• Volume 55,Issue 5,2018 Table of Contents
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    • >Reviews and Comments
    • Progress in Researches on Effect of Iron Promoting Accumulation of Soil Organic Carbon

      2018, 55(5):1041-1050. DOI: 10.11766/trxb201802260035

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      Abstract:The content of total organic carbon in soil is a major indicator reflecting the content of total organic matter and further on soil fertility. There are numerous factors that affect accumulation of organic carbon in soil. Among them, iron plays an essential role in "capturing" organic carbon and forming "rust sink", thus promoting accumulation of soil organic carbon. A number of scholars have studied stabilizing mechanisms of soil organic carbon. In this paper, attempts were made to summarize the studies that had been done. It is found that the stabilizing mechanisms mainly include physical preservation of aggregates, chemical preservation of minerals, biological preservation of microorganisms and preservation of organic carbon per se. Among the four mechanisms, the first two are the main ones. Iron is closely involved in the mechanisms of physical, chemical and biological preservations. In physical preservation, iron promotes formation of soil aggregates. In chemical preservation, iron adsorbs and precipitates with organic carbon. At the same time, iron affects activity of soil microorganisms in biological preservation. All indicate that iron plays an important role in soil organic carbon accumulation. And the protective effect of organic carbon per se is mainly reflected in the anti-decomposition of a certain portion of organic carbon. In the end, the authors put forward several suggestions. More attention should be paid to the mechanisms of organic carbon sequestration and functional recovery of the carbon sink in the soil systems that are active in oxidation reduction and remarkable in ecological service function, to quantitative researches on and comparison between the different mechanisms in importance, and to simulation experiments, so as to better realize the goal of theory serving practice.

    • >Research Articles
    • Comparison Analysis of Methods for Prediction of Spatial Distribution of Soil Organic Matter Contents in Farmlands South Jiangsu, China

      2018, 55(5):1051-1061. DOI: 10.11766/trxb201711250563

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      Abstract:【Objective】Soil organic matter(SOM) plays a key role in maintaining soil quality and functions and crop productively and a critical role in global C recycling. Therefore, knowledge and understandings of spatial distribution patterns of SOM are important to sustainable utilization of soil resources, guarantee of food security, and mitigation of the momentum of global climate change.【Method】A total of 413 cropland topsoil samples (0~20 cm) were collected from the southern parts of Jiangsu Province for analysis of SOM contents, and ordinary kriging (OK), regression kriging (RK), and random forest (RF) methods were employed for mapping spatial distribution of SOM contents. Auxiliary data such as soil type, topographic factors derived from DEM, climate, soil temperature and moisture, soil properties, and agricultural management practices (N fertilization rate and C input by crop residues) varying in spatial resolution were first scaled into grids 300 m in resolution using either the kriging interpolation or neighborhood averaging method, and then the auxiliary factors screened by a stepwise-regression process were used in RK and RF predictions of SOM. Moreover, to identify impacts of the correlations between auxiliary factors and SOM content on spatial prediction of SOM contents in accuracy, the root mean square errors (RMSE) derived by RK and RF methods were also compared between the situations of removing and retaining the auxiliary factor with highest correlation coefficient.【Result】The SOM spatial distribution patterns derived with the OK, RK and RF methods were quite similar, that is to say, SOM contents in the eastern parts of the study area are relatively high, whereas those in the western parts are low. But local differences did exist in detail of SOM distribution prediction between the methods can be intuitively observed. The OK method was the lowest in prediction accuracy, with mean RMSE being 6.97 g·kg-1 and lower than the RK and RF methods, of which the mean RMSE of the RK and RF methods was lowered down to 5.25 and 4.97 g·kg-1, respectively, when total nitrogen (TN) of the auxiliary factors that were most closely related to SOM was integrated. However, when TN of these auxiliary factors was removed, the RMSE predicted with RK and RF was lower than that with OK, being 6.21 and 6.29 g·kg-1, respectively, while the average explained variance was decreased to 29% and 28%, respectively. However, the RK and RF methods are still better than the OK method, as the RMSE derived by OK was as high as 6.97 g·kg-1, and the explained variance of OK was only 9.7%.【Conclusion】RK and RF are both higher than OK in prediction accuracy, however, the difference in prediction accuracy between RK and RF depends on degree of the correlation between the auxiliary factors and SOM. When auxiliary factors most closely related to SOM, such as TN was included in the prediction, RF was better than RK; while those were excluded, , RK was slightly better than RF, indicating that RK is still promising due to the relatively high-cost of TN measurement. In addition, prediction accuracy of RF largely depends on degree of the correlation between the auxiliary data and SOM, when TN was removed from the RF prediction, the predicted RMSE increased significantly, indicating that the current easily attainable and available low-cost auxiliary are still facing many challenges in improving SOM prediction accuracy in plain regions with strong anthropogenic influences. Consequently, developments of new scaling methodology for raw auxiliary data or new higher resolution auxiliary data for quantifying relationships between auxiliary data and SOM are critical for improving accuracy of the prediction of SOM in plain areas with intensifying anthropogenic influences.

    • Distribution of Clay Minerals of Chunhua Loess-paleosol Sequence and Its Paleoenvironmental Significance

      2018, 55(5):1062-1073. DOI: 10.11766/trxb201711200459

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      Abstract:【Objective】The loess-paleosol sequence on the Loess Plateau of China has been considered as an important information carrier recording changes in the global environment and climate of the Quaternary peroid. As weathering products of land surface, clay minerals are widely found in Quaternary sediments, and their paleoenviromental significance has also attracted more and more attention. It has been documented that the formation and transformation of clay minerals is closely related to climatic conditions. However, so far, few studies have been reported on characteristics of the clay mineral in loess-paleosol profiles in the southern part of the Loess Plateau. Besides, previous researches about paleoclimate evolution in the south Loess Plateau focused mainly on Holocene, with little attention to climate changes in the Pleistocene. 【Method】 In this paper, a typical loess-paleosol profile of the Loess Plateau was selected in Chunhua County, Shaanxi Province, south of the Loess Plateau as research object. With the aid of the X-ray diffraction method, qualitative and semi-quantitative analyses of the soil samples from different layers of the Chunhua loess-paleosol profile were carried out for analyzing relative contents of clay minerals, illite/chlorite ratio (I/C value) and illite crystallinity (IC value), as well as regularities of their evolutions, and further for relationships of the characteristics of the clay minerals in the profile with changes in paleoclimate and eventually, for regularities of the evolution of the paleoclimate and paleo-environment in the Pleistocene in the south Loess Plateau. 【Result】Results show: (1) The three indices, i.e. relative content of clay minerals, ratio of illite to chlorite (I/C values) and illite crystallinity (IC value) of the Chunhua loess-paleosol profile are good indicators to be used in reversion of paleoclimate changes in the Pleistocene. (2) All the soil layers of the profile had the same clay minerals, but relative contents of the clay minerals varied significantly from layer to layer. During the period from the early Pleistocene to the mid-middle Pleistocene (WL-3~S5), the clay minerals were composed mainly of illite-montmorillonite-chlorite-kaolinite-vermiculite, and this period could be divided into two stages according to the changes in relative contents of the clay minerals. From the early Pleistocene to the early middle Pleistocene (WL-3~L11), the relative content of illite was comparatively low while the relative content of chlorite was quite high, which indicates that a cool temperate climate prevailed in this period. However, in the mid-middle Pleistocene ( S10~S5), the relative content of illite increased, while the relative content of montmorillonite and chlorite decreased, which indicates that the climate was relatively warmer and more humid in this period. In the late middle Pleistocene (L5~S1), the composition of clay minerals turned to be of illite-chlorite-vermiculite-kaolinite-montmorillonite, and the relative contents of illite and chlorite increased, implying a dry-cold climate dominated this period. Therefore, the changes in relative contents of the clay minerals in the Chunhua loess-paleosol profile indicate that from the early Pleistocene to the late middle Pleistocene, the climate generally became dry and cold, and experienced changes from cool temperate to warm wet and to cold dry. (3) The ratio of illite to chlorite (I/C value) and illite crystallinity (IC value) also exhibited phased variations from the bottom to the top of the Chunhua profile, that is increasing first and then decreasing. The distribution of I/C ratio and illite crystallinity indicates that the climate in the Pleistocene underwent an evolution process similar to that of the clay minerals in relative content. 【Conclusion】All the findings in this research are found to be conductive to the exploration of changes in the climate and environment of the south loess-paleosol during the Pleistocene, and may serve a scientific basis for comprehensive exploration of changes in climate and environment of various regions of the Loess Plateau during the Quaternary period of the Pleistocene.

