Abstract:Atmospheric nitrogen (N) and phosphorus (P) deposition increases soil nutrients available for plants, change chemical quality of the substrates, as well as composition and function of the soil microorganisms, thereby affecting storage and stability of the soil organic matter (SOM) in forest soils. However, the studies reported in the literature focused mainly on effects of N enrichment on carbon (C) sequestration in natural forest ecosystems, with little eyesight on effects of P enrichment and interaction of N and P on soil organic carbon (SOC) sequestration of in artificial forests as well as their microbiological mechanisms. In this paper, a review is presented of effects of N and P enrichment on C transformation and net C exchange fluxes, priming effect of SOM, chemical composition and stability of SOM, and composition and functions of microbial communities mediating C turunover in forest soils; moreover, the authors also shed light on deficiencies in the present researches, as follows. (1) Nonlinear response equations of soil C flux and its components in response to N and P enrichment in forest soils as well as their critical thresholds have not yet been determined; (2) Little is known about effects of N and P enrichment on priming effect of SOM in forest ecosystems and microbial mechanisms; (3) In-depth researches on mechanism of the physico-chemical synergic stabilization of SOM under N and P enrichment are far from sufficient; and (4) It is still unclear how composition of soil active microbial community and SOM chemical structure is related to SOC accumulation. Therefore, the authors hold that future researches should foucs on the following aspects: Based on the established multi-level N and P addition and ¹³C-labeled incubation experiments, effects of N and P addition and their interaction on soil C emission and loss fluxes, microbial priming effect, composition and chemical stability of SOM, and functional microbial community composition are to be determined using the techniques of in-situ monitoring, soil chemistry (¹³C-NMR and Py-GC/MS), and macrogenomics of molecular biology, etc.. Besides, more efforts should be laid on (1) defining the nonlinear equations for responses of soil C emission and loss to N and P addition as well as critical loads of atmospheric N and P depositions; (2) elucidating coupling relationships between composition of the soil decomposing microbial community and SOC transformation and stability; and (3) exposing microbial mechanisms responsible for the effects of N and P interaction on soil C accumulation and depletion in forest ecosystems, especially in subtropical plantations. All the findings in this review will help control C losses from forest soils, reduce uncertainties in assessing “N promoted C sink” in terrestrial ecosystems, and hence provide a scientific basis for subtropical plantations or forest ecosystems to deal with global change.

Abstract:Soil-borne diseases have become a major bottleneck restraining sustainable development of the agriculture in China. Rhizosphere is a window displaying how efficiently a crop uses soil nutrients, a key micro-domain of plant-soil-microbe interactions, as well as a major scene where soil-borne diseases develop. Today when metagenomics is developing so rapidly, any knowledge about interactions between rhizosphere microorganisms and soil-borne fungal diseases is conducive to exploration for effective ways to prevent and control soil-borne diseases from the aspects of microbial community, metabolic function, and disease suppressants. With reference to the databases of Scopus, Web of Science and China National Knowledge Infrastructure, a review is presented in this paper summarizing relationships between soil-borne fungal diseases and rhizosphere microorganisms, discussing pathogenesis of soil-borne disease fungi, and pointing out shortages of the current researches and focal points for future researches. Currently, the incidence of soil-borne fungal diseases is very high in agricultural production of the country, and incidence of most soil-borne fungal diseases is the result of complex infections of a variety of pathogens. Oriented optimization of the structure of rhizospheric microbial communities is an effective way to enhance their antagonism to soil-borne fungal diseases for control of incidence of the diseases. So it is a noteworthy method. So far, quite a number of papers are found in the literature addressing relationships between rhizosphere probiotic microorganisms and health and growth of plants, but few are exploring impacts of harmful bacteria in the rhizosphere on incidence of soil-borne diseases and crop growth. Studies in future should be oriented to systematically assess the incidence and damage of soil-borne fungal diseases, classify soil-borne pathogens by type, explore in depth micro-ecological mechanism of rhizosphere in incidence of soil-borne diseases, and develop a comprehensive technological system for management of soil-borne diseases.

