Abstract:Soil is the largest terrestrial organic carbon sink, and soil organic matter is the main form of the carbon stored in the sink. In view of the fact that soil organic matter plays an important role in the ecological system and carbon storage, the topic of soil minerals adsorbing organic matter and its mechanism is getting more and more attention from scientists the world over. This paper presents a review of the papers published in the past years about the mechanisms of soil minerals adsorbing organic matter and its major affecting factors. It is reported that among a huge number of soil minerals, hydrated iron, aluminum oxides and clay minerals are quite high in organic matter adsorbing capacity, ligand exchange, complexation, hydrogen bond, cationic bridge, condensation and Van der Waals force, the main mechanisms, and soil pH, the key factor that influences surface charge and adsorption sites of the mineral and hence adsorption of organic matter. Amount of the soil organic matter already adsorbed on the surface of the minerals also affects somewhat capacity of the minerals keeping on adsorbing organic matter, because the already adsorbed organic matter forms a layer covering part of the surface of the minerals and adsorbing sites thereon, and the closer the layer to the surface of the minerals, the tighter it adsorbed onto the minerals. Stability of the soil organic matter is affected significantly by the interaction between the organic matter and the minerals. Generally speaking, the adsorption of organic matter via chemical bond is the most stable and followed by that via Electronic “Donor-Acceptor” mechanism (which shows inner-sphere complex between functional groups on the surface of the minerals and the organic matter), and that via Van der Waals force and electrostatic force, in the end. In recent years, with the development of analytic equipment and technologies, some new characterizing and probing methods, such as TG, DSC, FTIR, SEM, TEM, AFM, STXM/NEXAFS, Neutron Scattering, have been invented and used in the studies on mechanisms of mineral-organic matter associations (MOAs). These instrument developments will undoubtedly bring important new insights into mechanisms of MOAs. However, relatively little has been reported about effects of microorganisms on mineral adsorption of organic matter, formation and evolution of MOA, though it is quite obvious that their effects are crucial.

Abstract:For a long time, quite a number of people one-sidedly believe that soil science is merely an applied science, and its research tools are merely experimental, while its research methodology should be holistic and integrative. In this paper, systems analysis was done of the perniciousness of this one-sided presumption to development of the soil science, and it was proposed that development of the soil science in future should stress the use of analytical methods and a natural systematic integration should be realized on the basis of such in-depth analyses. Three basic viewpoints were then put forward and elaborated: 1) it is essential to be fully aware that the peculiarities of the soil systems root in their fundamental impacts on subatomic structures. For example, in common aqueous solutions, Li , K and Cs will definitely not exceed 1.00 in effective charge and instead should fall below 1.00 due to cationic volumes and hydration effects; however, their effective charges burgeon respectively to 1.05, 1.94 and 2.40 when these ions are placed at the interface of clays in aqueous solutions, as a result of the profound impact of clay on the energetic and quantum states of these cation electrons. In other words, cations (as well as atoms and molecules) at clay interfaces are essentially different from those in aqueous solutions. 2) Considering peculiarities of the soil systems, methodologically the soils should be hierarchized by scale i.e. macroscopic, mesoscopic, molecular, atomic and subatomic scales, and eventually analyzed by means of the principles and methodology of quantum mechanics at the subatomic scale. And 3) Through researches based on the quantum effect unique to the soil, direct correlations between subatomic structures, soil microscopic mechanisms and macroeffect could be established, hence to realize, an natural conversion of scientific principles between different scales of soil. And in the end an independent and self-consistent pedological knowledge system will be constituted. Here it is a must to emphasize that this paper is intended to provide some ideas about methodology of the research on basic soil science. Although it may be too much of a generalization for our arguments to be just supported by several special examples, the particularities of the soil systems those samples reflect sufficiently express the necessity to establish an independent and self-consistent knowledge system for soil science, and the importance of analytical methods in the establishment.

Abstract:【Objective】 Soil aggregate is a basic unit in soil structure and its stability is an important index describing soil’s resistance to breakdown in the process of water erosion. However, in splash erosion how raindrops function through mechanical impact and slaking effect on soil aggregates and what are the mechanisms and contribution rates of the two are still unclear. This study is oriented to investigate effects of mechanical impact and slaking effect of rain drops on breakdown of soil aggregates during splash erosion. 【Method】 A series of indoor splash erosion experiments were carried out in the State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, China. Samples of Loessal soil (Sandy loamy soil) collected from Yan’an and Lou soil (Loamy loam soil) collected from Yangling in Shaanxi province, two typical soils in the Loess Plateau, were tested in the experiments. A home-made needle type rainfall simulator, consisting of three parts: water supply apparatus, needle nozzles and support frame, was used to simulate rain drops of ultra-pure water and alcohol to determine effect of mechanical impact alone and joint effect of mechanical impact and slaking on soil aggregates, separately. The splash erosion experiments were designed to have two type of soils and 5 treatments in height for rain drops to fall, i.e. 0.5 m, 1 m, 1.5 m, 2 m and 2.5 m. 【Result】 Results show that in the two soils soil aggregate stability exhibited an order of MWD_fw < MWD_ws < MWD_sw. Slaking effect (Fast wetting) was the major mechanism of the breakdown of soil aggregates, and followed by mechanical disturbance (Wetting and Shaking), and then chemical slaking (Slow Wetting) in the end. The soil of loamy clay was higher than the soil of sandy loam in RSI (Relative Slaking Index), suggesting the former is more susceptible to slaking effect than sandy loam soil, while the latter is more to mechanical impact. In splash erosion, when rain drops fell from the same height, splash erosion rate was lower in loamy clay soil than in sandy loam soil, and splash erosion rate caused by rain drops of pure water through the joint effect of mechanical impact and slaking was higher than that caused by drops of alcohol through mechanical impact alone in both soils. Regardless of pathways of the rain drops affecting soil aggregates, splash erosion rate increased with rising kinetic energy of the rain drops, and power function could be used to well describe the relationship between splash erosion rate and rain drop kinetic energy. The splash erosion rates caused by slaking effect and/or mechanical impact of rain drops both increased with rising rain drop kinetic energy or rising height where rain drops fell from. The slaking effect contributed more than 50% to the splash erosion rate, indicting slaking effect was the main factor causing aggregate breakdown effect, but the slaking effect decreased in contribution to splash erosion rate with rising rain drop kinetic energy, while the mechanical impact acted reversely. In the cases the same in rain drop kinetic energy, the contribution of slaking effect was higher in loamy clay soil than in sandy loam soil, but that of mechanical impact was just the reverse. 【Conclusion】Contribution rates of slaking effect and mechanical impact vary with rain drop kinetic energy and soil type. All the findings in this study could be of great significance to evaluation of aggregate stability and to in-depth understanding of the mechanism of aggregate breakdown during splash erosion.

Abstract:【Objective】The Freezing-thawing action refers to daily, annual and secular climate change that might lead to freezing and thawing of the earth’s surface in a certain climatic region. When the soil is frozen, soil water is frozen, too, thus expanding in volume and the expansion destroys the connectivity between soil particles, and hence change particle size distribution of soil particles. And during the thawing period, owing to the existence of both thawed soil layer and frozen soil layer at the same time, the soil differs sharply in erodibility from those completely frozen or thawed. However, studies focused mainly on changes in soil erodibility before and after freezing and thawing and gave little attention to studies on erodibility of frozen soils. Under the joint actions of hydraulic erosion and freezing-thawing erosion, the slope varies sharply in soil erosion and sediment particle size fractionation from those under the single action of hydraulic erosion, however, it is still unclear how soil erosion and sediment particle size fractionation varies under the joint actions.【Method】 Therefore, an indoor experiment was carried out using simulated rainfall to explore effects of freezing/thawing on water erosion during the thawing period on slopes of loess, processes of soil erosion on frozen and thawed slope and particle size fractionation of sediment. 【Result】Results show that affected by rain, runoff initiated 173 seconds earlier on the thawed slope than on the frozen one, while runoff rate and sediment yield was 9% and 105% higher, respectively. In terms of MWD of sediment particles generated during the processes of soil erosion on the two slopes, an order was observed as splash particles > scouring particles, but MWDs of the two types of particles were both significantly higher on frozen soil slopes than on thawed soil slopes (p < 0.05). During the erosion process with the rainfall going on, the contents of clay and fine silt increased first and then decreased, but the contents of coarse silt and sand did reversely, on the thawed slopes, while the sediment got dominated with coarse particles. However, particle size fractionation of the sediment on frozen slopes did not vary much with the time going on.【Conclusion】On frozen slopes, the existence of an aquiclude aggravates the soil erosion, but during the hydraulic erosion process, the erosion was low in selectivity of sediment in particle size relative to that on thawed slope. This paper is expected to provide some valuable reference for better understanding the mechanism of soil erosion.

