Abstract:Soil erodibility K-factor is an indispensable parameter in soil erosion prediction models, such as USLE and RUSLE. Immeasurable error might result from direct indiscriminate use of these empirical models in estimating K-factor. Based on observed K factors of seven typical soils in subtropical China, uncertainties of five K-factor prediction models (i.e., nomogragh model, modified nomogragh model, EPIC model, Geometric mean particle model, and Torri model) are evaluated by means of statistics such as mean absolute error(MAE), mean relative error(MRE), root mean squared error(RMSE) and accuracy factor (A_f). Results show that the five models could be lined in the order of Torri modelMRE for the Torri model is only 0.291, it is still high in uncertainty. However, an optimized Torri model can minimize the uncertainty. Its linear regression coefficient between observed K factors and predicted K factors is b =1.028 (R²＝0.921，^p<0.01), with an MRE being 0.120. It is therefore applicable to prediction of soil erodibility K-factor of certain soils in subtropical China.

Abstract:Soil erosion prediction models are of great significances in formulating reasonable strategies for soil and water conservation. Rill erosion is an important component of hillslope soil erosion. To well understand and predict rill erosion is essential for hillslope erosion prediction. In this study, a physical-process-based model for predicting rill erosion is developed, encompassing water flow continuity equation, hydrodynamics equation, sediment transport equation, for a well-defined rill channel. Finite element model was used to numerically solve the hydrodynamic and sediment continuity equations. Rational model parameters were used in this simulation study. A series of case studies were conducted with parameters determined of a silty loess soil from the Loess Plateau of China to compare outputs of the model with spatial changes in sedimentation processes for a better understanding of rill erosion dynamics. The comparisons of the experimental results with the simulation outputs of the model were used to validate the model. The model is capable of simulating the dynamics of rill erosion processes, with good prediction performance. Therefore, the model is proven to be valuable for further development of the dynamic prediction model for temporal and spatial variation of rill erosion.

Abstract:The composition and distribution of mineral, major elements and rare earth elements (REE) in the granodiorite weathering crust in Antoun area in Attapeu Province of PDR of Lao was determined by means of rock thin section, XRD, XRF and ICP-MS etc. Results show all the samples, except for granodiorite, are acid. There is a thin siliceous crust on the top soil of the weathering profile. Quartz content reaches the highest in top soil where kaolinite and iron oxide contents are lower than layer under it. These are some typical characteristics of Spodosols. With intensifying weathering reaction, Fe₂O₃, TiO₂ and Al₂O₃ are enriched, and Na₂O, CaO and MgO, K₂O are leached in weathering material. It is assumed that some clay minerals in the top soil are washed away by rainfall and leached by acid solution in wet season, and that SiO₂ moves up to the top soil from the lower layers in dry season. The Chondrite normalized REE pattern shows typical enrichment of LREE, with ∑REE peaking up to 318 mg kg^-1 in central layer of the profile. Both Ce and Eu have a similar trend of variation in the profile, i.e. positive anomalynegative anomalypositive anomaly from bottom to top The highest ∑REE value occurs where negative Ce and Eu anomaly and relatively higher Fe²⁺/Fe³⁺ values also occur. Furthermore, there is a relatively significant correlation between ∑REE and Fe₂O₃ throughout the whole profile, reflecting that REE enrichment is related to adsorption of iron-aluminum oxides and relatively reductive-acid environment.

Abstract:With the aid of polarizing microscope and Sisc Ias V8.0 software, micromorphological features of the soils from typical farmland and a Chinese prickly ash plantation in the East Guanzhong region were observed and analyzed. Results show that the two sampling sites had the same soil profile structure, Ap1-Ap2-BC, and their fractions of coarse granule minerals were dominated with quartz and feldspar In comparison with the former, the latter was higher in content of organic matter, C/F_{(10 μm)} ratio, content of residual clay and amorphous iron, but lower in the trend of coarse particles becoming round and small, which indicates that the effect of “grain for green” is not significant on soil profile structure or mineral composition, but great on soil micromorphology. The soil in the Chinese prickly ash forest plantation is more capable of absorbing and reserve moisture, and tends to have higher organic matter.