    • Vertical Distribution of Soil CaCO3 Content / Lime Reaction in Mountainous Regions of North China and its Genetic Explanation

      2018, 55(5):1074-1084. DOI: 10.11766/trxb201801020586

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      Abstract:【Objective】Papers available in the literature show that loess dust precipitation exists generally in North China, becoming an important source of topsoil in the region. It brings in a large amount of fine mineral particles and nutrient elements, especially, CaCO3, to the soil. CaCO3 is an important component of the soils in arid, semi-arid and semi-humid regions, and hence a major indicator reflecting development degree of a soil. The purpose of this paper is to study vertical distribution of CaCO3 content and its characteristics in the mountainous soil of North China, in an attempt to explain causes of this phenomenon from the perspective of soil genesis. 【Method】A total of 257 soil profiles of various soil series in Beijing and Shanxi Province were investigated for mechanical composition, CaCO3 content and lime reaction and statistic analysis was performed of the data. On such a basis, vertical distributions of CaCO3 content and lime reaction in the mountainous soils of North China and their characteristics were summarized, and causes of the phenomena explained with the theory of soil genesis.【Result】Results show that the topsoil in North China is mainly composed of silt, which is similar to loess, indicating that loess dust precipitation is an important source of soil minerals, bringing in CaCO3 to the topsoils of the mountainous soils in North China. As soil humidity varies sharply from area to area due to difference in elevation, soil CaCO3 content does too. In areas above 1 500 meters in elevation, the soils are quite high in humidity (varying in the humid and damp regime)_due to relatively high precipitation (mean annual precipitation of over 600 mm) and relatively low temperature (varying in the gelic or cryic soil temperature regime), and good to vegetation, which in turn reduces surface runoff, but enhances downward leaching of CaCO3. As a result CaCO3 is leached out of the soil, no matter what it is derived from, and no lime reaction is detected throughout the solum. So in these areas, bio-climatic conditions play a leading role affecting soil CaCO3 content and lime reaction. However, in areas ranging between 500 and 1 500 meters in elevation, the soils are relatively low in soil humidity (varying in the semi-arid-humid/humid regime) due to relatively low precipitation (mean annual precipitation of < 600 mm) and higher soil temperature (varying in the frigid/temperate regime), and hence not so good to vegetation, As a result, CaCO3 leaching is weakened and lime reaction could be found almost everywhere. Therefore in these areas bio-climate conditions descend from the leading role to a major role, following behind the role of parent material. Whatever, no obvious characteristic of the distribution of soil CaCO3 content and lime reaction could be summarized in areas below 500 meters in elevation.【Conclusion】In conclusion, the characteristics of the vertical distribution of soil CaCO3 content / lime reaction caused by leaching process, strong or weak, is one of the typical soil genetic characteristics of the mountainous soils in North China.

    • Taxonomy of Soils Featuring Organic Soil Materials in West Sichuan, China

      2018, 55(5):1085-1097. DOI: 10.11766/trxb201711210493

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      Abstract:In certain regions of West Sichuan, the climate and topography is not very conducive to mineralization and decomposition of organic materials in the soil, thus making the soil enriched with organic soil materials and significantly different from mineral soils. 【Objective】In order to study where to put the soils rich in organic soil material in the western part of Sichuan in the soil taxonomy, this study was conducted. 【Method】Six soil profiles featuring such soils were selected in areas as research objects. Forming conditions, morphological characteristics and physicochemical properties of the soils were analyzed to determine diagnostic horizons and diagnostic features of the soils, by referring to the “Keys to Chinese Soil Taxonomy (third Edition)” and then find niches for these soil in the soil taxonomy. 【Result】Results show that the selected soils could be sorted into three soil orders (Histosols, Argosols and Gleyosols), and further into three suborders, four soil groups and six subgroups. According to the “Criteria for Establishment of Soil Family and Soil Series in the Chinese Soil Taxonomy”, the six soils were ruled into six soil families and six series. 【Conclusion】It was found that the soils rich in organic soil material were not necessarily always to be Histosols, while they could be either Argosols or Gleyosols. And Histosols might not necessarily have a Histic epipedon. The Histosols of Buric subgroup were good examples. Compared with the soil genetic classification system, the soil taxonomy could distinguish more accurately soil types from each other in the same area under similar bioclimatic conditions.

    • Characteristics of Soil Macropores in the Gully Area of Loess Plateau as Affected by Terrain

      2018, 55(5):1098-1107. DOI: 10.11766/trxb201712230496

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      Abstract:【Objective】 Soil macropores play an important role in hydrologic processes, such as rainfall infiltration, runoff occurrence, soil water movement and sediment deposition. As soil erosion varies with terrain (bottom and costa colpi of gully and the damland) in generation and development process, the soil forms under soil erosion vary too in soil texture and soil porosity. However, so far little has been done on effect of terrain on characteristics of soil macropores. 【Method】 In this study, undisturbed soil columns were collected at the three different landforms for analysis of macroporosity and rules of its variation with terrain and soil depth using the computerized tomographic scanning method. 【Result】 (1) Terrain did have a significant effect on macropore parameters. Damland was much higher than gully bottom in soil macroporosity, number and roundness of macropores and mean area per macropore. However, the effect of terrain on macropores was lower than that of vegetation as documented in previous studies. (2) Macropores also varied significantly in parameter with soil layer (50 mm each). Mean macroporosity and variation coefficients of the macropores in the soil at costa colpi varied sharply around the depth of 102mm. Macroporosity in the soil at the bottom of gullies fluctuated slightly, but did more significantly in the upper layer than in the lower layer. However, in the soil of damland, macropores varied in a similar trend in the upper and lower layers. (3) Soil macroporosity was significantly or extra-significantly and positively related to the number of soil macropore number and mean size per macropore, while the number of macropores was significantly and negatively related to clay content and saturated hydraulic conductivity. Equivalent diameter of the macropores was positively related to silt content and negatively to sand content. And (4) the macropores in the bottom of gullies were much higher in pore connectivity than those in the costa colpi and damland. From the point of view of reasons of the formation of macopores, those in the bottom and costa colpi of gully were formed under the impact of plant root systems, while those in damland were under the impact of long-term sedimentation and water infiltration. 【Conclusion】CT scanning showed that the differences in characteristic between soil macropores in the bottom, costa colpi and damland of gullies may be attributed to soil erosion and deposition processes.

    • Parameter Estimation and Uncertainty Evaluation of a Soil Solute Transport Model Using GLUE

