• Volume 56,Issue 6,2019 Table of Contents
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    • >Reviews and Comments
    • Sediment Source Fingerprinting: Progress in Uncertainty Analysis

      2019, 56(6):1279-1289. DOI: 10.11766/trxb201812100570

      Abstract (1687) HTML (939) PDF 433.84 K (2226) Comment (0) Favorites

      Abstract:Sediment fingerprinting is a technique critical to researches on sources and dynamics of sediment in recent years. However, the technique does have certain limitations, for instance, its multiple assumptions often differ from practical conditions, thus bringing about a series of uncertainties. The process of sediment transportation from source to sink is subject to the interference of natural environment and anthropic activities, so potential variations of source characteristics, migration path, and properties of sediment are all factors of uncertainty in fingerprinting procedure. Moreover, sampling designing, fingerprint selection method, and use of mixing models are subjective factors that further expand sources of uncertainty. Uncertainty analysis is a significant component of the sediment fingerprinting technique, and it is also an important basis for assessing reliability of fingerprinting to identify sources of sediment. This paper reviewed the series of issues of uncertainty in sediment fingerprinting, and progresses in researches addressing these problems and described status quo of the research on quantitative assessment of the uncertainties in an attempt to provide certain recommendations for further investigation.

    • Progress in Researches on Interactions between Organic Phosphates and Soil Minerals and Their Environmental Impacts

      2019, 56(6):1290-1299. DOI: 10.11766/trxb201811100553

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      Abstract:Soil organic phosphate (OP) is an important fraction of phosphorus in the soil environment. Its reactions in interfaces of the environment affects transport, transformation, bioavailability and environmental behaviors of phosphorus. This paper is a review that summarizes (1) reaction characteristics of adsorption-desorption and dissolution-precipitation of typical OPs on the surface of soil minerals and their microscopic mechanisms, and (2) environmental impacts, i.e., effects of the interaction between OPs and soil minerals on the speciation of OPs, interfacial reactions of metal ions, and colloidal chemical stability and dissolution-transfomation of the minerals. Soil OPs generally contain multiple phosphate groups and have large relative molecular mass and high charge density. OPs could interact strongly with environmental minerals through interfacial reactions, which affects the charge properties of minerals, adsorption characteristics of co-existing metal ions, and colloidal chemical stability of minerals. Interfacial reactons of OPs and their mechanisms are affected by a number of factors, such as type and crystallinity of the mineral, relative molecular mass of OP, pH, temperature, and coexisting ions. Sorption density of OP on the surface of minerals generally decreases with increasing pH of the system, crystallinity of minerals, and relative molecular mass of OP. OPs may generally form inner-sphere complexes (hydrogen bonding interactions also plays a role in some cases) on the surfaces of minerals, and surface complexes can even transform to surface precipitates. The adsorption of OP and metal ions on mineral surface generally has certain synergistic effects, especially under low pH conditions, i.e., metal ions promote the adsorption of OP and vice versa; adsorption mechanisms vary with reaction system, including mainly formation of ternary surface complexes and surface precipitates, and in most cases simultaneously involve multiple ones. In the end of the paper, discussion is conducted on main research hotspots and directions for future researches related to interaction between OP and minerals in the environment.

    • >Research Articles
    • Responses of Organic Carbon and Total Nitrogen in Hydragric Anthrosols to Variation of Water Regime and Cultivation in Age

      2019, 56(6):1300-1308. DOI: 10.11766/trxb201812190421

      Abstract (1581) HTML (927) PDF 750.71 K (1591) Comment (0) Favorites

      Abstract:【Objective】Though carbon sequenstration of agricultural soils is one of the focuses of current concern, little has been reported on how soil carbon and nitrogen varies dynamically in Hydragric Anthrosols different in water regime and cultivation age. 【Method】Taking advantage of the long-term paddy cultivation history in China, four types of Hydragric Anthrosols along the chronosequence from a dozen years to a thousand years, were specified in Jinxian of Jiangxi (Jinxian sequence), Cixi of Zhejiang (Cixi sequence), Zhongshan of Guangdong (Zhongshan sequence) and Baoying of Jiangsu (Baoying sequence) for exploration of how organic carbon (SOC) and total N (TN) in the soils responds to changes in water regime and cultivation history. 【Result】Soil organic carbon accumulation was mainly affected by water regime and content of soil organic carbon. For the Jinxian sequence (surface water type), soil organic carbon accumulated mainly in the anthrostagnic epipedon within the first 100 years of rice cultivation and then in subsoil with cultivation going on. For the Cixi sequence (well-drained water type), soil organic carbon accumulated only in the anthrostagnic epipedon and reached to the point of saturation within the first 50 years of rice cultivation. For the Zhongshan sequence (ground water & well-drained type), soil organic carbon reached to the point of saturation within the first 30 years of rice cultivation and then slightly decreased in content with cultivation going on as the groundwater table lowered. In contrast, for the Baoying sequence (also ground water & well-drained type), soil organic carbon was relatively stable in content within the first 5 years of rice cultivation and then significantly decreased with the groundwater table within the following 15 years. All the four types of Hydragric Anthrosols tended to be similar in carbon/nitrogen ratio in the cultivated horizon with paddy cultivation going on for long and had similar carbon-nitrogen coupling balance in highly mellowed plow layers of the Hydragric Anthrosols. The paddy soils of the Jinxian sequence could be deemed as a stable organic carbon sink within 300 years though their carbon sequestration rates tended to be low. For instance, SOCD of the soils increased on average by 3 g•m-2•a-1 only. Following the current normal management and utilization levels, the paddy soils of the Cixi, Zhongshan and Baoying sequences would have their soil carbon pools saturated up to a level compatible tto their water regimes within 15~50 years, thus keeping SOC in a relatively stable balance. In soils relatively high in ground water table, high yield oriented practices, such as drainage, could lower the ground water table, which could lead to rapid depletion of soil organic carbon. 【Conclusion】Evolution of the soil organic carbon pool in and carbon sequestration capacity of Hydragric Anthrosols are highly subject to the impacts of water regime and initial organic carbon content in the soil. It is, therefore, essential to pay enough attention to adoption of certain high-yield oriented agricultural practices and agricultural policies that may cause changes in water regime and their impacts on the soil organic carbon pool in paddy fields. The Jingxian, Zhongshan and Baoying sequences of Hydragric Anthrosols are basically consistent in evolution characteristics of TN and SOC. Hydragric Anthrosols of the Cixi sequence contain relatively more inorganic N and differ quite sharply from the others in evolution characteristics of TN and SOC. So adequate attention should be paid to evaluation of impacts of excessive accumulation or depletion of N in Hydragric Anthrosols that are high in inorganic N content on long-term rice cultivation.

    • Diversities of Soil Forming Parent Materials and Spatial Distribution of Soils in Henan Province