Abstract:Soil moisture is an integral part of the water, energy and biogeochemical cycle. The information about soil moisture is of great significance to researches on water resources management, agricultural production and climate change. Soil moisture monitoring can be divided into three categories in light of data acquisition method: direct measurement at monitoring sites, simulation and assimilation of soil moisture, and inversion based on remote-sensing data. The remote sensing technology features large-scale synchronous observation, covering a range that is not limited by the distribution of ground stations. Then the remote-sensing data based inversion algorithm of soil moisture is an important means of obtaining soil moisture information. However, as soil moisture is strongly influenced by a variety of factors, such as soil properties, surface coverage and meteorological conditions, it is high in spatial heterogeneity. So, it is very difficult to derive large-scales high quality soil moisture data just based on inversion with a single method or single data source. In this paper, factors affecting the inversion of soil moisture were collated, four synthetic multi-featured models for soil moisture inversion were summarized, and existing problems and developmental trends of the inversion processes analyzed. The eigenvariances currently used in soil moisture inversion can be generally sorted into three categories: soil, vegetation and meteorological characteristics. Soil characteristics can be further divided into soil optical reflectance, thermal infrared, microwave brightness and temperature and microwave backlash scattering coefficient, and vegetation characteristics into vegetation optical reflectance and thermal infrared, while meteorological characteristics include rainfall, wind speed, and evapotranspiration and so on. In this paper, synthetic models for mult-featured eigenvariance inversion of soil moisture were summarized, that is, Temperature Vegetation Soil Moisture Dryness Index model (TVMDI), partition statistics model, benchmark value plus variation model, and artificial neural network model. TVMDI is a cubic model based on land surface temperature, vertical vegetation index and soil moisture, and its use enhances correlativity of prediction with measured value. The partition statistics model is to choose an optimal model for each region for inversion, through analyzing types of land cover. The benchmark value plus variation model is to divide the variation of soil moisture during a specified observation period into benchmark value and variation. The former represents the bottom of soil moisture during that period, and the latter depends on precipitation, evapotranspiration and some other meteorological factors, while integrating remote-sensing meteorological information. The artificial neural network model integrate multi-featured eigenvarianes into soil moisture inversion. The analysis of existing problems in and developmental trend of the use of eigenvariance in soil moisture inversion process indicates that the research on adoption of the theory of eigenvariance in soil moisture inversion is insufficient and comprehensive application of the theory is not deep enough, and stresses that coupled application of various ergenvariances may improve accuracy of soil moisture inversion, which is the hot spot of future researches.

Abstract:Rapid development of greenhouse cultivations has made substantial contributions to meeting the increasing demands of the urban and suburban resident population for vegetable and fruits and to improving farmers’ economic status in China in the past four decades. However, due to inappropriate applications of nutrients, phenomena of soil degradation, like acidification, secondary salinization, nutrient unbalance, and unusual accumulations of N, P, K, and S appear commonly in the soils under greenhouse only a short time after setting up of the greenhouse, seriously affecting sustainable development of the greenhouse farming in China. As scientific researches in this aspect lag far behind the rapid developments of the greenhouse cultivation, nutrient management of greenhouse cultivation encounters a series of scientific and technological problems that call for urgent solution. In the paper, issues, like how to determine appropriate nutrient application rates for greenhouse cultivations, how to judge whether the soil nutrient supply, including macro-, medium-, and micro-elements, is in balance, how to evaluate environmental impacts of the nutrient management in greenhouse cultivation, and how to remove unusual surpluses of nutrients in the greenhouse soils, particularly sulfur, which is usually applied with phosphorus and potassium fertilizers, are discussed. It is held that it is essential and urgent to organize forces to launch system researches on the micrometeorology, soil water movement, growth and nutrient uptake of crops, and soil nutrient transformation in greenhouses with high multiple cropping index, particularly mechanisms of the interactions between water, soil, air and crops and their effects on soil nutrient availability, so as to alter the status of scientific researches lagging behind the production practices as quick as possible.

