Abstract:【Objective】Soil organic matter (SOM) is an important indicator of soil fertility, and also the basis for carrying on build-up of cropland quality and scientific fertilization. Based on the data of the project of soil test based fertilization and the Second National Soil Survey in 2005-2014, analysis was performed for variation of soil organic matter in top soils of the croplands of China. The objectives of the present study are (1) to report current status of SOM in the croplands of China; (2) to explore changes in SOM content in the croplands of China over the last three decades in nationwide; and (3) to discuss causes of the changes. 【Method】 In this paper, the data of SOM in croplands were cited from the Soil Survey Data of China and Soil Fertility of China, covering a total of 131 627 000 hm² of croplands and the data of the national soil test based formulated fertilization project from the “Basic Nutrient Dataset of the Soils under the Project of Soil Test-Based Formulated Fertilization” covering a total of 8 467 083 data points. As a total of 2 948 agricultural counties (district or city) and farms participated in the project, covering a total of 121 716 000 hm²of croplands calculated according to the data of cropland area by the end of 2008 published by the National Statistics Bureau of China. The distribution of soil sampling sites of the project of soil test-based formulated fertilization was consistent with the data of cropland distribution at the end of 2008, covering 66 700 m²~133 400 m²(on average) in plain areas, 20 010 m²~53 360 m² in hilly areas, and 6 670 m²~13 340 m² of vegetable land All soil samples were collected from topsoil (mainly 0~20 cm for crop field and 0~30 cm for vegetable field) in autumn after crops were harvested. Contents of soil organic matter were measured with the oil heating and potassium dichromate-volumetric method. A total of 8 467 083 soil samples were collected nationwide. The data of the soil-test-based formulated fertilization were mathematical means of the soil samples for each province. The massive data bases acquired from the project of soil test-based formulated fertilization and the second national soil survey were analyzed for variation of soil organic matter content in cropland of the country over the last three decades. Based on the data of soil organic matter contents in the croplands of the Second National Soil Survey, the croplands could be sorted into six grades, i.e.>40 g kg^-1, 30 g kg^-1~40 g kg^-1, 20 g kg^-1~30 g kg^-1,10 g kg^-1~20 g kg^-1, 6 g kg^-1~10 g kg^-1 and ≤6 g kg^-1【Result】Results show that the average content of soil organic matter in plough layer of the country is found to be 24.65 g kg^-1, with the highest in Heilongjiang province being 40.43 g kg^-1and the lowest in the Ningxia Hui Autonomous Region being 13.61 g kg^-1, and 4.85g kg^-1 or 24.49% higher than the average of the second national soil survey. The content of soil organic matter in the croplands of the grade of 30 g kg^-1~40 g kg^-1 increased by 3.64 percentage points, in those of the grade of 20 g kg^-1~30 g kg^-1 by 5.68 percentage points, and in those of the grade of 10 g kg^-1~20 g kg^-1 by 5.36 percentage points, but in those of the grade of > 40 g kg^-1 decreased by 1.38 percentage points. In most provinces or regions, soil organic matter increased or remained almost unchanged in content over the past three decades, but in Beijing and Qinghai, it was found to have been decreased slightly. The increases in content of soil organic matter in the plough layers of the country could be attributed to the farming practices of straw incorporation, zero or minimum tillage, and application of organic and green manures. Also, leaving crop stubs in the field is an important practice increasing soil organic matter content.【Conclusion】The average content of soil organic matter in the plough layers of different croplands in China is found to be 24.65 g kg^-1. Most of the croplands have been varying in the range from 10 to 30 g kg^-1, and exhibiting a rising trend in soil organic matter content over the past three decades, although in some regions croplands originally high in soil organic matter content have decreased somewhat. So the content of soil organic matter in the plough layers will keep on increasing with increasing organic matter input into the croplands in future.

Abstract:【Objective】Soil moisture is a key variable in parameterization of a land surface. Soil moisture content varies spatially and temporally, and plays an important role in material and energy exchanges occurring in the earth-atmosphere interface. It is a basic indicator for prediction of crop growth and crop yield, and also an important parameter in the numerical weather prediction model that helps efficiently forecast improvement in the physics of land surface processes on regional or global scales. However, it is very difficult to obtain an accurate soil moisture parameter just through field measurement temporally and spatially, especially at large spatial scales. Remote sensing technology has widely been used in estimation of soil moisture contents for it features capability of observing a large area synchronously, timely and economically. In the present study, a total of 39 soil samples were collected from an oasis in the Weigan-Kuqa Delta, Xinjiang of China.【Method】Temperature Vegetation Dryness Index(TVDI) is an important tool that can be used to reflect soil moisture regime through inversion. In this study DEM data were introduced to correct the data of land surface temperature(Ts) on the basis of the researches on TVDI in an attempt to mitigate the impact of undulation in land relief on secondary distribution of energy. The study area was divided into different land use types by threshold. Based on the synchronously field measured data, a piecewise inversion model was used to inverse soil moisture distribution in the delta oasis, and then spatial distribution pattern of soil moisture in the studied area and rules of its variation were further analyzed.【Result】Results show as follows: (1) Based on TVDI, DEM was introduced for terrain correction. Comparing the data before and after the terrain correction demonstrates that Ts-MSAVI and the determination coefficient of the field measured soil moisture content in the topsoil layer were higher after the correction than before the correction. After the correction, R² rose from 0.44 to 0.53, and all were above the 0.01 significance level; (2) The soil moisture regime of the delta oasis reflected in the classification maps of TVDI demonstrates an apparent rule of spatial variation of soil moisture that on the whole, soil moisture declines from west to east and from north to south. Based on the variation coefficient of the mean soil moisture contents in the six soil layers of the 0~100cm soil profiles different in land use type in the study area, soil moisture variation coefficient of the oasis and ecotone was 28% and 36%, respectively. From the distribution of the soil moisture variation coefficients of the soil layers in the soil moisture vertical variation coefficient map, it is discerned that the closer to the surface, the higher the variation coefficient, and that the vertical variation coefficient of soil moisture varied with land use type even in the same soil layers. However, the overall trend was quite similar, that is, it declines with soil depth; (3) By comparing the piecewise inversion model with the original model in inversion, it is learnt that the determination coefficient between the measured soil moisture and that predicted using the piecewise model and original model was 0.72 and 0.64, with RMSE being 0.03 and 0.04, respectively. Obviously, the coefficient of determination increased by 0.08 and RMSE decreased by 0.01. 【Conclusion】Based on all the above-described findings, it could be concluded as follows: (1) In this study, DEM elevation data were used for terrain correction of TVDI, and the corrected TVDI better reflected the soil moisture regime; (2) On the whole, soil moisture declines from west to east and from north to south, and remains quite consistent in the oasis, but varies drastically in the ecotone. Soil moisture vertical variation coefficient varied as a whole, showing a declining trend of a power function; (3) By comparing the piecewise inversion model and the original model in inversion, it is learnt that the piecewise inversion model should be used to invert soil moisture in soils different in land use, which may effectively supplement each other, thus improving accuracy of the inversion as a whole. It is, therefore, worthy of attention and application in researches on regional soil moisture regime.

Abstract:【Objective】Soil organicmatter is an important index of soil properties, because it is vital to crop growth and soil quality.The technology of hyperspectral analysis is a rapid, convenient, low-cost and alternative method andexhibits an increasingly remarkable development potential in estimation ofsoil organic matter. However, when hyperspectral reflectance is usedin the field, there are several external environmentalfactors, including soil moisturecontent, temperature, and surface of the soil that may affect soil spectra. Especially soil moisture content, a major limit to field hyperspectralsurvey, might mask the absorption features ofsoil organic matter, and hence dramatically lower accuracy of the prediction of soil organic matter. Therefore, it is essential to find a method capable of removing the impact of soil moisture content on spectral reflectance, so as to improve the accuracy of quantitative prediction of soil organic matter. In this paper, the EPO (external parameter orthogonalization)algorithm was introducedfor that purpose.【Method】A total of 217 soil samples were collected from the 0～20 cm soil layer in theJianghan Plain.In the laboratory, the soil samples were air-dried andground to pass a sieve with mesh < 2 mm. Then the soil samples were analyzedseparately for soil organic mattercontentwith the potassium dichromate external heating method.The total of 217 soil samples werefurther divided into three non-overlapping subsets: a model calibration set (S0), consisting of 122 samples and dedicated to development of amultivariate model for soil organic matter; anEPO development subset (S1) consisting of 60 samples forEPO development; and a validation subset (S2) consisting of 35 samples for independentEPO validation. Then, the samples in S1 and S2 were rewetted in line with the following procedure: from each soil sample 150 g oven-dried soil was weighed out, put in a black cylindrical box and rewettedalong the gradient of soil moisture contentincrementwith interval being 4% each, making up a total of 9 treatments in soil moisture content along the gradienti.e. 0, 4%, 8%, 12%, 16%, 20%, 24%, 28% and 32%. An spectrometer was used to acquire hyperspectral reflectances of the samples of three subsets (S0, S1 andS2, including the rewetting samples)on 350 to 2500 nm. And then influences of the soil moisture content on the soil spectra were analyzed, and the scores of the first two principal components inthe principal component analysis were used for comparison to determine performance ofEPOalgorithmin removing the effects ofsoil moisture contenton spectral reflectance of the wet samples. In the end,modeling for the S0 subset was done using the partial least squares regressionand support vector machine regression, and the S2 subset of wet samples were used as external validation setbefore and after calibration with EPO. The coefficient of determination (R²), root mean squared error (RMSE) and the ratio of prediction to deviation (RPD) between the predicted and measured values of soil organic matterwere used to compare the 3 models in performance: High R², RPD and low RMSE were indicators of optimal models for partial least squares regression (before EPO calibration), EPO-partial least squares regression and EPO-support vector machine regression. 【Result】Results show that (1) Soil moisture content does have obvious influence on spectralreflectance, and the reflectance decreases in value across the entire wavelengthdomain with increasing soil moisture content, making it more challenging to identify usefulfeatures of soil organic matterwith spectra; (2) For Subset S2 before EPO calibration, no spectral overlaps are observed between the wet and dry samples, and spectra of the wet sample cluster in spaces free from those of the dry sample (mutual independent space). However, after EPOcalibrationof Subset S2 set, the spectra of the wet sample appear almost in the same positions as those of the dry sample do within the eigen space, demonstrating that the two groups of spectra are highly similar; (3) Before EPO calibration, the partial least squares regression model is the poorest in prediction accuracy (the validation RPD=1.16). EPO calibration has improved prediction accuracy of the model up to an acceptable level (the validation RPD=1.76). And EPO-support vector machine regression model performs better than the other two with validation R² reaching 0.78, and RPD = 2.15, which indicates that the effects of soil moisture content on spectra are successfully eliminated.【Conclusion】In the future, this approach willfacilitaterapidmeasurement ofsoil organic matter for this study area.