      2019, 56(6):1309-1320. DOI: 10.11766/trxb201810260482

      Abstract (1882) HTML (2120) PDF 3.67 M (2341) Comment (0) Favorites

      Abstract:【Objective】According to the classical Dokuchaev soil genesis theory, soil is formed under the comprehensive effect of five environmental factors, i.e. parent material, climate, biology, topography, and time, among which parent material is the very fundamental one, very closely related to soils. Researchers have made certain progresses in the study on relationships of soils with the factors, but, apart from some early preliminary studies in this aspect, few in-depth reports are found in the literature on relationships of soil parent material with soil factors from the angle of diversity. So this study selected Henan Province for a case study to explore soil elements and composition and soil classes or types in various soil classification system in relation to diversity of soil forming parent materials, effects of soil forming parent material on dispersiveness of spatial distribution of soil great groups, and characteristics and correlations of spatial distribution diversity of the two on a 5 km×5 km grid scale with the classical and modified Shannon entropy methods, in an attempt to enrich steadily the knowledge about the trend of evolvement of the research on soil diversity to that on land diversity. 【Method】Both the classical Shannon entropy formula and modified Shannon entropy formula were used to characterize the composition and spatial distribution diversities of soil forming parent materials and soils. First of all, data of soil forming parent materials were extracted from the data of soil parent materials on the soil genus level based on the soil parent material classification. And with the aid of the spatial data processing and analysis function of ArcGIS10.2 software, the soil farming parent materials in Henan Province were sorted into 6 groups. Then the richness index and composition diversity of the various parent materials and soil elements were calculated with the classical Shannon entropy formula. And number of soil types and bifurcation ratios relative to each group of parent materials and corresponding relationships of the two in occurrence were analyzed for further analysis of effects of parent material on the spatial distribution diversity of soil types with the modified Shannon entropy formula on a 5 km×5 km grid scale. In the end, spatial distribution diversities of parent materials and soils (soil group level) in Henan Province were worked out with the modified Shannon entropy formula and correlation of the two discussed.【Result】Results show that (1) although the parent materials in Henan are very limited in type, they are higher in composition diversity than the soils, which is related to bifurcation ratio of the two in classification. (2)Among the 6 types of parent materials, the type of eluvium and deluvium is the largest in area and the most complex in soil development. The richness index of soil types increases with soil classification going from group, subgroup to family in level. The 15 soil types are related to 6 types of parent materials in one to many, one to one and many to one patterns. (3)Soil types developed from different parent materials vary in dispersiveness of spatial distribution. Carbonati-Orthic Primosols is the dominant type of soil developed on eluvium and deluvium type of parent material, while Hapli aquic cambosol and Shajiang aquic vertosol are on river alluvium and lacustrine sediments, respectively. Yellow ustic argosol and Hapli ustic argosol are the two types of soils well developed on proluvium, loess and laterite types of parent materials. And sandy orthic primosol is the only one developed on the aeolian deposit type of parent material. (4)Hapli aquic cambosol and river alluvium type of parent material is the type of soil and the type of parent material the largest in area and the highest in spatial distribution diversity, respectively, in Henan Province. And soil forming parent materials and soil types are related in spatial distribution diversity to a varying extent. The relationships of the river alluvium type of parent material with Hapli aquic cambosol soil and of the aeolian deposit type of parent material with sandy orthic primosol are the highest, while the relationship of the loess and laterite type of parent material with Shajiang aquic vertosol is near nil, which is reflected in the fact that the area of soil patches common to the two is very limited nearly nothing.【Conclusion】 To sum up, viewing from the angle of diversity, the 6 types of soil forming parent materials and the 15 soil groups in Henan Province vary in composition diversity and spatial distribution dispersiveness. Moreover, the two are related in spatial distribution diversity to a varying extent.

    • Influences of Sample Size and Spatial Distribution on Accuracy of Predictive Soil Mapping on A County Scale

      2019, 56(6):1321-1335. DOI: 10.11766/trxb201811210470

      Abstract (1643) HTML (1046) PDF 19.31 M (1615) Comment (0) Favorites

      Abstract:【Objective】 This study was conducted to investigate influences of sample size and spatial distribution on prediction of soil mapping, which is contributive to formulating soil sampling strategies scientifically and improving soil prediction accuracy effectively. 【Method】 Out of 5 403 soil samples, a validation dataset and training sub-datasets different in number of soil samples were derived randomly, and each subset encompassed five examples different in sampling site spatial distribution pattern. Influences of sample size and spatial distribution on predictive soil mapping, embodied by spatial distribution characteristic and prediction accuracy, were explored on the basis of the prediction of organic matter content (OMC) in topsoil layer with the Ordinary Kriging (OK)or Inverse Distance Weighted (IDW) interpolation method. 【Result】 Results show that when the number of soil samples decreased from 5 000 to 39 the OMC predictive maps based on OK or IDW interpolation was gradually losing details of local variation, and when the number dropped down to 20 or 10, the predictive maps became distorted. When the number varied in the range of 5 000~1 250, the predictive maps based on OK interpolation were quite similar in accuracy with r varying in the range of 0.55~0.59, and RMSE in the range of 3.03~3.15, but when the number dropped down to 625, the predictive maps based on OK interpolation declined significantly in accuracy, and varied sharply between the five groups different in spatial distribution pattern of sampling sites even in the same training subdset. The predictive map based on IDW interpolation varied in accuracy with the number and the distribution pattern of soil sampling sites on a trend similar to that based on OK interpolation, except that the predictive map based on IDW interpolation declined significantly in accuracy with the number of samples starting to drop from 1875 and varied sharply with spatial distribution pattern of the sampling sites. On average, the predictive maps based on OK interpolation were obviously higher than those based on IDW interpolation in accuracy before the map began to turn distorted. 【Conclusion】 All the findings in this study indicate that both sample size and spatial distribution pattern have certain impacts on predictive soil map, and the impacts are quite limited when the sample size is large enough. However, when the sample size drops below a certain level, the predictive maps will lose details of some local variations and prediction accuracy as well, while spatial distribution of sampling sites turns up to be the main affecting factor. Compared with OK, IDW is lower in accuracy and responds to the changes in sample size and spatial distribution earlier before the predictive map is distorted.

    • Quantitative Relationship between Hydraulics Parameters and Soil Erosion Rate on Remolded Soil Slopes with Different Textures

      2019, 56(6):1336-1346. DOI: 10.11766/trxb201812270440

      Abstract (1622) HTML (534) PDF 1.58 M (1689) Comment (0) Favorites

      Abstract:【Objective】 Water erosion is one of the factors driving land degradation, water non-point source pollution and soil erosion, which involves a complex processes that include soil detachment, sediment transport and deposition owing to the interaction of raindrops and overland runoff. Soil detachment refers to the dislodging of soil particles from the soil surface triggered by water flow, and soil detachment rate (or soil erosion rate at erodible beds) is a key parameter in process-based erosion models. However, the study on the pattern of soil erosion rate among different texture soils is still unclear. 【Method】Therefore, an indoor experiment of running overland flow on erodible beds with remoulded soils of different textures was conducted. Thirty five combinations included 2 slopes (5° and 15°), 4 discharges (2, 4, 6 and 8 L•min-1 ) and 5 types of remoulded soil (0, 30%, 50%, 70% and 100% in sand contents) were carried out on a steel flume (3 m long, 1 m wide and 0.35 m high) adjustable in slope gradient. The five types of remoulded soil were prepared by mixing red soil and normal engineering sand at different mass fraction and were labeled as S1, S2, S3, S4 and S5 treatment, respectively. Those texture were silty clay, clay, sandy clay, sandy loam and sandy soil from S1 to S5, respectively. The prepared soil was packed layer by layer (5 cm depth per layer) in the flume to ensure the soil uniform in bulk density (1.35 g•cm-3). The packed flume was pre-wetted (30 mm•h-1) with a rainfall simulator to make the soil moisture saturation. When the moisture content in the soil reduced to 30%, the test started, and ended 15 minutes after surface runoff was initiated. During the test, flow surface velocity was measured with the dye tracing method (using potassium permanganate), and flow width, mean rill depth and mean rill width were measured by using a steel ruler at 20 cm intervals along the tick marks along the edge of the flume (amount to 15 sections). Runoff volume and sediment yield were measured with plastic bottles (at 30 s intervals) and plastic buckets (at 1 min intervals) at the outlet of the flume. 【Result】Results show: (1) Slope gradient and flow discharge were the two basic factors affecting soil erosion rate, both show a close relationship, but the former as more significant. Besides, soil texture had a significant effect on the soil erosion rate, making the latter appear in “monomodal” distribution pattern in the same test condition, with the peak being the maximum in S3 treatment (sandy clay, 50% in sand content); (2) The mean rill depth and rill cross-section width-depth ratio represented obvious regularity with the variations of slope gradient, flow discharge and soil texture. Furthermore, soil erosion rate closely correlated with mean rill depth and the rill cross-section width-depth ratio (r=0.943 and -0.865, P<0.01, respectively), which could be used as indicators of slope erosion and sediment yield; (3) Slope gradient, flow shear stress, stream power and unit stream power were all remarkably related to soil erosion rate, especially the unit stream power was the best hydraulic parameter to describe soil erosion rate (r=-0.911, P<0.01), and their relationship can be well described quantitatively with a power function (Dr =49.96Pr2.07, R2=0.795); and (4) Considering the effect of soil properties on slope erosion, soil cohesion was introduced into quantitating the relationship between unit stream power and soil erosion rate (Dr =165.22Pr2.36 C -0.44R2=0.816), so as to make the quantitation more reliable. The new equation based on soil cohesion make the tests more dependable in predicting soil erosion rate regardless of soil texture.【Conclusion】All the above described findings show that soil erosion on slopes varies regularly with soil texture, and unit stream power and soil cohesion are proper parameters in quantifying soil erosion patterns. Since acquisition of the parameters in the equation is relatively simple, the equation has a wider adaptation range and a higher reference value in practical applications.