Abstract:【Objective】It is a precondition for making proper use of these precious data like soil maps to judge mapping precision of historical soil type maps.【Method】A map marked as 1: 250 000 scale Fujian Province soil map plotted on the basis of the soil survey data of the Second National Soil Survey, was collected and digitized into a vector soil map, which was rasterized by taxonomical hierarchy. From each level of the hierarchy, 50 raster grains, varying in interval from 30 m to 8 000 m, were selected for calculation of 15 landscape indices of each grain in three taxonomical levels, i.e. great group, subgroup and family, separately, using Fragstats 4.2, a software for landscape pattern analysis, and further for analysis of responses of the landscape indices to variation of the raster grains. Five landscape indices, i.e. TA, PR, PRD, SHDI and SHEI, were selected as indices to quantitatively evaluate soil mapping precision. The landscape indices corresponding to grains 30 m×30 m in size were set as benchmarks. Comparison was made of landscape indices corresponding to grains of various sizes with the benchmarks. Given that when the absolute values of relative variability (VIV, %) of all the selected landscape index are less than 1%, the corresponding maximum grain size is deemed as the optimal characterization grain size for data conversion from parent vector soil map to raster soil map. Then based on the functional relationship, y= -0.80×10^-6x² + 0.0 228x + 0.0 211（R² = 0.9994，P< 0.05), between optimal characterization grain size and soil mapping scale, soil mapping scales could be deduced and mapping precision of the map quantitatively evaluated. 【Result】Results show that landscape index is obviously grain-size dependent, and based on the trend of landscape indices varying with rising grain size, grain-size dependence of landscape indices could be divided into four types, i.e. Type I: landscape indices increasing with rising grain size, such as PAFRAC and AREA_SD; Type II: landscape indices declining with rising grain size, such as TE, LSI, COHESION and AI; Type III: landscape indices varying irregularly with rising grain size, such as LPI, DIVISION, MESH and SPLIT; and Type Ⅳ: landscape indices remaining almost unchanged or fluctuating later on with rising grain size, such as TA, PR, PRD, SHDI and SHEI. The optimal characterization grain size at the soil great group level, subgroup level and family level is 4.00 km×4.00 km, 3.45 km×3.45 km and 1.90 km×1.90 km, respectively, and their corresponding soil map scale, 1: 1 800 000, 1: 1 600 000 and 1: 850 000, respectively, which all differ significantly from the marked map scale 【Conclusion】This study provides a novel and effective way and method to judge mapping precision of historical soil maps, which is of great value to correctly judge and utilize precious historical soil data.

Abstract:【Objective】Soil bulk density (ρb) is one of the most important soil physical properties and can be used to characterize soil quality and soil productivity and as a basic parameter to assess soil carbon and nitrogen storage. Furthermore, ρb has a significant effect on transport of soil water and solutes. However, large-scaled soil databases do not encompass much ρb data, owing to the time- and labor-consuming methods to acquire such data, especially the data of deep soil layers in the field. This study was conducted to (1) explore characteristics of regional spatial variation of ρb relative to soil layer across the loess area, (2) determine effects of soil texture, topography, climate and land use on ρb and (3) compare the stepwise regression method with the pedotransfer function method in simulation of spatial variation of ρb.【Method】A total of 243 sampling sites were set based on a grid sampling scheme (40 km×40 km) in the loess area, and ρb of the soils at the depth of 0~10, 10~20 and 20~40 cm of the soil profile and relevant environmental variables, were collected separately, at each sampling site. Spatial variation of ρb was analyzed with the classical statistic method and geostatistical method, respectively. Stepwise regression equation and pedotransfer function equation was used to simulate spatial distribution of soil ρb, separately.【Result】Results show that ρb varied moderately within a soil layer, and generally increased with soil depth in the profile loess area. ρb variability in the 0~40 cm soil layer was moderate according to the coefficient of variation. In general, cropland was the highest in mean ρb, and followed by forestland and grassland. Semivariance of soil ρb of the 0~10, 10~20 and 20~40 cm soil layer can be best fitted by the exponential model, the exponential model and the spherical model, respectively. Soil ρb of the 0~10 cm soil layer exhibited strong spatial dependence and those of the 10~20 and 20~40 cm soil layer did moderate ones. The optimal interval between sampling sites was 5.6~11.2, 70.9~141.7 and 195.4~390.8 km for the 0~10, 10~20 and 20~40 cm soil layer, respectively. Silt content, land use, elevation and slope gradient were the key factors affecting soil ρb in the 0~10 cm layer; silt content, elevation, multi-year mean annual air temperature, aridity and land use were in the 10~20 cm soil layer; and silt content, elevation, land use, multi-year mean annual precipitation, slope gradient and aridity, were in the 20~40 cm soil layer. The pedotransfer function equation explained 38%~52% the variation of ρb, while the stepwise regression equation did only 34%~39%.【Conclusion】Spatial distribution of soil ρb varies significantly with soil depth and vegetation type across the loess area, and is affected jointly by soil texture, topography, climate and land use at the regional scale. The pedostransfer function equation is recommended for modeling and predicting spatial distributions of ρb, particularly for soil layers below 40 cm in the loess area of China.

