• Volume 51,Issue 5,2014 Table of Contents
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    • >Reviews and Comments
    • The concept and meanings of nitrogen fertilizer availability ratio ―Discussing misunderstanding of traditional nitrogen use efficiency

      2014, 51(5):921-933. DOI: 10.11766/trxb201405130230

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      Abstract:Since the invention and application of nitrogen (N) fertilizer, people always wanted to measure the effects of N fertilizer application by nitrogen use efficiency (NUE). The traditional NUE is the percentage of fertilizer N uptake by crop to N fertilizer rate, which didn’t consider the replenishing effect of fertilizer N to soil N consumption. Due to the defects of the concept and calculation, and the poor interpretations and understands of the results, there are a lot of misunderstands in the literature and daily communication. Therefore, many improved method for calculating NUE were proposed by researchers. However, although these methods had been involved the residual effects of N fertilizer on succeeding crops, they didn’t touch the core issue of the replenishing effect of fertilizer N to soil N consumption. Based on the main N flows in the soil-crop system and the relationships between the fertilizer N, soil N and crop N uptake (called three N), I proposed the concept and calculation of nitrogen fertilizer availability ratio (NFAR) in this study. The core item for NFAR is that the residual fertilizer N is regard as the replenishing to soil N consumption. I recognize that the NFAR is 50%~60% and the loss rate of N fertilizer is 40%~50% under current N management practices in China based on the analysis the data from the 15N tracer field trial, which reflects the high loss of fertilizer N in practices. It is possible to increase NFAR to 70%~90% by improved fertilizer N and agronomic managements. The NFAR expand the idea for the effects of N fertilizer application. It would be important for demonstrating the real effects of crop N uptake and soil N fertility maintain by N fertilizer, and would reflect real loss to environments of N fertilizer application.

    • Advancement in research on polybrominated diphenyl ethers (PBDEs) in soil

      2014, 51(5):934-943. DOI: 10.11766/trxb201311140540

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      Abstract:Polybrominated diphenyl ethers (PBDEs), being extensively used as brominated flame retardant (BFRs) in a huge variety of commercial products, such as computers, televisions, furniture, etc., have now become a novel class of organic pollutants. Since they are physically added into, rather than chemically bound with products, PBDEs in products will inevitably be released into the environment through production, transport, usage, handling and disposal. Excessive PBDEs released into the atmosphere may accumulate in the soil through deposition. The disposal of PBDEs-containing wastewater and sewage sludge will also lead to PBDEs contamination of the soil. At present, PBDEs have been detected in soil in many places of China. It is, therefore, highly important to conduct research of spatial and temporal distribution of PBDEs in soil. Some PBDEs congeners are banned by the Stockholm Convention and prohibited from being produced and used. The concerns about PBDEs will continue due to their possible adverse effects on wildlife and human beings, persistence in the environment and potentiality for bioaccumulation. Currently the techniques available for remediation of PBDEs-contaminated soils are mostly based on bioremediation and photolysis degradation. A review is presented here of recent researches of PBDEs in soil and their sources, levels, migration and degradation. Furthermore, prospects of and proposals for researches of PBDEs in soil in future are brought forth,with a view to providing some theoretical reference for further in-depth study in this aspect.

    • >Research Articles
    • Spatial variability and distribution pattern of soil nutrients in bohai coastal area

      2014, 51(5):944-952. DOI: 10.11766/trxb201311150544

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      Abstract:To study spatial variability and distribution of soil nutrients on a large scale is an important prerequisite for regional balanced fertilization and precision agriculture, but rather time-consuming, labor-consuming and costly because it involves large volumes of soil samples that have to be collected from the fields and analyzed in lab for contents of soil nutrients. The geostatistical and GIS interpolation techniques available can help effectively solve this problem. Based on the 432 soil sampling sites in the Bohai coastal area, spatial variability and distribution patterns of soil nutrients in 0~30 cm and 30~60 cm soil layers of the region were explored. Soil nutrients, such as alkalytic nitrogen, available phosphorus, readily available potassium, organic matter and total nitrogen, in the samples were measured for conventional statistical and geostatistical analyses and mapping using the kriging spatial interpolation method. Results show that the variations of the same one nutrient element in the 0~30 cm and 30~60 cm soil layers were the similar in degree, and all the elements varied moderately except potassium, which did quite vigorously. The nutrients were higher in the 0~30 cm soil layer than in the 30~60 cm one in mean content. All the nutrient indicators in the two soil layers show good spatial structure. The soil in the studied area is relatively rich in available P and readily available K, but rather poor in alkalytic N, organic matter and TN. Generally speaking, the soil is rather infertile and the 30~60 cm soil layer is more than the 0~30 cm soil layer.

    • The rice yield trends in three hydragric paddy soils in south China and its fertility factors

      2014, 51(5):953-962. DOI: 10.11766/trxb201307160339

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      Abstract:A long-term (over 10 year) fertilization experiment on the double rice cropping system was conducted in three types of hydragric paddy soils in Guilin, Qinzhou and Yulin of Guangxi, South China to investigate variation of crop grain yield and soil fertility with time and differences between the three experimental sites in contribution of the major fertility factors to crop yield and relationship between the two using path analysis, The experiment was designed to have two treatments, CK (no fertilizer) and F (conventional fertilization). Results show that under Treatment CK, grain yield varied in the range of 666~846 kg hm-2, showing a significant decreasing trend with time at the site of Guilin where the basic soil fertility is rather low, but it was relatively stable, varying in the range of 3 500~4 577 kg hm-2, at the sites of Yulin and Qinzhou where the basic soil fertility is relatively high. However, under Treatment F it increased by 522% over that in Treatment CK, showing a significant rising trend at the site of Guilin, but at the sites of Yulin and Qinzhou, it did only by 20%~67%. Soil fertility in Treatments F remained almost unchanged or increased to a varying extent. For instance, soil available P increased sharply to a significant extent at the sites of Guilin and Qinzhou where its initial value was lower than 10 mg kg-1, but it did not change much at the site of Yulin where its initial value was 50 mg kg-1. Soil organic matter and total nitrogen content also varied from site to site. Soil organic matter displayed a rising trend and TN content was high (>3 g kg-1) at the site of Guilin where the temperature is lower, while at the sites of Yulin and Qinzhou where the temperature is higher, the former displayed a declining trend and the latter was relatively low (1~2.5 g kg-1), showing differences between the sites in accumulation and release of soil organic matter. Differences between the sites in major fertility factor contributing rice yield were also observed. Soil available phosphorus is the primary factor at the site of Guilin while at the sites of Yulin and Qinzhou, soil organic matter and total nitrogen are. Therefore, taking proper measures in light of the soil properties of a region is a guarantee of sustainable effective soil building.