      2018, 55(5):1108-1119. DOI: 10.11766/trxb201801260022

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      Abstract:【Objective】Computer programs, such as CXTFIT, are commonly used to calibrate soil hydraulic and transport parameters, such as dispersion coefficient and retardation factor. CXTFIT can be used to fit observations quite well, which leave researchers in this aspect such an impression that the “optimum” parameter sets simulated with this program can be used directly for modeling prediction. However, in the process of parameter simulation, inherent uncertainties do exist and are often underestimated. The objectives of this study were to assess and even quantify the uncertainties that may occur in parameter estimation using the convection-dispersion equation (CDE) and in adoption of the parameters in modeling prediction with the non-linear least squares (NLLS) and generalized likelihood uncertainty estimation (GLUE) methods. 【Method】 In this study, with the aid of CXTFIT, NLLS and GLUE coupled with the Latin hypercube sampling strategy was used to fit concentrations of bromide and copper nitrate in transport through three oil columns different in texture (i.e. Sandy loam, loamy sand and sandy clay loam), separately. And the parameters were optimized and analyzed to quantify the uncertainties that may occur in these processes by means of three quantitative metrics, that is, MNS (maximum coefficient determination coefficient ), P95CI (the percentage of observations included within the 95% confidence intervals) and ARIL (average relative interval length).【Result】Results show that the only “optimum” parameter set obtained with the NLLS technique fits the curve of solute outflow quite well with determination coefficients (R2 ) all > 0.98 for fitting Br- transport and > 0.937 for fitting Cu2+ transport, and with root mean square error lingering at the magnitude of 10-2, but it fails to cope with a large number of equivalent parameters. R2 being high in value only indicates the “optimum” parameter set is a proper fit of observation, but it does not mean the “optimum” parameter set is the true characterization of solute transport. The parameter set corresponding to the MNS of solute outflow fitted with can be used to simulate the observation as well as NLLS (R2 >0.937). But the value range of acceptable parameters determined by GLUE are much wider than that of NLLS (the length of 95% confidence intervals of GLUE is about more than 5 times as high as that of NLLS), which means that a large number of parameter sets that are high in likelihood value fall outside of the 95% confidence intervals determined by NLLS. The 95% confidence intervals of outflow concentration determined by NLLS covered 28.13%, 64.00%, and 46.01% of the data observed separately in the soil columns different in texture, leaving almost half uncovered on average, whereas those determined by GLUE did 87.62%, 80.93%, and 84.3%, separately, which indicates that it is not a good choice to use NLLS to optimize parameters and uncertainties of the model output. 【Conclusion】 To put all into a nutshell, GLUE performs better than NLLS in both parameter and response surface uncertainty analysis, for NLLS underestimates significantly the uncertainties in estimation of major transport parameters. GLUE has a much wider acceptable parameter valuation range and 95% confidence intervals for outflow concentration, which indicates that the “optimum” solution acquired by NLLS does not show any robustness as the solution acquired by CXTFIT does. So the usage of only “optimum” parameter sets to predict solute transport has to face high risk and high uncertainty.

    • Effects of Cd/Cu/Pb on Adsorption and Migration of Sulfadiazine in Soil

      2018, 55(5):1120-1130. DOI: 10.11766/trxb201712190581

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      Abstract:【Objective】Veterinary antibiotics are extensively used in livestock rearing industries all over the world for preventive and therapeutic treatments and growth promotion of poultry and/or animals. Due to the use of chemical fertilizers and compost, pollution from the industry and/or irrigation with sewage, etc., the content of heavy metals in the soil is getting higher and higher. It is, therefore, often found that the two kinds of pollutants, antibiotics and heavy metals exist simultaneously in the soil, affecting each other in adsorption and migration. Their pollution of the soil has become an environmental issue that can’t be ignored. Therefore, investigation of leaching and adsorption behaviors of these antibiotics and heavy metals in the soil is the first logical step to assess their ecological risks and then develop corresponding pollution control strategies.【Method】 In this research, the soil was exposed to different concentrations of Cd, Cu and Pb. Effects of the pollutants on adsorption and migration of Sulfadiazine (SDZ) in the soil were studied via both batch and column experiments. Adsorption isotherm of SDZ was fitted with Freundlich, Langmuir and Linear models and breakthrough curves of SDZ with the coexisting heavy metals were measured and modeled using numerical models that took into account reversible and irreversible kinetic sorption sites with the aid of the Hydrus-1D software.【Result】No influence of Cd was found on adsorption of Sulfadiazine, when Cd was 100.0 mg·kg-1 in concentration, but it did promote the adsorption of SDZ when 10.0 mg·kg-1 in concentration, and reduce the adsorption of Sulfadiazine, when 1.0 or 300.0 mg·kg-1 in concentration. When Cu, Pb and Cd, all 300.0 mg kg-1 in concentration, coexisted with SDZ, they displayed an order of Cd > Cu > Pb in effect on SDZ adsorption of Sulfadiazine. In the soil column leaching experiment, it was found that Cd, 10.0 mg·kg-1, slowed down the migration of SDZ, while no significant effects were found with Cd higher or lower in concentration. Comparison between the three elements shows that Cu promoted and Cd slowed down the migration of SDZ. The Linear equation was the best in fitting, with R2 being above 0.98. Compared with the OSM model, the TSM model simulated better the migration process of SDZ, with R2 >0.907 and RMSE <0.051. Instantaneous adsorption (f) was found quite high in the process of sulfadiazine migration. 【Conclusion】 Under complex pollution of SDZ and heavy metals, adsorption and migration of SDZ is affected by type and concentration of the heavy metal in the soil. The findings in this study may not only help improve knowledge of the mechanisms of adsorption and transport of SDZ in heavy metal contaminated soils, but also serve as a certain theory basis for management of environmental pollution.

    • Characteristics of Preferential Flow in the Intermediate Zone between Paddy Field and Ridge

      2018, 55(5):1131-1142. DOI: 10.11766/trxb201712070530

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      Abstract:【Objective】Studies available in the literature have shown that the ridges around the paddy fields are likely to lead to low water use efficiency and pollution of shallow groundwater. Preferential flow is a physical process of water and solutes moving along certain pathways, like pores and fissures in the soil, while bypassing the part of soil matrix and is ubiquitous in the paddy field under continuous flooding. Therefore, to study the status of preferential flow in paddy soil and its influencing factors may help quantify characteristics of water leakage in paddy fields and improve water and fertilizer utilization efficiency, and hence reduce the risk of pollution of shallow groundwater by agricultural chemicals in paddy regions. In order to elucidate effects of the ridges on soil water leakage in the intermediate zone between fields and ridges, comparison was made of different monitoring points in the field, transition zone and ridges for differences in characteristics of preferential flow.【Method】Field bright blue dye tracer experiments were conducted of the soils in the two typical intermediate zones (i.e., the intermediate between field and ridge and the intermediate between ridge and ditch ) of > 100 years old paddy field in the Jianghan Plain, Hubei Province.【Result】Results show that stained soil area ratio (SAR) fluctuated downwards with depth of the soil profile and a peak was observed in the 0~20 cm soil layer, accounting for 53.85%~88.55% of the total SAR of the soil profile; that the field was the highest in SAR in this soil layer, and followed by the transition zone, and the ridge; that although SAR was quite low in soil below 20 cm in depth at all the monitoring sites, the ridge was still 3.15 times as high as the field in mean SAR; that staining of the soil appeared quite consistent horizontally and vertically, that with increasing soil depth, the area of staining at horizontal levels gradually decreased from a plane to a dot. The ridge, impact in soil texture, was higher than the field in staining path number (SPN) that in the 0~29 cm soil layer. staining path width (SPW) varied in the range 10~80 mm and beyond, while in the soil layers down below, only a few paths <10 mm were observed; that the water flow in the field was mainly of the type of heterogeneous finger flow – highly-interacted macropore flow, while in the transition zone and ridge, it was mainly of the type of mixing macropore flow- highly-interacted macropore flow, for the SPW therein varied in the range of 10~80 mm and below. When water flowed from the field into the transition zone, it lost through seepage vertically and laterally, the two typical pathways, (i) via earthworm pores, root pores and fissures, which were more plentiful in the ridge, facilitating vertical and horizontal seepage of the water, while the plough pan in the field made it hard for the water to leach downwards, thus forcing the water to flow into the ridge and then percolate rapidly into deep soil layers; and (ii) further into ditches through the intermediate between ridge and ditch, of which the two were relatively different in elevation, so the water infiltrating into the ridge continued flowing vertically through the ridge and eventually into the ditch, besides percolating downwards.【Conclusion】Affected by the distribution of macropores in the field, transition zone and ridge, only a small amount of water in the field infiltrated through the plough pan and a large one lost through seeping laterally into the ridge and then percolating quickly and vertically into deep soil layers through macropores, thus leading to low water use efficiency and nitrogen pollution of water bodies. It is, therefore, essential to pay high attention to the influence of water flow in the ridges on leakage of soil moisture and solutes from paddy fields.

