Abstract:Engineered nanomaterials (ENMs), a kind of intentionally produced materials formed of particles varying from 1 to 100 nm in particle size, possess unique physicochemical properties that are not shared by any of their corresponding bulk materials. Due to their unique physicochemical properties, ENMs are getting more and more extensive in application to a wide range of technical fields in human production and life. Hence, it has become inevitable for ENMs to get released into the environment. ENMs enter into farmlands with ENM-containing pesticides, fertilizers and slurries from wastewater treatment facilities, posing potential risks to agricultural ecosystems. Being the essential components of an agricultural ecosystem, plants and soil microorganisms play critical roles affecting fate and transport of ENMs in the environment though adsorption, uptake and bioaccumulation. Therefore, how they affect plants and microorganisms ecologically attracts increasing attention from researchers the world over. Their researches may provide some valuable information to a better understanding of the consequences of introducing ENMs into ecosystems. Besides, as plants and microorganisms are closely related to each other, interact with each other and mutually influence each other, they form a plant-microorganism ecosystem. In this review, influences of ENMs on plants and microorganisms in the ecosystem are summarized. First, mechanisms of the potential ecotoxicities of ENMs and their relationships with the special properties of ENMs were collated and then researches of influences of ENMs on plants, soil microorganisms and plant-microorganism ecosystems were expounded. The review reveals that ENMs may have some impacts, varying in degree, on plant and microbes, and degree of the impact is related to kind of ENMs and species of the object and could be divided into three categories, negative, positive and insignificant. Moreover, researches have found plants and microbes may have some potentials to affect bioavailability of ENMs, which may serve as feedback to the ecological effect of ENMs on the plant-microorganism ecosystem. Recent studies on actual plant-microbe ecosystems found that ENMs affected functioning of arbuscular mycorrhizal fungi and azotobacters and excretion of iron chelator from soil microbes in the plant rhizosphere, thus altering eco-effect of ENMs, which suggests that to deem plants and soil microbes as an entity in the research may help the researchers go further in depth in studies on eco-effects of ENMs. Finally, the review lists out problems existing in the current researches with their pathways and techniques and focal points as well in ongoing researches.

Abstract:In 1974, Satoshi Ōmura, a Japanese microbiologist and expert in isolating natural products, isolated new strains of Streptomyces from soil samples. He found that this strain can produce a bioactive compound named Avermectin, which was subsequently chemically modified to a more effective compound called Ivermectin by Williman Campbell from Merck Company. Ivermectine was later tested in humans with parasitic infections and effectively killed parasite larvae, leading to a Nobel Prize in 2015. The rapid advance of new techniques such as single-cell isolation and high-throughput screening may revolutionize culture-dependent study and downstream applications. This will dramatically change the landscape of DNA/RNA-based research of microbial resource on Earth, and soil microbiology represents one of the most important research fields in future.

Abstract:Decomposition of organic materials in cropland soils is critical to recycling of soil carbon (C) and nutrients. We collected data from the 56 published studies during 1980—2013 that have examined the decomposition of organic materials across China. Our objectives were to to quantify the fraction of C remaining after one year’s decomposition (h₁) and to investigate the impact of types of organic materials (green manure, straw, root and manure) and agricultural regions (Northeast, Northwest, North and South China). Overall, h₁ ranged from 0.10 to 0.75 g g^-1, with an average of 0.335 ± 0.005 g g^-1 across China, and was significantly affected by types of organic materials and agricultural regions and their interactions. On the whole, in terms of h₁ the four major types of organic materials displayed an order of green manure < straw < root and organic manure, and the regions, an order of South China ≈ North China < Northwest China ≈ Northeast China. However, the regional variation of h₁ was also affected by type of organic materials. For instance, h₁ of straw, root and green manure were lower in North China than in South and Northeast China, whileh₁ of organic manure did not differ much between regions. On the other hand, h₁ of organic materials also varied with the regions. For example, in humid and semi-humid Northeast, North and South China, h₁ of root was higher than that of green manure and straw, while in the arid and semi-arid Northwest China, h₁ did not differ much between types of organic materials, because of aridity. Step-wise regression analyses shows that lignin:N ratio is the major factor regulating decomposition of straw, root and green manure, while mean annual temperature and aridity follows in the effect. However, decomposition of organic manure, which had already been decomposed or semi-decomposed, was not significantly affected by climatic factors, nor by quality (chemical composition) of the organic material. In addition, a singer factor, either of climate or of quality of organic materials, could maximally explain no more than 15% of the variability of h₁, and the combination of climatic factors and quality of the organic materials could only explain less than 40% of the variability, which suggests that to predict accurately the decomposition processes of organic materials in cropland, more attention should be paid to impacts of the regional or site-specific characteristics, such as soil physic-chemical and biological properties.

Abstract:Soil erosion is a major ecological and environmental issue concerned globally. It causes soil degradation and some environmental problems as well. Based on Revised Universal Soil Loss Equation (RUSLE) and GIS spatial analysis technique, this research quantitatively analyzed the spatial distribution of soil erosion and soil nutrient loss in Anhui Province, and explored relationships of soil erosion intensity with elevation and slope based on ArcGIS zonal statistics. Results show that in 2010 the total amount of soil erosion was 3 454 × 10⁴ t a^-1, and the mean soil erosion modulus was 256.9 t km^-2a^-1. The soil erosion in the province as a whole was dominantly trivial in degree, with 90.10% or 121 200 km² in the grade of trivial erosion, and 1.12% or 1 521 km²in the grade of intensive erosion distributed mainly in the hilly region of South Anhui and the Dabieshan mountain region of West Anhui. The grade of light erosion contributed 1 016 × 10⁴t a^-1, 29.42 % to the total amount of soil erosion, the grade of trivial erosion did 677.6 × 10⁴ t a^-1 or 19.62%, and the grade of highly intensive erosion did 125.3 × 10⁴t a^-1 or 3.63%. Spatially, soil erosion intensified from north to south. Trivial soil erosion, the dominant grade of soil erosion, was distributed mainly in the North Anhui Plain, the riverine plains alongside the Huaihe River and the hilly region between the Yangtze River and the Huaihe River, while intensive soil erosion, in the hilly region of South Anhui and the mountains of West Anhui. Intensity degree of the soil erosion in the study area was closely related to elevation and slope. The soil erosion on slopes, 15° ~ 25° in gradient and 200 ~ 500 m in elevation, was the most severe. Distributions of soil erosions different in intensity in areas different in elevation and slope displayed a similar rule, that is, with rising elevation and slope, the soil erosion gradually increased in intensity, and the area of trivial soil erosion shrank gradually, while the areas of the other grades of soil erosion expanded gradually. The total loss of soil nutrients caused by soil erosion reached 106.6 × 10⁴ t a^-1, of which soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and total potassium (TK), accounted for 47.94 × 10⁴, 4.934 × 10⁴, 1.295 × 10⁴, and 52.47 × 10⁴ t a^-1 respectively, or 3.57, 0.37, 0.10, and 3.90 t km^-2 a^-1, respectively, on average. The soil nutrient loss showed a spatial variation trend similar to that the soil erosion did, that is, rising from north to south. The North Anhui Plain was the lowest in mean and total loss of the four soil nutrients, and the hilly region of Southern Anhui the highest. As a whole, the findings may help understand how soil erosion and soil nutrient loss is spatially distributed, and then provide certain data basis for soil and water conservation.

Abstract:Wind-water alternate erosion was the main form of soil erosion in the regions subjected to wind and water alternate erosion. The knowledge of effects of wind-water alternate erosion on soil particle size composition is very important to further in-depth research on coupling mechanism of the wind-water alternate erosions and its impact on the environment. In this paper, a simulated rainfall experiment was carried out in the State Key Laboratory of Eco-Hydraulic Engineering at the Xi’an University of Technology in China from July to August 2013, and particle size composition of the sediments down the sand-covered slope, as affected by rainfall intensity and thickness and length of the sand cover, was analyzed from September to October 2013, in order to further illustrate sediment yielding process of the erosion on sand-covered slopes. The study on variation of the particle size composition of the sediments down the sand-covered slope, as affected by rainfall intensity and thickness and length of the sand cover, was done with the aid of the statistic indices of the Malvern 2000 calculation samples,, including the median particle diameter d50, maximum particle diameter and mean, particle diameter. Enrichment rate and fractal dimension were worked out, and SPSS18.0 was used to analyze relationships of the characteristics of their particle size composition with d50, fractal dimension and enrichment rate. Results show that after the slope was covered with sand, clay and silt decreased by 0 ~ 18% and 11% ~ 29% in content, and by 0.7% ~ 17% and 11% ~ 29%, in enrichment rate, respectively, while sand increased by 17% ~ 48% in content and by 17% ~ 51% in enrichment rate. The erosion sediment was dominated with coarse particles., In the two test soils (loess and sand), only the clay enrichment rate was higher than 1 and with the sand cover increasing in thickness (length), fractal dimension of the erosion sediment decreased, but d50 increased; on the sand-covered slope, the initial 0 ~ 10 minutes of runoff flow contained a large volume of silt and sand; and thickness (length) of the sand cover on the slope was higher than rainfall intensity in effect on fractal dimension and d50.

