Abstract:Arsenic, a highly toxic metalloid, widely exists in the natural environment. Plants (especially wetland plants) can easily absorb and accumulate arsenic from the soil environment. Arsenic accumulated by plants is tranfered to animals along the food chain, and threatens human health. In addition to the physical and chemical properties of the soil, the biological transformation of arsenic in the soil heavily affects the bioavailability and fate of arsenic in soils. It has been found that dissimilatory arsenate(As(V))-respiring reduction, cytoplasmic As(V) reduction, arsenite (As(III)) oxidation, As(III) methylation, and organoarsenic demethylation play important roles in biogeochemical processes of arsenic in soils. With the development of analytical chemistry and molecular biology, some recent studies have found that soil organisms are also involved in the synthesis of organoarsenic, such as arsenosuagrs, arsenosugar phospholipids, arsenobetaine, arsinothricin, and thio-arsenic. Trivalent monomethylarsenic MAs(III) and arsinothricin can be used as primordial antibiotics. However, the synthesis mechanism and ecological functions of organoarsenics need to be further investigated. In this paper, four co-selective resistance mechanisms of microorganisms to both of antibiotics and heavy metals via the evolution were introduced in details: co-resistance, cross-resistance, co-regulation and biofilm induction. In particular, a new research direction of coupling arsenic pollution with antibiotic resistance in soil was put forward.. In the end, the future directions of arsenic biotransformation and co-resistance mechanism to arsenic and antibiotic were prospected.

Abstract:Fast and real-time acquisition of farmland information is the basis of precision farming. The technology of using unmanned aerial vehicle (UAV) as a platform for low-altitude remote sensing of farmlands features high spatial resolution, real-time and low cost, and can be used to fill the gas between field survey and high-altitude remote sensing in measuring scale. Therefore, the technology has a wide prospect in application to accurate monitoring of farmlands for real-time information. In recent years, with the technology advancing rapidly, UAV is more stable in flight and easier to operate, and airborne remote sensing equipment is getting light and diversified, capable of acquiring different remote sensing information such as visible light data, multispectral information, hyperspectral data and three-dimensional point cloud data. Moreover, recent development of the remote sensing data processing technology has enabled investigators to process data faster and more accurate. Hyperspectral data is well known to be abundant in information and hard to process, too. Fortunately, a number of dimensionality reduction methods have been developed. Comentropy is the most straightforward method. Principal component analysis and independent component analysis are also widely used to choose mean wave bands or vegetation indexes. There is a wavelet basis more practical for wavelet decomposition method too. Thermal infrared data is a powerful tool to reflect field temperature and moisture, and just because of this, it can also objectively reflect crop diseases and pests. Because the monitoring can cover an area as large as an entire tract of fields, even the conventional multispectral data can be interpreted into accurate information of crop growth. Three-dimensional point cloud is a newly booming data in farmland monitoring and capable of providing information of plant height and accurate position of the plant as well. So more information is available for assessing crop growing conditions. Three-dimensional point cloud can be obtained by LiDAR. The first step to process this kind of data is to remove and smooth noise points caused by system error or overlight of target surface or accidental factors, fix vulnerable and missing parts of the point cloud, and in the end fine field model is achieved. SfM features three-dimensional point cloud with real color and can be used to build a field model with visible-light images. This method uses two images as initial homologous photographs to establish a three-dimensional coordinate by feature matching, front and back rendezvous calculation. Then add in new images, find new matchable feature points and adjust them till optimum, Repeat the steps until all images are added in. All these extraordinary technological advances together make the application of UAV-based remote sensing possible in precision farming. Unmanned flying technology reduces monitoring costs for it needs less fuel and no pilot. And investigators can conduct monitoring more frequently to enhance timeliness. Suitable flight height combined with high-performance sensor makes it possible to acquire data superior in spatial resolution. For the features given above UAV-based remote sensing can fill up the gap between ground monitoring and high-altitude remote sensing, such as satellite remote sensing, in the measuring scale. Therefore, the technology has a bright application prospect in application to gathering information for precision farming. In addition this paper has also summarized findings and achievements in related researches at home and abroad, introduced the commonly used remote sensing technologies and data processing methods, as well as specific application directions and their implement effects are discussed too. This paper also addresses the existing problems and future development directions, in an attempt to promote the usage of UAV remote sensing in farmland monitoring. It is hoped that this technology can be more widely used in precision agriculture.

Abstract:Rare earth elements (REEs), which are important strategic resources in the world, play an important role in modern high-tech industries and agricultural production. With the demand for REEs increasing steadily day by day, exploitation of rare earth mines is intensifying nowadays. The mining of REEs also produces large volumes of tailings that occupy large tracts of land and pollute farmlands, thus posing potential threat to the local environment and health of the local residents. Phytomining refers to the practice of growing metal-hyperaccumulating plants in metal-polluted land and harvesting the aboveground biomass of the plants to recover metals, while restoring vegetation and remedying polluted soil. So it is an in-situ, low-cost and potentially profitable means of soil remediation. The study on mechanism of metal accumulation and translocation in hyperaccumulators is the fundament for realizing phytomining. However, the studies on hyperaccumulators of nickel, zinc, and arsenic aside, little has been reported on mechanisms of REEs hyperaccumulation. In this study, a review is presented of advancement in the researches both at home and abroad on mechanisms of the four key processes of REEs accumulation, translocation, distribution and detoxification and their relationships with REE fractionation in the soil-plant system, and a conceptual model brought forth of REEs fractionation in hyperaccumulators. Roots of the plants absorb mainly REEs of free ion form, whereas types and concentrations of organic ligands, pH, organic matter and ion diffusion in rhizosphere soil solution would reduce or increase bioavailability of the REEs in soil solution through complexation, adsorption, desorption and precipitation, which in turn affects REEs accumulation and fractionation of the hyperaccumulators. REEs absorption by roots involves both apoplast and symplast pathways, of which the latter include transmembrane transport systems such as Ca ion channel diffusion and Al transport protein. Because of the variation of absorption pathways, Dicranopteris dicthotoma tends to enrich light REEs (LREEs) whereas Phytolacca americana L. does LREEs, but not so intensively. Once absorbed, REEs are further transported upwards along the xylem. As D. dicthotoma is relatively weak in compartmentalization of REEs in the roots, more LREEs in the form of free ions in the xylem move upwards along with transpiration flow into shoots. On the contrary, in the xylem of P. americana heavy REEs (HREEs) are more likely to get complexed with organic acids and move upwards into shoots, especially citric acid, which plays an important role in REEs long-distance transport in xylem. In the end, large amounts of REEs are stored in leaves of the hyperaccumulators. Most of LREEs in the leaves of D. dicthotoma are absorbed by cell walls and stored in apoplasts or deloaded into vacuoles, or may also enter into the cells and get complexed with proteins and chlorophyll for detoxification. The detoxification mechanisms of REEs in the leaves of P. americana are still unclear. It is presumed that P. americana may have its own function of compartmentalization,in detoxifying HREEs and hence enriches HREEs in its leaves.