Abstract:Lou soil (a well developed agricultural soil) in Loess Plateau can be sorted as a subgroup under the eumorthic anthrosois in the Chinese Soil Taxonomy (Revised Proposal). Soil moisture regime is an important diagnostic characteristic of the anthropic cumulic epipedons (the earth-cumulic surface horizon) and the sub-surface horizon (the argic horizon) of the diagnostic surface horizon. With soil retention capability, evaporation capability and soil water movability as starting point, soil hydrologic effect of the earth-cumulic surface horizon and the argic horizon of Lou soil is discussed in this paper.

Abstract:Soil temperature is an important soil physical property. Seasonal and regional variations of soil temperature affect growth, propagation and distribution of soil organisms, which are closely related to agriculture and eco-environment. Based on the data of mean monthly soil temperature and air temperature and precipitation in China from 1971 to 2000, seasonal and regional variations of soil temperature in China and impacts of air temperature and precipitation on soil temperature were analyzed. Results indicate that seasonal variation of soil temperature in China was distinct. It was the most distinct from spring to summer, when the 20℃ contour line jumped up beyond 25℃ in latitude from south to north, and the mildest from winter to spring. The seasonal variation differed significantly from region to region. The relationships of soil temperature with air temperature and precipitation also varied with the region. In the temperate zone and the Qinghai-ibet Plateau, soil temperature was mainly affected by air temperature, while in the tropical and subtropical zones, both air temperature and precipitation contributed to the seasonal variation of soil temperature.

Abstract:In order to study the soil salinization along the river and seacoast in the Yangtze River estuary in autumn after the Three-Gorge Reservoir impounded water for two years, soil samples were collected there and soil salt composition tested. With the aid of a statistic software, principal component analysis was conducted of types and characters of the saline soils therein, and cluster analysis of the soil salt profile types. Results show that in the two years after the Three-Gorge Reservoir began to impounded water the main type of soil in the Yangtze River estuary in autumn is saline fluvoaquic soil, of which the cation composition is dominated with Na⁺, whereas the anion composition with SO₄ ^2- which is a little more than Cl^-. Salt accumulation occurs mainly in the upper layers of the soil profiles and displays both shortterm peaks and a longterm accumulating trend. The aggravation of soil salinization was mainly caused because of the dry year. The extent of impacts of the Three-Gorge Reservoir needed further study. On such a basis, the author calls for sitespecific rational irrigation/drainage practices and measures to ameliorate Na⁺ type saline soil.

Abstract:Influence of antecedent soil moisture content on features of soil aggregates of a typical black soil farmland in Northeast China compacted mechanically was investigated by analyzing distribution of dry and waterstable soil aggregates, percentage of aggregate disruption (PAD_0.25), fractal dimension (D), mean weight diameter (MWD), mean weight soil specific area (MWSSA). Results show that dry aggregates over 2 mm were predominant in the black soil and the proportion of waterstable aggregates was increasing with declining particle size. Composition profile and fractal character of soil aggregates of compacted black soil were obviously affected by its previous soil moisture content. When soil moisture content was low, mechanical compaction promoted aggregation to a certain extent, but accumulated compaction of repeated mechanical operations with equal load reduced water stability and mechanical stability of the soil However, when soil moisture content was high, mechanical operations were relatively more liable to create negative effect on soil aggregation in black soil, e.g. aggravating destruction, inhibiting aggregation, reducing their water stability and mechanical stability. Moreover, it was also discovered that MWSSA had extremely significant linear relationships with PA_0.25, MWD, D and PAD_0.25, so MWSSA could also be cited an effective index in analyzing and studying soil aggregates. The findings may serve as theoretical basis for scientifically guiding operation of heavy machinery.