Abstract:【Objective】The technology of using chemicals to control soil erosion is mainly implemented through spraying high molecular compounds over on the surface soil layer to improve its soil structure, to enhance stability of its soil aggregates, to prevent dispersion of its clays and hence to increase rain water infiltration rate and eventually to control surface runoff and soil erosion. Jag S is a kind of neutral polysaccharide and a new type of high polymer. This study on effect of the use of this high polymer on rainwater infiltration rate in loess slopes is intended to lay down a new theoretic basis for applying the technology of using chemicals to control soil erosion to the Loess Plateau in arid and semi-arid regions for erosion control and water conservation. Control of soil erosion with chemicals is a new method, which is developed on the basis of the modern chemical industry and different from the traditional soil and water conservation methods. 【Method】An indoor experiment was conducted in the Rainfall Simulation Hall at the State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau at the Institute of Soil and Water Conservation. A rainfall simulator system with side-sprinklers was used to simulate rainfall events different in intensity ranging from 0.5 to 3.5 mm min^-1. The sprinklers were 16 m high above the experimental field, providing simulated rainfall events over 80%in uniformity and raindrops 0.25 to 0.375mm in diameter, when a rainfall event was set at 1 ~ 2 mm min^-1in rainfall intensity. Kinetic energy of the raindrops striking at surface soil of the field ranged from 365 to 847 J h^-1 m^-2. The indoor simulated rainfall experiment was designed to explore relationships of rain water infiltration rate and initiation time of runoff with dosage (1, 3 and 5 g m^-2) of Jag S used relative to slope gradient (10°, 15° and 20°) and rainfall intensity (1.0, 1.5 and 2.0 mm min^-1). 【Result】Results show that compared with the CK slope, all the slopes sprayed with Jag S regardless of rate were lowered in infiltration rate during the initial period of all rainfall events. However, the spraying of 1 and 3 g m^-2 Jag S significantly raised rain water infiltration rate on all loess soil slopes in the late stages of the rainfall events, and reduced the buffering effect during the initial periods of the rainfalls. Consequently, the rain water infiltration rate increased by 21.53% and the infiltration enhancement rate by 9.17%. On the contrary, the spraying of 5 g m^-2 Jag S weakened the rainfall water infiltration rate in all rainfall events except for the one lowest in intensity (1.0 mm min^-1) and in all the loess slopes. The soil slopes sprayed with Jag S, regardless of rate, differed very slightly in runoff initiation time, however, they had runoff initiated earlier than the CK slope. The higher the Jag S spraying rat, the earlier the runoff initiated. Obviously the effects of a high Jag S spraying rate and a high slope gradient on runoff initiation were significant. The runoff initiation advancement rate on slopes sprayed with 1, 3 and 5 g m^-2 was 47.26%, 50.47% and 66.28%, respectively, under rainfalls the same in intensity. 【Conclusion】All the finding indicate that Jag S is to a certain extent, effective to improve soil structure of the loess slopes and increase rainwater infiltration rate and hence reduce soil erosion. Consequently, spraying of the neutral polymer Jag S on surface soil of a loess slope is a potential alternative to control soil erosion on the Loess Plateau. The findings of this study may serve as a scientific basis for soil and water conservation using polymers.

Abstract:【Objective】The Qilian Mountains is the main water head of the HeiheRiver Valley in Northwest China. To balance the need of water between socio-economic development and natural ecology protection, it is very important to understand the hydrology and other scientific basis of water management. Situated at the headwater area of the basin, soil properties especially soil physical properties such as particle size distribution in the Qilian Mountains have significant impacts on hydrological processes. Mode of profile distribution (PDM) of soil particle size composition and its relationships with various environmental factors were discussed in an attempt to further understand quantitatively the transport of water, nutrient, gas and heat in soil and to develop 3D predication and mapping of soil particle size distribution. 【Method】A total of sixty-nine soil profiles ≥1m in depth typical of the Qilian Mountains were investigated and soil samples collected from layers of the profiles for fractionation of clay, silt and sand fractions with the laser diffraction method. Sand fraction, the most variable one, was selected to study mode of its vertical distribution in the profile and its relationships with environmental factors, including elevation, slope, aspect, annual mean precipitation, plan curvature, profile curvature, terrain wetness index, land use and parent materials. 【Result】Results show that the sand fraction in that region had 6 PDMs, i.e., uniform, increasing, decreasing, increasing-decreasing,decreasing-increasing and irregular, which were little related to anyquantifiable environmental factors.We predicted the PDM with random forest, the accuracy was low. It is difficult to predict the PDM with quantifiable environmental information.【Conclusion】Because of the diversity of soil forming parent materials and complex landform and land relief in the Qilian Mountains, migration and discontinuity of parent materials often occurs as a result of land use. So it is difficult to predict PDM quantitatively only with single environmental variables, and therefore, its essential to explore in depth the issue from the angle of composite environmental variables.

Abstract:【Objective】Effects of sampling scale on spatial variability of soil properties are of great significance to soil digital mappings, soil survey, and agricultural production. So, in this study, a tract of the grey eel-mud field (Soil Species), a special land use—soil type complex unit(Lu-SoTy), in Dongxiang County, Jiangxi Province, a hilly red soil region in South China was selected as an object. Using the multi-level nesting sampling protocol to ensure that the total number of soil sampling points remains unchanged whatever sampling scale is used, the study is to exposit characteristics of spatial variability of soil total element concentrations with soil sampling scale and provide important implications and scientific references for rationalizing layout of sampling points based on Lu-SoTy.【Method】In the light of spatial distribution of soil sampling points, eight soil sampling scales (from the smallest to the largest is coded in turn as A1~A8) were designed with smaller scales located inside larger ones. By taking into full account vastitude and uniformity of spatial distribution of the sampling points, each soil sampling scale had 60 points distributed evenly. Using the multi-level nesting sampling protocol, 337 sampling points were laid out across the County. In December 2014 after the crop of late rice was harvested, soil samples were collected from the 0～20cm topsoil layer at all the sampling points for analysis of soil total element concentrations. Scale characterization indices were calculated using ArcGIS 10.2.2, variability characterization indices using SPSS 20.0, and regression fitting analysis of scale characterization indices and variability characterization indices, using SPSS 20.0. Based on the level of significance and R² of the regression, the best characterization indices and the best fitting functions were screened out. 【Result】Results show that the scale effects on spatial variation of soil total elements are obvious; and coefficients of variation (CV) of TN, TP and TK go up with expansion of the sampling scale, but the increasing rates display a decreasing trend; the scale effects on the spatial variability differed with soil total element: the best fitting function for charactering the scale effects on CV (%) is CV = b× D^a for TN and TP (R²>0.87, p<0.001), and CV = e^{(a/D b)} (R²>0.93, p<0.001) for TK (D is a scale index of sampling points; namely: average distance to the nearest one point or maximum distance (km) of all the sampling points); the shifting points of scale effects between rapid and slow changes of CV varied with soil total element, for example, the shifting point of TN, TP and TK is D ₀ = 6.756 km, D₀ = 9.061 km and D₀ = 3.408 km, respectively (at this point, the angle between the tangent to the curve and the horizontal axis is about 30°). All the findings demonstrate that independent sampling protocols and analysis skills need to be considered in studying spatial distribution of different soil total elements. 【Conclusion】The scale effects characteristic of spatial variability of soil total elements in soil of a special complex Land Use-Soil Type unit, could provide important implications and scientific references for laying sampling points at county scale soil surveys in hilly red soil regions.

