Abstract:To perform sustainable land use management, it is essential to predict accurately spatial distribution of soil fertility quality and identify problem areas in soil fertility quality. Based on the soil fertility quality data of a total of 99 samples of topsoil (0~20 cm) from Yucheng City, the sequential Gaussian simulation (SGS) method was applied to a conditional stochastic simulation in this paper to quantitatively assess the uncertainty of spatial distribution prediction of soil fertility quality and identify problem areas in soil fertility quality. Results show that the southwestern and the central parts of Yucheng City are higher than the northern part, the northwestern and the southeastern parts in soil fertility quality. By making use of the relationship between soil fertility and crop yield, the threshold value for identifying problem areas in soil fertility quality is determined to be 0.55. The soil quality indices of most parts of the city are beyond the value. Using this cutoff value and the spatial uncertainty assessment, only a total of 2 494 hm² of land is identified as problem area. The main limiting factors are soil texture and low soil total phosphorus content in the northern part of the study area, soil salinization in the northwestern part, and low soil nutrient availability nutrient, soil salinization, poor soil texture and low soil total nitrogen content.

Abstract:A SVM (Support Vector Machine)-based method for productivity evaluation of Standard Cultivated Land (SCL) and a GASA-optimized algorithm for selecting of SVM parameters is put forward in this paper. Based on determination of the indices for productivity evaluation and grading of SCL, this method first made use of the data of the samples in the farmland productivity survey and its evaluation results of traditional integrated productivity factors method in building up a SVM sample set, trained SVM with the GASA-optimized algorithm, and set up a SVM model for evaluation and grading of SCL. This method was tested on productivity evaluation of SCL in Lucheng District of Wenzhou City, Zhejiang. The results indicate that the second grade and third grade of SCL accounts for 45.04% and 54.96%, respectively, of the total SCL in area ( 115.7 hm² ) which the test samples stand for. The evaluation using this method reached 100% in accuracy. The evaluation of the test samples using the BP networks method was only 90% in accuracy. The findings show that the SVM method is much higher in accuracy than the BP networks method, and therefore this effective new method can be used efficiently to evaluate and grade SCL in productivity．

Abstract:Soil series is the basement of the soil taxonomy and also a bridge connected with their productivity and eco-environmental evaluation, Therefore, they are of great theoretical and practical significance to soil classification and its application. On the basis of the data collected during of the second national soil survey and ongoing researches, through field observation and soil investigation of and analyses for soil physical and chemical properties and trace elements in Rugao County, Jiangsu Province, soils of the county were classified by series and their productivity and eco-environmental features studied. In line with principles, basis and diagnostic soil horizons for soil classification set in the study, the soils of the county were sorted into 9 soil series. The differences between the series in basic soil physical and chemical properties and trace elements validated reliability of the classification methods. The differences between various series were significant differences in particle size compositions, chemical properties, nutrient properties, and trace elements reflecting that each soil series has its own unique productivity and eco-environmental characteristics.

Abstract:A typical subtropical agricultural catchment named Sunjia catchment in Jiangxi province was chosen and the WaSiM-ETH distributed hydrological model was employed to simulate hydrological processes and to quantify interflow at catchment scale. The results suggested that the WaSiM-ETH simulation showed acceptable accuracy and precision in simulation although there were complicated hydrological processes and various land use types in the studied catchment. Relative error of the simulated to measured outflow varied from 3.7% to 4.3%, and linear regression determining coefficient ( R²) reached as higher as 0.96. During the period of 2002-2003, the model predicted annual evapotranspiration ranged from 672 mm to 804 mm, accounting for 39.6%～52.5% of annual precipitation. Annual interflow of the catchment ranged from 542 mm to 666 mm, took 35.4%～39.2% parts of annual precipitation, being higher than 8.8%～21.4% of ratio for annual overland flow. Based on our collective data in this study, we may conclude that the WaSiM-ETH model is flexible and capable of the hydrological simulation in subtropical agricultural catchments as it can not only model the surface hydrological process, but also quantify interflow at catchment scale.

