• Volume 53,Issue 6,2016 Table of Contents
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    • >Reviews and Comments
    • Progress and Prospect of the Study on Crop-response-to-Fertilization Function Model

      2016, 53(6):1343-1356. DOI: 10.11766/trxb201605170103

      Abstract (2625) HTML (0) PDF 1.14 M (6134) Comment (0) Favorites

      Abstract:In the past 40 years, the study and application of crop-response-to-fertilization function model has made significant progresses and has already become the main technical basis for and a branch system of the project of soil-test-based formulated fertilization. The quadratic polynomial model is the most commonly used fertilizer effect model under study and in application. This paper reviewed briefly progresses that have been made in the study on types, applicabilities, experimental designings and, parameter estimation empirical fertilizer effect models, class characteristic fertilizer effect models, non-typical recommended fertilization optimization method and combination of function methods with soil testing and so on. On such a basis, the paper points out that the prevailing fertilizer effect model in the present days has three problems, i.e. multicollinearity, heteroscedasticity and unreasonable professional hypothesis. In quadratic polynomial models strong multicollinearity exists between the one-degree term and the quadratic term, the one-degree term and its interaction effect terms, the quadratic term and its interaction effect terms, and in the square root polynomial model, exists severer multicollinearity. The serious multicollinearity causes errors in “+” or “-” signs of the model coefficient or difficulty to evaluate relationships between independent variables in contribution to crop yield. Model residual analysis shows that fitting residual error of the quadratic polynomial model displays a gradually dispersing funnel-like distribution pattern with increasing rice yield, which indicates that residual variance differs with yield level. Serious heteroscedasticity causes the least squares parameter estimation to be no longer valid, and t test and F test no longer reliable. Besides, the prevailing quadratic polynomial model has two defects in being conformable with practice, that was, linear relationship is used in the function between yield increment per kg nutrient and fertilization rate, and symmetrical relationship is in the function between yield-increasing effect of fertilization before the maximum rate and yield-reducing effect after the maximum rate, which makes it difficult to reflect the actual relationship quantitatively between field fertilization rate and crop yield in the field. The paper also analyzes causes of the problems and their diagnostic method. Therefore, it is suggested that in-depth study should be done to explore remedial measures to eliminate or relieve the impacts of the defects the multi-factor fertilizer effect model and proper conditions for its application, to develop non-structural fertilizer effect models so as to overcome the irrationality of the professional hypothesis of the empirical model, to unfold development of fertilizer effect parameter identification technologies on the basis of the large volumes of "3414" experimental data, and eventually to realize microscopic guidance using fertilizer effect models and to provide theoretical modeling basis for development of a software system for fertilization recommendation.

    • Progress of the Research on Potential Environmental Risk of Polycyclic Aromatic Hydrocarbons (PAHs) in Biochar

      2016, 53(6):1357-1370. DOI: 10.11766/trxb201606150183

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      Abstract:Biochar is a kind of highly aromatic carbonized material produced through thermal decomposition of biomass under reductive conditions (i.e. in the absence of or with a limited supply of oxygen). Biochar is found to be able to play an important role in mitigating global climate change, removing pollutants from water and soil, as well as maintaining functions of ecosystems. During the pyrolytic processes of biological materials, a certain amount of organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs), would form and remain on the surface of the biochar. Consequently, increasing application of biochar may bring about a certain risk to the environment. Current researches pay much attention to the positive effects biochar may have, while ignoring its potential hazards to the ecosystem. To assess environmental risk of the PAHs in biochar, it is necessary to determine the contents of total and bioavailable PAHs in biochar. At present, the following four methods, i.e. Soxhlet extraction, accelerated solvent extraction (ASE), ultrasonication extraction and thermal extraction, are available for determining total PAHs in biochar. However, the four methods were often used to determine semivolatile organic compounds in solid matrix (soil or sediment). Among the four methods, the Soxhlet extraction and ASE methods are the most commonly used ones, because of their higher recoveries of target compounds. However, when they are used to extract PAHs in biochar, PAHs recoveries depend highly on solvents and the biochar per se. In the case of determining bioavailable PAHs, limited information is available besides the polyoxymethylene (POM) passive sampling method. Altough PAHs in biochar are formed mainly through two pathways, i.e. low temperature pyrolysis (< 500℃) and high temperature pyrolysis (> 500℃), the formation process is still very complicated, because there are a lot of factors that affect yield and composition of PAHs in biochar, including feedstock resource, pyrolysis temperature, heating rate, holding time, etc. With the respect of feedstock, little information is available concerning relationship between content of lignin and/or cellulose and PAHs in biochar. As regards pyrolysis temperature, biochar out of low-temperature pyrolysis generally contains more low-molecule-weight/high-vapor-pressure PAHs, whereas biochar out of high-temperature pyrolysis contains more high-molecule-weight /lower-vapor-pressure PAHs. However, the relationship between temperature and PAHs yield is still controversial. Heating rate and holding time of the pyrolysis are two important factors influencing PAHs yield in biochar. Generally speaking, during the process of slow pyrolysis with long holding time, PAHs are more likely to escape into the atmosphere as gas whereas during the process of fast pyrolysis, they are more likely to get condensed and adsorbed onto the surface of biochar. The other factors that influence PAHs content in biochar include ash content and moisture content of the feedstock, and presence of oxygen during the process of pyrolysis or the post-pyrolysis cooling process. Researches demonstrate that feedstock is high in ash and moisture content plus presence of a little oxygen facilitates formation of more PAHs in biochar. To minimize environmental risk of the PAHs in biochar, it is recommended firstly that feedstock free of PAHs contamination should be used for biochar preparation, and secondly that the technology of slow pyrolysis (heating rate <100 K min-1 and pyrolysis temperature <400℃) could reduce apparent total PAHs and bioavailable PAHs concentration in biochar. However, it should be noticed that high-temperature biochar is much higher than low-temperature biochar in specific surface area and adsorption capacity, and hence in applicability to pollutant removal, moreover, the PAHs in high-temperature biochar is lower in bioavailability and therefore in environmental risk, too. Obviously, high-temperature biochar (>600℃) is a better option. In order to find a professional and standardized protocol for quantitative analysis of PAHs or other toxic organic compounds in biochar, it is essential to do more researches that should lay more emphasis on pollutant yield relative to property variability of the biochar per se. In addtion, in-depth studies should also be done on long-term impacts of biochar on ecological environment. Both laboratory researches and field experiments should work jointly to deepen our understanding of how various biological and non-biological factors influence environmental behavior of PAHs in biochar.

    • >Research Articles
    • Particle Size Composition of Erosion Sediment from Colluvial Deposits of Collapsing Hill as Affected by Rainfall Intensity and Coverage

      2016, 53(6):1371-1379. DOI: 10.11766/trxb201602220557

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      Abstract:【Objective】Collapsing hills are widely distributed in granite-covered areas of tropical and subtropical South China, characterized by being high in erosion rate, strong in explosiveness and difficult to control. Colluvial deposits, formed of materials accumulated at the foot of the collapsing wall, are an important component of a collapsing hill, and meanwhile as they are loose in texture, high in content of coarse particles and high in erodibility, they become the main source of erosion sediment in the area. The erosion of colluvial deposits has aroused widespread attention, however, the current study on colluvial deposits still has some shortages. For instance, so far nothing has been reported on characteristics of the disturbed soil of colluvial deposits and laws of the erosion thereon.【Method】Therefore, to study properties of erosion sediment from colluvial deposits, an indoor rainfall simulation experiment was carried out on slopes of colluvial deposits, 30° in gradient, different in coverage (0, 25%, 50%, 75%, 100%) and different rainfall intensity (60, 90, 120 mm h-1), SPSS18. 0 was used to analyze relationships of the characteristics of particlesize composition with coverage.【Result】Results show as follow: (1) The mean content of coarse sand was much lower, and the mean content of fine silt much higher than that in the test soil. During the process of rainfall,runoff on the slopes carried long with it soil, particles small in size first; The mean enrichment rates of fine sand, coarse silt, fine silt and clay were all higher than 1 in the sediment. (2) The content of coarse particles (gravel and coarse sand) reduced first,then rose again and the content of fine particles (fine sand, coarse powder, fine silt and clay) did not very much with increasing coverage. (3) On slopes, varying in the range of 0~25% in coverage, the content of fine particles reduced slowly, while the content of gravel and coarse sand rose gradually with the rainfall going on; on slopes 50% in coverage,the content of fine particles remained high, while the content of coarse particles stayed low throughout the rainfall event; and on slopes reaching 75% in coverage, the content of soil particles various in size fluctuated sharply during the course of a rainfall event, and in this case, collapse of the slopes occurred readily. (4) And the mean weight diameter (MWD) of the erosion sediment decreased first and then increased with increasing coverage. 【Conclusion】MWD of sediment particles was found to be significantly related to coverage of the slope, rather than rainfall intensity. When the coverageof the slopewas around 50%, the effect of sediment reducing was better. Therefore, in the process of prevention of erosion, we should pay attention to the control of the coverage on slopes.