Abstract:According to the pedogenetictheories, soils in similar soil landscapes, like climate, parent material, landforms, plants, animals’ activities,are supposed to have similar characteristics as a result of pedogenesis. However, there are no soil pedonsabsolutely the same, even though they have developed in the same landscape, for their developments could have been drastically affected by various soil forming factors. Specially, in classification of basic soil species in the soil geographico-genetic classification and of basic soil series in the soil taxonomy, a specific or diagnostic soil horizon is cited to differentiate soil structures. Yet, the specific soil horizon diversifies and is still blurred in specification. Diagnostic horizons were created and used for the first time during the 2nd national soil survey. Then the concept and the nomenclature of diagnostic horizons are accepted and used in classification of basic soil series in the soil taxonomy for the purpose of distinguishing structures of soil profiles. As diagnostic horizons play such a crucial role in interpreting structure of a soil series, it is necessary to redefine and collate them systematically. In this paper, soil seriestypicalof Henan were cited as examples, of which diagnostic horizons involved in classification of soil series were collated and summarized. They have been subjected to clayification, calcification, anthrogenetic processes, humic accumulation, etc. during their development. So in terms of the cause of genesis, diagnostic horizons could be sorted into 3 groups, i.e. those formed during the soil genesis under modern soil forming environments, those formed under soil forming environments of geological origin or geologic epoch, and those under human activities. On such concepts of soil series, a classification and retrieval system is brought forth for diagnostic horizons with a view to making the concept of diagnostic horizons, more systematic, more comprehensive, opener and easier to apply.

Abstract:Accurate assessment of soil organic carbon storage based on the database established on the basis of the attribute data of soil profiles is the basis of the research on global carbon cycling and improvement of soil fertility for agriculture. However, it is still unclear how source of soil profile data and scale of mapping affects assessment of soil organic carbon storage. In this study, a total of 3.93×10⁶ hm² of upland in the 29 counties (or cities) of North Jiangsu was cited as a case for study. Systematic analysis was performed of how the four sources of soil profile data, namely, “Soils of County”, “Soils of Prefecture”, “Soils of Province” and “Soils of China”, and the six scales, i.e. 1:50 000, 1:250 000, 1:500 000, 1:1 000 000, 1:4 000 000 and 1:10 000 000, used in the 24 soil databases established for the four soil journals, affected assessment of soil organic carbon. Results show that the soil organic carbon density (SOCD) and storage (SOCS) in the top layer (0~20 cm) of the uplands in the region in the 1:50 000, 1:250 000, 1:500 000, 1:1 000 000, 1:4 000 000 and 1:10 000 000 scaled databases was estimated to be 1.56 kg m^-2 and 61.20 Tg, 1.53 kg m^-2 and 61.32 Tg, 1.51 kg m^-2 and 61.22 Tg, 1.44 kg m^-2 and 55.19 Tg, 1.60 kg m^-2 and 65.08 Tg, 1.59 kg m^-2 and 63.11 Tg, respectively, based on 983 upland soil profiles in the “Soils of County”, 1.63 kg m^-2 and 63.92 Tg, 1.71 kg m^-2 and 68.78 Tg, 1.64 kg m^-2 and 66.37 Tg, 1.62 kg m^-2 and 62.06 Tg, 1.70 kg m^-2 and 69.25 Tg, 1.72 kg m^-2 and 68.24 Tg, respectively, based on the 209 upland soil profiles in the “Soils of Prefecture”, 1.27 kg m^-2 and 49.88 Tg, 1.25 kg m^-2 and 50.06 Tg, 1.72 kg m^-2 and 69.64 Tg, 1.43 kg m^-2 and 54.84 Tg, 1.40 kg m^-2and 56.99 Tg, 1.52 kg m^-2 and 60.18 Tg, respectively, based on 64 upland soil profiles in the “Soils of Province”, and 1.74 kg m^-2 and 68.31 Tg, 1.70 kg m^-2 and 68.08 Tg, 1.81 kg m^-2 and73.52 Tg, 1.75 kg m^-2 and 66.78 Tg, 1.75 kg m^-2 and 71.33 Tg, 1.19 kg m^-2 and 47.21 Tg, respectively, based on 21 upland soil profiles in the “Soils of China”. Compared with the most detailed 1:50 000 soil database based on 983 upland soil profiles containing 17 024 polygons. the other five databases varied from 1.94% to 23.53% and from 0.02% to 22.86%, respectively, in relative deviation of the assessment of SOCD and SOCS. T test shows that extremely significant differences existed between the assessment based on the 1:50 000 database of “Soils of County” and the assessments based on the databases of other scales (p＜0.001), indicating that it is essential for scientists to use soil data from proper sources and of proper mapping scales when trying to assess SOCS of the country or a region in future.

Abstract:Conventional soil maps are what soil survey experts turn out after field soil survey and interpretation of corresponding aerial photos, and often used as major data sources of information about spatial distribution of soils, which is essential to watershed management and eco-hydrology. With the development of geographic information technique, traditional soil survey methods are already far from efficient to meet the requirements of soil information services. As they used to be based on the experts’ empirical model of thinking, their products are often hard to express, exchange and store; the qualitative characteristics they described of a soil entity are often inconsistent with the characteristics of its spatial distribution, which tends to lead to low accuracy of the survey; and they are very costly and also limited to certain regions, which makes it hard to have information updated. Therefore, how to make full use of the existing historical resources and data is very important to retrieving efficiently soil maps higher in accuracy from the available information in Digital Soil Mapping (DSM). In this study, from the conventional soil maps and terrain data extracted were data of soil type and environment factors, based on which, a soil environment relationship model was established using the spatial data mining method, and finally, reliability and accuracy of the mapping was validated by field sampling. The Nieshui river basin in Huajiahe Town, Hongan County, Huanggang City, Hubei Province was selected for case study. The conventional soil maps of the study area plotted during the Second National Soil Survey were used to demonstrate processes of the research. The proposed method consists of five major steps. 1) Select seven environmental factors that were closely related to the process of pedogenesis and establish a geographic information system (GIS) database, which should contain a modified soil parent material map and data of terrain factors (elevation, slope, aspect, plan curvature, profile curvature and topographic wetness index) extracted from 10 m resolution Digital Elevation Model (DEM). 2) Extract 1410 typical sample data of soil types and environment factors by following the principle of frequency distribution, so as to reduce noises and abnormal data that would often occur in traditional soil mapping, because traditional soil mapping used to be done manually and contain some hard-to-reflect knowledge ( or noise) of the experts’ about proper relationship models. It is, therefore, essential to have the data properly pretreated. 3) Retrieve detailed expertise implied in the soil map product, using the spatial data mining techniques. Compared with the other algorithms, the decision tree algorithm is the most suitable one for extracting and expressing knowledge of the soil-environment model. So, the See5.0 decision tree algorithm is selected to perform spatial data mining and hence, obtain knowledge of soil and environment relationships. 4) Predict soil spatial distribution through inferring and mapping in Soil-Land Inference Model (SoLIM) based on the soil-environment knowledge and environment data obtained. SoLIM uses similarity degree as measurement parameter and fuzzy logic as basis to calculate similarity between soils. Within a given pixel, a number of corresponding soils have a variety of similarity degrees, which can be represented in fuzzy membership degree. Finally, the soil type represented by the highest fuzzy membership degree among the similarity vectors of a pixel is defined as the soil type of the pixel. A soil type distribution map can be obtained by hardening the fuzzy membership degree map. A large number of case studies have demonstrated that SoLIM is a more accurate than the traditional manual subjective method in soil mapping. 5) Verify accuracy of the proposed method through sampling at 270 field validation points using three sampling strategies: regular sampling, subjective sampling and transect sampling. Results show that the soil map obtained through fuzzy inference provides more detailed information about soil spatial distribution than its corresponding conventional soil map and is about 11% higher in accuracy and significantly higher in number of patches. It is therefore concluded that the proposed method which retrieves soil-environment relationships from a traditional soil map is more accurate than the conventional mapping method in judging and delineating and more convenient for use to update soil maps.

Abstract:The Loess Plateau is one of the areas that suffer the most serious soil erosion and the soil in the area is characterized by low soil fertility and high soil erodibility. Thanks to its inherent characteristics and physicochemical properties, biochar has become a novel soil structure amendment. However, so far studies on biochar have mostly focused on its effects of improving soil physical and chemical properties and plant growth conditions, reducing greenhouse gas emission and remedying polluted soil, and demonstrated that its positive effects on soil quality, soil bulk density, soil porosity, quantity and structure of soil aggregate and soil water dynamics. Little has been reported on its effects on soil resistance to erosion. Getting to know the effects of biochar on soil erosion will be of great significance not only to soil and water conservancy, but also to soil building and crop yield. An indoor artificial rainfall experiment was carried out to explore effect of biochar on sheet erosion on loessal soil slope. The experiment was designed to have one rainfall intensity (90 mm h^-1), five application rates (0%, 1%, 3%, 5% and 7%) and three particle sizes (<2mm, <1mm and <0.25mm) of biochar of sawdust. Results show that the effect of biochar application on erodibility of loessal soil plow layers is attributed mainly to its effects altering composition and porosity of the soil and the effect of its own properties on water, which were embodied in delayed runoff and reduced runoff and sediment yields and sediment in runoff. Incorporation of biochar, the same in particle size, shortened the duration of runoff and the effect intensified with rising application rate of biochar. However, when the application rate was lower than 3%, it delayed runoff, but when the rate went on rising, it affected runoff reversely. Incorporations of biochar, the same in rate, but different in particle size, did not show much difference in affecting time of runoff yield. Incorporation of biochar of any size at a rate of 1% demonstrated runoff and sediment reducing effects in every rainfall event. So, in exploring effects of biochar application rate on runoff and sediment yields, it is essential to take into account particle size of the biochar. Biochar application rate, biochar particle size, interaction of the two elements and other uncontrollable factors were responsible for 21.35%, 7.27%, 41.19% and 30.20%, respectively, of the variation of runoff yield brought about by rainfall and for 32.9%, 8.66%, 35.21% and 23.23%, respectively, of the variation of sediment content in runoff. As the biochar particle size does not have much influence on soil erodibility and sediment yield, ,biochar application rate, interaction between content and particle size of the biochar, and other uncontrollable factors, are the factors contributing 37.16%, 34.46% and 28.38%, respectively, to variation of soil erodibility and 32.48%, 35.59% and 31.94%, respectively, to variation of erosion. Obviously, biochar application rate and interaction between content and particle size of the biochar are major factors affecting rainfall erosion significantly, and particle size of biochar is a minor one. Though this study is a small scale research on mechanism of biochar affecting soil erosion, the findings in this study may serve as reference of scientific significance to large-scale researches on effect of biochar on soil erosion in future.

