Abstract:The process of microbial extracellular electron transfer (EET) is an important driving force of element cycling and energy exchange in epigeosphere. While the previous studies focused on the interaction between soil particles and ions, recently, the biogeochemical processes of the EET among microbe–humus–mineral received widespread attention. The current EET studies enlightened us with new insights into the epigeosphere from the perspectives of chemistry and microbiology. Since microbes, humus and minerals are very essential factors of the biogeochemical processes on earth surface system via their interactive redox reactions, the main aim of this review is to reveal the detailed mechanism of the EET among microbe–humus–mineral and illustrate their biogeochemical significances on the earth surface system. The paper introduces, first, pathways via which electrons flow from inside to outside of a microbial cell, and then, two pathways via which electrons transfer from the surface of microbes to humus and minerals: (i) direct electron transfer, including direct contact and nanowires; (ii) indirect electron transfer mediated by humus, including “electron shuttling processes” and processes of bonding between humus and membrane c-type cytochromes. In this review, based on the key processes and key factors of the thermodynamics, energy transport processes of the whole EET chain of the microbe–humus–mineral system was discussed on a theoretical basis. The importance of redox state of c-type cytochromes on EET was highlighted through those discussions, which suggests that the standard redox potential (E⁰) and electron transfer capacity (ETC) of humus play dominant roles in the humus-mediated electron shuttling processes. Furthermore, the mass transfer and reaction rates under molecule level are also analyzed using a kinetic approach, which suggests that mediated nanowire-network-mediated electron transfer might be the most efficient way for facilitating EET processes. In this field, there are several new technical means available to solve the key scientific issues, including: (i) spectroelectrochemistry, combining electrochemistry and spectroscopy, is a useful approach for correlating thermodynamics and kinetics; (ii) molecular biology techniques are essential for recognizing the functional proteins responsible for EET processes; (iii) high-resolution imaging techniques are very conducive to the study on micro-structure of the nanowires; and (iv) time-resolved techniques are essential to determination of the rapid reaction occurring in the EET processes. To sum up, the future studies in this field should encompass the following four aspects: (i) studies related to extracellular respiring bacteria, which may help build a complete picture of the bacterial community, and will be helpful for the reorganization of other unknown strains; (ii) The summary on the functions of the proteins responsible for EET will help understanding their roles in this EET process; (iii) The discussion on humus and minerals, especially their structure, can improve the understanding of their functional mechanism and highlight their microbial ecological significances; (iv) The modeling of EET processes from thermodynamics and kinetics can provide a quantitative understanding of the intrinsic factors controlling EET processes.

Abstract:Application of synthetic nitrogen (N) fertilizer has been playing a critical role in enhancing the supply of food to an increasingly growing world population. However, large inputs of mineral N fertilizer in excess of the crop requirements may lead to low N use efficiency and cause a series of negative environmental impacts, such as eutrophication of surface waters, nitrate pollution of groundwater, soil acidification and greenhouse gas emissions. Such environmental problems are getting worse due to predictable increase in the use of mineral N fertilizer in the future. Therefore, optimal N fertilizer management strategies synchronizing N supply with crop demand should be developed to maintain crop yield and economic profit while minimizing negative environmental impact. Organic fertilizer as substitute for mineral N fertilizer has been advocated and practiced to increase soil carbon (C) sequestration and improve soil fertility. It has also been suggested that application of organic fertilizers, either alone or in combination with mineral N fertilizers, is effective in mitigating N-related pollution, improving soil fertility, and increasing crop yield. At present, how to fertilize rationally, improve crop yields, build up soil fertility and meanwhile maintain a sound ecological environment is one of the major challenges to agricultural research. Which step of N transformation in the soil would long-term application of organic manure affect thus influencing N supplying capacity and N retaining mechanism of the soil? What is the mechanism behind long-term application of organic manure decreasing N-related pollution and the increasing crop yield? This review elaborated effects of long-term fertilization on key processes of soil nitrogen cycling in agricultural soil in expectation to provide some theoretical basis for rationalization of long-term fertilization and improvement of N fertilizer utilization rate. The review proceeded from the angle of primary N transformation rate of the processes of soil nitrogen cycling to discuss effects of fertilization (mineral or organic fertilizers) on key processes of the soil nitrogen cycling. Soil N mineralization and assimilation are two crucial links in the cycling and factors that determine soil N supplying capacity. Long term application of nitrogen fertilizers could increase soil organic N and C contents and provide crops with available N slowly through mineralization of soil organic N and subsequent nitrification. Large volumes of long-term fertilization experiments demonstrate that long-term application of N fertilizers could stimulate soil primary N mineralization rate by increasing soil organic N and C contents. Long-term application of chemical N fertilizers or organic manure both have some influence on assimilation of soil ammonium nitrogen, which is reflected as a whole in better effect of organic manure raising soil ammonium assimilation rate than that of chemical fertilizer. Generally speaking, long-term application of N fertilizer, especially organic manure, could significantly increase soil N primary mineralization and assimilation turnover rate, and stimulate soil autotrophic nitrification, too, which may be attributed to the difference between chemical fertilizer and organic manure in stimulation mechanism. The experiments also demonstrate that the application of either chemical fertilizer or organic manure could increase soil denitrification rate, and the effect is more apparent with the application of organic manure. Being a substitute of chemical fertilizer, organic manure has been advocated and used to improve soil fertility and carbon sequestration capacity. Researches indicate that the application of organic manure, either singly or in combination with chemical fertilizers can effectively reduce nitrate pollution, and improve soil fertility and crop yield, but in terms of application rate, it could not be said as the more the better. Like chemical fertilizer, organic manure, if applied excessively, may also increase the risk of N loss. Rational fertilization with its impact on eco-environment taken into consideration is the only way to raise crop yield, maintain soil fertility and pursue sustainable development of the agriculture. The study on effects of long-term fertilizer on various processes of soil N cycling will help us understand how long-term fertilization affect soil N supplying and retaining capacities and lay down a scientific basis for rationalizing N fertilization.

Abstract:With the rapid development of intensive cultivation, soil-borne diseases of crops are very common and severe in China due to inappropriate management, consecutive monoculture, direct incorporation of crop residues into soil etc. The issue has become one of the main drives of continuous increase in pesticides consumption in order to achieve high crop yields and threatened the sustainable production, food quality, environment and ecosystems safety. However, soil scientists almost ignore the research on soil-borne pathogens. Since the functions of soil-borne pathogens are known, they are ideal objects to explore the influences of soil microbial biodiversity on soil microbial functions, the relationships between host plants and pathogens, between pathogen and antagonistic microbes, and influences of soil physic-chemical properties on the activities of soil microbes. Soil science owns special advantages to understand the growth, production, and functions of soil-borne pathogens because there are components of soil. The understandings of soil environments for the survival and growth of soil-borne pathogens are the basis to control the soil-borne diseases caused by soil-borne pathogens and to realize the zero increase target of pesticide consumption by 2020 in China. Therefore, soil science takes an unavoidable responsibility to control the populations of soil-borne pathogen. Meanwhile, soil science itself will develop greatly with the deep insight into the soil-borne pathogens and solution of crop diseases caused by soil-borne pathogens.

Abstract:The loess-paleosol sequence in the Loess Plateau of China contains a complete set of climate environment information since Quaternary, of which the extraction uses geochemical analysis as an important approach. In this paper, the key issue under discussion is whether the knowledge in the past coincides with the profile configuration and soil properties of the S₃ paleosol developed during 336 to 307 ka BP in the Guangzhong region and the paleoclimate conditions under which it was developed. For that end, this study took the Shaolingyuan profile of S₃ paleosol in Xi'an as subject, for exploration of, element migration in and chemical weathering characteristics of the profile and their implications in terms of paleoclimatic change through field investigations and geochemical analysis. The authors conducted three field investigations in March, 2014. Based on the field observation and measurement, the author divided the S₃ profile in configuation and collected 61 soil samples, one every 8 cm on average along the profile for analysis of, chemical composition and CaCO₃ content. Geochemical elements were determined with a PW2403 X-Ray fluorescence spectrometer analyzer of the Holland Panalytical Corp., and CaCO3 was with a BW14-08.53 calcium analyzer of the Holland Eijkelkamp Corp.. Results show as follows: The profile could be divided into argillic horizon (Bts), weathered and leached loess horizon (BC) and CaCO₃ nodule illuvial horizon (Bck) in the light of development of ferruginous clay film and migration of CaCO₃, and the argillic horizon of the Shaolingyuan Profile S₃ was formed of three layers (Bts1-Bts2-Bts3). In Horizon Bts, migration of CaO and CaCO₃ was the most significant, with leaching rate reaching up to －99.31% and －83.06%, respectively, and that of Sr, Na₂O and MgO was significant, too, but Fe₂O₃, Al₂O₃and Rb accumulated slightly, particularly, Al₂O₃and Fe₂O₃ in Bts3 layer. The Shaolingyuan Profile of S₃ paleosol lied in the transient phase between the primary weathering stage and the moderately strong weathering stage, with weathering displaying a rising order of BC < Blt2 < Blt1 < Blt3 in intensity. The Bts3 layer had basically completed the primary chemical weathering process characterized by leaching of Ca and Na, but had not yet started the next process characterized by leaching of K. In the light of migration and accumulation of CaCO₃ and Fe₂O₃, it could primarily be determined that the soil of the Bts3 layer was slightly alkaline during its development, and the soils in the other two layers, Bts1 and Bts2 were alkaline, and, the Shaolingyuan profile S₃ belonged to yellow cinnamon soil. During the period of S₃ paleosol development, the annual mean precipitation in Xi’an region was calculated to be around 800 mm.

