• Volume 54,Issue 3,2017 Table of Contents
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    • Simulation Study on Bare Subsoil Runoff and Sediment Yield on Karst Slope

      2017, 54(3):545-557. DOI: 10.11766/trxb201609050206

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      Abstract:【Objective】The unique “dualistic structured” (land surface and underground) hydrologic system in the karst areas of Southwest China has the areas subjected to two types of soil erosion simultaneously, i.e. surface erosion and underground erosion. Relevant researches show that soil erosions on the land surface and in the underground crevices are the two pathways for and components of the soil and water loss in the karst region. In recent years, with the intensified development in the karst region of Southwest China, construction of industrial parks and urbanization has become a hot spot. Consequently large areas of forest land and/or cultivated land have or are being stripped of topsoil for construction projects, thus depriving the land of its vegetation protection and topsoil cover, and making it completely nude and exposed to rainfall erosion. Currently, though much effort has been done studying underground soil and water loss in karst area, almost nothing has been reported about characteristics of the soil erosion on slope land with topsoil stripped of, and the researches, done or being carried on, fail to illustrate either characteristics of the spatial distribution of runoff and sediment in the surface and underground of slopes or effects of affecting factors, like rainfall, slope, underground fissure porosity, etc. of slope soil erosion on characteristics and mechanisms of runoff and sediment generation on stripped slopes in the areas. Therefore, this study is oriented to illustrate and analyze distribution characteristics of runoff and sediment in the surface and underground along stripped slopes, and further to explore effects of rainfall, slope, underground fissures, pores and holes on soil erosion. 【Method】An indoor experiment was carried out using steel troughs filled up with rocks and soil to simulate the "dualistic structure" of stripped slopes the karst area. In the experiment, troughs were adjusted to slope gradient, 10°, 15°, 20° and 25°, separately, and rainfalls different in intensity (30, 50 and 80mm h-1) were simulated on troughs of artificial slopes, different in fissure porosity (10°, 15°, 20° and 25°), to explore how the three factors affecting soil erosion on the slopes.【Result】Results show that: (1) On stripped slopes, underground erosion became more elusive and tended to be neglected when the rainfall event was low in intensity. When rainfall intensity rose up to 30 and 50 mm h-1, underground soil and water loss turned to be in dominancy and surface runoff was observed only on slopes ≥15°in gradient. With rainfall rising in intensity, underground soil and water loss varied in a curve of saddle shape, and the variation with rainfall intensity displayed an order of 80<30<50 mm h-1 in magnitude. (2) On gentle slopes,≤15°, soil and water loss occurred mainly in the fissures and pores underground, and was not observed on the surface, while on slopes, 20°or 25°ingradient, the underground sediment yield accounted for 85% ~ 97% and 59%~ 84% of the total on the slope.(3)The effect of underground holes and porosity on underground soil and water loss was significant, and a positive relationship was observed of underground runoff and runoff coefficient with underground fissure porosity. The higher the fissure porosity, the bigger the channels for soil and water loss and the more soil and water lost underground, and hence the higher the proportion of the underground soil and water loss to the total.【Conclusion】To control soil erosion in karst areas, it is not wise to pay attention only to surface soil erosion. Downwards erosion or underground soil and water loss should be the focus of attention in the karst region. In development and construction projects, it is crucial to control underground leakage, so as to avoid leakage-triggered collapse of underground karst caves. All the findings in this study are expected to be of some theoretical and practical significance to future studies on underground soil and water loss as well as guidance of soil erosion prevention and control in the karst areas.

    • Contrast Study on Simulated Runoff Erosion of Two Engineering Accumulation Slopes

      2017, 54(3):558-569. DOI: 10.11766/trxb201609050271

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      Abstract:【Objective】Complex in composition, loose I structure and low in cohesion, engineering taluses are places where hazards, like soil erosion, mud-rock flow and landslip, are likely to occur under the action of rainfall runoff. 【Method】 Based on field investigations of the engineering taluses formed during town construction processes in Chongqing, engineering taluses of purple soil and yellow sandy earth, commonly seen in the region, were selected as the objects of the study. On the taluses, field water scouring experiments were carried out to explore dynamic processes and mechanisms of water infiltrating, flow generating and sediment yielding on the underlying land surface under taluses different in rock content, relative to hydraulic condition, in an attempt to illustrate morphology and evolution process of the erosion and distribution characteristics of sediment particles in the erosion on the talus slopes. The field scouring experiments, designed to have three flow rates (i.e. 5, 10, 15 L min-1) and three slope gradients (i.e. 30°, 35° and 40°), were conducted during the peiord from August to November, 2012 at the Stationary Soil Erosion Experiment Site for Production and Construction Projects in the Southwest University, Chongqing. 【Result】Results show: (1) water infiltration rate in the soils of the taluses declined rapidly first and then gradually leveled off with scouring going on and magnitude of the fluctuation varied with scouring flow rate; water infiltration rate on the underlying surface varied in the range of 0.4 ~ 1.7 mm min-1, and the mean infiltration rate was in a power function relationship with the scouring flow rate, and so was the erosion modulus on the underlying surface of the taluses of different nature. It is, therefore, feasible to estimate erosion moduluses of taluses formed during the processes of various urban construction projects by scouring flow rate; (2) runoff yield rate on the talus slopes rose first and then fluctuated, exhibiting a wave-like curve with the scouring going on, which indicates that scouring flow rate is the major factor affecting runoff rate on the slope. With rising flow rate runoff rate increased significantly. When the scouring flow rates were the same, the mean runoff rate on talus slopes of yellow sandy earth was 1.89 times that on talus slopes of purple soil; (3) sediment concentration in runoff on talus slopes on different underlying surfaces rose first and then leveled off with the scouring going on and varied in the range of 0.21 ~ 1278.49 g L-1 relative to scouring flow rate; during the scouring process, soil erosion transformed from surface erosion to gully erosion, affecting significantly or multiplying sediment concentration in runoff by 13.73 times to the most extent; the erosion process on the talus slopes consisted of three stages, i.e. sudden changing stage, active stage and stabilization stage, corresponding to the three stages of erosion transformation from surface erosion to gully erosion, i.e. surface erosion, rill erosion and waning of rill erosion; contingency and randomness of the occurrence of rills were the two major contributors to the fluctuation of sediment yield;(4) particle size distribution of the erosion sediment from engineering talus slopes varied sharply with scouring flow rate and with composition of the talus slope; the particles of the erosion sediment from the talus of purple soil were larger in size than those from the talus of yellow sandy earth. The erosion sediment from the talus of purple soil varied in the range of 2 ~ 10 mm in particle size, and that from the talus of yellow sandy earth in the range of 0.1 ~ 0.5 mm; roughing of the talus slope as a result of erosion makes it harder to restore ecology of the waste dumping sites. 【Conclusion】All the findings of the study may serve as important scientific basis for prediction of soil and water loss and restoration of vegetation and ecology on engineering taluses in Chongqing.

    • Hydrodynamic Characteristics of Erosion in Different Soil Layers in Granite Collapse Region

      2017, 54(3):570-580. DOI: 10.11766/trxb201607140306

      Abstract (2531) HTML (0) PDF 1.47 M (2992) Comment (0) Favorites

      Abstract:【Objective】 Soil detachment rate refers to the quantity of soil detached by water flow in a unit of time and/or area. Quantitative analyses of the soil detachment processes in different soil layers in granite collapse regions is of great theoretical and practical significance to accurate prediction of soil detachment processes and construction of a physical model for erosion of collapsed hills. 【Method】 Collapsing hill erosion is a speci?c type of soil erosion in hilly granitic regions of tropical and subtropical South China, and may result in extremely rapid water and soil loss. Knowledge of how collapsing hill erosion affects the soil physical and chemical properties of different soil layers in the region is important to understanding the evolution of soil quality. In this study, an in-lab runoff scouring experiment was conducted on artificial slopes of top soil layer, red soil layer, sandy soil layer and detritus layer developed in the collapsed granite hills in Tongcheng, Hubei Province. The runoff scouring experiment had the slopes set at 8.8%, 17.6%, 26.8%, 36.4% and 46.6% in gradient and scoured with flow varying in rate (0.2 L s-1, 0.4 L s-1, 0.6 L s-1, 0.8 L s-1 and 1.0 L s-1), separately for cross checking . The artificial slope was prepared on a steel trough 0.2m high on both side, 0.2 m wide and 3.8 m long and on the top of the trough was a water tank, 0.2m high, 0.4 m wide and 0.2m long, filled with water to supply water flow steadily at a required rate. The experiment was to investigate relationships of soil detachment rate with various hydrodynamics parameters in four different soil layers and to explore hydrodynamic mechanisms of the erosion in collapsing granite hills. 【Result】 Results show that under the condition of a certain slope, soil detachment rate increased with increasing runoff flow rate, and varied sharply with soil layer; the highest detachment rate was found in the detritus layer, which was followed by sandy soil layer, red soil layer and top soil layer; under the same runoff flow rate, soil detachment rate decreased with the scouring going on and tended to level off, regardless of type of soil layers. Besides, the complex effect of slope degree and flow rate on detachment rates in all soil layers could be well fitted with the two-variable power function equation (R2 > 0.878). The effects of shear stress and stream power of the runoff on detachment rate on all soil layers could be well described with the linear equation (R2 > 0.926), yielding a correlation coefficient much higher than that of the fitting of unit stream power with the polynomial equation (R2 < 0.830). Therefore, shear stress and stream power of the runoff can be used as hydrodynamic parameters to describe the soil erosion in different soil layers of collapsed hills. The threshold of runoff shear stress varied with soil layer in a decreasing order of top soil layer > red soil layer > sandy soil layer > detritus layer or 0.28 Pa > 0.13 Pa > 0.10 Pa > 0.07 Pa. 【Conclusion】 The detritus layer is the highest in erodibility, followed by the sandy soil layer, red soil layer and top soil layer. Hence, the resistance of the soil layers against runoff erosion gradually decreases with soil depth as the soil layers exist vertically in the soil profile in the collapsing hill region.