Abstract:【Objective】In order to comprehensively understand how the soils in the Helan and Liupan Mountains of Ningxia Province were developed and should be classified in soil taxonomy, a total of 10 soil profiles were selected out of the typical ones dug and prepared during the Soil Series Survey of Ningxia Province, 5 (Profile 3, 11, 13, 14 and 108) in the Helan Mountain and 5 (Profile 73, 82, 119, 120 and 121) in the Liupan Mountain area, for the study. 【Method】Firstly, locations of the 10 soil profiles were defined with the aid of ArcGIS and GPS; the profiles re-prepared for examination with soil-forming environment and profile morphology described and documented; and then soil samples collected from each soil layer of the profiles for analysis of physicochemical properties. 【Result】Based on the morphological characteristics and soil physicochemical properties of the 10 profiles, attempts were made to elucidate soil development features and determine niches in soil taxonomy. Results show that in the Chinese Soil Taxonomy, the 10 soil profiles could tentatively be sorted into the four soil orders, i.e. Primosols, Cambosols, Argosols and Isohumosols, five soil suborders, i.e. Orthic Primosols, Ustic Cambosols, Udic Cambosols, Boric Argosols and Udic Isohumosols, and six soil subgroups, i.e. Calcaric Aridi-Orthic Primosols, Typic Hapli-Ustic Cambosols, Typic Molli-Ustic Cambosols, Mollic Bori-Udic Cambosols, Typic Hapli-Boric Argosols, and Mottlic Hapli-Udic Isohumosols. Further on, they could tentatively be sorted into 10 soil families, i.e. Coarse bone sandysilica mixture mesic-Calcaric Aridi-Orthic Primosols, Coarse bone sandyfeldspar typical mesic-Calcaric Aridi-Orthic Primosols, Sandyfeldspar mixturecalcareous frigid-Mollic Bori-Udic Cambosols, Sandysilica mixture calcareous frigid-Mottlic Hapli-Udic Isohumosols, which are completely separated ones, and still further into 10 soil series, including Putaoquan series, Yidui series, Gunzhongkou series, Liupanshan park series, Lvyuanyao series, etc. 【Conclusion】Altitude is the major factor affecting development characteristics of the soils in the mountains of Ningxia. With rising altitude the soils show apparent humus accumulation processes, intensifying leaching processes through the solums, weakening lime reaction till nil, and improving soil moisture regime. At the bottoms of the solums of the mountain soils high in altitude, weak redox reaction occurs, forming iron and/or iron-manganese colloids and reducing soil pH, thus causing certain changes in soil acidity and alkalinity. Affected by the soil forming environment and factors, soil development rules are reflected in the diagnostic horizons as a certain vertical variation rule along the altitude. The diagnostic surface horizons have their mollic epipedons turned into ochric epipedons, their soil moisture regimes from aridic/ustic into udic, and their soil temperature regimes from mesic into frigid.