    • Soil Profile Weathering Feature of Eroded Weathering Granite Slope at Different Sections

      2016, 53(6):1380-1388. DOI: 10.11766/trxb201603240644

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      Abstract:【Objective】Strong soil erosion affects profoundly soil development on slopes. On slopes the same in parent material, but different in erosion intensity, soil varies sharply in weathering development degree. In the granite hill and mountain areas of Southeast China, the soil developed on weathering residual slopes suffers severe water erosion, and differs distinctly from other zonal soils in soil weathering development profile. 【Method】 This study in oriented to characterize weathering development of soil profiles at different landform positions of an eroded weathering granite slope. A typical weathering granite slope was selected in Shengzhou, Zhejiang province for monitoring of soil erosion with the help of the Shengzhou Soil and Water Conservation Monitoring Station. On the slope where the station sits, three typical soil profiles (140 cm in depth) were selected at sites different in erosion intensity along the slope from top to bottom, and soil samples were collected 20 cm apart from bottom to top in each soil profile. So a total of 21 soil samples were gathered for analysis of basic physicochemical properties and chemical total contents in various soil layers. On such a basis, calculation was done of main chemical weathering coefficients of the soil layers and total weathering intensity of the soil profiles, separately. As the zonal soil of the studied is red soil, of which the main chemical weathering processes are enrichment of iron and aluminum and leaching of dissolved salts. Therefore, the chemical weathering indices selected in this study were dominantly those that may reflect enrichment of iron and aluminum and leaching of dissolved salts, they are ① Al2O3/SiO2, ② Fe2O3/SiO2 ③ R2O3/SiO2, ④ Al2O3/(RO+R2O) and ⑤ R2O3/(RO+R2O). In order to analyze weathering intensity of each soil layer relative to the bottom layer in the same soil profile and facilitate comparison between the soil layers in weathering intensity, further calculation was performed of relative weathering intensity (I relative) of each soil layer relative to the bottom one. 【Result】The following conclusions were drawn from the analysis and calculation:(1)The soil of the profile at the site of severely eroded weathering residual granite slope is on the whole rather slow in soil developing and maturing process, and differs sharply from the typical zonal soil in further development, and severe erosion greatly hinders maturing processes of the soil; and the severer the erosion, the poorer the soil developed;(2)The soil profile as a whole is not very high in weathering intensity; the variation in weathering intensity between soil layers in the soil profile is very gentle; the peak of weathering intensity appears in the 40~60cm soil layer, instead of the surface soil layer; the processes of desilication and aluminum enrichment weaken with profile depth and intensifying weathering degree; and the decreasing trends of Al2O3/SiO2 ,Fe2O3/SiO2 and R2O3/SiO2 are quite obvious in all the three soil profiles, which demonstrate that soil weathering degree lowers with profile depth;(3)Chemical stratification of the soil profiles is not distinct, with all the weathering indices forming a boundary layer at about 60cm in depth; the layers above it are obviously affected by water erosion and those below mainly inherit the properties of the residual soil parent material;(4)In terms of weathering intensity, the three soil profiles display an order of bottom profile < mid profile < top profile, which is just the reverse of that in terms of erosion intensity; (5)Weathering degree is significantly and positively related to the contents of organic matter and clay, and also to physical properties of the soil under erosion; However, the influence of organic matter content is greater than that of clay content in the soil in deposition environment. 【Conclusion】Affected by erosion, the illuvial horizon of soil profile does not develop on slopes, the false illuvial horizon is a certain weathering degree weathering residual layer, but is not formed by eluviations, which leads to the division of soil layer developed from hill and mountain areas differs from conventional method.

    • Soil Erosion Resistance of Sloping Farmland under Soybean Cultivation Relative to Growth Stage

      2016, 53(6):1389-1398. DOI: 10.11766/trxb201603220030

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      Abstract:【Objective】Soil erosion resistance is one of the main factors affecting development of soil erosion. As the Loess Plateau is one of the most severe soil erosion areas in China, it is especially important to characterize the soil erosion resistance of the region to management and control of soil erosion on the Loess Plateau. Soybean, high in drought resistance, is one of the major crops commonly grown on the Loess Plateau, and the one that grows in the season when heavy rain showers occur frequently, and consequently soil erosion tends to take place in the region. Therefore, a field experiment was conducted to determine characteristics of the erosion resistance of the soil and their relationships with soybean root system relative to growth stage of soybean.【Method】Soil anti-scourability and anti-erodibility are two important parameters to evaluate soil resistance. This study determined the soil anti-erosion ability characteristics based on soil anti-scourability and anti-erodibility. Based on the determination of the two indices, soil anti-scourability and anti-erodibility, soil erosion resistance was characterized. As soil anti-scourability index and soil disintegration rate can well reflect characteristics of soil anti-scourability and anti-erodibility, these two parameters were selected to evaluate soil anti-scourability and anti-erodibility.Soil anti-scourability index refers to the time it takes for rain water to wash off a gram of soil (min g-1), and soil disintegration rate to the amount of soil disintegrated within a set unit of time (g min-1). The effect of soybean roots enhancing soil erosion resistance is evaluated by measuring how much soil anti-scourability and soil anti-erodibility is enhanced by the root system of soybean at different growth stages of the crop. 【Result】 Results show that soil anti-scourability and anti-erodibility varied with the crop growing, showing a similar trend.Soil anti-scourability index increased significantly from the seedling stage to the pod bearing stage of the crop, peaked at the initial grain forming stage, and then decreased somewhat from the initial grain forming stage till the grain filling stage, while soil disintegration rate decreased significantly from the seedling stage to the pod bearing stage, dropped to the bottom at the initial grain forming stage and then rose a little bit from the initial grain forming stage till the grain filling stage. With the crop growing, soil erosion resistance displayed a decreasing order of initial graining forming stage > grain filling stage>pod bearing stage> blooming stage> branching stage> seedling stage. At the seedling and branching stages, soil erosion resistance was the highest in the 0~5cm layer and the lowest in the 10~20 cm layer, but during the period from the blooming stage till the grain filling stage, it was the highest in the 5~10 cm layer and the lowest in the 10~20 cm layer was worst from blooming stage to seed-filling stage. However, soybean roots could significantly strengthen soil erosion resistance. The effect was the lowest at the seedling stage and the highest at the initial grain forming stage. Soil erosion resistance was significantly and positively related to root weight density, root volume, root surface area and total root length. Therefore, soybean root system plays a key role in soil and water conservation and prevention of occurrence of soil erosion. Therefore, root weight density, root volume, root surface area and total root length can also be used as the parameters to evaluate soil erosion resistance.【Conclusion】Soil erosion resistance varies with the crop growing and depth in soil profile. It is quite low at the seedling and branching stages and in the 0~5 cm soil layer. It is, therefore, recommended that measures be taken to strengthen soil erosion resistance in the early growth period of the crop. Meanwhile, some rational agronomic management measures, like mulching, use of cultivars that tend to have developed root systems, could also be adopted to improve soil erosion resistance of soybean fields.