    • Correlations between Characteristic Curves of Physical Properties of Weathered Granite Soils

      2017, 54(3):581-589. DOI: 10.11766/trxb201606110214

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      Abstract:【Objective】Researches on moisture content and contraction characteristics of weathering crust of granite are the basis for evaluation of stability of granite soil and studies on erosion mechanism of the soil. However,direct measurement of the two parameters is very tedious, time consuming, and errors prone. Therefore, a number of indirect measuring methods have been developed to predict soil water retention curves by means of determining particle-size distribution, but most of these methods often yield intermittent soil moisture characteristic data because they are only capable of predicting soil moisture characteristic at individuals points along the curves. It is, therefore, essential to explore for a new method to plot characteristic curves of soil water content and contraction of weathering crust of granite. For that end, it is a first priority to understand relationships between soil moisture retention curve, contraction characteristic curve and particle-size distribution curve, as well as relationships between all the three curves and physical properties of the soil. 【Method】To comprehensively understand the relationships, soil samples different in weathering degree were collected from Southeast Hubei for analysis. Based on the similarity of the soil water retention curves, contraction characteristic curves and particle-size distribution curves, the Van Genuchten (VG) model was used to fit the curves of the soil samples different in weathering degree and explore fitting parameters of the curves and linear and non-linear correlations of the fitting parameters with soil physical properties. 【Result】 Results show that, the VG model may well fit all the three curves of granite soils different in weathering degree. Certain linear relationships were found between the fitting parameters, particularly between parameter a1 of the particle-size distribution curves and parameter QS of soil water retention curves (r=-0.884, p<0.05) and but highly significant negative linear ones were between a1 and parameter vr of the contraction characteristic curves (r=-0.990, p<0.01); Meanwhile, certain linear relationships were also found between the curve fitting parameters and basic soil physical properties, especially those of the parameters of water retention curves with soil texture and bulk density. And the linear relationships of parameters vr and vsof the contraction characteristic curves with basic soil properties were closer than those of all the others; Besides non-linear relationships also exsited between fitting parameters of these curves and between the parameters and basic soil physical properties. Significant quadratic nonlinear relationships were found of parameter a2 of the water retention curves with the clay and parametera1 of the particle-size distribution curves, while significant cubic ones were between parameter a3 of the contraction characteristic curves and sand, and between parameter vs of the contraction characteristic curves and parameter n1 of the particle-size distribution curves. 【Conclusion】 In this paper, the VG model was used to fit paricle-size distribution, soil moisture content and contraction characteritics of granite soils different in weathering degree and analyze linear and non-linear relationships between soil water retention curves, contraction characteristic curves and particle-size distribution curves, between fitting parameters of the three types of curves and between the fitting parameters and basic physical properties of the soil. All the findings will certainly be useful to future study on relationships between the three types of curves and have demonstrated that it is feasible to predict soil moisture content and contraction characteristics of granite soils based on their particle-size distribution and physical properties.

    • Characteristics of the Diversity of Terrain, Soil and Surface Water Body of Henan Province in Pattern

      2017, 54(3):590-600. DOI: 10.11766/trxb201606210300

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      Abstract:【Objective】In studies on diversity of soil-water resources , terrain factors have great influences on their spatial distribution and internal relationships. Henan Province is selected as a case for study. Through processing the DEM data of the region, a terrain classification map and a surface water distribution map of the province were acquired. First of all, the modified Shannon entropy formula on a 1 km×1 km grid scale was used to work out terrain spatial distribution diversity and soil spatial distribution diversity (soil group level) and correlation analysis of the two was performed. Then Henan Province was divided into six regions similar in area by ecological environment, social development and land use, and terrain constituent diversity and soil constituent diversity of the regions were worked out with the spatial distribution area index (Yh), while surface water body diversity was with the spatial distribution length index (MSHDLI). In the end characteristics of and correlations between terrain composition, soil composition and surface water body diversity were analyzed.【Method】First, the 3D spatial analysis, raster surface analysis and contour analysis tools of ArcGIS were used to process the DEM data of Henan Province were processed to extract terrain classification maps by referring to the five basic terrain sorting standard, and the hydrological analysis module was used to plot a river network map or a surface water body distribution map of the province with threshold vactor being 50000.Then soil constituent diversity, terrain constituent diversity, and soil and terrain spatial distribution discreteness were analyzed with the modified Shannon diversity area index (MSHDAI) method, and surface water body diversity was with the modified Shannon diversity length index (MSHDLI) method. In the end, to determine correlation between terrain diversity and pedodiversity (soil group level), correlation coefficient between the two was worked out by calculating spatial distribution diversity of terrain types and common patches of soil types and fitting them into relevant equations. In six different partitions of similar sub-areas, Characteristics of and correlation between terrain constituent diversity and surface water body diversity, soil constituent diversity and surface water body diversity, terrain richness and soil constituent diversity were analyzed with the Pearson product moment correlation coefficient of the IBM SPSS software.【Result】Results show that in Henan Province, plain is the type of terrain the biggest in area and the highest in spatial diversity distribution discreteness (0.959), and fluvo-aquic soil is the type of soil, the highest in diversity (0.908) and the biggest in area, and followed by cinnamon soil in the next and alkali soil and solonchak in the last being the types of soil, the lowest in spatial distribution discreteness. Terrain and soil are closely related with high correlation, of which the coefficient r is higher than 50%, being over 76%. In all the six regions, terrain constituent diversity is found in linear relationship with the number of terrain types, with determination coefficient R2 being 0.616, and moreover, the MSHDKI index of surface water body diversity is in positive relationship with length of the surface water body, with determination coefficient R2being 0.788. The region in the east of the province is composed of solely plain and comes the second in MSHDLI value, which means the water system is well developed in the region, while the region in the west of the province is rather complicated in terrain and dominated with mountains and hence the lowest in MSHDLI value is the lowest, which demonstrates that the water system in the region is developed very simply because of mountains. In the case that the six regions are similar in area, the value of soil group composition diversity depends mainly on evenness of the distribution of different types of soil in area, and the two are negatively related, with determination coefficient R2 being 0.94, while terrain type richness is significantly and positively related to soil group constituent diversity, with the determination coefficient R2 being 0.909 and fitting function being linear one. But in different regions, areal terrain constituent diversity, soil constituent diversity index and linear surface water body diversity index do not have any significant correlationship between them.【Conclusion】To sum up, terrain, soil and surface water body are the three main elements closely related to each other, affecting each other and jointly determining spatial distribution of geodiversity of a region.

    • Composite-Model-Based Indirect Reversion of Soil Available Iron Spectrum of Forest Soil in Lushan

      2017, 54(3):601-612. DOI: 10.11766/trxb201606210174

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      Abstract:【Objective】As iron is one of the nutrient elements essential to plant growth, the content of soil available plays an important role in evolution of forest environment. The technology of hyper-spectral remote-sensing (RS) provides anew means for determination of soil physical and chemical components in laboratory.【Method】In this study, the relationship between soil organic matter and available iron was used to predict the content of available iron in soil indirectly. Besides the traditional single factor prediction model has its own limitation. In order to solve the problem of errors with the single-factor model, this study brought forth a composite model to improve accuracy of the prediction of soil organic matter contents in forest soils at a regional scale with the Vis-NIR spectrum technique. A total of 190 soil samples were collected from the 0~20 cm soil layers of the forests typical of Lushan region in Jiangxi Province. An ASD FieldSpec3 spectrograph diameter equipped with a high intensity contact probe was used to measure original spectral reflectance of the samples in line with standard procedure of the laboratory conditions, and mean while, the soil samples were analyzed for physical and chemical properties. Out of the 190 soil samples, 143 were picked out as samples for modeling and the remaining 47 verification ones. 【Result】The results showed that a significant positive correlation was found between the contents of soil organic matter and soil available iron, and then the binomial model can be built. Based on the results of spectral inversion of soil organic matter content, the contents of soil available iron were retrievable indirectly. Among the spectral inversion models, based on the full band (400~2450 nm) of soil spectra in this study, PLSR (partial least square regression) of the optimal linear fitting model and RBF(Radial Basis Function)neural network of the nonlinear fitting model were selected to form a combination to figure out arithmetic mean weight coefficients and to project an optimal combination model based on squared, reciprocal and entropy weight coefficients. Accuracies of the predictions of soil available iron content were evaluated by root mean squared error (RMSEp), ratio of partial deviation (RPD) and determination coefficients (R2). Results show that the combination model is superior to the two separate models in prediction accuracy. Among the combination models, the entropy weight coefficient combination model is the best, with determination coefficient (R2) in verification model, root mean squared error (RMSEp) and ratio of standard deviation of determination to standard deviation (RPD) of the soil organic matter prediction being 0.81, 11.54 g kg-1and 2.18, the soil available iron indirect prediction being 0.70, 21.60 mg kg-1and 1.77, respectively. The combination model is able to make use to a maximum margin of various information of the samples for prediction, reduce effectively the impacts of random factors in using single prediction models, enhance prediction stability and raise prediction capability of the models. 【Conclusion】All the findings of the study demonstrate that it is feasible to in directly predict soil available iron contents in forest soils by making use of hyper-spectral RS data. In the end, it can be concluded that the combination model can play a pretty good role in predicting soil organic matter content and indirect predicting soil available iron content.