    • Application of SGS and LHS to analyzing uncertainties in digital soil quality assessment

      2014, 51(5):963-973. DOI: 10.11766/trxb201309130415

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      Abstract:Transmission of uncertainty of soil information in spatial analysis is an issue critical to digital soil assessment. To cope with the issue, coupling of the sequential Gaussian simulation (SGS) and the Latin hypercube sampling (LHS) methods, i.e., SGS-LHS, was proposed with a view to making full use of the advantages of the two methods as complementation to overcome their respective drawbacks, so as to improve accuracy and efficiency of the transmission and analysis of the uncertainty. The new method, (including two pathways: SGS-LHS1 and SGS-LHS2), SGS and LHS were tested in soil quality assessment of farmlands in Hong Kong for comparison. Results show that the uncertainty of the analysis using the SGS-LHS method was similar to that using SGS, but different to a certain, rather a big extent from that using LHS, and the combination method was approximate to SGS, but higher than LHS in accuracy, although LHS appeared to a little bit more accurate in terms of mean width of the confidential intervals. Therefore, the combined SGS-LHS method is recommended for analysis of transmission of soil information uncertainty in spatial analysis.

    • Effects of slope gradient and rainfall intensity on particle size composition of erosion sediment from colluvial deposits of benggang

      2014, 51(5):974-982. DOI: 10.11766/trxb201403160116

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      Abstract:A particular type of gully erosion with a steep collapsing wall, locally called “Benggang”, is widely distributed in the granite-covered areas of tropical and subtropical South China. These gullies develop fast and erupt suddenly, cause great damage. “Benggang” is generally composed of upper catchment, collapsing wall, colluvial deposit, scour channel, gully mouth, and alluvial fan. Colluvial deposits are materials accumulated at the foot of the collapsing wall. They were originally part of the collapsing wall and surface of mountain slopes and fell apart under hydraulic pressure and gravity. As a type of disturbed soil, colluvial deposits feature high contents of gravel, sand, and loose materials, so that they are often weak in structure, low in cohesion, poor in stability steep in slope (generally varying between 20 and 40°) and high in erodibility. Furthermore, rainfall splash erosion and runoff scouring erosion occur easily because in addition to the above listed properties, they lack vegetation cover and organic matter. As a result, erosion of colluvial deposits triggers redistribution of materials from the collapsing walls, generating large volumes of sediments, which in turn aggravate the harm of Benggang. Particle size composition of sediment is an important factor of soil erosion. The study on peculiarity of erosion sediment will be of great significance to illustration of mechanism of the erosion on slopes of colluvial deposits. However, so far few reports are available on erosion of colluvial deposits. To study properties of erosion sediment from colluvial deposits, rainfalls were artificially simulated, with intensity ranging between 1.00 and 2.33 mm min-1 over a plot 5 m2 (5 m×1 m) in area and 20~40°in slope. Results show the following: (1) Changes in sediment particle size composition and enrichment rate: As fine particles are washed preferentially by rainfall, after each rainfall event, the mean enrichment rates of clay, fine silt, course silt, and fine sand are all higher than 1; With rising rainfall intensity and slope gradient, both the content and enrichment rate of coarse particles increase in the sediment, making it coarser in texture. (2) Processes of sediment generation during a rainfall event: At the initial stage of runoff generation, as a result of splash erosion caused by rain drops, fine particles display a process of rapid increase, while coarse particles do a reverse one, which is especially obvious under rainfalls 1.00 and 1.33 mm min-1 in intensity. At the interrill erosion stage, interrill flow is far from strong enough in transport capacity, and carries only fine particles, like clay, fine silt, coarse silt and fine sand, of which the enrichment ratios all exceed 1; but the formation of crust reduces loss of soil particles. After rills form on the slope, scouring capacity of runoff enhances, so content of coarse particles, especially coarse sands and gravels, increases while that of fine particles decreases correspondingly, and then particle size composition gradually becomes stable and approximate to that of the original soil. So, with rainfall going on, particle size of erosion products turns gradually from fine into coarse and levels off in the end. During rainfalls, high in intensity, interrill erosion - rill erosion manifests “overall transport” of original soil. (3) Mean weight diameter (MWD) of sediment: The sediment MWD of rill erosion is greater than that of interrill erosion; which once again shows that sediment becomes coarser in particle size after rill erosion starts. Sediment MWD increases with rising rainfall intensity. Sediment MWD of inerrill and rill erosion varies with slope gradient and comes across a critical gradient, around 30°~35° under rainfalls 1.00 or 1.33 mm min-1 in intensity,, but no such phenomenon was observed during rainfalls with intensity either higher or lower. Under rainfalls 1.67, 2.00, and 2.33 mm min-1 in intensity, MWD of rill erosion sediment is higher than that of the test soil (1.96 mm), on slopes higher than 30° in gradient, which demonstrates that at the late stage of a heavy rainfall event, erosion sediment is coarser than the original soil in particle size. Therefore, MWD varies with rainfall intensity and slope gradient as well, and particles are selectively transported in light of particle size. Dual-factor variance analysis show that rainfall intensity is higher than slope gradient in effect on MWD of rill-interrill erosion sediment.

    • The influence of soil particles fractal and rainfall on runoff and sediment yield in shenfu coalfield

      2014, 51(5):983-992. DOI: 10.11766/trxb201311080521

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      Abstract:During the processes of development and construction of the Shenfu coalfield, generated were large tracts of disturbed land, and large volumes of translocated soil and waste slag, which, unique in soil constitution and complex in underlying surface layer, have become the major source of serious surface runoff and soil and water loss. An artificially simulated rainfall experiment was carried out to explore effects of rainfall intensity and soil fractal dimension on runoff and sediment yielding from undisturbed land, disturbed land, and piles of translocated soil or waste slag, with undisturbed land as CK. Detailed investigation found that the piles of translocated soils and waste slag had slopes at 40°, their natural angle of repose and the disturbed and undisturbed lands had slopes at 18°. Plots in the experiment field were designed to be 3m × 1m, each, and had two sections, each, set up for monitoring of water flow. Rainfall intensity in the experiment was designed to vary from 1.0 ~ 3.0mm min-1, forming five levels with a interval of 0.5mm min-1 between every two levels. Before the experiment, the rainfall intensity was calibrated repeatedly until uniformity coefficient of the rainfalls reached 85% or higher. Soil particle compositions of the plots were determined with the pipette method. During every rainfall, flow velocity was measured with the dye tracing method and width and depth of the flow with a thin steel rule. For the first 3 minutes of runoff, samples of runoff and sediment were gathered once a minute, and after that once every 3 minutes. Results show that (1) on piles of translocated soil and waste slag, runoff followed the process of spurting-declining-leveling off, while on undisturbed and disturbed lands, it did the process of rising – leveling off. Runoff rate on the underlying surfaces increased with increasing rainfall intensity. (2) Fractal dimension of soil particles on the underlying surfaces of the four plots displayed an order of D1 (abandoned residue) < D2 (abandoned soil) < D3 (disturbed ground) < D4 (undisturbed ground). Volume of runoff caused by a single rainfall event was found to be in a significant linear relationship with rainfall intensity and a significant power function relationship with fractal dimension. Moreover, between D1 and D2 and between D3 and D4 existed two critical fractal dimensions, i.e. 2.229 and 2.479, which can be used to distinguish types of underlying surfaces. (3) Erosion on the pile of waste slag followed the process of fluctuating – leveling off, while on the pile of translocated soil, it was characterized by multiple peaks and valleys. On undisturbed and disturbed lands, erosion increased in rate first and then gradually leveled off under rainfall 1.0 ~ 2.5 mm min – 1 in intensity, and fluctuated drastically under rainfall 3.0 mm min-1 in intensity Erosion rates on all the four underlying surfaces increased with increasing rainfall intensity. (4) Amount of erosion was found to be in a significant power function relationship with rainfall intensity, and with fractal dimension of soil particles, too. (5) Volume of runoff was in significant linear relationships with rainfall intensity and fractal dimension of soil particles (Mw=-147.43Di+123.46Pi 268.96, R2=0.952), while yield of sediment was in significant exponential function relationships with the two (lnMs=-11.32Di 1.32Pi 25.83,R2=0.844). The above findings indicate that disturbed land and piles of translocated soil and waste slag, all formed as a result of mining, differ sharply from undisturbed land in rules of runoff and sediment yield, and underlying surface is an affecting factor of runoff and sediment yield that should not be ignored. Fractal dimension of soil particles, as a quantitative indicator of underlying surface, can be used to effectively predict runoff volume and sediment yield. Obviously this study has some important scientific significance to the establishment of a soil erosion model for mining areas.