Abstract:The knowledge about chemical structure of soil organic matter (SOM) is crucial to accurate assessment of stability and function of SOM in the soil ecosystem. In the study on chemical structure of soil organic matter, the technology of solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy possesses a unique advantage of being capable of depicting chemical structure of nature soil organic matter, nondestructively and state-of-the-artly. Although extensive studies have been carried out on stability and molecular structure of SOM at a regional-climatic belt and ecosystem-community scale, little has been documented about chemical characteristics of SOM and its relationships with environmental factors at the global scale. This study presents a review on uses of the ¹³C NMR technology in determining chemical structures of organic carbons in bulk soil, soil aggregates, density fractions and humus components, and analyzes factors that alter the chemical structure of SOM. Organic carbons in bulk soils, regardless climate conditions, type of vegetation, land use pattern, soil type and content of organic carbon in the soil, were quite similar in chemical structure, all being the highest in O-alkyl C, which was followed by alkyl C, aromatic C, and carbonyl C in the end. It is widely accepted that soil organic carbon is mainly derived from plant residues, which are quite similar in chemical structure, so that soil organic carbons are similar in chemical structure, too. Differences in environment condition, soil property and microbial activity may cause some variations, but very minor, of the chemical structure of soil organic carbon, and the variations in soil particles and chemical components of the soil are quite significant. O-alkyl C abundance of the organic carbon is the highest in large-sized soil particles, while alkyl and carbonyl C are in small-sized or mineral associated particles. Chemical structure of organic carbon in silt-clayed particles and humic acid components vary quite sharply between soils different in type. Future researches should focus on quantitative analysis of SOM sources, contribution of soil microbes to the composition of SOM and stability of its structure and regulatory mechanisms, biophysico-chemical protection mechanisms of soil organic carbon stability, coupling mechanisms of spatial large-scaled environmental factors/soil ecological processes with microscopic scaled molecular structure of soil organic carbon, and interdisciplinary means and techniques to determine chemical structure of soil organic carbon.

Abstract:【Objective】The existence of a plinthitic red earth (PRE) layer greatly affects the mass flow and energy flux in the red soil region of South China due to its unique physical structure, so it is of great significance to the study of Quaternary Environment and to precision agriculture as well. However, the costly traditional soil survey down to the bedrock or subsoil through dense sampling is destructive to soil, time-consuming and laborious. Meanwhile, it is unable to soil layers horizontally, which greatly affects scope and depth of the investigation. Therefore, ground penetrating radar (GPR) is a mature and widely used means to conduct shallow geophysical surveys that help overcome the shortage of the traditional soil surveys. 【Method】The Sunjia mini-watershed of Yujiang Town, Yingtan City, Jiangxi Province was set as the study zone for the research. The zone under the subtropical monsoon climate varies in elevation between 48.1 and 66.9 m, and is covered mainly with red soil developed from Quaternary red clay and red sandstone. Meanwhile, a field survey was carried out in a watershed located in the red soil region with an area of 50.5 hm2, using indirect measurement (i.e., GPR with three frequency antennas) and direct measurement (i.e., hole-drilling investigation). An AKULA-9000C, a product of the Swedish Geoscanners Company, consisting of four parts, i.e. computer, transmitting antenna, receiving antenna and control unit was used, with the antenna working on frequencies, 60 MHz, 120 MHz and 200 MHz. Six boreholes were drilled deep to the soil–bedrock interface and photographed to document PRE layers. Water content analysis method was performed to validate thickness of the soil layers. Meanwhile, a linear regression model was established to fit and evaluate radiogram interpretation based on different radar measurements. 【Result】Results show that the common midpoint method (CMP) can be used to accurately calculate propagation velocity of the electromagnetic waves in soil layers different in depth. Propagation speed of the electromagnetic waves in the PRE layer varied in the range of 0.052 m•ns-1 ~ 0.065 m•ns-1, with an average of 0.058 m•ns-1. Variation of soil water content in the soil profile was concerted with distribution of soil layers. Soil water content increased gradually in the PRE layer and peaked at the bottom of the PRE layer. At the same time, soil water content decreased with soil depth below the weathered layer. The average soil moisture content of the PRE layers was 28.95%, higher than that of the weathered layer and bedrock. The radar working on 60 MHz and 120 MHz could easily and accurately distinguish upper and bottom interfaces of the PRE layer were accurately distinguished. Depth of the two interfaces of the layer was fitted with R2 being 0.93 and 0.86, respectively. Compared with the thickness of the PRE layer detected with the radar of a single antenna working on 60 MHz, the radar with a combination of antennas, working on 200 MHz and 60 MHz antenna greatly improved accuracy of the detection, by reducing its potential deviation from 16.2% to 6.8%. Notably, the GPR working on 60 MHz could also distinguish interfaces of the bedrock and groundwater tables. 【Conclusion】GPR is an effective instrument to identify PRE layers in red soil regions because dielectric constant differs between different red soil layer. The radar working on 60 MHz and 120 MHz can relatively accurately distinguish the upper and bottom interfaces of the PRE layer, but is still not so good as that working o 200 MHz. Therefore, it could be concluded that antennas high in frequency have short wavelength that allows a higher resolution in characterizing subsurfaces. At the same time, higher frequencies At the same time, higher frequencies attenuate more vigorously in the medium, which reduces penetration depth of electromagnetic waves. Therefore, it is difficult to achieve a win-win situation between the resolution and penetration depth of GPR. The suggested combined antenna method can be used to identify PRE layers and improve accuracy of the detections. The utilization of the GPR technology is promising to improve field survey efficiency and to promote the technology of three-dimensional soil mapping.

Abstract:【Objective】 A karst valley has not only surface/underground double-layered structure, but also two special geological structures, bedding slope and reverse slope. During rainstorms, bedrocks seem to form a discontinuous impermeable area, which reduces soil and water loss. Although it seems obvious that rock layer inclination influences hydrology in karst areas, little has been reported in the literature on this subject. Therefore it is of great importance to launch a study on rules of water transport with runoff in Karst Valley areas. So the objective of this study is to investigate roles of rock layer inclination in guiding surface water flow on slopes in karst valleys. 【Method】 Based on field investigations, a simulated rainfall experiment, designed to have bedding/reverse slopes (30°, 60° and 90° in gradient), 3 levels of rainfall intensity (30, 60 and 90 mm h^-1) and a bare slope as CK, was carried out on a slope approximate to the critical gradient (25°) of the nearby karst valley to explore runoff rate and hydrodynamic parameters and their relationships with bedding/reverse slopes. A total of 18 treatments and 3 duplicates for each were laid out and conducted in the experiment. The characteristics of soil hydraulics measured included flow velocity, Reynolds number (R_e), Froude number (F_r), Darcy-Weisbach roughness coefficient (f), and surface/underground accumulated runoff.【Result】Results show that with the rainfall experiment going on, runoff on the bedding slopes and inverse slopes was dominated with shallow watersplash. Over on bedding slopes, the overland flow slowed down in velocity, with rising inclination angle of the rock layer, while on reverse slopes the inclination angle of 60° was the threshold. Surface runoff flew faster on the bare slope than on bedding slopes and reverse slopes. Reynolds number (R_e) and Froude number (F_r) was higher on bedding slopes than on reverse slopes, but lower than on bare slopes, Darcy-Weisbach roughness coefficient (f) was lower on bedding slopes than on reverse slopes but higher than on bare slope. Value for Froude number (F_r) indicated that the water flow was a subcritical one, and was generally higher on bare slopes than on bedding slopes and reverse slopes. Darcy-Weisbach roughness coefficient (f) was much lower on bare slopes than on bedding slopes and ireverse slopes, showing order of reverse slope ＞ bedding slope ＞ bare slope, and decreased with increasing Reynolds number (R_e), which was in an extremely significant positive power relationship with Reynolds number (R_e). Accumulated surface runoff varied with rock layer inclination in the order of bare slope ＞ bedding slope ＞ reverse slope , while accumulated underground runoff followed an order of reverse slope ＞ bare slope ＞ bedding slope.【Conclusion】Overall, the findings may provide certain data support for analysis of the mechanism of runoff generation and scientific basis for further research on processes of the runoff and models of the soil erosion in karst valley areas. Meanwhile, these findings are expected to be of some help for building prediction models for soil erosions in similar environments different in rock layer inclination.