Abstract:Soil salinization is one of the primary environmental problems, which affects sustainable development of the windbreak forest belts alongside the Tarim Desert Highway. In order to study soil salinization caused by irrigation with saline water of the windbreak forest belts along the Highway since their establishment, distribution of soil salts under the forest belts was investigated. By utilizing the data collected during the soil salt survey before the establishment of the forest belts, the methods of statistical analysis, correlation analysis and grey relational analysis were adopted in the primary study of soil salt ions, status quo of soil salinization and its driving force in the 40 monitoring posts distributed alongside the highway. Results show that after the establishment of the windbreak forest belts, the contents of various salt ions increased significantly in the soil, with cations showing a decreasing order of Na⁺+K⁺＞Mg²⁺＞Ca²⁺in content and anions one of Cl^-＞CO₃^2-＞SO₄^2-＞HCO₃^-. Soil salinization in the forest belts was dominated by Chloride and Sulfate-chloride, which accounted for 84.2% and 15.8%, respectively, of the monitoring posts. About 81.6% of the monitoring posts reported moderate soil salinization. The grey relational analysis reveals that irrigation history is the major driving force of soil salinization in the forest belts and is then followed by mineralization, pH and water table of the grounderwater.

Abstract:Behaviors of Cu²⁺ in adsorption-desorption in three variable charge soils and two constant charge soils as affected by its concentration were studied. It was found that the curves of pH and Cu²⁺ adsorption rate always intersected in the section of low pH, and the curves tendedd to lean towards the right when Cu²⁺ rose in concentration, and confirmed that in variable charge soils, adsorbed copper ions could be desorbed with deionized water and desorption peaks observed. The study on change in pH of the adsorption system as affected by desorption revealed that when the system adsorbing Cu²⁺ was lower than 5.0 in pH, its pH would rise after desorption of the ions, but when the system was higher than 5.0 in pH, ts pH would decline, which suggest that pH5.0 is probably another turning point where the mechanism of the soil adsorbing Cu²⁺ changes. Existence of weak adsorption state in specific adsorption and causes of its formation were also discussed.

Abstract:As an important parameter, Reduction capacity (RC) is recognized for evaluating redox characteristics of humic acids (HA) in environment. In this study, three HAs (tagged as SH, TJ and JY respectively) from different sources were selected and pretreated through methods of saturated hydrogen oscillation and soil solution incubation respectively for determining chemical reduction capacity (CRC) and microbial reduction capacity (MRC) by reduction of two electron acceptors including ferric nitrate (Fe(NO₃)₃) and ferric citrate(FeCit), in comparison with native reducing capacity (NRC) obtained through the same measurement method based on HA samples without any pretreatments. The results suggested that HA extracted from local humus layer of soil in JinYun Mountain had the greatest RC among three humic acids, which showed the highest RC values of 20.21±0.26 mmol_cmol^-1C(NRC), 26.02±1.12 mmol_cmol^-1C(CRC) and 29.29±1.56 mmol_c mol^-1C(MRC), respectively. Meanwhile, Of the two electron acceptors, Fe(NO₃)₃ induced much higher RC than FeCit. In addition, HA in solution status showed higher RC than in solid status. All the above findings demonstrate that reduction capacity (RC) of HA is a variable parameter, which is closely related to the structure and properties of the HA per se and also affected by its initial status (e.g. solution or solid) and electron acceptors. Comparison between the RC indexes of the HAs shows that CRC and MRC were evidently higher than NRC, however no significant difference in magnitude was observed between CRC and MRC. However, whether it is feasible to use CRC to characterize MRC needs further study for validation.