Abstract:【Objective】The red soil hilly region in South China is one of the areas of the country suffering serious soil erosion. Currently, the researches on loss of soil organic carbon with soil erosion in this region were executed mainly via simulated rainfall tests, without much in-situ field quantitative monitoring under natural rainfalls or comparison between fields different in land use. This study was intended to explore relationships of surface runoff and sediment loss with organic carbon carried in runoff and sediment under natural rainfall, so as to characterize responses of soil organic carbon transfer and loss to changes in rainfall, soil erosion and land use, and to deepen the scientific knowledge about relationship between soil erosion and carbon recycling.【Method】Tracts of bare land, grassland,, citrus orchard, and secondary splash pine forest were selected for the experiment as runoff plots in the Jiangxi Soil and Water Conservation Ecological Science Park. Surface runoff, sediment loss and soil organic carbon carried therein were monitored under 24 typical rainfalls between March to August, 2015 in order to illustrate selective transfer of soil organic carbon. 【Result】Results show as follow: (1) Runoff coefficients and the soil erosion modulus increased with increasing rainfall intensity during all the 24 rainfall events. With the conversion of land use in type from bare land to orchard, grassland and forest, the effects of land use reducing runoff and sediment increased. Rainfall intensity was the major factor affecting runoff volume, while the latter was the one affecting sediment loss, with correlation coefficient being 0.89~0.92 (p <0.001) and 0.95~0.98 (p <0.05), respectively. (2) Under natural rainfalls, the concentration of organic carbon was 5.00, 7.68, 6.11 and 10.02 mg L^-1 in runoff and 7.69, 8.58, 8.08 and 8.93 g kg^-1 in sediment on the bare land, grassland, orchard and forest, respectively. The concentration of organic carbon in runoff was significantly and negatively related to volume of the runoff and so was the concentration in sediment with the volume of sediment loss. The sediment-associated loss of soil organic carbon in the four plots accounted for 64.67%, 47.38%, 53.94% and 36.03% of the total lost with the erosion, and reached 560.3 mg m^-2, 1.98 mg m^-2, 122.5 mg m^-2 and 2.66 mg m^-2 in intensity, respectively. (3) The organic carbon enrichment ratio of the sediment in the bare land, orchard, grassland and forest was 1.27, 1.10, 0.80 and 0.58, respectively, and decreased gradually with increasing rainfall intensity. Selective transfer of organic carbon was more evident in weak rainfalls.【Conclusion】Under natural rainfalls, soil erosion has very important impacts on migration of soil organic carbon in slope fields in the red soil region. Selective migration of soil organic carbon with surface runoff or sediment is determined mainly by rainfall characteristics (especially rainfall intensity) and land use pattern. In all the lands, regardless of land use, intensified soil erosion makes it easier for soil organic carbon to migrate with sediment, and organic carbon enrichment ratio of the sediments also increases with intensifying soil erosion. However, organic carbon enrichment ratio of the sediment decreases with rising rainfall intensity.

Abstract:【Objective】Accurately assessing soil cumulative infiltration is essential to many field irrigation management and saline soil amelioration projects. However, the measurement of soil cumulative infiltration using the conventional methods has a number of defects, like costly, destructive and time-consuming. In addition, because soil infiltration is spatially variable, these point measurement techniques are of limited value in assessing the soil cumulative infiltration over a large area. The technique of Ground Penetrating Radar (GPR) can be used to collect the data non-destructively and instantly over a large area. Therefore, the technique is much higher than the conventional methods in potentiality and applicability for use to assess soil cumulative infiltration on a field scale.【Method】In order to show that soil cumulative infiltration can be extracted from low frequency GPR data in the case of a loamy soil, a controlled soil and irrigation experiment was carried out. During the experiment, a 250 MHz antenna was used to collect GPR data for analysis of radargrams before and after the irrigation. Based on the radargrams obtained a soil infiltration estimation model was constructed using the electromagnetic wave amplitude recorded by the GPR. Then the model was compared with the electromagnetic wave speed model in accuracy and time window stability.【Result】Results show that the determination coefficient of electromagnetic wave speed and soil cumulative infiltration was 0.8, 0.1 and 0.12 in the 2.2m time window, 1.57m time window and total of the samples, respectively, indicating that the electromagnetic wave speed model depends on time windows, and is low in stability and precision, so the model is not good enough to reflect soil cumulative infiltrations. While GPR amplitude was found to be more sensitive to variation of soil cumulative infiltration. Among the electromagnetic wave amplitude parameters, the determination coefficient of trough amplitude of Reflection Wave I and soil cumulative infiltration was 0.999, 0.986 and 0.962 in the 2.2 m time window, 1.57 m time window and total of the samples, respectively, and the determination coefficient of the trough amplitude of Reflection Wave II and soil cumulative infiltration was 0.981, 0.999 and 0.925, respectively.while the determination coefficient of trough amplitude of the ground direct wave and soil cumulative infiltration was 0.920, 0.965 and 0.943, respectively. By following the principle of the highest determination coefficient, this paper selected the trough amplitude of Reflection Wave I in constructing the GPR model for detection of soil cumulative infiltration, thus bringing the determination coefficient up to 0.96.【Conclusion】In brief, the electromagnetic wave amplitude model is higher than the wave speed model in precision and stability, and can be used to monitor and estimate soil cumulative infiltration. The trough amplitude of Reflection Wave I is an ideal indicator to be used to effectively monitor soil cumulative infiltration. Therefore, the low frequency GPR can be used to accurately detect soil cumulative infiltration. All the findings in this research may provide a new way for the detection of soil cumulative infiltration on field scales, and also a scientific basis for further application GPR to the filed of soil science.

Abstract:【Objective】 The Pearl River Delta Plain, located in South China, has a more-than-one-thousand-year cultivation history, so that the soil therein has been subjected to impacts of intensive anthropogenic activities in its evolution. The knowledge of how the soil evolves under anthropogenic activities is sure helpful to sustainable utilization and management of the soil resources. Being highly active and geochemically sensitive, iron oxides in soil tend to be affected by any slight change in environmental condition in formation and property, so they are often used as an indicator of soil pedogenic process, and considered as a function of soil genesis and development. Therefore, characterization of soil iron oxides has been one of the major fields of the study on soil genesis. In this study an investigation was performed of characteristics of iron oxides in bulk soil and soil clay relative to cultivation age and affecting factors in the Pearl River Delta Plain, in an attempt to reveal how the soil forms and evolves under anthropogenic cultivation in the region. 【Method】 Samples were collected from genetic horizons of the soils derived from marine deposits with cultivation age being 30 a, 100 a, 600 a and 1000 a, separately, of the soils derived from fluvial deposits with cultivation age being 200 a, 400 a, 900 a and 1 000 a separately and of the soils derived from delta deposits with cultivation age being 50 a, 90 a, 150 a and 350 a, separately, in the Pearl River Delta Plain for analysis of physicochemical properties, and total iron (Fe_t), free iron (DCB-extractable iron, Fe_d), ratio of Fe_d to Fe_t (Fe_d / Fe_t) in bulk soil and clay (Fe_d(clay)/Fe_t(clay)), Fe_d sedimentation coefficient (ratio of Fe_d in the genetic horizon beneath the surface horizon to Fe_d in surface horizon) and enrichment rates of Fe_t and Fe_d in clay (Fe_t(clay)/Fe_t and Fe_d(clay)/Fe_d).【Result】 Results show that: (1) Among the soils derived from marine deposits, those, 30 a in cultivation age, were all >1 in Fe_d sedimentation coefficient, regardless of horizon; those, 100 a and 600 a in cultivation age, were > 1 only in some genetic horizons, and those, 1 000 a in cultivation age, were all < 1. In the soils derived from fluvial deposits, the generic horizon where Fe_d sedimentation occurred went deeper with the cultivation age. Among the soils derived from delta deposits, those, 50 a, 90 a, 150 a and 350 a in cultivation age, were found to have genetic horizons as deep as 40cm, 45cm, 80cm and 90cm, respectively. (2) In the soils derivd from marine deposits, the distribution of Fe_d in clay (Fe_d(clay)) in soil profile varied irregularly with cultivation age, while in the soils derived from fluvial and delta deposits the content of Fe_d(clay) in soil layers below 40 cm and 60cm depth, respectively, declined with cultivation age. (3) The contents of Fe_t and Fe_d in clay were higher than their corresponding ones in bulk soil, Among the soils derived from marine deposits, those, 30 a and 100 a in cultivation age were lower than those, 600 a and 1000 a in cultivation age, in Fe_tand Fe_d enrichment rate. In the soils derived from fluvial deposits Fe_t and Fe_d enrichment rates increased with cultivation age in the soil layers below 40cm. And among the soils derived from delta deposits, those, 350 a in cultivation age, were lower than those younger in cultivation age in Fe_t and Fe_d enrichment rate. And (4) Fe_d and Fe_tin bulk soil was extra-significantly and positively related to Fe_d and Fe_t in clay, and so was Fe_t(clay)/Fe_t and Fe_d(clay)/Fe_d to Fe_t(clay) Fe_d(clay) and Fe_d(clay)/Fe_t(clay), and Fe _t(clay)/Fe_ttoFe_d(clay)/Fe_d, however Fe_t(clay)/Fe_t and Fe_d(clay)/Fe_d was extra-significantly and negatively related to Fe_t, Fe_d, Fe_d/ Fe_t and clay content. 【Conclusion】With agricultural cultivation going on, Fe_d in the soils derived from fluvial and delta deposits tends to leach down and deposit in the lower and lower soil layers; Fe_d content tends to decline in the hydroponic redox layer of the soils derived from marine deposits; iron oxides tend to increase in enrichment rate in clay of the soils derived from marine deposits, but decline in clay of the soils derived from fluvial and delta deposits. However, the iron oxides accumulating in clay of the soils were dominated with Fe_d, and clay content in the soils is the major factor affecting iron oxide enrichment rate.