Abstract:【Objective】Soil color is a reflectance spectra characteristic of the soil in the visible light band and also a kind of visual perception. The Munsell color chart is a traditional tool to determine Munsell color of soils, however, soil color determination by color charts may be subjective due to the impacts of human subjective consciousness and environmental conditions. With advancement of the optical technology, numerous instruments have been developed one by one for determining soil colors, such as spectrographs, digital cameras, and even more convenient mobile phones that can all be used to determine soil colors. However, spectrometers are often quite expensive and bulky, and digital cameras and mobile phones are not so easy to get calibrated. So portable colorimeters pop up as a new type of tool that has the advantages of being small in size, easy to carry, and moderate in price. The use of colorimeters to determine soil colors helps to avoid subjective factors and some objective environmental factors, and hence improves work efficiency. The object of this study is to compare the New Standard Soil Colour Charts with two types of portable colorimeters in determining Munsell color of soils, in an attempt to find out differences between them and select a superior one for determination of Munsell color of soils.【Method】A total of 97 soil samples of 27 soil series were collected in the Central Sichuan hilly region, for determination of Munsell color after they were purged of plant and animal residues, air-dried, ground to pass a sieve, and mixed to get homogenized, separately. Each sample under went three treatments, that is, determination of Munsell soil color, with the New Standard Soil Colour Charts, Nix and CM600d, separately. The data of hue, value and chroma of soil Munsell color could be achieved directly via ocular estimation of the sample against the New Standard Soil Colour Charts, the use of CM600d, and the use of the color conversion formula to process the CIE XYZ data obtained with NIX. Then with the help of statistical parameters and rules for grading differences in Munsell soil color, comparison was done of the data obtained with the three different methods.【Result】The hue of the air-dried soil in Central Sichuan hilly area lingered mainly in YR, with 5YR and 10YR appearing the most frequently, or 33 and 30 times, respectively. The soil classified as purple soil in the Chinese Soil Genetic Classification System, after being air-dried, did not show any hue of RP, and lingered in the range of 4~8 in value and in the range of 2~6 in chroma, with "value/chroma" ratio being 5/3, 5/4, 6/4 and 7/4, the most frequently, indicating that the soils tested were quite high in value, but low in chroma. With the result of the ocular estimation method as reference for comparison, the Munsell soil color obtained with the colorimeter method tended to be yellowish and agreeable value and chroma. The RMSE of hue, value and chroma measured with the CM600d was 1.74, 0.98 and 0.97 unit, respectively, and that with the NIX was 2.04, 0.57 and 0.88 unit, respectively. The difference between the ocular estimation method and the colorimeter methods in Munsell soil color could be graded into “Faint”, “Distinct” and “Prominent”, which was 90.72%, 8.25% and 1.03%, respectively, for CM600d and 84.54%, 14.43% and 1.03%, respectively for NIX.【Conclusion】 The two kinds of colorimeters are useful to help researchers measure Munsell soil color, and improve accuracy of the measurement, too. The Nix method is closer to the ocular estimation method in measuring value of the Munsell soil color and moreover superior in price.

Abstract:【Objective】Remote sensing technology has successfully been applied to monitoring and inversion of soil parameters. In order to further promote application of the Synthetic Aperture Radar (SAR) technology to less-destructive soil monitoring and environmental management, based on the field survey and sampling, laboratory experiments and interpretation of microwave radar images, this study explored possibilities of inverting and predicting soil hydraulic parameters of semi-arid grassland basins on the premise of no large scaled damage.【Method】In this paper, the Xilin River Basin, Inner Mongolia was set as subject for the study. The study area had 5 major types of soils, i.e. Thick chestnut soil, Meadow swamp soil, Desert aeolian soil, Limy meadow sandy soil, and Pale black soil. From the surface layers of the soils, soil samples were collected for analysis of particle size composition, bulk density, organic matter content, saturated hydraulic conductivity ( K_s) and some other physical and chemical properties. First of all, distributions of soil parameters in soil layers, 10 cm each, of the five types of soils were characterized. Then Saxton, Cosby, and Wosten models, three saturated soil hydraulic conductivity pedo-transfer functions (PTFs) and nonlinear multivariate empirical regression models, were used for fitting of K_sin soil layers, 10cm each, within the 0~30 cm soil layers of the 32 sampling sites for modeling. Based on the averages of the soil parameters of these 32 sampling sites for modeling and backscattering of quadrupolarized Radarsat-2, a multivariate linear equation was established, using the radar data of the 10 sampling sites for validation to validate the fitting of K_s.【Result】Results show that the study area is extremely high in soil sand content, almost nil in clay content and low in organic matter content. The parameters do not vary much with soil depth from layer to layer. In terms of PTFs, the four models reach 0.778, 0.985, 0.958, and 0.966 in modeling accuracy separately. Among them, Saxton model is the highest, with RMSE being 0.262 and layer average validation accuracy reaching 0.989. In terms of inversion of surface soil parameters based on back scattering coefficient of quadrupolarized RADARSAT-2, the inversions of bulk density and sand content are the best. In using the backscattering coefficient of the 10 validating sampling sites to validate PTFs, Saxton model is superior in fitting, with simulation coefficient reaching as high as 0.964. Consequently, this study has finally chosen Saxton model to predict surface soil saturated hydraulic conductivity on an 8 meter precision extended scale based on remote-sensing images of the study area, by combining Radarsat-2 radar data.【Conclusion】All the findings indicate that compared with inversion directly using SAR to predict surface soil K_sin a large-scale, PTFs may better depict saturated conductivity of the surface soil layer in semi-arid grassland watersheds. However, the effect of PTFs are not directly related to the number of parameters contained in the model. Surface soil K_s in the degraded grassland varies generally in the range of 4～8 m•d^-1. Under natural conditions, the region lacks vegetation and high in sand content, which are the main reasons for rapid water transfer. In developed areas, like irrigation zones or urbanized regions, surface soil K_sdeclines by a large margin, indicating that human activity is one of the main influencing factors of its change. The use of remote sensing to predict surface soil KS over a region is still not fully developed, so more efforts should be done to perfect and validate it.