    • Prediction of soil organic matter and total phosphorus with vis-nir hyperspectral inversion relative to land use

      2014, 51(5):993-1002. DOI: 10.11766/trxb201303280147

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      Abstract:Effects of spectral modeling methods and land use patterns were explored on hyperspectral inversion of soil organic matter (SOM) and total phosphorus(TP) in soil samples collected from paddy fields, peach orchards and vegetable gardens in the Zhihugang catchment, Taihu Lake Region. Results show that the PLSR (Partial least square regression) model was quite high and stable in modeling and prediction precision; the GRNN (General regression neural network) of ANN (Artificial neural network) was also quite high in prediction precision, but prone to overfitting; the BPNN (Back Propagaton Neural Network) was relatively stable, but slightly low in precision; and the combined PLSR-ANN model improved in prediction precision by combining the advantages of the two in handling complicated samples. The spectral inversion of SOM was better than that of TP, and among the three patterns of land use, paddy fields were fitter than the other two for use of the models in prediction of SOM and TP. In the current study zone, patterns of land use did not have much effect on spectral inversion of SOM, but did much on that of soil TP. It is, therefore, essential to calibrate the models in light of land use patterns in conducting spectral inversion of soil TP.

    • Spectral characteristics and quantitative estimation of SOM in red soil typical of Ji’an County, Jiangxi Province

      2014, 51(5):1003-1010. DOI: 10.11766/trxb201303260139

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      Abstract:The objectives of the study were to analyze spectral characteristics of red soils different in SOM (soil organic matter) content in Ji’an, Jiangxi, for establishment of county-scale SOM quantitative estimation models based on SOM reflectance bands, it was found that red soil and paddy soil differed sharply in soil spectral characteristic. The wave range of 560~710 nm was the spectral absorption band specific of SOM in the soils of Ji’an county. Correlation coefficient of the log of the absorption area in the range of characteristic absorption bands with soil SOM was 0.86, fitting equation was y=-20.91 ln(s)-27.26, and determination coefficient was 0.74. After calibration with the data of SOM in various types of soils, the determination coefficients for prediction(R2), the root mean square error (RMSE) and the relative error analysis(RPD) was found to be 0.75, 0.61 and 1.88, respectively. The partial least squares regression (PLSR) model, established on continuum removal and logarithm processing of reciprocal of the reflectance, was the highest in estimation accuracy, with prediction determination coefficient R2 being over 0.83, RMSE less than 5.00 and RPD more than 2.4. These findings indicate the model based on specific absorption bands 560~710 nm can be used to quantitatively estimate soil SOM in red soil regions.

    • Estimation of soil carbon using a field ambulatory infrared spectroscopy device

      2014, 51(5):1011-1020. DOI: 10.11766/trxb201309220429

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      Abstract:Abstract To improve accuracy of the prediction of soil carbon using a soil carbon calibration model, feature transformation and feature selection was done to soil infrared reflected spectral (NIRS) data obtained with a field ambulatory infrared spectroscopy device in situ. Firstly, feature transformation was done of the soil NIRS data through independent component analysis (ICA), principle component analysis (PCA) or wavelet analysis (WA), and then feature selection was through uninformative variable elimination (UVE), successive projection algorithm (SPA), uninformative variable elimination in combination with successive projection algorithm (UVE-SPA), and genetic algorithm with partial least squares regression (GA-PLS), separately. And in the end, a soil carbon calibration model was established. Results show that after the processing, a prediction model, better than subjecting the NIRS data to direct wave band selection in accuracy, can be built up, while the combination of the feature selection method with PCA or WA could only achieve some similar effects to those of subjecting NIRS data to direct wave band selection. Therefore, it is feasible to establish a more reliable soil carbon prediction model through feature transformation and selection with the feature selection method coupled with ICA of the NIRS data acquired with a field ambulatory device under complicated environmental condition.

    • Quantitative analysis of reflectance spectrum of black soil as affected by soil moisture for prediction of soil moisture in black soil

      2014, 51(5):1021-1026. DOI: 10.11766/trxb201310300500

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      Abstract:To study effect of soil moisture on soil reflection spectrum, Black soil, as a single soil class, was selected as subject for the study. Soil samples were collected and prepared to have different water contents. And then, hyperspectral reflectances of the samples was obtained in lab for analysis, statistics and quantitative description. On such a basis, a reflection spectrum-based model for prediction of soil moisture in black soil was established. Results show that with more water added to a certain threshold (300 g kg-1), the phenomenon of oversaturation would appear with soil reflectance. However, the problem could be solved with its derivative of log-transformed reflectance (DDW), of which the response to soil moisture displayed a 3-phased variation, thus resulting in nonlinear variation of DDW at 1 870 nm. It is, therefore, essential to use piecewise functions to rapidly and accurately predict soil water content with spectral data.

    • Application of in situ direct imaging method to study on dissolution of biotite

      2014, 51(5):1027-1034. DOI: 10.11766/trxb201401170036

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      Abstract:The in-situ direct imaging method (or in-situ atomic force microscopy) was used in studying interfacial reaction of biotite with low molecular weight organic acid. The low molecular weight organic acid used in the research is citric acid, which is one of the most important components of root exudate and, therefore, ubiquitous in the soil-plant system. Biotite, belonging in the mica group, is a kind of phyllosilicate mineral, which contains potassium (K), magnesium (Mg) and iron (Fe), essential for the crop growth. In order to observe how biotite is dissolved and changed in morphology changes in soil, an experiment was carried out with two pH treatments (4.0 and 6.0). Observation on the near-molecular scale reveals that biotite is a typical unit of layered structure, about 1 nm in height. The surface of biotite (001) is not smooth but full of terraces, debris and etches pits, which would disturb the dissolution process of biotite. In citric acid solution, 6.0 in pH, the terraces on the biotite (001) surface were dissolved at a constant rate of 0.01 μm2min-1 within the first 45 min, and afterward, at a declining rate, and the original etch pits on the surface did not change much in area, but had edges blurred. Meanwhile, no new etch pits formed on the (001) surface. When treated with citric acid solution 4.0 in pH for 89 min, the biotite had a large number of irregular shaped tiny etch pits formed, which were randomly distributed on the (001) surface and mostly, about 0.7 ~ 1.1 nm in depth, and in addition quite a number of mini pits were forming and expanding into large ones. The original terrace on (001) surface also did not dissolve notably in area compared to that of the beginning situation. It is learnt from understanding of the theory of interactions on water-mineral interface that in weak acid environment, dissolution of biotite starts from defect/kink sites on the surface, one layer by one layer, and develops along the [hk0] direction, while releasing K from between layers and Si, Al, Mg and Fe from crystal lattices. ,To study dissolution of minerals under normal pressure and temperature, macroscopic researches usually require a long response time and a high dose of acid (e.g., strong acidity and high concentration), which may lead to deviation from the characteristics of minerals reaction under real conditions; on the other hand, the reaction process could not be visualized and the results need to be fit and explained with the help of other models and theories , which would usually make it more difficult to get results and the results more uncertain. But, the in-situ atomic force microscopy technology can overcome the shortcomings of the macroscopic method and realize real-time characterization of the reaction in the interface between phyllosilicate minerals and water through visualization, and hence validate macro research. Moreover, this technology may also provide information of high reference value to interfacial reaction in other fields.

