied significantly from one geographical region to another. There was obvious trend that SOM contents decreased with increasing soil pH, showing a significant negative correlation with soil pH ( r = -0.332~-0.530, p < 0.001). Partial correlation between them, with controlled annual mean temperature, annual mean precipitation and altitude, was also significant at 0.01 level (r_p= -0.217~-0.322). An exponential equation (SOM = a e ^{b pH}, a and b were fit constants) can well describe the relationship between SOM content and soil pH The variance of soil pH is found to contribute 12.2% ~22.9% to the total variance of SOM content in the country and the six geographical regions.

Abstract:A batch equilibrium experiment was carried out to study adsorption and desorption of Chlortetracycline (CTC) in four types of soils, namely Ustic Cambosols collected form Fengqiu of Henan, Udic Argosols collected from Nanjing of Jiangsu, Gleyic-Stagnic Anthrosols collected from Changshu of Jiangsu and Ali-Perudic Ferrosols collected from Yingtan of Jiangxi. Results show that the linear model is not appropriate to describe any of the experimental sorption-desorption data, while the Freundlich model and the Langmuir model fit pretty well. Different sorption behaviors of Chlortetracycline were observed in the four tested soils, with K_f values varying sharply, 1 135 L kg^-1 for Cambosols; 1 250 L kg^-1 for Argosols; 2 618 L kg^-1 for Anthrosol; and 4 315 L kg^-1 for AliHaplic Acrisol. The apparent sorption/desorption hysteresis was quantified for each sample. It had been observed that K_f values are in a significantly negative correlation with soil pH.

Abstract:Characteristics of nitrogen mineralization in different soil layers were studied in a seven-year-old protected tomato field irrigated in three ways, infiltration irrigation, drip irrigation and furrow irrigation, using the long-term intermittent leaching aerobic incubation method (Stanford and Smith). In infiltration irrigation, transpiration semi-soft pipes were laid down 30 cm down in the soil. The experiment was managed in the same way as in the local farming production in irrigation, fertilization and field management. When the water suction in the soil reached 40 kPa at 20 cm in depth, irrigation began. The irrigation rate of infiltration irrigation and drip irrigation was half the rate of furrow irrigation in each event. Results show that mineralized N decreased with soil depth in content. Based on the correlation curve of cumulative amount of mineralized N and incubation time, the soil within the depth of 0～50 cm could be divided into three layers, i.e 0～20, 20～40 and 40～50 cm in both infiltration irrigation and drip irrigation, and 0～30, 30～40 and 40～50 cm in furrow irrigation. A two-pool model was used to fit N mineralization in different layers. Comparison between irrigation methods showed that in the 0～10 cm soil layer, the content of mineralizable N (N₁) followed the order of drip irrigation > furrow irrigation > infiltration irrigation, and that drip irrigation was the highest in mineralization rate ( k₁) of mineralizable organic N, suggesting that drip irrigation facilitates formation of mineralizable organic N in the surface layer of the soil. Compared with infiltration irrigation and furrow irrigation, long-term drip irrigation is more conducive to improving quality of soil organic nitrogen in protected fields.

Abstract:Structure of a production water microbial community in a Daqing petroleum reservoir was investigated by T-RFLP (Terminal Restriction Fragment Length Polymorphism) and clone libraries approaches. Small subunit rRNA gene (16S rDNA) was retrieved from the samples sampled in July and October 2005. T-RFLP analyses were conducted with the results that the archaeal community was less diverse than the bacterial community. Time change resulted in the shift of microbial community structure; however, the structure of the archaeal community was not remarkably different between July and October 2005. In contrast, the patterns of bacterial community showed significant difference in these two months The archaeal 16S rDNA partial sequences were mainly affiliated with Methanosarcinales and Methanomicrobiales. The bacterial phylotypes were very closely related to the “Betaproteobacteria” “Gammaproteobacteria” “Deltaproteobacteria” “Epsilonproteobacteria” , Bacteroidetes, and Deferribacteres as well as a deepbranching microbial cluster which was predominant microorganisms in the production water from October 2005.

Abstract:A field experiment was conducted to investigate effects of inoculation of faba bean with rhizobium GS374 on total yield and nodulation of faba bean in a fababean/maize intercropping system receiving nil or 225 kg hm^-2 N. Results show that biomass or grain yield of fababean in Treatment N₀ where fababean was inoculated rhizobium GS374 was similar to those in Treatment N₂₂₅ where fababean was not inoculated with rhizobium regardless of whether planted sole or intercropped. However, in Treatment N₂₂₅, nodulation of faba bean was facilitated by rhizobium inoculation. Biomass of fababean was significantly enhanced by rhizobium inoculation, intercropping or N fertilization as compared with their respective check, while grain yield was increased only by intercropping. Both biomass and grain yield of maize were significantly improved by N fertilization. In Treatment N₂₂₅no significant effects of rhizobium inoculation and intercropping were observed on biomass of maize, while in Treatment N₀, the effect of inoculation on grain and biomass yield of maize in the intercropping system was significant, increasing by 343% and 256%, respectively. Inoculation also significantly improved grain-yield-based land equivalent ratio (LER) in treatments receiving N and biomass-based LER in Treatment N₀. In addition, rhizobium inoculation markedly increased nodule number and nodule dry weight per faba bean plant, but its effect on nodule number was less in the intercropping system than in the sole system. So it is held that inoculation of bean crops with appropriate rhizobium is an approach to further promoting the merits of the legumious/gramineous intercropping system.