    • Erosion-controlling Effects of Revegetation on Slope of Refuse Dump in Mining Area Relative to Vegetation Pattern

      2019, 56(6):1347-1358. DOI: 10.11766/trxb201806260346

      Abstract (1366) HTML (1123) PDF 1.39 M (1605) Comment (0) Favorites

      Abstract:【Objective】 In order to study effects of revegetation varying in pattern controlling runoff and sediment yield on slopes of refuse dumps in opencast coal mining fields, a field experiment was conducted on the slope of a refuse dump in the Yongli Coal Mining Area, Inner Mongolia. 【Method】 Five plots different in vegetation pattern were selected on the slope that had been revegetated for four years for the experiment using in-site scouring method. The five plots included Plot C3H7 (Agropyron planted on the upper slope accounting for 30% in area plus Artemisia desertorum on the lower slope accounting for 70% in area), Plot C7H3 (Agropyron planted on the upper slope accounting for 70% in area plus Artemisia desertorum on the lower slope accounting for 30% in area), Plot QC (Agropyron planted on the whole slope), Plot CG (Agropyron mixed with Artemisia desertorum in plantation) and Plot BS (Bare slope) as control, all being 8×1 m in area and 38°in slope gradient. Water flowed down on the top of the slopes or plots at a gradually increasing rate (5-10-15-20 L•min-1). During the flow scouring events, runoff flow velocity was monitored with the dye tracing method. In the first 6 minutes of runoff, samples of runoff were collected once every minute, and afterwards once every 3 minutes for analysis of sediment content, using the oven-drying ied weighing method. 【Result】 (1) At the initial stage of the increase (0~9 min) in flow rate, runoff rate and erosion rate increased sharply, and follow-up-fluctuation decreased. When the flow increased, runoff rate on the slope increased stepwise with the duration of runoff prolonging. Compared to the initial flow at a rate (5 L•min-1), the flow increasing to 10, 15 and 20 L•min-1 made the difference in runoff rate between protected surface and unprotected surface narrower. Meanwhile,the variation of erosion rate with the variation of flow rate was lower in magnitude than that of the variation of runoff rate, and the erosion rate tended to decline in the late phase of the scouring test even when the flow rate was quite high; (2) In Plot C3H7, C7H3, QC and CG, runoff was reduced by 31.99%, 18.72%, 15.29% and 34.36% and sediment was by 81.28%, 87.29%, 84.80% and 58.73%. Plot CG (mixed Agropyron-Hippophae)” and C7H3 (70% Agropyron Hippophae – 30% Artemisia desertorum) was obviously the most effective pattern of vegetation for controlling runoff and sediment yield, respectively; (3) Agropyron Hippophae and Artemisia desertorum are different in root system, i.e. taperoot system and fibrous root system. The vegetation formed of or properly arranged with mixed plants different in root system has better soil and water conserving effects than the one formed of only a type of plant does; (4) In all the slopes, regardless of vegetation pattern, erosion rate and runoff rate formed an extremely significant power function and linear (C7H3) relationship. And (5) Vegetations of all patterns in this experiment had certain functions to resist scouring erosion caused by continuous heavy storms. 【Conclusion】 All the findings in this experiment may serve as scientific a basis for reasonable ecological restoration in the mining area.

    • Water Infiltration in Soils Developed from Loess Affected by Surface Electric Field and Simulation

      2019, 56(6):1359-1369. DOI: 10.11766/trxb201809110457

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      Abstract:【Objective】The Loess Plateau of China is one of the world’s most severely eroded regions. In this region water shortage is the main limiting factor in agricultural production and ecological environment construction. Therefore, it is of great significance to improve utilization efficiency of the limited water resources in the region to the maintenance of regional ecological environment security and efficient development of green agriculture. The process of soil water infiltration not only determines utilization rate of the limited water sources, such as precipitation and irrigation, but also profoundly affects intensity of surface runoff and soil erosion. Soil water infiltration is mainly affected by soil organic matter content, bulk density, texture, structure stability and soil porosity, water quality and so on. Recent researches have demonstrated that soil surface electric field influences soil water infiltration by affecting stability of soil aggregates and distribution of soil pores. Although quite a number of studies have been reported on water infiltration, water availability and their affecting factors in soils developed from Loess, it is still not clear that how soil interfacial properties (surface electric field and surface potential of soil particles) vary in the process of water infiltration and affect water infiltration characteristics and how applicable the classical soil water infiltration model is when effect of the surface electric field is taken into account. So further studies need to be done. 【Method】In this study, two representative Loess soils, Lou soil and Cinnamon soil, were used. According to the double layer theory of charged particles, the surface electric field of soil particles could be quantitatively adjusted by applying a series of electrolyte solutions different in concentration. Soil water infiltration rate, moisture front migration and cumulative infiltration in the two soils was determined. The Kostiakov model and the Philip model was used to fit the process of soil water infiltration. 【Result】Results show: (1) Wetting front movement, infiltration rate and cumulative infiltration decreased with decreasing electrolyte concentration and increasing surface potential (absolute value), which indicates that surface electric field of soil particles strongly affects soil water infiltration; (2) When electrolyte concentration in the bulk solution was less than 0.01 mol•L-1 or absolute surface potential value of the Lou soil and Cinnamon soil was more than 233 mV and 223 mV, the temporal variation curves of soil water infiltration in the two soils were close to each other, which indicates that 233 mV and 223 mV is the critical potential value of the soil water infiltration process in Lou soil and Cinnamon soil, respectively; and (3) The Kostiakov model and the Philip model were both applicable to simulating infiltration processes in Lou soil and Cinnamon soil. Further analyses of the fitting parameters—correlation coefficient (R2), residual sum of squares, and root mean square error (RMSE) shows that the Kostiakov model was more suitable than the Philip model. 【Conclusion】All the findings demonstrate that the process of soil water infiltration is greatly influenced by soil surface electric field. There are critical surface potentials controlling water infiltration. The findings provide a theoretical reference for development of new techniques to regulate water infiltration based on soil internal forces.

    • Effect of Tillage Practices on Soil Physical Properties and Maize Growth in Shajiang Black Soil (Vertisol)

      2019, 56(6):1370-1380. DOI: 10.11766/trxb201902280624

      Abstract (2068) HTML (0) PDF 770.49 K (1772) Comment (0) Favorites

      Abstract:【Objective】 Shajiang black soil is one of the major types of soil low or medium in productivity in China. As its parent material is dominated with montmorillonite and high in clay content, the soil is high in bulk density and strength and low in water permeability. These characteristics of the soil are the main factors limiting root development and yield of crops. Tillage practices, such as subsoiling and deep ploughing, have been considered as effective management practices to improve soil structure, but their adaptability varies quite significantly with region. How to adopt effective tillage practices to improve soil structure, expand available water capacity, promote root development and increase crop yield is of great significance to safety and stability of the grain production in this region. The objective of this study was to evaluate systematically effects of tillage practices on soil physical properties and maize growth in Shajiang black soil.【Method】A long-term field experiment in the Longkang Farm, Anhui Province was initiated in 2015 and designed to have four treatments different in tillage practices, including no tillage, rotary tillage, subsoiling and deep ploughing. Each treatment had three replicates, making up a total of 12 plots, laid out in a single factor randomized block design. Soil bulk density in the 0 ~ 10 cm, 10 ~ 20 cm and 20 ~ 40 cm soil layers and penetration resistance of the 0 ~ 45 cm soil layer were measured separately at different growth stages of maize. Features of the root system of maize in the soil profile were measured only at the milk-ripe stage. Soil available water capacity, saturated hydraulic conductivity and some other soil physical properties in the three layers were determined separately and yield of the crop was calculated after the crop harvested. At the end, relationships between crop growth with physical properties were analyzed.【Result】1) Compared with the other three treatments, the no-tillage one was higher in bulk density (1.52~1.57 g·cm-3) and in soil penetration resistance (926 ~ 1 748 kPa ), but lower in soil available water capacity (0.12 cm3·cm-3) and in saturated hydraulic conductivity (3.5×10-5 mm·min-1) in the 0 ~ 40 cm soil layer depth throughout the entire maize growing period. Consequently, the root length density and root dry biomass density in that treatment were significantly declined 42.5% ~ 117.1% and 35% ~ 73.9%, respectively, in the 0 ~ 10 cm soil layer than those in the other treatments. The no-tillage treatment was also 8%~ 12% lower than the others in crop yield for three successive years. 2) Relative to the treatments of rotary tillage and subsoiling, the treatment of deep ploughing was lower in bulk density (1.39 ~ 1.51 g·cm-3) in the 10 ~ 20 cm soil layer and in soil penetration resistance (725 ~ 1 575 kPa) in the 10 ~ 30 cm soil layer, but higher in saturated hydraulic conductivity in the 0~10 cm soil layer and in soil available water capacity in the 0 ~ 20 cm soil layer. Consequently, the plants in that treatment were higher in root density and crop yield than those in the other two treatments. 3) Pearson correlation analysis shows that plant root density was significantly and negatively related to soil bulk density (r= -0.74**, P< 0.01) and soil strength (r= - 0.73**, P < 0.01) for the whole growing period.【Conclusion】It is, therefore, concluded that the deep ploughing may be a more appropriate tillage practice to improve soil physical properties and promote crop agronomic performance in the Shangjiang black soil.