    • Extraction and Modeling of Regional Soil Salinization Based on Data from GF-1 Satellite

      2016, 53(6):1399-1409. DOI: 10.11766/trxb201601270650

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      Abstract:【Objective】Soil salinization, being one of the main causes of land degradation in arid and semi-arid regions, poses a great threat to sustainable development of the local social economy and ecological system. 【Method】How to extract the information of spatial distribution of soil salinization is the foundation for management of soil salinization. Therefore, the Weigan-Kuqa Oasis, an area rather fragile in ecology, was selected as an object in this study, using the GF-1 satellite multispectral images of the date of July 19, 2014 as the main data source. A total of 16 spectral indices i.e. Normalized difference vegetation index(NDVI), soil adjusted vegetation index (SAVI), normalized differential salinity index (NDSI), salinity index (SI-T), brightness index (BI), salinity index (SI), salinity index 1 (SI1), salinity index 2 (SI2), salinity index 3 (SI3), salinity index (S1), salinity index (S2), salinity index (S3), salinity index (S5), salinity index (S6), intensity index 1 (Int1), intensity index 2 (Int2), and four bands, i.e. band 1 (B1), band 2 (B2), band 3 (B3) and band 4 (B4), were chosen for analysis. The images in pretreatment were computed by band in line with the spectral index formulas with the aid of software ENVI4.8. Hence, gray scale maps of different spectral indices were derived and pixel values of the 36 sampling points corresponding to the gray scale maps were extracted. The data of electrical conductivities in the surface soil layers (0~10 cm) of those sampling sites during 22~28 July 2014 were also collected for analysis of Pearson correlation with the pixel values using software SPSS 19.0. Thus sensitivities of different spectral indices to the data of soil salinization were figured out. PLSR models were built and validated for relationships of the mathematical formulas for five different electrical conductivities (i.e. measured conductivity, reciprocal of measured conductivity, logarithm of measured conductivity, MSR of measured conductivity and reciprocal of the logarithm of measured conductivity) with spectral indices. Measured conductivities of 24 samples were used for modeling and the remaining 12 samples for validation with the aid of the Unscrambler X10.3 software. 【Result】Results show: 1) the measured surface soil conductivities are closely related to spectral indices, and moderately to SAVI, NDVI, NDSI, SI, SI1, S5, B3 and B4, with all correlations being significant at the 0.01 level; 2) based on the GF-1 satellite images PLSR was used for modeling of surface soil salinization in the Weigan - Kuqa Oasis. The model based on reciprocal of electrical conductivity is better than all the others with R2 =0.69 and RMSE=0.58 dS m-1. For the validation model R2 is 0.78 and RMSE 0.53 dS m-1. In the images of satellite vertical projection salinized and non salinized patches in the land cover can be clearly distiquished from each other, with little confusing or mistaking information. Characteristic texture of salinization relative to degree is distinct, showing a clear layered structure, easy to distinquish and making the visual interpretation of the images more consistent with the actual degree of soil salinization. Consequently the effect of information extraction of soil salinization is quite good and high in precision; 3) this study made full use of the information contained in GF-1 images, thus improving precision of the extraction of soil salinization information from GF-1 images. Non-salinized soil and slightly salinized soil in the oasis accounts for 42.88% and 17.16%, respectively, of total in area. Soil salinization is quite mild in the middle by east and southeast of the oasis, which suggests that the oasis may expand towards that direction in future. Moderately salinized soil, severely salinized soil and salinized soil in the oasis accounts for 29.51%, 8.57% and 1.88%, respectively, of the total in area. The severely salinized soil is distributed closely on the north/west and southwest of the oasis and has already posed a serious threat to healthy development of the oasis economy and calls urgently for management. 【Conclusion】The study on use of GF-1 images to evaluate soil salinization may provide a scientific basis for prediction of salinization in future and assessment of the current situation and for the government in decision-making for management of soil salinization.

    • Characteristics of Salinization of Deserted Farmland in Hetao Plain, China

      2016, 53(6):1410-1420. DOI: 10.11766/trxb201512100605

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      Abstract:【Objective】To explore characteristics of the salinization of deserted farmlands in the Hetao Plain. 【Method】In this study soil samples were collected from the farmlands and analyzed with the classical statistics and principal component analysis methods for total salt content, pH, anion and cation composition, and distribution of alkalization degree.【Result】Results show that the abandoned farmlands in the Hetao plain were mild to severe in salinization, with soil salt content, pH and alkalization degree varying between 2.80 and 6.69 g kg-1, 9.20 and 9.69, and 10.97% and 33.33%, respectively and distributed similarly along the soil profile, that is, accumulating in the surface and bottom. The salt content decreased with soil depth in the 0~60 cm soil layer, increased with soil depth in the 60~120 cm soil layer. The cations in the soil profile were dominated with Na+ and K+ while the anions were with SO42−. All the salinization indices, except soil pH, showed extremely strong spatial variability. Contents of SO42−, Ca2+,Mg2+ and total salt varied sharply from soil layer to soil layer.The correlations of Cl-with K+and Na+declined in significance with soil depth. Soil pH and alkalization degree were significantly correlated with the content of CO32−. Principal component analysis shows that the total salt and SO42−could be used as diagnostic factors of soil salinization; while CO32−, HCO3 and pH as diagnostic factors of soil alkalization in this research area, explaining 88.74% of the total variance.【Conclusion】Therefore, it is quite obvious that the deserted farmlands in the Hetao Plain are severe in salinization degree, and it is essential to lower soil salinity or alkalinity, regulate soil ion composition and improve soil structure during the soil amelioration process. It is expected that this study may provide certain theoretical basis for ameliorating and utilizing salinized soil, and improving regional ecological environment of deserted farmlands in the Hetao Plain.

    • Evapotranspiration of Farmland on Loess Tableland and Its Major Influencing Factors

      2016, 53(6):1421-1432. DOI: 10.11766/trxb201603140625

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      Abstract:【Objective】 Evapotranspiration (ET) is a major part of water balance and energy balance, and is the main pathway of water consumption in farmland ecosystems. In Xianyang District of Shaanxi, the annual evapotranspiration accounts for about 90% of the annual precipitation. There are quite a few methods for evaluating or measuring evapotranspiration, such as eddy covariance, Bowen ratio and microclimate. Currently the eddy covariance method is more widely used than the other two because it can be used to measure evapotranspiration continuously on an ecosystem scale, and to measure simultaneously various meteorological factors and various components of energy, as well, in most of the eddy-covariance-related systems, which is conducive to analysis of relationships of various impact factors with components of energy balance. The present study is oriented to explore basic laws of water movement in soils different in land use, but under a similar plant growth environment and also to find a scientific method for estimating water consumption in soil. 【Method】In order to explore laws of diurnal dynamics of evapotranspiration and its influencing factors in farmlands on loess tableland, with the help of some soil water and conventional micrometeorological observatory systems, the eddy covariance method was used to analyze characteristics of the evapotranspiration of the crops (winter wheat and spring corn) in the farmland studied during the growing season (from April to October) of 2013 and their influencing factors. 【Result】Closure analysis of energy balance in the studied area using the eddy covariance method shows that the regression line was 0.54 in gradient and the determination coefficient R2 0.80, both being in the ranges reported in most papers in the literature. Soil moisture is an important factor affecting evapotranspiration, and precipitation is another. After a rainfall event, daily evapotranspiration would increase to a certain extent. Soil water content in the 0~100 cm soil layer varied drastically with CV being quite high, while crop roots were distributed mainly in the 0 ~ 80 cm soil layer, so the soil water in the 0~100 cm soil layer was closely involved in evaporation process. Cumulative evapotranspiration was higher in a sunny day than in a cloudy day, while evapotranspiration started later in a cloudy day than in a sunny day. The daily evapotranspiration was 4.5 mm d-1 on average in the sunny day and 3.8 mm d-1 in a cloudy day, with a difference being 0.7 mm d-1. Moreover, evapotranspiration in a cloudy day was more susceptible to the disturbance of meteorological factors. Net radiation was the main factor affecting evapotranspiration rate, regardless of weather conditions, and the two varied in a similar trend, but the latter lagged somewhat behind the former temporally in variation because it takes some time for energy to flow. The regression equation for analysis of relationships between evapotranspiration rate and its influencing factors in a sunny day does like: ET = 0.833Rn + 0.513Ta -0.333v-0.486; and that in a cloudy day does like: ET = 0.858Rn + 0.219VPD-0.001. Evapotranspiration also varied drastically in process and intensity as affected by soil water regime. 【Conclusion】The influence of weather on evapotranspiration is also obvious and varies sharply with weather conditions. Cumulative evapotranspiration is higher in a sunny day than in a cloudy day, while evapotranspiration starts later in a cloudy day than in a sunny day. And the evapotranspiration under a cloudy weather was more susceptible to the disturbance of meteorological factors. Net radiation is the main factor influencing evapotranspiration rate under all weather conditions. In fields under water stress, the daily evapotranspiration is relatively low because the crops try to maintain their physiological and biochemical processes, thus forming an extensive “evapotranspiration plateau”, while in fields sufficient in soil water, the daily evapotranspiration is high, and the “evapotranspiration plateau” lasts short in duration, and evapotranspiration rate stays high for a long time.