Abstract:【Objective】The isotherm of soil water vapor adsorption is one of the basic hydraulic characteristics of soil. Simulating the isotherm accurately is of great significance to studying mechanism of the interaction between soil and water molecules and predicting migration of volatile organic gases in soil. 【Method】In this study, seven typical soils of different regions of China were collected for determination of water vapor sorption isotherms with vapor sorption analyzer, separately, in lab. During the process, the water activity of the sample was controlled with the range of 0.1~0.9, and temperature was at 25 °C. Then the GAB (Guggenheim-Anderson-deBoer) model was used to evaluate effect of the simulation of water vapor sorption isotherms, and its performance was evaluated by root mean square error and determination coefficient. Factors influencing factors of water vapor adsorption behavior and mechanism of the interaction between water molecules and soil particles were discussed. 【Results】For simulation of water vapor adsorption and desorption curves of the seven types of soils investigated, the root mean square error of the GAB model was lower than 0.000 7, while the determination coefficient was higher than 0.995. Compared with the soil water vapor desorption process, the monolayer water adsorption during the water vapor adsorption process was quite lower, but the molecules free enthalpy of pure liquid water and single-layer adsorbed water was rather high. Monolayer water content during the adsorption and desorption processes and hysteresis index were ultra-significantly and positively related to the organic carbon content. Monolayer water content was higher during the desorption process (M₀ = 0.002 8~0.031 4) than during the adsorption process (M₀ = 0.001 2~0.023 0) in the seven types of soils. The relation of monolayer water content with clay content was affected by type of soil mineral. And no significant relationships were observed between soil physico-chemical properties (such as organic carbon content, clay content and so on) and other GAB model parameters (for instance,C, K ) during the adsorption and desorption process. 【Conclusion】The GAB model is proved to be able to accurately describe water vapor adsorption and desorption processes in the investigated soils. Soil water vapor sorption capacity is highly affected by soil organic carbon content, clay content and type of soil mineral. Hysteresis occurred in all the investigated soils, and varies with soil physico-chemical properties.

Abstract:【Objective】During the production and construction processes in North Shaanxi, large stacks of soils formed, triggering serious soil and water losses. The existence of gravels in the stack is an important factor affecting the soil erosion in characteristic. Therefore, this study was oriented to explore impact of gravel concentration on runoff and sediment yielding processes on slopes of the gravel-containing aeolian sand stacks. 【Method】In this study an indoor simulated rainfall experiment was carried out on stacks. The experiment was designed to have three levels of gravel concentration (10%, 20% and 30%), four levels of rainfall intensity (1.0 mm?min^-1, 1.5 mm?min^-1, 2.0 mm?min^-1 and 2.5 mm?min^-1) and one pure soil slope (containing zero gravel) as control. The experimental plots were 5 m × 1 m × 0.5 m each in size and laid on slopes 25 ° in gradient. The nozzles of the rainfall simulator were 18 m high above the ground, providing artificial rainfall over 80% in uniformity. Rainfall intensity was determined before the start of each artificial rainfall event to ensure the artificial rainfalls < 5% higher or lower than the designed one. During the experiment, flow velocity of runoff on the slope was measured with the dyeing method, flow width measured with a steel ruler, duration of sediment pooling recorded with a stopwatch, and mass of the sample determined with an electronic scale. 【Result】Results show: (1) Under artificial rainfalls, 1.0, 1.5, or 2.5 mm?min^-1 in intensity, runoff rates were 5.03% ~ 39.99% lower on the slopes 10% in gravel concentration than on CK, but 7.48% ~ 74.56% and 19.51% ~ 84.31% higher on the slopes 20% and 30% in gravel concentration, respectively; runoff rates on all the slopes increased with rising rainfall intensity, displaying an exponential function relationship; (2) Runoffs on all the slopes formed laminar flows; on CK runoffs rushed a bit, while on the slopes containing gravels they flew slowly; Under rainfalls varying in intensity, drag coefficients of runoffs on slopes, 10%, 20% and 30% in gravel concentration increased by 24.07% ~ 114.10%, 51.84% ~ 141.57% and 89.04% ~ 288.16%, respectively; (3) Under rainfalls 1.0 and 1.5 mm?min^-1 in intensity, soil erosion rate on CK and the slopes 10% in gravel concentration displayed a variation trend with rainfall going on, i.e. decreasing – stabilizing – increasing, and under rainfalls 2.0 and 2.5 mm?min^-1 in intensity, it fluctuated more vigorously; Under rainfalls regardless of intensity, soil erosion rate on the slopes 20% and 30% in gravel concentration decreased slowly and then increased steadily; (4) Under rainfalls 1.0 mm ?min-1 in intensity, CK was the lowest in soil erosion rate and under rainfalls ≥ 1.5 mm ?min^-1, soil erosion rate decreased by 41.08% ~ 63.27%, 22.80% ~ 67.80%, 28.89% ~ 68.50% on the slopes 10%, 20% and 30% in gravel concentration, respectively; (5) Soil erosion rate was significantly and positively related to runoff rate, Reynolds number, and Freud number, but negatively to drag coefficient. 【Conclusion】All the findings in this study will provide a theoretical basis for establishment of a model for predicting water and soil losses of engineering stacks of aeolian-sand soil in North Shaanxi.

Abstract:【Objective】 This study was conducted to investigate spatial variation of the effect of soil-testing-based-formulated-fertilization of wheat, as compared with conventional fertilization, in an attempt to provide a scientific basis for adjusting technical parameters and optimizing fertilizer formula specifically for a farmland. 【Method】 Data were collected from 296 field experiment sites set for demonstration of soil-testing-based-formulated-fertilization (STBFF) of wheat in Nanyang city for analysis and evaluation of effects of STBFF on yield and income of wheat at various locations as compared with conventional fertilization, based on spatialized estimation of fertilization rate and modeling of geographically weighted regression (GWR) for relationship between wheat yield and fertilization rate. The spatial variation of the effect of STBFF of wheat, embodied by increment in wheat yield and income, was evaluated on the basis of the prediction of wheat yield and analysis of its spatial distribution pattern. 【Result】 The spatial distribution pattern of wheat yield of the STBFF was similar to that of the conventional fertilization. The wheat yield was increased from 5 970 kg?hm^-2 to 6 672 kg?hm^-2, when conventional fertilization was converted into STBFF, with an average increment of wheat yield being 11.76% (the increment varied with the county in the range of 7.04% ~ 17.91%) and an average increment of income being 1 232 Yuan?hm^-2 (the increment varied with the county in the range of 713 Yuan?hm^-2 ~ 1 672 Yuan?hm^-2). 【Conclusion】 Spatial variation of the effects was quite obvious. The regions enjoying high increments of wheat yield and income were distributed mainly in Nanzhao, Xixia, Zhenping, Xinye and Sheqi counties, however, some regions in Neixiang, Tanghe and Tongbai counties suffered negative effects. Although STBFF can improve generally yield of the wheat in Nanyang city, the spatial distribution pattern of wheat yield in this area is affected by some factors like physical conditions, soil conditions and agricultural management level of a region.