Abstract:【Objective】The water-bearing layers in the Dagu River Basin are distributed mainly in a long and narrow strip of area alongside the middle and lower reaches of the Dagu River, forming a huge underground reservoir, which is one of the major water sources supplying water to Qingdao. Currently, the groundwater resource in the Dagu River Basin has been over-exploited causing a series of environmental problems, like seawater intrusion, surface subsidence, etc. With rapid development of the economy and population in the region, the problem of water resource shortage significantly constrain sustainable development of Qingdao. To enhance comprehensive management of the water resources in the region, it is essential to accurately assess groundwater recharge. Although much work has been done on groundwater recharge, few of the relevant researches have taken into account the transformational relationship between soil water and groundwater, which has resulted in big gaps between the calculation of groundwater recharge and the reality. This study aimed to establish a soil water and groundwater coupled model, with which to analyze movements of soil water and groundwater in the studied region, and further to calculate accurately groundwater recharge in the Dagu River Basin under the current precipitation and irrigation conditions.【Method】Based on the principle of the software of HYDRUS package for MODFLOW coupled with the GIS technology, a basin-scaled (4 781 km²) soil water and groundwater coupled model (SWGCM) was developed. The model was used to simulate moisture movement between vadose and saturated zone, flux at the bottom of a profile was worked out through multi iteration of the Richards-1D equation, using the HYDRUS sub-model within each time step of the MODFLOW model, and through calculation of the acquired flux, the MODFLOW model yielded a new groundwater table, which was used as water head value at the bottom boundary for the next step of calculation. With all the relevant data put under comprehensive consideration, including precipitation, evaporation, plant water absorption, soil texture, aquifer distribution, and soil water and groundwater related parameters, such as groundwater exploitation capacity, soil moisture content, and groundwater table, the SWGCM model was used to simulate movement of soil water and groundwater in the Dagu River Basin, and accuracy of the model was varied through fitting of soil water content and groundwater in the soil profiles.【Result】Results show that the simulated soil profile moisture content and groundwater table well agree with the measured data. In the calibration phase, the determination coefficient of the soil profile moisture content in the soil profile varies in the range of 0.65~0.91, and the RMSE in the range of 0.005~0.01; and that of the groundwater table does in the range of 0.52~0.68, and of 0.12~0.38, respectively, while in the validation phase the determination coefficient of the soil profile moisture content does in the range of 0.53~0.86, and the RMSE in the range of 0.006~0.011 and that of the groundwater table in the range of 0.56~0.81 and of 0.17~0.19, respectively. The fitting of soil profile moisture content and groundwater table indicates that the SWGCM model is good enough to simulate water movement in variably-saturated porous media and groundwater recharge. In the calibration phase, the groundwater recharge is 315 million m³, and in the validation phase, 477 million m³.【Conclusion】To accurately assess groundwater recharge, it is necessary to take into account the relationship between soil water and groundwater in movement. The SWGCM model can be used to accurately simulate spatio-temporal variation of the soil water and groundwater in the Dagu River Basin, and hence to calculate vertical infiltration supplementary capacity of groundwater in the region with quite high reliability and accuracy. Therefore, the SWGCM model may provide certain scientific basis for development of a rational allocation of water resources of the basin and an effective approach, too, to accurate assessment of groundwater recharge.