Abstract:A field experiment was carried out to explore dynamics of bacteria，fungus and actinomyces in population in rhizospheric and nonrhizospheric soils of winter wheat growing under different concentrations of atmospheric ozone (100 and 150 nl L^-1). Results suggest that with the succession of the growing stages, the microbes in total showed a regular curve, reaching a peak at the heading stage. In the rhizospheric and non-rhizospheric soils, bacteria and fungi displayed a saddleshaped curve, rising first and declining later, reaching a peak at the heading and booting stages, respectively, whereas actinomyces a declining trend throughout the growing period. During the entire growth period，O₃treatment had significant effect on microbes, with bacteria dropping significantly in population under elevated O₃ concentration. However, fungi varied sharply only at the mature stage and actinomyces did insignificantly at any stage.

Abstract:Plenty of reports about effects of intercropping improving yield and reducing disease incidence are available, but little was reported about the mechanism of the effects. RAPD and T-RFLP methods were used to study effects of intercropping of cucumber with wheat, vicia villosa and clover, individually, on cucumber disease indexes, cucumber rhizosphere soil microbial community diversity and yield. Results showed that intercropping of cucumber with wheat and vicia villosa increased soil microbial community diversity in cucumber rhizosphere, and the effect of the latter was the most prominent. All intercropping modes increased cucumber yield significantly (p< 0.01), and the effect of the intercropping of cucumber with wheat was more significant over that of the others. Meanwhile, intercropping decreased disease indexes of angular leaf spot, powdery mildew, downy mildew and Fusarium wilt, and decreased population of Fusarium oxysporum no matter with what plant. So it is quite obvious that intercropping increasees soil microbial community diversity and yield of cucumber, but mitigates diseases.

Abstract:Paddy fields are an important source of atmospheric methane. One of the objectives in methane researches is to estimate exactly the amount of methane emission from paddy fields. Currently there are mainly four methods: 1) extrapolation based on field measurements or specific emission coefficient and the acreage of paddy fields the value represents; reckoning by combining conversion coefficient of rice net primary production with models; conversion based on amount of organic carbon newly applied into the soil or the intrinsic soil organic carbon; and calculation by modeling. Besides, there are some other methods, like combining modeling with GIS technique or others. Spatial and temporal variation of methane emission from paddy fields are the primary factors leading to uncertainty of estimation. Statistic analysis shows that the amount methane emission emitted from the paddy fields in China is estimated at 8.4(7.2~9.5)Tg a^-1.

Abstract:Rice paddy field is an important source of CH₄ and N₂O emissions to the atmosphere. Not only does application of nitrogen fertilizer affect CH₄ and N₂O emissions, but also lead to NH₃ volatilization, NO₂^- and NO₃^- leaching and N loss in the form of N₂O and N₂. The addition of urease inhibitor and nitrification inhibitor decreased N₂O emission considerably by slowing down urea hydrolyzation and inhibiting nitrification and denitrification. However, controversial reports were available on their effects on CH₄ production and emission. HQ and DCD are a pair that has currently attracted more attention in the research of this field. In this paper review is presented on general properties and mechanism of nitrification inhibitor and denitrification inhibitor, application of HQ/DCD in the paddy ecosystem and its effect and problems, and in particular, mechanism of HQ/DCD affecting CH₄ emission, with a view to providing some theoretical bases for reasonable application of HQ/DCD, effective reduction of emission of greenhouse gases and high use efficiency of nitrogen fertilizers in paddy field.

Abstract:Phosphorus is one of the important nutrients in growth and development of plants. In global agriculture, deficiency of soil available phosphorus is a major factor restricting plant production. However, soil has a large pool of fixed phosphate, which is not readily available to plants, but potentially accessible to crops. Different approaches have been tried to increase their availability. Among them bio-solubilization of phosphate plays an important role in solubilizing soil fixed phosphates. In the process, the functional genes of phosphate solublising microorganisms could be crucial in manipulation of the release of soil phosphate. Therefore, understanding molecular mechanisms of this process is essential in exploiting phosphate solublising microorganisms in efficiently tapping the soil phosphate resources for agricultural production.

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