    • Effects of Rotation and Fallow in Paddy Field on Distribution and Stability of Soil Aggregates

      2018, 55(5):1143-1155. DOI: 10.11766/trxb201712220590

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      Abstract:[Objective] Proportion and stability of soil aggregates are important factors affecting healthy and sustainable development of paddy soil. [Method] A long-term stationary experiment on effects of crop rotation systems, including multi cropping, crop rotation and winter fallow, on paddy field was carried out in the years from 2012 to 2017. The experiment was designed to have five treatments: Double-cropping rice plus winter fallow land, double-cropping rice plus milk vetch in winter, double-cropping rice plus canola in winter, double-cropping rice plus garlic in winter and double-cropping rice plus ?. Soil samples were collected from the 0~50 cm soil layers of the plots of the five treatments for analysis, using the wet screening method, of proportions of the aggregates, 1 ~ 2 mm, 0.5 ~ 1 mm, 0.25 ~ 0.5 mm and 0.25 mm in particle size, separately and then, mean weight diameter (MWD), mean geometric diameter (GMD) and fractal dimension (D) of the fractions of soil aggregates was calculated, separately. [Result] Results show that regardless of treatment, the soil aggregates in the 0~50 cm soil layer were dominated with the fractions of 0.25 ~ 0.25 mm and < 0.25 mm in the time periods after the early or the late rice was harvested, and the two fractions reached 78.1% ~ 84.8% and 85.6% ~ 91.1%, separately, in cumulative content, while the fraction of aggregates of 1 ~ 2 mm and 0.5~1 mm, was only 13.1% ~ 21.9% and 8.9% ~ 14.4%, respectively. Obviously the cultivation of early and late rice increased the fractions (>0.25), but reduced those (< 0.25mm), and the effect of early rice was more prominent than that of late rice. The two crops also affected MWD and GMD significantly, but not D. [Conclusion] It is, therefore, quite obvious that the systems of multiple cropping rotations and two crops of rice plus straw returning are favorable to formation of large-sized aggregates rather than fine aggregates and the effect of increasing water-stable aggregates is more significant with early rice than with late rice, which in turn improves yield of the two crops. All the findings in this experiment are of great significance to the sustainable development of rice production in South China.

    • Stoichiometrc Characteristics of Soil Aggregates in Subtropical Eroded Red Soil under Vegetation Restoration

      2018, 55(5):1156-1167. DOI: 10.11766/trxb201801300070

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      Abstract:【Objective】This study was done to elucidate C, N and P distributions in soil aggregates and their stoichiometric characteristics in eroded red soil under vegetation restoration relative to history of the restoration. 【Method】Six sample plots were set up on slope lands of typical eroded red soil under vegetation restoration with different restoration history (0, 5, 10, 15, 30 and 80 years) located in Hetian Town, Changting County, Fujian Province of Subtropical China. Soil samples were collected from different soil layers (0~20 cm and 20~40 cm) of the six plots for analysis of contents of organic carbon, total nitrogen, total phosphorus in soil aggregates different in particle size (>5 mm, 2~5 mm, 0.5~1 mm, 1~2 mm, 0.25~5 mm and <0.25 mm). 【Result】 Results show that the contents of organic carbon, total nitrogen, total phosphorus in soil aggregates varied in the range of 2.06~27.71 g•kg-1, 0.54~2.12 g•kg-1 and 0.034~0.189 g•kg-1, respectively, and C:N, C:P and N:P did in the range of 3.06~13.05, 21.4~185.6 and 5.62~18.20, respectively. On the whole the contents of organic carbon, total nitrogen, total phosphorus and C:N increased in all fractions of soil aggregates in both soil layers with the restoration going on (P<0.05), and the trend was more significant in the 0~20 cm soil layer than in the 20~40 cm layer, while soil C:P and N:P displayed a rising-falling-rising trend, and . C:P deceased with soil depth, and N:P did not vary much. The contents of organic carbon, total nitrogen and total phosphorus, and C:N and C:P on the whole increased with the aggregates going down in particle size (P<0.05), except for the plot of 0 year, while N:P did not vary much with aggregate particle size (P>0.05). The content organic carbon, total nitrogen and total phosphorus in soil aggregates were remarkably positively related to their respective ones in the soil. In the soil aggregates the contents of organic carbon and total N positively related to C:N, the content of organic carbon was to C:P, and the content of total phosphorus was to N:P. 【Conclusion】All the findings in the study demonstrate that vegetation restoration mitigates soil erosion and significantly increases the contents of organic carbon, total nitrogen and total phosphorus and improves the function of soil aggregates as carbon and nitrogen pools, and what is more, P in the aggregates is the major factor restraining rehabilitation of the degraded ecosystem.

    • Nitrogen Output through Runoff on Red Soil Slope and Its Composition

      2018, 55(5):1168-1178. DOI: 10.11766/trxb201712200550

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      Abstract:【Objective】The development of agriculture in the sloping uplands of red soil has been restricted by low water use efficiency, high temperatures and low fertilizer use efficiency.Interflow in the soil has been playing a important role in runoff generation, nutrient loss and soil erosion. Carrying soil nutrients along, it merges into rainfall-induced runoff, which flows into water bodies, thus causing environmental problems, like waterbody eutrophication.Nitrogen (N) as one of the common soil nutrients causing eutrophication is highly mobile in the soil because it is hardly absorbed and fixed by soil particles, so it moves easily with surface runoff and interflow as its main pathway of migration.Consequently, to study soil nitrogen loss related to the joint effect of surface runoff and interflow on slope lands is of great significance. In some regions, plentiful and concentrated rainfall results in surface runoff and interflow that enhances nutrient migration.Recently, researchers have studied patterns of nitrogen migration in red soil through surface flow and its impacting factors, as well as generation of interflows and its influence on nitrogen output.However, so far little has been reported on investigations that have taken into full account the joint effect of surface flow and interflow on nitrogen migration in red soil.【Method】In order to explore characteristics of nitrogen output in sloping uplands of red soil under natural rainfall, large-scale lysimeters were used in a field experiment carried out during the year from May 2015 to May 2016, on a sloping upland of quaternary red soil in Jiangxi, China. The experiment had three treatments, i.e. planted with grass, mulched with straw, and bare land laid out for observation of forms of nitrogen lost with surface flow and interflow (30, 60 and 105 cm) relative to treatment under natural rainfall.【Result】 Results show: (1) Interflow at 105 cm depth was an important channel of N loss on the slope of red soil where erosion wasn’t serious. The interflow in the soil layer 105 cm in depth contributed more than 71% of the total N loss while surface runoff and interflows in the soil layers 30 and 60 cm in depth did less than 23% and 6%, respectively; (2) N in the interflow was mainly in the form of dissolved N, composed principally of dissolved inorganic nitrogen (DIN), especially nitrate nitrogen. The proportion of DTN (dissolved total nitrogen) in TN was 54.8%~86.9% and that of DIN in DTN was 57.8%~97.1% in the interflow. The proportions of various forms of N in the surface runoff varied with the treatment; and (3) Grass coverage effectively reduced N runoff loss, while straw mulch increased the risk of N leaching loss. 【Conclusion】All these findings in the experiment provide certain scientific support to control of N runoff loss from red soil slopelands by establishing a suitable vegetation cover. The key to reduction of nitrogen loss from agricultural fields is to control the formation of interflow or subsurface runoff in sloping uplands of red soil slope and to reduce content of nitrate nitrogen in interflow.