Abstract:The technology of image spectroscopy has been widely used in soil attribute mapping in the past few decades.However,vegetation cover seriously affects the acquisition of soil spectral information, leading tomisestimating of soil attributes by visible and near-infrared (vis-NIR) spectroscopy. The traditional solution dealt with vegetation cover interfering soil spectra by masking out the areas with high vegetation coverage, thus resulting in absence of soil information for these areas. Some researchers also tried to use vegetation indices to estimate soil attributes, with results showing that the general applicability and transferability of these vegetation indices was limited by study areas and crop varieties. Therefore, how to remove the influence of vegetation on soil spectrum has become a crucialissue in estimating soil components, such as salt content over partially vegetated surfaces. The residual spectral unmixing method was previously used to separate different components of a mixedspectrum, however, the percentage of each component had to be known as a prerequisite. Recently blind source separation (BSS), a method previously often used in signal separation analysis, has successfully been appliedto separating soil spectral information from vegetation spectral information. In order to verify the effectiveness of BSS, in theHuanghai Raw Seed Growing Farm in Dongtai of Jiangsu, was selected as an experiment site, with its field delineated into plots diversified in soil salt content by amending the soil with salt and vegetated sparsely by seeding in different densities The experiment eventually had a total of 50 plots, 5 levels in soil salt content and 10 in sowing density. Then spectra, photos and soil samples of each plot were collected regularly until the soil surface was fully covered by vegetation. A total of 189 groups of field spectral reflectance of the plots various in vegetation coverage, soil salinity and growing season, were analyzed for influences of vegetation on estimationof soil salt content, and effectiveness of BSS removing the interference of vegetation. Results show that vegetation cover seriously affected accuracy of the estimation of soil salt content with R2_cv=0.53, RMSE_cv=3.54 g kg^-1, RPD_cv=1.47, R2_p=0.50, RMSE_p=3.33 g kg^-1 and RPD_p=1.41. However, the BSS algorithm, based on equation z=tanh(y), effectively eliminated the interference of vegetation on soil spectral reflectance, and improved accuracy of the estimation of soil salt content in the over partially vegetated areas using vis–NIRspectroscopy, with R2_cv =0.66, RMSE_cv=3.10 g kg^-1, RPD_cv=1.70, R2_p=0.63, RMSE_p=2.89 g kg^-1 and RPD_p=1.57. However, the effectiveness of BSS weakened when vegetation coverage was getting high, because it was unable to capture enough soil information from the mixed spectra. Additionally, choosing a suitable number of source spectra was essential to the results, and two was the best choice in this case. The method proposed here is expected to broaden the use of spectroscopy, which is usually limited to bare soil, and facilitates wider application of remote sensing images to map soil salinity overpartially vegetated surfaces.

Abstract:Soil organic matter (SOM) is not only an important indicator of soil fertility but also an important source and sink in the global carbon cycle. Therefore, it is essential to acquire the information of SOM for soil management. The visible and near-infrared (VIS-NIR) reflectance spectroscopy technique, known as a novel, rapid, accurate, environment-friendly and efficient approach when compared with conventional laboratory analyses, is a promising one to acquisition of soil properties. Construction of a calibration set is key to use of VIS-NIR quantitative analysis in building up a quality prediction model. Conventionally, selection of samples for the calibration set is based on soil physical and chemical properties or soil spectral information, like the concentration gradient method(C) and Kennard - Stone (KS) method, which are able to select samples that may be representative of physical and chemical properties or spectra, but not of geographical space and multivariate information. Impacts of the shortages on prediction accuracy of the model have rarely been reported. The aim of this paper is to explore how sample selection methods affect accuracy of the VIS-NIR reversion model in estimation of SOM, using soil samples collected from lands under different types of land use in the riparian areas of the Jianghan Plain. A total of 270 soil samples were collected, air dried and ground to pass a 2 mm sieve, for analysis of VIS-NIR spectra using a FieldSpec3 spectrometer. The spectral curves were preprocessed with log10, Savitzky-Golay (SG), multiplicative scatter correction (MSC) and mean center (MC). A total of four categories of ten sample selection methods based on multivariate soil information were proposed for constructing calibration sets. The first category, including the concentration gradient method and the method adopted several properties (P-KS), depends on soil physical and chemical properties; the second category, including the KS method and the Reduce on Neighbor Samples (RNNS) method, is based on spectral information; the third category, including the C-KS and C-RNNS methods, combines soil physic-chemical properties with spectral information; and the forth category uses land use type hierarchy in combination with all the aforementioned methods. The P-KS method takes into comprehensive account parameters, like SOM, Fe, N, P and bulk density (BD), that may be quite high in weight of impacts on soil spectra and uses KS algorithm to select soil samples representative of a variety of physical-chemical properties for construction of the calibration set. The C-KS and C-RNNS methods divide SOM concentration into six levels, from each of which two-thirds of the samples were selected using the KS and RNNS methods to form the calibration sets. The methods based on land use type hierarchy divide the entire sample set into three categories, namely dry land, paddy field and the others. For each category, soil samples representative of SOM distribution or soil spectra were selected in combination with the concentration gradient method, KS, RNNS and C-KS, separately to form calibration sets, which were then merged into a calibration set representative of land use type. On such a basis, a partial least squares regressions (PLSR) model was established, showing that in the first and second categories, the models with calibration sets formed with the C, KS and RNNS methods, representative of SOM distribution or soil spectra singularly, were not so good in prediction accuracy; and those with the P-KS method were much better, with determination coefficient for prediction (R_p²)being 0.55, root mean squared error of prediction (RMSE_p) being 7.54 and ratio of performance to standard deviation (RPD) being 1.47. The models with calibration sets formed with the C-KS method, representative of both physical and chemical properties and spectra, were good in accuracy with R_p² being 0.64, RMSE_p being 7.13 and RPD being 1.66. The inclusion of land use type in forming calibration sets, greatly improved the models using the C, RNNS and C-KS methods in prediction accuracy, bring R_p² up to 0.70, 0.59 and 0.68, RMSE_p to 6.34, 6.47 and 6.58, and RPD to 1.84, 1.84 and 1.51, respectively. It is therefore, quite obvious that the use of calibration sets formed with soil samples representative of multi-layers of soil information can improve the models in prediction accuracy. The L-C method has turned out to be the best method for sample selection in construction of calibration sets for VIR-NIR models for prediction of soil organic matter contents in the riparian areas of the Jianghan Plain.

Abstract:Soil organic matter is closely related with soil fertility, so the knowledge about spatial distribution of soil organic matter is conducive to rationalization of fertilization management and improvement of land use potential. As carbon source, soil organic carbon is an important factor affecting regional carbon budgeting. Remote sensing data has widely been used in digital soil mapping, which may improve accuracy of the prediction of soil properties to a certain extent. With the aeolian sandy fluvial land and loess hills in Yuyang District cited as subject, this study tried to predict soil organic content and distribution in the topsoil layer of the region of a varying resolution (30 m, 56 m and 250 m), using random forest (RF) algorithm and relevant thematic mapper (TM), Advanced Wide Field Sensor (AWIFS), Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM) data, separately, and in addition, other various factors affecting distribution of soil organic matter, and to validate the predictions with soil samples collected from 324 sampling sites. Variables in the prediction were screened in the light of out-of-bag (OOB) errors the RF algorithm may yield. The mean error (ME), mean absolute error (MAE), root mean square error (RMSE) and Pearson correlation coefficient (R) were used to evaluate the differences between predicted and observed values of soil organic matter relative to resolution. Entropies of the prediction, using the RF model, of distribution of soil organic matter in regions different in topography were compared. Besides, explanation of spatial variability of soil organic matter with the RF model was compared relative to resolution, and at the same time, various environmental variables in the aeolian sandy fluvial land area and loess hilly area were ranked in importance relative to resolution of the TM, AWIFS and MODIS data used, so as to identify the most important environmental variables affecting distribution of soil organic matter; and based on the partial dependence map of soil organic matter on the variables, specific range of the impacts of the main variables were delineated. Results showed that: 1) in the aeolian sand fluvial land area, the prediction using the RF model and the AWIFS data is the highest in accuracy, with OOB error being 3.52 and correlation coefficient between predicted and measured values reaching 0.67, regardless of percentage of the samples taken for validation, while in the loess hilly area, the prediction based on the TM data is the highest, with OOB error being is 3.31 and correlation coefficient reaching 0.71. The prediction is better in the loess hilly area than in the aeolian sand fluvial land area, with MAE being in the range of 1.27 ~ 1.57 g kg^-1 in the former and in the range of 1.46 ~ 2.08 g kg^-1 in the latter. 2) In the aeolian sand fluvial land area, vegetation is the most important factor affecting distribution of soil organic matter, and mostly in positive relationship with soil organic matter. Among the TM data, reduced simple ratio (RSR) is the highest in effect on soil organic matter, or > 7.5 g kg^-1, among the AWIFS data, normalized difference vegetation green index (NDVI) and ratio vegetation index (RVI) are, or > 8.5 g kg^-1, and among the MODIS data, NDVI is or > 8 g kg^-1. Elevation is the second one and its impact varies the most sharply when it ranges between 1 200 and 1 260 m and peaks at 1 220 m. Distance from water source is the third one. As water sources in the aeolian sandy fluvial land area are quite scattered and small in area, their impacts on soil organic matter seldom exceed 500 m. 3) In the loess hilly area, elevation is the most important factor affecting soil organic matter and negatively related to soil organic matter. Geographic location is the second one, soil organic matter declines in content from southwest to northeast in the area. Vegetation is the third one, in positive relationship with soil organic matter, but in all the three types of datasets, the impacts of vegetation indices on soil organic matter never go beyond 8 g kg^-1. So, it is quite obvious that in areas relatively simple in topography, it is advisable to use data relatively low in resolution instead of data high in resolution in predicting soil organic matter and the RF model is more effective in predicting in areas complex in topography.