    • Profile Distribution of Soil Inorganic and Organic Carbon in Farmland in Arid and Semi-Arid Areas of China

      2016, 53(6):1433-1443. DOI: 10.11766/trxb201603140654

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      Abstract:【Objective】The objective of this study was to investigate distribution of soil inorganic (SIC) and soil organic carbon (SOC) in farmland in the arid and semi-arid areas of China, and analyze factors influencing SIC and SOC stocks. 【Method】Data of SOC and SIC contents in farmland were collected from some articles published after 2000 and some unpublished sources, involving 178 soil profiles(0~100 cm in depth) located in natural farmlands and long-term field stations. Linear regression analyses of the data were performed to evaluate relationships of SIC and SOC with soil physical properties (i.e. pH, and bulk density) with Sigmaplot (version 12.5) and ArcMAP (version 10.1). 【Result】Results show that SOC content decreased with soil depth. However, vertical distribution of SIC content varied from field to field. In general, SIC content increased with soil depth in natural farmlands, but decreased in the fields of the long-term experiment stations, which indicates that climate condition (i.e. annual precipitation) and soil properties might be the factors influencing vertical distribution of SIC. On average, the SOC and SIC of these soil profiles was 8.33 and 15.83 kg m-2, respectively, in density. SOC was mainly accumulated in topsoil (0~30 cm), whereas SIC in subsoil (30~100 cm). The SOC in topsoil accounted for 45% of the total in profile 100 cm in depth, whereas SIC in subsoil accounted for 71% of the total. Soil bulk density and soil pH were important factors influencing SOC and SIC stocks. Significantly negative correlations of SOC density with soil pH (R2 = 0.61, p< 0.01) and soil bulk density (R2 = 0.64, p< 0.01) were found in this study, while profoundly positive relationships of SIC density with soil pH (R2 = 0.56, p< 0.01) and soil bulk density (R2 = 0.63, p< 0.01) were.【Conclusion】 The study on profile distribution and total SOC and SICstocks in farmlands in the arid and semi-arid areas of China may provide some basic data and theoretical support to carbon budgeting in inland terrestrial ecosystems.

    • Adsorption Dynamics and Distribution Characteristics of Humic Acid on Surface of Biotite

      2016, 53(6):1444-1451. DOI: 10.11766/trxb201605190254

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      Abstract:【Objective】 An in-situ atomic force microscopy (ScanAsyst) was used to study adsorption dynamic and morphological variation of humic acid on the surface of K-bearing biotite. 【Method】 Humic acid is a principal component of humic substances, which are the major organic constituents of soil, peat, coal, eutrophied lakes, and ocean water. Humic acid solutions, the same in pH (6.0), but different in concentration (0 mg L-1, 100 mg L-1 and 1 000 mg L-1) were prepared out of dried humic acid solid. The mineral sheet used in the in-situ observation was biotite, a kind of phyllosilicate mineral belonging in the mica group (2:1 type structure), commonly found in soil. The chemical formula of biotite is K(Mg2.46Fe0.45Ti0.09)[AlSi3O10](OH) 2

    • Possibility of Axenically Cultured Cyanobacteria Forming Humic Substances

      2016, 53(6):1452-1463. DOI: 10.11766/trxb201605080084

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      Abstract:【Objective】Cyanobacteria are the oldest photoautotrophic organisms on the earth. As they lived commonly in the ancestral protohydrosphere and entered into the geosphere with geological changes, they got profoundly involved in the formation of primitive soil humic substances (HS). Since contain large volumes of protein, polysaccharide and even some humic-like acid substances in their cells, extra- and intra-cellular metabolites, is it possible for cyanobacteria cells to form HS spontaneously? If the formation process needs catalysis of some microorganisms, what are the differences between different groups of microorganisms in role in the process? These scientific problems need to be solved. 【Method】 In view of the above-mentioned scientific problems, this research adopted the source control and shake-flask liquid axenic culture method to get axenically cultured samples of Anabaena flos-aquae,a representative species of cyanobacteria, in different growth stage and products of Anabaena flos-aquae used as the only substrate and treated with different microbes. The products were analyzed for structural characteristics, using the method of element composition and fourier transform infrared spectroscopy (FTIR), with a view to exploring possibility of cyanobacteria spontaneously forming HS or acting as substrate in HS formation and hence to make up and specifying the role of cyanobacteria in the origination and formation of soil HS. 【Result】The following findings were obtained. Under the experimental conditions, Anabaena flos-aquae had a long life cycle and remained quite constant in carbon content during their growing period. However, during the logarithmic phase, the carbon content in the thallus was relatively high, while in the extracellular metabolites it rose steadily but remained much lower than that in the thallus. None of the FTIR spectra of the cyanobacteria samples showed any peaks characteristic of the carboxyl C=O bonds at 1 720 cm-1, instead, the spectra intensified somewhat at 1 650 cm-1 and 1 530 cm-1. Relative to soil HS, cyanobacteria thallus were rich in organic nitrogen, but poor in organic carbon and high in protein and components of polysaccharide. The extracellular metabolites of cyanobacteria contained a large amount of hydroxy and carboxyl functional groups. The ratio of 2 926/1 650 revealed that during the logarithmic period and the late decline phase, Anabaena flos-aquae thallus contained a high amount of aromatic substances, which were quite approximate to soil fulvic acid (FA), but lower than soil humic acid (HA) in complexity. Relative to soil humus, Anabaena flos-aquae thallus were high in both H/C ratio and (O+S)/C ratio, which means that they were low in condensation degree and high in oxidation degree. Although it was found that the possibility of cyanobacteria spontaneously forming HS was very low, it could not be ruled out that under extreme conditions (abnormal temperature or pressure) cyanobacteria might get combined with other polymers, forming HS, or form HS by the action of microbes as during their long life cycle some organic substances complex in structure may be produced. Under aerobic conditions, Anabaena flos-aquae was used as the only carbon source and treated with Bacillus megaterium, Sreptomyces sp. and Trichoderma viride and the resultant thallus mixture contained more aromatic substances, but the peak at 1 530 cm-1 disappeared in the FTIR spectra of the thallus mixtures, which indicates that part of the C=C bonds and amino acid-like materials in the mixture were decomposed by microorganisms. The thallus mixture was lower in aromaticity, higher in oxidation degree and simpler in structure, which indicates that once the cyanobacteria culture was inoculated with aerobic microbes, the microbes first made use of the sugar components in the culture for cell proliferation first, and then began to play their limited role in decomposing cyanobacteria cells. The Van-Krevelen plot shows that the thallus mixture formed after the treatment with aerobic microbes differed more sharply from soil HS in structure. By comparing how much they differed, it was learnt that actinomyces and bacteria were more capable of decomposing cyanobacteria, thus simplifying the thallus mixture in structure, while fungi made the thallus mixture of cyanobacteria closer to soil FA and more complicated in the structure.【Conclusion】In a word, under the lab conditions, the thallus mixture formed by cyanobacteria per se and/or using cyanobacteria as the only substrate does differ from soil HS, but the thallus mixture, thanks to its composition and structure, may serve as substrate for HS formation. The findings may provide a certain scientific basis for the research on formation and origin of soil HS.