Abstract:【Objective】Plant polyphenols may alter forms of the elements existing in soil through complexation.The study is oriented to explore effects of epigallocatechin gallate (EGCG) relative to concentration and pH and the interactions between its concentration and pH on soluble, free, amorphous and complex forms of Al, Fe and Mnin Yellow soil.【Method】A two-factor experiment laid out at random was carried out by extraction of the tested soils, of which each had 3 replicates. Firstly,soilwas collected from the 30~50 cm soil layer (surface)in a Yellow soilfield as a sample for test, air-driedand ground to pass through a 10-mesh nylon sieve.Then a total of 48 portions, 10 g each, were weighed out of the prepared soil sample and placed into 250 ml polyethylene bottles, respectively. Into the bottles, prepared EGCG solution was added, 100 mL each. Then the bottles were placed into a constant temperature oscillater for 24 h oscillationunder room temperature (25°C). At the end of the oscillation, the suspensions were filtered for extracts, which were then analyzed for soluble Al, Fe and Mn (Al_s, Fe_sand Mn_s). The second step was to have the remainders from filtration dried up in an oven at 60°Cfor 48 h and reground with an agate mortar to pass through a 60-mesh nylon sieve for determination of oxidized forms of Al, Fe and Mn.Free Al, Fe and Mn(Al_d, Fe_dand Mn_d), amorphous Al, Fe and Mn (Al_o, Fe_o and Mn_o), complex Al, Fe and Mn (Al_p, Fe_p and Mn_p) were extracted by the dithionite-citrate-bicarbonate (DCB) method, acid ammonium oxalate (AAO) at pH=3 in the dark and Na-pyrophosphate(Na₄P₂O₇) at pH=10, respectively. Contents of all the above-mentioned fractions of Al, Fe and Mn were determined with ICP-AES. 【Result】Concentration of the EGCG solution was found to have a very significant effect on the content of Al_s, Fe_s, Mn_s, Al_p, Fe_p, Mn_p, Al_o or Fe_o in Yellow soil; and pH of the solution had a significant or extremely significant effect on the content of Al_s, Fe_s, Mn_s, Al_o, Fe_oor Mn_o in Yellow soil, while the interaction between the two did on the content of Al_s, Fe_s, Mn_s, Al_o, Al_p or Mn_d in Yellow soil. The addition of EGCG affected the elements both in content and in form, but their relative contents did not change much. In terms of content, the soluble forms displayed an order of Al>Fe>Mn, the freeforms, did an order of Fe>Al>Mn, and the amorphous and the complex forms both followed an order of Al>Fe>Mn. However, concentration of EGCG was not a factor affecting the content of Al_d, Fe_d and Mn_d, and neither was pH of EGCG affecting the content of Fe_d, Mn_d, Al_p, Fe_pand Mn_p, while the interaction between the two did not have much effect on the content of Al_d, Mn_d, Fe_o, Mn_o, Fe_p and Mn_d in Yellow soil. Correlations analyses show that Al_o, Fe_o and Mn_o was closely related to Al_s Fe_s and Mn_s, respectively, which suggests that EGCG solution affects mobilization of the elements by changing their oxide forms, especially the amorphous ones and hence contents of the soluble ones . The more Al_o in the soil, the more Al_s in soil solution, and all the same with Fe and Mn. On the other hand, pH of the EGCG solution was significantly and negatively related to Al_sand Mn_s,which suggests thatreactivation of Al and Mn may lower pH of the extractant, posing a potentialrisk.【Conclusion】The study has further verified that the effect of EGCG solution on Al, Fe and Mn mobilization varies with its concentration and pH of the solution and interaction between the two. All the findings in this study may help orient the study on causes of soil acidification in tea gardens and serve as reference for prevention of plant Al/Mntoxication. It is, therefore, worthwhile to note when plant polyphenols are used to prevent Al/Mn toxicity, adequate attention should be given to control of soil acidification.

Abstract:【Objective】This study is oriented to acquire theoretical values (or baseline value) of As and Hg in purple soils different in developmental stage, to understand migration and accumulation processes of the elements in the soils, and to provide an accurate and reliable basis for evaluation of heavy metal pollution of the soil. 【Method】Samples of the purple parent rock of the Jurassic Shaximiao Formation (J₂s) and various soils species derived from the same parent rock, but different in developmental degree were collected according to the traditional nomenclature in Hechuan District of Chongqing, for analysis to determine and verify development degrees of the soil with the "titanium value" method of soil; To measure total As and total Hg in the soils, to build up environmental geochemical baseline models for As and Hg in the soils of the gray brown purple soil genus in the purple soil group, and to define the chemical baseline values for each soil along the developmental line. 【Result】Results show that in terms "titanium value", the soils followed an order of parent rock > stony sub-soil > half sand half mud > big-eye mud > purple yellow mud, which reflects that the sequence of the soils in development degree coincides with the traditional order of the soils along the soil development line and that the soil sampling complied with the requirements of the study; The environmental geochemical baselines of As and Hg in the soils were found both on the trend of slight accumulation with deepening soil development, in terms of baseline value of As, the soils followed an order of parent rock < stony sub-soil < half sand half mud < big-eye mud < purple yellow mud, while in terms of baseline value of Hg, the soils followed another order: parent rock < stony sub-soil < half sand half mud < purple yellow mud -1,) and Hg (29.0 μg kg^-1) in the deeply developed soil be used as the reference for evaluation of soil pollution in the soils of the gray brown purple soil genus of the neutral purple soil subgroup in Chongqing area.