Abstract:Soil samples for analysis were collected at different depths within 0~60cm from three plots different in irrigation mode in the same protected field where an irrigation experiment had been going on for 13 years to explore the effect of irrigation mode on characteristics of soil acidification. Analysis of the samples show that the soil active acidity and the content of exchangeable acid decreased with soil depth in all the treatments. Soil active acidity in the 0 ~ 40 cm soil depth varied sharply between the treatments, displaying a general order of furrow irrigation > subsurface irrigation > drip irrigation, while the differences in content of exchangeable acid between the treatments were significant mainly at the depth of 0 ~ 30cm, showing an order of subsurface irrigation > furrow irrigation > drip irrigation. Content of exchangeable Al³⁺ increased first and then decreased with increasing depth in all the three treatments, but the lowest in the treatment of drip irrigation. Soil BS increased with soil depth and showed an order of drip irrigation > subsurface irrigation > furrow irrigation in the 0~30cm soil depth. Soil pH was negatively related to exchangeable acid and nitrate nitrogen, but positively to base saturation, especially exchangeable Ca²⁺ saturation, both to an extremely significant extent. The proportion of Al³⁺ against exchangeable acid was negatively related to organic matter content, also to an extremely significant extent. In conclusion, soil acidification in protected fields is closely related to content of nitrate nitrogen, base saturation and content of organic matter. Compared with furrow irrigation and subsurface irrigation, drip irrigation is conducive to inhibition of soil acidification.

Abstract:Models are often used to estimate regional greenhouse gas emissions by scaling up verified point data to a region, and errors may arise in this spatial up-scaling process. To compare the error sizes of different up-scaling methods, we collected input data of 59 sites required by CH4MOD in Jiangsu Province of China to simulate CH₄ emission from rice paddies, and applied three upscalling methods: 1) Take the average of all input parameters of 59 sites as the input parameters to model, then calculate the regional CH₄ emission, which is average-parameter method; 2) Apply the parameters of one representative sample site to the model, and extend the estimation directly to the regional scale, which is typical-point method; 3) Generate 100 virtual sites randomly according to the statistical characteristics of the parameters of 59 samples, then input them to run the model 100 times and get the average of simulated results as the regional CH₄ emission, which is the Monte Carlo method. The results showed that, when compared with the average of simulated results of the 59 individual sites, the average-parameter method and the typical-point method have a relative error of -19.60% and -19.74%, respectively, whereas the Monte Carlo method can effectively reduce the relative error to 3.29%. We also analyzed the error sources of average-parameter method and the typical-point method.

Abstract:Currently, limited information is available regarding the effects of different farmland management practices on fluxes of methane (CH₄) and nitrous oxide (N₂O) from the fields. In this study, diurnal and seasonal variations of CH₄ and N₂O fluxes from fields under different farming practices, i.e. nowadays commonly used mulched drip irrigation (MD) and traditional mulch-free flood-irrigation (MFF), were monitored with closed static chambers and a modified gas chromatograph (HP4890). This study was conducted in a cotton field in Xinjiang, Northwestern China. Results show that the diurnal variations of CH₄ in treatments MFF and MD were in sharp contrast. In the former CH₄ flux descended first and then ascended, while in the latter it proceeded reversely. Over the whole cotton growing season, however, it had no clear pattern to follow. The soil in the former absorbed a total of CH₄ 0.7 ~ 23.1 mg m^-2a^-1 from the atmosphere, while the soil in the latter released a total of CH₄ 45.2 ~ 52.5 mg m^-2a^-1. As for N₂O fluxes, the two treatments exhibited similar diurnal and seasonal patterns of a curve going up first and down later. However, in treatment MFF daily N₂O flux was much higher than in treatment MD. Over the whole cotton growing season, the total N₂O emission was higher in treatment MFF (N₂O 99.3 ~ 320.0 mg m^-2a^-1 ) than in treatment MD (N₂O 60.0 ~ 259.0 mg m^-2a^-1). All the findings suggest that the MD system could alter the direction of the CH₄ flux between the soil and the atmosphere of field agro-ecosystem in the arid region. It enhanced considerably CH₄ emission, but did not affect much the diurnal or seasonal variation of N₂O fluxes, however, it did reduce N₂O emission from the soil quite significantly.