Abstract:Collapse mound, a serious soil erosion phenomenon in granite areas of South China, occurs mainly on mound or hill slopes under the interaction of water and gravity, causing severe destructions and threats in a wide range, including Hubei, Hunan, Jiangxi, Anhui, Fujian, Guangdong, and Guangxi, mainly south to the Yangtze River, and hence a grave impact on the economy in these hilly regions. So far a lot of research work has been done on mechanisms of how mount collapses occur. In the aspect of water regime in collapse mounds, related scientists have analyzed permeability of the colluvial deposits from collapse mounds, revealing that colluvial soil reaches the level of steady permeation in a relatively short time, and also studied soil permeability of collapse mounds at different depths. Analysis from the angle of initial infiltration rate, stable infiltration rate, average infiltration rate, and infiltration angle shows that permeability declines steadily from the red earth layer down to the detritus layer. Therefore, this article proceeds from collapsing of mounds and water regime of the soil per se, with a view to elaborating water movement processes during the collapse of mounds or cliffs, exploring soil water characteristic curves of collapse mound profiles, including topsoil layer, red earth layer, streaked layer, and detritus layer, and their fitting processes with equations, and analyzing the mechanisms of how collapse mounds occur from the angle of soil moisture and pority. The study adopted field sampling and in-lab analysis together. Two typical profiles of collapse mounds in Southeast Hubei, Wuli and Yanglong were selected as subjects of the study. Soil water characteristic curves in various soil layers were plotted with the aid of a CR21G high-speed thermostat centrifuge of the Hitachi Corp. and on the basis of the soil water characteristic curves, soil porocities of the various soil layers were analyzed. Meanwhile, equations were screened for fitting the various soil water characteristic curves of the profiles. Results showed as follows: (1)In the Wuli and Yanglong profiles, soil release rate varied regularily with soil water suction rate. In the streaked soil layer and sandy soil layer, soil water release rate was high when their soil water suction was low, and the soil water characteristic curves in various soisl layers all leveled off. The topsoil and the red earth layers were higher than the streaked and detritus soil layers. (2)Based on the field-measured values of the water characteristic curve and the calculated equivalent porecity, pore size distribution in the profiles of collapse mounds was studied. It was found that the two profiles followed a similar law in soil pore size distribution, that is, the proportion of large pores increased while that of capillary pores decreased with soil depth going down from the topsoil layer to the detritus layer. The increase in number of large pores created a favorable condition for water movement, thus enhancing the probability of collapsing soil erosion. (3) The van Genuchten equation and the Gardner equation were tested to fit the curves, and the fitting was evaluated. It was found that the van Genuchten equation was better to fit the measured data of the soil moisture characteristic curve of the topsoil and red earth layers with relatively little deviation, while the Gardner equation was better to fit those of the steaked soil layer and the debris layer. On the whole, the van Genuchten equation is higher in fitting accuracy. Evaluation using the residual square sum method indicates that generally speaking, it is advisable to use the van Genuchten equation to fit soil water characteristic curve of granite soil.

Abstract:The subtropical red soil hilly region in South China, rich in hydrothermal and soil resource, is one of the most important grain production regions, playing a key role in development of the agricultural economy of the country. With the economy developing so fast, human activities in the region are getting too intensified, leading to destruction of large tracts of natural vegetation and consequently, declining soil and water conservation capacity. Abundant rainfall in the region causes large volumes of surface runoff eroding the thin soil layers on the slopes, which not only results in soil nutrient loss and soil quality degradation, but also brings about serious environmental problems in the lower reaches of the river valleys. Therefore, it is imperative to develop researches of mechanisms of the soil erosion and nutrient translocation for conservation of the red soil resources. In order to understand influences of shallow clear-water flow scouring on soil erosion and solute transport, a laboratory scouring experiment, designed to have three scouring inflow rates (10 L min^-1, 15 L min^-1 and 20 L min^-1), was conducted on artificial slopes of red soil derived from quaternary red clay and effects on the transport processes of non-sorbed chemicals (bromine) in runoff and sediment during the processes of soil erosion caused by surface runoff were evaluated. Results show that flow velocity of the runoff on the slope surface increased with increasing volume of the incoming flow from the upper slope; no matter how the flow conditions were in the upper slope, runoff yielding rate increased rapidly at the initial water releasing stage and then tended to level off; an apparent linear relationship was observed between cumulative runoff volume and duration of runoff yielding; when water flew down at a rate of 10 L min^-1, 15 L min^-1 and 20 L min^-1from the upper slope, the cumulative runoff volume reached 263.2 L, 295.1 L and 291.04 L, respectively; the higher the volume of the flow from the upper part, the stronger the scouring effect of the sheet surface runoff: sediment content in runoff fluctuated sharply with time, especially at the initial runoff scouring stage (0~5 min); when water flew down at a rate of 15 L min^-1, sediment yielding rate dropped drastically with time, whereas when water flew down at a rate of 20 L min^-1, sediment yielding rate displayed a trend of rising first and then declining; 20 L min^-1; cumulative sediment volume changed with time, showing a power function relationship; the cumulative sediment volume when water flew down at 15 L min^-1 and 20 L min^-1was 1.42 times and 4.25 times that when water flew down at 10 L min^-1, respectively; at the initial runoff scouring stage(0~5 min); the higher the water flow rate, the higher the sediment content n runoff; sediment content in runoff varied with time in a pattern similar to that sediment yielding did in and sediment yielding rate decreased gradually with the time going on regardless of how the flow rate was. Concentration of bromide decreased as a power function of the duration of runoff-yielding; especially at the initial 4 minutes of runoff scouring, concentration of bromide decreased significantly. All the findings indicate that the loss of soil solute with surface runoff depends mainly on degree and time of the interaction between soil and runoff. Based on the comparative analysis of effects of water flow rate from upper slopes on variations of volume of runoff, sediment content in runoff and soil solute in runoff with time, it is concluded that both runoff and sediment productions vary in a wavy pattern no matter how the water flows; the higher the water flow rate, the higher the runoff yielding rate on the slope. Sediment yielding rate acts differently. It is quite flat in fluctuation when the water flow rate is low, fluctuates drastically at the initial runoff yielding stage when the water flow rate is and tends to level off when erosion gullies gradually develop in shape. Cumulative sediment volume is a power function of cumulative runoff volume. Concentration of soil solute in runoff displays a similar relationship with duration of runoff production, regardless of how water flow rate is. Variation of soil solute concentration in runoff can be divided into two stages: rapid decline at the initial runoff yielding stage (0~5 min) and slow decline to a low value after 5 min. Through fitting with equations, it is found that the equation of power function can be used to describe the characteristics of solute attenuation in runoff. The findings of the experiment have some great practical significance to effective prediction and control of soil erosion on red soil slopes and soil nutrient loss with the erosion.

Abstract:Landslide accumulations in the earthquake area of Wenchuan are formed typically of mixtures of rock fragments and soil, loose in structure. Drastic rill or gully erosion tends to occur with rainfall runoff, thus leading to grave soil and water loss. Therefore it is of great importance to launch a study on rules of water and sediment transport with runoff on landslide accumulation slopes. Based on field investigation, an indoor scouring experiment, designed to have 4 treatments in rock fragment and soil ratio (0:1, 1:3, 1:2 and 1:1), 3 treatments in water flow rate (4, 8 and 12 L min^-1) and 2 treatments in nearest dwell angle (34° and 36°) was carried out to study variations of soil erosion rate and hydrodynamic parameters and their relationships on landslide accumulation slopes in the Wenchuan earthquake area. Results show that with the souring experiment going on, the soil erosion rate, flowing power and specific flowing power gradually decreased, while water flow shear force increased at first then decreased, and specific energy at water flow cross-section decreased at first, then increased and decreased at last. On slopes, 0:1, 1:3 and 1:1 in rock/soil ratio, soil erosion rate, water flow shear force, flowing power, and specific energy at water flow cross-section, increased with increasing water flow rate, but on slopes, 1:2 in rock/soil ratio, only soil erosion rate increased with increasing water flow rate and the other indices varied irregularly. In this study, the effects of water flow shear force, flowing power and specific energy at water flow cross-section on soil erosion rate could all be described with power function equations, and the effect of specific flowing power was not so obvious. All the findings in this study may help lay down a foundation for establishment of a model for predicting soil erosion on landslide accumulation slopes in the earthquake areas of Wenchuan.