Abstract:【Objective】Triclosan (TCS) and triclocarban (TCC), are typical pharmaceutical and personal care products (PPCPs) that are extensively detected in soil, posing potential risks of raising soil microbes’ drug resistances and inhibiting soil respirations. However, so far little is known about their influences on soil gross N transformation processes and N₂O emissions in soil. 【Method】 In view of this, an indoor incubation experiment was carried out using the ¹⁵N diluting-enriching method coupled with a N transformation numerical model to investigate influences of TCS and TCC, applied alone or in combination, at varying rates on preliminary N transformation rate and N₂O release rate in paddy soil. 【Result】Results show that the treatment of applying 1 mg·kg^-1 TCC or 5 mg·kg^-1 TCS+2 mg·kg^-1 TCC did not have much influence on N mineralization-assimilation in the paddy soil, but all the other treatments did quite reversely (P < 0.05). Besides, all the TCC and TCS treatments significantly inhibited autotrophic nitrification, microbial immobilization of nitrate and dissimilatory nitrate reduction to ammonium (Dissimilatory nitrate reduction to ammonium, DNRA), except for the treatment of applying 2 mg·kg^-1 TCS or 5 mg·kg^-1 TCS+2 mg·kg^-1 TCC. It is noteworthy that all the treatments (P< 0.05) increased cumulative emission of N₂O significantly or by 1.13～1.44 folds as compared with the control. 【Conclusion】All the findings in this study suggest that TCS and TCC alter aerobic N transformation processes, which may bring about adverse effects on N recycling in the paddy field ecosystem, and promote N₂O emission, which may enhance the potential contribution of the paddy field ecosystem to greenhouse effect and damage of the ozone layer. Therefore, in evaluating soil ecological risks of TCS and TCC in future, it is essential to take into account their potential influences on N transformation and N₂O emission.

Abstract:【Objective】As a toxic heavy metal element, Cd (Cadmium) pollution of the soil is a global threat to human health. Compared to the other heavy metals, Cd is easily absorbed by roots and transported to tender shoots of plants and accumulated therein, thus contaminating the edible parts of a variety of crops. Rice ( Oryza sativa) is liable to absorb Cd from soil and store it in grain. Therefore, Cd pollution in paddy soil is becoming an increasingly serious problem in China. In view of the current situation of soil Cd pollution in China, i.e. low in pollution level and extensive, in pollution area, in-situ remediation technology has become one of the hot spots in the study on remediation of heavy metal contaminated farmland soil in China. Therefore, this study is oriented to explore effects of Cd pollution passivators, organic and inorganic, on Cd adsorption and accumulation and yield rice as affected by combination of the paasivator.【Method】Paddy fields that yielded rice with Cd exceeding the standard for food safety in Guizhou Province were selected as research object, and soils were collected from the fields to cultivate rice in a pot experiment, which was designed to have 15 treatments, that is, Treatment 1 (L as quicklime); Treatment 2 (M as chicken manure); Treatment 3 (D1 as Silicon-sulfhydryl ≥45% in effective ingredient); Treatment 4 (D2 as mixture of CaO≥20%, SiO2 4%, K2O:4%, MgO 5%, S 2%, free water 8% and organic carbon 8%), Treatment 5 （D3 as mixture of CaO 24%, SiO2 3%, free water 8% and organic carbon 8%）; Treatment 6 (D4 as mixture of CaO 30%, SiO2 35%, MgO 5%, Fe(OH)2 3 %, free water 5% and organic carbon 8 %); Treatment 7 (L+M) ; Treatment 8 (L+D1); Treatment 9(L+D2); Treatment 10 (L+D3); Treatment 11 (L+D4); Treatment 12 (L+D1+M); Treatment 13 (L+D2+M); Treatment 14 (L+D3+M); and Treatment 15 (L+D4+M). At the end of the exchangeable Cd content in the paddy soil, Cd content in root, straw, husk, and brown rice and rice yield were measured and analyzed in attempt to screen out the most effective treatment to mitigate Cd hazard and increase rice yield.【Result】15 treatments increased soil pH by 0.25~1.04, soil CEC by 2.65%~50.96% and soil organic matter by 0.22%~17.20%. and reduced exchangeable Cd content by 5.21%~20.56% in the soil. And they reduced Cd content in root, straw, husk and brown rice by 6.66%~45.58%, 12.88%~49.76%, 27.15%~59.79%, and 12.85%~68.62%, respectively, while increasing rice yield by 20.59%~62.14%. Cd enrichment coefficient of rice root, straw, husk and brown rice varied in the range of 1.01~1.67, 0.16~0.28, 0.12~0.22 and 0.09~0.24, respectively. Obviously root was the highest in Cd enrichment capacity. It was found in this experiment that Cd bioconcentration factor (BCF) of root, straw, husk, brown rice varied in the range of 1.01~1.67, 0.16~0.28, 0.12~0.22 and 0.09~0.24, respectively, All the findings illustrate that root is the highest in Cd enrichment capacity, and the application of the 15 kinds of passivators reduces Cd accumulation in rice. Treatments 12, 13, 14 and 15 or the application of L+D1+M, L+D2+M, L+D3+M, L+D4+M are the most effective in reducing Cd content in various rice organs and increasing rice yield. What is more important is that, the above four treatments keep Cd content in brown rice below 0.2 mg•kg^-1, which meets the requirement set in the National Food Standards(GB 2762-2017）. 【Conclusion】In a word, the passivators of L+D1+M, L+D2+M, L+D3+M and L+D4+M can reduce Cd absorption and accumulation in different parts of rice, and increase rice yield. The findings may provide a certain scientific basis for the improvement and utilization of Cd-polluted paddy soil and ensure safe production of rice in mountainous areas of Guizhou Province.