Abstract:Soil bulk density, which can be measured through several labor-intensive procedures, is often missing from most soil databases. However, it is an essential parameter in calculation in many cases and models, and it is feasible to derive soil bulk density from some other attributes of the soil. As China has a huge variety of soil types, whether the existing pedotransfer functions (PTFs) are still applicable to the various soils calls for in-depth analysis. The soil data involved in this study were cited from the Second National Soil Survey of China, from the database for the Chinese Soil Taxonomy and from other publications, covering all the major types of soils in China. The data gathered during the Second National Soil Survey were converted into the Chinese Soil Taxonomy system by means of approximate reference between the two systems using a WebGIS-based inquiry system. After screening of the data in quality and depleting some abnormal values, a total of 2 441 complete soil datasets were obtained, covering all the major types of soils in China. In this paper, 2 published PTFs were evaluated and compared in prediction accuracy and applicability for different types of soils, and a PTF, the most adaptable to the major types of soils in China, was developed through regression analysis using SPSS. In addition, exploratory stepwise regression models were proposed and the parameters of the nonlinear model that used only the OM variable were revised based on taxonomical partitioning of the data. Results show that the two existing models varied in performance and were not high in prediction accuracy when used for some types of soils. The bulk density MPE values acquired with the polynomial model of Histosols, Halosols, Gleyosols, Isohumosols and Cambosols were negative (-0.06～-0.01), while those of Anthrosols, Ferralosols, Aridosols, Ferrosols, Argosols, Primosols and Vertosols were positive (0.00～0.02), indicating that the model overestimated BDs of the soils in the former group, and underestimated those in the latter group. The MPE values obtained with the nonlinear model of Aridosols, Halosols, Isohumosols and Ferrosols were negative (-0.02～-0.01), while those of Histosols, Anthrosols, Ferralosols, Gleyosols, Argosols, Cambosols, Primosols and Vertosols were positive (0.00～0.10), indicating the model overestimated BDs of the soils in the former group, and underestimated those of the soils in the latter group. Comprehensive comparison of the scattergraphs of MPE, RMSPE, R2 and measured and predicted BDs indicates that the two models did not vary much in prediction accuracy when used for soils of the same soil order. The PTF developed after the data of the soil taxonomy were partitioned significantly improved the model’s performance. The new PTF was pretty high in prediction accuracy when used for Histosols, Ferralosols, Gleyosols, Isohumosols, Ferrosols, Argosols, Cambosols, Primosols and Vertosols, but it tended to be low in accuracy when used for Anthrosols, Halosols and Aridosols. So the model should be used with care. Besides, in using PTFs, it is essential to pay special attention to area and scope they are applied to.

Abstract:Soil water, as the major component of water in desert ecosystems, is the most important environmental factor which limits the growth and productivity of the vegetation. Specifically, soil water plays a significant role in the development, evolution and productivity of sand soils, as well as in maintaining the structure stability and function of desert ecosystems. Besides, it can make a great difference on the windbreak and sand-fixation, etc. The Tarim Desert Highway, crossing the Taklimakan desert, is protected by the artificial plantation shelterbelts along the highway. Due to high evaporation demand and extremely low rainfall in this region, it is very difficult to maintain the water balance of the sandy soil along the plantation shelter, thus leading to failure in meeting the normal water demand of plants without irrigation. Consequently, how to meet the water demand of plants is the key problem to sustain the plantation shelterbelt. Currently, pumped saline groundwater has been utilized to supplement the soil water loss in the shelterbelt. However, the soil salinization, caused by the long-term saline water(especially the saline water of high salinity) irrigation, inevitably hampers the construction and maintenance of the plantation shelterbelt. Solution for this problem is highly dependent on the understanding of the soil water and salt dynamics. Based on these, it is very necessary to carry out the dynamics of the soil water and salt in this region, and so on. In order to reveal the laws of spatial and temporal dynamics of the soil water and salt in the soil under artificial shelterbelt drip-irrigated with saline water in the center of the Taklimakan Desert, a field study was carried out to monitor temporal variation and two-dimensional spatial distribution of soil water and salt in the soil between April and July during which four irrigation events occurred at the interval of 15 days. Results show that (1) in the soil under artificial shelterbelt drip-irrigated with saline water, dynamics of the soil water and salt displayed an obvious periodic rule, that is, within an irrigation cycle (15 days), soil water dropped rapidly in content during the first period from D1 to D4, slowed down in changing during the second period from D4 to D10 and leveled off during the third period from D10 to D15, and the variation as a whole fitted the law of diminishing power function (y＝8.746t-0.270，t＝1, 2, 3…), while soil salt was being leached out in the first 7 days and then accumulating in the following 8 days (7~15 d), and the variation as a whole fitted the equation of Parabolic Function (y＝0.009t2－0.138t＋2.269，t＝1, 2, 3…); and (2) in the 0～60 cm soil layer, soil water displayed a monistic linear diminishing pattern in horizontal distribution, while soil salt, a monistic linear increasing pattern; and in the 0～120 cm soil profile, the distribution of soil water displayed a single-peak curve with the peak appearing at 20 cm in soil depth, while the distribution of soil salt fitted the inverse function model, and salt accumulated in the surface of soil (0～5 cm) forming a circle around the nozzle 45～60 cm in radius, where the salt content might reach as high as 10～20 g kg^-1. Our results suggest that the dynamics of soil water and salt in the artificial plantation shelterbelts, affected by varying environmental factors such as irrigation, evaporation, air temperature, precipitation, vegetation, as well as the spatial variability of the soil properties, exhibit both generality and differentiation, regardless of spatio-temporal scales. Thus our study may provide theoretical basis for predicting dynamics of the soil water and salt, evaluating soil salinization and further optimizing the present irrigation regime for the artificial plantation shelterbelts in this region.

Abstract:Soil moisture is the main restrictive factor for the growth of desert vegetation in the Gurbantunggut Desert. Three soil moisture monitoring sections (include 23 soil moisture monitoring points) were set to research the spatio-temporal variation of soil moisture in a fixed dune at the southern edge of Gurbantunggut Desert in December 2012, two of the monitoring sections were set along the transverse section of dune, the third one which is vertical to the above-mentioned two soil moisture monitoring sections was set in the interdune. The soil moisture monitoring points were located in the interdune, west slope, east slope and top of the dune, respectively. In-situ observation was performed from December 2012 to November 2013 of soil moisture in the 0~400 cm soil layer of the fixed sand dune with a neutron probe, to explore spatio-temporal variation of moisture content in different slope positions of the fixed dune and impact of Haloxylon ammodendron on soil moisture content in the root zone of the plant at its different growth stages. Results show that (1) a 0~400 cm soil profile could be divided into two parts according to average soil moisture content: soil moisture content is higher and vary a lot with the depth in 0~200 cm soil layer, soil moisture content is lower and relatively constant with depth in 200~400 cm soil layer; based on the variation coefficients of soil moisture content, a 0~400 cm soil profile could be divided into 3 layers: active layer (0~40 cm), sub-active layer (40~200 cm) and relatively steady layer (200~400 cm); (2) the difference in soil moisture content was not significant between slope positions, in the west slope, east slope and top of the dune, but it was significant between interdune and the above-mentioned three slope positions (p<0.01), and the soil moisture content in the former was relatively higher; the difference of soil moisture content in different slope positions in active layer, sub-active layer and relatively steady layer consistent with the difference of soil moisture content in the whole profile (0~400 cm); in active layer, soil moisture content in the interdune is 1.25 times, 1.26 times, 1.21 times of the soil moisture content in the west slope, east slope and top of the dune, respectively; in sub-active layer，soil moisture content in the interdune is 1.30 times, 1.36 times, 1.25 times of the soil moisture content in the west slope, east slope and top of the dune, respectively; in relatively steady layer, soil moisture content in the interdune is 1.20 times, 1.22 times, 1.17 times of the soil moisture content in the west slope, east slope and top of the dune, respectively; (3) soil moisture content has obvious temporal variation, the annual variation of soil moisture content could be divided into 3 periods, i.e., moisture gaining period (from March to May), moisture losing period (from June to October) and moisture stable period (from November to February the following year); Soil moisture recharge is more than discharge in moisture gaining period and less than discharge in moisture losing period, soil moisture recharge and discharge are almost same in moisture stable period; (4) soil moisture content was much lower in autumn than in spring and summer in the root zone of the Haloxylon ammodendron of different growth stages; was quite low in all the four seasons in the root zone of grown-up Haloxylon ammodendron; varied sharply between seasons in the root zone of young Haloxylon ammodendron and between the grown-up plants and the young plants in spring and summer.