Abstract:An indoor experiment was carried out of having leaf litters from Pinus tabulaeformis and from other 10 species of trees decomposed, separately or mixedly to explore effects of the decomposition on soil properties and any synergic or offsetting actions between the two in mixture. It was found that decomposition of the leaf litters separately significantly increased the activities of soil enzymes, like urease, dehydrogenase and phosphatase, and contents of organic matter and available N, but varied sharply in the effect on available P and CEC in the soil. The decomposition of leaf litter from P. tabulaeformis mixed with that from Platycladus orientalis, Populus simonii, Robinia pseudoacacia, or Ulmus pumila , separately showed obvious synergic effects on total soil microbe. In decomposition, its mixture with that from Hippophae rhamnoides affected activity of the soil enzyme of phosphatase, synergically, but its mixture with the leaf letter from P. orientalis, Betula platyphylla or U. pumila , separately, did reversely. Its mixture with leaf litters from most of the trees, separately, showed a synergic effect on soil available K content, but, reversely on soil available P content. Its mixture with that from P. simonii, H. rhamnoides or Amorpha fruticosa , separately, displayed a synergic effect on soil organic matter content. In terms of soil properties as a whole in their effects, its mixture with leaf litter from H. rhamnoides, R. pseudoacacia, P. simonii or A. fruticosa , separately, all acted synergically, whereas its mixture with that from P. orientalis, Quercus liaotungensis, B. platyphylla, Larix principis-rupprechtii , or Caragana microphylla , separately, did reversely.

Abstract:A pot experiment was carried out using brown earth collected from local farmland to study effects of soil bulk density on photosynthesis of maize (photosynthesis rate, stomatal conductance, intercellular carbon dioxide concentration) and chlorophyll(a,b), and their regulation through application of organic manure and tillage. Results show that between treatments different in bulk density little difference was observed in chlorophyll concentration in leaves of maize before its jointing stage, but much was afterwards (p＜0.01), continuous increase in chlorophyll concentration was found during the growth stages under study; photosynthesis rate was negatively related to soil bulk density and intercellular carbon dioxide concentration, but positively to stomatal conductance; in soils high in bulk density, application of organic manure to raise soil organic matter up to 40～50 g kg^-1 showed an ideal regulatory effect, while in soils low in bulk density, the effect of soil organic matter in the set range of the study was always significant. Soil organic matter around 15 g kg^-1 restricted the growth of maize, and should be raised at least to 3% or more; tillage improved physiological indices of the maize, however, depth of the tillage had little significant effect on chlorophyll and photosynthesis indexes; when the tillage reached 30～40 cm in depth, its effects on various indices peaked and any further increase in tillage depth did not improve the effectcor.

Abstract:Effects of long-term fertilization on SOC pools and their turnover rates of a red soil were studied using soil organic carbon (SOC) physical fractionation and chemical analysis methods. Results showed that balanced fertilization (NPK, 2NPK) and organic fertilizer application (NPKOM, OM) significantly enhanced maize yield and reduced the temporal variation of yields, and increased the contents of SOC and labile organic carbon (LOC) as compared with control (CK). Based on the five physically fractionated SOC pools, s+c_mM and s+c_M associated C accounted for 31%～53% and 28%～38% of SOC，followed by fPOM (8%～15%) and iPOM_mM (7%～21%)，and then by cPOM (5%～12%)。Organic fertilizer application (NPKOM, OM) significantly increased POM associated C pools (cPOM、fPOM and iPOM_mM), but had no significant effect on mineral associated C pools (s+c_M and s+c_mM). As a result, the turnover rates of SOC were the fastest in the two treatments. The turnover rate was positively related with the ratio of LOC to SOC (r=0.66^﹡), but not with SOC. We can conclude that the balanced fertilization and organic fertilizer application can improve soil fertility but also benefit SOC accumulation.

Abstract:Differences between two paddy soils, high and low in soil fertility in the red soil region were explored in content of mineral N (NH₄⁺ and NO₃^-1) and nitrification intensity at the root surface and rhizosphere of rice and in the bulk soil, as well as in growth and N accumulation of rice seedlings at 40, 50 and 60 d after sowing. Results show that soil fertility had no significant effect on NH₄⁺-N content at the root surface and rhizosphere of rice, while high fertility significantly increased NH₄⁺-N content in the bulk soil, and NO₃^-1-N contents and nitrification intensity at the root surface and rhizosphere of rice and in the bulk soil, as well. The highest nitrification intensity was observed at 2 mm away from the root surface in both soils, being 0.20 and 0.31 μmol kg^-1 h^-1 in the low and high fertility soils, respectively. Nitrification intensity in the bulk soil decreased with the increasing distance from the root surface, and approximated to the background value at 10 ~ 40 mm and 20 ~ 40 mm away from the root surface in the low and high fertility soils, respectively. Rice planting significantly enhanced nitrification intensity in the rhizosphere of the plant as compared with CK (rice plant free). High fertility improved the growth of rice significantly, especially rice root growth and aerenchyma formation and increased N accumulation in the plant. The difference in soil fertility of paddy field might cause differences in rhizospheric nitrification intensity and rice NO₃^-1absorption, which might lead to stronger rice growth potential and N accumulation ability of the plant in the soil high in fertility. Hence, appropriate increasing soil fertility of red soil paddy fields is of great significance to improving nitrification in rhizosphere of the plants and rice N nutrition in the red soil regions of subtropical China.