    • Effect of Laccaria Bicolor Inoculation on Contents of Inorganic Phosphorus and Labile Aluminum in the Rhizosphere Soil of Pinus massoniana Saplings

      2018, 55(5):1179-1189. DOI: 10.11766/trxb201802120407

      Abstract (1647) HTML (486) PDF 1.25 M (2059) Comment (0) Favorites

      Abstract:【Objective】 In most soils, TP (total phosphorus) is generally plenty, but its availability to plants is very low. When the soil is getting acidified, soil Al is liable to get activated and then bound with HPO42-,H2PO4-, and PO4-, turning them into hard-to-dissolve P, thus further lowering soil P availability. Some ectomycorrhizae (EM) are found to be able to deactivate soil Al, thus letting Al-complexes release bonded P in available form, for plants to take up. That is to say, some EMs could be introduced into acid soils to improve soil P availability and plant growth. In experiments of in vitro cultivation of EM fungi, some demonstrated their ability to raise P availability in soils neutral or slightly acidic, but little has been found in the literature validating such ability in the field. The present study aimed to assess effects of inoculation of EM fungi on inorganic P availability and Al activity in the rhizosphere soil of saplings planted in acid soil, and to explore mechanism of EM colonization improving host plants' resistance to Al toxicity. 【Method】 Germinating Pinus massoniana seeds, inoculated with three strains of Laccaria bicolor, namely Lb 270, Lb S238A, and Lb S238N, separately, were imbedded into pots of cold sandy yellow soil collected from a P. massoniana stand, and irrigated twice a day to maintain a proper moisture regime for 16 weeks under the natural conditions. At the end, comparison was made of Pinus massoniana saplings inoculated with EM fungi with those in the control (without inoculation). 【Result】 Results show that inoculation of L. bicolor significantly affected the contents of inorganic P and labile Al in the rhizosphere soil of the saplings and the effects varied with the strain. Compared with the control, inoculation with any of the three L. bicolor strains significantly improved growth and P and Al, uptake of the saplings. In terms of the effect, the three strains exhibited an order of Lb S238N > = Lb 270 > Lb S238A. Inoculation with Lb270 significantly decreased soil pH, the contents of available P, iron-bound P (Fe-P), calcium-bound P (Ca-P), total Al, and exchangeable Al, and the proportion of exchangeable Al in the fraction of labile Al, but increased the proportion of aluminum-bound P (Al-P) in the fraction of inorganic P, and the contents of labile Al or hydroxyl-Al and their proportions in total Al. Inoculation with Lb S238A significantly reduced Al-P, the proportion of Al-P or Fe-P in the fraction of inorganic P, total Al, labile Al, exchangeable Al, organic-complexed Al, and the proportion of exchangeable Al and organic-complexed Al in the fraction of labile Al, but raised soil pH, the content off available P, the proportion of occluded-P (O-P) in the fraction of inorganic P, the proportion of labile Al in total Al, and proportions of hydroxyl-Al or acid-soluble Al in the fraction of labile Al. Inoculation with LbS238N significantly decreased soil pH, the contents of available P, total Al, exchangeable Al, and the proportions of exchangeable Al and organic-complexed Al in the fraction of labile Al, but increased the content of hydroxyl-Al, the proportion of labile Al in total Al and that of hydroxyl-Al in the fraction of labile Al.【Conclusion】All the findings in this experiment demonstrate that inoculation with L. bicolor can improve the resistance of P.massoniana saplings to Al toxicity, which may be attributed to the ability of the fungi to enhance bio-availability of soil P, but their abilities to lower Al activity vary with strain of the fungi.

    • Study on Mechanism of Demethylation of Pectin Promoting Reutilization of Cell Wall Phosphorus in Rice (Oryza sativa) Root

      2018, 55(5):1190-1198. DOI: 10.11766/trxb201801250063

      Abstract (1984) HTML (1264) PDF 1.14 M (3325) Comment (0) Favorites

      Abstract:【Objective】Plants can survive under the stress of phosphorus (P)-deficiency by coordinating inorganic phosphorus (Pi) acquisition, translocation from roots to shoots and redistribution within the plant. Studies in the past have demonstrated that cell-wall pectin contributes greatly to reutilization of rice cell-wall Pi under the stress of P-deficiency, but not how to. Therefore, it calls for further studies for clarification. 【Method】Two rice cultivars, ‘Nipponbare’ (Nip) and ‘Kasalath’ (Kas), were selected as the subjects in the experiment to explore changes in endogenous phosphorus availability in the plants and difference between the two growing under the stress of phosphorus deficiency, and their specific reasons. Rice seedlings were cultured in the normal solution for two weeks and then moved into a nutrient solution with (+P) or without (-P) P for cultivation for a week. Roots and shoots of the seedlings were sampled and pulverized in a pestle with a mortar in liquid nitrogen, separately and by cultivar too. A portion of each pulverized sample was prepared into cell walls. To determine availability of endogenous phosphorus, inorganic phosphate (Pi) was extracted from fresh roots and shoots, separately, with 5% (v/v) sulfuric acid solution, and cell wall P was extracted fromdried cell wall with 2 mol·L-1 HCl solution. Concentration of phosphorus in the extracts was determined with the Mo-Sb colorimetric method. Then, in the late-on in vitro P analysis experiment, pectins different in methyl esterification degree were used to study relationship between the degree of methyl esterification degree of pectin and ability of the pectin to release hard-to-dissolve phosphorus. To follow changes in methyl esterification and activity of pectin methyl esterase (PME) in samples of the seedlings under the stress of P deficiency, root samples were treated with high-salt buffer solution to extract PME, which is able to trigger hydrolysis of pectin into methanol, which is then oxidized into formaldehyde. The activity of PME can be scaled according to the color reaction of formaldehyde with the Purpald reagent. Pectin in root was extracted from dried cell wall with hot water. Content of uronic acid in the pectin hydrolysates was determined with the colorimetric method, and methyl ester in the pectin hydrolysates was measured to characterize content of carbomethoxy in pectin. Then methyl-esterifcation degree of pectin was calculated based on the contents of uronic acid and carbomethoxy. 【Result】The present study shows that soluble phosphorus in rice was reduced rapidly when the plant suffered phosphorus deficiency. The content of soluble phosphorus in roots kept declining for 5 days and then leveled off, while the content in shoots started to decline obviously some time later, and the downward trend went on even after the 7th day. However, Nip was always found to be higher than Kas in content of soluble phosphorus in the roots and shoots of the plants, and released more cell wall phosphorus from its root, which, indicates that Nip is higher than Kas in ability to recycle its endogenous phosphorus. The in vitro experiment shows that the lower the methyl esterification degree of the pectin, the higher the capacity of the pectin of activating hard-to-solve phosphorus. Once coming under the stress of P deficiency, Nip kept methyl esterification of pectin low in degree by improving the activity of pectin methyl esterase, while Kas did not vary much in activity of pectin methyl esterase and hence unable to lower pectin methyl esterification degree of the root. 【Conclusion】All the findings in this study suggest that under the stress of phosphorus deficiency, rice may keep cell wall pectin low in methyl esterification degree by improving the activity of pectin methyl esterase, thus promoting P release from root cell wall to raise the content of endogenous soluble phosphorus for use by other organs of the plant.

    • Characterization of Reduction of Iron Oxide and Oxidation of Ferrous Iron in Upland Cinnamon Soil Profiles in West Henan, China