Abstract:【Objective】In recent years, due to aggravating acid deposition and highly intensive agricultural production, involving steadily growing chemical fertilizer application rate, permanent nutrient removal with harvested crops, etc., soil acidification of farmlands is speeding up. Soil acidification of large areas of paddy fields in South China has become an important problem in rice production. Therefore how to ameliorate or remedy the acidifying paddy soil and to exposit its mechanism has become a subject of important theoretical and practical significance to rebuilding healthy soils and guaranteeing food security of the nation. Although lime has already been extensively used as soil amendment to remedy acidified soils, Long-term application of a large amount of lime would not only cause the soil to harden, but also disturb the balance between calcium, potassium and magnesium in the soil. Silicon-calcium-potassium-magnesium (SCPM) fertilizer may be used as an alternative due to its lower solubility and comprehensive nutrient supply. The purpose of this study is to make clear functions of SCPM and its effects on soil acidification in paddy fields. 【Method】A four-year stationarly field experiment was conducted to investigate effects of SCPM on soil pH, electrical conductivity (EC), exchangeable acidity, exchangeable base cation, pH buffer capacity (pHBC) and net base production in the paddy soil. The experiment was designed to have five treatments, i.e. CK (Traditional fertilization practice of the local farmers): Treatment I (CK plus 750 kg·hm^-2 SCPM); Treatment II (CK plus 1 125 kg·hm^-2 SCPM): Treatment III (CK plus 1 500 kg·hm^-2 SCPM); and Treatment IV (CK plus 1 875 kg·hm^-2 SCPM), for comparison.【Result】Results show that CK lowered soil pH in the soil layers (0~30 cm), causing soil acidification at a rate of 2.88 kmol·hm^-2·a^-1, while the SCPM treatments raised soil pH by 1.22~1.58 and 0.35~0.64 units in the topsoil (0~15 cm) and the subsoil (15~30 cm), respectively, and produced alkali in the two soil layers, as much as 9.93~13.82 kmol·hm^-2·a^-1, of which 80% was in the topsoil. Compared to CK, SCPM treatments significantly increased soil EC, exchangeable Ca²⁺, exchangeable Mg²⁺ and base saturation in the two soil layers, and soil exchangeable K⁺ in the topsoil layer, and decreased soil exchangeable acid in the two soil layers, particularly soil exchangeable Al³⁺. In the SCPM treatments, the effects became more significant with rising SCPM, especially in the topsoil layer. The exchangeable base cations and alkali released by SCPM contributed 104.3% to the total reduction of soil exchangeable acid, which suggests that it is the main path to reduction of soil exchangeable acid. In Treatments III and IV, pHBC was significantly increased or by 34.85% and 48.51%, respectively, as compared with CK, which was mainly attributed to the increase in soil cation exchange capacity.【Conclusion】 In a word, SCPM can not only effectively lower soil acidity in the top- and sub-soil layers of paddy fields, but also greatly increase soil exchangeable Ca²⁺ and exchangeable Mg²⁺ in the two layers, and soil exchangeable K⁺ in the topsoil layer. The higher the SCPM application rate, the more significant the effects. SCPM releases Ca²⁺, Mg²⁺ and alkali, which is believed to be the main mechanism of dulling soil acidification in paddy fields.

Abstract:【Objective】The binary quadratic polynomial fertilizer response model is set up on the assumption that crop yield increment per unit of nutrient is linearly related to fertilizer application rate, thus leading to a symmetric relationship in crop response to fertilization between before the maximum application rate and after the maximum application rate of fertilizer is applied. This model obviously tends to be low in modeling success ratio mainly because of its set biased error and existence of multicollinearity and heteroscedasticity. This study has developed a binary non-structural fertilizer response model, which is designed to have better applicability. 【Method】On the basis of the unary non-structured fertilizer response model and the principle that the functions of plant nutrient elements cannot be replaced by each other, a binary non-structural fertilizer response model is constructed. Its fitting effect and its reliability in recommendation of fertilization rates is verified via NPK binary combination field experiments on crop response. 【Result】 The model is OKed through all the statistical significance tests in all the 17 field experiments on crop response of rice, peanut, potato, edamame, winter wheat and summer maize, but only 58.8% of the total test sites showed typical crop responses, and 41.2% did non-typical ones with irrational algebetic symbols of monomial or quadratic term coefficient in model and extrapolated fertilizer recommendation. Fitting tests of the model demonstrate that it has been OKed through all the statistical significance tests, with 88.2% of the test sites showing typical crop responses, and only 11.8% non-typical ones, all of the type of extrapolated recommendation, which demonstrates that the new model has improved in modeling success rate by 29.4% as compared with the binary quadratic polynomial fertilizer response model. Both models show significant linear positive relationships between maximum fertilization rate for highest crop yield and economic fertilization rate for highest crop yield, but the first term coefficient of the linear regression equation is 0.915 3 and 0.916 1, only, which means that for the increment of each kg of fertilizer recommended by the binary quadratic polynomial fertilizer response model only 0.915 3 kg and 0.916 1 kg is recommended by the new model. The new model has fairly well overcome the problem of the quadratic polynomial model’s recommendation tending to be higher. 【Conclusion】 All the analyses indicate that the binary quadratic polynomial fertilizer response model is a simple and specific one of the binary non-structural fertilizer response model. The new model has a wider range of applications.

Abstract:【Objective】Content and composition of soil humus are major factors that may influence yield and quality of flue-cured tobacco. Tobacco is widely planted in China in a number of soils, different, complex and verified in soil-forming factor and soil type. However little information is available now in the literature about characteristics of soil humus composition at a country scale. 【Method】In this study topsoil samples were collected from 425 tobacco fields in 47 tobacco-planting areas typical of the 12 high-quality tobacco production regions of China for analysis of composition of topsoil humus. 【Result】Results show: (1) Total carbon of the soil humus varied in the range of 23.18 ~ 6.04 g·kg^-1 with a mean of 13.91 g·kg^-1; humic acid carbon, humin acid carbon, humin acid carbon, fulvic acid carbon and H/F ratio did in the range of 12.23 ~ 3.66 g·kg^-1, 6.17 ~ 1.41 g·kg^-1, 10.95 ~ 2.38 g·kg^-1, 6.99 ~ 2.24 g·kg^-1 and 1.03 ~ 0.45 with a mean of 8.10 g·kg^-1, 3.22 g·kg^-1, 5.81 g·kg^-1, 4.88 g·kg^-1 and 0.72, respectively: (2) Total carbon in humus was significantly higher in Nanling mountain region than in the other regions, but significantly lower in Zhongyuan region and Central Shandong than in the other areas. Humic acid carbon, humin acid carbon and humin carbon was the highest in Nanling mountain area and the lowest in Central Shandong, while humus in Panxi region was relatively high in humin but lower in other components; (3) According to content and composition of soil humus (six indices), the 47 areas could be divided into four groups, differing sharply in humus content and composition.【Conclusion】The tobacco planting areas are quite different in content and composition of humus in topsoil. The areas in South China are higher than those in North China. The 47 areas are sorted into four groups in terms of content and composition of topsoil humus and the four groups vary significantly in humus content and composition.