    • Montmorillonite-Iron Oxides Complex:Characterization and Features of Adsorbing Phosphates Different in Form Complex of Montmorillonite

      2019, 56(6):1381-1389. DOI: 10.11766/trxb201902150626

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      Abstract:【Objective】In soils iron oxides often congregate with lamellar phyllosilicates into various complex-like structures, thus generating significant impacts on physical and chemical properties of the soils. Phosphorus is an essential nutrient for growth of organisms in ecosystems, but may lead to eutrophication and deterioration of water quality, once it accumulates excessively in the soils. In soils phosphorus tends to be adsorbed onto minerals, and hence its mobility and bioavailability is significantly affected. Its adsorption by iron oxide-phyllosilicates associate differs from that by iron oxides and phyllosilicates separately in behavior. Yet, little has been done to explore effects of iron oxides-montmorillonite complex on speciation and bioavailability of phosphorus in soils. 【Method】In this paper, Montmorillonite-goethite complex (Mt-Goe) and complex of montmorillonite with amorphous or poorly crystalline iron oxides (Mt-HFO) were prepared, separately, and analyzed for structure, surface properties and features of adsorbing phosphate (Pi) and myo-inositol hexakisphosphate (IHP). 【Result】In Mt-Goe a small amount of hydroxyiron ions entered into the layers of montmorillonite, thus expanding the interlayer space, while montmorillonite was covered with goethite particles on the surface. In Mt-HFO, Fe3+ in-between the layers of monymorillonite hydrolyzed into hydroxy iron oxide and formed a layer of amorphous iron oxides on the surface of monymorillonite. The specific surface area of montmorillonite, Mt-Goe and Mt-HFO was 258.7, 185.4 and 226.4 m2 ?g-1 respectively, with surface fractal, isoelectric point and surface hydroxyl contents being on a rising order; and when pH was 5.5, the surface Zeta potential of the three was -46.1, -13.6 and -19.4 mV respectively. Pi and IHP adsorptions on the three types of samples were all dominated by homogeneous surface mono-layer adsorption. In terms of Langmuir saturated adsorption (qmax) and adsorption affinity, the three samples followed a decreasing order of Mt-HFO > Mt-Goe > montmorillonite. The pseudo-second-order kinetic model could be used to well fit Pi and IHP kinetic adsorption processes of the three samples, with adsorption rate constant following an order of Mt-HFO > Mt-Goe > montmorillonite. Compared to Pi, IHP was significantly lower in adsorption kinetic rate constant on the three samples, but significantly higher in qmax, and particularly low in adsorption rate on Mt-HFO, but much higher in qmax. 【Conclusion】Compared to montmorillonite, Mt-Goe and Mt-HFO are both lower in Pi and IHP adsorption rate, but higher in adsorption capacity. Among the two complexes, Mt-HFO is lower in Pi and IHP adsorption rate, but higher in adsorption capacity. All the three types of samples, montmorillonite, Mt-Goe and Mt-HFO, are lower in IHP adsorption rate than in Pi one, but much higher in IHP adsorption capacity than in Pi one.

    • Distribution Inhomogeneity of Cd Pollution of Farmland Soil on A Plot-scale

      2019, 56(6):1390-1400. DOI: 10.11766/trxb201902180052

      Abstract (1453) HTML (0) PDF 654.15 K (1749) Comment (0) Favorites

      Abstract:【Objective】In plain areas like the Yangtze River Delta in China, where farmlands are highly fragmented and the contradiction between limited farmland resources and a big population is outstanding, the problem of how to control heavy metal pollutions, especially Cd pollution, of farmland soil has long been an issue attracting extensive attention. The new finding of distribution inhomogeneity of Cd pollution of farmland soil on a plot-scale in the regions is of great reference value to control of the pollution and remediation of the polluted farmlands therein. Though in the literature quite a number of papers can be found systematacially exploring and discussing distribution of heavy metals and trace elements in farmland soil and inhomogeneity of the soil as well, on a plot-scale, few dealt with distribution inhomogeneity of Cd pollution. Hence, this paper is devoted to analysis of the distribution inhomogeneity of Cd pollution in farmland soil on a plot scale.【Method】In this study, a total of 42 soil samples were collected from the topsoil layers (0~20cm) and sedimentary soil profiles (0~220cm) of 5 typical tracts of farmland in the studied areas with the aid of special soil sampling tools for analysis of content distributions and geochemical indices of As Cd, Cu, Pb, Zn, Cr, Ni, Hg, As, Sb,Se, pH and TOC, with the aid of ICP-MS,XRF and some others.【Result】Analysis of the environmental geochemical survey data obtained from the typical farmland soils in the Yangtze River Delta shows that when soil Cd were higher than 1.0 mg.kg-1 in concentration in a farmland plot, significant spatial inhomogeneity of Cd pollution could be observed. In a field less than 0.13 hm2, soil Cd varied sharply in concentration from plot to plot, and differed by dozens of times to the most possible, and that soils mild, moderate and severe in Cd pollution coexisted in a farmland plot. In a long strip of farmland plot, Cd pollution distributed somewhat in an exponentially declining trend. The more serious the closer to the pollutant source, and the more inhomogeneous in upland plots than in paddy plots. Distribution heterogeneity of Cd pollution mainly appeared horizontally, and vertically Cd pollution concentrated mainly in the surface toplayer (0~ 20 cm). Contrast to soil Cd, other heavy metal elements, like Cu, Pb, Zn, As, Cr, and so on, were distributed normally in the farmland plot in a relatively even manner. [Conclusion] The uneven distribution of Cd pollution is universal in farmland soil on a plot-scale in the Yangtze River Delta and similar plain areas, and attributed mainly to differences in micro-topography and farming practices. The knowledge about the characteristics of Cd distribution in the soil on a plot scale is quite practical and helpful to remediation of Cd contaminated farmlands in the Yangtze River Delta and similar areas.