Abstract:Saline ice water irrigation must go through two processes: saline ice melting and melt-water infiltration, which determine the effect of irrigation together. An in-lab saline ice melting experiment was conducted using saline water, two in salinity (7.5 g L^-1 and 15 g L^-1) to investigate changes in quantity, quality and ion composition of the saline water during the ice melting process, and a simulated soil column irrigation experiment designed to have four treatments in irrigation water: Treatment FW (irrigation with fresh water), Treatment SW (irrigation with saline water 7.5 g L^-1 in salinity), Treatment SIW(7.5) (irrigation with saline ice melted water 7.5 g L^-1 in salinity), and Treatment SIW(15) (irrigation with saline ice-melted water 15 g L^-1 in salinity), and two treatments in irrigation mode (irrigation with water directly and irrigation with ice), was also conducted to explore effects of irrigation with saline melt water on water and salt movements in the coastal saline soil(silt loam in texture). Results show that saline ice, regardless of salinity level, melted similarly in melting process with melt water higher in volume, salinity and sodium adsorption ration (SAR) at the initial melting stage and lower in the late stage, and ion content and electrical conductivity (EC) of the melt water displayed a similar pattern. Only about 25.46% and 32.78% of the melt water flowing out from saline ice, 7.5 g L^-1and 15 g L^-1 in salinity, respectively, during its thawing process was less than 3 g L^-1, which was critical in soil salt elution. In Treatment FW of the soil column experiment, soil water and salt movement lasted the longest, soil hydraulic conductivity dropped the fastest and soil water content in the surface soil layer after the irrigation water completely infiltrated into the soil was the highest, reach 33.88%, followed by 30.16% in Treatment SIW(15), 29.40% in Treatment SIW(7.5) and 28.64 in Treatment SW. In the four treatments, mean soil salt content reached 2.32 g kg^-1 in Treatment FW, 2.80 g kg^-1 in Treatment SIW(7.5), 3.87 g kg^-1 in Treatment SIW(15) and 4.31 g kg^-1 in Treatment SW. Among the four treatments, the same in irrigation volume, Treatment SIW(15) was the lowest in salt leaching effect. Soil ion analysis indicates that SAR in the 1~25cm soil layer in Treatments FW and SIW(7.5) dropped significantly far below that in Treatments SW and SIW(15). In Treatment FW, the feature of soil alkalization was the most outstanding. All the findings indicate that the relationship between wetting front depth and time follows a power function in Treatments FW and SW, however, the wetting front depth is associated with time linearly in Treatments SIW(7.5) and SIW(15); the fast dropping hydraulic conductivity in Treatment FW is attributed to swelling and dispersion of soil particles; the lower SAR in the top soil layer in Treatments FW and SIW(7.5) is due to the water with lower SAR leaching. SAR is positively related to salt in the soil profile, and soil alkalization is positively correlated with pH. To sum up, in areas deficient in fresh water source, but sufficient in saline water source, moderately saline water subjected to freezing and thawing process can be used in irrigation to effectively lower salt content in the topsoil and to meet the demand of the agricultural production for water.

Abstract:Soil temperature regime refers generally to soil temperature at 50 cm (T50) in soil depth or at the interface between lithic or paralithicsubstance and soil in soil profiles thinner than 50 cm. It is an importantparameter charactering soil properties and a diagnostic feature and basis in modern soil classification systems for dividing soil classification units. However, so far none of the existing observatory stations iscapable of providingobservatory data all by itself sufficient for dividing attributes of soil temperature. Fortunately, as soil temperature at any observatory stationis closely related to geographic position (coordinates, altitude, etc.), meteorological conditions and some other environmental elements of the locality the station sits in, some researchers have built up several models by makinguse of these obtainable environmental indexes for assessing soil temperature regime. Currently the following five methods are commonly used in researches on soil temperature regime in China: “Soil temperature interpolation method”, “Direct estimation method”, “Newhall model-based estimation”, “National air temperature-based regression estimation”and “Coordinates and elevation-based regression estimation”. These methods have been extensively applied to researches on soil temperature regime in various regions of the country with some good results. However, little has been reported on the work In GuizhouProvince. In this paper, based on the ground climatic data (1951/71~1980) pooled from 86 meteorological observatory stations all over GuizhouProvince, the five methods were either used directly or modified in the light of the actual situation in Guizhou. Withthe soil temperature interpolation method, T50 is deduced from the soil temperatures measured at 40 cm and 80 cm in depth, with interpolation, namely, mean annual T50 =mean annual soil temperature at 40cm+[mean annual soil temperature at 80 cm-mean annual soil temperature at 40 cm]/4. Withthe direct estimation method, the mean annual soil temperature at 20 cm in depth is deemed as T50. Withthe Newhall simulation model method, some modification has been made of the model in the light of the close relationship between soil temperature and air temperature in Guizhou, likeassumingthat the mean annual T50 is 1.8 ℃ higher than the mean annual air temperature. The air temperature-based regression estimation method is developed by Feng Xueming, using the mean annual air temperaturesof 150 meteorological stations scattered in 30 provinces of China as (x) and mean annual T50(y), namely "y=2.9001+0.9513x" (r=0.9889).On the basis of the Feng Xuemingmethod, a multiple regression equation is put forward and used to reflect the influence of latitude (x_1) and elevation(x_2)besides the air temperature, namely "y=40.25-0.7166" x_1 "-" 0.002389x_2(r=0.9515). Direct use of the coordinates-based regression estimation method may have some deviation. It is, therefore, modified into y"=132.979-0.54×latitude (" x_1)"-0.005" 〖×elevation (x〗_2)"-0.9×longitude"(x_3) (r=0.910). In the end, in view of the special terrains of Guizhou, a series of regression estimation models are established to fit regions different in elevation, namely, for regions ≤ 800m in elevation, the model of y"=129.57-0.551" x_1 "-0.006" x_2 "-0.864" x_3(r=0.910) is used；forregions between 800m and 1400m in elevation, the model of y"=133.693-0.514" x_1 "-0.005" x_2 "-0.916" x_3 (r=0.864) is; and for regions above 1400m in elevation, the model of y"=141.454-0.724" x_1 "-0.005" x_2 "-0.945" x_3(r=0.976) is, separately. Results show that the five methods, some ofwhich have been modified, may yield basically similarestimations, which indicates that they are all applicable to estimation of soil temperature regimes in Guizhou. But for regions lacking sufficient soil or air temperature data the method of longitude-latitude-elevation based regression estimation method is more commonly used. The soil temperature regimesin Guizhoucan be sorted into three categories:hyperthermic, thermic and mesic; Guizhou has 80 counties (cities) in the category of thermic temperature regime;Weining and Dafang of Bijie in the category of mesictemperature regime; and four counties in between the two categories, like Shuicheng, Kaiyang and Xishui counties where both mesic and thermictemperature regimes exist, and Luodian where both thermic and hyperthermic temperature regimes do. Besides, when temperature regime is used as diagnostic feature in soil classification in Guizhou, attention should be paid to the fact that the meteorological stations may represent most of the areas under the influence of the atmosphere, but not the maintain areas where variations along vertical zones and microrelieves exist. As two categories of soil temperature regimes exist in Shuicheng, Kaiyang, Xishui and Luodian counties, it is essential to take into account soil forming environmental conditions, especially topographic conditions, in applying the methods to estimation of soil temperature regimes.

Abstract:Soil temperature is one important environmental factor affecting soil formation and plant growth, especially in the alpine environment. The studies on plateau soil temperature may help researchers understand how soil heat is conducted during the freezing and thawing process as well as how fragile the ecosystem of an alpine region is. However, so far the studies on soil temperature of alpine regions are not so helpful and instead affect proper characterization of the variation of soil temperature, because they are often conducted in fields different in vegetation, topography, latitude and longitude, etc. This study was laid out in a typical shrub meadow area of the Lhasa River Valley on a mountain slope uniform in natural conditions, including vegetation type, slope degree and aspect. The slope is covered dominantly with Rhododendron primuliflorum, making the total vegetation coverage up to 82%. The soil on the slope is of the type of sub-alpine shrub meadow soil, slightly acidic. Nine monitoring points were distributed over the slope from elevation of 4 000 m to 4 800 m with a gradient of 100 m; and in each point 2 temperature recorders (The Onset HOBO Company of USA; The type is U23-003; Operation range Internal sensors: -40°C to 100 °C) were placed, each with 4 temperature sensors placed at the depth of 5, 10, 20and 30 cm, separately. Data were collected once an hour from October 5, 2013 to September 15, 2014. As the monitoring points at 4 000 m, 4 400 m and 4 700 m were damaged owning to unknown causes, only the data collected from the points at 4 100, 4 200, 4 300, 4 500, 4 600 and 4 800 m were analyzed with the typical statistical method for characteristics of the variation of soil temperature with elevation and soil depth gradients. Results show that (1) in a year, the daily mean soil temperature within the 0 ~ 30 cm soil layer followed a cosine function curve, fluctuating within the range from -9.05 °C to 14.21 °C and averaging 2.94 °C; it rose at a rate of 0.11 °C d^-1 and fell at a rate of -0.19 °C d^-1, and it displayed a rising trend for 106 days and a declining trend for 73 days, and remained frozen for 147 days in a year; (2) the soil temperature followed a quasi-sine curve in daily variation, fluctuating within the range of 2.8 °C; it varied sharper in summer than in fall; the rising trend of soil temperature lasted shorter than the declining trend did: and especially in winter, the former lasted for only 4 hours, the shortest among the four seasons; but in summer it did for 8 hours and peaked at 17:00 and the soil temperature bottomed at 10:00 within a day; (3) the annual mean soil temperature decreased with rising elevation, at a rate of -0.63 °C (100 m^-1), and the phenomenon was more obvious in summer than in the other seasons, with the rate being -0.76 °C (100 m^-1) and the least in fall, being only -0.37 °C (100 m^-1); variation coefficient of the soil temperature increased with rising elevation, which indicates that soil temperature varies sharply and intricately with elevation; (4) the annual mean soil temperature was a power function of soil depth; with increasing depth, soil temperature varied less and less, the difference between soil layers in temperature became narrower and narrower, and the occurrence of peak and bottom values was delayed; during the temperature rising period, soil heat transferred downward, while during the temperature declining period, it did reversely; during the period when the soil was frozen, variation of soil temperature tended to be uniform regardless of soil depth; however, freeze-up of the top soil layer lasted the longest, for about 149 days; and soil heat transfer at 20cm in depth was relatively steady during the freezing-thawing process; and (5) in the sight of diurnal variation of soil temperature relative to soil depth, soil temperature descended in variation range and peak value with increasing soil depth, but ascended in bottom value; and in soil layers below 10cm, the occurrence of peak and bottom values of soil temperature was delayed by 2 h (10 cm^-1).