Abstract:【Objective】 A pot experiment had been carried out to investigate effects of soil amendments (pig manure compost, humic acid, EDTA) and a switched polarity DC electrical field on phytoremediation of Cd contaminated soil with hyperaccumulator Sedum alfredii. 【Method】 In this experiment, plants of Sedum alfredii, a species of hyperaccumulator, were planted into pots containing loamy soil pretreated with 15 g kg^-1 of pig manure compost, 10 g kg^-1 of humic acid, or 5 mmol kg^-1 of EDTA, separately, as treatments and with nothing as control. In addition, the pots were subjected to another treatment: no-voltage (without electrical field) or direct current (DC) electrical field (1 V cm^-1 with switching polarity every day). At the end of the experiment, dry weights of shoots and roots of the plants, cadmium (Cd) concentration in the plants and soil available Cd (diethylene triamine pentaacetic acid (DTPA) extractable) were determined. 【Result】 Available (DTPA extracted) Cd in the soil increased significantly in the treatments subjected to DC electrical field and amended with pig manure compost, humic acid, or EDTA. The former increased DTPA-extractable Cd by 6.06%~15.64%, while the latter did by 5.74%~7.16%, 8.80%~10.32% and 4.77%~5.91%, respectively, with DC field on and by 2.84%~3.32%, 7.70%~9.47% and 7.10%~7.75%, respectively, with DC field off. Cd concentration in the plant shoots significantly increased in the pots with DC field on, varying in the range of 226.2~313.7 mg kg^-1, and lingered in the range of 178.7~212.6 mg kg^-1with DC field off. Soil amendments (pig manure compost, humic acid, EDTA) also had significant effects on Cd concentration in the plant shoots (p<0.05). In addition, Cd concentration in the plant shoots was increased by 7.33%~37.0%, 19.0%~38.7% and 6.13%~12.0% by the addition of pig manure compost, humic acid and EDTA, respectively. By switching the polarity of the DC electrical field, significant pH variation from anode to cathode can be avoided, and thus no significant impact was observed on shoot biomass of the plants. Soil amendments (pig manure compost, humic acid, EDTA) had significant effects on shoot biomass of the plants (p<0.05). The addition of 15 g kg^-1 pig manure compost and 10 g kg^-1 humic acid increased shoot biomass by 40.3%~43.7% and 16.3%~18.2%, respectively, while the addition of EDTA decreased shoot biomass by 7.3%~7.5%. Cadmium concentration in shoot and plant shoot biomass are the most crucial factors for determining efficiency of the phytoextraction. The findings in this pot experiment demonstrate that DC field increases significantly (p<0.01) Cd accumulation in the plants in all the treatments, as compared with those with DC field off. Cd accumulation in shoots of the plants was in the range of 2 088~4 014 μg pot^-1 with DC field on, and 1 677~2 635 μg pot^-1 with DC field off. In addition, Cd accumulation in shoots of the plants was increased by 54.3%~92.2% and 38.4%~63.9% in the pots pretreated with pig manure compost and humic acid, respectively, because of their simultaneous effects of increasing Cd concentration in shoots and shoot biomass. However, no noticeable effect was observed in the EDTA treatment in comparison with the control, which can be ascribed to the inhibition of plant growth by EDTA. The combined use of pig manure compost-DC field and humic acid-DC field enhanced Cd accumulation in shoots by 134% and 100%, respectively. 【Conclusion】 Based on the findings, the amendment of pig manure compost or humic acid coupled with switched polarity DC electrical field could significantly enhance Cd phytoextraction by hyperaccumulator Sedum alfredii.

Abstract:【Objective】A one-year-round field experiment, monitoring nitrous oxide (N₂O) emissions during the growing seasons of four consecutive vegetable crops and yields of the crops, was conducted to investigate effects of reduced application of nitrogen (N) fertilizer andapplication ofchlorinated pyridine (CP), a kind of nitrification inhibitor, on N₂O emission and vegetable yield. 【Method】During the observation period from May, 2015 to May, 2016, four different species of vegetables were cultivated one by one, namely, amaranth, water spinach, cilantro and baby bokchoy. The experiment was designed to have two treatments in N input i.e.640 and 960 kg hm^-2a^-1,or a reduced N dose (Nr) and a normal N dose (Nn). Urea was applied as N fertilizer coupled with CP (CP-N) or without CP (N). Phosphate and potassium fertilizers wereapplied in the form of calcium/magnesium phosphate (12% P₂O₅ and potassium chloride(60% K₂O)at a rate of 960 kg hm^-2a^-1.All the fertilizers were evenly distributed among the four crops. Each treatment had three replicates. N₂O fluxes were monitored with the static-closed chamber method and gas phase chromatography. Air samples were collected normally once a week and once every two or three days during the 7 ~ 10 days after the application of N fertilizer.【Result】Results show that N₂O flux varied significantly with the season in all the treatments, showing a trend of rising higher in the period from May to September and staying lower in the rest of the year.The N₂O flux during the growing season of water spinach was the highest and reachedN 6426 μg m^-2 h^-1 soon after N fertilization, which could probably be attributed to the high temperature in the season.But no apparent peaks were observed during the growing seasons of cilantro and baby bokchoy, when the highest N₂O fluxreached N664.9and 914.9μg m^-2 h^-1 respectively. N₂O flux was found significantly and positively related to soil water content and soil temperature (p<0.05) and to N fertilizer application rate too. In treatment Nr, CP-Nr, Nn and CP-Nn, N₂O flux varied in the range of N 3.2~4280, 5.0~3293, 3.2~6427 and 1.2~6097 μg m^-2 h^-1, respectively. During all the four vegetable growing seasons, treatment Nr was always lower than treatment Nn in N₂O flux. Compared with treatment Nn, treatment Nr could reduce cumulativeN₂O emission by 27.1% on average without significantly affecting yield of the crops (p<0.05). In the treatments equal in N application rate, amendment of CP reduced cumulative N₂O flux, which indicates that CP is capable of mitigating N₂O emission in the vegetable field.During the year of the experiment, treatment Nn was found to be the highest in cumulative N₂O emission, reaching up to N59.2±4.4 kg hm^-2, while treatment CP-Nr the lowest, getting down to 31.2±2.2 kg hm ^-2. Comparison between treatments equal in N application rate, CP amendment reduced total cumulative N₂O emission by 29.4% and 26.0%, N₂O emission factor by 60.9% and 42.4%, and yield-scaledN₂O emission by 32.1% and 30.3%, respectively, in treatment CP-Nn and CP-Nr, without significantly affectingcrop yield.In the soil of the vegetable field, the content of NH₄⁺-N and NO₃⁻-N variedin the range of 10.8 ~ 803.9 and 0.9 ~ 520.0 mg kg^-1, respectively. The average NO₃⁻-N content in the soil of treatment Nr, CP-Nr, Nn and CP-Nnwas 31.6, 33.2, 35.7 and 43.3 mg kg^-1, respectively, and the average NH₄⁺-N content, 51.0, 50.9, 53.8 and 60.4 mg kg^-1, respectively. Obviously, with rising N application rate, the content of inorganic N gradually increases in all the treatments. 【Conclusion】Taking into account cumulative N₂O emission, N₂O emission factor, yield and yield-scaled N₂O emission, Treatment CP-Nr is capable of reducing N₂O emission and getting high vegetable yields simultaneously. Hence, the practice of reducing N fertilizer application rate by one third coupled with CP amendment can be used as an effective vegetable field management measure in intensive vegetable production to mitigate N₂O emission and maintain crop yield.

Abstract:【Objective】 The use of the diffusion method coupled with mass spectrometry to determine δ¹⁵N of inorganic nitrogen in soil and water samples in researches in the environmental, ecological and agricultural fields. Compared with the distillation method, the diffusion method consumes less labor and material resources, and can be used in massive operation. The diffusion method not only works when the sample is low in nitrogen content, but also avoids the risk of cross contamination and the need for fractionation. However, for application of the diffusion method, it is essential for the researchers in China to have a sound diffusion-incubation system which is able to perform rapid and accurate determination of δ¹⁵N of inorganic N in the soil. 【Methods】The diffusion method proceeds as follows: put a set amount of soil extract in a small airtight grass container; add some alkaline reagent to convert NH₄⁺-N into NH₃, which is adsorbed by acid-spiked filter paper; for determination of NO₃^--N, titrate some alkaline reagent to remove NH₄⁺-N in the sample; and add some Devarda’s alloy to reduce NO₃^--N into NH₄⁺-N. In the light of characteristics of the variation of inorganic nitrogen in soil extracts, diffusion conditions, such as incubation temperature, incubation time, type and rate of reagents were tested and optimized. 【Results】Results show that for soil extracts, >2 mg L^-1 in inorganic N concentration, only 20 ml soil extract is needed. put it into a 250 ml flask; hang 2 pieces of filter paper spiked with 10 μl 1 mol L^-1 H₂C₂O₄ each in the flask; add 0.1 g MgO, and then incubate the sample for 24 h at 25 ℃ on a rotator running at 140 r min^-1 to complete the processes of diffusion and recovery of NH₄⁺-N; and then replace the used filter paper with two new ones also spiked with H₂C₂O₄; incubate it on a rotator running at 140 r min^-1 for 48 h to remove remaining NH₄⁺-N; and again replace the used filter paper with two new acid-spiked ones, add 0.1 g Devarda’s alloy, and incubate it for 24 h to complete the processes of diffusion and recovery of NO₃^--N. For soil extracts < 2 mg L^-1 in inorganic nitrogen concentration, 50 ml is needed to ensure accuracy of the determination once the same incubation procedure is followed. The experiment also reveals that nitrogen impurities that may affect accuracy of the determination, come mainly from highly purified water, filter paper, acid absorbent, MgO and Devarda’s alloy. To avoid the effects of the nitrogen impurities, samples should be incubated at 25 ℃ for 24 h, and filter paper dried as far as possible in NH₃-free environment. In addition, results of the determination should be calibrated against that of the control.【Conclusions】 It can be concluded that this method greatly shortens the incubation cycle of the general incubation method and is capable of accomplishing diffusion and recovery of both NH₄⁺-N and NO₃^--N simultaneously, decreasing the amount required of a sample and reducing the risk of contamination by nitrogen impurities by optimizing the rate of MgO and Devarda’s alloy. However, the diffusion method discussed here is oriented towards determination of ¹⁵N-labeled soil extracts, 2~8 mg L^-1 in inorganic N concentration, but not applicable to determination of soils samples natural in ¹⁵ N abundance or low in nitrogen concentration. Consequently, in future studies, efforts should be devoted to such issues as how to remove nitrogen impurities and quickly, how to rule out the interference of soluble organic nitrogen in the soil.