    • Effects of 20 Consecutive Years of Potassium Application on Soil Potassium Quantity-Intensity(Q/I)Relationship in Flue-cured Tobacco-rape Rotation System

      2019, 56(6):1401-1413. DOI: 10.11766/trxb201811200543

      Abstract (1389) HTML (0) PDF 866.16 K (1266) Comment (0) Favorites

      Abstract:【Objective】This study was to explore effect of long-term potassium application on soil potassium supply capacity, so as to provide certain scientific basis for rationally potassium application and continuing research on development of agricultural soil.【Method】From a long term potassium fertilization experiment on a tobacco-rape rotation system, which was designed to have 0,187.5 or 375 kg·hm-2 K2O applied to flue-cured tobacco and 36 kg·hm-2 to rape, soil samples were collected for analysis of apparent balance and Quantity-Intensity (Q/I) of soil potassium, and relevant parameters, i.e. K equilibrium activity ratio (ARe), soil labile K (KL), non-specific labile K (-ΔK0) and specific labile K (KX), potential buffering capacity (PBC), K and Ca+Mg exchange free energy (-ΔG), and soil properties, like readily available K (Kav), slowly available K (Knex), K saturation degree (KS), clay minerals components and so on, and moreover, relationships between Q/I parameters and soil properties in the flue-cured tobacco-rape cropping system.【Result】 Results show that after 20 years of the stationary experiment, ARe varied in the range of 0.38×10-3~8.91×10-3(mol·L-10.5, -ΔK0 of 0.02~0.55 cmol·kg-1, KL of 1.61~2.16 cmol·kg-1, KX of 1.06-2.14 cmol·kg-1, PBC of 6.20~7.76 cmol·kg-1(mol·L-1)-0.5, and -ΔG of 11.70~19.72 kJ·mol-1. Obviously K application enhanced both ARE and -ΔK0, but reduced KL, KX, PBC, and -ΔG. Kav, Knex, KS and Kab were extre-significantly and positively correlated with ARe and -ΔK0, but negatively with KL, KX, PBC and -ΔG. Significant relationships were observed between the parameters of the Q/I curve of soil K, and these parameters could be integrated into a principal component index, which was significantly lower in K application treatments than in no K application treatments. Soil potassium was retained mainly interlaminarly in clay mineral crystals and lower in bio-availability in the soils with no K applied, but on joint position interface of the clay mineral crystals and higher in bio-availability in the soils applied with K. Hence, the soils with no K applied were higher in vermiculite content, but lower in illite content than the soils with K applied.【Conclusion】All the Q/I curve parameters, such as ARe, -ΔK0, KL, KX, PBC,-ΔG, can be used as indicators for evaluation of soil potassium supply capacity. Apparent balance of soil potassium is a major factor driving changes in K Q/I curve shape and differentiation of its parameters, variation of potassium supply capacity and evolution of soil minerals. The higher the K application rate, the higher the soil potassium surplus and the higher the soil supply capacity. In the soils under long term potassium deficiency, mineral potassium transforms into specific labile K at a higher rate than specific labile K does into non-specific labile K. Long-term potassium deficiency causes transformation of illite into vermiculite.

    • Effects of Groundwater Tables and Long-term Fertilization on Mineralization of Organic Carbon in Red Paddy Soil

      2019, 56(6):1414-1424. DOI: 10.11766/trxb201810230472

      Abstract (1552) HTML (0) PDF 686.38 K (1555) Comment (0) Favorites

      Abstract:【Objective】 As an essential biochemical process in soil, mineralization of soil organic carbon (SOC) is closely related to release of soil nutrients, maintenance of soil quality, and formation of greenhouse gases. Mineralization of soil organic carbon varied in characteristic with soil properties and environment, while fertilization and groundwater table are two key environmental factors affecting soil properties. The objective of this study is to explore dynamics and characteristics of SOC mineralization in red paddy soil under long-term fertilization relative to pattern of the fertilization and groundwater table, in an attempt to provide certain guidance for rationalizing nutrient management programs. 【Method】A long-term field experiment, initiated in 1982, was designed to have 3 fertilization treatments (2/3OM, 1/3OM and NPK) and 2 groundwater tables (at 20 cm and 80 cm in depth). In Treatment 2/3OM organic manure was applied at a rate to make up 2/3 of the total N supply; in Treatment 1/3OM organic manure at a rate to make up 1/3; and in Treatment NPK, Urea to make up the total N supply. In all the 3 treatments, P and K was applied the same in rate. Each treatment had 3 replicates. Soil samples were collected from the topsoil layer, 0–10 cm in depth, before ploughing in 2017. Cumulative emission and mineralization rate of carbon dioxide were determined with the incubation method. First-order kinetic model was used to calculate potential mineralization and turnover rates. 【Result】Groundwater table had a significant impact on characteristics of organic carbon mineralization; SOC content in Treatment 2/3OM, 1/3OM and NPK was 20.66%, 23.30% and 17.97%, respectively, higher when the groundwater table was at 20 cm in depth than when it was at 80 cm in depth; Mineralization rate, cumulative mineralization and potential cumulative mineralization (C0) of SOC in Treatment 2/3OM and 1/3OM was also higher in the former case than in the latter case, whereas in Treatment NPK reverse tendencies were observed; Obviously mineralization of SOC in red soil varied significantly with fertilization pattern and depth of groundwater table. In terms of content, mineralization rate and cumulative mineralization of SOC, the three treatments exhibited an order of 2/3OM>1/3OM>NPK. When the groundwater table was at 20 cm in depth, Treatment 2/3OM and 1/3OM was 53.32% and 15.44% higher than Treatment NPK, respectively, in SOC cumulative mineralization rate, but when the groundwater table was at 80 cm in depth, Treatment 2/3OM and 1/3OM was 5.56% and 17.95%, respectively, lower. Meanwhile, in the case of the former, Treatment 2/3OM and 1/3OM significantly higher than Treatment NPK in potential mineralizable soil organic carbon (C0), but in the case of the latter, Treatment 1/3OM was significantly lower than Treatment NPK, and in the case of the former, the treatments did not vary much in SOC turnover constant (k), whereas in the case of the latter, Treatments 2/3OM and 1/3OM were significantly higher. 【Conclusion】 In conclusion, high groundwater table is conducive to accumulation of soil organic carbon, increase of cumulative mineralization, cumulative mineralization rates and potential cumulative mineralization of SOC in red soil under long-term application of organic manure, but lowers SOC cumulative mineralization rate in the soil under long-term application of chemical fertilizer. The effects of long-term fertilization on cumulative mineralization rate and potential cumulative mineralization of SOC in red paddy soil vary with depth of groundwater table.

    • Evolution of Soil Organic Nitrogen Composition with Degradation of Zoige Alpine Marsh Wetland

      2019, 56(6):1425-1435. DOI: 10.11766/trxb201812240572

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      Abstract:【Objective】This study was oriented to characterize the evolution of organic nitrogen composition and bioavailabilities of its components with degradation of alpine wetlands, in an attempt to provide certain basic data for restoration of degraded alpine marsh wetlands. 【Method】Soil samples were collected from 4 types of wetlands, including relatively pristine marsh (RPM), lightly degraded marsh (LDM), moderately degraded marsh (MDM), and heavily degraded marsh (HDM) in the Zoige Wetland Nature Reserve. Organic nitrogen in the soil samples were fractionated using the Bremner method. Multivariate stepwise regression analysis was performed to determine contribution of each fraction of organic nitrogen to availability of soil nitrogen.【Result】With RPM turning into MDM and HDM, soil total nitrogen (TN) decreased significantly or by 33.4%~77.8% and 69.4%~93.7%, respectively, and alkalytic nitrogen (AN) by 36.8%~80.2% and 57.6%~82.2%, respectively, in content. In terms of contents of acidolytic ammonia nitrogen, amino acid nitrogen and unknown nitrogen, the four types of wetlands exhibited an order of RPM > LDM > MDM > HDM. With a marsh degrading, amino sugar nitrogen therein increased first and then decreased in content, and the proportion of amino sugar nitrogen and ammonia nitrogen to TN increased, while that of amino acid nitrogen to TN decreased. The main organic nitrogen fraction affecting the content of soil available nitrogen in RPM and HDM was ammonia nitrogen and unknown nitrogen, respectively; whereas that in LDM and MDM was amino acid nitrogen. 【Conclusion】 Degradation of the Zoige Alpine Wetland reduced the contents of soil TN and the fraction of acidolytic nitrogen, weakened nitrogen "sink" function of the soil, and changed the contribution of each organic nitrogen fraction to nitrogen availability.