Abstract:【Objective】 In order to explore effects of oxygen level (0%, 1%, 3%, 10% and 21%) and carbon input on major sources of N₂O emission in greenhouse vegetable soil, an on-line robotized monitoring and incubation system was used to automatically monitor real-time dynamics of O₂, N₂O and N₂ in greenhouse vegetable soil after a crop of tomato was harvested. In addition, dicyandiamide (DCD), a kind of nitrification inhibitor, was added to investigate contribution of nitrification to N₂O emission from the soil relative to carbon source and oxygen level.【Method】 A certain amount of soil sample collected from a vegetable field under greenhouse after a crop of tomato was harvested, was washed with deionized water and divided into two groups, labeled as T1 and T2, separately. T2 was spiked with glutamate, whereas T1 was not. NH₄NO₃ was added as nitrogen source for both groups. Then the pretreated soil samples were put into 120ml vials, 10.0 g in dry soil weight in each. Deionized water or solution containing NH₄NO₃, C₅H₈NO₄Na·H₂O or DCD was sprayed onto the soil surface to adjust moisture content of the soil up to 250 g·kg^-1 in line with the requirement of the treatment, T1 or T2. Then the soils in the sealed vials were placed in a thermostatic (20°C) waterbath trough for incubation. Concentrations of O₂, N₂O, N₂ and CO₂ in the headspace of a vial were monitored online at intervals of 6 h, and pure O₂ was supplemented with a hermetic syringe in the light of the monitoring results of the gases in the headspace to maintain an approximately constant oxygen concentration (1%, 3%, 10% or 21% (v/v)) in the sealed vials. 【Result】Results show that N₂O emission declined exponentially with rising soil oxygen partial pressure (OPP) (R²=0.82, P＜0.001). It peaked when OPP was 0% or 1%, and fell below 30% of the peak when OPP got equal to or higher than 3%. Addition of available carbon into the vial reduced N₂O and N₂ production in the soil under aerobic conditions, while significantly increasing the contribution of the process of heterotrophic denitrification in the soil to N₂O emission under near-anaerobic conditions (P＜0.01), which suggests that this kind of soil is highly capable of triggering heterotrophic denitrification, and anaerobicity and near-anaerobicity is more favorable to N₂O emission. Compared with Group T1, Group T2 was 64.4% and 88.8% lower in N₂O emission, 23.4% and 18.6% lower in N₂ emission, and 14.5% and 62.3% lower in N₂O/(N₂O+N₂) index (I_N2O), respectively, when OPP was 1% and 3% and no carbon supplemented. However, when carbon was supplemented, the two groups did not vary much in N₂O and N₂ emissions and I_N2O, which suggests that strong nitrification occurs in the soil with no carbon supplemented and N₂O comes mainly from heterotrophic denitrification process (HD) under aerobic conditions in the soil with sufficint carbon supply. DCD would lower the accumulation of NO₂^-, a substrate of nitrification-coupled denitrification (NCD), which is considered to be an important contributor to N₂O emission under aerobic conditions; nevertheless, the process of NCD is still a heterotrophic one in nature. That is to say, DCD would reduce N₂O emission from nitrification processes, and from heterotrophic denitrification processes, too. With OPP rising from 1% to 3%, N₂O emission from nitrifier-induced denitrification (ND) increased from 17.2% to 42.6%, however, the contribution of ND to N₂O emission in the vegetable soil was still quite low due to the drastic reduction in total N₂O emission. Moreover, the commonly used dual isotopic labeling method would lead to overestimation of the contribution of ND to N₂O emission because this method may rule partial NCD or HD processes into ND. As the soil in this study was quite high in pH and remained almost unchanged in nitrate content after the treatment with DCD, simultaneous heterotrophic nitrification-denitrification processes might be very weak. 【Conclusion】Soil N₂O emission mainly occurs under anaerobic and near-anaerobic conditions (OPP=1%). Heterotrophic denitrifiers make the biggest direct contribution to soil N₂O emissions, especially when carbon sources are abundant. NO₂^- is an important substrate of the process of nitrification-coupled denitrification.