    • Effect of cultivation and irrigation with sediment laden Yellow River water on SOM composition in profile depth

      2017, 54(3):613-623. DOI: 10.11766/trxb201607010301

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      Abstract:【Objective】 Soil organic carbon (SOC), which is the largest storage of organic carbon in the terrestrial ecosystem, is subject to influences of a number of factors, such as climate, geography, human activities, etc. Irrigation is an effective measure to ensure crop production as well as to increase SOC content, particularly, in arid and semiarid areas. Northwest China is an area that has a long history of irrigation with sediment laden river water, where a special layer of anthropogenic soil or irrigation-silt has formed. The layer is quite uniform in soil color, composition, texture, calcium carbonate content, and organic carbon content. When the layer of irrigation-silted is > 50 cm in thickness, it is termed as irrigation-silted soil. The soil is > 4 g kg-1 in SOC content, even at the bottom of the irrigation-silted layer. Composition of the soil organic matter (SOM) in fraction, heavy or light is the major factor affecting stability of the SOC storage in the layer.【Method】An irrigation zone in Ningxia Province, Northwest China, was selected in the study to evaluate effects of cultivation and irrigation with sediment laden Yellow River water on content and fractionation of SOC. The Yellow River flows through northern part of Ningxia from south to north. Irrigated-alluvial soil, Light sierozem soil, Aeolien sandy soil, Fluvi-aquic soil and Fluvent soil are the types of soils commonly distributed in the Zone. Based on that, a total of 45 soil profiles were specified, including 6 in non-cultivated and non-irrigated natural fields as control, and 39 in irrigated fields different in irrigation history. Each profile was divided into four layers (0~20, 20~30, 30~60 and 60~100 cm). Soil samples were collected from the layers for analysis of SOC content and for fractionations of SOC, light and heavy by density using 1.7 g m3 NaI solution, so as to illustrate effects of the irrigation with Yellow River water on content and fractionation of SOC. 【Result】Both light and heavy SOMs were found to have increased in content after years of irrigation, but the increment varied with the duration of irrigation and the fraction. The longer the history of irrigation, the higher the content of both light and heavy OMs in the soil regardless of type. As a result of farming cultivation, including fertilizer or manure application, the contents of OM increased the most significantly (p <0.001) in the plow or surface layer (0~20 cm), and the content and the increment declined along the profile and varied with the type of soil. Irrigated-alluvial soil with a long history of irrigation was found to be highest in OM content, which implies that soil type is another important factor influencing accumulation of SOM. Compared to non-irrigated and non-cultivated soils, irrigated soils exhibited a close relationship between the fraction of light OM and the total SOM in the 0~60 cm soil layer, and the relationship weakened with increasing soil depth, but a very close relationship was found between the fraction of heavy SOM and the total SOM in all the soil layers of both irrigated and non-irrigated fields, which indicates that heavy organic matter is the major component of SOM and accumulates more rapidly than light organic matter. 【Conclusion】 Irrigation with sediment laden Yellow River water helps increase SOC storage, either light or heavy in the Ningxia Irrigation Zone. Heavy OM is the major component of SOM, while light OM is more sensitive to cultivation and irrigation. And the former plays a better role than the latter does in sequestrating soil carbon.

    • Effects of Mapping Scale on Simulation of Soil Organic Carbon in Upland in the Scenario of Elevated CO2

      2017, 54(3):624-636. DOI: 10.11766/trxb201607270373

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      Abstract:【Objective】Agro-ecosystem models have been extensively used to predict changes in soil organic carbon (SOC) in farmland in the scenario of elevated CO2in future. However, currently most of the studies rely on maps of only one or certain one scale, and little has been done on influence of map scales on prediction of SOC dynamics in the scenario of elevated CO2. China has a total of 140 million hm2 of farmlands, consisting of 110 M hm2 of uplands and 30 M hm2 of paddy fields. As upland soil is enormous in area and high in carbon storage, it plays an important role in sequestrating carbon and mitigating climate change. Owing to the complexity of carbon turnover processes and dynamic response of carbon to environmental conditions, recent years have seen progresses in using process-based models to simulate historic patterns and future trends of SOC variation in agricultural systems. The DeNitrification–DeComposition (DNDC) model based on human activity data, land use, soil parameters, daily temperatures, and precipitation is used to describe biogeochemical processes of C and N recycling in the terrestrial ecosystem. Currently it has been extensively used to explain mechanisms of carbon turnover as affected by the complex interactions among soil management, crops, and climate. 【Method】 Based on the uplands in North Jiangsu, China, the 1980—2009 meteorological data and 2009 farmland management data of the region, soil databases of six different mapping scales, i.e., 1:50 000, 1:250 000, 1:500 000, 1:1 000 000, 1:4 000 000, and 1:10 000 000, and 3 different scenarios set for the period of 2010-2039 with atmospheric CO2 elevation rate being 1.5, 2.0 and 3.0 times, respectively, the normal rate (1.9 ppm a-1), this study used the DNDC model to predict carbon sequestration rate and potential as affected by CO2 elevation rate in the region with the data of the most detailed 1:50 000 map and quantify the uncertainties of using the soil databases different in mapping scale to simulate SOC dynamics in the upland-crop ecosystem.【Result】Results show that based on the 1:50 000 map and in the scenario of the atmospheric CO2 concentration rising at a rate 1.5, 2.0, and 3.0 times the normal rate, the average annual SOC sequestration rate in the topsoil (0~50 cm) layer of the upland of North Jiangsu during the period of 2011—2039 was predicted to be 357, 360, and 365 kg hm-2 a-1, respectively, and the total SOC sequestration was 42.08、42.38 and 42.93 Tg C, respectively. However, the prediction varied sharply with scale of the map used. When the average annual C sequestration rate predicted based on the 1:50 000 map was used as baseline, the use of the other maps would generated deviations ranging from 0.89% to 58.09%, 0.81% to 60.13% and 0.88% to 58.92%, in terms of average annual C sequestration rate and from 0.60 to 59.22%, 0.37 to 59.39% and 0.02 to 59.71% in terms of total C sequestration, respectively, in the three scenarios.【Conclusion】 It could be concluded that the effect of scale of the map used on prediction of SOC in the scenarios of elevated CO2 is significant. In general, heterogeneity of soil properties in a region would often lead to variation of the prediction of SOC, which is mainly attributed to the disappearance of some soil types and spatial distortion when the map of small scales is polygonized. It is, therefore, essential for studies in future to use soil maps of large scales for data in quantifying regional SOC dynamics.