Abstract:【Objective】 Quality of mapping based on prediction of geographic variables is greatly affected by the layout of the sampling sites. Due to the limitation of sampling cost, it is generally expected to have fewer sampling sites that will be able to provide more information for accurate prediction. To achieve such a target of efficient sampling, it is advisable to proceed from the following two point: first, set up sampling sites that are highly representative of the area of interest for better prediction accuracy, and second, reduce the number of sampling sites as many as possible without risking any loss of required accuracy. Based on the assumption that the more similar the two sites in geographic environment, the more similar their geographic elements, it is held that every sampling site can be used to represent an area similar to the site in environment, and the similarity between the sampling site and the sites to be predicted can be used to determine reliability of the prediction, meanwhile, the similarity within the sampling site set can be used to determine redundancy of the sampling site set. So, the layout of efficient sampling sites needs to keep balance between reliability of the prediction and redundancy of the sampling site set. 【Method】 In this paper, a sample differentiation and fusion strategy is set forth for designing of sampling. The differentiation strategy is to increase the number of sampling sites so as to improve reliability of later on predictions, while the fusion strategy is to merge over-similar sampling sites, so as to reduce redundancy of the sampling site set. Through repeated differentiation and fusion, a preset requirement is finally met for prediction reliability and sampling site redundancy. The method has been tested in a case study of a small watershed in Raffelson, Wisconsin of USA. First, a comparative analysis was done of sampling sites varying in prediction reliability with 99 validation sampling sites to determine relationship between prediction reliability and validation accuracy. Then, verification was performed of effectiveness of the proposed strategy improving prediction reliability in its first phase and reducing redundancy of the sampling site set in its second phase. And in the end, comparison was done of the proposed method in this paper with other sampling methods (grid sampling and stratified simple random sampling) using the same number of sampling sites (15, 20 and 25, separately). 【Result】 Results show that prediction reliability is positively related to prediction accuracy, so the former can be used as a better indicator of the latter. From the specific processes of the strategy, it can be discerned that, the differentiation can effectively raise the prediction reliability, while the fusion reduce the redundancy of the sampling site set, and what is more, have little impact on the prediction reliability. The comparisons show that the proposed method is higher in prediction reliability and lower in redundancy, and is 17.3%(n=15), 14.8%(n=20) and 16.2%(n=25) lower than the grid sampling method, and 16.5%(n=15), 15.3%(n=20) and 17.0%(n=25) higher than the stratified simple random sampling method in lowest prediction reliability, respectively, while 8.8%(n=15), 12.8%(n=20) and 20.3%(n=25) lower than the grid sampling method, and 6.4%(n=15), 12.4%(n=20) and 19.6%(n=25) lower than the stratified simple random sampling method, respectively, in redundancy. 【Conclusion】 Therefore, it can be concluded that the proposed method provides a means for obtaining a high prediction reliability and low sampling redundancy in sampling, and hence is a more efficient method for designing sampling schemes than the grid sampling and stratified simple random sampling methods.

Abstract:【Objective】As of yet Chinese Soil Taxonomy (CST) doesn’t have any explicit diagnostic basis for characterizing soil profiles with artifacts. With rapid development of industrialization and urbanization, the impact of human disturbance on soil is becoming more and more significant. It is, therefore, essential to intensify the research on soils containing artificial artifacts, or it would be very hard to explain reasonably how some changes occur in pedogenesis.【Method】In this paper, 10 soil profiles containing artificial artifacts (shortened as artificial soil) typical of Henan Provinc were selected as objects for the study, including 3 at ancient cultural relic sites, 5 at urban sites and 2 at reclaimed farmland sites in industrial and mining areas.Besides 3 natural soil profiles (free of any artificial artifacts) were chosen in the same regions as control for comparison in configuration and physic-chemical property. Then the 10 soil profiles were classified in line with world soil resources reference basis (WRB) and Soil Taxonomy (ST) and CST and analyzed for soil diagnostic layer and diagnostic characteristic specific of these profiles. On such a basis, a proposed scheme was put forward, applicable to classification of the artificial soils specific of China. 【Result】Artificial soils are complicated in structure and property and vary sharply in particle size, bulk density, pH, and contents of organic carbon, total nitrogen and total phosphorus with type and intensity of human activities. The most intuitive feature is the fact that the content of coarse particles is much higher in the artificial soil profiles than in the natural soil profiles. The urban soils, in particular, are very high in content of coarse particles, up to 90%, and peculiar in soil penetrability, which is hindered by a soil layer formed of miscellaneous construction waste in these soils. In view of the characteristics of these artificial profiles, WRB is found not fully suitable soils because it lacks sufficient modifying prefix or suffix to describe diagnosis of these artificial soils containing artifacts; in ST, soils containing artifacts appear in the various soil orders and subgroups; and CST lacks specific diagnostic basis to describe and explain soil properties of these artificial soils. 【Conclusion】By referring to some standards in WRB and ST pertaining to artificial artifacts in soil, this paper has brought forth a definition for soils containing artificial artifacts, including an augment of “technical disturbance layer” as diagnostic feature, which is added as an index for search of entisol and as a supplement into the definition for the suborder of entisol in CST formulated standards specific to artificial artifacts in CST, and created a new soil group “Technical anthropogenic entisol”, which will be first searched out under the suborder of entisol and three subgroups, i.e. calcareous, acidic and ordinary technical anthropogenic entisal under the group of Technical anthropogenic entisol. Moreover, when artificial soils do not fit in with the diagnostic features described in the preceeding paragraphs, it is suggested that artificial soils should be added as a new type into the soil family to distinguish artificial soils from natural ones. This proposed scheme for soil classification is believed to be able to reflect effects of human activities varying in type on soil, which fills a gap by a certain degree in the study on classification of this type of soils.

Abstract:In order to better understand pedogenesis and taxonomy of the anthropogenic-alluvial soil in the Yellow River Irrigation Zone of the Ningxia Hui Autonomous Region, five typical soil profiles were prepared by pit-digging with the aid of Arcgis software and GPS in the zone for studying.【Method】From the data collected during the soil-series surveys of Ningxia in recent years after 2014 and the data and information acquired through profile observation and analysis of samples collected from the profiles by layer, it was found that the anthropogenic-alluvial soil was formed through mellowing processes triggered by artificial cultivation, redox process caused jointly by irrigation and groundwater, sedimentation of silt in irrigation water, and salinization process, as well, in some areas.【Result】By referring to and identification in line with “the Keys to the Chinese Soil Taxonomy (third Edition)”, it was found that the five typical profiles had the following diagnostic horizons and characteristics, siltigic epipedon, fimic epipedon, cambic horizon, and ustic soil moisture regime, frigid temperature regime, calcaric property, redox features and calcic evidence. In the Chinese Soil Taxonomy, the five typical profiles could be sorted into the soil order of Anthrosols, the suborder of Orthic Anthrosols, the soil groups of Siltigi-Orthic Anthrosols and Fimi-Orthic Anthrosols, and the subgroups of Mottlic Siltigi-Orthic Anthrosols, Siltigi Fimi-Orthic Anthrosols and Typic Siltigi-Orthic Anthrosols. According to the criteria for classification of soil families and soil series in the Chinese Soil Taxonomy, the five soil profiles were sorted divided into five soil families, i.e. loamy mixed type calcareous frigid-Mottlic Siltigi-Orthic Anthrosols, sandy feldspar mixed type calcareous frigid-Siltigi Fimi-Orthic Anthrosols, sandy silica mixed type calcareous frigid-Typic Siltigi-Orthic Anthrosols, Sandy feldspar mixed type calcareous frigid-Mottlic Siltigi-Orthic Anthrosols and Loamy feldspar type calcareous frigid-Mottlic Siltigi-Orthic Anthrosols, in the light of their soil particle size composition and mineral composition, and then further into five soil series, such as Chengguan series, Xigang series, Jinji series and so on.【Conclusion】In addition, the reference studies of the five soil profiles in different soil classification systems show that between the two soil classification systems, the Chinese Soil Genetic Classification and the Chinese Soil Taxonomy, does not exist any simple one to one relationship, the corresponding relationship between the two is significant. In the Chinese Soil Genetic Classification, the five soil profiles all belong to anthropogenic-alluvial soil, while in the Chinese Soil Taxonomy, they are sorted into 2 soil groups, and in the US Soil Taxonomy into the soil order of Inceptisols, the suborder of Ustepts and the soil group of Haplustepts. The comparison shows that the Chinese Genetic Classification and the US Soil Taxonomy are relatively stable in classification, whereas the quantitative Chinese Soil Taxonomy is more differentiable, thus making the classification more complete and detailed.