Abstract:【Objective】 Purple soil is weak in erosion resistance, and its soil aggregates are also vulnerable in structure. This study was oriented to explore how to reasonably utilize organic material resources, like crop straw, and improve structure of the purple soil, and how organic carbon is distributed in soil aggregates of the purple soil in the Sichuan Basin. 【Method】A tract of farmland under the rape/maize rotation ecosystem was selected for an in-situ filed experiment to explore effects of application of chemical fertilizer coupled with biochar and/or crop straw on content and stability of soil aggregates and soil organic carbon of the purple soil and distribution of organic carbon in aggregates by fraction. The experiment was designed to have control (CK) and 5 treatments, that is, CK (application of chemical fertilizer only), BC (application of chemical fertilizer + 8 000 kg•hm^-2biochar), CS (application of chemical fertilizer + 8 000 kg•hm^-2straw), 0.5BC (application of chemical fertilizer + 4 000 kg•hm^-2 biochar), 0.5CS (application of chemical fertilizer + 4 000 kg•hm^-2 straw) and BC+CS (application of chemical fertilizer + 4 000 kg•hm^-2biochar and 4 000 kg•hm^-2 straw). 【Result】Results show: (1)compared with the control (CK), all the treatments, except for Treatment 0.5BC, increased the content of >2 mm aggregates, while reducing the content of <0.053 mm aggregates. They also increased mean weight diameter (MWD) and geometric mean diameter (GMD) of the water-stable soil aggregates and content of the >0.25 mm aggregates (R0.25), with Treatment CS, in particular, where the effects became more significant with rising straw application rate. Treatment CS+BC significantly increased the content of 0.25~2 mm water-stable aggregates. (2)Except for Treatment CS, all the treatments significantly increased the content of total soil organic carbon as compared with CK. Among them, Treatment BC and CS+BC treatment did by 45.55% and by 44.45%, respectively (P<0.05), and the effect of Treatment CS was not so significant. With rising biochar application rate, the content of total organic carbon in the soil increased correspondingly. The increase was especially significant in <0.053 mm and >2 mm fractions of soil aggregates; Compared with other treatments, Treatment BC increased the content of organic carbon in all soil aggregates in the soil, regardless of size fraction, and followed by Treatment CS+BC in this effect. (3)By calculating contribution rate of each fraction of aggregates to total organic carbon in the soil, it was found out that the effects of the treatments increasing contribution of soil aggregates to total organic carbon in the soil were the most significantly reflected in the 0.25~2 mm and <0.053 mm fractions of soil aggregates. However, Treatment CS was the only one that significantly increased the organic carbon contribution rate of the >2 mm fraction of soil aggregates, or by 53.53% as compared with CK, and Treatment CS+BC and 0.5BC increased the rate of the <0.053 mm fraction of aggregates by 26.20% and 48.63%, respectively. (4)Application of straw and/or biochar increased the biomass and economic yield of maize and rapeseed, especially Treatments CS, BC, and CS+BC in the experiment. 【Conclusion】Combined application of straw and/or biochar with chemical fertilizer is an effective practice to improve structure of and increase carbon content in the purple soil.

Abstract:【Objective】 Composition and component ratio of soil humus are important indicators for assessing soil organic carbon quality, and also have important influences on soil structure and quality. Soil humus varies in combination form and hence in effect on soil structure and soil fertility as well. Therefore, it is of great significance to rational fertilization in facilitated vegetable production to study effect of application of nitrogen(N) fertilizer and organic manure on component contents, composition and profile distribution of soil humus under greenhouse. 【Method】For this study a field fertilization experiment was conducted in a greenhouse growing tomato for five consecutive years. The experiment was designed to have four treatments (N0, N1, N2 and N3) of applying merely N fertilizer at a rate of 0, 187.5, 375.0, and 562.5 kg·hm^-2, respectively, and four (MN0, MN1, MN2 and MN3) combined application of N fertilizer and organic manure that is, each of the four N treatments coupled with organic manure (M: 75 000 kg·hm^-2). Total organic carbon (TOC), water soluble organic carbon (WSOC), soil loosely and stably combined humic acid carbon (HA-C) and fulvic acid carbon (FA-C) in all the eight treatments were monitored for content, composition and profile distribution in the greenhouse soil. Soil water soluble substance (WSS), loosely combined humus and stably combined humus were extracted with Fu Jiping, soil humic acid (HA) and fulvic acid (FA) separated with the modified humus component method, and organic carbon content of each determined. 【Result】 In all fertilization treatments, the contents of TOC, WSOC, stably combined humic acid carbon (HA₂-C) and fulvic acid carbon (FA₂-C) gradually decreased with soil depth, whereas the contents of loosely combined humic acid carbon (HA₁-C) and fulvic acid carbon (FA₁-C) increased first and then decreased with soil depth. But the contents of soil TOC, WSOC and humus components were the highest in the 0~20 cm soil layer. Compared with application of mere N fertilizer, combined fertilization increased the content of TOC, WSOC, HA1-C, FA₁-C and HA₂-C by 12.44%~87.38%, 11.01%~168.32%, 10.15%~235.54%, 2.41%~205.21% and 3.42%~92.61%, respectively, in the 0~50 cm soil layer. The effect was especially significant for TOC, WSOC, HA₁-C, FA₁-C and HA₂-C in the 0~20 cm soil layer (P< 0.05) and for HA₁-C, FA₁-C and HA₂-C in the 40~50 cm soil layer (P< 0.05). Combined fertilization also significantly improved the ratio of HA₁/FA₁, HA₂/FA₂, and HA/FA and PQ₁ (HA₁-C/(HA₁-C+ FA₁-C)), PQ₂ (HA₂-C/(HA₂-C+ FA₂-C)), and PQ (HA-C/(HA-C+ FA-C)) in the 0~20 cm soil layer (P< 0.05), increased the C/N ratios of HA1, HA₂ and FA₁, but slightly decreased that of FA₂ in the 0~20 cm soil layer. Besides, combined fertilization also decreased E₄/E₆ (The ratio of absorbance at 465 nm and 665 nm wavelengths) of the soil HA, but increased E₄/E₆ of the soil FA.【Conclusion】 Under the conditions of tomato cultivation in the greenhouse, combined fertilization for 5 consecutive years not only significantly increases the amount of soil organic carbon in the 0~20 cm soil layer, but also helps FA transform to HA, promotes formation and accumulation of humic acid, especially loosely combined humic acid, and consequently improves quality of the soil organic carbon significantly. It is, therefore, concluded that combined application of 187.5 kg·hm^-2 N fertilizer and 75 000 kg·hm^-2 organic manure is the best option to improve quantity and quality of soil organic carbon.