      2018, 55(5):1199-1211. DOI: 10.11766/trxb201712070430

      Abstract (1719) HTML (781) PDF 1.44 M (2348) Comment (0) Favorites

      Abstract:【Objective】Iron redox processes are important microbial processes, which are closely related not only to bioavailablity of heavy metals and degradation of organic pollutants in anaerobic environment, but also to soil fertility of upland soils. Therefore, the issue has aroused much attention the world over. Iron redox process in plough layers of paddy fields and upland fields was already well documented, however, it is still unclear whether iron redox process exists in the soil underneath the plough layers, or what are characteristics of the iron redox processes. 【Method】In the present study, samples of upland cinnamon soils, collected from different layers of a 0~100 cm deep soil profile, were prepared into slurries, separately and then incubated anaerobically in darkness or in light, 0.5 mol·L-1 HCl extractable Fe(II) in the soisl samples was analyzed dynamically to study characteristics of the reduction and oxidation of iron oxide in the soil profile. To explore transformation of C, N and S coupled with the iron redox process in the profile, organic carbon, inorganic carbon, nitrate and sulfate in the profile soil samples before and after incubation were extracted by water and analyzed with a TOC analyzer and Ion Chromatography. 【Results】Fe(II) accumulation was found in all the samples during anaerobically incubation. Iron reduction potential decreased with soil depth in the profile. Fe(II) re-oxidation appeared only in the 0~80 cm soil layer of the profile under illuminated incubation. Ferrous oxidation decreased with depth in the profile from 20 cm to 80 cm. Water soluble organic carbon and iron oxide reduction both decreased with depth in the profile under incubation in light illuminated or in darkness. Water soluble inorganic carbon increased in the soil during the incubation in darkness, while it decreased in illuminated incubation. Water soluble nitrate decreased by 83.4%~98.6% in the soil incubated either in darknss or in light, and the range of the decrease narrowed with depth in the profile. The range of the decrease in water soluble sulfate narrowed with depth in the profile under incubation in darkness, while water soluble sulfate increased with depth in the profile within the range from 0~40 cm under illuminated incubation. Correlation analysis shows that iron reducing potential and ferrous oxidation was positively and significantly related to increase and decrease in water soluble inorganic carbon, respectively. Rate constant, max velocity of iron reduction and ferrous oxidation velocity was positively and significantly related to water soluble organic carbon. While decrease in nitrate was positively related to reducing potential, max velocity of iron reduction, re-oxidation and velocity of iron oxidation. Sulfate reduction was positively and significantly related to reduction potential, and max velocity of iron reduction under incubation in darkness, while it was negatively to amount and rate of ferrous oxidation under illuminated incubation. 【Conclusions】Results show that iron reduction process exists throughout the whole profile from 0 to 100 cm, and iron reduction potential, and maximum velocity of iron reduction decreased significantly with depth in the profile. Phototrophic ferrous oxidation appeared in the 0~80 cm soil layer in the profile; the amount and rate of ferrous oxidation was much higher in the 0~40 cm soil layer in the profile than in the 40~80 cm soil layer. Correlation analysis of iron redox process and soil properties in the vertical direction of the upland cinnamon soil shows that iron redox process in the profile was not only affected by soil organic carbon, but also limited by the contents of soil nutrients including N and K. The findings may help improve the cognition of the habitat of iron redox microbes, and serve as certain basis for in-depth understanding of the iron redox processes in upland cinnamon soil.

    • Visible Light Spectrum Based Segmentation of Sandalwood Image and Prediction of Total Iron Content in Plant

      2018, 55(5):1212-1221. DOI: 10.11766/trxb201803160003

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      Abstract:【Objective】To explore relationship between color of sandalwood leaves and content of total iron in the plant, a visible-light-spectrum-based sandalwood image segmentation method was bought forth for prediction of content of total iron in the plant.【Method】 First of all, Otsu’s method was used to remove the pigments of soil and the other green plants, by segmenting Channel b, and then Channel L was extracted, and again Otsu’s method was used to extract the image of sandalwood out of its background. Then burrs of the image were smoothened through median filtering and morphological operation. Based on the fact that new and old leaves varied differently in color under iron stress, a method for determination of new and old leaf ratio was developed. First, the minimum circumcircle of the segmented sandalwood was to be defined, and then calculation was done of the ratio of the canopy breadth measured last time to that measured this time, and then the ratio was multiplied by the radius of the minimum circumcircle to gain radius of the concentric circle. The ring part between the two concentric circles represented new leaves and the rest old leaves. Color value of each channel (R, G, B, H, S, I, L, a and b) was calculated. Then four groups of comparison were designed (spectral value of the whole plant, spectral value of new leaves, ratio of the spectral values of new leaves and the whole plant, and ratio of spectral values of new leaves and old leaves). And in the end, predictions of the content of total iron were analyzed using the BP neural network modified with different methods.【Results】(1) The segmentation algorithm proposed in this paper is better than the support vector machine in result, with pixel error ranging within 5%, and the errors of all RGB channels controlled within 3%. (2) The optimum content of total iron in sandalwood leaves varies between 250~300 mg kg-1. When the content of total iron in leaves is less than the optimum value, the color value of Channel G increases while that of Channels R and B decrease with rising content of total iron. But when the content of total iron in leaves gets beyond the optimum value, the trend goes reversely, which indicates that being either too high or too low iron content would be a factor causing chlorosis in leaves. (3) Comparison shows that the prediction based on the ratio of spectral values of new leaves and old leaves is the best, while that based on the spectral value of the whole plant, the worst, which indicates that the method, proposed in this study, of comparing new and old leaves in spectral value is the most effective one, reflecting the content of total iron in the plant. And (4) In terms of efficiency and effectiveness, the four kinds of neural network models exhibits an order of GA-BPNN > PSO-BPNN > BPNN-Adaboost > BPNN, which indicates that optimization is better than the iteration, and that appropriate initial value and threshold value have more influence on prediction ability of the neural network models .【Conclusion】All the findings of this research have a guiding significance for nutritional diagnosis of precious tree species in terms of micro-elements, and provide a new way of thinking for precision forestry.

    • Distribution of Microplastics and its Source in the Sediments of the Le’an River in Poyang Lake

      2018, 55(5):1222-1232. DOI: 10.11766/trxb201803010115

      Abstract (2193) HTML (1853) PDF 3.62 M (2483) Comment (0) Favorites

      Abstract:【Objective】Microplastics (< 5 mm in particle size) in the environment as a new type of pollutant have become a widely concerned issue in recent years. Microplastics may pose certain risks to marine ecosystems because they are very small in particle size, high in abundance, and ubiquitous in distribution and hence readily ingested by marine organisms, such as fish, shellfish, etc. and to wetland ecological environments, too. Recent years have witnessed rapid growth of the number of research reports about microplastics pollution the world over, but just initiation in China. In this study, the Le’an River Section of the Poyang Lake, a tract of wetland, was defined as its research site and samples of sediments were collected from the wetland for analysis of content of microplastics so as to explore distribution and sources of the microplastics in the region, and provide some scientific data for studies of microplastic pollution in inland lake and river wetlands. 【Method】This study combined field surveys and sampling for indoor analysis methods. Samples of sediments were collected from the nine sampling sites distributed in three typical sections of the region, that is,, the upper-stream of the Le’an River, the tributary (the Dawu River) of the Le’an River and the mid- and down-streams of the river, for microscopic, SEM-EDS and FTIR analyses. Abundance, surface morphology, composition and source of the microplastics in the sediments was determined. 【Result】 Results show that the microplastics in the surface sediments of the region were composed mainly of those in the shape of fragment (58.3%), fiber (21.5%), films (13.8%) and foam (6.4%). The average of the 9 sampling sites in abundance of microplastics was 1 800 ind•kg-1,whih tended to be on the high side as compared with the findings of the researches in other areas. The average of the upstream of the Le'an River, the tributary River (Dawu River) and the downstream of the Le'an River, was 1 121 ind•kg-1, 2 871 ind•kg-1 and 1 366 ind•kg-1, respectively, forming an order of tributary > upper-stream > mid- and lower-streams. Source analysis of the microplastics reveals that industrial pollutants discharged from industries in the neighborhood, and plastic wastes discarded from cities and towns alongside the river and fishery activities were the major sources; SEM-EDS analysis shows that the microplastics were weathered to a varying degree with rough surface and apparent tears; And energy spectrum analysis demonstrates that onto the surface of the microplastics adsorbed were substances and elements, such as Si, Fe, Mg, O, Al, Ca, etc., which aggravated hazardness of the microplastics to the environment and the organisms therein. 【Conclusion】There are 4 kinds of microplastics in the sediments of the Le’an River and the Poyang Lake, in terms of morphology, that is, are fragments, foams, films and fibers. The average abundance of microplastics in the region is 1 800 ind•kg-1, which is sorted to be moderate tending to be on the high side, compared with that of other regions similar in environment. The microplastics come mainly from nearby industries, residential settlements and fishery activities. The microplastics appear to be weathered to a varying degree with rough surface and obvious tears and gibbosities, which lead to expansion of their specific surface areas, and enhancement of their adsorption capacities for organic pollutants, heavy metal ions and microbes, thus aggravating their hazardness to the environment and organisms therein.