    • Spatially Non-stationary Relationships between Cation Exchange Capacity and Related Control Factors

      2017, 54(3):637-645. DOI: 10.11766/trxb201606300245

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      Abstract:【Objective】Soil cationic exchange capacity (CEC) directly reflects capacity of the soil supplying and buffering cation nutrients, and hence plays a very important role in conserving soil fertility. The knowledge about spatial distribution of soil CEC and effects of its control factors (i.e., clay, soil organic matter (SOM), and soil pH) at a regional scale may help precisely regulate soil fertility in the region. This paper explored soil CEC and its related control factors (i.e., Clay, SOM and soil pH) in the topsoil (0~20 cm) and subsoil (20~40 cm) of Jinxian County, Jiangxi Province, China for analysis of spatial non-stationary relationships between them, with a view to providing some critical information for the region to formulate specific soil fertility building measures.【Method】In the past, the traditional least squares regression (OLS) method was used to explore effects of relevant factors on soil CEC. The method, however, is a population regression one, and assumes that the relationships between soil CEC and its control factors are constant, thus ignoring spatial non-stationary relationships between soil CEC and its control factors across the region. Geographically weighted regression (GWR) - a local spatial regression model, can be used to solve this problem. With this model, spatial locations of the data are embedded into the linear regression model in exploring spatial non-stationary relationships between variables. And the regression coefficients of the model have been estimated separately by spatial data location. Therefore, compared with the OLS model, GWR is obviously advantageous in exploring spatial non-stationary relationship between soil CEC and its related control factors.【Result】Results of the descriptive statistical analysis show that soil CEC varies moderately in Jinxian County. The topsoil is higher than the subsoil in soil nutrient retention capacity. Soil CEC is relatively high in the western part of the county, but lower in the northern and southeastern parts and always higher in the topsoil than in the subsoil. The GWR analysis shows that the relationships between soil CEC and its related control factors (i.e., soil pH, clay soil, and SOM) were not constant and varied spatially, demonstrating the existence of certain spatial non-stationarity. The effects of the control factors on soil CEC varied with the soil layer. For example, clay in the topsoil affected soil CEC more in the southwest than in the northeast; while that in the subsoil did more in the southeast than in the northwest. Furthermore, effects of the factors varied from sub-region to sub-region. For instance, in topsoil, the effect of SOM was low in the south, but quite high in the northwest. The soil CEC spatial distribution map and the regression coefficient map of soil CEC and its control factors demonstrates that in the northern region where soil CEC is quite low, soil CEC is more sensitive to changes in SOM than in any other regions. In this case, more organic manure should be applied to improve soil CEC and hence soil nutrient retention capacity. However, in the southeastern region where soil CEC is relatively low, clay is the major factor affecting soil CEC in both soil layers, and pH in the topsoil is another. In this case, either alteration of soil texture or application of alkaline fertilizer in this region would effectively increase soil CEC.【Conclusion】The findings show that the control factors vary sharply in effect on soil CEC with sub-region and soil depth. Meanwhile, the model of GWR effectively reveals that spatial non-stationary relationships exist between soil CEC and its related control factors. Based on the soil CEC spatial distribution map, it is recommended that more organic manure and/or alkaline fertilizer be applied to alter soil texture and improve soil fertility in the northern and southeastern regions.

    • Effects of Long Term Application of Organic Manure and Chemical Fertilizer on Structure of Humic Acid in Fluvo-aquic Soil

      2017, 54(3):646-655. DOI: 10.11766/trxb201611230392

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      Abstract:【Objective】Fertilization has become increasingly common to increase soil organic matter (SOM) content and improve soil fertility. Research suggests that fertilization promotes production of humic acids (HAs), one of the most important component of SOM.However little is known about the quantitative effects of fertilization on structural characteristics of HAs. Based on the long-term field fertilization experiment in Fegnqiu of Henan, effects of application of organic manure (OM), chemical fertilizer (NPK) and nothing (CK) on structure of HAs in fluvo-aquic soil were assessed. 【Method】Soil samples were collected from the surface soil layers of three treatment plots, i.e. OM, NPK and CK, of a long-term winter wheat (Triticumaestivum L.)-summer maize (Zea mays L.) rotation experiment in Fengqiu, China.HAs were exhaustively extracted from the soil samples with a combined 0.1 mol L-1NaOH and 0.1 mol L-1 Na4P2O7 solutionand obtained through precipitation after acidification with 6 mol L-1HCl. HF:HCl (1%:1%) solution was then used to purify the HAs obtained. In the end, the purified HAs were characterized with advanced solid-state 13C nuclear magnetic resonance (NMR) spectroscopy coupled with elemental analysis and isotopic analysis (δ13C). The NMR techniques included multiple cross-polarization/magic angle spinning (multiCP/MAS), dipolar-dephasing (DD), chemical-shift-anisotropy (CSA) filter and spectral editing of immobile CH2 and CH. 【Result】Results show that long-term fertilization changed the element compositions, δ13C ratios and carbon functional groups of HAs, particularly significant in Treatment OM, and increased saturation degree, oxidation degree and polarity of HAs, but decreased condensation degree of HAs. The decrease of HAs in δ13C valuesindicated incorporation of new organic carbon into HAs. Advanced NMR techniques revealed that HAsin fluvo-aquic soil were composed predominantly of aliphatic compounds with alkyl being the highest in percentage (24.1% ~ 26.3%).OCH3 and NCH signals both resonated around δ64 ~ 44, while the latter was prominent in proportion. Besides, the proportion of nonprotonated carbon was very low in anomeric and O-alkyl. Among the aromatics of HAs, they were dominated with protonated carbon inδ142 ~ 113, while only a little aromatic carbon existed in δ113 ~ 93, which cannot be detected with the routine cross-polarization/magic angle spinning (CP/MAS) NMR. It was also found that long-term fertilization reduced the percentages of COO/N-C=O and aromatic carbon of δ142 ~ 113, but increased the percentages of O-alkyl and OCH3. Moreover, application of organic manure also increased the proportions of aromatic C-O and NCH, but decreased that of alkyl.【Conclusion】In conclusion, all the findings in this study indicate that HA structure tends to be less hydrophobic with decreasing degree of decomposition. The application of either OM or NPK increases the content of carbohydrates in HAs. The application of OM also increases the contents of lignin and peptides, but decreases the content of lipids. The study also suggests that the advanced NMR techniques could provide great insight into HA structure and mechanisms of HA formation relative to fertilization pattern.

    • Effects of Planting and Incorporation of Chinese Milk Vetch Coupled with Application of Chemical Fertilizer on Active Organic Carbon and Nitrogen in Paddy Soil

      2017, 54(3):656-668. DOI: 10.11766/trxb201607050273

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      Abstract:【Objective】 Being the most active part of soil organic carbon and nitrogen, soil active organic carbon and nitrogen play important roles in soil carbon and nitrogen cycles and are very sensitive to fertilization. The practice of planting and incorporating Chinese milk vetch coupled with application of chemical fertilizer has been proved to be an effective way to improve rice yield and soil fertility. Here in this paper, effects of this practice on soil active carbon and nitrogen, rice yield, nitrogen use efficiency and soil fertility, as well as relationships of soil active carbon and nitrogen with rice yield and soil nutrients were studied, to explore significance of soil active organic carbon and nitrogen to soil fertility and productivity and provide a scientific basis for using this practice to increase crop yield and soil fertility.【Method】Based on an 8-year field experiment on planting and incorporation of Chinese milk vetch coupled with application of chemical fertilizer in Xin Yang, Henan province, topsoil samples (0~20 cm) were collected after rice was harvested for analysis of variation of soil active carbon and nitrogen, and soil nutrients and further of their relationships with rice yield and soil nutrients. The experiment was designed to have seven treatments, i.e. CK (no fertilizer), Treatment G (planting and incorporation of Chinese milk vetch), Treatment 100% F (conventional chemical fertilizer N, P, K at 225 kg hm-2, 135 kg hm-2 and 135 kg hm-2, respectively), Treatment G 100% F (Chinese milk vetch combined with 100% conventional chemical fertilizer), Treatment G 80% F, Treatment G 60% F and Treatment G 40% F. 【Result】The results showed that compared with CK, Treatment 100% F had little effect on soil water soluble organic carbon (WSOC), but it increased soil water soluble organic nitrogen (WSON), soil microbial biomass carbon (SMBC) and soil microbial biomass nitrogen (SMBN) by 20.61%, 10.49% and 2.70%, respectively. Treatment G increased WSOC, WSON, SMBC and SMBN by 25.52%, 36.30%, 19.16% and 9.36%, respectively. And the treatments of G F of whatever rate increased WSOC, WSON, SMBC and SMBN by an extent varying in the range of 12.99%~22.80%, 26.66%~56.61%, 19.01%~29.56% and 12.80%~26.25%, separately. Fertilization increased the proportion of soil active organic carbon and nitrogen, separately, in soil organic carbon and total nitrogen, however, the effects of Treatment G and Treatment G F are obviously higher than those of Treatment 100% F. Soil active carbon and nitrogen is positively related to rice yield, SOC, TN and Ammonium nitrogen at significant or extremely significant levels, but negatively to nitrate nitrogen and available potassium. Fertilization increased rice yield and the effect was the most significant in Treatment G 80%F (10 026 kg hm-2 in yield). Compared with Treatment 100% F, Treatment G 80% F, Treatment G 60% F and Treatment G 40% F saved the use of chemical fertilizer by 20%~40% without affecting crop yield, while increasing nitrogen agronomic efficiency and nitrogen partial factor productivity by 11.64%~149.65% and 2.66%~149.92%, separately and the contents of SOC, TN and ammonium nitrogen, too, but did decrease the contents of available phosphorus and available potassium.【Conclusion】Compared with application of chemical fertilizer, planting and incorporation of Chinese milk vetch coupled with application chemical fertilizer were more conducive to building up soil active carbon and nitrogen. By taking into full account crop yield, nitrogen fertilizer utilization efficiency, and soil fertility, the practice of incorporating 22 500 kg hm-2 of Chinese milk vetch, keeping the normal P and K applications and reducing N application rate by 20% was thought to be the optimal one.