Abstract:【Objective】 Soil organic phosphorus (P) is one of the important P sources for plants. A large number of studies have shown that rhizospheric processes improves bioavailability of soil organic P through stimulating mineralization of soil organic matter. 【Method】 In the present study, investigation were made of contributions of the rhizospheric processes of maize and faba bean to mineralization of soil organic P through an experiment combining root mat culture in greenhouse and in-situ measurement in the field, and exploration done of effect of soil organic P concentration on organic P mineralization in black soil, which is high in organic matter concentration. 【Result】No big differences were observed in dry weights of shoot and root of the maize and faba bean in greenhouse between low P (CK) and high P treatments (NPKM); Root/shoot ratio of the maize reached 0.25 in either treatment, and was 0.08 higher than that of the faba bean in CK and 0.07 higher in NPKM. Fertilization did not affect much P concentrations in shoot and root of the maize, and neither in shoot of ther faba bean. However, it did increase P concentration in root in the faba bean in NPKM by 57.6% as compared with CK. Rhizosphere pH of the maize in CK was 0.09 higher than the pH in bulk soil, and rhizosphere pH of the faba bean in NPKM was 0.11 higher than the pH in bulk soil and 0.09 higher than that of the maize. Acid phosphatase (APase) activity in rhizoshpere of the maize was significantly higher in CK than in bulk soil. No significant difference was observed in APase activity between rhizosphere and bulk soil. APase activity in rhizoshpere of the faba bean was 93.4% higher than that of the maize in NPKM. Soil organic P concentration in CK varied in the range of 214 mg·kg^-1 ~ 218 mg·kg^-1, and was 103%～171% lower than that in NPKM. Organic P in rhizosphere was depleted by crops in NPKM and by 138 and 86 mg·kg^-1 with maize and faba bean, respectively. The organic acid anions in rhizosphere of the maize and faba bean included tartrate and malate anion. Tartrate concentration in rhizosphere of the maize was 77.0% lower in CK than in NPKM, and Tartrate concentration in rhizosphere of the faba bean did not vary much between in CK and in NPKM. In the field, rhizosphere pH of the maize was higher in CK than in NPK, NPKS and NPKM. Compared with the pH in bulk soil, rhizosphere pH of the above four treatments decreased by 0.3~0.51 units. Rhizosphere pH of the faba bean did not differ much between NPKM and NPKS. But pH of bulk soil was significantly lower in NPKM than in NPKS. But, NPK was significantly lower than all the other treatments in pH of bulk soil and of rhizosphere soil. APase activity was higher in rhizosphere than in bulk soil in all the treatments. No significant difference was observed in APase activity in rhizospheres of between the treatments. And APase activity in bulk soil did not vary much with treatment. Malate concentration in rhizosphere was higher in NPKM than in CK, but did differ much between CK, NPK and NPKS.【Conclusion】Mineralization of rhizosphere organic P was regulated by both rhizosphere processes and concentration of organic P in soil. Long-term fertilization promotes accumulation of organic P in black soil and increases concentration of the substrate of mineralization, which is beneficial to mineralization. Rhizospheric process of maize in the field enhances this process, thus maintaining P supply intensity in the root layer. Thus, building a high organic P pool and selecting crop varieties that are highly efficient in using organic phosphorus is an effective strategy to maintain P supply capacity of black soil and achieve the target of reducing P fertilization and improving its efficiency.

Abstract:【Objective】 Rhizosphere is a specific compartment that is significantly influenced by soil microorganisms in the plant root system in soil. Rhizosphere extends from the surface of the main root for a few millimetres, and is an important zone where plant-soil-microorganism interactions occur. In the rhizosphere, bacteria and fungi coexist and interact with each other, playing a critical role in recycling of nutrients in the ecosystem and sustaining of plant health and growth. Ecological network analysis can visualize interactions between microbial communities, and uncover co-occurrence patterns of the species in microhabitats and their main influencing factors, which provides a new approach to explaining complex structure of the microbial communities. Network analysis can also be used to explore mechanisms of microbial interactions driving biogeochemical coupling of important elements in soil, which is an important step towards predicting and improving service functions of a soil ecosystem. Unique in structure and composition, biochar can improve soil properties in a number of aspects, for instance, promoting formation of soil aggregates, enhancing cation exchange capacity, nutrient absorption capacity and water holding capacity, and dulling excessive acidification. So it can be applied beneficially to soil amelioration and raising of crop yield. In addition, the unique aromatic surface, excellent porous structure and high moisture and nutrient adsorption capacity of biochar can also provide soil microorganisms, such as bacteria and fungi, with benign habitats, and hence increase biomass of the microorganisms. The application of biochar can alter structure and enzyme activity of the microbial community, which benefits accumulation of soil organic matter and transformation of soil nutrients and then indirectly improves growth of the plants. Therefore, a comprehensive understanding of the effects of biochar on the interactions between bacterial and fungal communities in rhizosphere soil is of great significance to how to improve soil nutrient transformation. 【Method】 In order to explore effects of biochar on interactions between bacteria and fungi in rhizosphere soil, a pot experiment was designed to have CK and a treatment of adding 2% (w/w) biochar and performed for comparison in interaction network between rhizosphere bacteria and fungi and its affecting factors. The soil used in the experiment was collected from the topsoil layer (0~10 cm) of a paddy field in Changzhou, Jiangsu Province, air-dried, screened with a sieve 2 cm in mesh, and ground fine. Then the soil homogeneous in texture was left in rest for 24 hours, before being put in pots, 3 kg each. Full ryegrass seeds were sown into the pots, 30 each. Soil and plant root samples were collected from the pots on the 0th, 5th, 10th, 15th, 20th, 25th, 30th, 35th and 40th days after germination of the seeds, from three pots each time as replicate. So the experiment had a total of 54 pots of ryegrass plants. The samples were analyzed separately and soil geochemical properties, rhizosphere microorganisms, and morphological parameters of the ryegrass roots were determined. 【Result】 Network analysis shows that in the treatment, the association between bacteria and fungi in their co-occurrence network became more complicated with number of nodes and interaction enhanced. Positive interactions within the bacterial community and between bacteria and fungi communities were significantly enhanced (P < 0.05). Modular analysis of the interaction networks in CK and Treatment found two modular structures with highly interconnected nodes. In the treatment, Flavobacterium was found to be the key group of the co-occurrence network, while in CK, Sunxiuqiniaand Pichia were. Mantel test indicates that soil pH (r= 0.385, P = 0.003) and soil ammonium nitrogen (r = 0.501, P = 0.003) had more significant effects on the interaction between rhizosphere bacteria and fungi in the treatment. 【Conclusion】 Application of biochar significantly enhances interactions between bacterial-fungal communities in the rhizosphere soil, while improving positive associations within the bacteria community and between bacteria and fungi.

Abstract:【Objective】 Imbalance of soil microflora in rhizosphere is an important cause impeding continuous cropping of crops. And crops under different cropping systems may have certain specific rhizospheric soil microbial communities that would mitigate or aggravate the impediment to continuous cropping. 【Method】 By employing the classic culturable method and molecular classification method, this study investigated variations of the soil microbial communities in the rhizoplane, rhizosphere and bulk soils of peanut under continuous cropping and rotation systems and their relationships with impediment to continuous cropping.【Result】 Compared with the peanut under rotation, the crop under continuous cropping was 45.8% lower in pod yield, 57.5% lower in number of root nodules, and 24.1% lower in plant biomass, but 2.9 times and 2.4 times higher in incidence of bacterial wilt and root rot, respectively. In the peanut fields under either rotation or continuous cropping fields, distribution of bacterial and fungal populations varied significantly, displaying a decreasing trend from rhizoplane, rhizosphere to bulk soils. Particularly, the number of microbes in the rhizoplane was 2.83 to 329 times higher than that in the rhizosphere. Further investigations found that population of soil microbes in the rhizoplane differed sharply between the peanuts under rotation and continuous cropping. The former was 1.06 to 3.28 times higher in bacterial population and 1.14 to 14.44 times higher in fungal population than the latter. The difference was more significant than that in the rhizosphere and bulk, which indicates that the soil microbial community in the rhizoplane was affected the most significantly by physiological and metabolic activities of peanut root and the most closely related with impediment to continuous cropping. Molecular identification of culturable microbial groups shows that the proportion of beneficial microbes, including Pseudomonas sp., Geotrichum candidum, in the rhizoplane of peanut under rotation was higher than that under continuous cropping, while the proportion of pathogenic microbes ( Talaromyces sp., Aspergillus niger, Clonostachys rosea , Serratia sp.) was in a reverse trend. 【Conclusion】 All the findings in this study suggest that continuous cropping favors pathogenic fungi colonizing in rhizoplane, thus inhibiting growth of the beneficial bacteria, which could be the major cause of sharp increase in soil-borne diseases under continuous cropping.