Abstract:【Objective】 Knowledge about the transport patterns of sediment helps to understand the erosion-induced biogeochemical processes of C, N and P. The sediment transport distance is closely associated with its settling velocity distribution, which is dependent on the size, shape, density and porosity of sediment particles. In fact, aggregation processes turn fine particles into large aggregates, speeding up the settling velocity of individual particles and shortening their transport distances. However, most of the soil erosion models currently available are using soil texture or mineral particle distribution, therefore cannot fully reflect the transport behavior of sediment particles. 【Method】 Two typical types of soils in China, red soil (Hapli-Udic Ferrosols) and loess soil (Loessi-Orthic Primosols), were investigated in this study. The two soils had similar texture, but were distinctive in aggregate stability and soil organic carbon content. They were, therefore, considered as suitable objects in this study to explore the potential differences between settling velocity distribution and mineral size distribution. The two soils were fractionated by two methods: conventional wet-sieving into mineral size distribution; and settling tube fractionation into settling velocity distribution. The weight distribution, total organic carbon concentration and total inorganic carbon concentration of individual classes were measured and compared. 【Result】 Results show that, compared with the conventional soil mineral size distribution, fractionation using settling tube is more effective in distinguishing the settling velocity distributions of red soil and loess soil. This is because clay-sized particles are more likely to be cooperated into aggregates, which facilitate the settling velocity of individual mineral particles, and thus largely shorten their potential transport distance. In particular in the better aggregated red soil, about 86.9% of the soil organic carbon was associated with fine particles ≤32 μm, which is very likely to stay as suspension and thus transported downstream once erosion occurs. However, as a matter of fact, about 90.5% of the soil organic carbon was combined with coarse aggregates of equivalent quartz size ≥63 μm, which would probably be deposited at the footslope immediately after short transport distance. Similar patterns of soil inorganic carbon distributions were observed in the loess soil. All the findings demonstrate that aggregation effects can effectively shorten the transport distance of soil organic and inorganic carbon and skew their distributions towards the terrestrial system than if otherwise predicted by mineral size distributions. 【Conclusion】 Settling velocity specific redistribution of sediment particles casts new light on our current understanding of C, N and P biogeochemical processes during soil erosion and sediment transport and deposition. Therefore, settling velocity specific distribution of sediment particle should be considered as a soil erodibility parameter to be applied to soil erosion models.

Abstract:【Objective】Fish-scale pits measure is a widespread and typical soil and water conservation engineering measure in Loess Plateau that can be used to impound runoff and reduce the soil erosion mass and create a good water condition for vegetation growth. In order to clarify erosion evolution processes and flow hydraulic characteristics of fish-scale pies measure under the condition of continuous rainfall. 【Method】In this paper, we analysed the erosion evolution with 3D laser scanner and realized graphical and digital process of erosion evolution on fish-scale pies slope by laboratory five rainfalls simulation. 【Result】The results showed that: (1)Dynamic process of fish-scale pits erosion could be presented as splash erosion－sheet erosion－drop pit－rill erosion－longitudinal erosion－headward erosion－collapse. By the end of the 5th rainfall, the largest rill length、width and depth respectively increased to 80 cm、22 cm and 7.8 cm. During the first two rainfalls, fish-scale pits played a significant role in water storage and silt detention, sheet erosion and rill erosion occurred at some parts of slope; Later, due to excessive water of pits and high moisture content of side slope, leading to collapse phenomenon in pits and longitudinal erosion, rill headward erosion at down-slope, also increased erosion. (2) As the rainfall duration increases, the down-slope velocity and runoff depth were increased with fluctuation because the rainfall could be hold up in pits. What’s more, vortex accurred in pits and streams scour accurred in slope surface.The order of the average flow velocity and the average water depth is: the up-slope>mid-slope>down-slope. The velocity and depth in rill were significantly larger the slope. The Reynolds number of up-slope and mid-slope was less than 500, and for down-slope, it was over 500 at the end of 5th rainfall. When rainfall accumulated duration reached 58 min and rainfall increased to 87 mm, erosion increased dramatically. Fish-scale pits unable to played a positive effect. (3) During five rainfalls, the upslope and mid-slope flow regime was laminar flow. With the down-slope pits being filled, slope runoff fluctuated greatly, down-slope flow became turbulent flow from laminar flow and changed between subcritical flow and supercritical flow. (4) Resistance mainly comes from rain, grain and form resistance, and form resistance that orginated from the rugged slope was the dominant resistance. Due to the callapse、scour and fluctuant change of terrain, resistance decreased with rainfall accumulation duration accompanied by minor fluctuations. The order of resistance was form resistance> grain resistance> rain resistance.【Conclusion】The study was of momentous significance to clarify the fish-scale pit slope erosion and its mechanism, also provides theory basis and decision support for loess plateau area to layout fish-scale pits reasonably. Only if we layout fish-scale pits reasonably in Loess Plateau area can we improve and keep soil moisture greatly.

Abstract:【Objective】Soil erodibility K is an international index of soil susceptibility to erosion, and can be used as an important quantitative parameter in evaluating soil erodibility. The Yanhe Valley is located on the Loess Plateau, where soil erosion is very severe, and also very severe in soil erosion. In this case, it is particularly important to conduct research on soil erosion models for this region. In recent years, in studies on soil erodibility of loess, soil erodibility factor K is often used as an index for evaluation of soil erosion. Though certain progress has been made in the research on using the formula method to assess soil erosion factor K in the loess area, it is still infeasible to go on doing researches on estimating K values in some parts of the Loess Plateau due to limitation of data availability and inconsistency between standard plot and observation plot. Besides, the reliability of the formula method still need to be validated. So, it is necessary to design an equation that is workable for estimating soil erodibility K even when inadequate data of soil physical and chemical properties are available. The purpose of this study is to pick out of the three methods currently available for estimating soil erodibility K one that fits the special situation of the river valley.【Method】In this study, comparison was performed between the three methods, i.e. Torri.D model, EPIC model, and Shirazi formula in applicability to estimation of K for the nine catchments of the Yanhe Valley. Collection analysis and Model-based estimation methods were used to process and analyze the data and compare predicted K with measured K, so as to screen out the most suitable one.【Result】Results show that the contents of soil organic carbon, clay and silt gradually increased from north to south with the increasing vegetation coverage. In terms of mean weight diameter (D_MW), the three types of vegetation in the valley followed an order of forest > forest-steppe > steppe, and D_MW was positively related to the K predicted with the EPIC model and Shirazi formula method, but negatively to that with the Torri.D model, which means that soil aggregate increased in stability and the soil in erosion resistance as the vegetation turned from steppe to forest-steppe to forest. The three predicted Ks displayed an order of K_Torri.D> K_EPIC > K_shirazi K_Torri.D varied in the range of 0.068 ~ 0.1475, higher than the measured one (0.0312~0.0796). Compared with the other two, Torri.D model was the lowest in uncertainly, with mean absolute error (MAE), mean relative error (MRE), root mean square error (RMSE) close to 0, and dilution of precision (A_f) close to 1, suggesting that Torri.D model is more suitable than the other two for use to evaluate soil erosion susceptibility and calculate soil loss.【Conclusion】To sum up, all the findings described above indicate that Torri.D model can be used to soil erosion susceptibility and predict soil loss of a region even when data of the region are incomplete or inadequate.