    • Study on Driving Factors of Soil Acidification Based on Grey Correlation-Structure Equation Model

      2018, 55(5):1233-1242. DOI: 10.11766/trxb201712120594

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      Abstract:【Objective】 Soil pH is an important indicator of soil fertility and also a factor significantly impacting crop growth and production. Soil acidification, as a result of the joint effects of a number of external and intrinsic factors, has become an urgent problem to solve for sustainable development of agricultural production in China. How these factors affect soil acidification differ significantly in pathway and effect. It is, therefore, of critical significance to elucidate region-specific key driving factors of soil acidification to the control of soil acidification and improvement of soil quality.【Method】The study set Fujian Province as its research object. Based on the 1:50 000 spatial cropland and soil type databases of the province, the data of topsoil properties of the 36 777 sampling sites investigated in 1982 and the 56 445 sampling sites in 2016, and other relevant data including climate elements at the meteorological stations, pH of the precipitation at the acid rain monitoring points and fertilizer application rates from 1982 to 2016 in Fujian Province, a spatial database of cropland soil acidification and its potential affecting factors of the province was established. On such a basis, in-depth discussion was performed of key driving factors of cropland soil acidification in the province during the period from 1982 to 2016 with the aid of the grey slope correlation (GSCM)-structure equation (SEM) model. 【Result】Results show that soil pH of the cropland had decreased on average by 0.34 unit and 70.67% of the cropland soils had been acidified in various degrees by 2016 in Fujian Province, and the acidification varied significantly and spatially in degree. GSCM analysis shows that the main driving factors of the cropland soil acidification in Fujian Province included annual mean fertilizer application rate, CEC, clay content, annual mean precipitation, annual mean pH of the precipitation and organic matter content. Grey correlation coefficient of their absolute values was higher than 0.620. The key driving factors of the cropland soil acidification illuminated by SEM included severe acid rain, high precipitation and high application rate of chemical fertilizers, reaching 0.38, -0.40 and -0.70 in direct effect, 0.11,-0.35 and -0.16 in indirect effect, and 0.49, -0.75 and -0.86 in total effect, respectively.【Conclusion】The model of SEM-GSCM proves to be a better method to explore for key driving factors of cropland soil acidification in different regions. An effective approach to control of cropland soil acidification in Fujian is to control acid rain through controlling the industry from emitting acidic exhaust gas, and optimize fertilizer management through extrapolating the use of organic manure to minimize chemical fertilizer application in agriculture.

    • Effects of Bio-manure combined with Chemical Fertilizer Reduced in Application Rate on Soil Fertility and Yield and Quality of Tomato

      2018, 55(5):1243-1253. DOI: 10.11766/trxb201802270062

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      Abstract:【Objective】The use of plant growth-promoting microbes to improve plant nutrition and hence reduce the rate of chemical fertilizer is becoming a popular strategy for sustainable agriculture.【Method】In this work, a field-pot experiment, designed to have four treatments, i.e. CF (control, 100% of chemical fertilizer at a conventional rate), Treatment OF (Chemical fertilizer, 75% of the conventional application rate plus organic manure, 50 g·plant-1), Treatment BF (Chemical fertilizer, 75% of the conventional application rate plus Trichoderma-enriched bio-manure), and Treatment SS (Chemical fertilizer, 75% of the conventional application rate plus Trichoderma spore suspension), was conducted on the crop of tomato.【Result】Results of the field experiment demonstrated that Treatment BF was almost the same in yield as CF, while Treatment OF and Treatment SS was significantly lower than CF. The field experiment and the pot experiment displayed the same trend. In the pot experiment of four successive cropping of tomato, Treatment OF and Treatment SS decreased by 6%~38% and 9%~35%, respectively, in tomato yield as compared with CF. Besides, the treatments significantly affected quality of the tomato fruit (p < 0.05), by reducing NO3- accumulation by 32%~46% in the fruit under greenhouse, while Treatments BF and OF increased the content of Vitamin C and the content of total soluble sugar in the fruit by 2%~23% and 35%~54%, respectively. The field experiment also showed that Treatments BF and OF increased the content of total soluble sugar in the fruit by approximately 40% while decreasing NO3- accumulation by 42%~57%. In the pot experiment, Treatments BF and OF were significantly higher than CF and Treatment SS in content of available P and K (p < 0.05), while CK was always the highest in content of ammonia-N among the 4 treatments throughout the 4 growing seasons. The soil nitrate-N gradually increased with the cropping going on in all the treatments, particularly Treatments BF and OF, which were significantly higher than CF. Moreover, Treatment BF was much higher than the other two and CF in population of soil microbes and in most cases, it sustained relatively big populations of bacteria, fungi and actinomycetes. Pearson correlation analysis shows that soil nutrients were closely related to population of soil microbes, and that the population of Trichoderma in the soil was positively and significantly related to that of soil fungi and actinomycetes, which may be attributed to the effect of Trichoderma, once colonized in Treatment BF, stimulating propagation of bacteria, fungi and actinomycetes in the rhizosphere of tomato and hence enhancing availability of soil nutrients. The population of soil microbes in the rhizosphere of the crop was also found positively and significantly related to numerous soil fertility indices.【Conclusion】To sum up, all the findings in the experiment suggests that the application of chemical fertilizer, 75% of the conventional application rate, plus Trichoderma-enriched bio-manure can effectively guarantee a stable yield of tomato higher in quality, and in the long run, increase the population of soil microbes and improve soil fertility.

    • Effects of Extraneous Nitric Oxide and Salicylic Acid on Physiological Properties of Wheat Seedlings under Salt Stress

      2018, 55(5):1254-1263. DOI: 10.11766/trxb201801230054

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      Abstract:【Objectives】Wheat is one of the most important crops cultivated in coastal saline soils. The seed germination period and seedling stage are two important growth stages in the life circle of wheat and the plants during the two stages are pretty sensitive to salt stress. This study was designed to explore effects of extraneous nitric oxide (NO) and/or salicylic acid (SA) applied alone or in combination, on growth and physiological properties of wheat under the stress of 120 mmol•L-1 NaCl in an attempt to evaluate the effects of extraneous NO and SA mitigating salt stress on growth of wheat seedlings, and to provide a theoretical basis for elucidating the mechanism of extraneous NO and SA enhancing salt tolerance of wheat. 【Methods】A hydroponic experiment was carried out, cultivating wheat (Triticum aestivum L.) and using extraneous sodium nitroprusside (SNP, a nitric oxide [NO] donor) and SA as regulatory substance to explore effects of extraneous NO and/or SA on growth and physiological properties of wheat under salt stress (120 mmol•L-1 NaCl). This experiment was designed to have six treatments; i.e. CK (Hoagland nutrient solution), NaCl (120 mmol•L-1NaCl), SA (120 mmol•L-1 NaCl+100 μmol•L-1 SA), SNP (120 mmol•L-1 NaCl+100 μmol•L-1 SNP),1/2 (SA+SNP) (120 mmol•L-1 NaCl+50 μmol•L-1 SA+50 μmol•L-1 SNP, and SA+SNP (120 mmol•L-1 NaCl+100 μmol•L-1 SA+100 μmol•L-1 SNP). Growth indices, root activity, photosynthetic pigment content, superoxide anion (O2•-) production rate, H2O2 content, MDA content, electrolyte leakage and antioxidase activities of the wheat seedlings in all the treatments were analyzed for comparison to explore effects of NO and/or SA. 【Results】Results show that Treatment NaCl was significantly higher in O2-1 production rate and H2O2content, but significantly lower in wheat growth and photosynthetic pigment synthesis. Treatment SNP or SA significantly mitigated the damage of wheat caused by salt stress, but the effect of Treatment SA+SNP was more significant. Compared with Treatment NaCl, Treatment 1/2(SA+SNP) was 74.26% higher in root activity and 39.58%, 24.46% and 33.06% higher in content of Chl a, Chl b and Car respectively, but 30.52% and 29.16% lower in O2-1 production rate in leaves and roots and 15.78% and 24.23% lower in content of MDA in leaves and roots, respectively. Besides, Treatment 1/2(SA+SNP) also significantly increased the content of antioxidase as well as the absorption of mineral elements, such as N, P, K and Ca. 【Conclusion】Compared with Treatment SNP or SA, Treatment SA+SNP is more effective in reducing ROS accumulation induced by salt stress, MDA content and electrolyte leakage, improving chlorophyll content, proline content and soluble protein content, antioxidase activity; enhancing root activity in absorbing mineral elements, as well as in inhibiting Na uptake and reducing Na content in the plants, thus relieving salt stress of the wheat seedlings. Among the treatments in the experiment, Treatment 1/2(SA+SNP) is the most effective in mitigating salt stress on wheat.