    • Dynamics of Soil Phosphorus as Affected by Tillage on the Loess Plateau in Central Gansu, China

      2017, 54(3):669-680. DOI: 10.11766/trxb201607220250

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      Abstract:【Objective】The Loess Plateau in Central Gansu is one of the most seriously eroded regions in China. In this area the soil is generally in lack of phosphorus, and the conventional tillage pattern prevailing in the region exacerbates the loss of phosphorus and other soil nutrients. Therefore, it is urgent to address the problem by improving farmland management and hence to uplift utilization efficiency of soil phosphorus. This study attempts to characterize dynamic changes of soil total phosphorus and phosphorus fractions in the soil under six different tillage patterns, so as to reveal mechanisms of the six tillage patterns affecting soil phosphorus, and provide a theoretical basis for remolding the original tillage pattern or establishing a new sustainable tillage pattern.【Method】For this study, a 13-year-long field experiment on tillage has been carried out in an upland farm on the Loess Plateau in Central Gansu. The experiment is designed to have six different tillage patterns, that is, conventional tillage (T), no-tillage (NT), conventional tillage with straw incorporation (TS), no-tillage with straw mulching (NTS), conventional tillage with plastic mulching (TP), and no-tillage with plastic mulching (NTP). For in-lab analysis, Tiessen’s modified Hedley method was used for fractionation of soil phosphorus. Six extractants were used sequentially from weak to strong in capacity to extract nine fractions of phosphorus, that is, Resin-Pi, NaHCO3-Pi, NaHCO3-Po, NaOH-Pi, NaOH-Po, D.HCl-Pi, C.HCl-Pi, C.HCl-Po and Residual-P.【Result】Results show: (1)During the experiment, soil total phosphorus in all the treatments increased year by year, with a rate ranging from 8.1% to 15.6%, and in terms of soil phosphorus increase rate, the six treatments exhibited an order of NTS>TS>NTP≈NT≈T≈TP. Total inorganic phosphorus also showed an increasing trend in all the treatments. In Treatments NTS and TS, total organic phosphorus increased the fastest or by48.7% and 46.0%, respectively, and in Treatments NTP and NT it did by 18.9% and 16.3%, respectively, while in Treatments T and TP it remained almost unchanged; (2) During the experiment, all the fractions of inorganic phosphorus were on a rising trend, except for Resin-Pi and NaHCO3-Pi, which declined slightly in 2011. Among all the inorganic phosphorus fractions, NaOH-Pi rose the fastest with an average growth rate of all the six treatments reaching up to 253.6%; Resin-Pi and NaHCO3-Pi followed, with an average growth rate being 128.6% and 66.9%, respectively; And the relative content of the three fractions also some what increased; (3) NaHCO3-Po and NaOH-Po showed an overall increasing trend except for a slight fall in 2011 in the five treatments of conservation tillage, however, they did not change much in Treatment T, throughout the entire experiment. C.HCl-Po increased year by year in Treatments TS and NTS, and remained almost unchanged in Treatment T, and showed overall downward trends in Treatments NT, TP and NTP;(4)The five patterns of conservation tillage raised the content of Resin-Pi、NaHCO3-Pi and NaOH-Pi, and no tillage was more effective than conventional tillage, when the same in supplementary measure, with Treatment NTS in particular, which increased the content of D.HCl-Pi. The effect of tillage on C.HCl-Pi and Residual-P was not obvious. The five treatments of conservation tillage, especially Treatments NTS and TS, increased the content of NaHCO3-Po and NaOH-Po, and Treatments NTS and TS, also raised the content of C.HCl-Po, but Treatments NT, TP and NTP reduced the content of C.HCl-Po, in comparison with Treatment T.【Conclusion】Phosphorus fertilizer would accumulate in the soil year by year, existing in the soil in the form of NaOH-Pi, moderate in activity and in the form of Resin-Pi and NaHCO3-Pi, high in activity, and the accumulation does not have much impact on fractions of organic phosphorus. Sparse rainfall is no good to accumulation of phosphorus of active fractions, such as Resin-Pi, NaHCO3-Pi and NaHCO3-Po, but conducive to that of phosphorus of stable fractions, such as D.HCl-Pi and C.HCl-Pi. Conservation tillages may increase the content of phosphorus of the fractions, moderate and high in activity, especially Treatment NTS. Therefore, it can be concluded that the adoption of conservation tillage can reduce the consumption of phosphorus fertilizer to a certain extent. Conservation tillage, especially the practice of no-tillage with straw mulching, is worth promoting in this area.

    • Study on Spatial Variability and Driving Factors of Stoichiometry of Nitrogen and Phosphorus in Soils of Typical Natural Zones of China

      2017, 54(3):681-691. DOI: 10.11766/trxb201608170269

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      Abstract:【Objective】 Nitrogen (N) and phosphorus (P) are two important nutrients and play important role in sustaining plant growth in natural ecosystems, and changes in structure and function of an ecosystem may reflect in stoichiometric characteristics of the elements in the soil. Natural zone, life form and elevation are major factors affecting soil nutrients in all climatic zones. Therefore, the study on stoichiometric characteristics on large spatial scales may help explore distribution characteristics of soil nutrients and driving factors of the evolution of soil nutrients, and provide important reference to studies to understand in depth global biogeochemical recycling of the soil nutrients and simulate regional responses to global change.【Method】 From the literature available regarding soil stoichiometry in the subtropical evergreen broad-leaved forest zone (SEB), warm temperate deciduous broad-leaved forest zone (WTD), temperate steppe zone (TSZ), temperate desert zone (TDZ) and Qinghai-Tibet Plateau Alpine vegetation zones (QST), a total of 594 data of N and P contents in natural soils, 0-20 cm in depth of various regions of the country and their stoichiometric analyses, covering a time span of 15 years were acquired using the aid of electronic search engines. Statistic analysis of the collected data were performed using methods of one-way analysis of variance (ANOVA), least significant difference (LSD), Spearman correlation coefficient analysis, and multivariate linear and non-linear autoregressive modeling (MAR), to explore distribution and variability of soil total nitrogen (TN) and total phosphorus (TP) and their stoichiometry in soil in relation to elevation, temperature and precipitation in the SEB, WTD, TSZ, TDZ and QST. 【Result】 Results show that soil TN and N/P varied significantly from natural zone to natural zone, but soil TP did not as much. The average TN content was 2.35 mg g-1, 1.13 mg g-1, 1.07 mg g-1, 3.59 mg g-1, and 5.66 mg g-1; the average TP content 0.80 mg g-1, 0.82 mg g-1, 0.75 mg g-1, 0.47 mg g-1, and 0.75 mg g-1; and the average N/P 4.04, 2.26, 2.49, 6.71, and 7.73 in the SEB, WTD, TSZ, TDZ and QST, respectively. In all the five zones, TN, TP and N/P varied with elevation, displaying a non-linear secondary relationship, and a single peak pattern. However, in the SEB and TSZ soil TN was mainly affected by temperature and elevation, and the impact of elevation was more significant in the TSZ. In the TDZ soil TN was influenced by elevation and precipitation. However, in the WTD and QST, soil TN was not so much affected by the three factors. In the SEB, soil TP was jointly affected by the three natural factors, which, however, followed a declining order of precipitation > temperature > elevation in extent, and in the WTD and TDZ and QST soil TP was mainly affected by elevation, while in the TSZ, precipitation was the dominant factor that affects soil TP. Furthermore, in the SEB, soil N/P was more affected by by precipitation than by elevation, and in the TSZ, TDZ and QST it was affected jointly by all the three factors, temperature, precipitation and elevation, while in the TDZ, elevation was the key factor affecting soil N/P and in the TSZ, temperature and precipitation were, but differed in degree of the effect. 【Conclusion】In different natural zones, the relationships of TN, TP and N/P in the soil with elevation, temperature and precipitation differ from natural zone to natural zone or from plant life form to plant life forms, which the impacts of elevation, temperature and precipitation on soil N, P and N/P vary with the natural zone or plant life form. Therefore, natural zone and plant life form are the important factors affecting spatial variability of soil nutrients, and elevation, temperature and precipitation are the driving factors of the variation of soil N and P. In the future, global warming may have significant effects on soil nutrients and the effects vary with elevation gradients. In areas low in elevation, increment of soil N/P may turn P into a major factor limiting growth of the plants, while in areas high in elevation, N may be the factor.