    • Differences in Yield Response and N Use Efficiency of Maize Crops in Different Ecological Zones of Jilin Province

      2016, 53(6):1464-1475. DOI: 10.11766/trxb201603230019

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      Abstract:【Objective】Jilin Province is one of the leading maize production regions in China, and could be divided into three ecological zones, i.e. Central semi-humid plain area (CSPA), Eastern humid mountainous area (EHMA) and Western semi-arid plain area (WSPA), based on their significant differences in environment including topography, landform, climate condition and vegetation. Interestingly, the maize crops growing in these eco-zones differ in yield, yield response to fertilization and use efficiency of N fertilizer. But how it comes about is still not well understood. 【Method】Hence, a field experiment, coded as “3414”, was conducted with plots distributed in all the eco-zones of Jilin Province as a part of the national soil-test-based fertilization recommendation program during the years of 2005-2013. The field experiment was designed to have two treatments, i.e. Treatment–N (No N fertilizer applied) and Treatment +N (N fertilizer applied as recommended).The data of the two treatments were collected for analysis of yield response to fertilization and use efficiencies of N fertilizer of the crop relative to eco-zone, and their influencing factors. 【Result】Results show that the crop varied sharply in yield with the eco-zone, being the highest in the CSPA, medium in the EHMA, and the lowest in the WSPA. On average, the maize yield of Treatments –N was 8.1 t hm-2 in the CSPA (ranging from 3.1 to 13.5 t hm-2), 7.3 t hm-2 in the EHMA (ranging from 2.4 to 12.7 t hm-2) and 7.2 t hm-2 in the WSPA (ranging from 3.7 to 11.7 t hm-2); while that of Treatments +N was 10.5 t hm-2 (ranging from 5.4 to 15.8 t hm-2), 9.8 t hm-2 (ranging from 5.3 to 16.9 t hm-2) and 9.4 t hm-2 (ranging from 4.3 to 14.9 t hm-2) in the three ecological zones, respectively. Not only was maize yield significantly affected by ecological zone, yield response of the crop to N fertilizer was too. The highest maize yield responses to N fertilizer were observed in the EHMA, being 2.44 t hm-2 and 38.4%, on average, in absolute and relative yield increase, respectively. Correspondingly, the absolute and relative yield increase was 2.40 t hm-2 and 34.3%, respectively, in the CSPA and 2.21 t hm-2 and 33.4%, respectively, in the WSPA. Under the present maize production condition, N use efficiency was significantly higher in the EHMA than in the others. On average, agronomic efficiency (AE), partial factor productivity (PFP), and fertilizer contribution rate (FCR) of N fertilizer was 16.6 kg kg-1, 65.9 kg kg-1 and 25.0%, respectively, in the EHMA13.6 kg kg-1, 60.2 kg kg-1 and 22.8%, respectively, in the CSPA and 13.6 kg kg-1, 58.2 kg kg-1 and 23.1%, respectively, in the WSPA. With the maize yield in Treatments-N rising, Treatments +N showed similar rising trends in yield, but declining ones in FCR in all the three eco-zones, but more significantly in the WSPA than in the others. The relationships fit the linear correlation and logarithmic regression models, respectively. The variability of maize yield of treatment +N and FCR with the yield of treatment –N were relatively higher in the WSPA, compared with those in the EHMA and CSPA. 【Conclusion】In conclusion, N fertilizer for maize production in Jilin Province should be allocated and applied appropriately in the light of regional environmental conditions and characteristics of the crop responding to N fertilization. It is suggested that the current N application rate be reduced properly in line with the demand of the crop for N in the CSPA, while it be increased slightly in combination with effective cultivation practices in the EHMA, aiming to counter the yield limiting factors, such as insufficient light and low temperature, and in the WSPA, the technology of efficient and water saving irrigation be widely extrapolated in addition to soil fertility building to bring the coupling effects of water and nitrogen into full play and thereby to achieve high crop yield and high N efficiency.

    • Interactive Effects of Nitrogen and Sulfur on Flag Leaf Senescence, Yield and Nitrogen Use Efficiency of Winter Wheat

      2016, 53(6):1476-1488. DOI: 10.11766/trxb201602220031

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      Abstract:【Objective】Nitrogen (N) and sulfur (S) are nutrient elements essential to winter wheat in growth and development. The purpose of this article was to determine the effects of nitrogen and sulfur and their interaction on flag leaf senescence, photosynthetic rate after anthesis, accumulation and distribution of dry matter, grain yield and nitrogen use efficiency (NUE) of winter wheat. 【Method】A field experiment, designed to have two cultivars (Yannong 19 and Wennong 6) of wheat, three levels of N application rate, that is 0 (N0), 120 (N120) and 240 kg N hm-2 (N240) and four levels of S application rate, that is 0 (S0), 20 (S20), 40 (S40) and 60 kg S hm-2 (S60), was carried out. 【Result】Results show that Wennong 6 was higher than Yannong 19 in all the four following indices, that is, superoxide dismutase (SOD) activity in flag leaf, photosynthetic rate (Pn) in flag leaf, yield, and NUE. Application of an appropriate rate of S in addition to the application of a certain amount of nitrogen significantly increased the activity of SOD, the concentration of soluble protein, Pn and dry matter accumulation in flag leaf after anthesis, and hence nitrogen accumulation in the shoot and grain yield in both cultivars of wheat. In the plots applied with 120 kg hm-2 of N and over 40 kg hm-2 of S or with 240 kg hm-2 of N and over 20 kg hm-2 of S, nitrogen accumulation in the shoot kept on rising, but no more positive effects on antioxidant ability and photosynthetic assimilation capacity of the flag leaf and grain yield were observed in Wennong 6, while SOD activity, soluble protein concentration and Pn in the flag leaf, nitrogen accumulation in the shoot and grain yield all declined in Yannong19. 【Conclusion】In the plots the same in N application rate, NUE of the two cultivars generally decreased with increasing sulfur rate. In the plots where soil available sulfur in the 0~20 cm soil layer was in the range of 38.9~42.1 mg kg-1, application of an appropriate amount of N and S could delay senescence of the flag leaves was delayed, thus increasing photosynthetic assimilation capacity of the flag leaf and grain yield in both wheat varieties, but the two varieties differed in response to application of relatively high rates of N and S. The one, higher in NUE, still performed quite well in photosynthetic assimilation and yield, while the one, lower in NUE, was not so good in adaptability to a high application rate of N or S and tended to start senescence earlier at the late stage, thus affecting its yield and NUE.

    • Spatial Distribution of Micronutrients in Farmland Soils in the Mid-Reaches of the Yangtze River

      2016, 53(6):1489-1496. DOI: 10.11766/trxb201604090017

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      Abstract:【Objective】 The mid-reaches of the Yangtze River Valley is an important agricultural zone of China. The region is very high in multi-cropping index and dominated with a cropping rotation system, i.e. rotation of paddy/upland or rice/rapeseed. Long-term application of a large amount of chemical fertilizers in that system has resulted in imbalance of soil micronutrients. 【Method】 To better understand nutrient status of the soil in the region, the five micronutrient elements (Fe, Mn, Cu, Zn and B) in the soil were cited as objects in the study and a total of 41 943 soil samples were collected from Hubei, Hunan and Jiangxi Provinces for analysis of contents of the five soil micronutrient elements and spatial distributions of the elements for plotting a farmland soil micronutrient element distribution map of the region, with the aid of the geostatistic function of ArcGIS. 【Result】 The statistical results show that the soil available Fe, Mn, Cu, Zn and B contents averaged 88.0, 27.2, 3.05, 1.71 and 0.41 mg kg-1, respectively, with coefficient variation (CV) lingering in the range from 63.1% to 112.2%, or at the medium or strong level. Among the five elements, B was the highest in variability. Distributions of the elements could be characterized by peaks that tended toward the right and to be medium or strong in variability, which was attributed to the joint effects of natural and human factors. Results of the semivariogram analysis via GS+ 9.0 show that the distributions of the nutrient elements appeared all to be in lognormal pattern, and the optimum theoretical model for all the five, except B, was the exponential model and that for B was the spherical model. The nugget and sill values in the model represented stochastic and structural deviations, respectively, and the mean nugget/sill ratio varied in the range of 50.1%~66.9%, indicating medium in spatial autocorrelation (25%~75%), and the variations of the micronutrient elements were attributed mainly to stochastic deviations. The spatial autocorrelation varied in the range from 99 km for Mn to 411 km for Zn, and disappeared when it went out of the range. Spatial distribution of the micronutrient elements could be visualized with the Kriging method, and properties, like content, of soil nutrients be assigned to evaluation units for farmland soils in the mid-reaches of the Yangtze region. Spatial distribution of soil micronutrient contents did not show any obvious tendency, but differed sharply between sub-regions. Fe and Mn contents were relatively low in the Jianghan Plain, Fe content relatively high in the center and south of Jiangxi, Mn content relatively high in the east and north of Hubei, Zn relatively low in Hunan, and Cu and B contents uneven in distribution. Soil micronutrient contents were sorted into five levels from extremely deficient to extremely rich according to the standard of the Second National Soil Survey (SNSS). Compared with the data of the SNSS, all the five soil micronutrients improved somewhat in content, especially Fe, Mn and Cu. Statistics by evaluation unit shows that the areas with soil Fe, Mn and Cu contents being sorted as rich or extremely rich were the highest in proportion, and the areas with Zn and B contents being sorted as moderate and rich were the highest. The areas deficient in soil available Fe, Mn and Cu accounted for merely 0.1%, 2.2% and 0.1%, respectively, and the areas deficient in Zn and B did for 30.8% and 17.7%, respectively. On the other hand, when the contents of the soil micronutrients were too high, the risk of metal poisoning would rise. In this study, effects of land use, soil type and parent material were also analyzed on micronutrient contents. Fe content was obviously higher in paddy soil than in upland soil, while contents of the other soil micronutrients was not much affected by land use. Among the soils derived from different parent materials, the soil derived from weathered crystalline rocks was the highest in Fe content (106.0 mg kg-1), while the soil derived from river and lake alluvial deposits the lowest (74.7 mg kg-1); the soil derived from weathered crystalline rocks was also the highest in Fe content (25.9 mg kg-1; Cu, Zn and B contents in soils derived from different parent materials varied in the range of 3.03~3.11, 1.70~1.86 and 0.36~0.45 mg kg-1, respectively. 【Conclusion】 With the contribution of soil micronutrients to agricultural production becoming more and more prominent, it is essential to regionalize the management of farmlands in the light of the spatial distribution of soil micronutrients, which will surely be conducive to scientific application of macroelements fertilizers.