    • Distribution of trace elements in soils of city parks of Su-Xi-Chang area and its significance as environmental indicator

      2014, 51(5):1035-1044. DOI: 10.11766/trxb201307020310

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      Abstract:On the basis of the provincial multi-target geochemistrical land survey at 1∶250 000 scale in Jiangsu, a total of 45 city parks in the Su-Xi-Chang region, like the Panmen Park in Suzhou, the Wujiang Park in Wujiang, the Huishan Park in Wuxi, the Zhongshan Park in Jiangyin, the Five-star Park in Changzhou, the Hualuogen Park in Jintan, and so on were elected as subjects in a systematic study on distribution of pH, TOC and 50 elements, including Cd, Hg, Pb, Zn, Sb, Sn, B, F, Se, N, REEs, etc. in the soils of these parks. Results show that the distributions of trace elements in city park soils are obviously different from those in polluted urban soils and normal farmland soils. The park soils, as a whole, tend to be low in heavy metal content and significantly lower than farmland soils in N and TOC content. No intensive anthropogenic enrichment of S, Se, Cd, Pb, Zn and TOC is found in the park soills. Heavy metal pollution there is very slight and dominated with Hg, which is related to human activities. The distribution of S, Se, Cd, Pb, TOC and pH in the 0~200cm soil layer is quite stable and does not vary much with soil depth. All the findings indicate that the distribution of trace elements in most of the park soils has rarely been disturbed by human activities as compared with that in general urban soils. Therefore, the soil environment of the city parks can be cited as reference essential to the study on impacts of human activities on urban soil environment.

    • Health risk of accumulation of cadmium and mercury in greenhouse vegetable production systems typical of south China

      2014, 51(5):1045-1055. DOI: 10.11766/trxb201401020003

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      Abstract:In recent years, greenhouse vegetable production has been growing rapidly, making up a sizeable proportion of the vegetable production in China. Excessive uptake of heavy metals by vegetables may pose potential risks to human health. Therefore, vegetable safety has aroused increasing concerns in the country. To ensure food safety, it is essential to know how heavy metals (Cd and Hg) accumulate in the greenhouse vegetable production system and pose health risks. The study on this subject may provide some scientific basis for heavy metals health risk assessment of Cd and Hg in the greenhouse vegetable system and decision-making in environmental management. Currently, the standard used for environment of environmental quality of greenhouse vegetable fields fails to take into account vegetable-type-specific bioavailability and human health risk of heavy metals. Hence, it is of critical importance to the management and production of safe greenhouse vegetables to have the standard for environmental quality evaluation of greenhouse vegetable fields established as soon as possible, based on crop-specific bioavailability and human health risks of heavy metals. For that end, a greenhouse vegetable production system typical of the Nanjing area was selected as a case for study on characteristics of Cd and Hg accumulation in the greenhouse soil-vegetable system, and exposure risks of Cd and Hg in vegetables relative to type, and environmental quality criteria were proposed for Cd and Hg in greenhouse vegetable fields based on the standard for vegetable and food hygiene and health risks of vegetable ingestion. Results show: (1) Cd and Hg accumulation was apparent in the topsoil of the greenhouse vegetable field, with the average content of Hg exceeding the Environment Quality Evaluation Standard for greenhouse vegetables production fields; (2) leafy vegetables were the highest in Cd and Hg enrichment capacity, and followed by root/tuber vegetables and then solanaceous vegetables; and some leafy vegetables were found to contain Cd and Hg higher than the upper limit of the standard for food hygiene; According to sensitivity analysis, the main contribution of different exposure parameters to target hazard quotient for Cd and Hg was concentration of Cd and Hg in vegetables (Cveg) and daily intake of Cd and Hg through ingestion of greenhouse vegetables (IRveg ). (3) approximately 21.2% of the greenhouse vegetables produced in the studied region were likely to pose potential Cd exposure risk through vegetable ingestion and only 1% in the case of Hg, Cd and Hg exposure risks varied with the type of vegetable, displaying an order of leafy vegetables > root/tuber vegetables > solanaceous vegetables; and (4) As environmental quality criteria of soil Cd and Hg vary sharply with the type of vegetables, it is essential to formulate vegetable-type-specific criteria separately for environmental quality evaluation of heavy metals in greenhouse vegetable fields in amending the standard for environmental quality evaluation of agricultural fields in future. The findings of this study suggest that as vegetables vary sharply in Cd and Hg enrichment capacity with the type, in soils relatively high in Cd and Hg, it is advisable to grow suitable vegetables, like root/tuber or solanaceous vegetables that are relatively lower in heavy metal absorption capacity, so as to lower the risk of Cd and Hg entering the food chain. The environmental quality criteria for Cd and Hg in greenhouse vegetable soils based on the Cd and Hg bioconcentration factors of vegetables and vegetable safety standard would be stricter than that based on vegetable target hazard quotient of Cd and Hg, and more approximate to the current environmental quality evaluation standard for farmland of greenhouse vegetables production in China. The findings of this study will facilitate better understanding of the accumulation characteristics and health risks of heavy metals in greenhouse vegetable production systems. Further study should focus on phyto-availability of Cd and Hg to greenhouse vegetables, and establishment of environmental quality evaluation standard for greenhouse vegetable production fields relative to soil type and vegetable type for better management of the greenhouse vegetables production in different regions of China.

    • Phytoremediation of inter-cropping with chemical enhancement of heavy-metal-contaminated acid soil: a long-term field experiment

      2014, 51(5):1056-1065. DOI: 10.11766/trxb201308110369

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      Abstract:In order to verify the effectiveness of long-term application of the technology of inter-cropping remedying heavy metal contaminated soils, a 3-year field experiment was conducted to have three treatments and 5 croppings, Treatment IC (inter-cropping of Sedum alfredii Hance and corn (Zea mays)), Treatment Mono-cropping ( Sedum alfredii Hance ) and Treatment IC + MC (mixture of chelators consisting of citric acid and EDTA). Plant yields and heavy metal contents in plant and in soil were monitored for comparison. Results show that the total Cd and Zn in the soil decreased continuously with the progress of the experiment. After the 5 croppings, the soils in Treatments IC and IC MC were remedied to meet the criteria of the National Standard for Soil Environmental Quality (GB15618 -1995). Soil Cd decreased from 1.21~1.27 mg kg-1to 0.29~0.30 mg kg-1 and soil Zn from 280~311 mg kg-1 to 196~199 mg kg-1. But no significant change was observed in soil Pb. MC did not enhance much phytoextraction of heavy metals from the soil. Heavy metal content in the plant of S. alfredii Hance and heavy metal phytoextraction rate of the plant was not decreased with the year. Mono-cropping of S. alfredii Hance was higher in biomass production than the plant in intercropping in all the four rounds and so in total phytoextraction of heavy metals. However, in Treatment IC, the corn turned out to meet the hygienical standard for feed and even the hygienical standard for food in the fourth cropping. Calculation based on harvested S. alfredii Hance shows that the plants contributed 32.5%~36.5% to the decrease in soil Cd, while corn did only 0.47%~0.60% and the remaining 63.0%~66.9% was attributed to leaching loss `and other factors. Soil Zn was in a similar case. These findings indicate that in the studied acid soil (pH 4.7) downward leaching and S. alfredii Hance .phytoextraction both play important roles in reducing soil Cd and Zn.