    • Effects of Succession of Halophytic Vegetation on Carbon Metabolism Diversity of Fungi in The Yellow River Delta

      2018, 55(5):1264-1275. DOI: 10.11766/trxb201712200461

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      Abstract:【Objective】 As an important component of the soil microorganisms, fungi play an important role in cycling nutrients, maintaining and building soil fertility and improving soil structure and so on. As a decomposer in the soil, fungi can effectively decompose various kinds of macromolecule materials and hard-to-decompose litters in the soil, promote nutrient uptake of plants, and be used as an indicator of ecosystem health. Carbon source utilization capacity of soil fungi reflects overall metabolic characteristics of the fungal communities. To explore relationships between soil fungal carbon source metabolism and succession of halophytic vegetation is an important step to elucidate variation of the ecosystem in internal structure and function. 【Method】 In the region of the Yellow River Delta, in line with the natural succession of the halophytic vegetation, sample plots of bare coastal tidal flats, flats covered with Tamarix chinensis and Angiospermae (highly salt-tolerant plant community), and flats of Imperata and A.venetum (mildly salt-tolerant plant community) were selected, three each, making up a total of 15 sample plots for soil sampling in the 0~20 cm and 20~40 cm soil layers. The soil samples were analyzed for physicochemical properties, and carbon source metabolic activity of soil fungi using the Biolog-FF microplate culture method, and further for characterization of the carbon metabolic activity of the soil fungi in the plots relative to halophytic vegetation. 【Result】 The Biolog-FF microplate tests show that in terms of average well color development in the 0~20 cm soil layer, the plots followed an order of Imperata > A. venetum > Tamarix chinensis > Angiospermae > Bare plot, while in terms of AWCD in the 20~40 cm soil layer, they did an order of Imperata> Angiospermae > Tamarix chinensis > A. venetum > Bare plot, which suggests that with the succession of the halophytic vegetation, carbon metabolism activity of the fungi in the soil increases significantly (P) and so was Shannon-Wiener index, richness index and Simpson index of the fungi. In all the sample plots, except for that under Angiospermae, all the three indices were higher in the 0~20 cm soil layer than the 20~40 cm one, which suggests that with the succession of halophytic vegetation going on positively, the fungi in the soil improve in diversity and abundance and in dominance of common species in the community. Correlation analysis of soil properties, fungal AWCD and fungal diversity shows that TN, AN, SOM, phosphatase and catalase significantly (P<0.05) promoted while soil salinity significantly (P<0.05) inhibited fungal metabolism of carbon sources. Principal component analysis shows that Fibric alcohol, ornithine and D-mannitol were the main carbon sources for fungal utilization in the 0~20 cm soil layer, whereas D-sorbitol , glycerol and L-aspartic acid were in the 20~40 cm soil layer, which suggests that saccharides, alcohols and acids are the main carbon sources that control carbon metabolism of the fungi in the soil. 【Conclusion】 As a whole, with the succession of the halophytic vegetation going on positively, the soil underneath declines gradually in salinization degree and improves in soil quality, and the fungal community in the soil is growing more and more stable in structure. All the findings about relationships between carbon source metabolism of soil fungi and succession of halophytic vegetation may lay down a theoretical foundation for the ecological restoration and utilization of the Yellow River Delta.

    • Effects of Application of Organic Materials to Apple Trees through Vertical Holes on Soil Nitrate Metabolism, and Leaf Photosynthesis of Apple

      2018, 55(5):1276-1285. DOI: 10.11766/trxb201712110499

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      Abstract:【Objective】Drilling of holes in soil can improve soil aeration, and application of organic material can increase soil organic matter content. The study was carried out to investigate effects of the two used simultaneously on soil nitrate metabolism, and leaf photosynthesis, water use efficiency (WUE) and plant growth of apple trees. In a field experiment of this study, four different kinds of organic materials were applied, separately, into the vertical holes dug within the root zone of the trees. This study was expected to be able to provide certain reference for development of new technology for soil management in apple orchards 【Method】 Four-year-old red Fuji apple trees cultivated in the root cellar were used as test material. Holes, 15 cm in diameter and 50 cm in depth were drilled around the trees within their root zones, and then corn stalks (CS), fruit tree branches (FTB), biochar (BC) and fermented sawdust of fruit tree branches (FFB), which are good in aeration, were applied, separately, into the holes. Nitrification and denitrification, nitrate reductase (NR) and nitrite reductase (NiR) activity, and inorganic nitrogen content in the soils of the root zones, net photosynthetic rate and transpiration rate of leaves, and WUE and growth of the plants were determined, six and ten months after the experiment started. 【Result】The determination, either six or ten months later, shows that application of CS or FFB improved soil nitrification and denitrification intensity, the most significantly especially CS, which did by 52.68% and 45.81%, respectively, 10 months after. BC exhibited similar effects, 6 months after the application. The determination 10 months after the application shows that all the four kinds of organic materials increased significantly soil nitrification and denitrification intensity. Both the determinatons show that all the four kinds of organic materials increased the activity of soil NR and NiR, except FTB, which decreased soil NiR activity in the first 6th months, and then ,increased soil NiR activity, but reduced NR activity in the 10 months. CS was the most significant in the effect, raising soil NR and NiR activities by 46.43% and 18.02%, respectively, in the first six months, while FFB was the most in the 10 month period, raising by 48.00% and 9.30%, respectively. The application of the organic materials in the experiment, regardless of kind, enhanced soil nitrate nitrogen content during the whole period as demonstrated by the determinations 6 and 10 months after the application, while CS, FTB and FFB reduced soil ammonium nitrogen content in the first six months and then raised the content thereafter. The four treatments also significantly increased relative soil water content in the 0~40 cm soil layer, relative chlorophyll content, and diameter and length of new shoots. Among the four, CS came on the top in the effect on relative soil water content in the 0~40 cm soil layer, and diameter and length of new shoots, being 7.80%, 11.63% and 17.19%, respectively, higher than the originals, and followed by FTB, whereas FTB and BC sat in the bottom in the effect on diameter of new shoots, and FFB did the same in the effect on length of new shoots. Besides, CS, FTB and BC significantly increased net photosynthetic rate and transpiration rate of leaves and WUE of trees as demonstrated by the determination 10 months after the treatment, especially CS which increased the parameters by 57.32%、22.22% and 29.12%, respectively, and was followed by BC and FTB. 【Conclusion】The practice of applying organic materials into vertical holes around the trees within their root zones has some positive effects on soil nitrate metabolism, leaf photosynthesis, WUE and plant growth, and the effects vary with kind of the organic material applied. Among the four applied in the experiment, corn stalk was the most effective.

    • >Research Notes
    • Variation of Soil Organic Matter in Transition Zones and Its Influencing Factors

      2018, 55(5):1286-1295. DOI: 10.11766/trxb201702080009

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      Abstract:The research on rules of spatial variation of Soil Organic Matter in plain-hill transitional zones and their affecting factors is of great practical significance to guiding agriculture. This study was oriented to explore variation of soil organic matter (SOM) and its influencing factors in a transitional zone between the Jianghan Plain and the mountainous area in West Hubei) in China. A total of 500 soil samples from the surface soil layer (0~20cm) were collected and analyzed for SOM content. By means of correlation analysis and stepwise regression analysis, out of the 14 affecting factors, seven variables, including elevation, slope, aspect, available iron, soil bulk density, soil gravel degree, clay content that were closely related to SOM, were selected as explanatory variables. OK and GWRK methods were used to interpolate the SOM data into the study area, and ME, MAE, RMSE, r, IP were used as validation indices for determination of prediction accuracy of the models. Results show that GWRK was higher OK and RK in prediction accuracy, which indicates that the local spatial regression model can be used to explain spatial variation of the SOM in the transitional region.The coefficient spatial distribution maps of the GWR model can be used to reflect degree of environmental variables affecting SOM spatial nonstationarity relative to geographical location, which may serve as a basis for exploring dominant affecting factors of SOM relative to terrain condition, and also as an important reference for plotting accurate SOM spatial distribution maps of transitional zones.

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