Abstract:Water-repellent soils, existingwidely in nature, havesome important effects on soil environment and crop growth. In order to analyze water repellency of sand and clay, models of sand and clay different in particle size were built. Results showed that no phenomenon of water repellency was found in sand soil when the contact angle of water with sand was small. Water repellency of sand soil was closely related to soil water content when the sand-water contact angle was big. Compactness of the soil was another important factor affecting soil water repellency. When the sand soil was highly compacted,whether the soil was hydrophilic or hydrophobic wasvery sensitive to water content, and it might switch from one state to another with changing soil water content. When the sand soil was quite loose, it was no longer sensitive to soil water content. In clay soil with soil-water contact angle being slightly less than 90°and wetting radius b being small, the phenomenon of water repellency was observed. But when the clay soil was much smaller than 90°in soil-water and bigger in wetting radius b, it was hydrophilic. When the clay soil was quite high in soil water content, soil-water contact angle was the factor determining soil water repellency.

Abstract:1,1,1-Trichoro-2,2-bis(p-chlorophenyl)ethane (DDT) is one of the most extensively used organochlorine pesticides worldwide. As a result, DDT can be detected in various environmental compartments in recent years, and its concentration is much higher in the soil than in the air and water. Therefore, it is of great significance to develop an efficient technology to remedy DDT contaminated soils. Reductive dechlorination seems to be a crucial pathway for DDT degradation under anaerobic conditions, because the five electrophonic chlorine substitients in a DDT molecule make aerobic oxidative degradation difficult. However, reductive dechlorination requires the addition of two electrons for each chlorine removed. Therefore, the existence of electron donor substance and electron shuttle is vital to electron transfer, and hence may affect the reductive dechlorination of DDT in anaerobic reaction systems. In order to investigate reductive dechlorination rate of DDT in Hydragric Acrisols which is widely distributed in tropical and subtropical regions and contains abundant iron oxides; to examine single and interactive effects of n-butyric acid as electron donor substance and AQDS as electron shuttle on soil microorganisms degrading DDT; and to elucidate relationship between DDT dechlorination and methane generation rate, a batch anaerobic incubation experiment of Hydragric Acrisols was conducted. The experiment was designed to have five treatments, i.e. (1) Sterile control, (2) Control, (3) n-Butyric acid, (4) AQDS, and (5) n-Butyric acid + AQDS, and three replicates for each treatment. The treated samples in sealed culture flasks were incubated at 25 ˚C in darkness for 20 days. During the incubation, gases in the flasks were sampled once every four days for analysis of CH4 concentration, and soil samples, too, for determination of Fe(Ⅱ) contents, DDT and its degradation products, and oxidation-reduction potential (Eh) of the reaction systems were measured simultaneously. Results show that after 20 days of incubation, DDT residue in treatment 1, 2, 3, 4 and 5 decreased by 44.5%, 85.2%, 90.2%, 93.2% and 96.3%, respectively, as compared with the initial value. In terms of first-order kinetic constants (k) of DDT transformation, the five treatments displayed an order of Treatment 5 > Treatment 4 > Treatment 3 > Treatment 2 > Treatment 1. DDD (1,1-dichloro-2,2-bis(4-chlorophenyl)-ethane) was found to be the dominant degradation product of reductive dechlorination of DDT in the current assay. DDE (1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene) and DDMU (1-chloro-2,2-bis(p-chlorophenyl)ethylene) were also detected as the secondary dechlorinated products of DDT, though not much, and the former was higher than the latter. Some non-extractable DDT and its degradation products were detected to be bonded by soil organic matter and clay particles, and hence retained in the soil as residues, mainly in the first 4 days of incubation. During the first 8 days of incubation, Treatment 3 significantly increased CH4 generation rate, but did not do much DDT dechlorination. However, in the days later, with declining CH4 generation rate and rising Fe(Ⅱ) content, DDT dechlorination rate gradually increased in the treatment. The findings indicate that the amendment of n-butyric acid leads to completition for electrons between methanogenesis and reductive dechloriantion of DDT during the early incubation period, which is not conducive to reductive dechloriantion of DDT. The amendment of AQDS significantly increased soil Eh values and accelerated reduction of Fe(Ⅲ) oxides into electron-donor Fe(Ⅱ), thus promoting markedly reductive dechlorination of DDT, which indicate that the quinone moieties in AQDS molecules act as redox modulator promoting DDT dechlorination under anaerobic conditions. Treatment 5, the addition of n-butyric acid + AQDS, was the most efficient in accelerating reductive dechlorination of DDT, but in this effect, no significant interactive effect between the two was observed. The present study has demonstrated that the application of both electron donor substance and electron shuttle is an ideal approach to acceleration of DDT dechlorination in the soil, and the findings may have some important meanings for developing efficient in situ remediation technology for DDT contaminated soils.

Abstract:Currently, crop straw return via mulching is a practice extensively applied in the fluvo-aquic soil zone of the North China Plain, however, the straw returned via mulching is not readily decomposed and hence unable to raise soil fertility and crop yield instantly.Moreover, straw decomposition needs to consume soil N in competition with crop growth, thus making it hard for the two to share the limited N supply harmoniously. A technique of deep burial of straw coupled with application of inorganic or organic nitrogen as primer was presented in this paper, and a continuous four-year (2011—2014) field experiment was conducted to study effects of the technique on soil fertility and wheat yield. The experiment was designed to have 3 treatments in straw returning method, i.e., Treatment NS (No straw returned), Treatment S (Straw returned via mulching, and Treatment IS (straw buried in deep furrows and then covered with crop planted in between the furrows). In addition, Treatment NS consisted of two sub-treatments, Sub-treatment NSF0(No straw returned and no fertilizer applied) and Sub-treatment NSFR (No straw returned, but fertilizer applied at a common rate); and Treatment IS did of three sub-treatments, Sub-treatment ISFR (Deep burial of straw plus conventional fertilization). Sub-treatment ISF (Deep burial of straw applied with chemical fertilizer as primer) and Sub-treatment ISOM (Deep burial of straw applied with organic manure as primer). And Sub-treatments ISF and ISGM was further divided into three Plots ISF1, ISF2 and ISF3, and Plots ISOM1, ISOM2 and ISOM3, corresponding to the proportion of nitrogen consumed by straw decomposition, 8%, 16% and 24%, respectively. Results show that (1) compared to control (Sub-treatment NSF0),all the treatments, except for Sub-Treatment NSF0 improved soil nutrient contents, especially Sub-Treatments ISF and ISOM. The effect of Sub-Treatments ISF was mainly on content of nitrate-N and the most remarkable in Plot ISF2, increasing the content of nitrate-N by 82.99%, while that of Sub-Treatments ISOM was obvious on almost all the other soil nutrients, and the most remarkable in Plot ISOM2, increasing the content of organic matter, microbial biomass carbon, microbial biomass nitrogen and total N in the soil by 60.84%, 123.2%, 207.7% and 90.91%, respectively; compared with 2011, 2014 saw sharp drops in all soil nutrients in Sub-treatment NSF0, but rises in all the treatments and sub-treatments, particularly in Sub-treatments ISF and ISOM, which suggests that the new technique may contribute significantly to improvement of soil fertility; (2) improved soil fertility improved the yield of winter wheat, compared with 2011, the yield decreased by 157.7% in Sub-treatment NSF0 in 2014, but increased by 28.91% and 30.83% in Sub-treatments NSFR and ISFR, and the positive effect was especially significant in Sub-treatments ISF and ISOM, particularly in Plot ISF2, where the yield was increased by 36.17%; and (3) among the indices of yield composition of winter wheat, 1000-grain weight and numberof grains per spike did not differ much between treatments and the increase in yield was manifested in number of effective spikes; all, except for NSF0 and SF0; the number of effective spikes increased with the experiment going on, particularly in Plot ISF2, where the number increased by up to 49.96%; In 2014, Sub-treatments ISF and ISOM increased the number of effective spikes of winter wheat by 144.7% ~ 169.1%, and the effect was the most significant in Plot ISF2, as compared to 2012. To sum up the treatment in Plot ISF2 is the most recommendable mode of straw returning for the studied area.

Abstract:Ozone (O₃) is one of the best-documented air pollutants in East Asia and in many parts of the world. Tropospheric O₃ concentration has rapidly increasing in East Asia since the 1990s, and the global average tropospheric O3 concentration is expected to have increased by 50% by 2020 relative to the 1980s. Since the concentration of tropospheric O₃ > 40 nL L^-1 would cause visible leaf injury, plant damage and reduction in crop and forest productions, the effects of tropospheric O₃ on terrestrial ecosystems have aroused considerable attention the world over. Currently many of these studies have focused on effects of O₃ on plants, and most agreed that O₃ inhibits plant growth and accelerates plant senescence. Elevated O₃ has also been demonstrated to reduce photosynthetic rate and productivity of crops and forests, and to alter carbon metabolism and subsequently allocation of resources (e.g. Carbon (C)) underground. The increasing atmospheric O₃ concentration has a negative effect on the plant-soil system, thus further affecting the turnover of soil organic carbon pool. This is important as it is well known that soils are important C sinks within the biosphere. Soil organic carbon in biogeochemical cycling is divided into different fractions of active organic carbon according to the ease and time with which soil organic carbon becomes available in the soil, including easily oxidized organic carbon, protected slow organic carbon, non-protected slow organic carbon, and passive carbon. However, not so much is known about the effect of elevated O₃ on sequestration and stability of the different fractions of soil organic carbon. Thus it is important to better understand C cycles in the context of predicted increases in atmospheric O₃. The paddy fields of the Yangtze River Delta region in Southeast China are one of most heavily O₃ -polluted regions of the country. In light of the larger amount of carbon deposition to paddy soils than to other agricultural soils, it is essential to have a understanding of responses of soil organic carbon and sequestrations of different fractions of active organic carbon under elevated O₃. Thus the main objective of this study was to determine whether an increase in atmospheric O₃ concentration would influence soil organic carbon and sequestration of each active carbon fraction. With the Chan-modified free-air O₃ concentration enrichment system and Walkley-Black method, effects of elevated atmospheric O₃ on different active soil organic carbon stocks in paddy soil were investigated. The paddy field under investigation had been under a rice-wheat rotation agroecosystem with elevated atmospheric O₃, 50% higher than the ambient O₃, for five years. Results showed that elevated atmospheric O₃ significantly decreased the contents of soil organic carbon in the 0 ~ 3 cm and 10 ~ 20 cm soil layer, with a total decrease of about 18.4% in the topsoil (0 ~ 20 cm). Elevated atmospheric O₃ significantly decreased the contents of easily oxidized organic carbon in the 0 ~ 3 cm, 3 ~ 10 cm and 10 ~ 20 cm soil layers, but increased the content of protected slow organic carbon by 10.8%, while decreasing the content of non-protected slow organic carbon by 59.7% in the 0 ~ 3 cm soil layer, and the content of protected slow organic carbon by 59.6% in the 10 ~ 20 cm soil layer. The effects of elevated atmospheric O₃ on the proportions of different fractions of active organic carbon to total organic carbon related to fraction and soil depth. Elevated atmospheric O₃ significantly decreased the proportion of easily oxidized organic carbon to total organic carbon by 15.1% in the 3 ~ 10 cm soil layer, did not affect the contents and distributions of passive carbon in all soil layers, but caused the stock of labile organic carbon, accounting for 59.3% ~ 69.8%, in total soil organic carbon pool to decline, which is probably the direct cause leading to decrease in soil organic carbon under elevated atmospheric O₃. It is quite obvious that long-time exposure to elevated atmospheric O₃ would decrease the content of soil organic carbon and change the distribution patterns of different fractions of active organic carbon in soil carbon pool and their turnover.