    • Uptake and Accumulation of Selenium and Iron Coating on Rice Root at Different Growth Stages

      2017, 54(3):692-701. DOI: 10.11766/trxb201609090340

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      Abstract:【Objective】Rice is a staple food for the people in China, so it is feasible to improve effectively the status of the Chinese people being generally insufficient in intake of selenium by increasing the content of selenium in rice grains. Therefore, it is of great practical significance to the country to study characteristic of Se absorption and accumulation by rice, to define critical periods of the crop absorbing and accumulating selenium, hence to effectively regulate Se intake with daily diet. Rice is a species of hydrophyte, growing for a long time in fields flooded with water, where poor in areation, the crop has a well-developed aerenchyma formed at the root, to adapt itself to the anaerobic environment. The aerenchyma releases oxygen into the rhizosphere of the rice, which acts jointly with rhizosphere microorganisms to form a thin layer of "iron coating" on the surface of the root. The coating readily adsorbs selenium, thus lowering its bio-availability. As the researches in the past focused mainly on kinetics of Se absorption by rice at the seedling stage and impact of the iron coating on Se absorption and transfer, little has been reported on Se absorption and accumulation by rice at different growth stages, and impact of the iron coating on rice root on Se absorption and accumulation in the whole growth period. 【Method】A pot experiment was carried out to study Se absorption by rice at various growth stages and accumulation in various parts of the plant, and mechanism of the iron coating on rice root surface affecting Se absorption and accumulation. 【Result】Results show that the jointing stage was the period of time when the nutritive organs of rice grew and accumulated the rapidest in biomass to store adequate nutrients for the growth of reproductive tissues of the rice at the next growth stage, namely, booting stage. Se content in the nutritive tissues varied with growth stage, and peaked in the root at the jointing stage. Se in the root and stem was transported to the other parts of the rice at the booting and maturing stages. About 50% of the selenium in the various tissues was absorbed by the plant at the jointing and booting stages, and 47.22% of the total selenium in the spikelets was filled up at the booting stage. Obviously, jointing and booting stages are the two critical periods for the plant to absorb and accumulate selenium in. Se content in the iron coating peaked at the seedling stage, accounting for 73.63% of the total in the plant, which was 4.87 times that (15.12%) in the stem. As the plant grew, Se content in the iron coating declined significantly down to 20.02% in proportion at the maturing stage, while Se content in the stem reached 65.42%, which shows that in the entire life cycle of rice, the iron coating on the root surface is able to accumulate a certain amount of selenium through sorption and serve as a Se source for the plant at the late growth stages, when soil solution contains less selenium. The selenium adsorbed to the iron coating can be absorbed and transported by the plant to its shoots. So the iron coating on the root surface plays a role of "buffer" in the process of Se absorption and transport. 【Conclusion】By illustrating Se absorption and accumulation by rice varying with growth stage, this study has defined that the jointing and booting stages are the two critical periods for the crop to absorb and accumulate Se in and the iron coating on the root surface plays a role of "buffer" in Se absorption and accumulation of rice. All the findings in this study may have certain theoretical and practical significance in producing selenium-rich rice grains.

    • Screening of Plant Growth-Promoting Rhizobacteria from Watermelon and Development of Bio-nursery Substrates

      2017, 54(3):702-712. DOI: 10.11766/trxb201608300287

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      Abstract:【Objective】In order to improve the technical level of industrialized seedling culture and find new methods to make use of plant growth-promoting rhizobacteria (PGPR), a new strain of functional bacteria that would promote growth of watermelon was isolated, cultured and inoculated into ordinary nursery substrate, thus forming a kind of bio-nursery substrate. 【Method】 A number of strains of bacteria were isolated randomly from the rhizosphere soil of watermelon plants and screened by plant growth-promoting properties. One strain which was found to possess complex functions and efficient rhizospheric colonization ability was further cultured and then inoculated into in ordinary nursery substrate in developing bio-nursery substrates. Repeated seedling nursing tests and pot experiments were performed in greenhouse and subsequently in the field to further validate effect of the novel bio-nursery substrate prepared by inoculating this bacterial strain into ordinary nursery substrate. In the end this strain was proved to be the right one for preparation of bio-nursery substance. 【Result】 Through screening, a strain of bacteria, N23, capable of both producing indole acetic acid and NH3 simultaneously and acting in antagonism against Fusarium oxysporum f. sp. niveum and Ralstonia solanacearum, was isolated from the rhizospheric soil of watermelon plants. Seedling raising experiments show that in the substrate inoculated with Strain N23, watermelon seedlings grew much better than those in the ordinary nursery substrate, in plant height, stem diameter and leaf area. Such an effect was further demonstrated in another three seedlings raising experiments, showing that the strain steadily promotes seedling growth in a number of growth indices. The pot experiments show that the plants growing in the bio-nursery substrate were significantly higher than those in the ordinary nursery substrate, in all measured parameters except SPAD (Soil and Plant Analyzer Development), which differed very slightly. In the field experiments, watermelon, cucumber, tomato, and pepper seedlings cultured in the bio-nursery substrate grew better than those cultured in ordinary nursery substrate, in plant height and stem diameter, which coincided with the results in the pot and seedling experiments. And in the two seasons of field experiments, the watermelon in the former was 12.5% and 25.4% higher than that in the latter, respectively. In the field experiments cucumber, tomato, and pepper in the former was 18%, 60% and 25%, than their respective one in the latter. Morphological and biochemical analysis and 16S rDNA gene sequencing of Stain N23 shows that the strain is one of Bacillus sp. 【Conclusion】 All the findings in this study demonstrate that the bio-nursery substrate prepared by inoculating Bacillus sp. N23 into ordinary nursery substances promotes seedlings and plant growth as well as yield of the crop. Consequently, this study has provided some novel ideas for making use of rhizobacteria and some theoretical and technical support to the development of PGPR agents for preparation of bio-nursery substances.

    • Effects of Organic Materials on Soil Protozoa and Nematodes in Microzones

      2017, 54(3):713-721. DOI: 10.11766/trxb201610170411

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      Abstract:【Objective】Application of organic manure or material may affect soil fertility and soil microbial community structure. However, uneven distribution of the organic materials applied in the soil may aggravate spatial heterogeneity of the soil, and hence affect structure and functions of the soil biota therein. To determine how much organic materials will affect spatial heterogeneity of the soil, an in-lab soil incubation experiment was conducted for observation of how soil protozoa and nematode community structure responded to organic materials (rice straw and white clover) in different microzones (0~1 cm, 1~5 cm). 【Method】Rice straw or white clover was proportionally mixed up with soil and put into net bags separately. Then the bags were put into the vessels of the tested soil, separately, for incubation under a constant temperature (25±1℃) for 70 days. Soil samples were collected from microzones adjacent to (0~1 cm) and far apart (1~5 cm) from the net bags, on D14, D35 and D70 for analysis of abundance, Shannon-Wiener index (H' ), structure index (SI) and maturity index (∑MI2-5) of nematodes, and soil dissolved organic carbon (DOC), dissolved organic nitrogen (DON), nitrate nitrogen (NO3-N), microbial biomass carbon (MBC) and nitrogen (MBN), as well, which may be related to changes in the microfauna in the soils amended with rice straw or clove. 【Result】In this experiment, it was found that on the whole kind of the organic material and duration of incubation were the two major factors affecting the numbers of protozoa and nematodes, however, it does not mean that location of the microzone for sampling had no impact on soil microbes therein. Within the initial period of incubation (0~14 days), in microzones of the soil amended with the same organic material, the numbers of soil microbes in the adjacent microzones (0~1 cm) were higher than those in the far-apart microzones (1~5 cm), which is more obvious in the soil added with white clover. With the incubation going on (14~70 days), relative abundances of plant-feeding and fungi-feeding nematodes were higher in the soil added with rice straw than those in the soil added with white clover, whereas relative abundances of soil amoeba, flagellates, total nematodes and bacteria-feeding nematodes went reversely. Different kind of organic material also triggered different changes in Shannon-Wiener indices, structure indices and maturity index of nematodes. Shannon-Wiener index and structure index in adjacent microzones were found higher than those in far-apart microzones in the soil added with white clover, however the disparity was not found in the soil added with rice straw. The number of flagellates decreased, while the numbers of amoeba and nematodes increased with the incubation going on. 【Conclusion】Therefore, it is quite obvious that during the initial period of incubation, distance of microzones from the net bag of soil does have some influences on both the numbers of protozoa and nematodes, especially nematodes, and dthe influence fades with the incubation going on, while, the difference in type of organic material is the factor eventually affecting abundance and community structures of the nematodes.

    • Effects of Long-term Plantation of Phyllostachys edulis on Evolution of Arbuscular Mycorrihizal Fungus Community in Soil