Abstract:【Objective】Aluminum (Al) toxicity is an important factor that inhibits growth of plants in acid soils. Different plant species are often different in Al tolerance, and so are different varieties of the same species. Through a series of hydroponic experiments, this paper was to explore difference between two varieties of rice, Nipponbare and Kasalath in Al tolerance and mechanism responsible for the variation.【Method】 Plump seeds of the two varieties of rice were selected and placed in an incubator for germination at 25oC. Then seedlings similar in growing were divided into two groups, one undergoing treatment with 0.5 mmol L^-1 CaClsub>2 and pH 4.5 for 24 h (Treatment CK) and the other with 50 μmol L^-1 AlClsub>3 in addition to 0.5 mmol L^-1 CaClsub>2 and pH 4.5 for 24 h, too (Treatment Al). Root length was measured before and after the treatment with a ruler. After the treatments, some roots tips (0~1 cm) of the seedling were cut down with a knife, and placed into plastic tubes containing 1 ml 2 mol L^-1 HCl, separately, for 24 h extraction. Then the solutions were analyzed for Al concentration with ICP. Besides, some root tips were put direct into liquid nitrogen for refrigeration at -80 oC for late-on RNA extraction. To compare the two varieties of rice in Al-induced citrate secretion from the root system, some two-week-old seedlings were treated as in Treatment Al for 24 h. Then solution from the treatment was diverted into a column containing 5 g of cation resin (Amberlite IR-120B resin) for adsorption and then into another column containing 3 g of anion resin (AG 1 × 8 resin). The anion-resin column was then eluted with 2 mol L-1 HCl and the eluate condensed into solid through evaporation in a rotary evaporator. Then, 1 ml of milliQ water was used to dissolve the solid adhered to the evaporator for determination of content of organic acids with HPCL.【Result】It was found that under Al stress, Nipponbare was less inhibited than Kasalath, for it had longer roots and less Al in root tips, which indicates that Nipponbare is an Al tolerant variety of rice, while Kasalath an Al sensitive variety. It was also found in further studies that the expression of NRAT1, which is responsible for controlling Al uptake, was much higher in Kasalath than in Nipponbare, and the high expression is possibly the major cause leading to the high Al concentration in the root tips of Kasalath, an Al-sensitive variety of rice. Furthermore, it was also found that under Al stress, Nipponbare secreted more citric acids than Kasalath did and the expression of OsFRDL4, a gene controlling root secretion of citric acid, was significantly higher in level in the former than in the latter, which demonstrates that citric acid may possibly play a critical role in rice tolerating Al and the variety of rice controls secretion of citric acid by regulating expression level of OsFRDL4 gene. However, tests were also done on other four genes that may be related to Al tolerance, but no direct relationship was observed. So further studies need to be done.【Conclusion】 Nipponbare and Kasalath shows different Al tolerance in the present study. Nipponbare is an Al tolerant rice variety, while Kasalath an Al sensitive one. The difference in Al tolerance between the two varieties of rice may be attributed to the differences in expressions levels of NRAT1 and OsFRDL4.

Abstract:【Objective】 Potassium is one of the essential mineral elements for normal growth of cotton and garlic. However, so far little has been reported on effect of controlled release potassium fertilizer on crops growth and soil potassium supply. The present study investigated effects of controlled release potassium chloride with or without the addition of sulfur as the alternates of potassium sulfate and potassium chloride on yield of cotton and soil available potassium content, in an attempt to provide a certain theoretic basis for rationalization of the use of potassium fertilizer. 【Method】 A three-year plot experiment was consecutively conducted in 2013, 2014 and 2015 under a cotton-garlic intercropping system in Northeast China. The experiment was designed to have six treatments: 1) basal application of potassium chloride (CK1); 2) basal application of potassium sulfate (CK2); 3) 50% of potassium chloride basal and 50% top-dressing at the full bloom stage (KClD); 4) basal application of potassium chloride with sulfur (KClS); 5) basal application of controlled release potassium chloride (CRK); and 6) basal application of controlled release potassium chloride with sulfur (CRKS), and three replicates for each treatment, and laid out randomly in plots separated from each other and isolated with cement boards. The K release of CRK in 25°C water and soil conditions was measured using the weight loss method in line with the “National Standard of the People’s Republic of China for Slow Release Fertilizer”. Samples of the soils and plants were collected for analysis of soil available potassium content, leaf SPAD value as well as net photosynthetic rate during cotton growth. Meanwhile, quality and yield of cotton were investigated, too. 【Result】Results show that the controlled release potassium chloride corresponded released K well in coincidence with the demand of cotton for potassium during its growth period. The contents of soil available potassium, leaf SPAD and net photosynthetic rate all increased in both Treatments CRK and CRKS after the full bloom stage especially at the initial boll-opening stage and harvest stage, as compared with the treatments of basal application of conventional potassium fertilizers (CK1 and CK2). The number of bolls per plant and weight per boll in Treatment CRKS increased significantly and hence the yield of lint did by 16.9%~30.9% over that of CKs, by 12.2%~16.1% over that of Treatment KClD and by 8.7%~10.4% over that of CRK. Treatment CRKS was also the highest in yireld of garlic bulbs and bolts, or 2.8%~27.9% and 4.8%~23.5%, respectively, higher than Treatment KCID and CRK. Treatment CRKS also significantly improved quality of the cotton, too, such as length, uniformity and specific elongation of lint fibre. After the three-year fertilization, the contents of soil water-soluble K and exchangeable K increased while the content of non-exchangeable K decreased in Treatment CRKS as compared with Treatments CK1 and CK2. 【Conclusion】 All the findings suggest that controlled release potassium chloride amended with sulfur is recommended to replace potassium sulfate and potassium chloride to achieve higher crop yields, higher soil K use efficiency, while improving crop quality under the cotton-garlic intercropping system.