Abstract:How to handle surplus crop straw has become an important topic that calls for urgent solution in the agricultural regions of China. Straw incorporation into the field is one of the main methods of straw utilization. The method of straw incorporation used to either overcast the straw on the surface of the field like mulching or incorporate the straw into the shallow topsoil layer, which would obviously bring about some problems, like hindering seed germination and seedling growth, impeding rise of soil temperature, and favoring incidence of plant diseases and insect pests, while its effect on accumulation of soil organic matter is so limited that it would not help solve the problems, like thinning of the plough layer and depleting of organic matter in the subsoil layer. Corn stover deep incorporation（CSDI） extends the extent of soil building from topsoil, as it was previously, down to subsoil, which would not only help solve problems, like thinning of the plow layer, shortage of organic manure, declining water holding capacity, but also reduce environmental pollution from burning of straw, while achieving the ends of sequestrating carbon, conserving soil water, building up soil fertility and raising crop yield. Although some reports are available on change in structure of Hu after CSDI , few have been published on Hu in soil aggregates. Soil samples were collected from an experimental corn field under long-term mono-cropping in the Jilin Agricultural University Experiment Station. The experiment field of black soil was divided into two plots, one cultivated under CSDI and the other without CSDI (CK). In the plot under CSDI, ditches were dug along the furrow in-between two rows of corn plants in November 2011, with a section like a bottom-up isosceles trapezoid, 60 cm wide in the upper opening, 40 cm wide in the bottom and 40cm in depth. In the process of digging, the soils of the toplayer (0~20 cm) and the sublayer (20~40 cm) were dug out layer by layer and placed separately on either side of the ditch. Once a ditch was dug into shape, corn stover, cut into 3~5 cm in length were applied into the deep ditch evenly at a rate of 12 000 kg hm^-2, together with N fertilizer (urea 450 kg hm^-2), and then the removed soil was placed back into the ditch, the sublayer soil first and then the toplayer soil forming a big ridge, which was let subside naturally. After the practice of CSDI finished, the two plots were cultivated with corn in the same pattern. The findings of the study may provide some theoretical basis for how to improve soil fertility and build up a proper plow layer with CSDI. Results show that the Hu in the plot of CSDI is higher in carbon content, varying in the range of 542~839 g kg^-1 and averaging 721 g kg^-1, with H/C in the range of 0.662~0.958，and being 0.776 in average, and higher than HA in carbon content and condensation degree. CSDI was found to increase carbon and nitrogen contents, and reduce Hu oxidation and aliphatic hydrocarbon degrees. The effects are more significant in the sublayer soil than in the toplayer soil. Besides, CSDI increases active structure of the Hu, but lowers its stability, To sum up, CSDI increases carbon and nitrogen contents in Hu, while making it simpler and younger in structure.

Abstract:Relative to dry land, paddy field originally referred to artificially irrigated fields, where either paddy rice or upland crops were planted. Now only the field where paddy rice or some other aquatic plants are planted is called paddy field, or rice field. Different from the orginal paddy field, it has ridges to store water. In South China, paddy fields are not only long in cultivation history but also be vast in area and studies on such paddy fields started quite earlier and are great in volume both at home and abroad, but only a few has been reported on paddy soil in North China. Rice is the main grain crop in China. A large proportion of the total grain output in this country comes from Northeast China, where the paddy fields reach over 66.7 billion hm² (including 53.3 billion hm² in Heilongjiang, and 6.6 billion hm² each in Jilin and Liaoning) and occupy an important position in the rice cultivation area of the country. However, the rice fields are mostly short in cultivation history and most of the paddy fields were turned from upland fields, and what’s more, some of the paddy fields were turned back into upland fields again due to incomplete water conservancy facilities. During this kind of irregular changes, the soils in the fields would certain change in carbon fixation capacity, soil fertility and CO₂ emission. But little has been done at home and abroad on how they evolve. Therefore, the study on paddy soils in Northeast China is of great significance. Rice yield depends mainly on soil fertility, of which soil organic matter is an important component. Soil humus, being an important component of the soil solid phase material, plays a huge role in the genesis and development of soil fertility, and hence is also an important indicator for soil fertility. It does not only influence productivity of the farmland ecosystem, but also have a great impact on CO₂ concentration in the atmosphere through decomposition of soil organic matter. The study on how soil organic matter in the paddy field varies in content and composition is very important to making full use of land resources, realizing quality crop production, increasing grain output and being friendly to the environment. Paddy fields different in cultivation history (5 a，20 a and 50 a) in Qingshan Village, Chaoyangshan Town of Panshi City in Jilin Province, were selected as subjects for the study on changes in content of soil organic carbon (SOC), composition of water soluble substance (WSS), fulvic acid (FA), humic acid (HA) and humin (Hu), structure of HA and content of soil nutrients as a function of cultivation histroy. Results show that with rice cultivation going on from 5a to 50a, changes occurred in the surface (0~15 cm) and the subsurface (15~30 cm) soil layers. (1) The electric conductivity increased by 74.8% and by 113.7% respectively and soil available nitrogen, available phosphorus and available potassium by 0.24%, 15.8% and 29.7% and by 0.24%, 6.92% and 14.7%, respectively , while soil pH remained almost unchanged; (2) Total soil organic carbon increased by 42.1% and by 47.9%, respectively, and WSS, HA and Hu increased by 28.4%, 51.9% and 76.2% and by 28.4%, 84.9% and 70.1%, respectively, while FA decreased by 9.2% and by 1.74%, respectively, which indicates that rice cultivation in paddy field favors accumulation of organic carbon in the soil; (3) HA/(HA+FA) ratio (PQ) increased, indicating that humification of the soil is intensified; and . (4) H/C, ∆LgK, E2920/1720 and E2920/1620 of HA all decreased, indicating that HA in the soil is enhanced in aromatization and condensation and becomes more complicated in structure.

Abstract:To investigate effect of change of ion-strength on change of pH(ΔpH) during successively desorption, a serious desorption tests were conducted on using electrolyte solutions, including de-ionized water, varied in NaNO₃ concentration from low to high, to desorbed successively copper ions or calcium ions adsorbed by two variable charge soils(Ali-Haplic Acrisol from Jinxian of Jiangxi and Hyper-Rhodic Ferralsol from Kunming of Yunnan). To explore relative mechanism further, kaolinite is also be used, and the similar experience processes have also been conducted without the addition of bivalent adsorbing cations. Results showed that de-ionized water and NaNO₃ electrolyte solutions differed in effect on ΔpH, when samples were successively desorbed in de-ionized water, 0.01 mol L^-1 NaNO₃, 0.1 mol L^-1 NaNO₃, 0.01 mol L^-1 NaNO₃, respectively, no matter if the addition of bivalent adsorbing cations, or the type of cations adsorbed (specific adsorption ions or electrolyte adsorption ions). Although the value of ΔpH is different in different condition of desorption and different samples, the tendency of change of ΔpH is just the same. In general, ΔpH was always positive, when the samples were desorbed in de-ionized water, and was generally negative when desorbed in NaNO₃. ΔpH will decrease with the increasing times of desorption in de-ionized water, and will be maintain not change or slight increase when desorbed in the same concentration of NaNO₃ solution for the second or the third times. There is seemly the similar point of beginning of pH_ad (pH of equilibrium suspension of adsorption) for the variable charge soils and kaolinite, which is relative to the ZPC(Zero Point of Charge) of kaolinite, when desorption occurred in de-ionized water and 0.01 mol L^-1 NaNO₃ for the first time. The tendency of change of value of ΔpH of which supporting electrolyte is 0.1 mol L^-1 NaNO₃, is sharper than that supporting electrolyte is de-ionized water, when pH_ad is above the special point, no matter the desorption was occurred in de-ionized water or in 0.01 mol L^-1 NaNO₃. As pHad is higher than that point that above-mentioned, the absolute value of ΔpH will become larger in most situation. For the first desorption in 0.01 mol L^-1 NaNO₃, ΔpH will get the largest absolute value. Because the pH of desorption liquid is just the same as that of the equilibrium suspension of the previous adsorption or desorption, the change of ΔpH should not be attributed to the difference of pH before and after desorbing, it can only attribute to the process of desorption, during which excluded the effect of other factors on ΔpH, for example, the hydrolysis of copper, the similar changes of ion-strength is always existed. According to the theory of four layer and newest report that was about the effect of change of ion-strength on the surface potential of variable charge surface, the increasing ion-strength is always lead to decrease of absolute value of surface potential, vice versa. Base on the above-mentioned observation, it suggest that one of the root causes that lead to this phenomena should be contributed to the change of surface potential of variable charge soils and kaolinite which caused by the change of ion-strength, on the other hand, considering the similar law of change of ΔpH with the increasing pHad, and kaolinite is the main component of the two variable charge soils tested, it can be assumed that kaolinite is the main factors that decide the regular pattern of change of ΔpH caused by the change of ion-strength in variable charge soils.