      2017, 54(3):722-734. DOI: 10.11766/trxb201611110479

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      Abstract:【Objective】Arbuscularmycorrhizal (AM) fungi are ubiquitous in the terrestrial ecosystem and capable of forming mutualistic relationships with most high plants, increase soil carbon sequestration via both direct and indirect pathways, and then play a key role in building up carbon storage in the forest ecosystem. However, little has been reported in the literature about variation of the AM fungus community in the soilunder long-term plantation of moso bamboo (Phyllostachysedulis). Hence, the primary concern of this study is to explore variation of soil AM fungus in biomass and community structure, and its key affecting factors in the soil under long-term planted moso bamboo forest.【Method】As the moso bamboo forests in this area were mostly converted from masson pine forests one by one in the past years, plots of moso bamboo stands different in plantation age (i.e. 5 a, 9 a, 15 a and 18 a,)for comparison with the plots of natural masson pine forest. Each plot (10 × 10 m) had three replicates and all the plots were laid out at least 10 m apart.Five sampling points were set randomly in each plot, and samples of topsoil (0~20 cm)were collected from the five sampling sites in each plot and thoroughly mixed up to make a single composite sample for each plot.The soil samples were analyzed forbiomass and community structure of AM fungi using the phospholipid fatty acid (PLFA) method and the high-throughput sequencing based on the IlluminaMiseqplatform method, respectively.Glomalin-related soil protein (GRSP) was extracted with citrate solution and measured by spectrophotometer using boving serum albumin as standard. Soil water-stable aggregates were analyzed using the wet-sieving method.【Result】Results show that soil nutrients decreased in content with the moso bamboo plantation increasing in age. Moreover, the 18 year old plots were significantly lower than the 5 plots in both GRSP content and AM fungal biomass. Pearson correlation indicated that the content of easily extracted GRSP in the soil was positively related to organic C, available K, and available N (p<0.05), and AM fungal hyphal biomass (16:1ω5 PLFA) positivelyand significantly to available N (p<0.01). Fractionation of soil aggregates reveals that water-stable macroaggregates (2~0.25 mm in diameter) comprised the largest fraction of soil aggregates, varying in the range from 57.79% to 72.40% and long-term bamboo plantation reduced the fraction significantly. The percentage of macroaggregates was found positively and significantly related to the biomass of AM fungal hypha (p<0.01). Results of high-throughput sequencing indicate that Glomus dominated in the AM fungal community, followed by Acaulospora. In soils under long-term moso bamboo plantation soil Glomus increased in relative abundance while Acaulospora decreased significantly (p<0.05). Non-metric multidimensional scaling (NMDS) analysis demonstrates that the AM fungal communities in the soils under moso bamboo plantation varied sharply from those under masson pine plantation (p=0.001) and also significantly with age as was observed on the first axis of NMDS. When environmental variables were fitted onto NMDS ordination, AM fungal communities were found significantly related to soil moisture (p=0.005) and available N(p=0.001), but marginally to available P(p=0.014). 【Conclusion】Long-term plantation of moso bamboodecreasesAMfungalbiomass,alters AM fungal community structure significantly and exhausts soil nutrientssteadily. The changes in soil moisture,available P and available N contribute significantly to the variation of soil AM fungal communities. Long-term plantation of moso bamboo also decreasesthe content of GRSP,and theproportion of soil water-stable macroaggregates (2~0.25 mm) significantly, which poses a negative impact on soil carbon sequestration and hence stability of the ecosystem.

    • Soil Bacteria Diversity in Rhizosphere under Two Types of Vegetation Restoration Based on High Throughput Sequencing

      2017, 54(3):735-748. DOI: 10.11766/trxb201603150062

      Abstract (2973) HTML (0) PDF 1.78 M (4353) Comment (0) Favorites

      Abstract:【Objective】Artemisia ordosica and Caragana intermedia are the two widely-distributed and efficient sand-fixing shrubs in the Hobq Desert that have received considerable attention because of the roles they may play in the vegetation restoration. Soil bacteria diversity is an important indicator of the state of soil microbial communities and one indicating progress of ecological restoration.This project is oriented to study changes in community structure and diversity of soil bacteria in the process of vegetation and ecological restoration in the Hobq Desert relative to type of vegetation. 【Method】In this study, two types of vegetations, naturally restored Artemisia ordosica and artificially planted Caragana intermedia, were chosen for comparison to see effects of the vegetations on community structure and diversity of soil bacteria with a tract of moving sand land as control. The sample plots were set up in 1995 and soil samples were collected from the rhizospheres of A. ordosica and C. intermedia and bulk soil in the 0~20 cm soil layer and CK in August 2014 for analysis of soil bacteria diversity using the high throughput sequencing method. And relationship between soil bacterial diversity and soil physic-chemical properties, and the effect of soil physical and chemical properties on distribution of bacterial community were also studied through canonical correlation analysis and Cononical correspondence analysis.【Result】(1) Chao1 index, shannon index and ACE index are important indicators of soil bacterial diversity and richness. In terms of Chao1 index and shannon index, the sample plots displayed an order of rhizosphere soil of A. ordosica > rhizosphere soil of C. intermedia > non-rhizosphere soil of A. ordosica > non-rhizosphere soil of C. intermedia > soil of CK, while in terms of ACE index, they followed another order: rhizosphere soil of A. ordosica > rhizosphere soil of C. intermedia > non-rhizosphere soil of C. intermedia > non-rhizosphere soil of A. ordosica > soil of CK.(2) Classification at the phylum level shows the bacterial communities in the samples were mainly composed of Proteobacteria, Acidobacteria, Actinobacteria, Bacteroidetes, Gemmatimonadetes, Planctomycetes, Verrucomicrobia, Firmicutes and Chloroflexi, accounting for 88.67%~94.19%. Proteobacteria, Acidobacteria and Actinobacteria were the dominant bacterial groups in the samples, and Proteobacteria was the highest in abundance. The four subbgroups under Proteobacteria followed a similar trend in variation. Relative abundance of α-proteobacteria in the rhizosphere and bulk soils under either vegetation exhibited a sharply rising trend, increasing in the rhizosphere of A. ordosica and C. intermedia increased by 106.46% and 70.60% respectively. (3) Soil organic matter, total N, total K, readily available N, readily available K, and soil water are the main soil factors affecting abundance and diversity of soil bacteria communities. Correlation analysis of soil physic-chemical properties with relative abundance of dominant soil bacteria groups shows that the abundance of Proteobacteria was significantly related to soil organic matter, total N, readily available N, readily available P, and readily available K, while the abundance of Acidobacteria was to soil organic matter, total N, readily available N, readily available P and readily available K. Intrestingly, the abundance of Actinobacteria was not so much related to soil factors. Cononical correspondence analysis indicates that soil organic matter, total N, total K, readily available K and readily available N play an important role in triggering variation of genetic diversity of the bacterial communities in the soils. 【Conclusion】Results show that compared to moving sand land, the two tracts of lands with vegetation restored have demonstrated positive effects on community structure and diversity of soil bacteria, whose abundance, diversity and evenness have been significantlt improved. Between the two types of vegetation restoration, the naturally restored A. ordosica vegetation was higher than the artificially plated C. intermedia vegetation in effect increasing abundance of soil bacterial community. Bacterial community in the untreated soil is quite simple in structure. The restoration of vegetation enriches soil microbial groups, making the community of soil bacteria diversified in the rhizosphere and non-rhizosphere soils. Relative abundance of a-proteobacteria under the vegetation of A. ordosica and C. intermedia significantly increased, especially under the vegetation of A. ordosica.

    • Effects of Leachates from Understory Medicinal Plants on Decomposition ofPopulusPurdomii Litters and SoilEnzyme Activity

      2017, 54(3):749-758. DOI: 10.11766/trxb201610270522

      Abstract (2040) HTML (0) PDF 1.35 M (2720) Comment (0) Favorites

      Abstract:【Objective】Planting medicinal plants is an effective way to improve economic benefit of forest lands. However, it is important to take into account whether leachates from medicinal plants would have allelopathic effects on decomposition of forests litter and soil, and it is also the key to selection of medicinal plant species to build a scientific and reasonable compound system of forest-medicinal plants.【Method】In this paper, a Populuspurdomii forest typical of the Qinling Mountains and nine species of medicinal plants ( Taraxacummongolicum, Corydalis bungeana, Menthahaplocalyx, Houttuyniacordata, Asarumsieboldii, Lonicera japonica, Nepetacataria, Gynostemmapentaphyllum and Prunella vulgaris ) common in the area were cited as objects in the study, a simulation experiment was carried out on litter decomposition by spraying leachate in water-extraction solution from stems and leaves of the medicinal plants, to study effects of the leachates on litter decomposition, nutrient release and soil enzyme activity. The sampling area in this experiment is the Houzhenzi Forest Farm of Zhouzhi County in the QinlingMountains of Shaanxi. The decomposing bag method was used in the indoors litter decomposition experiment with constant temperature and humidity and the experiment lasted for six months. During the experiment, leachate from the litter of medicinal plants was sprayed once every two weeks, and the decomposing bags were retrieved five times (in the first, second, third, fifth and sixth month after the start of the decomposition experiment), soil samples collected three times (in the first, third and sixth month after the start of the decomposition experiment), to determine decomposition rate, nutrient release and soil enzyme activity. At the same time, GC-MS was used to analyze chemical substances in the medicinal plants leachate.【Result】Turnover period and half-life of the decomposition of P. purdomii litter was extended by 230% and 29%, respectively, in the treatment using T. mongolicum leachate, by 67% and 23% in the treatment usingM. haplocalyx leachate, and by 120% and 34% in the treatment using H. cordata leachate. And leachate from all these three species of medicinal plants displayed significant inhibitory effects on nutrient release and soil enzyme activities during decomposition of P. purdomii litter. In order to facilitate the analysis, the experiment was divided into three phases; i.e. early (first month), middle (second to third months) and later (fourth to sixth months) phases. The inhibitory effects were significant on the release of nitrogen, copper, zinc and manganese in the early and late phases in all the three treatments, on the release of potassium in the middle and late phases, on the release of carbon in the early, middle or late phases, and on the release of phosphorus in the early or late phases. And the inhibitory effects were also observed on the activities of invertase, dehydrogenase and protease in the early or middle phase, on the activities of carboxymethylcellulase, polyphenol oxidase and phosphatase in the middle or late phase, and on the activity of β-glucosidase the early, middle or late phases.【Conclusion】The allelopathic substances released by the understory medicinal plants through rain or other ways, may affect decomposition of forest litter, nutrient release, soil enzyme activity, which hinders the maintenance of soil fertility and material recycling in the ecosystem and affects stability of the ecosystem. Therefore, it is suggested that T. mongolicum, M. haplocalyx and H. cordata should not be planted as understory in P. purdomii forests, or interplanting density of these plants should be kept lower to reduce the allelopathic effects.