Abstract:【Objective】As phytolith features super tolerance to high temperature, oxidation and decomposition, the organic carbon occluded inside the phytolith shell may exist and accumulate in soils and sediments for thousands of years and is hence named as Phytolith occluded organic carbon (PhytOC), which is, therefore, regarded as an important soil organic carbon pool, and contributes significantly to the carbon sink in the soil and global CO₂ balance. Forest ecosystem is a mainstay of the terrestrial ecosystem. However, the area of forests on the globe is shrinking drastically today, while the area of bamboo groves is still on a rising trend. So, bamboo groves are a growing carbon sink and playing a critical role in carbon cycling in the terrestrial ecosystem. As Dendrocalamus latiflorus Munro grows very fast and features large volumes of biomass, well-developed root system and outstanding ecological functions, it is favored to be one of the bamboo species extensively cultivated in South China. Nanjing County is known as “Land of Dendrocalamus latiflorus Munro in China” and one of the largest Dendrocalamus latiflorus Munro cultivation region in Fujian Province. In this paper an attempt was made to explore characteristics of the spatial distribution of PhytOC in the soil under the bamboo groves, aiming at providing some scientific basis for assessing the pool of PhytOC in the bamboo ecosystems of China.【Method】A total of 100 tracts of Dendrocalamus latiflorus Munro groves in Nanjing County was selected as object for the study. Soils in different soil layers were sampled for extraction and isolation of PhytOC using the microwave digestion method and then the centrifuging-heavy liquid floatation extraction method. In order to extract fairly pure Phytolith, the floatation extraction process was performed twice, using heavy liquid, Zinc bromide,2.35 and 1.60 in specific gravity sequently to remove impurities. The isolated pure phytolith was put into an ventilated oven at 65℃ for 48 hours till they were fully dried and constant in weight. And then, the Phytolith was weighed after the samples cooled down in a vacuum dryer. The Alkali Dissolution Spectrophotometry method was applied to analysis of the PhytOC and then spatial variability of the PhytOC in the bamboo soil analyzed using the software of ArcGIS 10.0 and the Geostatistic method.【Result】Results show that average content of PhytOC in the soil varied from 0.30～0.75 g kg^-1with soil layer uanging from 80.38 to 87.46%, which indicates a moderate degree of variability. Geostatistical analysis reveals that PhytOC contents in the 10～30 cm, 60～100 cm and 0～100 cm soil layers fit exponential models; in tnder Dendrocalamus latiflorus Munro groves in Nanjing County, with variation coefficients rhe 0～10 cm soil layer fit the Gaussian model; and in the 30～60 cm soil layer fit spherical models. Nugget /Sill ratio of the PhytOC varied from 8.7% to74.9%, displaying strong and moderate spatial correlation, moreover their SM/SRMS ratios were low, indicating that the models fit well. In the 0～100 cm soil layer under the bamboo groves, the pool of PhytOC reached 4.23 t hm^-2, significantly higher than that under the Chinese fir forest, Masson pine forest, broadleaf forest and mixed conifer-broadleaf forest. Kriging reveals that the contents of PhytOC displayed a decreasing trend with soil depth, which is quite similar to the distributions of Phytolith and total silicon in the top-soil. Besides that, a ultra-significantly positive correlation（p <0.01）was observed between them, and a significant positive relationship, too, between the content of PhytOC in the 0~100 cm soil layer and age of the bamboo forest, but a significantly negative one between the content of PhytOC and elevation of the groves（p <0.05）.【Conclusion】All the findings in this study suggest that to raise the content of soil silicon may help increase the content of soil Phytolith and soil PhytOC in the top-soil; and that Dendrocalamus latiflorus Munro groves can hold a large pool of PhytOC, because the plant per se has a high content of PhytOC, and the soil under the groves is highly capable of fixing and accumulating PhytOC, as well. Therefore, the Dendrocalamus latiflorus Munro ecosystem plays an important role in expanding the stable organic carbon pool in the soil.

Abstract:【Objective】Soil fertility quality assessment and constraint factors analysis of soil quality have vital theoretical and practical significances in regional soil improvement and utilization and guidance agricultural production. Paddy soil is an important component of the soil resources in China. Researchers have been using a set index system to evaluate soil fertility quality with results not so accurate. It is, therefore, essential to explore for a more accurate scientific method for the evaluation.【Method】 Jinxian County of Jiangxi Province was cited as a case for the study. A total of 103 soil samples were collected from the topsoil (0~20 cm) and subsoil (20~40 cm) layers of the paddy fields in the region proportional to their respective areas and types and 51 rice sampling sites set aside as a dataset for verification of the yield prediction based on remote sensing interpretation. A fairly more comprehensive dataset of soil properties was determined in the lab. Correlation analysis and principal component analysis (PCA) of the dataset with predicted yields were performed to determine minimum data set (MDS) and weight and membership read function models of the evaluation index system. Soil fertility was characterized in level with the comprehensive index method and main constraint factors of fertility quality in areas low in soil fertility quality. 【Result】To evaluate accuracy of remote sensing interpretation, a fitting equation was established between measured and estimated yields. In the light of the determination coefficient (R ²) and root of mean square error (RMSE) of the fitting equation, the normalized difference vegetation index (NDVI) can reflect more accurately crop yield. According to the yield prediction based on remote sensing interpretation, yield of the rice crop in the region varied in the range from 2.085 to 11.430 t hm^-2, and averaged 7.215 t hm^-2. Through principal component analysis MDS indices, including organic matter, cation exchange capacity (CEC), total potassium (TK), exchangeable calcium (Ex. Ca), bulk density (BD) and clay/silt, were acquired. CEC and TK were common ones in both topsoil and subsoil and the others standard ones . The correlation between soil quality comprehensive index (SQI) and rice yield was analyzed and calculated to be 0.73 (p<0.01) in coefficient, showing that SQI may be used to indicate fertility level of the soil accurately. Based on the average yield, 7.215 t hm^-2, of the region, threshold value of SQI for the region was determined to be 0.65. Areas with SQI value below the threshold value are subject to the risk of low yield. Further analysis of the indices via principal component analysis shows that the main constraint factors of soil fertility in the area are low organic matter content and heavy soil texture indicating low mellowness of the soil, deficiency of meso-nutrients indicating acidification, and low potassium content and high silt/clay ratio indicating poor soil physical structure. According to restraint-factor-based zoning, the county could be divided into three regions. In the hilly area, southeast of the county, soil acidification and poor soil structure are the main constraint factors; in the low mount and plain area, central and west of the county, soil acidification is; and in the lake area, north of the county, low soil mellowness is. Consequently, proper measures should be taken in correspondence to the areas facing different constraint factors so as to improve soil fertility of the paddy fields.【Conclusion】Yield-based soil fertility quality assessment is good for prediction of soil fertility accurately, and the models based on PCA, MDS, SQI and RS technologies can be used not only in paddy soil regions, but also in other types of region for evaluation of soil quality. Findings of the study show that over 30% of the paddy soil in the county are below the average level, but it is still not very clear what causes the low soil fertility. In order to reveal the reasons PCA will be performed to further reduce dimension of the evaluation indices, and zoning carried out on the town/township scale. Zoning on such a scale will sure be of great practical significance to the government in decision making and guiding agricultural production.

Abstract:【Objective】Phthalate acid esters (PAEs), also known as phthalate esters or "plasticizer", are the reaction product of phthalic anhydride and alcohol. PAEs are widely used in the production of a huge number of products such as agricultural plastic film, toys, medical bags and hoses for transfusion, food packaging, cleansers, vinyl floor and wallpaper, and personal care products. Among them, Di(2-ethylhexyl) phthalate (DEHP) is one PAE, the highest in output and consumption and also a toxic organic compound highly hazardous to human health, disturbing endocrine systems and causing cancers, mutation, oxidative damage and genetic toxicity. As DEHP is weakly bonded to the plastic matrix by hydrogen bond and van der Waals force, it is easily detached and diffused into the air, water and soil environments. Therefore, its pollution and hazard to human health has aroused more and more attention from the people. So far studies have proven that DEHP can enter organisms via a variety of ways, causing poisonous damage to tissues and organs of the organisms. As DEHP is extensively used in agriculture and hence exists in large volumes in the soil system, it is necessary to investigate its ecological and toxicological effects, such as oxidative stress and DNA damage, on typical soil animals, in the hope that the study may serve as scientific basis for reasonable assessment of soil ecological risk of DEHP.【Method】To explore eco-toxicological effects of DEHP on soil animals, Earthworms (Eisenia foetida), used as bio-indicator, were exposed to DEHP varying in concentration (0, 0.1, 1, 10 and 50 mg kg^-1) in artificial soil. Earthworms were sampled after 7, 14, 21 and 28 days of exposure for analysis of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and glutathione (GST), which are the indices reflecting the degree of DEHP activating oxidation of earthworms, reactive oxygen species (ROS), which is the indicator of cytotoxicity of DEHP to earthworms, and malondiadehyde (MDA) and olive tail moment, which are the indices reflecting genotoxicity of the substance to earthworms.【Result】 (1) DEHP, above 0.1 mg kg^-1 in concentration, significantly enhanced the activities of SOD, CAT, POD and GST in Eisenia foetida by a degree varying with the concentration of DEHP, which demonstrates that DEHP induces antioxidant enzymes in earthworms; (2) DEHP increased ROS concentration in earthworms as compared with control and the effect varied between treatments, displaying an apparent dose-effect relationship;(3) Comparison between the treatments shows that DEHP did have some effect on content of MDA, but the effect did not follow any specific rule and was the most obvious in earthworms exposed to DEHP, 10 mg kg^-1 and 50 mg kg^-1 in concentration; (4) In the presence of DEHP. GST in the earthworms was apparently activated, except for the treatment of 0.1 mg kg^-1, where the earthworms did not have much difference from those in control. The observation demonstrates that DEHP, higher than 0.1 mg kg^-1 in concentration induces GST in the earthworms; (5) Single cell gel electrophoresis shows that coelomocyte DNA of the earthworms was damaged in the presence of DEHP, regardless of concentration and Olive tail moment increased with the rising DEHP concentration, which suggests that DNA damage caused by DEHP is dose-dependent.【Conclusion】 Once DEHP enters earthworms, it activates the defense system of antioxidant enzymes (SOD, CAT and POD) and GST detoxification enzyme in the earthworms to protect the organisms from injury. Nevertheless, DEHP still raises ROS content in the earthworms, and excessive ROS triggers peroxidation of lipids, producing MDA. ROS and MDA act jointly damaging cell DNA of the earthworms. To sum up, DEHP may cause a certain degree of damage to organisms and DNA of the earthworms, manifesting fairly strong eco-toxicological effects. Therefore, adequate attention should be paid to DEHP disposal.