Abstract:The black soil region (122° ~ 132°E, 43° ~ 50°N) in Northeast China is the most important grain production region of the country. The paddy soil derived from black soil after long-term rice cultivation has become an important paddy soil resource in Northeast China. As the region is cold in weather with the soil kept frozen for a long time period each year, and the paddy soil has only a short period of time in a year remaining waterlogged, it is essential to elucidate nitrogen-mineralization capability and N supply capacity of the black soil derived paddy soil. For that end, soil investigations were carried out and soil samples collected in paddy fields in Qing’an County of Suihua, Central Heilongjiang in 2011. The soil samples were treated with the Bremner method and long-term waterlogged incubation method and analyzed for composition of soil organic nitrogen and mineralizable N in the paddy soil and relationship between the two relative to organic carbon content. Results showed that acidolyzable N and non-acidolyzable N in the soil varied in the range of 1 014 ~ 1 834 mg kg^-1 and 378 ~ 851 mg kg^-1, and averaged 383 mg kg^-1 and 633 mg kg^-1, respectively. The former accounted for 64.9% ~ 72.9% or 68.9% on average of the total N; and the latter did for 27.1% ~ 35.1% or 31.1% on average, Obviously, the former was much higher than the latter in both content and proportion to the total. Soil acidolysable N was significantly and positively related to organic carbon and total N (p<0.01) in content, with correlation coefficient being 0.985 and 0.985, respectively, and soil non-acidolyzable N (p<0.01) was too, with correlation coefficient being 0.981 and 0.977, respectively. In terms of content and the proportion of total N, components of the soil acidolyzable organic nitrogen followed an order of unknown N > amino acid N > ammonia N > amino sugar N. The content of acidolzsable ammonia N was significantly and positively related to organic carbon and total N (p < 0.01), with correlation coefficient being 0.987 and 0.973, respectively, and acidolyzable amino acid N was too, with correlation coefficient being 0.991 and 0.989, respectively, but the fraction of unknown acidolyzable N was significantly positive related to total N (p< 0.05) only, with correlation coefficient being 0.880. After 161 days of waterlogging incubation, cumulative NH₄ -N in the soil reached close to the maximum, ranging between 38.7 and 176.1 mg kg^-1, with an average being 99.3 mg kg^-1 and cumulative mineralized nitrogen content was in an extremely significant positive relationship with soil organic carbon (r = 0.975, p< 0.01), and a significantly positive relationship with total nitrogen (r = 0.957, p< 0.05), too. Nitrogen mineralization potential (N ₀) varied in the range of 38 ~175.3 mg kg^-1, and the mineralization rate constant (k ₀) in the range of 0.022~0.041 d^-1. Nitrogen mineralization potential (N0) was ultra-significantly and positively related to the cumulative NH₄ -N content , soil organic carbon and total N after 161 days of incubation, with correlation coefficient being 0.999, 0.978 and 0.962, respectively. Both soil C/N and pH were significantly and positively related to nitrogen mineralization potential (N ₀) (p < 0.01), but negatively to mineralization rate constant (k ₀) (p < 0.05 or p< 0.01). Obviously, soil organic carbon (N), C/N and pH are important factors that affect soil organic nitrogen mineralization. Among the components of soil organic nitrogen, acidolyzable ammonia N and acidolyzable amino N and non-acidolyzable N were significantly and positively related to N mineralization potential (N ₀) (p < 0.01), with correlation coefficient being 0.999, 0.986 and 0.999，respectively, but stepwise multiple regressions of the three with N mineralization potential shows that acidolyzable ammonia N was the largest contributor of mineralizable nitrogen. Path analysis further indicates that acidolyzable ammonia N and mineralizable nitrogen has a very high path coefficient (1.142), but acidolyzable amino acid N and non-acidolyzable-N a very low direct path coefficient, being 0.024 and 0.172, respectively. The findings suggest that acidolyzable ammonia N is a component that has important direct contribution to mineralizable nitrogen and hence the major source of soil mineralizable nitrogen.

Abstract:Red soil slopelands are one of the main land sources for agricultural production in South China, making the region an important agricultural zone of the country producing a huge variety of agricultural and forest products, thanks to its rich soil and hydrothermal resources and great biological production potential. However, owing to unreasonable development and its natural geographical environment, soil erosion in this area is getting more and more serious. The red soil region of South China amounts to a total of 2.03 million km², of which more than 60 million km² suffers a varying degree of soil erosion, putting the region next to the Loess Plateau in extensiveness and severity of soil and water loss in China. Hence soil erosion has become a major restraint hindering development of the agriculture production and improvement of the ecological environment and people's living quality of the region improvement. A number of biological water and soil conservation measures, like growing hedgerows, mulching the fields with straw, are now being applied extensively both inside and outside the country. They were found to be able to reduce soil erosion by more than 85%, increase the content of organic matter by 9%～13%, and improve soil aggregate structure and water-stable aggregates in number and quality, thus enhncing erosion resistance of the soil significantly. Soil labile organic carbon (LOC) refers to the labile fraction of soil organic metter. It is readily available, easily decomposed and mineralized by soil microbesy to move and to be oxidized and mineralized, and directly available to plants and soil microorganisms. Although LOC accounts for a limited proportion in the soil total carbon, size and turnover of the fraction is very important to content, circulation and utilization of soil available nutrients. As soil enzymes are involved in decomposition and transformation of soil labile organic carbon and major regulators of soil biological processes, their activity is a good indicator of soil’s capability of nutrient transformation. Most studies in the past used to focus on effects of various soil and water conservation measures on soil erosion, non-point source pollution, soil organic carbon and inorganic nutrients, with little attention given to effects of these measures on soil labile organic carbon, soil enzyme activities and their relationships. Based on the soil and water conservation field experiments that started in 2009 and was designed to have three treatments, Treatment H (Hedgerows of Vetiver Grass), Treatment M (Mulching with rice straw), and Treatment HM (hedgerows of Vetiver Grass + mulching with rice straw), investigations were carried out of effects of the water and soil conservation measures on soil labile organic content and soil enzyme activity in a gentle slopeland of red soil grown with peanut and analyses done of relationships of soil enzyme activities with soil labile organic carbon, in an attempt to provide some theoretical basis for choosing reasonable water and soil conservation measures for peanut-growing gentle slopeland of red soil from the angle of soil micro-ecology. Results show that 1) all the treatments, H, M and HM, increased soil microbial biomass carbon content significantly (p<0.05), with Treatment HM in particular. And the effects were more significant in the dry season than in the wet season, and the mulched rice straw was the main factor improving soil soluble organic carbon content. 2) although both Treatments M and HM improved soil enzyme activity significantly in the rainy season (p<0.05), mulched rice straw was the decisive factor, and the soil and water conservation measures, including Treatment H, did not have much impact on soil enzyme activity in the dry season; and 3) soil β-glucosidase and cellulose were well related to content of soil labile organic carbon (p<0.05), which has a great implication to evaluation of the functions of the soil and water conservation measures in protecting soil environmental quality and guidance of practical production in gentle slopelands of red soil.