    • Effects of Organic Materials on Soil Organic Carbon Combination Form and Composition of Humus in the Desert Soil

      2019, 56(6):1436-1448. DOI: 10.11766/trxb201811280536

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      Abstract:【Objective】In order to explore effects of organic material, relative to type, on soil fertility, a 7-year long field experiment was conducted in the desert soil of Hexi Oasis.【Method】The experiment was designed to have 8 treatments, that is, CK (no fertilization), NP (application of chemical fertilizers of nitrogen and phosphorus), NF (70%NP+cow manure), ZF (70%NP+pig manure), JF (70%NP+chicken manure), ZZ (70%NP+biogas sludge), JZ (70%NP+mushroom substrate residue) and WN (70%NP+sewage sludge). All the organic material treatments were the same in organic carbon input and in NP application rate equivalent to 70% of the rate in treatment NP.【Result】Results show that all the organic treatments significantly increased soil organic carbon content and stock as compared with the control (CK) and Treatment NP (P< 0.05), but the increase varied significantly in degree, and was the highest in Treatments JF and WN, which was followed by Treatment ZF and then the rest. The effect on free organic carbon content was significantly higher in Treatments NF, ZF and WN than in Treatments CK and NP, and so was that on soil combined humus content (P<0.05), except in Treatment NF. Moreover, soil loosely combined humus content increased significantly in all the organic treatments, except for Treatment JZ, and so did humic acid (HA) content in all the organic treatments (P<0.05), stably combined humus content in Treatments JZ and ZZ (P< 0.05), tightly combined humus content in Treatments JF, ZZ and WN (P< 0.05), fulvic acid (FA) content in Treatments JF, WN and ZZ (P<0.05), and humin content in Treatments NF and JF only (P< 0.05).【Conclusion】In conclusion, organic materials significantly affects free soil organic carbon and combined organic carbon in content and combination form and composition of humus, an hence soil organic carbon content and stock, and the effects of pig manure, chicken manure and sewage sludge improving soil fertility are higher than those of cow manure, mushroom substrate residue and biogas residue.

    • Effects of Liming on Rhizosphere Soil Microbial Communities of Dominant Plants in Fallowed Red Soil under Simulated Nitrogen Deposition

      2019, 56(6):1449-1458. DOI: 10.11766/trxb201808260218

      Abstract (1649) HTML (770) PDF 714.04 K (1983) Comment (0) Favorites

      Abstract:【Objective】Unreasonable anthropogenic activities tend to cause gradual increase in global atmospheric nitrogen deposition, which has become one of the most important environmental problems that arouses attentions the world over. Red soil, as an important soil resource in China, has come to face a series of serious ecological problems, such as soil acidification, biological degradation and so on, owing to its own development characteristics and specific climate factors. At the same time, nitrogen deposition is liable to exacerbate soil acidification and degenerate functions of the red soil ecosystem, posing a serious threat to the red soil ecosystem and impeding sustainable development of the economy and society of the red soil region. In order to promote restoration and sustainable development of the ecological functions of red soil, a series of practices have been adopted, such as leave farmlands in fallow or “grain for green” and stop artificial interference of the soil to let the vegetation and then the soil recover in biodiversity and ecosystem function through natural succession. This study was oriented to explore the effects of atmospheric N deposition on the soil microbial community in the rhizosphere ofSetaria viridis (L.) Beauv Beauv, the dominant plants in fallow farmlands in the initial phase of the succession, as affected by soil acidification, controlled by liming. The factors of global change and comprehensive impact of artificial management practices were also taken into account.【Method】For the study, a field experiment designed to have three levels of artificial atmospheric N deposition, through N application, i.e., 0 kg•hm-2,45 kg•hm-2 and 90 kg•hm-2 and two levels of liming, i.e., 0 kg•hm-2 and 110 kg•hm-2. Samples of rhizospheric soil under Setaria viridis (L.) Beauv were collected and analyzed for the structure of the soil microbial community.【Result】Results showed that the simulated nitrogen deposition significantly inhibited the soil microbial community in rhizosphere by reducing its microbial phospholipid fatty acid (PLFA) content, the ratio of gram-negative bacteria/gram-positive ones, fungi / bacteria ratio, and Shannon diversity. In the plots without nitrogen deposition (0 kg•hm-2), liming decreased microbial PLFA, but significantly increased the ratio of Gram-negative bacteria to Gram-positive ones. The interaction of nitrogen and lime restrained the adverse effects of applying nitrogen and lime separately alone on microbial biomass. PLFA in all groups of soil microbes increased with decreasing nitrogen deposition. The structural equation model (SEM) shows that the effect of liming was much stronger on the microbial community. Simulated nitrogen deposition and liming jointly through interaction affected soil pH, nutrient availability and competition for nutrient between soil microbes and plants, thus altering structure and diversity of the soil microbial community.【Conclusion】This study demonstrates that the interaction of nitrogen and lime could improve rhizosphere soil environment, mitigate soil acidification, increase soil productivity, promote microbial growth and maintain stability of the microbial community structure and diversity in fallow red soil. In conclusion, application of lime can offset the adverse impacts of atmospheric nitrogen deposition on soil microbial community by improving the habitat of fallow red soil, alleviating damage to the soil microbial community in rhizosphere and promoting restoration of the soil ecosystem.

    • Effect of Long-term Application of Phosphorus Fertilizer on Soil Bacterial Community Structure and Enzymatic Activity in Lime Concretion Black Soil Relative to P Application Rate

      2019, 56(6):1459-1470. DOI: 10.11766/trxb201805080149

      Abstract (2027) HTML (698) PDF 822.99 K (2158) Comment (0) Favorites

      Abstract:【Objective】Soil phosphorus is a major nutrient essential for plant growth and plays an important role in achieving high crop yields. Application of chemical phosphorus fertilizer is a common agricultural strategy to improve phosphate availability in lime concretion black soil, where shortage of soil phosphate is a limiting factor in agricultural production. Numerous studies have been done addressing effects of phosphorus application on crop yield and soil fertility, but few are found in the literature about the effects of long-term phosphorus application on diversity and composition of soil microbial community in lime concretion black soil. The overall object of this study was to investigate relationships between soil nutrient availability, soil enzymatic activity and soil bacterial community as affected by phosphorus application strategy. 【Method】A long-term P-fertilizer application field experiment, designed to have three treatments in P fertilizer application rate, that is P0 (No phosphorus applied); P1 (P2O5 45 kg•hm-2 applied) and P2 (P2O5 90 kg•hm-2 applied), was conducted in a tract of lime concretion black soil in the Mengcheng, Anhui. The technology of high-throughput sequencing of V4-V5 16s rRNA gene region was used to character bacterial community diversity and composition relative to phosphorus application rate. Activities of β-glucosidase, Protease, Acid phosphatase and Dehydrogenase were measured to represent functions of the soil bacterial community. 【Result】 Results show that after 21 years of phosphorus application improved soil fertilizer significantly. Compared with P0, P2 was 10.33%, 31.36%, 40.00%, 384.19% and 79.49% higher in content of soil organic carbon, soil dissolved organic carbon, total phosphorus, available phosphorus, and ammonium, respectively. The significant improvement in soil nutrient in turn altered composition of the soil bacterial community. The diversity (Shannon index) of soil bacteria improved by 2.49% and 4.52% in P1 and P2, respectively. Proteobacteria, Actinobacteria and Acidobacteria used to be the dominant phyla in the lime concretion black soil, accounting for 40.16%, 19.75% and 14.91% in relative abundance, respectively. Principal coordinate and Adonis analysis reveals significant differences between the treatments in structure of the soil bacterial community. In the soils applied with phosphate, phosphate-solubilizing bactria, including three phyla, i.e. Actinobacteria, Planctomycetes and Bacteroidetes, and three genera, i.e. Terracoccus, Flavisolibacterand Arthrobacter, increased significantly, whereas oligotrophic bacteria, including two phyla, i.e. Chloroflexi and Verrucomicrobia, denitrifying bacteria, including two genera, i.e. Kaistobacter and Rhodanobacter, and nitrogen-fixing bacteria, including two genera, i.e. Bradyrhizobium and Burkholderia, decreased significantly in relative abundance. Canonical analysis of principal coordinate (CAP) and multivariate regression tree analysis (MRT) reveals that soil bacterial community composition was significantly related to contents of soil dissolved organic carbon and total phosphate in the treatments applied with phosphorus. As expected, long-term phosphorus application increased the activities of β-glucosidase, Protease and Dehydrogenase, while phosphorus application had no significant effects on the activity of acid phosphatase. The above-described four soil enzymes were all significantly and positively related in activity to relative abundance of the bacteria (i.e., Bacteroidetes and Flavisolibacter) enriched in the soils applied with phosphorus. 【Conclusion】 In conclusion, the present study has demonstrated that long-term phosphorus application can improve soil fertility, increase microbial diversity, alter soil bacterial community structure and enrich phosphate-solubilizing bacteria, which in turn, increase soil enzyme activities in lime concretion black soil.