Abstract:【Objective】 Soil potassium is an essential macronutrient for crop growth and plays a key role in maintaining high crop yield. However, so far it is still unclear as to dynamics of soil potassium utilization, especially quantitative relationships of content of soil readily available K with input of extraneous and budgeting of cumulative soil potassium relative to fertilization method. Therefore, this study was oriented to analyze dynamics of crop K uptake, crop K recovery rate, soil K budgeting and content of soil readily available K and to explore quantitatively relationships of soil readily available K with input of extraneous K and budgeting of cumulative soil K relative to fertilization practice based on a long-term fertilization field experiment in a field of vertisol in North China.【Method】The long-term experiment, located at the Mengchen Agro-Ecological-Station in the Huang-Huai-Hai Plain, North China, was initiated in 1982 and designed to have five treatments, i.e., CK (no fertilizer), CF (mineral fertilizers), SCF (mineral fertilizers plus wheat straw), PCF (mineral fertilizers plus pig manure), and CCF (mineral fertilizers plus cattle manure), and four replicates for each. Plots, 70 m² each in area, of the treatments and replicates were laid out in a randomized block design and separated from each other with cement boards embedded 50 cm deep. Soil samples were collected randomly from the top 20 cm soil layer of each plot along a S-shaped line, after the crop of soybean was harvested in October each year, with a soil core sampler (inner diameter 7 cm). Chemical N, P and K fertilizer was applied in the form of urea, calcium superphosphate and potassium chloride, respectively, at a rate the same as the local farmers did, i.e., 180 kg N, 39.3 kg P, and 112 kg K hm^-2 yr^-1. Soil total K was measured with the sodium hydroxide melting - flame photometry, soil slowly available K with the nitric acid boiling - flame photometry, soil readily available K with the ammonium acetate extraction - flame photometry and crop K with the vitriol peroxide/hydroxidation - flame photometry. 【Result】 It was found that the mean crop K recovery rate varied in the range of 55.1% ~ 66.1%, relative to treatment and displaying an order of CCF > PCF > SCF > CF. The content of soil readily available K increased somewhat in all the treatments except in CK, where the content declined steadily over time. The over-year mean content of soil readily available K exhibited an order of CCF (289.5 mg kg^-1) > PCF (133.0 mg kg^-1) > SCF (128.4 mg kg^-1) > CF (82.4 mg kg^-1) > CK (72.3 mg kg^-1). On the whole, a significant (p< 0.05) positive linear relationship was observed between soil K budgeting and content of soil readily available K. The gain of each 100 kg hm^-2 in soil K budgeting raised the content of soil readily available K in Treatment CF, SCF, PCF, and CCF by 1.4 mg kg^-1, 1.8 mg kg^-1, 2.3 mg kg^-1 and 15.8 mg kg^-1, respectively. Besides, a significant (p < 0.05) positive linear relationships between input of soil K and content of soil readily available K was also observed in all the fertilization treatments. The input of each 100 kg hm^-2 increased the content of soil readily available K by 0.4 mg kg^-1, 0.5 mg kg^-1, 0.6 mg kg^-1 and 4.3 mg kg^-1 in Treatment CF, SCF, PCF, and CCF, respectively. Compared to the increase in Treatment CF, that in the treatment amended with organic material (wheat straw, pig manure or cattle manure), that is, Treatment SCF, PCF and CCF was 25%, 50% and 975% higher, respectively, which indicates that application of a proper rate of organic material may improve soil K supply capacity in soils the same in input of extraneous K and soil K budgeting. 【Conclusion】To sum up, application of organic material is an important practice regulating soil potassium utilization. Long term application of organic manure, especially cattle manure in the study, may increase crop potassium recovery rate and transformation rate of surplus soil K into readily available K. Therefore, the application of animal-digested crop straw is a recommended practice to achieve stable and high crop yields in fields of vertical under wheat-soybean cropping system in North China.

Abstract:【Objective】 Iron plaque on root adsorbs heavy metal elements in the soil, thus reducing the content of heavy metals in the environment the plant grows in, while selenium is antagonistic to heavy metal elements in plant roots, thus inhibiting the transfer of Cd, As, Mn and some other heavy metals in the roots of rice seedlings as was found in the researches. In the presence of a proper amount of iron plaque, selenium reacts with Cd, As, Mn, and so on to form insoluble compounds that accumulate in the iron plaque, thus reducing toxicity of these heavy metals to the plants. In this study, a hydroponic experiment was conducted to explore effects of the iron plaque on the surface of the roots of rice seedlings on absorption and transport of mercury by the plants treated with selenium. 【Method】Having been disinfected and washed clean, rice seeds were sown in Hoagland culture medium for germination. Out of the seedlings, 24 consistent in growth were selected and transplanted into two groups of vessels with Hogland culture medium, one treated without selenium (Se0) and the other with selenium (Se0.5, 0.5 mg L^-1 in the form of Na₂SeO₃), for cultivation for 2 weeks. Then the rice plants were moved into Fe² (FeSO₄)solutions (pH=5.5), 0, 25, 50 and 100 mg L^-1 in concentration, or Treatment Fe0, Fe25, Fe50 and Fe100, separately, for 24 h, to let iron plaque form on root surface. And then the rice plants were then transferred into HgCl₂ solution, 0.3 mg L^-1 in concentration for 72 h of cultivation. Each treatment had three replicates. 【Result】No significant effect of the iron plaque was found on growth of the rice seedlings, but selenium was to be able to increase the plants in biomass. With rising Fe concentration in the solution, iron contents in the shoots and roots of the plants and in the dithionite-citrate-bicarbonate (DCB) solution all increased. The iron content in the DCB solution (extraction of root surface iron plaque) reached 57.3%～96.2%, significantly higher than that (1.1%～17.5%) in the shoot and (2.7%～25.9%) in the root of the rice seedlings, Most of the iron in the seedling plants were accumulated in the iron plaque or DCB extract. With the rising amount of iron plaque on the root surface, the content of mercury in the roots and shoots of the plants decreased significantly. The addition of selenium did not affect much the content of mercury in the shoots and roots of the plants in Treatments Fe0 and Fe25, but it did reduce the content of mercury significantly in Treatments Fe50 and Fe100. With the formation of iron plaque on the root surface, the content of mercury in the shoots and roots reduced because the iron plaque adsorbed much mercury and the addition of Se(Ⅳ) enabled the iron plaque to adsorb more mercury, thus increasing the proportion of mercury in the iron plaque and consequently reducing that in the shoots of the plans. Quite obviously, Se significantly enhances Hg fixation capacity of the iron plaque on the root surface of rice seedlings. 【Conclusion】Under hydroponic conditions, iron deposits on the root surface to form iron plaque, which inhibits Hg adsorption by rice roots and upward transfer of Hg in the plant. With the forming of more iron plaque, Hg fixation capacity of the coating increases significantly, too, thus markedly reducing Hg accumulation in the rice seedling. Se(Ⅳ) can alleviate the effect of mercury stress on rice, inhibit Hg transfer from roots to shoots and reduce Hg accumulation in the shoots, thus playing a role in protecting rice from mercury toxication. This study has certain practical significance in improving the quality of rice in mercury contaminated area and ensuring food safety.

Abstract:【Objective】As an important agro-ecological region, the Weibei rainfed highland needs urgently measures to build up its soil fertility and improve its eco-environment because of its infertile soil and severe soil erosion. High in stress tolerance, leguminous green manure crops grow normally in severe ecological environment. Cultivation and incorporation of such crops may help reduce soil erosion as well as improving soil structure and soil fertility.【Method】In order to explore rules of changes in farmland soil nutrients and ecological stoichiometry characteristics as affected by cultivation and incorporation of green manure crops in summer fallow seasons, a field experiment was designed to have three different species of leguminous green manure crops [Mung bean (Phaseolus radiatus L.), soybean (Glycine max (L.) Merr. ) and Huai bean (Glycine ussuriensis Regel et Maack)], four nitrogen fertilization rates (N₀, 0 kg N hm^-2; N₁, 108 kg N hm^-2; N₂, 135 kg N hm^-2 and N₃, 162 kg N hm^-2) and three replicates for each treatment, laid out in a split plot design in a tract of farmland in the Weibei Rainfed Highland, and conducted for six years in a row. Soil samples were collected at the end of the experiment from each treatment for analysis of nutrient contents and eco-stoichiometric ratios of C:N, C:P and N:P.【Result】Results show that the long-term cultivation and incorporation of leguminous green manure crops improved soil organic carbon, total nitrogen, alkaline nitrogen contents significantly or by 4.47%~15.35%, 5.21%~6.25% and 11.00%~14.35%, respectively, as compared to CK (the fallow treatment), and the effects of Huai bean were the most obvious in all the treatments. Two weeks after the incorporation of green manure crops, soil total nitrogen, soil organic matter and alkaline nitrogen all increased in content, but the margin of the increase of the former was higher than that of the latter two. In the treatments with Huai bean, organic carbon, total nitrogen, alkaline nitrogen, total phosphorus and available phosphorus all increased significantly, either in a short term or a long term, indicating that the effect of the green manure crop of Huai bean on soil building is the most obvious. Huai bean, high in number of root nodules and in nitrogen content, is a crop widely cultivated in the local area. After the incorporation of a green manure crop into the soil, soil C:N declined for the first short period of time, but in the long run, soil C:N was increased, which is beneficial to the accumulation of soil organic matter and improvement of soil nutrient balance. The ratios of C:N, C:P and N:P in the experiment field are all quite low, because the soil is low in soil organic carbon and total nitrogen, but high in total phosphorus. Soil carbon and nitrogen are the two limiting soil nutrient elements in this region. In the process of improving soil fertility, it is essential to focus not only on dynamic changes of total carbon, nitrogen, phosphorus but also on nutrient balance, especially C:N. In the practice of agricultural production, it is a must to ensure soil N supply, and in addition, enough attention to input of organic materials in such ways as incorporating crop straw into soil and expanding application of organic manure, so as to maintain the balance of soil carbon and nitrogen.【Conclusion】Soil C:P and N:P is closely related to dynamics of soil carbon and nitrogen contents. Cultivation and incorporation of green manure crops in the summer fallow period significantly improves soil carbon and nitrogen status, and hence is an effective practice to build up soil fertility in the Weibei rainfed highland.