Abstract:Effect of application of ammonium-based N (NH ₄ ⁺) on N₂O emission was investigated in typical subtropical soils in China. Soil samples, collected from upland crop field (SU), brush-land (GB) and forestland (QF), were incubated with temperature kept at 30℃ and soil moisture at 60% of the water hold capacity (WHC) for 35 days after addition of ammonium sulphate, urea, and ammonium bicarbonate, separately. Each type of N fertilizer had three different application N rates 0, 100, and 250 mg kg^-1. Results indicate that in SU soil (pH=6.27), both nitrification and N₂O emission were stimulated by addition of ammonium sulphate, urea and ammonium bicarbonate. Net nitrification and N₂O emission increased with the fertilizer application rate. In acid GB (pH=4.82) and QF soils (pH=4.46), addition of ammonium sulphate inhibited nitrification, but dramatically stimulated N₂O emission; addition of urea and ammonium bicarbonate slightly stimulated nitrification, but slightly inhibited N₂O emission or showed no effect on both. Significant negative correlation was observed between the ratio of N₂O emission to net nitrification in acid soils treated with different forms of N fertilizers and the soil pH measured immediately after addition of N fertilizer. Mechanisms of the effects of different forms of N fertilizers on ratio of N₂O emission to net nitrification need to be further investigated.

Abstract:Distributions of water-stable aggregates and organic C, N and P were studied in upland red soils different in land use and fertility level. Results show that the content of aggregates >5 mm in wasteland was significant higher than in fields of other land uses. And peanut land and orchard was dominated with the fraction of 0.25~0.053 mm aggregates. Regardless of fertility levels, vegetable land was the highest in contents of soil organic C, N and P in all fractions of aggregates, except aggregates >5 mm, which illustrates that long-term fertilization in vegetable land has resulted in enrichment of soil organic C, N and P. In these upland red soils, soil organic C, N and P accumulated in aggregates of fractions >5 mm, 5~2 mm and 2~1 mm, which shows that soil nutrients in aggregate increased with the increase in particle size, especially soil organic C. Soil N followed a similar trend, but soil P was distributed quite evenly in water-stable aggregates. It was particularly so in high-fertility vegetable land and wasteland soil. The contents of 2~1 mm and 1~0.5 mm aggregates in upland red soils, regardless of land use, were extremely positively correlated with soil organic C, N and P.

Abstract:As shown in a previous study, soil carbon sequestration of the three typical paddy soils, i.e. Cabhaplic, Acihaplic and Typfec Stagnichydroagric Anthrosols in South China was related to physical protection in microaggregate size fractions, though varying with the soil types and management practices. Herewith the authors report a study on analysis of SOC binding forms in size fractions of micro-aggregates obtained by low-energy ultrasonic dispersion procedure from the studied types of paddy soils. Calcium bound SOC (Ca-SOC) was predominant in the coarse fraction of 2 000~200 μm, with the highest and the lowest content in purple paddy soil and in red paddy soil, respectively. On contrast, iron/aluminum oxyhydratesbound SOC(Fe(Al)-SOC) dominated the size fraction of <2 μm, with the highest and the lowest content in red paddy soil and in purple paddy soil, separately, which was in coincidence with the content distribution of Fe/Al oxyhydrates in various particle size fractions. Statistic analysis indicated significant positive correlation of ratio of LOC to SOC with that of Ca-SOC to SOC, and significant negative correlation of the ratio of LOC to SOC with that of Fe (Al)-SOC to SOC. Ca-SOC and Fe(Al)-SOC in coarse aggregates of 2 000~200 μm showed the most sensitive response to longterm tillage and fertilization practices, and SOC accumulation in paddy soils under good management practices was represented mostly as increase in Fe(Al)-SOC. Fe/Al oxyhydrates in coarse aggregates from the red paddy soil among the three showed the most intensive chemical protection of organic carbon. Thus, chemical protection of SOC physically protected in coarse fractions by binding with Fe/Al oxyhydrates during micro-aggregate turnover was supposed to be a prevailing mechanism of SOC sequestration in these paddy soils.