    • Effect of Straw Return, Directly or as Biochar, on Nitrifying Microbes in Fluvo-aquic Soil

      2019, 56(6):1471-1481. DOI: 10.11766/trxb201901290650

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      Abstract:【Objective】 Biochar has increasingly been used as soil amendment to increase soil carbon storage and improve soil chemical and biological properties. However, so far little has been found in the literature talking comparatively about effects of returning maize stalk, directly or as biochar on soil properties, nitrification and ammonia oxidizer communities. 【Method】 A 3-year field experiment was conducted in a field of typical fluvo-aquic soil under the wheat/maize rotation–system commons in the North China Plain. The field experiment was designed to have four treatments: Treatment S (application of straw); Treatment B (application of straw-derived biochar); Treatment SB (half straw and half straw-derived biochar) and Treatment CK (no straw or biochar applied). Soil samples were collected in the wheat and maize seasons for analysis of soil properties and community structure and diversity of, ammonia oxidizing archaea and bacteria with the terminal restriction fragment length polymorphism (T-RFLP) and clone library techniques.【Result】It was found that during the wheat season Treatment B significantly enhanced soil pH, soil organic carbon (SOC) and readily available potassium (AK), while decreasing soil bulk density, but did not affect the contents of total nitrogen (TN), NO3--N or soil, water as compared to Treatment S, and PNR in Treatments B and SB was measured to be 0.58 and 0.49 μg·h-1·g-1, respectively, significantly higher than that in CK (0.22 μg·h-1·g-1), but did not differ much from that in Treatment S (0.40 μg·h-1·g-1). During the maize season, Treatment B significantly increased soil water content, SOC and AK, and PNR on the whole was relatively lower in the maize season than in the wheat season, regardless of treatment, and much higher in Treatment B (0.27 μg·h-1·g-1) than in Treatments CK and S (P<0.05). During the wheat season, Potential nitrification rate (PNR) was closely related to AK, NH4+ and soil bulk density (P<0.05), but not so to ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) community structure. During the maize season, PNR was significantly related only to SOC and to AOB community structure as well. Redundancy variance analysis (RDA) shows that soil SOC, bulk density, pH and AK are the main factors significantly affecting community structure of soil AOA and AOB, which explained 76.4% and 75.5% of their total variation. Phylogenetic tree analysis shows that all archaeal amoA gene sequences were exclusively clustered with group 1.1b (Nitrososphaera); and almost all the bacterial amoA sequences in the fluvo-aquic soil belonged to Nitrosospira cluster 3.【Conclusion】To sum up, application of biochar stimulates nitrification in the sandy fluvo-aquic soil by changing soil SOC, bulk density, pH and AK. The finding in the sequencing and RDA further indicate that biochar application triggers changes of AOA and AOB in community structure. The finding may serve as theoretical references in rational utilization of straw and its biochar.

    • Decomposition of Plant Straws and Accompanying Variation of Microbial Communities

      2019, 56(6):1482-1492. DOI: 10.11766/trxb201810210315

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      Abstract:【Objective】 Plant residue is an important source of soil organic matter. Returning Straw to the field is an effective way to develop sustainable organic agriculture. In this paper, characteristics of the decomposition of plant straws, soil microbial functional diversity and their relationship was studied in an attempt to lay down a scientific basis for research on transformation of organic carbon in soil and rational exploitation of land resources. 【Method】The mesh bag method was used to explore how fresh plant straws decompose in farmland soil and the biolog plate technology was adopted to determine changes in soil microbial community relative to type of the plant straw incorporated.【Result】Results show that with decomposition going on, residue rate of fresh plant straws did not vary much. Corn straw decomposedfaster than bean straw. In terms of mean AWCD (the average well colour development ) of soil microbial communities, a declining order of FCN (Fresh corn straw + nitrogen fertilizer) > FC (Fresh corn straw) >FB (Fresh bean straw), indicating that the soil microbial community in the soil applied with corn straw was relatively high in density and stability, while that in the soil applied with bean straw was lower during the whole decomposition period. No significant difference in microbial AWCD was found between the three treatments (P>0.05), but sharp differences were between treatments different in types of straw and in duration of decomposition (P<0.01). Analysis of effects of microbial community structures on utilization efficiency of the six categories of carbon sources indicates that the predominant populations in the three treatments fed mainly on saccharides and polymers. When decomposition went on, hard-to-decompose substances gradually accumulated in the middle and later stages of the decomposition, showing that the populations were the weakest in utilization of aroma compounds. Polymers could reduce structure stability of the microbial community and affect residual rate of the straws under decomposition. Correlation analysis shows that decomposition residual rate was significantly related to soil pH, organic matter, alkalyic N, readily available K, soil temperature, the utilization of carbon sources, like amino acids and polyamines, and by a certain degree to soil water content and water content of straw. 【Conclusion】FCN with a proper C/N ratio is susceptible to impact of more factors than FB and FC, when decomposing in the field. Therefore, in the practice of returning straw in the field, it is recommended to adjust C/N ratio of the straw incorporated to a proper degree and to apply microbial agents that are capable of degrading the metabolites of polymers, so as to promote decomposition of the straws incorporated and improve utilization rate of the straws returned.

    • Effects of Long-term Monocropping of Lycium barbarum L. on Function and Composition of Fungal Community in Rhizosphere of Replanted Lycium barbarum L.

      2019, 56(6):1493-1503. DOI: 10.11766/trxb201807020355

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      Abstract:【Objective】 Owing to the growth characteristics of wolfberry ( Lycium barbarum L.) per se and the limitation of soil resources in the traditional wolfberry plantation regions, long-term monocropping of the plants has become one of the main factors hindering sustainable development of the industry of wolfberry production and causing serious economic loss and potential eco-problems. Previous studies found that monocropping could significantly affect diversity and composition of the bacterial communities in the rhizosphere of replanted L. barbarum, however, they did not deal much with responses of the fungal communities therein to the long-term monocropping. 【Method】Soil samples were collected from the topsoil layer (0~20 cm) near the plants in the long-term monocropping wolfberry fields and randomly in the control (no wolfberry cultivation history) with a soil auger (n). In order to have enough rhizosphere soils, root segments from at least ten individual plants were collected. Rhizosphere soil adhered to the roots were collected by washing with 10 mmol•L-1 NaCl solution and centrifuging. The genomic DNA was extracted from 0.1 g wet rhizosphere and bulk soil sample using the PowerSoil DNA isolation Kit, separately. The ITS2 region was amplified and sequenced with the Illumina HiSeq technique. Then metrics of α diversity (Shannon index and OTU richness) and weighted and unweighted UniFrac distances were calculated with the aid of QIIME. And real time PCR was used to quantify abundance of the bacterial and fungal populations in each DNA samples.【Result】 Real time PCR found that monocropping significantly increased abundances of the bacterial and fungal communities in both bulk soil and rhizosphere of L. barbarum as compared with what was found in the control fields (P < 0.05). However, the effect was much higher on fungi than on bacteria, and hence disturbed the balance between bacteria and fungi in ratio, thus making the microbial environments in the rhizosphere and bulk soil tend to be fungal dominant. Sequencing analysis discovered that Ascomycota, Basidiomycota, Zygomycota, Chytridiomycota, and Glomeromycota were the dominant phyla in all the samples, and that the relative abundance of Zygomycota in the rhizosphere of replanted wolfberry was significantly lower than that in the control, whereas an opposite trend was found with Glomeromycota (P < 0.05). And FUNGuild predication of fungal functions demonstrated that the relative of arbuscular mycorrhizal fungi (AMF) in the rhizosphere of replanted wolfberry in the monocropping fields decreased significantly relative to what in the control fields (P < 0.05). Non-metric multidimensional scaling analysis (NMDS) revealed that the fungal communities in bulk soil and rhizosphere of replanted wolfberry were quite similar to each other in the monocropping fields, but not so in the control, although they did not very much in diversity from those in the control. Furthermore, distance based redundancy analysis indicated that soil pH, electrical conductivity, and contents of nitrate nitrogen and readily available phosphorous were the main factors affecting soil fungal communities in the rhizosphere of wolfberry, while contents of nitrate nitrogen and readily available phosphorous were the ones explaining changes in soil fungal communities in the bulk soils (P < 0.05).【Conclusion】All the findings in this study suggest that long-term fertilization in the monocropping wolfberry fields might be one of the major causes driving the succession of soil fungal communities in the rhizosphere of replanted wolfberry and altering the interaction between wolfberry and soil fungal community. Therefore, the study may shed some new light on mechanism of the forming of the hazard of long-term monocropping of wolfberry to sustainable development of the industry of wolfberry production.