    • Spatial-temporal variation and source apportionment of soil heavy metals in Peri-Urban Area—A case study of Zhetang Town, Nanjing

      2014, 51(5):1066-1077. DOI: 10.11766/trxb201312240607

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      Abstract:Peri-urban areas are not only a buffer protecting the zoology, environment, and climate of a city, but also a supplier of large amounts of food to city residents and a dump site for disposal of city waste and garbage as well. Recently, the peri-urban areas of this country are facing an increasingly serious problem of soil heavy metal pollution due to rapid development of urbanization and industrialization of the areas. Therefore, it is very urgent to conduct investigations of soil heavy metal pollution in the areas. A case study of Zhetang Town of Nanjing was carried out with a view to exploring status quo, spatio-temporal variation and source apportionment of the soil heavy metal pollution in the peri-urban area. A total of 109 soil samples were collected in 2012 and 21 in 2002 from the topsoil layer for analysis of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn. With the aid of the GIS spatial analysis technology and related standards for soil heavy metal contents as reference, such as natural background values, green standard, Criteria Grade I and Ⅱ, status quo and spatial-temporal variation of the pollutions of the 8 soil heavy metals were analyzed. Probable sources of the soil heavy metals were also apportioned through Pearson’s correlation and principal component analysis. Results show that continuous accumulation of the soil heavy metals accompanied urban expansion and industrial development of the city of Nanjing. The average content of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn in Zhengtang Town was 14.0, 0.20, 77.6, 44.7, 0.17, 33.9, 36.2 and 103.7 mg kg -1, respectively. Most of the area was lower than the criteria of the Green Standard in heavy metals concentration, and only a very few regions maintained their background values. So, safety of agricultural produce was not a problem at the time of the study. The area of the soil with excessive heavy metals content is increasing with each passing day, gradually expanding from the urban outwards to surrounding farmlands and woodlands in the suburbs. Compared with 2002, 2012 witnesses varying extent of heavy metal accumulation in most of the area. The concentration of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn increased at a rate of 56.91%, 61.06%, 6.07%, 60.15%, 38.69%, 19.94%, 23.92% and 56.17%, respectively. Areas intense in human activity like down town area, villages and buffer zones along traffic ways, were high in heavy metals concentration, while the concentrations declined gradually outwards, forming a downward gradient towards peripheral areas and rural areas. Cd, Cr, Cu, Ni and Zn were concentrated mostly in the urban area and around factory sites; Cd, along river banks; Hg and Pb alongside traffic arteries, and As in towns and villages. Cr, Cu, Ni and a part of Zn probably came from urbanization construction and discharge of waste water, slag and gases from industrial production, which kept on expanding in scale; Hg, Pb and part of Zn from heavy traffic on highways and operation of the Lukou Airport, where so many flights a day generated large volumes of exhaust from the jet engines and dust from tire abrasion; Cd and part of Zn from urban construction and expansion, and development of fishery in the Qinhuai River, which is an important economic sector of Zhetang town; As from livestock and poultry breeding, discharge of sewage and application of sludge as manuren. Through the case study of Zhetang Town, it is not difficult to find the characters and trends of the heavy metals pollution in the peri-urban areas of Nanjing. The soil environment of that region was deteriorating in the process of urbanization and industrialization. The existence of heavy metals in the soil is often accompanied by environmental pollution, of which its sources are complex but ultimately attributed to various intense human activities. It is essential and urgent for scientists to determine the status of soil heavy metals, where they come from and what kind of countermeasures should be taken as soon as possible to protect the ecological environment and assure steady, healthy and sustainable development of the peri-urban areas in the country.

    • Distribution of soil organic carbon in mangrovewetlands ofhainan island and its influencing factors

      2014, 51(5):1078-1086. DOI: 10.11766/trxb201304230199

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      Abstract:Mangrove wetlands, typical of wetlands in subtropic and tropic area, are considered as a huge carbon pool along the coast. In this study, typical mangrove wetlands in the north, east, south and west coasts of the HainanIslandwere selected for soil sampling. A total of 630 soil samples were collected from 126 sites, five soil samples each site from 5 soil layers, 20cm each, in 42 quadrats scattered in 14 mangrove communities. The samples were analyzed for soil organic carbon (SOC) contents with the potassium dichromate external heating method and SOC density was worked out based on soil bulk density. Through comparison between the sites in community structure, soil physical and chemical properties and natural conditions, exploration was done of regularities of the distribution of SOC in the mangrove wetlands and major factors affecting the SOC stock therein. Results show that the distribution of SOC content and density varied sharply with soil depth; the peak of SOC content appeared in 20~40cm, while that of SOC density did in 0~20cm; SOC content also varied with mangrove community; in the Dongzhai Harbor area, the Bruguiera sexangula community was the highest in SOC content (20.89±6.75 gkg-1), while the artificial Sonneratia apetala community was the lowest (12.71±3.62 gkg-1). Further correlation analysis shows that SOC content was positively related with DBH(diameter at breast height)of the mangrove trees and coverage of the community, but not with plant height. As to spatial distribution, a decreasing order of Simi Bay Dongfang >Qinglan Harbor Wenchang >Xinying Bay Danzhou >Dongzhai Harbor Haikou > Sanya Bay Sanyawas observed. Finally, based on the area of the mangrove forests in HainanIsland, the mangrove forest soil in HainanIsland possesses a total stock of 2.39×106t organic carbon.

    • Spatial heterogeneity of soil organic carbon on the south coast of Hangzhou Bay

      2014, 51(5):1087-1095. DOI: 10.11766/trxb201309230432

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      Abstract:A study was carried out using Geostatistics and Geographical Information System(GIS) technologies to explore spatial variability of soil organic carbon content in different soil layers (0~20, 20~40, 40~60, 60~80, 80~100, 0~100 cm) in Cixi City, on the south coast of the Hangzhou Bay. Results show that the average contents of soil organic carbon in the soil layers varied from 3.49 g kg-1 to 7.95 g kg-1 in the study area, with variation coefficients ranging from 54.51% to 67.34%, indicating a moderate degree of variability. Geostatistical analysis reveals that the value of nugget effect varied from 0.141 to 0.372, displaying strong spatial correlation, and that the optimal semi-variance models for the soil layers from the surface down to the bottom of a soil profile were Gaussian, exponential, exponential, Gaussian and spherical model respectively; The results of Kriging demonstrate that soil organic carbon displayed an increasing trend from beach to inland in all the soil layers, and a decreasing trend with soil depth in a soil profile, and was distributed in the surface soil layer (0~20 cm) like a band in parallel with the coastline. Both different land use patterns and different reclamation history intensified spatial variability of soil organic carbon. All the findings indicating that the spatial variability of soil organic carbon is mainly caused by structural factors in Cixi City, may provide soil organic matter reference to the study to understand characteristics of the distribution of organic carbon in soils on the south coast of the Hangzhou Bay.