Abstract:As a critical organic pollutant in soil environment, atrazine has aroused people’s concern about its fate and ecological risk in recent years. Adsorption-desorption behavior of atrazine is a key factor governing translocation, transformation, fate and bioavailability of the substance in the soil, while it is affected not only by physico-chemical properties of the soil, but also by some important components of the soil, such as minerals and organic matter (SOM). There have been large volumes of studies demonstrating that SOM is the major factor governing adsorption of atrazine in the soil, and some others indicating that soil minerals may be almost equal to or higher than SOM in such an effect in the case that SOM is relatively low in content in the soil. However, most of the researches were concentrated merely on relationships of atrazine adsorption with soil minerals and content of SOM in natural soil. As soil is very diversified in type and very complex in composition, so far nothing has been done demonstrating quantitatively extents of the effects and contribution rates of SOM and minerals on and to atrazine adsorption. The aims of this study were to investigate characteristics of the adsorption-desorption of atrazine by SOM and minerals, so as to provide some theoretic basis for quantitative analysis of contribution rates of SOM and minerals in atrazine sorption, and some scientific evidence for better understanding and evaluating ecological risk of the organic pollutant in soils different in physic-chemical properties. Six pure minerals (montmorillonite [Mont], kaolinite [Kaol], Ca-saturated of montmorillonite [Mont-Ca] and kaolinite [Kaol-Ca], amorphous hydrated Al and Fe oxides [AHOs-Al, AHOs-Fe]), and three types of soil humic acids (HAs), which were extracted from soils and purified, were selected as the representative sorbents for the study. Structures and physico-chemical properties of the sorbents were analyzed with an X-ray diffractometer (XRD), a surface area analyzer (BET), and total nitrogen and total carbon analyzers. And then adsorption-desorption behaviors of atrazine on these soil minerals and HAs were analyzed with the isothermal batch equilibrium method. Results show that the isotherms of atrazine sorption to all the tested sorbents could well be described with the Frundlich equation (r≥0.982, p<0.01). Humic acid (HA) was the key factor influencing atrazine sorption in soils. A linear adsorption isotherm as was described with the Frundlich model was found (N≈1), with Kd being nearly constant despite changes in Ce. The adsorption of Atrazine was controlled mainly by the mechanism of distributive dissolution and highly reversible. The effects of the three HAs on adsorption of Atrazine and the effect of delaying desorption of Atrazine were significantly related to content of TOC, N, or H in the HAs. Clay minerals (especially Mont) also showed strong Atrazine adsorption capacities, with Kd rising with increasing Ce and an isotherm being S-shaped (N>1), indicating that the adsorption is effected mainly by surface hydrophilic interaction. However, once saturated with Ca ions the clay minerals (Mont and Kaol) reduced their effective adsorbing sites on the surface and in the interlayer lattices and in turn their effects on adsorption and desorption of Atrazine. Kd of AHOs decreased with increasing Ce values and leveled off when Ce reached a certain level. The isotherms all appeared in the shape of an L (N<1), indicating that the adsorption is effected mainly by chemical bonding between the hydroxy on the surface of AHOs and atrazine molecule and moreover, the lowest in reversibility.

Abstract:In response to the growing demand for fruits, farmers in the Taihu Lake region are rushing to convert paddy fields into fruit orchards in recent years. Changes in land-use and management may affect or alter physico-chemical properties of the soil, and hence cycling of soil N and fate of N fertilizer. Up to date, little has been reported on quantification of effects of changes in land use on soil N gross transformation rate, besides some works that have been mainly focused on effects of the conversion of non-agricultural land into agricultural land, and rarely on the effects of the conversion from one type to another type of agricultural land use. In the Taihu Lake region, paddy fields under rice-wheat crop rotation and orchards coverted from paddy fields are the two typical types of agricultural land-use, which differ sharply in water regimes (periodically waterlogged for paddy fields and water-unsaturated for orchards) and fertilizer management (no input of organic manure for paddy fields and combined application of chemical fertilizer and organic manure for orchards). Therefore, gross N processes (e.g., nitrification and denitrification) in the soils under the two types of land use also differ sharply, as affected by their different aeration conditions and fertilizer managements. The paddy field under rice-wheat crop rotation and the vineyard converted from paddy field under study are located in the upper-streams of the Zhushan Bay Catchment in the Taihu Lake Region of China. Gross transformation rates of soil N under the two types of land use were measured using the ¹⁵N tracing technique combined with the Markov Chain Monte Carlo (MCMC) algorithm-based numerical optimization model, and effects of the conversion on soil N supply and N retention capacity were investigated. Results show that the conversion reduced soil pH (from 5.74 in paddy field to 5.14 in vineyard, on average) and contents of soil organic C and total N, though not much. In the soils of the paddy field and vineyard, the inorganic-N pools were dominated with nitrate, with NH₄⁺/NO₃⁻ being 0.26 and 0.06, respectively, and the gross N mineralization rate (mineralization of labile and recalcitrant soil organic matter) was N 3.90 mg kg^-1 d^-1 and 4.52 mg kg^-1 d^-1, respectively. Obviously the differences between the two were not very sharp. In the paddy field, the gross NH4+ assimilation rate was 0.56 mg kg^-1 d^-1, accounting for only 14% of the total NH4+ produced, while in the vineyard it was almost negligible. The gross N autotrophic nitrification rate in the vineyard was 15.85 mg kg^-1 d^-1, significantly higher than that (13.65 mg kg^-1 d^-1) in the paddy field, while the gross heterotrophic nitrification rate and NO₃⁻ assimilation rate were both negligible in both soils. Through fitting with the MCMC algorithm-based numerical optimization model, consumption of NO₃⁻in the soils was found to have two pathways, namely assimilation of NO₃⁻ and dissimilatory reduction of NO₃⁻ to NH₄⁺ (DNRA). However, in both of the soils, NO₃⁻assimilation was not detected, turning DNRA into the major pathway of NO₃⁻ consumption, moreover, the two soils did not differ much in DNRA rate. The ratio of total nitrification to gross NH₄⁺ assimilation (N/NA) in the soil was 24 in the paddy field and 793 in the vineyard, indicating that ammonia oxidizing bacteria are stronger than heterotrophic nitrifiers in competition for NH4+, and hence autotrophic nitrification is the dominant fate of NH₄⁺, especially in the vineyard. On the whole, the conversion of paddy field into vineyard significantly affects soil autotrophic nitrification, increasing the N autotrophic nitrification rate in the soil, but its influence on NH₄⁺ assimilation rate was almost negligible, thus making autotrophic nitrification the only fate for NH₄⁺ in the vineyard. The decreased NH₄⁺ assimilation rate and the increased autotrophic nitrification rate in the vineyard enhanced NO₃⁻ accumulation in the soil, which may in turn increase the risk of N leaching and losing with runoff. It is recommended that nitrification inhibitor and/or organic manure high in C/N ratio should be applied to mitigate the risk.

Abstract:The Loess Plateau of East Gansu is a typical area where rainfed farming prevails. To understand effects of long-term fertilization on soil nitrogen in soil profile is something very meaningful to farmers in doing fertilization in this area and to researchers in enriching scientific knowledge of soil nitrogen nutrition as well. From wheat fields of a long-term fertilization experiment that started in 1978 and had six treatments, i.e., no fertilizer (CK), nitrogen only (N), nitrogen and phosphorous (NP), nitrogen and phosphorous combined with straw return (SNP), manure only (M), nitrogen and phosphorous combined with manure (MNP), soil samples were collected during the booting and summer fallow stages of wheat in 2014 for analysis of soil total nitrogen (total-N), soil available nitrogen (ava-N), soil mineral nitrogen (min-N) and composition of min-N. Results showed that treatments M and MNP obviously improved soil nitrogen nutrition and were significantly higher than the other treatments in total-N, ava-N, min-N in the 0～40 cm soil layers. No big difference in soil total-N was found between the two treatments. They both increased soil total N by 26.2% on averagely in the 0～20 cm soil layer over the original value in the year of 1978 when the experiment started. Treatment SNP was higher in total-N and ava-N than CK but significantly lower than treatments M and MNP. However, total-N in treatment SNP remained almost the same as or was just slightly higher than the original value. Though treatment NP was quite low in total-N and ava-N, it was still higher than treatments N and CK. Treatments N and NP were 13.1% and 6.4%, respectively, lower than the original value in total-N of the 0~20 cm soil layer. The treatments did not vary much in absolute value of NH₄⁺-N concentration in the soil profiles, but treatment N stood out in NO₃^--N concentration throughout the 0～100 cm soil profile, while the other treatments were higher in the topsoil and sub-topsoil layers than in the 40～100 cm or 60～100 cm soil layer. All the fertilization treatments, particularly treatments M and MNP, lowered NH₄⁺-N/ NO₃^--N ratio in the topsoil layer. Treatment SNP tended to increase the proportion of NH₄⁺-N in soil total N and hence NH₄⁺-N/ NO₃^--N ratio in the middle and lower soil layers. The phenomenon was getting more significant with soil depth in the profile during the summer fallow season. To sum up, under rainfed farming in the Loess Plateau of East Gansu, the practices of applying NP in combination with organic manures are superior to the others in building up soil fertility. The application of N or NP only fails to maintain balance of total-N in the soil. The application of chemical nitrogen alone aggravates downward leaching of NO₃^--N, while the practices of manure, NP and NP plus manure application are proved to be able to reduce NO₃^--N leaching. However, NH₄⁺-N is not much affected by fertilization practices. Fertilization changes composition of min-N, but the effects of manure application and straw incorporation differ quite sharply. It is, therefore, suggested that more efforts should be dedicated to the study on fate and transformation of soil nitrogen under rainfed farming in future.