Abstract:Ecological stoichiometric ratios of C, N and P are important indices characterizing process and functions of a forest ecosystem. Picea crassifolia is an important constructive or dominant species of the subalpine mountain forest vegetation in the Qilian Mountains, and its forest is a typical kind of water conservancy forest. Based on field survey and laboratory analysis, the objective of this study with the Picea crassifolia forest in the Pailugou watershed of the Qilian Mountains selected as subject, the leaf、litters and soil at different elevation gradient (2 900 ～3 300 m) were selected to measure their organic carbon (C), total nitrogen (N) and total phosphorous (P) contents, carried out on ecological stoichiometric characteristics of carbon, nitrogen and phosphate in the leaf-litters-soil systems of the Picea crassifolia forest different in elevation gradient and their correlations using the principles and methodology of ecological stoichiometry. Results show that carbon, nitrogen and phosphorus ecological stoichiometric ratios of Picea crassifolia forest in elevation gradient indicate that different variation laws and significance of difference with altitude increasing. Among them, C:N ratio in leaf and soil of Picea crassifolia forest increased gradually, C:N ratio in litter increased gradually with the increase of altitude and then decreased at 3 300 m. C:P ratio in leaf first increase and then decrease, at an altitude of 2 900 m was significantly lower than other altitude C:P (p < 0.05). C:P ratio in litter has no obvious change. C:P ratio in soil first increases and then decreases, only at an altitude of 2 900 m was significantly lower than other altitude C:P (p< 0.05). N:P ratio in leaf and soil first increases and then decreases, the N:P ratio of the low altitude (2 900～3 100 m) was significantly higher than that of the high altitude (3 200 ~ 3 300 m) (p < 0.05). In this systems along the elevation gradient, C:N ratio in leaf, litters and soil varied in the range of 22.95～36.72, 21.41～41.61 and 12.41～20.70, respectively, and in terms of average of the ratios, the three components of the system followed an order of litters ＞ leaf ＞ soil; C:P ratio did in the range of 510.2～739.8, 398.6～698.1 and 134.1～219.7, respectively, and N:P ratio did in the range of 18.13～26.86, 6.71～26.28 and 7.96～16.56, respectively, and in terms of average of either C:P or N:P ratio, the three followed an order of leaf ＞ litters ＞ soil. All the ratios in all the three components varied sharply with rising altitude, except for soil C: N ratio, which did not as much (p＞0.05). Three components were significantly positively related (p＞0.05) to each other in C:N ratio, while both leaf and soil were negatively related to litters in C:P ratio (p＞0.05). And the relationships of leaf with soil C:P ratio and with litters and soil in N:P ratio were not obvious (p＞0.05). The findings of the study help further understand interactions between carbon, nitrogen and phosphorus in the three components of the Picea crassifolia forest system and their laws and mechanisms.

Abstract:Rice fields are major source of atmospheric methane (CH₄). However, 30%~90% of CH₄produced in paddy soils is oxidized by methanotrophs before it escapes to the atmosphere. China holds the largest rice production in the world, but it remains largely unknown about the active methane oxidizers in paddy soils. In this study, soil microcosms of six paddy soil incubated with ¹³CH₄ were constructed to assess active methanotrophs by tracing the isotopically labeled ¹³C-DNA/RNA. Six paddy soils collected from Yingtan City of Jiangxi Province (YT), Ziyang City of Sichuan Province (ZY), Jiaxing City of Zhejiang Province (JX), Changshu City of Jiangsu Province (CS), Yangzhou City of Jiangsu Province (YZ), and Wuchang City of Heilongjiang Province (WC), were incubated with 400 µmol^-1 L labeled ¹³CH₄ or unlabeled ¹²CH₄ to determine aerobic methane oxidation kinetics. The destructive sampling was conducted when 400 µmol^-1 L CH₄ was consumed. ¹³C-DNA and ¹³C-RNA were obtained through ultracentrifugation of total DNA and RNA, respectively. Clone library of pmoA genes from ¹³C-DNA and 16S rRNA genes from ¹³C-RNA were constructed to analyze composition of active methanotrophic community. After ultracentrifugation of total DNA and RNA, the agarose gel electrophoresis of pmoA gene amplicons and methanotrophic 16S rRNA reverse transcription amplicons from the fractionated DNA and rRNA, respectively, were performed, indicating the incorporation of ¹³C-substrate into methanotrophs during the aerobic methane oxidation. DNA-SIP and rRNA-SIP each have their advantages. In contrast to DNA, the incorporation of labeled substrate into rRNA is much faster, and a greater unspecific background of ‘heavy’ nucleic acid was observed in ‘heavy’ fractions in rRNA-SIP than DNA-SIP, indicating the more efficient separation for DNA. The separation of differentially labeled rRNA was effective, however, it was not as quantitative as for DNA. This resulted in a greater unspecific background of ‘heavy’ rRNA in ‘light’ fractions, which may be caused by their strong tendency to form secondary structure. Phylogenetic analysis of pmoA gene from total DNA of background paddy soils indicated that dominant methanotrophs in situ were type II in six paddy soils. It may be explained by the fact that type II methanotrohs can be better adapted to oligotrophic environments. Interestingly, consistent results were obtained from both clone libraries of pmoA genes from ¹³C-DNA and methanotrophic 16S rRNA transcripts from ¹³C-RNA, indicating that type I methanotrophs dominated active aerobic methane oxidation in the six paddy soils. All type I was composed of type Ia in YT and WC sample, whereas type I was composed of Ia and Ib in ZY, JX, CS and JD sample. The fast growth found for type I methanotrophs are in agree with a r-strategy lifestyle. Sufficient available nutrient e.g. CH4 may be prerequisite for the proliferation of type I methanotrophs. Phylogenetic analysis of pmoA gene from ¹³C-DNA and 16S rRNA transcript from ¹³C-rRNA revealed that the active methanotrophs responsible for aerobic methane oxidation in six paddy soils were type I. The results indicated that methanotroph-specific 16S rRNA and pmoA genes can be of great help for identification of ¹³C-DNA/RNA from methanotrophs grown on the labeled substrates.

Abstract:Phosphate-solubilizing bacteria (PSB) are a group of beneficial bacteria capable of hydrolyzing organic and inorganic phosphorus from insoluble compounds. P-solubilization ability of the microorganisms is considered to be one of the most important traits associated with plant phosphate nutrition. A number of PSB strains have been screened out from soils in laboratory, however, few reports are available on their successful application in fields. More and more evidence suggests that root colonization of PSB is very important for phosphate solubilization; therefore, survivability of PSB in plant rhizosphere is one of the basic principles for PSB screening. In present study, 20 strains of PSB with phosphate solubilization halos ranging from 7.9~20 mm were isolated from the rhizosphere of the corn growing in calcareous soil with the Pikovskaya medium plate method. Ten of the 20 strains of PSB, coded as X3, X5, X6, Z2, Z3, Z4, Z5, Z7, Z8 and Z9, with bigger phosphate solubilization halos were further tested for phosphate-solubilizing capacity in the NBRIP medium. Results show that gram-negative (G-) PSB (X3, X5, X6, Z2, Z3andZ5) solubilized much more phosphate than gram-positive (G+) ones (Z4, Z7, Z8 and Z9) did. The mean phosphate concentration in the NBRIP medium of the G- PSB treatments was 449.7 μg ml-1, with phosphate concentration in Treatment G- PSB Z3 being the highest, reaching to 562.2 μg ml-1. However, the highest phosphate concentration obtained by G+ PSB was only 46.9 μg ml-1. In further experiment, 8 strains of PSB (G+: Z4, Z7, Z8 and Z9; and G-: X5, X6, Z3 and Z5) were evaluated for corn root exudate utilization capacity. All of the 8 strains of PSB were found to be able to utilize corn root exudate as sole carbon source and the G- PSB grew much better than G+ ones. Consistent with the findings in the culture in NBRIP medium, G- PSB solubilized much more phosphate than G+ PSB did when using corn root exudate as sole carbon source. Based on phosphate-solubilization and root exudate utilization capacities, two G- strains of PSB, X5 (Pseudomonas fluorescens) and X6 (Pseudomonas poae), and two G+ strains of PSB, Z4 (Bacillus megaterium) and Z8 (Bacillus subtilis) were selected for further experiment to test their IAA and siderophore production and phosphate solubilization capacities and effect on corn growth in greenhouse. X6 and Z4 was found to be able to produce both IAA and siderophore. Z8 was able to produce IAA but not siderophore, and X5 was able to produce siderophore but not IAA. The greenhouse experiment shows that application of mixture or any one of the four strains of PSB increased corn biomass and soil available phosphate, as compared with the control (no inoculation). Z4 was found to be the highest in effect on plant growth (plant height and dry weight) among the four tested strains of PSB. The treatments inoculated with mixture of PSB strains were significantly higher the treatments inoculated with only one single strain in soil available phosphate content and corn biomass Therefore, it can be concluded that X5 (P. fluorescens), X6 (P. poae), Z4 (B. megaterium) and Z8 (B. subtilis) are potential PSB that can be prepared into a mixed inoculum or an efficient bio-fertilizer for use in areas deficient in P to improve overall performance of the crops therein.

Abstract:Low fertility of the red soils in tropical and subtropical regions of China is a major factor restricting development of the agricultural productivity of the regions. Different types of land use and/or different cultivation practices may have different impacts on soil physicochemical and biological properties. Soil nematodes play an important role in the detritus food webs, and have been used as a sensitive indicator of changes in soil ecosystems caused by different agricultural practices. In order to explore the effects of farming cultivations, different in history, on community composition of soil nematode in upland red soils, and relationships between nematode communities and soil physicochemical and microbial properties, red soil peanut fields and vegetable gardens, 10, 20 and 50 years in cultivation history, and a tract of red soil wasteland were selected for comparison in the following indices; soil organic C (SOC), total N (TN), pH, mineral N (MN), available P (AP) , microbial biomass C (MBC), microbial biomass N (MBN), microbial biomass P (MBP) , basal respiration (BR), qCO₂ and soil nematode community. It was found that compared with the wasteland, the peanut fields, regardless of cultivation history, all displayed declining trends in all indices of soil fertility, while the vegetable gardens did reversely. The 20-year old peanut field was the lowest in SOC, TN, MBC and (AP, and the 50-year old vegetable garden was significantly higher than the 10-year old one in all the indices (p < 0.05). In addition, soil nematodes showed a significant increase (p < 0.05) in the soil after 50 years of farming as vegetable garden, but it stayed almost unchanged in the 10- or 20-year old gardens from that in the wasteland. In the peanut fields,. plant-feeding nematodes gradually decreased in proportion in the soil with the cultivation going on (p < 0.05), from 45.89% in the wasteland to 2.60% in the 50-year old peanut field, while bacterial-feeding nematodes increased steadily in proportion with the cultivation going on, from 20.84% in the wasteland up to 67.29% and 54.51% in the 50-year old peanut field and vegetable garden, respectively. No significant changes, increase or decrease, were found with the proportion of fungal-feeding nematodes with the history of cultivation in the peanut fields, but significant decreases were after 20 and 50 years of cultivation in vegetable gardens (p < 0.05). Moreover, no significant difference was found either in the proportion of predators-omnivores between the peanut fields or between the vegetable gardens different in cultivation history. Analysis of nematode ecological indices shows that the soil food webs in the peanut fields were more stable than those in the vegetable gardens that were subjected to more frequent fertilization and tillage. It was found in this study that soil physicochemical and biological properties varied significantly with the cultivation going on in both the peanut fields and the vegetable gardens. Therefore, changes in soil nematode community can be used as an indicator of upland red soil ecosystems, and may provide some complementary information about structure of the red soil ecosystem, and hence help understand comprehensively dynamics of soil ecosystem of the red soil farmlands with cultivation going on.