    • Formation of rice root regulated by nitrogen deficiency

      2014, 51(5):1096-1102. DOI: 10.11766/trxb201401290057

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      Abstract:The ability of plants to sense available nutrients in the soil and to respond accordingly is of fundamental importance for their adaptation to the environment. The plasticity of root in development in response to nitrogen (N) deficiency is vital, as N is a major nutrient essential for plant growth and development. Changes in root morphology under the stress of N deficiency are complex and vary with experimental conditions and plant species. Little attention has been paid to root growth under the stress of N deficiency, possibly because of the inconsistent response of primary root in length to N deprivation depending on plant age and N concentration supplied. Thus root morphology in rice under the stress of N deficiency has not yet been characterized in detail. Root formation is regulated by both environmental conditions and intrinsic factors. Auxins play a key role in rice plants establishing and developing root morphology. Few studies have evaluated the role of auxins in regulating root growth under low N conditions. To what extent, if any, auxin transport in rice roots is regulated by N deficiency remains unclear. In this paper, a hydroponic media experiment was carried out on N concentration regulating auxin transport and relationship between root formation and transport and distribution of auxins in rice. In this study, biomass, N concentration, seminal root length and lateral root density (LR density) of rice plants and auxin concentration in the plant and relative expression of OsPIN family genes of auxin outflowing protein were investigated relative to N concentration (0.01, 0.2, 1, 2.5 and 5 mmol L-1) in hydroponic media. Comparison of the plants under two N concentrations (0.01 and 2.5 mmol L-1) reveals that the ratio of root to shoot increased significantly with decreasing N concentration, partly resulting from decline of the plant root in biomass relative to shoot. However, compared with the plants under normal N concentration (2.5 mmol L-1), the plants under low N concentration (0.01 mmol L-1) were 33% lower in root N concentration, 25% longer in length of seminal root and 26% lower in lateral roots density. Besides, the latter were 140% higher in auxin concentration in the 1st leaf from the top but 22% and 60% lower, respectively, in the root-shoot junction and the root, indicating that N deficiency probably resulted in inhibition of auxin polar transport from the shoot to root. RT-PCR analysis shows that the relative expression of OsPIN1a-bOsPIN2OsPIN5a-b and OsPIN9 markedly decreased in rice root of the plants under the stress of low N concentration as compared with their respective one in the plants under normal N concentration. Application of exogenous 1-Naphthaleneacetic acid ( NAA),to plants under the stress of low N concentration inhibited growth of their seminal root in length, but stimulated growth of their lateral roots on seminal root in density to form a root system structure similar to that of the plants under normal N concentration, while application of N-1-naphthylphthalamic acid (NPA), a kind of auxin transport inhibitor to plants under normal N concentration stimulated growth of their seminal in length, but inhibited growth of their lateral root density on seminal root to form a root system structure similar to that of the plants under the stress of low N concentration. It could, therefore, be concluded that the inhibition of polar transport of auxin from the first leaf next to the top down to root in the plant by N deficiency was one of the physiological mechanisms of the response of rice roots to the stress of N deficiency.

    • Influence of freezing and thawing cycles on net nitrogen transformation and enzyme activity in black soils

      2014, 51(5):1103-1109. DOI: 10.11766/trxb201312240610

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      Abstract:The black soil area in China is typically characterized by freeze-thaw alternation, however, little is known about impacts of the freeze-thaw cycles on N availability in black soil. An indoor bacth experiment was conducted to investigate effects of freeze-thaw cycles different in temperature range (-25—5 ℃ and -10—5 ℃) on net nitrogen transformation and soil enzyme activity in black soil. Soil ammonium nitrogen and nitrate nitrogen content was determined with the 2 mol L-1 (1:5 soil liquid ratio) KCl extraction method, and analyzed with the automatic chemical analyzer, Smartchem 200. Soil urease activity measured with the indophenol blue colorimetric method and soil invertase activity determined with the 3,5-dinitrosalicylic acid assay method. Results show that the contents of ammonium nitrogen and nitrate nitrogen increased gradually with frequency of the freezing and thawing alternation and varied with intensity of the cycle. In terms content of ammonium nitrogen, the following order was observed: cycles moderate in intensity (-10—5 ℃) > cycles high in intensity (-25—5 ℃) > control (5 ℃), except for the first round of freeze-thaw cycle moderate in intensity. However , freezing-thawing cycles did not have much influence on soil nitrate nitrogen. On the whole, freeze-thaw cycles reduced soil nitrogen mineralization and nitrification rates,, and the effect was obviously affected by the intensity of freezing and thawing, but at the end of the experiment, the cycles displayed a tendency of promoting nitrification. As affected by low temperature and the alternation, the activities of urease and invertase in the soil under the cycles moderate in intensity were higher than that in the soil under the cycles high in intensity (except for the first cycle), however, both were lower than control. So the effect of soil freezing and thawing on black soils has an important influence on nitrogen transformation and soil enzyme activity. Urease activity and soil nitrogen supply capability are significantly correlated. Besides, invertase activity is affected by soil geochemical cycles through carbon source supply and temperature.

    • Effects of phytase transgenic corn on content and composition of phosphorus in rhizosphere soil under field conditions