Abstract:【Objective】Soil erosion and declining of soil fertility is becoming a severe problem in vegetable fields in South China. In practice, mulching system has become one of the effective measures for solving this problem. However, the study of the different mulching on soil biological properties and bacterial diversity in vegetable fields were rarely investigated.【Method】Soil samples were collected from pepper fields with different mulching treatments in South China. Soil temperature, water contents, soil microbial biomass, enzyme activity were analyzed by traditional ways and bacterial diversity was studied by using high-throughput sequencing techniques. 【Result】The soil temperatures in different layers from the depths of 5 cm, 10 cm, 15 cm and 20 cm were increased 0.05～2.93 ℃, 0.06～1.88 ℃, 0.45～2.16 ℃ and 0.23～2.46 ℃, respectively. Meanwhile, soil water content was increased 13.3%～19.4% under different mulching conditions which compared to control. By contrast, soil pH was also raised from 0.01 to 0.19 under different mulching conditions which compared to CK. In addition, the enzyme activity and microbial biomass were also significantly increased which relative to type of the mulch, i.e. in turn, colorless transparent film, black film and silver film which are all made of polyethylene. Soil bacterial diversity, Flavobacterium, Lysobacter, Alcaligenes Sphingomonas and Bacillus turned out to be the dominant groups and the soil bacteria therein were higher in richness, diversity and evenness in soils under different mulching conditions which compared to CK. In particularly, soil bacteria, such as Lysobacter and Bacillus, that are capable of protecting the ecology and promoting plant growth, were found accumulating in the soils of mulching conditions. 【Conclusion】 The colorless transparent plastic film mulching is the best for increasing soil temperature, water content and enzyme activity. And all the mulching treatments not only can improve the soil physical and chemical characteristic, increase the soil microbial biomass and enzyme activities, but also can accumulate some of the plant growth promoting bacteria (PGPB) in pepper fields. All the findings indicate that instead of degrading soil quality of the pepper fields, the current practice of film mulching will help build up soil fertility and improve soil health

Abstract:The existing methods for measuring soil bulk density are found to have a number of deficiencies, for instance, they fail to meet the demands of rapid development of precision agriculture, modeling of ecological environment, and assessment of soil carbon storage for a large volume of accurate bulk density data. Therefore, researchers have worked out a technique that combines gamma-ray attenuation and visible-near infrared spectroscopy for determination of soil bulk density, and has been successfully applied to estimating soil carbon storage. In order to test this method for accuracy and applicability in measuring soil bulk density in hilly regions of South China, soil samples were collected from a hilly area of Nanning, Guangxi for analysis of soil bulk densities with this method. And then comparison was made of this method with the traditional one of using cutting rings to collect soil samples and oven-drying the samples for weighing in accuracy of the measurement. Results show that two methods were similar in accuracy, and both quite high in regression R² , up to 0.92, and low in root mean square error between the two, accounting only for 4.48% of the means of the soil bulk densities obtained. It is, therefore, concluded that besides being time-saving, inexpensive and non-destructive, this method using γ-ray attenuation and visible-near infrared to determine soil bulk densities is quite high in accuracy and applicability in the hilly regions of South China.

Abstract:The discovery of Comammox（complete ammonia oxidizers）is considered to be an important progress in the study on nitrogen recycling, but further efforts need to be done to elucidate environmental driving mechanisms of the coexistence of Comammox with AOA（ammonia-oxidizing archaea）and AOB（ammonia-oxidizing bacteria）in the complex soil environment. Soil samples were collected from a long-term stationary experiment on purple paddy soils, which had two treatments, i.e. PF (plant rice in summer and keep the field flooded all the year) and FD (fallow all the year and keep the field dried up in winter), for analysis of effects of fertilization and water management on nitrification potential and abundance of ammonia-oxidizing microorganisms in paddy soils. The analysis shows that PF was higher than FD in nitrification potential, which reached 25.0 mg•kg^-1•d ^-1 and 2.11 mg•kg^-1•d ^-1, respectively. Obviously, the former was 12 times as high as the latter. Real-time quantitative PCR (Q-PCR) shows that Comammox, AOA and AOB were detected in the paddy soils of PF and FD, and displayed an order of Comammox> AOA>AOB in abundance. The abundance of Comammox was 8.5 times that of AOA and 77.3 times that of AOB in the PF paddy soil, and 4.1 times that of AOA and 490.3 times that of AOB in the FD paddy soil. Compared with FD, PF stimulated growth of the Comammox Clade A, AOA and AOB in the soil, making the three 9, 3 and 42 times higher, respectively, in population. But the Comammox Clade B dropped 2 times as fast. All the findings in the 28 year-long experiment indicate that compared with FD, PF keeps ammonia-oxidizing microorganisms in the paddy soils under the long-term stress of O2 deficiency and selectively promotes growth of the Comammox Clade A and AOA in the soils, while fertilization at a high rate significantly promotes growth of the AOB; and Comammox Clade A and AOA can adapt to a wide range of ammonium nitrogen substrates. In future, the technique of DNA-SIP (stable isotope probe) may be used to identify functional significance of Comammox, which is dominant in population in paddy soils and its relative importance to AOA and AOB.

Abstract:In order to study spatial distribution and movement of soil moisture and salt in coastal saline-alkali land and its effect on photosynthetic production and yield of cotton, and further discuss how elevation and soil bulk density affects spatial distribution of soil moisture and salt content in cotton fields of coastal saline-alkali soil, four cotton fields, quite different in elevation and soil bulk density were selected in a coastal saline-alkali area. Soil moisture and salt contents and soil pH in the 0~200 cm soil layers of the fields were monitored during the period of April~October and characterized for analysis of their influences on photosynthetic production and yield of cotton. Results show that in the cotton field, mild in soil salinity and alkalinity but high in elevation, a high-bulk-density interlayer was formed, 141~160 cm in depth, low in soil salinity and pH. In that cotton field, soil moisture content was low during the rainy season (July~August) and apparently higher than that in the cotton field moderate in soil salinity and alkalinity during the late cotton growing period (September~October). So the cotton in that field suffered less salt stress, and had its photosynthetic production highly coinciding with availability of prime hydrothermal resources and hence a long active dry matter accumulating period. In the cotton field, moderate in soil salinity and alkalinity and relatively high in elevation, higher elevation and bulk density inhibited rise of salt and pH, thus relieving the crop from salt stress during the rainy season, but salt stress was still quite obvious during the early and late cotton growth periods (April~June and September~October), so the crop did not have a good coincidence of its photosynthetic production with availability of prime hydrothermal resources. In the cotton field high in soil salinity and alkalinity and low in elevation, soil buld density did not seem to have much impact on water and salt movement, and the crop was subjected to a long-term high soil stress and hence low in capacity and yield of cotton. Therefore in ameliorating the coastal saline-alkali fields, it is advisable to raise them in elevation properly and help them form a high bulk density interlayer of a certain thickness, to improve them water storage and drainage capacity, which is believed to be a soil ameriolating measure contributive to photosynthetic production.