Abstract:The study on changes in microbial properties as affected by addition of carbons of different sources and N concentration at the fertisphere is of great significance to understanding of effects of carbons of different sources regulating nitrogen transformation in fertispheres different in concentration and improving nitrogen use efficiency. Samples of paddy soils typical of the subtropical region of China were collected and treated with ammonium sulphate at different rates and carbons of different sources, separately to simulate different fertispheric nitrogen concentrations. The treated soil samples were then incubated in lab and analyzed for changes in biomass carbon and nitrogen of the soil microbes, nitrogen mineralization and functions of the microbial communities. It was found that after 7 or 35 days of incubation, in treatments high in N application rate, addition of glucose, cellulose and lignin separately increased microbial biomass carbon by 5.0%~126.8%, 17.5%~210.9% and 14.7%~210.0%, respectively, and microbial biomass nitrogen by -15.4%~109.3%, 32.0%~173.1% and -34.2%~194.8%, respectively, and in treatments, medium or low in N application rate addition of any of the three types of carbon also stimulated somewhat increase of microbial biomass carbon and nitrogen. Regardless of fertispheric N concentrations, the treatments with glucose were the highest in CO₂ emission, those with cellulose came the next and those with lignin the last. BIOLOG analysis showed that AWCD value and Shannon, Simpson and McIntosh indices were all quite low in treatments either high or medium in N application rate, and they were increased after addition of carbon. In treatments with carbon added alone or treatments with carbon and N fertilizer added at a normal rate, AWCD value, Shannon, Simpson and McIntosh indices were all relatively high. In treatments high in fertispheric N concentration, addition of any of the three, glucose, cellulose or lignin increased soil microbial activity. So, in the current condition of using large volumes of inorganic N fertilizer, it is advisable to use organic manual in addition, which helps reduce the risk of nitrogen loss.

Abstract:A field study was conducted to evaluate effects of hedgerows reducing nitrogen and phosphorus leaching loss from intensively managed Phyllostachys praecox stands. Three types of hedgerows composed of Lolium perenne L., Photinia X. and Ligustrum japonicum mixture, and extensively managed P. praecox groves, separately, were set up. Samples of subsurface leachate were taken at 0.3m depth on both sides of the hedgerows between June and October in 2010 for analysis of concentrations of nitrogen and phosphorus. All the three types of hedgerows intercepted large amounts of nutrients, thus significantly reducing concentrations of nitrogen and phosphorus in the leachates collected at the down slopes of the hedgerows. But the effects varied only slightly between hedgerows, showing a decreasing order of hedgerow of natural P. praecox (N 81.3 kg hm^-2 and P 4.9 kg hm^-2 ) > hedgerow of L. perenne (N 81.1 kg hm^-2 and P 4.7 kg hm^-2 ) > hedgerow of Photinia X. and L. japonicum mixture (N 77.0 kg hm^-2 and P 4.3 kg hm^-2 ). Up to 61% of the nitrogen and 49% of the phosphorus in the leachate from the upslope P. praecox stands were intercepted by the hedgerows. Among the three types of hedgerows, the one of extensively managed P. praecox groves was the most worthy of extrapolating, because it does not only reduce N and P non-point source pollution, but also save time and labor in setting up the hedgerow and produce marketable bamboo shoots as well.