    • Effects of Interplanting of Atractylodes lancea in Monocultured Peanut Fields on Soil Nematode Community

      2016, 53(6):1497-1505. DOI: 10.11766/trxb201603020025

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      Abstract:【Objective】In this study, responses of soil nematodes community in composition and diversity to interplanting of A. lancea in monocultured peanut soil were explored and mechanisms of the effects analyzed.【Method】Soil samples were collected from a 10-year monocultured peanut field for a pot experiment, which was designed to have two treatments, i.e. monocropping of peanut and interplnating of A. lancea with peanut. At the maturing stage of peanut, population of nematodes in rhizosphere soils of the peanut and A. lancea was measured, separately, and composition and diversity of the nematode communities were analyzed.【Result】Results show that in the treatment of interplanting, the peanut significantly increased in plant height, main root length, straw yield and pod yield and the nematodes changed in density, diversity and community structure. Interplanting significantly decreased the population of nematodes in the rhizosphere soils of both peanut and A. lancea, especially the number of plant-parasitic nematodes, which used to be the dominant group. Interplanting significantly enhanced the relative abundance of bacterivores, fungivores, and predators/omnivores, but significantly inhibited plant-parasites in the rhizosphere soils of peanut. Analysis of nematode ecological indices shows that the interplanting treatment was more stable in soil ecosystem, and it raised Shannon-Wiener index (H') and evenness index (J), and lowered dominance index (λ) of the nematodes in the rhizosphere soil of peanut, while, increasing evenness index (J) and altering little diversity index of the nematodes in rhizosphere soil of A. lancea. Interplanting also significantly increased Wasilewska index (WI) and maturity index (MI) of the nematodes in the rhizosphere soil of peanut, while reducing plant parasite index (PPI) of the nematodes in the rhizosphere soil of peanut and affecting little Nematode channel ratio (NCR) of the rhizosphere soil. 【Conclusion】In conclusion, the study has found that interplanting of A. lancea with peanut can increase diversity of the nematodes community, and improve its structure of the nematodes in peanut fields under monoculture, and further on, strengthen ecological function of beneficial nematode and mitigate the obstacle for monocropping of peanut.

    • Effect of Grazing on Soil Nematode in Alpine Meadow on East Edge of the Tibetan Plateau and Its Mechanism

      2016, 53(6):1506-1516. DOI: 10.11766/trxb201512190508

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      Abstract:【Objective】The Tibetan Plateau has a unique function in physical environment and ecosystem because of its unique geographical features. Grazing is the main practice of management of grassland ecosystems and plays a crucial role in maintaining biodiversity and ecological processes. So volumes of researches have been reported on plant communities and soil physicochemical properties of the grasslands in the Tibetan Plateau, however, little has on the impacts of grazing on diversity of soil nematodes in this alpine regions, although soil nematodes play an important role in process of the ecosystem. The unique properties of the alpine grassland mean that grazing may have impacts distinct from what the other terrestrial ecosystems have on soil nematode communities. It is, therefore, critical to do more researches on impacts of grazing on population and biodiversity of the soil nematode communities in this region and how grazing affects soil nematode communities, through altering plant communities or soil physicochemical properties.【Method】In this study effects of grazing on soil nematode communities, plant communities and soil physicochemical properties, relative to degree of grazing (light, Moderate and heavy) were explored. Effects of timing of sampling and grazing management and their joint effects on these indices were analyzed via repeated measurements and ANOVA. Changes in biomass of the nematode communities and the plant communities and soil physicochemical properties were observed and the data gathered were analyzed to explore relative importance of alternative pathways of the effect of grassing on nematode communities with the structural equation modeling (SEM) method.【Result】The effects of grazing on nematode communities, plant communities and soil physicochemical properties were related to degree of grazing, time of sampling and their interactions. Population of bacterivores nematodes, biomass of plant roots, biomass of plant litter, soil moisture content and soil organic carbon content were all the highest in grasslands lightly grazed (p<0.05); biomass of ruderal weeds was the highest grasslands moderately grazed; and population of omnivorous nematodes was the lowest in grasslands heavily grazed (p<0.05). Soil nematode communities was significantly related to plant communities and soil physicochemical characteristics (p<0.05). SEM analysis shows that grazing affects plant feeders and bacterivores nematodes by changing plant communities. 【Conclusion】This study reveals that grazing can change soil nematode communities, biomass of plant communities and soil physicochemical properties. All the findings in this study suggest that changes in nematode communities are mainly caused by changes in plant communities. This study is the first effort that has been done by the authors on effects of long-term grazing on soil fauna in alpine meadows of the Tibetan Plateau and its mechanism. This study may have laid down a foundation for future researches on ecological processes of above-ground and underground ecosystems. It is suggested that in future studies, emphasis should be laid on effects of plant community diversity and individual plant properties on soil nematode communities.

    • Effects of Biochar and Nitrogen Fertilizer Amendment on Abundance and Potential Activity of Methanotrophs and Methanogens in Paddy Field

      2016, 53(6):1517-1527. DOI: 10.11766/trxb201604210087

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      Abstract:【Objective】Amendment of biochar has a significant impact on methane (CH4) emission in paddy field, but it is still unclear about its mechanism, so further study should be done to clarify the issue and to provide a scientific basis for the use of biochar in the rice-wheat rotation system.【Method】Soil samples were collected from a paddy field of a field experiment on amendment of biochar and nitrogen (N) fertilizer after the crop of wheat was harvested in 2015 for analysis to assess effects of biochar and N fertilizer amendment on soil physiochemical properties, methane oxidation potential and methane production potential as well as gene abundances of methanotrophs and methanogens with the real-time PCR technology. Biochar was added once to the paddy field before rice transplanting on June 10, 2012. The field experiment was designed to have five treatments in triplicate, that is, Treatment N0B0 (no nitrogen (N) and biochar (B) amended) as control, Treatment N0B1 (only biochar amended, 20 t hm-2), Treatment N1B0 (only N fertilizer amended, 250 kg hm-2 urea), Treatment N1B1 (250 kg hm-2 urea and 20 t hm-2 biochar amended, and Treatment N1B2 (250 kg hm-2 urea and 40 t hm-2 biochar). 【Result】Results show that Treatments N1B1 and N1B2 significantly increased soil organic carbon and microbial biomass carbon (p < 0.05), and soil pH, too, as compared with Treatment N1B0 treatment. Moreover, the abundance of methanotrophs and methanogens were found significantly related to some soil physiochemical properties. Statistical analysis shows that the copy number of pmoA gene was significantly and positively correlated with soil microbial biomass carbon (r = 0.563, p < 0.05), but negatively with soil NH4 -N content (r = -0.573, p < 0.05). In addition, the copy number of mcrA gene was positively related to soil total N (r = 0.675, p < 0.01), microbial biomass carbon (r = 0.713, p < 0.01) and soil organic carbon (r = 0.696, p < 0.01). Besides, methane oxidation potential was positively related to biochar application rate in the presence of N fertilizer (p < 0.05), and In Treatment N1B2, methane production potential increased from 0.001 mg kg-1 h-1 in Treatment N1B1 to 0.002 mg kg-1h-1. Methane oxidation potential was 44.4% higher in Treatment N1B1 than in Treatment N1B0, while being 31.6% lower than in Treatment N0B1. Relative to Treatment N1B1, Treatment N1B2 increased methane oxidation potential from 0.26 to 0.40 CH4 mg kg-1 h-1. Treatment N0B1 significantly increased the log copy number of pmoA gene, from 6.56 g-1d.w.s in Treatment N0B0 up to 6.94 g-1d.w.s (p < 0.05). Compared with the control or Treatment N0B0, Treatment N1B0 inhibited increase in copy number of pmoA gene a certain extent, while increasing the copy number of mcrA gene by 3.0%, which indicates that nitrogen fertilizer can significantly stimulate growth of methanogens. Compared with Treatment N1B0, Treatment N1B2 was higher in copy number of both pmoA gene and mcrA gene, but Treatment N1B1 remained almost unchanged, which suggestes that biochar amendment at 40 t hm-2 can significantly raise the abundance of methanotrophs and methanogens. Compared with Treatment N0B1, Treatment N1B1 greatly decreased pmoA/mcrA ratio from 1.01 to 0.94, and methane oxidation potential by 31.6%. However, biochar amendment increased pmoA/mcrA ratio in the treatments the same in nitrogen fertilizer level (p < 0.05).【Conclusion】All the findings in this experiment demonstrate that biochar amendment promotes methanotrophs and methanogens in abundane, but the effect is much higher on the former than on the latter, and consequently on methane oxidation capacity than on methane production potential. Therefore, it can be concluded that the practice of biochar amendment helps mitigate methane emissions in the paddy field during the wheat growing season.