    • >Research Notes
    • Distribution of Soil Organic Matter Content and its Affecting Factors in Oases Typical of Arid Region

      2017, 54(3):759-766. DOI: 10.11766/trxb201611100468

      Abstract (2736) HTML (0) PDF 1.64 M (4418) Comment (0) Favorites

      Abstract:A field survey was carried out of the Weigan-Kuqa River Delta Oasis in South Xinjiang, collecting a total of 156 samples of topsoil (0~20cm) and subsoil (20~40cm) at 78 sampling sites laid out in the light of land use for analysis of soil organic matter (SOM) content and pH and their distributions, and variations of SOM in the topsoil and subsoil layers as affected by crop type, land use and soil pH. Results show that SOM varied in the range of 3.7~24.1gkg-1 in content, and averaged 11.0 4.2gkg-1 in the topsoil layer (0~20cm), and in the range of 2.7~12.9gkg-1, and 7.0 2.2gkg-1; in the sub-subsoil layer (20~40cm). The topsoil layer was much higher than the subsoil layer no matter in mean of SOM contents or standard deviation in soils under different types of crop and patterns of land use, with a variation coefficient being 20%~50%. Obviously the variation was at a moderate level. Variance analysis and stepwise regression analysis shows that the factors affecting SOM content also varied in effect. The integrated effect of the three factors, crop, land use and pH, could explain 45.1% of the variation of SOM content in the topsoil layer and 43.7% of that in the subsoil layer. Comprehensive analysis shows that crop type is the most important factor affecting SOM content in the study area.

    • Study on the Controlled Release Performance of Modified Polyacrylate Coated Controlled Release Fertilizers

      2017, 54(3):767-774. DOI: 10.11766/trxb201607120247

      Abstract (2246) HTML (0) PDF 1.27 M (3046) Comment (0) Favorites

      Abstract:To solve the problems existing in the pilot scale production of water-soluble polymer coated fertilizer using the fluidized bed coating machine, this study was performed on effects of cross-linker dosage on surface structure and hydrophobicity of the coating and effects of different post-processing techniques on performance of controlled release. Results showed that when the cross-linker (aziridine) added into the water-soluble-polyacrylate-latex-dominated coating material, increased from a rate of 1% to the rate of 2%, surface structure of the fertilizer coating became smoother and denser, as well as higher hydrophobicity. Consequently, the coating performed much better in controlling nutrient release. When the two coated fertilizers different in cross-linker rate (1% and 2%) added into the coating material were soaked in still water at 40℃ in temperature for 9 days, it was found that the former released more than 90% of the total nutrients, whereas the latter just released about 40%. However, the performance varied with different post-coating treatment, and it was much better when the coating was oven-dried than when it was microwave-dried. When the coating was low in cross-linker dosage (0.3%), higher processing temperature (60℃-80℃) significantly improved its performance, but when the coating was high in cross-linker dosage (> 1%), raising temperature almost did not have much effect.

    • Effectiveness Evaluation of the Use of Phase Incubation Method to Determine N Mineralization in Paddy Soil

      2017, 54(3):775-784. DOI: 10.11766/trxb201608170302

      Abstract (2618) HTML (0) PDF 1.51 M (2690) Comment (0) Favorites

      Abstract:As not much correlation was observed between rice N uptake in Treatment N0 (No N fertilizer applied) and N mineralization rate measured with the traditional In situ incubation method, modification was made of this method in an attempt to improve its accuracy in measuring soil N supplying capacity. The traditional one is a continuous incubation method, which goes like this: collect some soil from a paddy field before seedling transplanting, mix it with water at 1:1 in volume, pack the mixture in ziplock bags, put the bags back into the field for In situ incubation, and then sample the soil in the bag once every 30 days for measurement of inorganic N. The modified one adopts phase incubation and goes almost the same as the traditional one in preparation for incubation, and then put the bags in centrifuge tubes full of water and the tubes back into the field for incubationIn situ and sample the soil in the bag for analysis of inorganic N once every 30 days, while removing the ziglock bags of the last phase of incubation. Results of the 2013-2015 experiment show that with the incubation going on, mineralized N content rose first and fell as was measured with the traditional method. Compared with the maximum value, cumulative mineralized N dropped by 6.7%~28.6%. However, the modified one did not see any decline. So the measurement using the traditional method was 30.0%~67.7%(p <0.05)lower than that using the modified one. Duration of the incubation is a major factor affecting the content of mineralized N. When incubation went on continuously over 40 days, it might pose a risk of inhibiting N mineralization. So, each incubation should not last too long or over 40 days. The content of mineralized N measured with the modified method was found to be closely and positively related to rice N uptake measured in Treatment N0, with R2 being 0.621 (p <0.01). Therefore, it is suggested that when measuring soil mineralized N in paddy field, measurements using the modified one be cited as an indicator to evaluate soil N supplying capacity.

    • Effect of Spraying Intensity on Migration of Sr-90 in Soil

      2017, 54(3):785-793. DOI: 10.11766/trxb201608160166

      Abstract (2166) HTML (0) PDF 1.19 M (2339) Comment (0) Favorites

      Abstract:Based on the dynamic soil column method in laboratory, experiment was conducted on studying the migration of radionuclide Sr-90 in Sand relative to different spraying intensity(spraying intensity was designed to 120 ml d-1, 60 ml d-1, 30 ml d-1,and the corresponding experimental time were 51, 102 204 day respectively).Results showed that migration distance of Sr-90 concentration peak in the soil columns more or less the same, were 42.3 cm、46.2 cm、44.4 cm, Which was positively related to intensity and duration of the spraying. In addition, the concentration distribution curves of Sr-90 in soil column section all exhibited asymmetry and “tailing” phenomena under the three different spray intensity, i.e. After Sr-90 was leached down from the source layer, it was adsorbed to the Sand, thus lagging behind and getting desorbed after the peak concentration passing the observation point, hence Sr-90 concentration remained to be quite high in soil columns for a long time. With the aid of HYDRUS-1D software, two numerical models were established for radionuclide migration, one based on equilibrium adsorption and the other on non-equilibrium adsorption. It was found that the non-equilibrium sorption model, which took into account the first-order rate coefficients β, could be used to better explain the asymmetry and tailing phenomena. Based on fitting the measurements of Sr-90 concentrations in the soil columns, distribution coefficient of Sr-90 in the Sand was figured out to be 0.73 ml g-1, 0.70 ml g-1 and 0.72 ml g-1 relative to intensity of the spraying, which shows that intensity of the spraying did not have much effect on distribution coefficient of Sr-90.

    • Genetic Diversity of Hydrocarbons Degrading Microbial Functional Gene (bssA) in the Farmland Soil Typical of Jianghan Oilfield

      2017, 54(3):794-804. DOI: 10.11766/trxb201611040324

      Abstract (2281) HTML (0) PDF 1.50 M (3090) Comment (0) Favorites

      Abstract:Farmland soils in oil fields are liable to get polluted with petroleum hydrocarbons (PHs), which consequently leads to enrichment of some special PHs degrading microbial groups in the soils. In this study, soil samples were collected from typical farmland fields near five different oil wells in the Jianghan Oilfield located in Qianjiang City, Hubei Province for analysis of PHs degrading microbial groups, using bssA (benzylsuccinate synthase gene), a functional gene key to anaerobic benzenes degradation as biomarker, and community structure of the PHs degrading microbial groups was determined with T-RFLP (Terminal-restriction fragment length polymorphism) and clone library. On such a basis, environmental factors affecting community composition of the soil bssA were discussed. Results show that the content of polycyclic aromatic hydrocarbons (PAHs) in the soil varied in the range of 0.21~2.01 mg kg-1, which indicates that the soil in this region was not seriously contaminated with PHs. Meanwhile, the T-RFLP analysis indicates that bssA diversity varied significantly from soil sample to soil sample in this oilfield, being the highest in the soil sample the highest in PAHs content, and its dominant group was in a fairly close kinship with sulfate-reducing bacterium or Geobacter. Furthermore, RDA (Redundancy analysis) reveals that the contents of soil available nitrogen, phosphorus and PAHs were all main factors affecting soil bssA diversity. To sum up, all the findings indicate that the bssA-bearing microbial groups in the soil of this oilfield are Beta -proteobacteria andDeta -proteobacteria, and in close kinships with Thauera, Azoarcus and Geobacter in phylogenesis. All these microbes might degrade PAHs through reducing metabolic processes of nitrate, sulfate, and iron.

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