Abstract:【Objective】The purpose of this study is to illustrate effects of incorporation of organic material on organic carbon of the heavy fraction and composition of soil aggregates in the soil in the hope that the work may be of some important significance to scientific evaluation of the effects of incorporation of crop straw into the soil on soil fertility and the environment.【Method】An in-lab experiment was carried out incubating for 120 days columns of albic soil with corn stalk incorporated into top soil and parent material at a varying rate, and then analyses done for accumulation of organic carbon of heavy fraction, composition of soil aggregates and distribution of organic carbon in various fractions of soil aggregates as affected by incorporation rate of corn stalk.【Result】It was found that content of the organic carbon of heavy fraction in both the top soil and parent material increased simultaneously with the increasing incorporation rate of corn stalk. The two soils did not differ much in increment of the content of the organic carbon of heavy fraction, showing a slight difference of being only 0.34 g kg^-1. However, they varied sharply in increasing rate of organic carbon. In the top soil, organic carbon increased by 85.51% only and in the parent material by 556.23%. It was also found that, the incorporation of stalk promoted transformation of small aggregates (<0.25 mm) to large aggregates (> 0.25 mm) in the soil. When the amount of corn stalk added is too high, > 2 mm size aggregates no longer increase but decrease. When corn stalk was incorporated at a rate of 3% and 2%, the fraction of large aggregates contributed the most to the content of organic carbon in the soil reaching up to 69.90% and 65.48%, respectively.【Conclusion】 In this study, the addition of stalk promoted accumulation of organic carbon of heavy fraction and formation of large-sized aggregates and increased organic carbon content in aggregates in various particle-size ,adding the appropriate amount of corn stalk can increase the contribution rate of organic carbon in the large-sized aggregates fractions. Compared to the top soil, that in the parent material soil had organic carbon increased by a far more high rate. The effect of the addition of extraneous carbon increasing organic carbon content in aggregates of all particle sizes was more apparent. The soil in the parent material layer was much higher than the top soil in carbon sequestration capacity, in the case that the former almost contained nil of organic carbon.

Abstract:【Objective】Soil fauna play a significantly crucial role in decomposing organic debris, altering physical and chemical properties, and promoting material and energy recycling of and in the soils. In addition to this, they are a key link between the above- and under-ground ecosystems. Change in land-use may bring about great impacts on the ecosystems. However, little has been reported on impacts of changes in land use on soil fauna communities in the Changbai Moutains. In this study, a field investigation was conducted in 2014 on composition, diversity and distribution of the soil fauna communities in four tracts of land different in land-use (secondary deciduous broad-leaf forest, shrubbery, cut-over land and farm land) in the Changbai Mountains. 【Method】 Sampling plots, 5 m×5 m each, were set up in the cut-over land and the farm land, and, 10 m×10 m each in the secondary deciduous broad-leaf forest land and shrubbery land. Within each plot, five subplots were set using the diagonal process for duplicate sampling, 25 cm × 25 cm each for macro-fuana and 10 cm × 10 cm each for meso-fauna, and samples were collected from the litter layer, 0~5, 5~10 and 10~15 cm soil layers in each subplot during spring, summer, and autumn 2014. Soil macro-fauna were picked out and collected by hand and soil meso-fauna with the Tullgren funnel extractor. One-way ANOVA and LSD were adopted to analyze differences in soil fauna community between lands under different land use, and RDA (redundancy analysis) to analyze relationships of soil fauna community with soil physico-chemical properties relative to land use.【Result】A total of 59 groups and 16 344 soil animals were collected and could be sorted into 3 phyla, 7 classes and 21 orders/suborders. Among these, Oribatida (27.04%), Actinedida (20.94%) and Isotomidae (16.05%) were the dominant groups. Differences between the four tracts of land were significant in soil fauna distribution at the community level. In the cut-over land, individual density of the soil meso-fauna varied significantly with the season, while in the farm land the number of soil meso-fauna groups did. In the secondary deciduous broad-leaved forest land and shrubbery land, the soil fauna community declined drastically in distribution with with soil depth, while in the cut-over land and farm land did not so drastically. Even in the same season, the four lands differed in Margalef index (D index) and Shannon-wiener index (H’ index) of the soil macro-fauna. Only in the cut-over land, D index varied significantly with the season. In the same season, the four lands differed in D index and H’ index of the soil meso-fauna. The secondary deciduous broad-leaved forest land, cut-over land and farmlands varied significantly in H’ index of the soil meso-fauna, while the secondary deciduous broad-leaved forest land and shrubbery land did in D index. Redundancy analysis shows that soil fauna was significantly related to pH, organic matter, readily available P, readily available N, moisture content and temperature in the soil in community diversity and distribution. 【Conclusion】Obvious differences did exist between lands different in land use in distribution of soil fauna in community level in the Changbai Mountains. In the cut-over land the soil meso-fauna varies significantly with the season in individual density, while in the farm land, it does in number of groups. In the secondary deciduous broad-leaved forest land and shrubbery land the soil fauna communities decline drastically with soil depth, while in the cut-over land and farm land they do quite mildly. The shrubbery land is the highest in soil fauna community diversity and the farm land the lowest. RDA shows that soil pH, soil organic matter content and the content of readily available P and readily available N are the main factors affecting distribution of the soil fauna communities in all the four types of lands in the hilly regions of the Changbai Mountains.

Abstract:Samples of subtropical acidic forest soil werecollected for incubation in an in-lab microcosm chamber. Some of the samples wereamended with organic carbon or organic nitrogen. Then the incubated soil samples were analyzed for soil nitrification activity and abundance of functional genes of bacteria AOB and archaea AOA, and further for rules of extraneous organic carbon and organic nitrogen affecting ammonia oxidation in the soil. Results show that the amendment of extraneous organic nitrogen stimulated significantly soil nitrification activity.Acetylene inhibition tests demonstrate that autotrophic ammoxidation explained over 90% of the soil nitrification in the subtropical acidic forest soil. The addition of organic carbon did not have much effect on nitrification activity, nor did the amendment of organic carbon and inorganic ammonium simultaneously. However, the addition of organic nitrogen enhanced soil N mineralization, thus causing soil ammonia contentto increase, which may probably be the main cause of the significant increases in soil nitrification activity and abundance of AOA and AOB.

Abstract:The pulse labeling technique was used to label ¹³C-enriched wood residue of Cunninghamia lanceolata sapling, which was then mixed, separately, with soil samples collected from the topsoil layers of a citrus orchard (Citrus aurantium ), a fir plantation (Cunninghamia lanceolata), a secondary forest of Castanopsis carlesii, and a natural forest of Altingia gracilipes). To trace dynamics of fresh carbon in soil aggregates, the mistures were incubated at 20 ℃ for 90 d and then analyzed for distribution of ¹³C-labeled wood residue carbon in the three fractions of soil aggregates, i.e. >250 μm, 53~250 μm and <53 μm. Results show that in the soil samples amended with 13C-labeled wood residue, δ¹³C value increased in all the fractions of soil aggregates, especially in the soil samples of the orchard. In all the soil samples, regardless of land use, δ¹³C value was the lowest in the <53 μm fraction of soil aggregates, and the highest in the 53~250 μm fraction. Once extraneous carbon was amended into the soil samples, the content of fresh carbon therein increased instantly. And the content of fresh carbon and δ¹³C value was higher in the root than in the leaf, as the ratio of C/N is higher in the former. In terms of content of fresh carbon, the three fractions of soil aggregates displayed an order of <53 μm > 53~250 μm > >250 μm, which indicates that a short term of incubation facilitates accumulation of fresh carbon in micro soil aggregates.