      2014, 51(5):1110-1119. DOI: 10.11766/trxb201401240049

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      Abstract:Phosphorus (P) is one of the mineral elements essential to growth of all animals. However, corn as a major source of energy and feed to animals, is fairly low in content of P available to monogastric animals and about 80% of the phosphorus in corn is phytate-P. In monogastric animals, phytate-P is very low in utilization rate because the animals lack endogenous phytase. Therefore, inorganic P is routinely added to the feed of the animals to satisfy their requirement for P, As a result, a unutilized portion of the dietry P is excreted with faeces of the animals, thus polluting the soil and water sources. Moreover, phytic acid is also a kind of anti-nutritional factor that seriously affects animal uptake of Ca, Fe, Zn, and some other nutrient elements. Supplementation of exogenous phytase extracted from microbial fementation into feed has been considered to be one of the most effective ways to reduce P output. However, the extraction of phytase is rather costly, thus limiting its extensive commercial use. Phytase genes of Aspergillus niger were transferred into the endosperm of corn, turning out corn seeds that contain Aspergillus niger phytase. After generations of breeding and screening, obtained was a corn homozygous line of phytase transgenic corn (PTC) that is able to stably express phytase and inherite stably generation after generation. Feeding this kind of corn can improve P utilization rate of monogastric animals and reduce P content in their faeces, thus eliminating P pollution of the environment. Compared with conventional corn, PTC planted in the field may have some potential risks. However, phosphorus is a nutrient element essential to crops and an important pollutant as well deteriorating water environments. Commercial plantation of PTC has aroused ecological concerns with respect to potential effect on content and composition of soil P. On the one hand, PTC may directly affect soil P level through release of phytase into the soil, and on the other hand, the changes in chemical composition or quality of crop residues, like roots and straw left in the soil may have some effect on soil biological communities and biochemincal activity of the soil, thus in the end affecting the processes of fixation and mineralization-release of soil inorganic and organic P. Therefore, theoretically planting PTC will generate some effect on soil P transformation processes, and in turn further alter soil fertility of the field and quality of its surrounding water bodies. Nevertheless, to our knowledge, little has been reported on effects of planting PTC on soil P. A field experiment started in 2011, planting phytase transgenic corn (BVLA430101) and isogenic corn (Yingyu 35), separately, as Treatment PTC and Treatment CK, each of which has 5 replicates, making up a total of 10 plots. Soil samples were collected at different corn growing stages in 2012 and 2013 for analysis using the modified Hedley phosphorus fractionation method to investigate effects of planting PTC on content and compositions of soil P. Results show that the effects of PTC on soil P varied with timing of sampling and fraction of P. The soil in Treatment PTC was much lower than the soil in Treatment CK in content of water soluble P (H2O-Pi), NaOH extractable inorganic P (NaOH-Pi) and NaOH extractable organic P (NaOH-Po) before seeding in 2012 and at the heading stage in 2013, and in content of NaHCO3 extractable organic P (NaHCO3-Po) before seeding in 2012 and at the maturing stage in 2013. However, the two soils differed significantly in content of microbial biomass P (MBP) only at the maturing stage in 2013. Growing PTC had no significant effects on the contents of total P (TP), diluted HCl extractable inorganic P (Dil.HCl-Pi), concentrated HCl extractable inorganic P (Conc.HCl-Pi), concentrated HCl extractable organic P (Conc.HCl-Po) and residual P (Residual-P). The soil in Treatment PTC was much higher than the soil in Treatment CK in phytase activity throughout the two corn growing seasons, and in alkaline phosphatase activity as well before seeding in 2012 and during the whole corn growing season in 2013. Anyway, growing PTC three years in row had some effects on contents of labile P and moderately labile P and activity of alkaline phosphatase in the soil only at certain growth stages, and significant effects on phytase activity during the two corn growing seasons. It is, therefore, necessary to take into account the crop and the soil related in evaluating effects of planting PTC on soil P and studying mechanisms of the effects, and what is more, to maintain long term monitoring at different sites.

    • Effect of calcium and phosphorous on migration, propagation and quorum sensing of rhizobia in acid soil under aluminum stress

      2014, 51(5):1120-1131. DOI: 10.11766/trxb201312050579

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      Abstract:Soil acidification has become a serious challenge to farmers in the past decades as a result of acid rain, fertilizer application, climate change, etc. In the year of 2000, about 21% of the arable land soil was defined as acid soil in China. At the same time, about 50% of the agricultural soil the world over has become acid soil. Researchers have been working in fields related to acid soils from the aspect of its biological perspectives in order to remedy and exploit the soil. In the past years the authors have been focusing on the subject of acid tolerance of rhizobium, which may help its legume host, including alfalfa, one of the most sensitive plant to soil acidity, to survive in acid soil. What the authors found in previous studies has shown that acid-tolerant rhizobia improve rhizospheric environment for growth of their legume hosts in acid soil by secreting alkaline substance. Application of a proper amount of calcium (5 mmol kg-1) enhances growth and multiplication of acid-tolerant rhizobia, which leads to better growth of the legume host manifested in significant increase in the concentration of total N in the plant (p<0.05) as compared with CK or Treatment Ca0P0, i.e. no P and Ca addition. At the same time, the quorum sensing of the rhizobia in the rhizosphere improves, too. Addition of phosphorous, as demonstrated in volumes of researches, stimulates root extension and helps the plant stand a number of environmental stresses. Nevertheless so far few papers are available on effect of addition of P and Ca together on growth of rhizobia in acid soil and hence on tolerance of the host plant to acid in soil. To explore the effects, a pot experiment on alfalfa and an acid-tolerant stain of rhizobia, Sinorhizobium meliloti 91522 was carried out using the dual-chamber culture method. In the experiment, the pots were packed with acid soil (pH4.45), which was amended with Al3+ till Al3 toxicity of the soil reached medium in level and each pot was divided into two chambers, i.e. inner and outer chambers. Rhizobia 91522 were inoculated into the soil in the outer chamber, far from the plant in the inner chamber, to test. Results show that within the 97 days after the inoculation the number of rhizobia was all significantly higher in the pots amended with 5 mmol kg-1 Ca2 than in CK. For example, the maximum number of rhizobia in the soil, 1~2 cm from alfalfa root in the pots treated with Ca2 but no P was 615 times that in CK. On such a basis addition of P enhanced the effect of Ca on growth of rhizobia, e.g. the number of rhizobia, increased up to 9.4 times that in CK. Therefore, it could be concluded that interaction existed between Ca and P in the effect. Addition of Ca2 and P also significantly raised the concentration of N-acyl-homoserine actones (AHLs) - the indicator of quorum sensing of rhizobia in the soil under acid and aluminum stresses. For this effect, the addition of 5 mmol kg-1Ca2 worked better than that of 10 mmol kg-1 Ca. The rhizobia in the near root area (1~2 cm from the root) and the far root area (6~8 cm from the root) had similar trends in variation of population during the culturing period, i.e. one week after inoculation, rhizobia spread gradually from the far root zone to the near root zone, peaked in population about 30 days after inoculation, and afterwards the populations of rhizobia in both zones started to decline and level off, However, the population of rhizobia was much bigger in the near root zone than in the far root area all the time except the first two weeks after inoculation, showing that the rhizospheric micro-environment of the host plant is also an important factor affecting the population of rhizobia and quorum sensing. It is tentatively held that addition of 5 mmol kg-1 Ca2 and 30 µmol kg-1 P is an optimal treatment, which helps better survival, migration and quorum sensing of acid-tolerant rhizobia in acid soil under aluminum stress, and hence growth of alfalfa under the aforementioned stresses. The plant in this treatment was 4.67, 3.10, 3.47 and 14.74 times that in CK in root fresh weight, shoot fresh weight, nitrogen concentration and number of nodules, respectively.

    • Effects of vegetable cultivation on soil cation exchange capacity in greenhouse

      2014, 51(5):1132-1137. DOI: 10.11766/trxb201311250561

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      Abstract:Soil samples were collected from vegetable fields under greenhouse and upland fields in their vicinity in Yuhong District of Shenyang, Liaoning Province, China, for determination of organic matter, CEC, exchangeable base composition and soil base ion saturation, and hence analysis of effects of vegetable cultivation on soil cation exchange capacity in greenhouse. Results indicate:(1)the protected fields were much higher than the control (upland field) in soil organic matter content, being about 35.6 g kg-1 and 18.0 g kg-1 or 2.1 and 1.8 times higher in mean content in the upper and lower soil layers, respectively; and the soil in the former displayed a rising trend in CEC; and an extremely significant and positive relationship between organic matter content and CEC; and (2) in the vegetable fields, total soil exchangeable base increased somewhat in all the soil layers, with exchangeable K+, Mg2 and Na , doing significanty, and soil exchangeable Ca2 remaining almost unchanged; and the former three ions were much higher in saturation degree than those in the control, while the latter was lower in saturation degree and so was the soil base.