Abstract:Facing a rapidly growing population, Tibet has to improve its agricultural productivity so as to provide sufficient food. To improve agricultural production and enhance crops yields, farmers have increased the use of fertilizers. However, the Tibetan plateau environment is so sensitive and fragile that any increased usage of these chemicals may put the plateau environment at risk of agricultural non-point source pollution. How to harmonize economic benefits with ecological ones is a significant challenge to development of Tibetan agriculture. Nutrient absorption and nutrient balance of a farmland ecosystem is one of the key factors affect productivity and environmental quality of the system. Raising Geese in Corn Fields (hereinafter referred to as RGICF) is a compound production pattern based on the principle of “Agro-pastoral Integration”, a concept proposed in 2011. This conceptual farming method relies on the use of weeds and bottom leaves of the crops in the fields as feed sources to raise poultry with. To evaluate differences between the two systems of RGICF and conventional corn cultivation in nutrient absorption, nutrient balance, nutrient distribution in the plant, and nutrient input and output of the system, a field experiment was conducted at Village Zhangmai of Bayi, Tibetan Autonomous Region, in Southwest China 2013. Two treatments, RGICF and conventional corn cultivation (hereinafter referred to as CK), were laid out in the experimental field. Each treatment was designed to have three blocks or plots, and each plot covered an area of 80 m^-2. Logs were kept of RGICF and CK from May 2013 to May 2014 about nutrient inputs and outputs, while chemical analysis were conducted of samples of the corn for nutrient (N, P and K) concentration and distribution in stalks and grains, and samples of the soil, too, for nutrient budgeting. Results show that no significant differences were found between RGICF and CK in N, P and K concentration in corn grains and stalks. Correlation between nutrient adsorption and corn yield exhibited and order of P＞K＞N in RGICF and P＞N＞K. No significant differences were found either between RGICF and CK in nutrient harvest, adsorption efficiency and utilization efficiency of N, P and K. Nutrient budgeting of the systems revealed nutrient disbalance in the systems, particularly N and K deficits in the soil after harvest. Compared with RGICF, CK was 39.0% and 34.90% greater in N and K deficit. The differences were significant (p＜0.05). However, the deficit of P was relatively small in CK, while it turned into P surplus in RGICF, showing extremely significant difference (p＜0.01). In the aspect of economic benefit, though RGICF suffered certain loss (6.22%) in corn yield, the was compensated or even over-compensated by geese raising, making RGCIF much higher in economic benefit than CK of avoiding the application of herbicides, used in CK fields. In all, RGICF does not have much influence on nutrient adsorption and utilization, but improves somewhat soil nutrient balance and yields higher economic benefit. Therefore, it can be concluded that RGICF can be extrapolated as an important production pattern for sustainable agriculture in the future in Tibet.

Abstract:The Xinjiang Uyghur Autonomous Region is the main processing tomato production area of China. So production of processing tomatoes is the backbone of the local economy. To meet the demand for processing tomatoes of the market, continuous cropping or monocropping is widely adopted for the production of processing tomatoes, but unfortunately it has become the main factor limiting stable production and high yield of the crop in the region. It is, therefore, important to understand the mechanism of continuous tomato cropping regulating soil microbial activity. The objective of this study was to explore effects of continuous tomato cropping on physical, chemical and biological properties of the soil, in a view to providing a theoretical basis for sustainable development of the processing tomato industry in Xinjiang. A mono-cropping field experiment started in 2007 at the experiment station of the Agriculture College, Shihezi University. The cultivar of processing tomato used in the experiment was “Ligeer 87-5”. Soil samples were collected for analysis from plots different in cultivation history, 3, 5, and 7 yr of continuous cropping and from the control plot which had been undergoing fallow for 3 years before tomato was planted in 2014. Results show that with continuous cropping going on soil pH increased and soil total P, available P and total K increased first and then decreased; soil bulk density did not change much. After 7 years of continuous cropping, soil organic matter content, total N, and readily available K decreased by 8, 21 and 29%, respectively. Moreover, soil microbial biomass C (SMBC), soil microbial biomass N (SMBN), and the microbial quotient (qMB) all displayed declining trends as continuous cropping went on and decreased by 52, 79, and 48%, respectively, after 7 years of continuous cropping. Soil microbial biomass P (SMBP) increased during the first three years of continuous cropping, peaking up to 1.6 times as high as that in the control and then decreased. Continuous cropping significantly increased the activity of soil catalase, but reduced the activities of urease, sucrase, polyphenoloxidase, and phosphatase. And what is more important, it led to a significant drop, as much as 34%, in yield of processing tomato, (p<0.01) in the treatment of 7 years as against the control. Correlation analysis shows significant correlations between soil pH, soil microbial biomass, qMB, soil enzyme activity and soil nutrient content. All the findings indicate that variations of soil microbial biomass and microbial activity may reflect changes in soil quality and thus can be used as biological indicators in evaluating soil fertility. Continuous cropping of processing tomato significantly increases soil pH and electrical conductivity and inhibites the activity of soil microbes, thus lowering soil fertility, and eventually yield of the crop. So the negative effects of continuous cropping are obvious. To maintain soil fertility and improve processing tomato production, it is essential to rotate processing tomato with cereal crops. In regions where farmland is limited in area, it is advisable to cultivate the crop continuously no more than three years.

Abstract:Mechanism of hexadecyl trimethyl ammonium bromide (CTMA) modifying the surface of dodecyl dimethyl betaine (BS-12) modified bentonite was studied. Judging by changes in the Sum of CTMA and Calcium ion (S_CC) on the surface of BS-12 modified bentonite and CTMA adsorption as affected by temperature, 20℃or 40℃, it was found that there were two modes of CTMA adsorption on BS-12 modified bentonite: ion exchanging and hydrophobic bonding. On the surface of BS-12 modified bentonites (25BS, 50BS and 100BS) varying in modification degree, 25%, 50% and 100%, the adsorption of CTMA in the mode of hydrophobic bonding reached its critical level in proportion (R _C), that is, 20.30%, 11.56% and 2.00%, respectively, and the percentage of hydrophobic bonding increased with increasing CTMA modification ratio (R ) and mole fraction. The critical ratio (R _C’) reached 200%, 150% and 100%, respectively, when hydrophobic bonding assumed its absolute dominancy. On the surface of bentonites modified with BS-12 only or with BS-12 and CTMA, 50% and 200% was the turning point for hydrophobic bonding to appear and to assume absolute dominancy, Separately. When R < R _C, CTMA adsorption was mainly in the ion exchanging mode; when R _C ≤ R ≤ R _C’, it was in both modes, ion exchanging and hydrophobic bonding; and when R > R _C’, it was overwhelmingly dominated with hydrophobic bonding mode. R _C、R _C’ and the maximum adsorption of CTMA (q_m) displayed an order of 25BS>50BS>100BS. With rising temperature, q_mdeclined.

Abstract:Planosol is one of the major low yield upland soils in the Northeast part of China. The Aw horizon with 20 cm in depth beneath the topsoil in its solum has low aeration and water permeability, also low soil enzyme activity, that caused the topsoil suffer alternately excessive water and drought during the growing season, and its available layer for upland crops roots is only about 20 cm. Since 1980’s mechanical improvement Methods including subsoiler have been gradually developed as the major means for planosol improvement. To compare the effects of different mechanical improvement Methods on Planosol, three kinds of machines, namely the conventional subsoiler (CK), the stalk subsoil mixing plough (SSMP) and the subsoil interval mixing plough (SIMP) were operated in the large scale test field, in which the field operated by the conventional subsoiler functioned as control. After operation by the machines, soil physical properties and enzyme activities were investigated. Items of the soil physical properties include soil hardness, soil three phases and soil bulk density. Items of the soil enzyme activity include catalase, urease, intervase activities of the soils. The test fields were operated in the 853 farm, Heilongjiang province, and the indicator crop was soybean. The results showed that after operation by the SSMP and the SIMP, the soil hardness of the Aw horizon（albic horizon） was 7~9 kgf cm^-2 while the CK was 10~14 kg cm^-2. Their solid phase was 47.74 %、50.13 % respectively while the CK was 53.16 %，the soil bulk density of the both treatments was 14.01 %、10.19 % lower than the CK. Comparing with the CK, the SSMP and the SIMPtreatments deceased catalase activities of the soils, and the SSMP treatment deceased the urease, intervase activities of the Aw horizon, and increased the urease, intervase activities of the B horizon（argillic horizon, beneath the Aw horizon）. The two treatments increased soybean yield by 21.34 %，4.94 % respectively. The SSMP and the SIMP significantly improved the soil physical properties and the soil enzyme activity of Planosol. This research opened the new approach for the evaluation of the mechanical improvement for Planosol.