Abstract:To improve use efficiency of phosphorus in farming, a phosphate-solubilizing strain of fungi (PSF) labeled as B1-A was isolated from the rhizosphere of peanuts growing in red soil and identified as Aspergillus niger according to its colonial morphological characteristics and ITS rDNA sequence analysis. In the culture prepared out of two hard-to-dissolve phosphates (FePO₄ and AlPO₄), B1-A was added at a rate of 1%, 3% and 5% separately. It was found that the P dissolution rate in and pH of the culture varied with the time, that a significant negative correlation existed between the rate and the pH, and that the former was also related to B1-A inoculation rate, incubation time and the concentration of rock phosphate powder (RPP) in the solution as well. Results show that B1-A demonstrated its highest capability when the solution was 3 g L^-1 in Yunnan and 5 g L^-1 in Jiangxi RPP concentration, inoculated with 3%~5% of B1-A, and incubated for 168 hours. B1-A was quite good at dissolving tricalium phosphate, aluminium phosphate, ferric phosphate and RPP, and might dissolve as much as 418.7, 942.3, 242.2 and 177.4 mg L^-1, respectively. So B1-A is a promise microbial resource for development of high efficiency biological phosphorus fertilizer for use in latosolic red soil.

Abstract:Seven strains of Rhizobium sp. were cultured in liquid mediums using soil as the sole source for phosphorus to investigate effect of the strains on mobilization and release of phosphorus in soil. The control treatment was set in the same way except inoculation of Rhizobia . Results suggest that the bacteria released a large amount of hydrogen ions, thus making the concentration of the ions multiplied by at least 20 times, which resulted in a significant decrease in pH of the solution. Different strains of Rhizobia released different types and amounts of organic acids, including oxalic acid, malic acid, succinic acid, formic acid, acetic acid, citric acid and lactic acid. However, most of the strains exuded acetic acid. The treatments were significantly higher than the control in total phosphorus in the liquid culture mediums, while the total inorganic phosphorus in the soil immersed in the liquid behaved otherwise. Taking into account the soil being the sole phosphorus source, it could be concluded that Rhizobia could promote mobilization and release of inorganic phosphorus from the soil. Correlation analysis shows that total phosphorous was extremely positively related to pH of the liquid (r= 0.893^﹡﹡，n = 8), suggesting that the secretion of hydrogen ions from the bacteria is one of the causes for dissolution of inorganic phosphorus in soil. Inoculation of Rhizobia reduced occluded phosphorus in the soil remarkably, and also Al-P, Fe-P and Ca-P but to an extent varying with the stains of Rhizobia , which might be attributed to the different amounts and types of organic acids they could secret. The phenomenon of Rhizobia releasing hydrogen ions and a variety of organic acids suggests that inorganic phosphorus in the soil is mobilized in a number of ways, which demonstrates that inoculation of Rhizobia may help legume crops make use of various forms of unavailable phosphorus in the soil, thus making them adapted to different soils low in phosphorus.

Abstract:The study on microbial mechanism of straw decomposition process is the theoretical basis of regulation straw returning and enhancing of fertility on farmland. Reciprocal translocation experiment was set to investigate the changes of metabolic activity (expressed as AWCD, Average Well Color Development) during decomposition in Phaeozem, Cambisol and Acrisol under cold temperate, warm temperate and mid-subtropic climate conditions. Litter bag method avoiding soil entering was used to identify microbial communities responsible for straw decomposition. The results showed that the AWCD decreased with the increase of temperature and rainfall during half and one year decomposition. AWCD in 0.5 year showed that Hailun (0.765±0.060) > Fengqiu (0.737±0.165) > Yingtan (0.326±0.076), AWCD in 1 year showed that Hailun (0.630±0.092) > Fengqiu (0.319±0.096) > Yingtan (0.291±0.029).However the tendency was weak after two-year decomposition. Climate condition is the key factor that influenced the microbial carbon utilization activity. In addition, by principal component analysis, the microbial metabolic properties in Hailun and Fengqiu were quite different from that in Yingtan after 0.5 year, and the microbial metabolic properties in Fengqiu and Yingtan were quite different from that in Hailun. After two-year decomposition the microbial metabolic properties became similar under different climate conditions, which all had largely utilization to nitrogen compounds.