    • Effects of Nitrification Inhibitors on Soil N2O Emission and Community Structure and Abundance of Ammonia Oxidation Microorganism in Soil under Extensively Managed Phyllostachys edulis Stands

      2016, 53(6):1528-1540. DOI: 10.11766/trxb201603120052

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      Abstract:【Objective】Combined application of nitrification inhibitors and ammonium-containing fertilizers is considered an effective means for improving N utilization efficiency and reducing pollution risk. To determine effects of the use of two nitrification inhibitors: dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP), separately, on N2O emission, nitrogen transformation rate, and community structure and abundance of ammonia-oxidizing bacteria (AOB)) and ammonia-oxidizing archaea (AOA) in soils applied with ammonium-containing fertilizers.【Method】 An in-lab incubation test was conducted of soil samples collected from an extensively managed Phyllostachys edulis plantation. The soil samples were subjected to six treatments, separately, that is (1) CK(no fertilizer); (2))Urea (Urea); (3) Urea 1% DMPP (1% of Urea in quantity); (4) Urea 1.5% DMPP; (5) Urea 10% DCD; (6) Urea 15% DCD. Dynamics of N2O emission and soil parameters at the time of N2O emission turning point (10 d, 50 d and 90 d) were determined. 【Result】Results show that both of the two nitrification inhibitors greatly reduced N2O emission during the 160 days of incubation. The reduction rate in Treatments Urea DMPP (both 1% and 1.5%), Treatment Urea 10% DCD, and Treatment Urea 15% DCD was 54%, 28%, and 41%, respectively. Significant differences were found in cumulative emission of N2O (p<0.05) between the treatments, but not between the two Urea DMPP treatments. The treatments in which urea was combined with nitrification inhibitors were similar to Treatment CK in N2O emission rate during the first 40 days of incubation, and then the formers began to rise gradually with the incubation going on and exceeded CK. Significantly lower N2O cumulative emission was observed in Treatment Urea 15% DCD than in Treatment Urea 10% DCD. Soil NH4+-N levels due to urea application increased rapidly to a maximum and then decreased gradually, with Treatment Urea being lower than all the urea inhibitor treatments on D50 and D90 of incubation; NO3--N concentrations exhibited an opposite trend. The DGGE profiles of soil ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) revealed that DCD and DMPP significantly inhibited AOB in abundance. The effect began to be obvious on D10 of incubation and remained to be significant on D50 and D90 in Treatments Urea MPP, but faded on D90 in Treatments Urea DCD. Treatment Urea was obviously much higher than all the urea inhibitor treatments in abundance of AOB amoA except for Treatment Urea 10% DCD on D 90 of incubation. In contrast, little effect of the use of inhibitors was detected on AOA community, with AOA amoA copy number actually increasing in all treatments. In summary, the dynamics of N2O emission, soil NH4+-N content, and abundance of AOB amoA and AOA amoA did vary synchronously, indicating that N2O emission was controlled by different factors in different time periods for the two bacterial groups. The effect of nitrification inhibitors suppressing AOB led to low N2O emission during the first 40 days of incubation. Although the soil was sufficient in ammonium content and abundant in AOA, the slightly acidic condition (pH about 6.0) may have limited nitrification activity of the group. During the period of D50-D90 of incubation, Changes in AOA triggered by decrease in soil pH with time may be responsible for the increase in N2O emission because the AOB amoA abundance was still low. 【Conclusion】In conclusion, nitrification was mainly controlled via inhibition of AOB activity and application of DMPP at a 1% rate appears to be sufficient to reduce nitrification. It is also suggested that adjusting soil pH to nearly neutral may prolong the effect of the inhibitor DMPP.

    • Ecological Stoichiometric Characteristics of Grassland Soils and Plant Roots Relative to Enclosure History on the Loess Plateau

      2016, 53(6):1541-1551. DOI: 10.11766/trxb201603140545

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      Abstract:【Objective】The knowledge about vegetation succession, is essential to vegetation restoration, especially in steppe regions on the Loess Plateau. Recently stoichiometry has been effectively used to illustrate plant community succession and vegetation restoration. Balance of carbon (C), nitrogen (N), and phosphorus (P) in plant has been a hotspot of the research on biogeochemical cycle and plant ecology. However, most of the studies have focused on nutrients in plant leaves, and few did on the elements in plant roots, let alone, on ecological stoichiometrical characteristics of the soils and plant roots in steppe regions under enclosure on the Loess Plateau, relative to enclosure history. 【Method】This paper explored ecological stoichiometrical characteristics of the soils and plant roots in grasslands different in enclosure history (1 a, 12 a, 20 a and 30 a) on the Yunwu mountain of Ningxia Province. The steppe region under study is located between 106°26′E and 106°30′E and between 35°59′N and 36°02′N. The Yunwu Mountain lies across the center of the Loess Plateau, with an altitude ranging from 1 000 to 1 800 m above sea level. The study area has a semi-arid climate, characterized by heavy seasonal rainfalls causing recurrent flooding and drought, with mean annual temperature being 5 °C and mean annual precipitation being 445 m. The typical natural vegetation of this region is grassland. Samples of the soils and plant roots in the region were collected and analyzed for organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP), and their stoichiometrical ratio and interrelationships, using the time-space substitution method, based on the principles of stoichiometry. 【Result】Result show that with the enclosure going on, soil bulk density decreased gradually, SOC and TN varied more significantly, while TP did less. In the early years of enclosure, SOC and TN declined first and then rose till the enclosure reached 20 or 30 years old, when they leveled off. Soil organic carbon, total nitrogen and total phosphorus varied in the range of 12.88~22.37, 1.41~2.48 and 0.66~0.74 in the 0~20 cm soil layer and in the range of 9.58~18.45, 1.09~2.12 and 0.58~0.70 in the 20~40 cm soil layer, respectively. Soil C:N, C:P and N:P ratio varied in the range of 9.04~9.63, 19.62~32.27 and 2.14~3.37, respectively, in the 0~20 cm soil layer and in the range of 8.68~9.22,15.74~26.32 and 1.80~3.03, respectively, in the 20~40 cm soil layer. Soil organic carbon, total nitrogen and total phosphorus were significantly correlated with each other. C, N and P concentration in the roots varied in the range of 357.6 to 381.4 g kg-1, 7.35 to 8.18 g kg-1 and 0.54 to 0.70 g kg-1, respectively. In the root, C concentrations increased gradually with enclosure going on, whereas N and P concentrations were lower than the world’s average. C:N, C:P and N:P ratio in the root varied in the range of 44.52~59.02, 574.7~793.9 and 10.87~15.14, respectively, during the period of enclosure, showing that C:N varied more drastically, while C:P and N:P did less. Ecological stoichiometric characteristics of C: N: P in plant roots were more affected by soil than by the root per se. Soil TP affected the ecological stoichiometrical characteristics of carbon, nitrogen, and phosphorus in plant roots (p<0.01) more significantly than soil TN did (p<0.05). Besides, the vegetation in this region tended to be restrained by soil N concentration after the grassland was enclosed. 【Conclusion】The study on effects of enclosure on C, N and P in the soil and plant root of the grassland, their ecological stoichiometric characteristics and interrelationships may provide some scientific bases for the study on material recycling in the grassland ecosystem and nutrient restraints in the vegetation ecosystem, and some scientific references for accurate evaluation of ecological benefits of the policies or strategies of “Grain for Green” and “Enclosure of grassland”.