    • Effects of Logging Residue on Composition of Soil Carbon and Activity of Related Enzymes in Soil of a Young Chinese Fir Plantation as Affected by Residue Handling Mode

      2019, 56(6):1504-1513. DOI: 10.11766/trxb201812110500

      Abstract (1863) HTML (1002) PDF 648.38 K (1917) Comment (0) Favorites

      Abstract:【Objective】In this study, analysis was done of effects of logging residue on soil carbon composition and activity of related soil enzymes in different soil layers as affected by residue handling mode in the soil of a young Chinese fir plantation in the Castanopsis kawakamii Nature Reserve located in Sanming, Fujian, China.【Method】Logging residue was handled in the following ways, i.e., residue retained (RR), residue removed (R) and residue burnt (RB). Soil organic carbon was divided into 3 fractions: labile C I (LP I-C), labile C II (LP II-C) and recalcitrant C (RP-C). Acidolytic organic carbon and residue of acidolysis was separated using two-step sulfuric acid hydrolysis. Activities of β-1,4-glucosidase (βG) and cellobiohydrolase (CBH) were measured using a spectrophotometer at 410 nm with methylumbelliferone (MUB) as substrate, whereas activity of peroxidase (PER) was at 460 nm with L-dihydroxyphenylalanine (L-DOPA) as substrate.【Result】Results show: (1) RR significantly increased the content of soil organic carbon and those of its fractions. Treatment RR (24.74 g·kg-1) was significantly higher than Treatment R (13.43 g·kg-1) and Treatment RB (20.14 g·kg-1) in soil organic carbon content in the 0~10 cm soil layer. Treatment R (43.5%) was significantly higher than Treatment RR (32.6%) and Treatment RB (36.1%) in labile index of the soil organic carbon (ratio of the fraction of labile organic C to total organic C) (P<0.05). Treatment RR and Treatment RB (67.4% and 64%) was 1.2 and 1.1 times higher than Treatment R (56.52%), respectively, in soil organic carbon recalcitrance index. Obviously, Treatment RR and Treatment RB were quite similar in this aspect (P>0.05); (2) Treatment RR and Treatment RB did not differ much in soil organic carbon content in the 10~20 cm soil layer(P>0.05), but significantly higher than R (10.8 g·kg-1). Treatment RR was the lowest in labile index and the highest in recalcitrance index. Labile index was higher in the 10~20 cm soil layer than in the 0~10 cm soil layer, while recalcitrant index was just contrary; (3) Treatment RR was higher than Treatment RB and R in activities of βG, CBH and PER. In Treatment RR, βG and CBH activities were significantly higher in the 0~10 cm soil layer than in the 10~20 cm soil layer, while in Treatment RB CBH activity was significantly higher in the 0~10 cm soil layer than in the 10~20 cm layer (P<0.05). In contrast, no significant differences were found in activity of the three enzymes between the two soil layers in Treatment R (P>0.05). (4) Correlation analysis shows that βG and CBH activities were significantly and positively related to contents of LP I-C and LP II-C, while PER activity was significantly related to content of RP-C.【Conclusion】Organic carbon content in the surface soil was significantly higher in Treatment RR than in Treatments R and RB. Contribution of RP-C to soil organic carbon was higher in Treatment RR than in Treatments R and RB, and soil enzyme activity was higher in Treatment RR than in the others. Therefore, it can be concluded that Treatment RR has some positive effects on soil organic carbon in content and stability, and hence improve soil nutrient availability and soil quality as well.

    • >Research Notes
    • Research on Dynamics of Total Nitrogen in Tai-Lake Paddy Soils of China Based on 1:50 000 Soil Database

      2019, 56(6):1514-1525. DOI: 10.11766/trxb201809180422

      Abstract (1446) HTML (964) PDF 2.86 M (1781) Comment (0) Favorites

      Abstract:Accurately assessing changes in soil total nitrogen content (STN) in farmland soil is the basis for effective field management. In this study, an area of 2.32 M hm2 of paddy soils, or 37 counties (or cities) of in the Tai-Lake Region, was delineated as study zone. The 1:50 000 high accuracy paddy soil database developed and based on the analysis of the 1 096 samples of topsoil collected during the Second National Soil Survey in 1982 and the 1 393 samples of topsoil collected during the “973” Project in 2000 in this region was used as the basis for quantifying dynamic changes in STN in the paddy soils of the region over the past 20 years. Results show that STN in the paddy soils increased by 0.21 g•kg-1 in the period from 1982 to 2000, displaying a significant accumulating trend, especially in degleyfied paddy soil, in which STN increased the most significantly or by as high as 17.0%. But in gleyfied paddy soils, it decreased by 26.2%. The dynamics of STN also varied with landform. In the low mound and hill areas it increased significantly or by 31.8%, while in the Tai-Lake plain region and polders it increased slowly up or by only 9.8%. Moreover, the dynamics of STN varied, too, with administrative zone, the mean STN of Anji, Changxing, Chuansha, Minhang, Yuhang and Chongming increased by more than 40%; while that of Wu, Qingpu, Jiashan and Danyang decreased somewhat. It is quite clear that as a whole, the soil total nitrogen in paddy soil of the Tai-Lake Region varied sharply with area, so it is imperative to reduce field fertilization, case-specifically in the light of soil subgroups, sub-regions and regional nitrogen enrichment degree so as to prevent soil nitrogen loss and water eutrophication.

    • Effect of Conversion of Upland into Paddy Field on Content of Carbon in Soil Aggregates along Soil Profile of Red Soil in Critical Red Soil Zone

      2019, 56(6):1526-1535. DOI: 10.11766/trxb201806200338

      Abstract (1441) HTML (625) PDF 512.73 K (1456) Comment (0) Favorites

      Abstract:So far little has been reported in the literature on variation of carbon distribution in soil aggregates along a soil profile of a farmland converted from upland into paddy field at the Red Soil Critical Zone Observatory (RSCZO) in Yingtan, Jiangxi. This study was oriented to investigate (i) particle size composition and distribution of soil aggregates; (ii) changes in carbon content in soil aggregates, relative to fraction in particle size; and (iii) how iron-aluminum oxides affect carbon in the soil profiles of upland peanut fields, and old and new paddy fields of red soil. Soil samples were collected by layer from bottom to top in the profiles (0~120 cm) of upland peanut fields, new paddy fields (< 30 years) and old paddy fields (> 200 years) at the RSCZO located at the Sunjia watershed, Yingtan, Jiangxi Province of China. Soil aggregates in the soil samples were were collected and fractionated, by > 250 μm, 250~53 μm, and < 53 μm, kwith the wet sieving method. Carbon contents in the soil and aggregates were analyzed, and the relationships between soil iron-aluminum oxides and carbon in the soil aggregates were also discussed. Results show that the aggregates of the fraction of 250~53 μm accounted for 41.9%~58.2% of the total.in the soil profile, in all the three types of the field. The proportion of the fraction of > 250 μm, 250~53 μm and < 53 μm varied in a trend of "low - high - low", "high low low" and "low - low - high", respectively, in all soil layers with the land use pattern changing from upland peanut field to new and old paddy field. Carbon contents in the soil and soil aggregates increased significantly after the field was converted from upland to paddy, especially after long-term paddy cultivation. The formation of amorphous iron oxide in the soil affected significantly the content of total carbon in the soil of the upland peanut field and old paddy field. The content of soil total carbon in the soil profiles of all the fields decreased rapidly at first and then leveled off with soil depth, and in deep soil layers, the fraction of aggregates < 53 μm contributed the most to the increment in total carbon in the old paddy field.

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