    • Effects of winter snowpack on accumulation of humic acid and fulvic acid during humification of foliar litters in an alpine forest

      2014, 51(5):1138-1152. DOI: 10.11766/trxb201401020006

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      Abstract:Accumulation of humic substances, such as humic acid and fulvic acid, during humification of foliar litters is one of the main pathways of soil formation and carbon sequestration in alpine forest ecosystems, where low temperature and frequent geological activities often limit soil formation. Snow cover, a typical meteorological characteristic during winter in alpine forests, may play an important role in foliar litter humification thanks to its insulation effect during the snow covering stage and its leaching effect during the snow cover melting stage. What’s more, the ongoing climate change is altering the pattern of snow cover, which could also have some essential effects on litter humification. However, the results so far available are still not clear which limits the understanding of foliar litter humification and its response to changes in winter snow regime in cold biomes. Therefore, to explore effects of snowpacks different in depth on accumulation of humic acid and fulvic acid during the early foliar litter humification stage, a field litterbag experiment was conducted in an alpine forest in Southwest China in the winter of 2012/2013. Air-dried foliar litters of six local species dominant in the region, namely, fir ( Abies faxoniana), cypress (Sabina saltuaria), larch (Larix mastersiana), birch (Betula albo-sinensis), willow ( Salix paraplesia) and azalea (Rhododendron lapponicum) were incubated under snowpacks different in depth (deep snowpack, moderate snowpack, thin snowpack and no snowpack), naturally formed at the forest gap center, canopy gap, extended gap and under the closed canopy, respectively. Thereafter, concentrations of humic acid carbon and fulvic acid carbon were measured, and for calculation of net accumulations at three critical stages, i.e. snow cover forming stage, snow covering stage and snow cover melting stage, in the first winter of the incubation as foliar litter humification proceeded. Results clearly showed that the concentrations of humic acid and fulvic acid carbons both displayed a rising tendency with the snow cover decreasing in depth during the three critical stages, and the net accumulations of the two humic substances also exhibited a similar trend at the snow cover forming and melting stages, but a reverse trend at the snow covering stage. However, net accumulation of the two humic substances was affected by the initial concentration of acid-insoluble residues in the foliar litters. In terms of net accumulation of humic acid carbon in the foliar litters incubated under snowpacks of any depth, the six different species of foliar litters followed an order of larch > willow > fir > azalea > birch > cypress. The net accumulation of humic acid carbon in the foliar litters of cypress, larch and willow significantly increased with the snowpacks decreasing in depth, but the net accumulation of humic acid carbon in the foliar litters of fir, birch and azalea were lower under thin and no snowpack than under deep and moderate snowpacks. However, fulvic acid carbon in the foliar litters except for that of birch was observed degrading to a varying extent, showing an order of larch > azalea > willow > cypress > fir > birch. Humic acid carbon accumulated in all foliar litters but fulvic acid carbon decomposed under snowpacks at the snow cover forming stage, and net accumulations of both humic acid and fulvic acid carbons in the foliar litter of fir, cypress, birch and azalea significantly increased with the snowpacks decreasing in depth. Humic acid and fulvic acid carbons in the foliar litters except for that of cypress decomposed at the snow covering stage, and net accumulation of fulvic acid carbon in the foliar litters except for that of willow significantly decreased with the snowpacks decreasing in depth. Most of the humic acid and fulvic acid carbons in foliar litters accumulated at the snow cover melting stage, and the net accumulation of humic acid carbon in the foliar litters of cypress, larch and willow and fulvic acid carbon in the foliar litters of fir, cypress, birch and azalea significantly increased with the snowpacks decreasing in depth. Meanwhile, the humic acid carbon to fulvic acid carbon ratios showed a significantly decreasing trend with the snowpacks decreasing in depth at the snow cover forming and melting stages, but increased at the snow covering stage, whereas the ratios in the foliar litters except for that of birch were lower than 1, suggesting that the formation of fulvic acid was faster than humic acid at the early foliar litter humification stage. In addition, canonical correspondence analysis showed that net accumulations of humic acid carbon and fulvic acid carbon were positively related to concentrations of nitrogen and acid-insoluble residues, but negatively related to concentrations of carbon, phosphorus and soluble components. These findings suggest that the early humification of foliar litter in alpine forests is promoted by reduced snow cover in the scenario of climate warming, but it is controlled by litter qualities and snowpacks at different stages through the winter.

    • >Research Notes
    • Spatial variation of soil organic carbon content in farmland and its influencing factors in Mengcheng County, Northern Anhui Plain

      2014, 51(5):1153-1159. DOI: 10.11766/trxb201303120111

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      Abstract:A total of 550 topsoil samples were collected from farmlands in Mengcheng County, a typical area of the Northern Anhui Plain for determination of soil organic carbon (SOC) content and further analysis of its spatial distribution and variability in the area in 2011 by means of statistics, geostatistics and geographical information system (GIS) technology. Results show that SOC contents in the farmlands ranged from 4.04 to 21.98 g kg-1 with an average of 10.41 g kg-1, and an variation coefficient of 24.12%, moderate in variation degree. The SOC semivariance model was a spherical one. Moreover a strong spatial autocorrelation of SOC content was observed. In spatial distribution SOC contents were generally high in the northeast, central and southwest parts of the county and varied sharply within the scope of the county, showing a trend starting from the northwest of gradually rising and then gradually declining towards the southeast, such a spatial variation was attributed mainly to mechanical composition (silt and sand) of the soil and then incorporation of straw.

    • Effects of bio-ash mixed with chemical fertilizer on ammonia volatilization

      2014, 51(5):1160-1167. DOI: 10.11766/trxb201310150462

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      Abstract:Bio-ash is produced from burning of biological solid waste, high in porosity, large in water absorption capacity, comprehensive in nutrient, sterile and non-toxic. An indoor incubation experiment was carried out using ashes of sawdust, rice husks, rice straws and corn stalks to explore effects of the ashes, when mixed at a varying ratio with chemical fertilizer on N volatilization from the fertilizer within a certain time period. N volatilization was determined with the alkali absorption method. Results show that the mixtures of the four kinds of ashes and chemical fertilizer regardless of N level (N1, N2 and N3), with the time going on, N volatilization increased first and then declined in both volume and rate, with peaks mostly appearing on D10~D15 of the incubation. In the mixture of rice husk ash, corn stalk ash and rice straw ash, addition of potassium dihydrogen phosphate significantly enhanced the effect of inhibiting volatilization of ammonia, while in the mixture of sawdust ash, the addition of potassium chloride or potassium dihydrogen phosphate had the same effect. Among the four kinds of ashes, sawdust ash was the lowest in the effect of inhibiting volatilization of ammonia. Therefore, ammonia volatilization was much higher in the mixture of sawdust ash than in the other three, and even reached as high as 5 times that of the others, especially, the mixtures were at N3 level. The effect of sawdust ash (pH12.8) varied with N level, displaying an order of N1 > N2 > N3. Elovich equation and parabolic diffusion equation can be used to fit the volatilization of ammonia from the mixtures over time, with correlation coefficients reaching an extremely significant level.

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