    • Determination of 15N Natural Abundance in Nitrogen Oxides from Major Anthropogenic Emission Sources

      2016, 53(6):1552-1562. DOI: 10.11766/trxb201604180064

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      Abstract:【Objective】Nitrogen oxides (NOx = NO and NO2) are now a critical kind of trace component that calls for strict control, for they threaten the environment and human health. As NOx has its unique isotope signature that varies with its source, the technique of stable isotope analysis can be used to investigate its origin and pathways. This study is to introduce a new method, chemical conversion process, for determination of 15N natural abundance (δ15N) of the nitrogen oxides from major anthropogenic sources. With the aid of this method, it is feasible for us to gradually understand the problem caused by NOx emissions and hence to design appropriate relevant strategies to manage it.【Method】Based mainly on the technique of isotopic analysis of nitrous oxide (N2O), the chemical conversion method is first to oxidize NOx into nitrate (NO3-) with hydrogen peroxide (H2O2) in an acid condition. The resultant NO3- was then converted into N2O under the joint effect of vanadium (III) chloride (VCl3) and sodium azide (NaN3) in a strong acid condition. The newly formed N2O is trapped in an automatic cryogenic system and then diverted into a gas chromatographic column for analysis. The isolated nitrous oxide is analyzed in a stable isotope mass spectrometer under the continuous flowing mode for determination of δ15N, which is then converted into that of the initial NOx using an equation. While testing this method, some other tests were carried out to optimize the experimental conditions for this method. After these tests, eventually NOx in gas samples of different sources can be trapped completely in the absorption solution, with absorption rate reaching as high as 99%. At this time, fractionation of stable isotope is inhibited due to incomplete absorption. As conversion of NOx into NO3- takes place in the absorption solution, it is possible to use standard nitrate solutions to simulate the absorption solutions that contained NOx standard gas sample. Usgs32 and usgs34 are mixed at different volume ratios to prepare standard reference solutions different in stable isotope ratio. After the NO3- in these solutions is converted into N2O using the above-described method and δ15N’s in the two are correlated one by one, a conversion curve between NO3- and N2O in acquired. This curve is equal to the one between NOx and N2O in value. Along with increasing concentration of NO3- in the solution, the curve rises in gradient, tending towards 0.5 in theoretical value. This phenomenon appears as a result of blank in experiment. When the conversion curve is collated through blank correction, the phenomenon disappears and then gradient of the curve approaches 0.5, the theoretic value.【Result】Determination using this method may reach 0.09‰ in precision. Moreover, the minimal amount of a sample for the test is only 7 μg in terms of nitrogen. Gas samples from different sources, including vehicles and power plants, can be analyzed using this method. It is found that δ15N Air of the NOx in vehicle exhaust is -3.6‰ on average, ranging from -17.4‰ to 4.0‰; and that in exhaust from power plants, 21.9‰, on average, ranging from 11.9‰ to 29.5‰, which are in good agreement with the findings in previous researches.【Conclusion】This method can be used for determining stable isotope ratio of NOx from a variety of anthropogenic sources, including power plants and vehicles, and is good enough in precision and accuracy to meet the needs of the researches on NOx.

    • >Communications and Comments
    • On Difficulties and Countermeasures in Describing Soil Series in Chinese Soil Taxonomy

      2016, 53(6):1563-1567. DOI: 10.11766/trxb201605240261

      Abstract (2299) HTML (0) PDF 935.64 K (3489) Comment (0) Favorites

      Abstract:Soil series is the bottom taxon of the Chinese Soil Taxonomy, which currently has a total of about 3 000 soil series, far short of the estimated total of 30 000. So making up the shortage will remain to be a focus of consummating the Chinese Soil Taxonomy for quite a long time in future. How to describe a soil series is the principal link of defining the soil series and the intuitive concrete expression of all the information related to the soil series. To ensure quality of the description, the Special Project of National Science and Technology Basic Researches, namely, “Investigation of Soil Series of China and Compilation of ‘Chinese Soil Series’ (2008FY110600)” had tentatively worked out a standard for description of soil series, The description of a soil series should encompass the following aspects: (1) name of the soil series, soil family it belongs in, names of its founder and authorizer, and dates it was found and authorized; (2) its spatial distribution and environmental conditions; (3) its characteristics and variation amplitude; (4) photos of its typical landscape and soil profiles and morphological description of its typical pedon; (5) soil series for comparison; (6) overview of utilization performance; and (7) reference soil species. However the standard was still found to have some problems with the criteria for soil series description, calling for clarification or solution. Therefore, while introducing the standard for description of soil series, this paper analyzed the existing problems and their causes, and put forth corresponding, in n attempt to further consummate the standard for describing soil series and make it more scientific, standardized, comprehensive and systematic so as to improve the quality of soil series description.

    • >Research Notes
    • Prediction and Mapping of Soil Organic Matter Based on Geostatistics and Remote Sensing Inversion

      2016, 53(6):1568-1575. DOI: 10.11766/trxb201602190434

      Abstract (2386) HTML (0) PDF 1.25 M (2999) Comment (0) Favorites

      Abstract:Soil moisture has a significant impact on soil spectral reflectance, while it was rarely involved in modeling for remote-sensing-inversion-based mapping of soil organic matter in the past. In order to improve the accuracy of spatial prediction of soil organic matter, by taking into full account the characteristics of soil sampling sites, such as spatial autocorrelation, independence and complex field environment, the paper gathered via geostatistis soil moisture spatial distribution data in the study area, based on which in combination of remote sensing reflectance a multivariable prediction model was built up and a soil organic matter spatial distribution map of the black soil region in Jilin Province was plotted. Results show that in remote-sensing mapping of soil organic matter, the involvement of soil moisture as a variable, made the model more consistent with the field reality, and improved significantly the prediction accuracy of the mapping, which fully reflected the variation of soil organic matter in the black soil region of Jilin Province.

    • Effect of Combined Soil Amendment Regulating Chemical Forms of Cadmium and Arsenic in Paddy Soil and Their Bioaccumulation and Translocation in Rice

      2016, 53(6):1576-1585. DOI: 10.11766/trxb201601260044

      Abstract (2872) HTML (0) PDF 982.69 K (3419) Comment (0) Favorites

      Abstract:For remediation of paddy soil complexly contaminated with cadmium and arsenic, a pot experiment with rice planting in the paddy soil collected from southern Hunan Province, China, was conducted to study effects of a combined soil amendment, HZB (hydroxyhistidinet zeolite biochar) on chemical forms of Cd and As in the tested soil and on accumulation and translocation of Cd and As in rice. Results show that application of HZB significantly increased soil pH (by 0.19~0.79) and soil CEC (by 22.1%~60.4%). In addition, it reduced the content of labile soil acid soluble Cd by 6.5%~22.9% by promoting transformation of soil Cd from soluble to insoluble ones. As a result, the content of soil organic Cd increased by 2.5%~56.5%. Application of HZB also promoted transformation of soil As from soluble to insoluble, thus increasing the content of calcium-bonded As by 2.8%~53.3%, and reducing the content of soil exchangeable As by 7.0%~39.5%. However, when the application rate of HZB reached beyond 4.0 g kg-1, the content of soil exchangeable As turned upwards again. It was found in this experiment that Cd bioaccumulation factor (BAF) of rice roots varied in the range of 0.65~1.21, while As BAF in the range of 0.033~0.049, showing obviously that bioaccumulation capacity of the plants was greater for Cd than for As; that among various rice organs, rice husk was the highest in Cd transferring capacity, while root was in As transferring capacity; that application of HZB decreased the Cd and As bioaccumulation capacity of rice roots; that the application of, HZB at a rate of 0. 5~0.2 g kg-1 could significantly lower Cd and As contents in various rice organs; and that when 2 g kg-1 of HZB was applied, Cd and As contents in brown rice were both lower than 0.2 mg kg-1, meeting the requirement set in the National Food Standards (GB 2762-2012).

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