Abstract:【Objective】Cadmium (Cd) is the major pollutant in farmland soils of China, especially in South China, where the rice produced in certain areas is very high in over limit rate. It is, therefore, essential to perform soil Cd risk assessment and explore for major pathways of the food chain getting exposed to Cd pollution. Based on the point-to-point data of Cd in the soil and brown rice of a certain tract of paddy field in Changsha, the Food Health Standard for Rice (GB 2762-2012) and the research target of protecting 95% of the bio-species in the ecosystem, a threshold value for soil Cd was worked out using the biological concentration factor (BCF) and SSD (species sensitivity distribution) equations, quantitative relationships of HC₅ (hazardous concentrations) with soil properties and their prediction models discussed and studies done to compare the threshold value with the criteria for Cd in the Standard for Soil Environment Quality of China.【Method】Some foreign research institutions and scholars usually use BCF as an important parameter in assessing effect and variety of the pollutant, and HC5 as the concentration of a substance in soil being toxic to 5% of bio-species in the ecosystem, in other words, protecting 95% of the bio-species in the ecosystem. HC₅ is the scientific basis for setting up soil environmental quality standards. In the present study, HC₅ for Cd in soil was derived using the species sensitivity distribution method and the concept of BCF based on point-to-point field data from paddy soils. Prediction models for Cd crop safety thresholds based on soil properties were also developed and a function of soil physicochemical properties established.【Result】Results show that soil pH is the main soil factor affecting soil Cd food safety thresholds, and followed by organic matter (OM) content and total Cd (TCd), explaining 62.2%, 19.4% and 18.3% of the variation of HC₅ in paddy soil, respectively. The two-factor (soil pH and OM) prediction models can predict Cd crop safety thresholds quite accurately with determination coefficients (R²) ranging from 0.802 to 0.817, while the three-factor (soil pH, OM and TCd) prediction models are more accurate than the two-factor ones. With rising soil pH or TCd, HC₅ increases in value, but the trend varies significantly. When the number of factors rises from two to three, the influence of TCd on HC₅ decreases in degree, while the effect of pH does not vary much. In the test range, OM and HC₅ show a certain negative relationship between the two. Soil Cd food safety thresholds vary with soil physical and chemical properties. The variation may lead to the the problem of insufficient protection and excessive protection at the same time, when the thresholds are used for controlling total Cd content by a single stage. In this study, a dynamic and quantitative food safety threshold model for Cd in soil was established.【Conclusion】The prediction models developed in the present study prove that quantitative relationships exist between soil properties and risk thresholds. And all the findings in this study are beneficial to developing and implementing soil specific, scientific and reasonable risk control of Cd in paddy soil and formulating regional soil environmental quality standards.

Abstract:【Objective】Contributions of long-term fertilization to soil fertility and carbon sequestration mechanism of aggregates in dark brown soil were explored. 【Method】A long-term field experiment was established to study effects of fertilization on contents and composition of humic substabce—humic acid (HA) in aggregates of dark brown soil, using element analysis and Fourier transformed infrared (FTIR) spectra. The experiment was designed to have four treatments in fertilization regime, i.e. no fertilizer (CK); horse manure (M) (once 3 year−1); low-level chemical nitrogen and phosphorus fertilizers (N1P1); and horse manure combined with high-level chemical nitrogen and phosphorus fertilizer (M+N2P2). Soil samples collected from the treatments were wet-sieved for macroaggregates (>2 mm and 2~0.25 mm), microaggregates (0.25~0.053 mm) and silt/clay fraction (<0.053 mm). 【Result】The soil aggregates in the dark brown soil were composed mainly of microaggregates, which were the lowest in content of soil organic carbon (SOC) and HA, while macroaggregates (>2 mm) the highest. Long-term application of horse manure significantly increased the proportion of macroaggregates (2~0.25 mm) or by 49.06% in Treatment M, but decreased by 31.04% in Treatment M+N2P2. Treatment N1P1 did not have much effect on aggregates composition. Application of either horse manure or chemical fertilizers increased SOC content, but did not have much impact on content of HA. In Treatment CK, HA in macroaggregates (2~0.25 mm) was quite lower in condensation degree, but the highest in oxidation degree and aliphaticity, while HA in microaggregates the highest in condensation degree, aromaticity, “age” and stability. Compared with Treatment CK, all the other treatments (i.e., M, N1P1, M+N2P2) reduced the condensation degree, increased the contents of aliphatic hydrocarbon carbon (C) and aromatic-C and enhanced aromaticity as the result of decreased ratio of aliphatic hydrocarbon-C to aromatic-C (aliphatic hydrocarbon-C/aromatic-C ratio) in the HA in macroaggregates, while reducing the condensation degree and increasing the contents of aliphatic hydrocarbon-C, and aromatic-C, and the ratio of aliphatic hydrocarbon-C/aromatic-C , and hence aliphaticity of the HA in microaggregates. In the experiment field, molecular structure of HA of silt/clay fractions varied with the treatment. Compared with CK, Treatment M increased aliphatic hydrocarbon-C and reduced aromatic-C in content and as a result, increased aliphatic hydrocarbon-C/aromatic-C ratio, condensation degree and aliphaticity of the HA. In Treatment M+N2P2, the HA in aggregates of silt/clay fractions increased in condensation degree and aromaticity as the result of increased content of aromatic-C and decreased aliphatic hydrocarbon-C/aromatic-C ratio. Moreover in Treatment N1P1, the HA in aggregates of silt/clay fractions decreased in condensation degree, aliphatic hydrocarbon-C and aromatic-C contents and aliphatic hydrocarbon-C/aromatic-C ratio, and as a result, increased in aromaticity. 【Conclusion】 Long-term application of horse manure increases the content of SOC, promotes formation of 2~0.25 mm macroaggregates, contributes favorably to stabilization of the HA in macroaggregates, thus helping carbon sequestration. In addition, it also enhances activity of the HA in microaggregates (0.25~0.053 mm) and aggregates of silt/clay fractions (<0.053 mm), which contributes to soil fertility supply. These aggregates can be used as important indicators for evaluating effects of long-term application of horse manure on quality of humic substance in the soil.

Abstract:【Objective】Nutrient release during the decomposition of organic materials in soils is an important process in the nutrient element biogeochemical cycle, which could be used as substitute for chemical fertilizer. It is a fundamental to build the best straw returning practices to know the coupling characteristics and mechanism for nutrient release during straw decomposition under different climate and soil conditions.【Method】In this study, we transplanted neutral black soil (Phaeozem), alkaline chao soil (Cambisol) and acidic red soil (Acrisol) in cold-temperate, warm-temperate and mid-subtropical zones, respectively and setup the Soil Reciprocal Transplant Experiment. Wheat and maize straws were packed in 200-mesh nylon bags and buried at the depth of 10~20 cm in three types of soils in parallel in three climate regions, and then sampled at 0.5-, 1-, 2- and 3-years of decomposition. The effects of climate, soil and straw condition on nitrogen (N), phosphorus (P) and potassium (K) release associated with the decomposition were examined.【Result】The results showed similar releasing patterns for nitrogen and phosphorus. In cold temperature zone, the N and P nutrients released in the pattern of an enrichment stage followed by a release stage, while in warm temperature and subtropical zones they showed a continuously release pattern. The N and P released directly in Phaeozem but enriched firstly then released in Cambisol and Acrisol. The K were released directly during the 3-year decomposition, and the mean K release rate (FtK, percentage of total K in wheat straw or maize stalk residue to that in the straw applied) amounted to 89.5%1.1% in the first half year. During the 3-year decomposition, the nutrient release rate decreased followed the sequence of K>P≈N. Climate conditions contributed to 19.55.3% and 19.55.0% of variation for N and P release amount, while soil conditions to 16.66.5% and 13.87.0%, respectively. Meanwhile the contribution of climate and soil conditions to the variation of nitrogen and phosphorus release amount decreased with the decomposition going on. The K release was significantly but slightly affected by the straw conditions which contributed to only about 2.230.07% of variation. Among the interaction effect of these factors, the climate × straw and soil × straw affected significantly the N and P release amount. At later decomposition stages (2-3 years of decomposition), the total contribution of all factors (climate, soil and straw) to the variation of the nutrient release was less than 30%, which suggested that the other environmental factors, especially the biological factor, may play an important role during the process of nutrient releasing. The stepwise regression equations between nutrient release rate and climate, soil and straw factors were Yt _N= -3.41 -0.40C/N +0.49TN +0.43AT (R²=0.67, p=0.001), Yt_P= -83.73 +0.49RH +0.42TN +0.25N/P (R²= 0.47, p=0.003), and Yt_K= 2 574.39 -0.87C/N -0.33N/P -0.30RH (R²=0.62, p=0.002) for N, P and K, respectively. In which, AT stands for annual mean temperature; RH for relative humidity; C/N for carbon/nitrogen in straw; TN for soil total nitrogen content; N/P for nitrogen/phosphorus in straw.【Conclusion】In general, during the 3-year decomposition of wheat and maize straw under different climate and soil conditions, the N and P were released mainly in the pattern of an enrichment stage followed by a release stage, or in a continuously release pattern. However, the K was released all in a direct and faster pattern. The climate and soil conditions are the main controlling factors for N and P release, while the straw quality was the main factor influencing the K release.