Abstract:Effect of long-term fertilization on topsoil organic nitrogen fractionation and organic carbon was explored through a 13 year-old experiment on Fluvo-aquic soil under a maize-wheat rotation system in Fengqiu County, Henan Province, China. Compared with CK (no fertilizer application) or application of mineral fertilizer, application of manure or manure mixed with mineral fertilizer significantly increased total nitrogen, acidolysable organic nitrogen, ammonium nitrogen, amino acid nitrogen, non-hydrolysable nitrogen and organic carbon. Organic nitrogen is mainly made up of ammonium nitrogen and amino acid nitrogen, and secondarily of unidentified acidolysable nitrogen, non-acidolysable nitrogen, and amino sugar, which accounts for the smallest proportion. Application of manure is especially favorable to the formation of amino acid nitrogen and non-hydrolysable nitrogen. Compared with that in the control, the proportion of acidolysable organic nitrogen to total nitrogen decreased mainly due to decreasing proportion of amino acid nitrogen and ammonium nitrogen to total nitrogen. Applying manure resulted in greater contents of total nitrogen and organic carbon than the initial contents when the experiment started. When the treatments were kept the same in NPK application rate, the application of manure mixed with mineral fertilizer increased soil N supply capacity, content of organic matter and crop yield, suggesting that it is the best fertilization method that favors environment protection and maintenance of soil fertility.

Abstract:A long-term fertilization experiment, designed to have nine treatments varying in application rates of N, P, K and pig manure, with or without incorporation of rice straw to the field, was carried out to determine effect of these treatments on the concentrations of Cu, Zn, Fe, Mn, Pb and Cd in soil, rice plant and brown rice. Results showed that the total soil Cu, Zn and Cd concentrations in Treatment MS(application of pig manure with incorporation of rice straw to the field), NMS(application of N, pig manure with incorporation of rice straw to the field) and NPKMS(application of N, P, K, pig manure with incorporation of rice straw to the field) were significantly higher than in the other treatments, however, they were not significantly different from each other in total soil Fe, Mn and Pb. Compared with CK(no fertilizer), all the fertilization treatments increased soil available Cu, Zn and Fe, and, the MS, NMS and NPKMS treatments did soil available Cu, Zn and Cd, significantly, but did not differ much in soil available Pb between the treatments. The Cu, Zn, Fe, Mn and Pb concentrations in brown rice varied slightly or insignificantly from treatment to treatment. However, the Cd concentration in brown rice in Treatments MS, NMS and NPKMS was higher than the upper limit of the criteria (>0.2 mg kg^-1) of the National Standard for Food Hygiene for Cd concentration. The amounts of Cu, Zn, Fe, Mn, Pb and Cd absorbed by rice plant and accumulated in the aerial part the plant was positively related with the biomass of the aerial part. Soil available Cu, Zn and Cd concentration was positively correlated with the total soil Cu, Zn and Cd concentrations in the soil, and only the concentration of Cd in brown rice could be predicted through total and available concentrations of Cd in the soil. Attention should be paid to the soil Cd pollution caused by long-term application of pig manure containing high concentrations of heavy metals.

Abstract:A GC/MS method, using soil incubated with ¹⁵N-NH₄ ⁺and glucose, was developed. The method is efficient in evaluating ¹⁵N incorporation into soil amino sugars and amino acid enantiomers, and in distinguishing between inherent and newly-synthesized amino compounds. As extraneous isotope nitrogen is rapidly assimilated and synthesized into amino compounds in the presence of active substrates, it is feasible to determinate change in peak intensity of the isotope with the aid of the mass spectrum technique. And as there is only one N atom in the molecule of amino sugar and neutral or acidic amino acid, ¹⁵N enrichment degree can be worked out by calculating ratio of the relative intensities of F+1 (isotope peak) and F (parent peak). Since mass spectrum fragment m/z 439 of lysine, a kind of alkaline amino acid, contains two N atoms, ¹⁵N enrichment degree can be calculated based on variation of the relative intensity of m/z 441 (F+2).¹⁵N enrichment degree in the target compound can by expressed as APE, but APE of D-amino acid needs to be calibrated by hydrolysisinduced racemization (HIR%). In general, APE value represents the turnover velocity of amino compounds. So it is a powerful means available for investigating soil nitrogen dynamics.