Abstract:Aquatic ecosystems are seriously threatened because of fragile Eco-environment and severe non-point pollution in Three Gorges Reservoir Area of China. Crop/mulberry intercropping is popular because of efficiency to reduce nitrogen (N) and phosphorus (P) loss and control agricultural non-point source pollution. However, there is a huge controversy to achieve optimal crop/mulberry intercropping in the Three Gorges Reservoir Area. In order to optimize the crop/mulberry intercropping pattern in purple dry slope-land so as to improve its effects of soil and water conservation and eco-environment benefits in the Three Gorges Reservoir Area, an experiment with five treatments (i.e. Treatment I: Contour tillage with contour mulberry tree lines on upper-slope, middle-slope and lower-slope, Treatment II: Cross cultivation with contour mulberry tree lines on upper-slope, middle-slope and lower-slope, Treatment III: Contour tillage with contour mulberry tree lines on middle-slope and lower-slopes, Treatment IV: Cross cultivation with contour mulberry tree lines on middle-slope and lower-slopes and Treatment V: Conventional contour tillage.) was carried out in Wangjiagou catchment of the Three Gorges Reservoir Area from January 1, 2014 to December 31, 2014. N and P in surface runoffs was analyzed for forms (ammonium nitrogen, nitrate nitrogen, total nitrogen (TN), dissolved nitrogen (DN), particulate nitrogen (PN) and total phosphorus (TP), dissolved phosphorus (DP), particulate phosphorus (PP)) and annual loading of N and P loss with surface runoff was assessed. Results showed that on the whole, crop/mulberry intercropping significantly retarded N and P losses with surface runoffs, but the effect varied sharply with rainfall intensity and pattern of the intercropping. Treatment II was the most effective in retarding the loss of TN, DN, PN, TP, DP and PP, regardless of rainfall intensity and Treatment III came the next. However, under rainfalls moderate or low in intensity (44.2 mm d^-1 and 53.9 mm d^-1), Treatment I was the most effective in retarding the loss of ammonia nitrogen and nitrate nitrogen, while under rainfalls high in intensity (122.4 mm d^-1), Treatment I was obviously lower than Treatment II and Treatment III in such an effect. Furthermore, the treatments also differed sharply in annual loading of N and P loss with surface runoff because the effects of cultivation practice, location of contour mulberry tree lines, and their interactions on N and P losses were different. Compared with Treatment V, Treatment III reduced TN by 12.8%, TP by 19.3%, DN by 20.2%, DP by 10.9% and PP by 25.7%; Treatment IV reduced TN by 41.7%, TP by 44.7%, DN by 44.7%, DP by 38.1%, PN by 36.1% and PP by 48.5%; Treatment I reduced TN by 23.7%, TP by 42.5%, DN by 25.5%, DP by 40.2% , PN by 19.7% and PP by 44.1%; and Treatment II reduced TN by 43.6%, TP by 58.8%, DN by 45.7%, DP by 55.4% , PN by 39.3% and PP by 61.1%. The nitrogen and phosphorus lost with runoff were dominated with DN (approximately 50.1% ~ 60.2%) and PP (approximately 54.9% ~ 59.6%), and the annual loading of NO₃⁻-N loss (approximately 0.19 ~ 0.27 kg hm^-2 a^-1) was higher than that of NH₄⁺-N loss (approximately 0.12 ~ 0.17 kg hm^-2 a^-1). In conclusion, because of combined effects of cultivation practice, location of contour mulberry tree lines, and their interactions on surface N and P losses, four kinds of crop/mulberry intercropping practices reduced surface runoffs, N and P concentration in surface runoff caused by each rainfall event, and N and P annual loading. But treatment II (cross cultivation with contour mulberry tree lines on upper-slope, middle-slope and lower-slope) is more pronounced in retarding and controlling N and P loss with surface runoff, and therefore it is an optimal intercropping pattern for exploiting the resources of purple dry slope-land in the Three Gorges Reservoir Area of China.

Abstract:Soil acidification is a main form of soil degradation and also a main factor limiting sustainable development of agriculture therein. In recent years, due to aggravating acid deposition and frequent agricultural practices, including increasing fertilization rate, harvesting crops with nutrients removed, etc., soil acidification of the farmlands is speeding up. Therefore how to ameliorate or remedy acidified soils and its mechanism have become subjects of some important theoretical and practical significance to rebuilding healthy soil and guaranteeing national food security. Based on a 34-year long stationary fertilization experiment, effects of no fertilization (CK), application of NPK fertilizer (NPK) and application of NPK fertilizer plus lime (NPK CaO) on soil pH, exchangeable acidity, hydrolytic acidity, soil cation exchange capacity, base-exchangeable ions, rice yield and plant cation absorption, and further on proportion of exchangeable H⁺, Al³⁺ to exchangeable acidity, soil base-exchangeable ions, base-exchangeable ions removal by plant with harvest and their relationships with soil acidity. Results show that long-term application of chemical fertilizers (NPK) leads to soil acidification, and mitigates the effect when lime is amended (NPK CaO). After 34 years of rice cultivation of double cropping system, Treatment NPK was 0.2 and 0.3 lower in soil pH, 2.3 and 4.2 times higher in exchangeable acidity, and 35.4% and 40.0% higher in hydrolytic acidity than CK (p＜0.05) in the soil under early rice and under late rice, respectively, while Treatment NPK CaO was 0.5 and 0.7 higher than NPK, and 0.3 and 0.4 higher than with CK in soil pH in the early and late rice seasons, respectively, and much lower than Treatment NPK and CK in exchangeable acidity and hydrolytic acidity in both rice seasons (p＜0.05). In terms of exchangeable H⁺ and exchangeable Al³⁺, the three treatments in the experiment followed an order of NPK CaO ＞ CK ＞ NPK. Exchangeable Al³⁺ was dominant to exchangeable acidity in acidic soil, and the ratio of exchangeable Al³⁺ to exchangeable acidity increased with increasing soil acidification. The effects of fertilization, regardless of fertilization mode, on soil CEC, exchangeable Ca²⁺, Mg²⁺, exchangeable base ions and base saturation were all very significant. Soil exchangeable base ions were dominated with exchangeable Ca²⁺, accounting for 81.8%-89.3%. Long-term liming significantly increased the content of soil exchangeable Ca²⁺ . Treatment NPK CaO was 40.1% and 62.9% higher in soil exchangeableCa²⁺ than Treatments CK and NPK, respectively. Exchangeable Ca²⁺, exchangeable base ions and base saturation were positively related to soil pH, but negatively to exchangeable acidity and hydrolytic acid, and exchangeable Mg²⁺ was negatively to exchangeable acidity and hydrolytic acid, while exchangeable Na⁺ was negatively to hydrolytic acidity only. Treatments NPK CaO and NPK did not vary much, but were both significantly higher than CK (p＜0.05) in yield of early and late rice. In terms of calcium uptake by rice, the treatments followed an order of NPK CaO ＞ NPK ＞ CK, in terms of potassium and magnesium uptake and total cation uptake by the crop, the followed an order of NPK ＞ NPK CaO ＞ CK, and in terms of sodium uptake they followed an order of CK ＞ NPK ＞ NPK CaO. The removal of Ca, Mg, K and Na and the cations in total with the crops harvested did affect soil pH, exchangeable acidity and hydrolytic acid to a varying extent, but no apparent relationships between them were observed. The findings in this experiment indicate that long-term fertilization plus liming significantly raises soil exchangeable Ca²⁺, exchangeable base cation and base saturation. From the angle of amelioration of acidified soils, long-term liming in addition of fertilization may alleviate the pressure of soil acidification of paddy fields to a certain extent and hence promote ecological remediation and ameriolation of acidic paddy soils.

Abstract:Effects of long-term fertilization on balance, forms and use efficiency of potassium in oasis grey desert soil under a typical crop rotation system as affected by fertilization treatment were studied in an arid area. The long term fertilization experiment was designed to have 9 treatments, i.e., CK (No fertilization), N, NP, NK, PK, NPK, NPKS (NPK plus straw), NPKM (NPK plus organic manure) and 1.5NPKM (1.5 folds of NPKM). Results show that the balanced fertilizer treatments were much higher than the unbalanced fertilizer treatments in yield (except the NP). However, Treatment NP was an exception, and did not differ much from the balanced fertilizer treatments in yield (p>0.05), indicating that the grey desert soil is not in deficit of potassium. Budgeting of soil potassium revealed that only Treatment NPKS was gaining in K, while all the others were losing, with K deficit reaching as high as 268 ~ 2 996 kg hm^-2. Among all the K treatments, Treatments NPKM and 1.5NPKM were the highest in apparent use efficiency of K, reaching up to 81.2% and 38.9%, respectively, much higher than all the others (p<0.05), indicating that addition of manure may improve potassium use efficiency. After the long-term fertilization experiment, potassium varied significantly in form in all the treatments. Treatments NPKM and 1.5NPKM were much higher than all the other treatments（p <0.05）in non-exchangeable K, non-specific absorbable K, water soluble K and exchangeable K, demonstrating the importance of addition of organic manure or straw to NPK in maintaining potassium fertility in grey desert soil. In short, the conventional fertilization method fails to meet K demand of the crops, leading to growing K deficiency in farmlands of grey desert soil. More attention should be given to application of more potassium fertilizer or addition of organic manure or incorporation of crop straw in the farmlands of grey desert soil.