Abstract:【Objective】Photosynthetic carbon (C), an important link of the carbon cycle in the atmosphere-plant-soil system, is closely related to the atmospheric environment and changes in soil quality, and plays a crucial role in the terrestrial ecosystem and global C cycling. Rice is one of the main grain crops in China, whose planting area is increasing year by year. Paddy soil is obviously quite high in C sequestration potential. Therefore, it is of vital significance to explore distribution of photosynthetic C in the paddy soil system and its variation to scientific evaluation of C cycling in paddy soil. 【Method】¹³C pulse-labeling and stable isotopic mass spectrometry technologies were employed to study variation of the assimilation rate and distribution ratio of photosynthetic C and their increasing rates in the rice-soil system relative to growth stage (regreening, tillering and heading stages) of the rice plants growing in a pot experiment. 【Result】The objectives of this study were toexplore turnover and distribution dynamics of photosynthetic C in therice-soil system at three different growth stages of the plants and to provide a theoretical basis for further researches on C cycling and renewal of soil organic C in the paddy ecosystem.Results show that photosynthetic C gradually decreased in total assimilation rate with the each passing day after ¹³C pulse-labeling (duration 5 h) of the rice-soil system conducted, separately, at the beginning of each growth stage. The total assimilation rate reached 75.92%~39.53%, 70.01%~52.02% and 86.38%~69.60% and the loss rate of assimilated photosynthetic C 47.93%, 25.70% and 19.43%, respectively, during the period from Day 2 after the labeling at the regreening, tillering and heading stageperiod. The assimilation rate of photosynthetic C was significantly higher in the heading stage than in the regreening and tillering stages, while an opposite trend was observed of the loss rate of photosynthetic C. The transformation of the photosynthetic C was offset between the above-ground and under-ground (including roots and soil) parts of rice in three growth stages. While the distribution ratio of photosynthetic C was much larger in the aboveground (mean 85.04%~73.10%) part than in the root (mean 12.50%~22.04%) and soil (mean 1.70% ~5.04%). The distribution ratio of photosynthetic C was higher aboveground, but lower underground at the heading stage than at the tillering and regreening stages.In addition, the increasing rate of photosynthetic C in soil during the three growth periods was 0.08% ~ 0.21%, 0.09%~0.17% and 0.19%~0.27%, respectively. The increasing rate of photosynthetic C in soil was higher during the heading period than during the regreening stage and tillering stage, and the photosynthetic C during the period was relatively stable in soil.【Conclusion】Under the experimental conditions, the assimilation and distribution of photosynthetic C in the rice-soil system varied with growth of the plants. The assimilation rate and distribution ratio of photosynthetic C aboveground was significantly higher at the heading stage than at the regreening and tillering stages, and the loss rate of photosynthetic C was significantly lower. The increasing rate of photosynthetic C in soil was higher at the heading stage than at the regreening stage and tillering stage, and the photosynthetic C at that stage was relatively stable in soil.

Abstract:【Objective】Summer fallow after winter wheat is harvested in dryland on the Loess Plateau is a very common practice to save rain water, and restore soil fertility for the next crop. Nowadays, the content of nitrogen (N) (mainly in nitrate form) in the soil of the dryland as residue of the fertilizer applied to winter wheat is increasing steadily. As summer is the rainy season in this region, whether or not the high rainfall would increase NO₃^--N leaching loss is an important issue deserving further study. The method of adding ¹⁵N labeled nitrate after winter wheat is harvested in dryland is one to quantitatively explore fate of the residual fertilizer N in the dryland under summer fallow in the Loess Plateau, and hence to provide a scientific basis for managing N in dryland. 【Method】The ¹⁵N labeled fertilization micro-plot (Polyvinylchloride column, 25 cm diameter and 25 cm long) method was used to study fate of the residual fertilizer N in the dryland under summer fallow in a field experiment, which had five tracts of cropland and two N treatments set up with and without N application (0 and 30 kg N hm^-2). ¹⁵N labeled nitrate was mixed with the surface soil (0~15 cm) in the micro-plot at a rate equal to the content of the residual fertilizer N in the field after winter wheat was harvested. At the end of the summer fallow, soil samples throughout the soil profile (0~200 cm) were taken from the micro-plots, for analysis the contents of soil total nitrogen, NO₃^--N, and their ¹⁵N abundance. 【Result】 Results show that at the beginning of the summer fallow, the content of NO₃^--N accumulated in the 0~200 cm soil was quite high, ranging between 205 and 268 kg hm^-2 and averaging 244 kg hm^-2; At the end of the summer fallow, apparent NO₃^--N accumulation peaks were found in the soil, 40~80 cm in depth, and ¹⁵N abundance ranged between 0.408% and 0.482% and averaged 0.429%, being the highest in the soil 60 cm in depth, averaged 0.372% in the soil 80 cm in depth, being higher than the background value of ¹⁵N abundance in the soil (0.367 ¹⁵N atom%), and was 0.369 % in the soil 100 cm in depth, more or less the same as the background value, in Treatments N30 in all the five tracts of cropland. In the five tracts of cropland, ¹⁵N labeled nitrate abundance was the highest in the 40~60 cm soil layer in the soil profiles (0~100 cm), averaging 2.151%; and the lowest abundance was in the 80~100 cm soil layer, averaging 0.407%, both significantly higher than the background value. Although the rainfall during the summer fallow season was only 157 mm, making it a dry year, it still leached ¹⁵N labeled nitrate down to 80 cm in depth, through a 45~65 cm thick soil layer, and even ¹⁵N labeled nitrate was found in 100 cm depth. At the end of the fallow, the content of residual N averaged 21.6 kg hm^-2 or ranged between 20.8 and 22.9 kg hm^-2 in the 0~100 cm soil profile, accounting for 71.9% of the applied N fertilizer in all the five tracts of cropland. The content of residual labeled N was 4.5 kg hm^-2, 2.9% of which was in the form of NO₃^--N in the 0~20 cm soil layer; Residual fertilizer N was mainly distributed in the 40~60 cm soil layer, and averaged 17.7 kg hm^-2 in content, accounting for 52.8% of the total N fertilizer applied, in which ¹⁵N labeled nitrate content was 6.8 kg hm^-2. After the summer fallow, the applied ¹⁵N labeled N fertilizer was found lost at a rate of 23.8%~30.8% (averaging 28.1%).【Conclusion】 Residual fertilizer N accumulated significantly in the 0~200 cm soil layer of the dryland after wheat was harvested, posing a potential risk of leaching. In 2014, though it was a dry year, the effect of rain water leaching NO₃^--N was still quite significant, indicating that the NO₃^--N leaching in the dryland during the summer fallow season should not be ignored and further studies should be done on mechanisms of its leaching loss.

Abstract:【Objective】Soil aggregates in the soil are important media capable of storing, transforming and activating soil phosphorus(P), and distribution and stability of soil aggregates is influenced by long-term fertilization. However, little has been reported on release pattern and adsorption capacity of P across various soil aggregates and their relationships in red soils as affected by long-term fertilization,which are essential to sustainable management of P sources in agricultural fields. The objectives of this study are to: (i) investigate changes in TP, available P, CaCl₂-P, PSI and DPS, in soil aggregates of different particle-size fractions in a red soil under long-term fertilization; (ii) to explore relationships between CaCl₂-P, available P, DPS; and (iii) to study how DPS andAvailable P affect P loss potential.【Method】A long-term fertilization experiment was established in 1988 and soil samples were collected from the 7 fertilization treatments, designed in the experiment as follows: NPK, NK, Control (CK), CK + peanut straw (PS), CK + rice straw (RS), CK + fresh radish (FR) and CK + pig manure (PM). The soil samples were fractionated, using the wet sieving method,into aggregates of different particle sizes (> 2.0 mm, 2.0 ~ 1.0 mm, 1.0 ~ 0.25 mm and 0.25 ~ 0.053 mm). Then the various fractions of aggregateswere analyzed for total P (TP), available P, CaCl₂-P, P sorption index (PSI) and degree of P saturation (DPS) and relationships between the parameters.【Result】Results show that Treatment NK was the lowest in TP, and DPS but the highest in PSI in all the aggregates, regardless of particle size fraction in the red soil. Compared with Treatment CK, TreatmentsPS, RS and FR were quite similar in effect on soil TP, PSI, Available P and DPS; but Treatment PM significantlydecreased soil P retention capacity with the highest TP and lowest PSI, and increased P release or loss potential in all the fractions of aggregates with the highest DPS, Available P and CaCl₂-P. All the fertilization treatments, irrespective of their pattern, significantly increased P content in the > 2.0 mm fraction of aggregates with PEC (P enrichment coefficient) >1, but in Treatment NPK + PM soil P was more easily enriched in macro-aggregates (> 0.25 mm). 【Conclusion】Correlation analysis indicates that the P accumulated in the soil may be subject to potential loss to the safety of water quality when available P was range in 168 ~ 260 mg kg^-1 or DPS < 28% in the red soil; otherwise P loss would be significant. Therefore, new strategies of using both commercial fertilizers and animal manures must be established and implemented to prevent P build up in the soil and to minimize P loss to water bodies in the red soil region.