Abstract:The main objective of this paper is to study characteristics of selenium distribution in soils and their relationships to genesis and physio-chemical properties of the soils in Nanning City. A total of 2 767 samples of surface soils (0~20 cm) and 711 of parent materials were collected for analysis of total soil selenium with atomic fluorescence spectrometry and soil properties with various methods. Results of the analysis show that concentration of total selenium in the surface soils ranged from 0.09 mg kg^-1 to 1.34 mg kg^-1 and averaged 0.57 mg kg^-1. Among the different types of parent materials, the lowest and highest concentrations were recorded in Permian carbonate was the highest in total Se content, averaging 0.79 mg kg^-1 and Cretaceous purplish clastic rocks the lowest, averaging 0.39 mg kg^-1, while among the different types of soils, Alluvial soil was the highest, averaging 0.89 mg kg^-1 and purple soil the lowest averaging 0.37 mg kg^-1. Obviously soil parent material is the major factor that influences selenium concentration and distribution in the soils in Nanning, whereas soil pH, and contents of organic matter, iron and aluminum are also factors of certain significance.

Abstract:The ¹³⁷Cs tracing technology has been used the most extensively in the study on soil erosion, but with the decay of¹³⁷Cs in the environment, it is of critical importance to find a replacement for ¹³⁷Cs. Compared with¹³⁷Cs, artificial radioactive species, plutonium isotopes, which originate from the same source, have a longer half-life (24 110 years for²³⁹ Pu and 6561 years for ²⁴⁰Pu), and are more easily to get adsorbed by soil particles. Especially with the development of measuring technology, the technologies of inductively coupled plasma mass spectrometry (ICP-MS) and accelerator mass spectrometry (AMS) are readily available for application, thus making the determination of Pu isotopes more efficient and more sensitive than that of ¹³⁷Cs. Consequently, Pu isotopes can be used as ideal replacements of ¹³⁷Cs as tracer in the study on soil erosion. In this paper analysis was done of the base for Pu isotopes being used as tracer in soil erosion from the three aspects: (1) source and distribution；(2) the adsorption and fixation of Pu in soil；(3) methods for measuring plutonium isotopes; a brief introduction was presented to the basic principles and application of Pu isotopes as tracer in the study on soil erosion; and discussions were conducted on orientation of the study on further application of Pu isotopes as tracer.

Abstract:Inorganic nitrogen (N) immobilization in soils could enhance the capacity of soil N retention and thus reduce the potential risk of NO₃^-1 leaching, NH₃ volatilization as well as N₂O and NO emissions losses. Biotic and abiotic inorganic N immobilization as well as their significance in soil N cycling is introduced in this paper. The paper discusses preliminarily the mechanisms and influence factors of both biotic and abiotic inorganic N immobilization and puts forward orientation of the future research. In particular, neither the mechanism nor the kinetics of abiotic immobilization of NO₃^-1-N are known. So far, only the ferrous wheel hypothesis could explain abiotic immobilization of NO₃^-1-N in forest soils. However, the ferrous wheel hypothesis has not been fully demonstrated and therefore further studies about abiotic immobilization of NO₃^-1-N are extremely needed.

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Abstract:Rill erosion is the main form of water erosion, and is an important link on the transition from sheet erosion to gully erosion, and is an important component of water erosion physical process on hillslope. As the rill erosion process with dynamic, random and temporal variation of the three major characteristics of nonlinear dynamics, therefore, traditional erosion model is difficult to accurately dynamic simulate and reproduce rill initiation and development process on slope. Most of the existing erosion and sediment yield models focus only on the general purpose of soil erosion prediction, while the lack of space-time simulation of dynamic rill morphology evolution processes. Combination of soil erosion and hydraulics knowledge, the cellular automata theory and methods into the process simulation of rill erosion, the establishment of a loess slope CA model rill erosion, rill slope during the development of a numerical simulation, and simulation results and experimental results are compared and analyzed, the model simulation results and experimental rill produce similar patterns, to verify reasonableness of the model design; In addition, by comparing the parameters of the rill erosion model to simulate the error analysis.

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