Abstract:Mercury emission from natural resources contributes greatly to global atmospheric mercury, thus having an important impact on circulation of atmospheric mercury. Mercury emission during the earth surface processes is a major natural source of mercury in the atmosphere. In view of the shortcomings of the current methods for determining mercury concentration in soil air, this study has developed a new method. To test the method, soil air was collected from profiles of paddy soils in the Nanjing Liuhe Circular Agriculture Ecological Zone for analysis of total mercury. Using the experimental device, an inverted funnel, soil air in the soil profile was pumped continuously at a low flow rate, into a gold-coated pipe for pre-enrichment of mercury in the soil air. Gold-coated quartz sands were used as adsorbent to collect gaseous mercury in the soil air and the adsorption process lasted 3 hours with adsorption efficiency reaching nearly as high as 100% and relative standard deviation being 2.4%~5.4%. The highest mercury concentration was detected in the soil air extracted from the topsoil layer (0~3 cm) and the concentration decreased significantly with soil depth, but leveled off after the depth went beyond 20 cm. The experiment on effect of sampling flow on accuracy of the measurement, shows that when the sampling flow rate was below 30 ml min^-1 RSD of the measurement was <10.0% and when the sampling flow rate went beyond 30 ml min^-1, RSD increased, which indicates that at a higher flow rate than 30 ml min^-1, the device may suck some air from the atmosphere into its chamber, and a flow rate of 20 ml min^-1 is a safe one that enables the device to extract soil air merely from the soil profile. Then the air samples were analyzed with the cold vapor atomic fluorescence (CVAFS) method. Results show that the absolute detection limit is 0.023 ng m^-3. Air mercury concentration in the paddy soils varied in range from 6 to 18.94 ng m^-3. When the parallel experimental device was used to determine mercury concentrations of the air in the laboratory and soil air in the farmland simultaneously relative standard deviations of two measurements were both <15%. The comparison experiments show that the device collects air samples merely from soil profiles, rather than from the atmosphere above the soil surface. Mercury concentration of the soil air in paddy soils peaked at noon, which may be attributed to the higher temperature in the topsoil, intensive light and effective radiation during the noon time, enhancing photochemical reactions of mercury and increasing mercury concentration in the soil air. The highest concentration of gaseous mercury in the soil air was detected in soils at 6 cm in depth of the soil profile and then in soils at 3 cm in depth, which suggests that mercury in the soil air of the topsoil escapes into the atmosphere rapidly and its diffusion at 6 cm is retarded by soil. Additionally, the higher water content at 6 cm than at 3 cm may provide profitable additions for mercury in soil and soil water to convert into Hg0 in soil air. The soil air in underlying soil layers is relatively stable and less changed, which further proves the method is reliable. This method has the following advantages: during the experiment, lithium batteries power the device, which is easy to operate in the field and capable of collecting soil air at different depths, and enables spatio-temporal synchronization of observation of mercury concentrations in the soil profile. But it should be noted that this experiment can only be carried out in paddy fields unsaturated with soil water and the use of rotameter may lead to errors in flow measurement. This experiment is characterized by simplicity of the devices, and easy operation in field and can be used to precisely and accurately measure gaseous mercury concentrations in soil air in unsaturated paddy fields.

Abstract:【Objecivet】Paichongding, a neonicotinoid type of insecticide recently developed in China, is easily absorbed by plant and transferred inside the plant. Now it is used mainly for controlling insects of homoptera and expected to have a bright future as a promising new pesticide. Once pesticides enter into the soil, they readily get adsorbed, desorbed and leached in the soil. Their sorption and desorption are the main factors influencing fate of the pesticides in the soil, and seriously affecting their behaviors, like chemical and microbial degradation, volatilization and leaching, and moreover, it is an important index in pesticide environmental safety assessment. The study on its adsorption and leaching characteristics is of important significance to prediction of its environmental behavior and pollution in the soil. 【Method】In order to provide a scientific basis for the study of environmental behavior, migration and transformation, of paichongding in the soil, the batch oscillating equilibration method and column leaching method were adopted to explore adsorption and leaching characteristics of paichongding in three typical soils, that is brown soil from Tai’an, red soil from Fujian and black soil from Northeast China, and effects of three soil amendments on leaching of the substance in the soils. Residue of the pesticide in the soil was determined with SPE-HPLC. As in the leachate, the concentration of paichongding was low, the solution underwent concentration and purification with SPE before determination of residue of paichongding in the leachate with HPLC. 【Result】Results show that the adsorption equilibrium time of paichongding was 12 h, 9 h and 12 h in the red soil, brown soil and black soil, respectively, by absorption dynamics. The Freundlich model and the Linear isothermal adsorption model can well be used to describe the adsorption processes of paichongding in soil. Of the pesticide, distribution coefficient, K_d, was 23.16, 11.24 and 4.68, and adsorption constant was 22.03, 11.69 and 5.05 in the black soil, red soil and brown soil, respectively. Among the three soils, black soil was the highest in paichongding adsorption capacity and brown soil was the lowest. The adsorption isotherms of paichongding in three different soils fitted fairly the Freundlich model and Linear model at 25℃, with K_OCbeing 1 619, 2 094 and 495, respectively, and the absolute values of free energy in all the three soils were less than 40 kJ mol^-1, so the adsorption of paichongding in these soils belonged to physical adsorption. Leaching of paichongding varied in the three soils. In the brown soil, paichongding migration rate was the highest, and slightly increased with rising dosage of the pesticide, and the variation with dosage was not significant; In the red soil and black soil, dosage did not have much effect on leaching rate of the pesticide, either, and Only a slight difference in leaching rate was found in the red soil between treatments applied with 200 μg and 500 μg of paichongding. One-way ANOVA analysis of the black soil shows that the effect of dosage was not significant. In the leachate from the brown soil, red soil and black soil, paichongding residue accounted for 16.69%~16.86%, 11.55%~13.52% and 8.98%~9.35% of the total applied, respectively. As the black soil was the highest in adsorption capacity, pesticide in the soil was the lowest in mobility. Residue of paichongding in the red soil and black soil decreased with soil depth, but by a little margin. Once activated carbon was added into the soils, it reduced not only migration and leaching rate of paichongding significantly, but also extractable residue by 34.8%, 36.79% and 16.93%, respectively, in the brown soil, red soil and black soil; No residue was detected in the leachates from the red soil and black soil, while 76.4% less residue was found in the leachate from the brown soil in the treatments amended with activated carbon. The addition of 0.5% humic acid and peat, separately, reduced the leaching rate of the pesticide by 25.1% and 17.1%, respectively, in the brown soil, by 29.7%% and 23.3%, respectively, in the red soil, and by 42.1% and 27.6 %, respectively, in the black soil. 【Conclusion】 In brief, the amendment of 0.5% activated carbon, humic acid and peat into the paichongding-contaminated soils can significantly reduce leaching rate of the substance, and hence its risk of polluting the groundwater.