Abstract:【Objective】Selenium (Se) is an essential element. About1 billion people the world over suffer Se deficiency, which may lead to a series of human health disorders. The purpose of this study was to explore pathways of Se transporting to grains at the milking stage of two varieties of rice, Xiushui 48 and S. Andrea, relative to form of Se fed to the crop and to better understand mechanism of the translocation of Se to grains of the plant, so as to improve Se content in rice and breed Se-enriched rice cultivars.【Method】Two cultivars of rice (Oryza sativa L.), Xiushui 48, an Se-enriched cultivar, and S. Andrea, a general one, turn out grains differing sharply or by 3 times in Se content. They were selected for comparison in Se accumulation in grains at the milking stage. Four different species of Se [Selenite, Selenate, Selenomethionine (SeMet) and Se-methyl-selenocysteine (SeMeSeCys) ] were supplied, separately, to excised panicles via stems subjected to girdling or none and flag leaves of intact rice plants of the two cultivars during the milking stage. 【Result】Results show that organic selenium could enter into phloem and then be translocated to grains via stem, while only 30% ~ 50% of the inorganic selenium in the phloem was remobilized and transferred into grains via stem, and the remaining transported through xylem. Sodium selenate could be transported to flag leaves via both phloem and xylem, while sodium selenite went mainly through xylem. When fed with sodium selenite or Se-methyl-selenocysteine, excised panicles with or without the stems girdled did not show much difference in Se concentration in grains between the two varieties. But when fed with sodium selenate and selenomethionine, excised panicles of Xiushui 48 with no stem girdled were much higher in grain Se accumulation capacity than those of S. Andrea, and not much difference was found between the excised panicles of the two varieties with stem girdled. It was also found that Xiushui 48 was more capable than S. Andrea of transporting selenate and selenomethionine from stem to grain. Obviously the former is capable of moving more Se from stem and flag leaf to grain than the latter is, which is probably the direct cause of higher Se concentration in grains of Xiushui 48. The finding also indicates that Xiushui 48 is much more capable (p= 0.05) than S. Andrea of transporting Se-Met and selenate through phloem from stems to grains, and from flag leaves to grains, too. 【Conclusion】Selenium-enriched Xiushui 48 can transport more Se from stems and flag leaves to grains than Non-Se-enriched variety, S. Andrea, which is probably the direct cause of the difference between the varieties of rice in grain selenium content.

Abstract:【Objectives】A five-year field experiment was conducted between 2007 and 2011 in the Weibei tablelands of Shaanxi, China to determine effect of different patterns of dual-mulching of ridge and furrow on soil fertility (soil organic matter and available nitrogen, phosphorus, potassium contents), enzyme activity (urease, phosphatase and sucrase) and crop productivity (maize yield and water use efficiency) in an attempt to provide some important theoretical and practical basis for perfecting micro-catchment crop cultivation in the sub-humid areas.【Methods】 In a tract of farmland under the ridge and furrow rainwater harvest system (RFRHS), ridges were covered with plastic film and furrows mulched with common plastic film, bio-degradable film, maize straw or liquid film, or left uncovered, and a tract of flat farmland under conventional cultivation without mulching, which is popular among local farmers, was used as control. 【Results】 After the spring maize was harvested in 2011, soil organic matter and available nutrients in all the treatments decreased in content with soil depth. Soil nutrients in the dual-mulching treatments obviously increased in content when compared with the initial background value in 2007, but decreased in the treatment that had ridges mulched and furrows uncovered and the control. The treatment that had ridges mulched with plastic film and furrows mulched with straw was significantly higher than the control in content of soil organic matter, alkalytic nitrogen, available phosphorus and readily available potassium in the 0~20 cm soil layer, and the treatment that had both ridges and furrows mulched with plastic film and the treatment that had ridges mulched with plastic film and furrows with bio-degradable film were somewhat higher than the control in content of soil organic matter alkalytic nitrogen, but significantly higher in content of available phosphorus and readily available potassium. All the dual-mulching treatments were slightly higher than the control in content of soil organic matter and available nutrients in the 20~60 cm soil layer, and in activity of urease, phosphatase and sucrase in the 0~20 cm soil layer, too. The treatment that had ridges mulched with plastic film and furrows with straw was the highest in activity of soil enzymes, and followed by the treatment that had both ridges and furrows mulched with the plastic film and the treatment that had ridges mulched with plastic film and furrows with bio-degradable film. Dual-mulching significantly increased maize yield water use efficiency in the region. The treatment that had ridges mulched with plastic film and furrows with bio-degradable film, the treatment that had both ridges and furrows mulched with plastic film and the treatment that had ridges mulched with plastic film and furrows with straw was 41.1%, 42.1% and 39.3%, respectively, higher than the control in maize yield and 38.0%, 39.6% and 37.0% in water use efficiency.【Conclusions】The dual-mulching technology has been demonstrated as an effective practice to improve soil fertility, promote soil enzyme activity and increase crop yield and water use efficiency in the Weibei tablelands. In terms of the effect, the treatment that has ridges mulched with plastic film and furrows with straw ranks first, and is followed by the treatment that has both ridges and furrows mulched with plastic film and the treatment that has ridges mulched with plastic film and furrows with bio-degradable film. Apparently, the technology is feasible and worth extrapolating for spring maize production in the rainfed agricultural zones of the Loess Plateau, China.

Abstract:【Objective】 Soils are an essential section of the terrestrial carbon cycle and act as either source or sink for carbon, depending on what fraction the carbon is in and its stability. However, few studies have been reported on relationship between soil carbon fractions and carbon fixing process (Calvin-Benson-Bassham cycle) in wetland soil systems. Ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) is a key CO₂ assimilation enzyme in the Calvin cycle, and its relationship with its large-subunit I gene and soil carbon fractions may provide some information about their relative importance to the genetic potential of CO₂ fixation. Meanwhile, RubisCO enzyme activity and soil physicochemical properties were determined, and statistical analyses were performed to identify key factors driving microbial CO₂ sequestration in wetland soils.【Method】In this study, soil samples were collected separately from wetlands under. Triarrhena lutarioriparia community (ND), Phragmites australis-Carex cinerascens community (HH), Carex cinerascens community (TC) and Zizania latifolia community (JB) and a bare shoal (LT) at Nanjishan of the Poyang Lake in China, for fractionation of soil carbon and analysis of soil organic carbon (SOC), soil microbial biomass C (MBC), and dissolved organic C (DOC), activity of RubisCO and its large-subunit I gene (cbbl ).【Result】Results show that content of total carbon, SOC, MBC and DOC in the soils varied in the range of 6 380~33 830, 1 209~2 259, 124.6~1 282 and 2.848~18.00 mg kg^-1, respectively, and the four patches of wetlands displayed an order of ND > HH > TC > JB in terms of variation of their means. RubisCO activity in the soils varied in the range of 38.08~125.1 nmol CO₂ kg^-1 min^-1 and was the highest in ND reaching 125.1 nmol CO₂ kg^-1 min^-1 and the lowest in TC falling down to 38.08 nmol CO₂ kg^-1 min^-1. Total number of copies of cbbl genes in the soils varied in the range of 36.07×10⁴~195.6×10⁴ copies g^-1, being the highest in ND (195.6×10⁴ copies g^-1) and the lowest in JB (36.07×10⁴ copies g^-1). RDA analysis indicates that the main factors affecting distribution of soil carbon fractions are Total N, pH, catalase activity and sucrase activity; and soil total N is the most important factor affecting soil carbon fractionation, followed by pH. Correlation analysis indicates that Total N and sucrase activity are positively related (p<0.01), while pH and catalase activity negatively related to carbon fractionation (p<0.01). The contact of the soil with the atmosphere might lead to a significant negative relationship between soil catalase and carbon. The correlation between MBC and carbon cbbl gene is the strongest, followed by DOC, which shows a significant positive correlation with cbbl gene (p<0.01), while total C and SOC are significantly and positively related to RubisCO activity (p<0.05). 【Conclusion】All the findings in this study suggest that soil carbon fixation enzyme and cbbl gene are positively correlated with soil carbon fractionation, which improves our knowledge of their roles in carbon sequestration and nutrient turnover. Obviously the study is of great significance to further researches on soil carbon cycle and its microbial mechanism in Poyang Lake wetlands.