Abstract:Nutrient release rate is the key to quality determination and evaluation of slow/controlled-release fertilizers. Nutrient release characteristics of five slow/controlled-release fertilizers were evaluated according to the industry standard of slow/controlled-release fertilizer (HG/T 3931-2007) and the standard recommended by the Committee of European Normalization (CEN) using water extraction method and soil incubation method. Nutrition release was accelerated when temperature of the solution in the water extraction method was raised from 25℃ to 100℃. The regression equation for prediction and forecast of the 100℃ fast extraction method fit a quadric equation in one variable with a correlative coefficient being >0.98, and could be used to quickly and precisely predict release duration of slow/controlled fertilizers. The difference between the measured value and predicted one was only one to three days. Besides, electric conductivity measurement could also be used to quickly and precisely predict nutrient release rate and duration. By using the electric conductivity measurement at 100℃, the release duration of CRF2 and CRF3 was predicted to be 65days and 81days, less than 3.5% in difference from their measured duration of 66 days and 84. Parameters, like initial nutrient release rate, mean release rate, and release duration, could be used for integrative evaluation of slow/controlled-release fertilizers.

Abstract:Investigation of interactions and energy relationships between cations (Na⁺、K⁺、NH₄⁺、Ca²⁺、Zn²⁺, and Cd²⁺) and clay fraction of red soil with the aid of Wien effect in dilute suspensions Results show that the mean Gibbs binding energies of the clay fraction of red soil with cations are 4.50, 7.35, 7.15, 9.12, 9.84, and 9.63 kJ mol^-1 for Na⁺, K⁺, NH₄⁺, Ca²⁺, Zn²⁺, and Cd²⁺, respectively, in the experimental condition. Electric conductivity increased very fast with field strength in the suspension containing Ca²⁺, at a similar rate in the suspension containing K⁺, Zn²⁺ or Cd²⁺, but very slowly in the suspensions containing Na⁺ or NH₄⁺. In terms of releasing rate, the cations in the red soil suspension are in the order of Ca²⁺ > K⁺ > Zn²⁺ = Cd²⁺ > Na⁺ = NH₄⁺. The mean Gibbs free adsorption energies, ΔG_ad, of the cations remained basically the same when the field strength was in the range of 15 to 80 kV cm^-1 , but when the field strength reached over 100 kV cm^-1 ΔG_ad of the divalent cations were more obviously higher than of the monovalent cations, following an order of NH₄⁺ ≤Na⁺ < K⁺ < Cd²⁺ < Zn²⁺ < Ca²⁺. However, when the field strength got high up to 150 kV cm^-1, ΔG_ad of the cations were 0.64, 0.80, 0.57, 1.66, 1.43, and 1.27 kJ mol^-1 for Na⁺, K⁺, NH₄⁺, Ca²⁺, Zn²⁺, and Cd²⁺, respectively, which shows that the mean Gibbs free adsorption energy of the divalent cations were about 2.5-3 times as much as that of the monovalent cations. The cations in the red soil suspensions at a low field strength ranging from 10 to 30 kV cm^-1 showed a decreasing order of Na⁺ >> K⁺ = NH₄⁺ > Ca²⁺ > Zn²⁺ = Cd²⁺ in mean dissociation degree. The increasing rate of mean dissociation degree, which is the increment of dissociation degree induced by the increment of 1 kV cm^-1 in field strength, is the highest with Na⁺ being 0.000427 cm kV^-1, the second with Ca²⁺ being 0.000221 cm kV^-1, and the lowest with other cations in the range of 0.00012~0.00014 cm kV^-1.