Abstract:The rhizosphere is a critical interface where exchange of substance takes place between plants roots and their surrounding soil. In the rhizosphere, interactions between the plant and soil microbes, though affected by a series of factors, such as physic-chemical properties of the rhizospheric soil, genotype of their host plant, can be beneficial to growth of the plant, the microbes or both. However, it is still not very clear how long-term cultivation of Lycium bararum L. would affect soil microbial community structure in the rhizosphere of the plant. Therefore, rhizospheric soil samples were collected from Lycium bararum L. fields different in cultivation history (5 a, 10 a and 15 a) in a farm of Nanliang, Ningxia, China, for analysis of physic-chemical properties, such as pH, electrical conductivity, SOM, total salt, total and readily available N, P and K, etc. Results showed that pH remained unchanged in all the fields, while total salt content, total and readily available phosphorus and electrical conductivity in the soil increased significantly with the age of cultivation. Total genomic DNA was isolated from the rhizosphere soil using a Power Soil DNA Isolation Kit for sequence analysis of V4 sections of 16S rDNA as indicator of bacterial diversity and ITS2 sections of 18S rDNA gene as indicator of fungal diversity, with the aid of the Illumina MiSeq system. Results of the sequencing were assembled and clustered with the FLASH, QIIME, and UPARSE pipeline software packages. In the end, is was found that the α diversity of the rhizosphere bacteria community did not vary much between the fields different in cultivation history, but fungal diversity did, and decreased with the cultivation going on from 5 a to 10 a (p﹤0.05). For analysis of changes in microbial community structure at the phyla and genus levels, the software of RDA Classifier to denote each OUT by species. It was found that Proteobacteria (22.2%), Crenarchaeota (15.1%), Bacteroidetes (13.9%), Acidobacteria (12.4%), Chloroflexi (10.3%), Gemmatimonadetes (4.8%), Actinobacteria (4.7%), Planctomycetes (4.0%) and Verrucomicrobia (2.0%) were the dominate bacterial groups and Ascomycota (29.5%) and Basidiomycota (11.7%) were the dominant fungal group in the rhizosphere of the plant. However, about 55.8% of the fungi found in the rhizosphere were still unknown in the taxonomy. Besides, the sequencing further demonstrated that soil microbial community structure in the rhizosphere varied sharply between the fields different in cultivation history and stood out uniquely in each field from the others. The variation between fields different in cultivation history was particularly significant in terms of the ratio of Acidobacteria, Actinobacteria, Bacteroidetes, Fimicutes, Chloroflexi, Crenarchaeota, Cyanobacteria, Gemmatimonadetes, Proteobacteria, Ascomycota, Basidiomycota and Zygomycota in the rhizospheric microbial community (p﹤0.05). The protion of unknown fungal groupsin taxonomy was much higher in the 10 a (76.6%) and 15 a (61.4%) Lycium bararum L. fields than in the 5 a (32.5%) fields (p﹤0.05). The analysis at the genera level also shows that the ratios of 27 genera of bacteria and 16 genera of fungi changed with the cultivation going on (p﹤0.05). In order to further analyze relationships of soil community, with soil physic-chemical properties, hundred-grain weight and cultivation history, SPSS 16.0 software was used to work out pearson’s correlation coefficients between the data, which show that cultural history is significantly related to richness of Firmicutes, Proteobacteria, Verrucomicrobia, Basidiomycota and Zygomycota (p﹤0.05), content of total phosphorus in the rhizosphere soil is to richness of Firmicutes, Gemmatimonadetes, Proteobacteria, Basidiomycota, Zygomycota (p﹤0.05) and content of readily available phosphorus is to richness of Acidobacteria, Gemmatimonadetes, Ascomycot, Basidiomycota and Zygomycota (p﹤0.05). The findings further demonstrated that the three factors, cultural year, total phosphorus and readily available phosphorus, are the key factors affecting soil microbial composition in the rhizosphere of Lycium bararum L. To sum up, cultivation history affects soil microbial community structure more than soil microbial diversity in the rhizosphere soil of Lycium bararum L., which may be related to soil phosphorus metabolism in the rhizosphere.

Abstract:Being the largest carbon pool of the forest ecosystem, soil carbon is a very important component of the carbon cycle in the system, and being a vital part of the soil respiration of the terrestrial ecosystem, soil respiration of the forest ecosystem influences significantly the global carbon balance. However, so far little research has been done on soil respiration of the forest ecosystems in southeastern Tibet. Therefore, in order to investigate soil respiration and its influencing factors relative to type of the forest ecosystem, a field experiment was conducted using an LI-8100 (Nebraska, USA) to measure soil respirations in four different types of forests [Alpine shrubs (AS), Sabina saltuaria (SS), Rhododendron forest (RF) and Abies georgei var. smithii forest (AGSF)], typical of the Sygera Mountains of the Southeast Tibetan Plateau, for analysis of soil respiration dynamics and their major affecting factors therein. Results show that the soil respirations varies sharply in a day and with the seasons. Diurnally, CO₂ emission flux follows an apparent one-peak pattern of peaking around 16:00 and bottoming around 06:00, while seasonally, it did another of beginning to rise in June when the weather turns warm and the vegetation starts to grow in June, peaking in July, when the air temperature is the hottest in a year in that region, and starting to decline in September, when the air temperature begins to descend. In the four types of forest ecosystems, soil respiration rate during the vegetation growth season is positively related soil temperature of the surface layer (10 cm) to a varying extent, but not so much to soil moisture content. In terms of soil respiration rate, the 4 different types of forest ecosystems follows an order of AGSF > RF > SS >AS. The determination coefficient of the relationship between soil respiration and soil temperature varies with the type of the forest ecosystem in the range of 0.47~0.72, demonstrating that the relationship reaches the significant level. On such a basis, it can be concluded that soil temperature is a primary constraint on soil respiration and soil water plays a secondary role. Type of the vegetation or ecosystem also affects soil respiration in the region, which causes differences between AS, SS, RF and AGSF in seasonal variation of soil respiration (p < 0.001). The Q₁₀ value of soil respiration is higher at high elevations than at low elevations. The findings indicate that in the case of global warming in the future, soils higher in elevation might contribute more CO₂ to the atmosphere. In short, the findings may serve as reference for the study on rules of the variation of soil respiration in forest ecosystems and mechanisms for controlling its affecting factors, and are sure of some important significance to budgeting of global carbon and assessment of regional carbon sources and pools.

Abstract:In arid and semi-arid ecosystems, shrubs often create patches of soil underneath spatially heterogenous in distribution of soil water and nutrients, which are called “fertile islands” or “resource islands”. Although the so-called “fertile island” is a phenomenon of spatial heterogeneity in distribution of soil water and nutrients at a plant scale, it may have some great impacts on vegetation distribution, productivity and evolution processes (like desertification) of the ecosystem. Therefore, the phenomenon of “fertile islands” has attracted more and more attention from more and more researchers. So far, researches have demonstrated that distribution pattern of the soil resources underneath shrub canopies was related to soil depth, plant species, plant development stage and spatial scales (e.g., rhizosphere, individual, population, geomorphology, and region). However, little has been reported on spatial pattern of soil resources relative to soil textured soil, especially in desert soils. This calls for further attention. In this study, two different types of native habitats of Haloxylon ammodendron in the Junggar Basin were selected: the Gurbantonggut Desert and nearby oasis. Haloxylon ammodendron is a dominant species in arid regions of Central Asian, playing a key role in maintaining structure and functions of these desert ecosystems. Aeolian sandy soil and grey desert soil are the zonal soils of the two habitats and have developed under the same climatic conditions and experienced the same weather process, but are markedly different in mechanical composition even though they are only 8 km apart. Specifically, the aeolian sandy soil is of loamy fine sand soil, and the grey desert soil is silt loam soil. The former is 2.1 ~ 2.4 times as high as the latter in sand content, while the latter is 3.0 ~ 3.6 and 2.9 ~ 5.1 times as high as the former in silt and clay content, respectively. This provides an ideal environment for determining whether the effect of individual plants on spatial variability of soil properties under their canopies might be mediated by soil texture. In each of the two native habitats, eight Haloxylon ammodendron plants similar in size (about 200 cm in plant height, about 10 cm in basal diameter and about 100 cm crown radius) were selected. For soil sampling, the soil under each plant was divided vertically into three soil layers, 0 ~ 20, 20 ~ 60, and 60 ~ 100 cm. Then in each soil layer, four sampling sites were set representing four micro-habitats, that is, near the taproot, in the center of the shrub canopy, at the edge of the canopy, and in the space between two shrubs, or at 5, 50, 100, and 200 cm away from the taproot, respectively. At each sampling site, soil samples were collected at four directions of the site, with an angle of 90˚ apart and then mixed into one for analysis of soil properties, soil texture, water, organic carbon, available nitrogen, and available phosphorus with a laser particle analyzer, the oven-drying and weighing method, the K₂Cr₂O₇–H₂SO₄ oxidation method, the alkalysis diffusion method, and NaHCO₃ extraction–Mo-Sb colorimetric method. Through comparative analysis of the soils under the canopies of Haloxylon ammodendron in the two habitats in spatial distribution of soil water and nutrients, attempts were made to characterize “fertile islands” in the two soils sharply different in texture. Results showed that (1) spatial heterogeneity of soil water and nutrients existed in both soils under the canopies of the shrubs, and weakened with soil depth; and (2) at the soil depth of 0 ~ 20 cm, the aeolian sandy soil was more obvious in spatial heterogeneity of the distribution of soil water and nutrients than the grey desert soil under the canopy of Haloxylon ammodendron, and higher in enrichment level of soil water and nutrients, too. The former was 4.6 ~ 12.3, 3.4 ~ 8.6, 3.0 ~ 4.9 and 2.1 ~ 2.6 times as high as the latter in enrichment rate of soil water, organic matter, available nitrogen and available phosphorus, respectively. All these findings indicated that the phenomenon of “fertile islands” caused by shrubs exists in both soils, and soil texture may determine intensity of the “fertile island” effect. Knowledge of the spatial variability pattern of plant resources at individual scale may help better understand spatial distribution pattern of the resources at the population, community, and ecosystem scales, as well as relationships between soils and plants. Further studies need to be done on such a phenomenon in different ecosystems.

Abstract:Samples of soils low in phosphorus availability were collected from the National Monitoring Base for Purple Soil Fertility and Fertilizer Efficiency for an indoor experiment, which was designed to have 9 treatments, in terms of phosphate application rate (P₂O₅ 0~150 mg kg^-1 ) and had the soil samples incubated for 75 days, after P fertilizer in the form of disodium dihydrogen pyrophosphate was amended. Analysis of the incubated samples shows that the application of a proper rate of P significantly stimulated the growth of nitrifying bacteria and that of a higher rate had a reverse effect. Treatment 20 (P₂O₅20 mg kg^-1) was the highest in number of the bacteria. Potential nitrification rates (PNR) of the soil samples were determined with the aerobic incubation method and the suspension method, separately. PNR increased in all the treatments to a varying extent and Treatment 50 (P₂O₅ 50 mg kg^-1) was found to be the highest in PNR. The effect of phosphorus on soil nitrifying capacity is similar to that on PNR in tendency. However, further study is needed mechanisms of phosphorus application rate affecting soil nitrification.