Abstract:【Objective】 Owing to the limitation of soil resources in the traditional wolfberry (Lycium barbarum L.) production regions, monocropping of the plants has become one of the major factors affecting sustainable development of the industry of wolfberry production and causing serious economic loss every year in Ningxia. It is, therefore, of great theoretic significance to sustainable development of the industry to explore effects of monocropping of the plants on evolution of the soil microbial community in the soil ecosystem. A wolfberry plantation, the Nanliang Farm in Yingchuan of Ningxia was selected as the subject for the study. The Illumina MiSeq sequencing technique was used to analyze the effects.【Method】 Soil samples were collected form rhizosphere and bulk soils of the monocropping wolfberry fields and control (non-monocropping field) for analysis of diversity and structure of the soil microbial communities, and plant samples were, too, for characterization of plant growth. Total genomic DNA was isolated form the rhizosphere and bulk soils using a Power Soil DNA Isolation Kit. Then V4 sections of 16S rDNA were sequenced with the aid of the Illumina MiSeq system and soil microbial communities in the rhizosphere and bulk soils were analyzed for diversity and structure with QIIME.【Result】It was found that soil available nitrogen and phosphorus were significantly higher in the monocropping field than in the control, while soil pH and electric conductivity exhibited a reverse trend; that monocropping significantly inhibited growth of the replanted wolfberry. The barcoded pyrosequencing data revealed that in the monocropping field, the number of soil bacterial species in the rhizosphere significantly decreased (p < 0.05) and the soil bacterial community structure substantially altered as compared with the control. However, no much difference in bacterial community diversity and structure was observed in bulk soil between the two fields. Proteobacteria, Actinobacteria, Gemmatimonadetes, Bacteroidetes, Acidobacteria, Cyanobacteria, Firmicutes, Verrucomicrobia, Chloroflexi and Planctomycetes were the most dominant bacterial phyla in all the soil samples, accounting for 93.8%~96.1% of the total taxon tags. Planctomycetes in rhizosphere significantly decreased in relative abundance in the monocropping field as compared with the control (p< 0.05). The analysis at the genera level also shows that 40 of the total 579 genera of soil bacteria obviously varied in relative abundance between the two treatments (p< 0.05). Pearson’s correlation coefficients analysis also shows that in the bulk soils significantly positive relationships were found between soil pH and Gemmatimonadetes and between nitrate nitrogen content and Proteobacteria, whereas highly negative ones were between Proteobacteria and pH, between Cyanobacteria and total nitrogen content, between Chloroflexi and ammonium nitrogen content, between Actinobacteria and nitrate nitrogen content, between Cyanobacteria and total phosphorus content, and between Firmicutes and available phosphorus content, while in the rhizosphere, positive ones were found between soil pH and Gemmatimonadetes, and between electric conductivity and Planctomycetes, whereas negative ones were between ammonium nitrogen content and Actinobacteria, between available phosphorus content and Gemmatimonadetes, and between available phosphorus content and Planctomycetes. Furthermore, distance based redundancy analysis (db-RDA) indicates that soil pH and available phosphorus content were the major factors affecting structure of soil bacterial community in the bulk soil, explained 41.8% and 35.4% of variances (p<0.05), respectively, whereas none of the soil properties was found responsible for the changes in the soil bacterial community structure in the rhizosphere.【Conclusion】 All the findings in this experiment demonstrate that monocropping of Lycium barbarum L. has caused serious soil problems, which in turn affect activity and composition of the soil bacterial community in the rhizosphere of the replanted Lycium barbarum L.

Abstract:【Objective】 As one of the three major pedogenic river deltas in China and the one that develops the fastest, the Yellow River Delta is an important reserved land resource. Developing mixed forests has been becoming a major strategy to develop the Yellow River Delta，because mixed forests can not only regulate temperature but also improve soil fertility. To improve the ecological system of the Yellow River Delta, a number of forest plantations have been established since the 1950s. Robinia pseudoacacia is the dominant tree species in most of the forest plantations, which contribute significantly to conserving soil and water and improving the ecological system of the Delta. Soil microbial community in plant rhizosphere plays an important role in plant nutrition and plant health. This research aimed to accurately evaluate how soil bacterial communities colonize in rhizosphere and in bulk soils under Robinia pseudoacacia in the Yellow River Delta. 【Method】 With the aid of the Illumina MiSeq technology, this research analyzed structure and diversity of the bacterial communities in the rhizosphere soil and the bulk soil under Robinia pseudoacacia for comparison. The differences in soil bacterial community between rhizosphere and bulk soil were expressed via the Weighted Unifrac Range of OTUs. 【Result】Results show that the bacterial community in the rhizosphere soil consisted of 214 genera of 36 phyla and that in the bulk soil 153 genera of 33 phyla. Proteobacteria, Actinobacteria and Acidobacteria were the dominant phyla of bacteria in both rhizosphere and bulk soils with relative abundance being more than 15%. Acidobacteria and Nitrospirae varied sharply in relative abundance between the rhizosphere soil and the bulk soil. Chloroflexi, Gemmatimonadetes, Planctomycetes, Nitrospirae, and Verrucomicrobia were the dominant taxa of bacteria with relative abundance being more than 1%. Rhodoplanes, Lysobacter, Thermomonas and Streptomyces in the rhizosphere soil and Rhodoplanes,Lysobacter, Streptomyces and Kaistobacter in the bulk soil all exceeded 4% in relative abundance. There were 29 and 32 genera of bacteria in the rhizosphere soil and 3 in the bulk soil being more than 1% in relative abundance, respectively. Significant differences were found in relative abundance of Novosphingobium, Aeromicrobium, Limnohabitans, Phycicoccus, aistobacter, Candidatus Nitrososphaera, DA101, Ramlibacter, and Methylibium between the rhizosphere soil and the bulk soil. Relative abundance of Azotobacter was significantly higher in the rhizosphere soil than in the bulk soil, while no significant difference was observed in relative abundance of potassium and phosphorus-dissolving bacteria between the two soils. Chao richness of bacterial community was 2 054 and 2 376 in the rhizosphere soil and in the bulk soils, respectively, showing a significant difference. Weighted Unifrac Range mof the soil bacteria between the rhizosphere and the bulk soil was 0.12～0.25. In this study, all the findings demonstrate that there are some differences in structure between the bacterial communities in the rhizosphere soil and in the bulk soil under Robinia pseudoacacia in Yellow River Delta. 【Conclusion】Significant differences do exist in relative abundance of Proteobacteria, Acidobacteria, and Nitrospirae at the phylum level, and Novosphingobium, Aeromicrobium, Limnohabitans, andPhycicoccus at the genus level between rhizosphere and bulk soils, and significant differences are also observed in bacterial diversity between rhizosphere and bulk soils. Analysis of bacteria 16S rRNA-bacteria dataset shows differernces in structure and diversity of soil bacterial community between the rhizosphere and bulk soila in the Yellow River Delta. But further research is still needed to get more detailed information about soil microorganisms.

Abstract:Certain achievements have been made in the study on soil erosion on slopes using magnetic tracers. However, the traditional magnetic tracer method is far from effective enough to meet the requirements of the study to characterize splash erosion caused by each rainfall event. Therefore, an in-lab splash erosion simulation experiment was carried out over on a bed of non-magnetic quartz sand mixed separately with nano magnetic materials, different in particle size (20 nm or 200 nm), at a rate of 1.5%, 2.5% and 3.5% in this study, Magnetic susceptibility meter and Three-dimensional Laser Micro-topographical Scanner was used to monitor variation of the magnetism of the land surface and its relationship with changes in topographic characteristics of the land surface subjected to splash erosion, and hence to study feasibility of using nano magnetic materials to characterize splash erosion. Results show that the 20 nm magnetic material was more effective than the 200 nm magnetic material in raising magnetism of the quartz sand over its background value, and the effect varied sharply with concentration or incorporation rate of the magnetic materials; and the higher the concentration of the material, the more durable the tracing effect. After splash erosion, surface magnetic susceptibility declined gradually with the time going on, displaying a high logarithmic function relation expressed asx₁=aln(t)+b; The use of 20 nm magnetic material, 3.% in concentration effectively characterized changes in splash erosion rate of the quartz sand (p<0.01) with a power function relation expressed as x₂=aM ^b (x₂= sediment susceptibility and M = splash erosion amount). The highly significant relationship between the variation of magnetic susceptibility of the 20 nm magnetic materials in the 3 minutes of splash erosion and the variation of microrelief demonstrates that the 20nm magnetic material can be used to characterize erosion degree, up to the range of -5~10 mm, of the land surface subjected to splash erosion within a short period of time. All the findings in this study prove that it is, to a certain extent, feasible to use 20 nm magnetic material to characterize splash erosion of land surface. Moreover, this study may help open up some new ideas and develop new methods for further study on utilization of the magnetic tracing method.