Abstract:Arsenic sorption is the primary factor that governs bioavailability and mobility of arsenic in soils. However, studies on arsenate (As(V)) sorption have been mainly limited to soil minerals, and sorption reactions in soils as a whole in the presence of dissolved organic carbon are poorly understood. Mechanisms of As(V) sorption on red soil in the presence of oxalate or humic acid (HA) were studied using sorption isotherms and X-ray absorption fine structure (XAFS) spectroscopy. Arsenate, mainly as H₂AsO₄^- in soil solution at pH 6.0, was extensively sorbed by red soil mainly through ligand exchange. Both oxalate and HA could significantly decrease As(V) sorption through competing for sorption sites, and the competition was getting stronger with increasing concentrations of oxalate and HA. The XAFS data indicated that the sorbed As(V) formed inner-sphere complexes of bidentate binuclear configurations characterized by an As-Al bond distance of about 0.317 nm and an As-Fe bond distance of about 0.328 nm in red soil. The two As(V) complexes were stable regardless of As(V) loadings varying in the range studied. Their structures were free from the influence of oxalate and HA. This study illuminated the characteristics of As(V) sorption on red soil in the presence of oxalate and HA from molecular level and the findings might be of practical importance in controlling arsenate mobility and toxicity in soils.

Abstract:A field experiment was conducted in 2004 to investigate effects of the system of rice intensification (SRI) on soil biological properties. The treatment was compared with the control (TF, Traditional Flooding) in soil cultureable microorganisms (bacteria, fungi, actinomycetes), microbial biomass C and N, soil enzyme (urease, invertase, alkaline phosphatase, catalase) activity and soil available N and P. Treatment SRI was significantly higher than the control in population of cultureable microorganisms, microbial biomass C and N, regardless of sampling date and 12.6%, 30.0%, 15.1% and 13.8% higher in activity of urease, alkaline phosphatase, invertase and catalase, respectively at the tillering stage. The treatment was also higher than the control in soil available N, and however, showed no significant difference in soil available.

Abstract:Characteristics of soil fauna communities in Heptacodium miconioides woodland (Hmw) in Tiantai Mountain, Zhejiang were investigated monthly from April 2000 to April 2001, to study influences of litters, season, altitude, and some other factors on structure of soil fauna community. Results show 1) Acarina and Collembola were the dominant groups in Hmw accounting for 57.06% and 21.21%, respectively, while Hymenoptera, Diptera, Symphyla, Oligochaeta and Coleoptera were the common groups, accounting for 4.72%, 3.65%, 2.74%, 2.68% and 2.57%, respectively. 2) The number of individuals of soil fauna peaked in May and November, while it declined distinctly during the xerothermic period (from July to August) in the three plots of Hmw. 3) The soil fauna of Plot P2, which is located in an area moderate in altitude, and showed co-dominancy in community, was the highest in density, number of groups and diversity index among the three plots of Hmw. 4) The vertical distribution of soil fauna showed a distinct characteristic of surface accumulation in the three plots, however, the number of individuals of soil fauna in the deep layer more than surface layer during the xerothermic period (from July to August).

Abstract:A review is presented of the nucleic acid extraction methods and the subsequent nucleic acidbased analysis applied in the study of soil microbial diversity. It is important to study microbial diversity not only for basic scientific research, but also for a better understanding of the relation between diversity and community structure and function. It is, therefore, essential to master and comprehend appropriate, reliable and accurate methods for studying soil microbial diversity. Traditionally, the analysis of soil microbial communities used to depend on culturing techniques. The inability to culture most of the microbes from soil samples is a fundamental obstacle to understanding soil microbial ecology and diversity. Other methods such as the community-level physiological profiling (CLPP), analysis of phospholipid fatty acids (PLFA) and nucleic acid-based methods are now used to mea sure a greater proportion of the soil microbial community. Nucleic acid-based methods include molecular fingerprints pattern based on PCR technique, nucleic acid hybridization, DNA microarrays technology and so on. These methods open up new approaches to measuring soil microbial diversity and help update understanding of soil microbial community and diversity. Given the current state of knowledge, the authors feel that the best way to study soil microbial diversity would be to use a variety of tests different in endpoints and degree of resolution to obtain more information regarding the microbes, which will eventually enhance our knowledge about soil microbial diversity.

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