Abstract:【Objective】soil nitrification potential (NP) and its main influencing factors in fluvo-aquic soils were studied based on a long-term fluvo-aquic soil fertilization experiment in Zhengzhou, Henan Province. 【Method】Three tracts of farmlands of fluvo-aquic soil different in fertility level, i.e. High (applied with chemical fertility plus organic manure); Moderate ( applied with balanced chemical fertilizers); and Low (applied with no fertilizer or no N fertilizer), were selected for soil sampling for analysis of total N (TN), ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N), microbial biomass C (MBC) and microbial biomass N (MBN). And stepwise regression analysis, path analysis and variance decomposition analysis (VDA) were performed to define main influencing factors in fluvo-aquic soil relative to soil fertility and quantify contribution of each factor to NP. 【Result】Results show that NP in the fluvo-aquic soils varied in the range of 0.3 mg•kg^-1•h^-1~1.1 mg•kg^-1•h^-1, and differed significantly between the soils. It was 7.9% higher in the soil high in fertility than in the soil moderate in fertility, and 162.5% higher in the soil moderate in fertility than in the soil low in fertility. Among all the soil fertility indices, MBC, NO₃^--N, TN and MBN were found to be the main influencing factors of soil NP. MBC, NO₃^--N and MBN affected NP directly, while TN did more indirectly. The contribution rate of microbial biomass (MBC and MBN), NO₃^--N and TN to NP variation is worked out to be 24.3%, 18.9% and 13.7%, respectively. The contribution of four main influencing factors’ interaction effects to the variation of soil nitrification potential has reached to 52.8%, while the total contribution of each variant and its interaction effects amounted to 92.9%. Therefore, it can be concluded that nitrification is much stronger in soils of high fertility than in soils low and moderate in fertility. 【Conclusion】As result of strong nitrification, ammonium nitrogen is nitrified into nitrate nitrogen, which is readily accumulated and/or leached. It is, therefore, essential to regulate soil water and nutrient regimes to a proper level so as to reduce soil nitrification intensity and eventually achieve the target of constructing a nitrogen nutrient pool and reducing nitrogen loss in fluvo-aquic soils.

Abstract:【Objective】 Soil carbon pool plays an important role in the process of global change. In eroded red soil, restoration of vegetation may enhance soil carbon sequestration, which is of great significance to retardation of global change. But how it does still remains unclear. Soil respiration is an important link between the soil and the atmosphere in CO₂ exchange. To a certain extent, the flux of soil carbon emission determines whether the soil is a sink or a source of carbon in the ecosystem. It is, therefore, essential to study impacts of vegetation restoration on soil respiration and its temperature sensitivity (Q10) for better understanding of the mechanism of soil carbon sequestration in severely eroded red soil. 【Method】In this study, two Pinus massoniana plantations, 13 years old (Y13) and 31 years old (Y31), in Hetian Town, Fujian Province, were selected for comparison with a tract of virgin land (Y0) nearby. Soil respiration in the three tracts of land were monitored monthly with a LI–8100 (Nebraska, USA) from April 2015 to March 2016, and soil temperature (in the 0~5 cm soil layer), soil water content (in the 0~12 cm soil layer), litter biomass, soil organic carbon, total nitrogen, C/N and soil microbial biomass carbon were also determined simultaneously. Besides, a structural equation model was developed to analyze relationships of soil respiration and its temperature sensitivity with soil and its environment factors so as to identify potential driving factors affecting soil respiration and its temperature sensitivity.【Result】 The highest peaks of soil respiration rate appeared during the period from June to August, while the valleys did from December to February, Soil respiration varied in the range of 0.89~1.44 μmol•m^-2•s^-1 in Y0, 2.00~3.85 μmol•m^-2•s^-1 in Y13 and 1.78~4.16 μmol•m^-2•s^-1 in Y31. Obviously it did not vary much seasonally in Y0 (P>0.05), but did in Y13 and Y31 (P<0.05). Soil respiration was significantly higher in Y13 and Y31 than in Y0 (P<0.05), but did not differ much between Y13 and Y31, and was much more sensitive to temperature in Y13 and Y31 than in Y0 (P<0.05), with Q10 being 1.66, 1.58 and 1.27 respectively. On a seasonal scale, no apparent relationship was observed between soil respiration rate and soil water content, but a positive one was between soil respiration and soil temperature in the surface layer (5 cm), with soil temperature explaining 25.3% of the variation of soil respiration rate in Y0, 66.5% in Y13 and 48.8% in Y31; Analysis of the affecting factors with the structure equation model demonstrate that soil respiration and its temperature sensitivity are dominantly affected by litter biomass and soil microbes.【Conclusion】All the findings in this study demostrate that ecological restoration significantly increases soil respiration, with increased litter input and henced enhanced soil biochemical processes being the dominant factors. It is, therefore, expected that they may serve as reference for the further study on rules of the variation of soil respiration and machanisms of the factors affecting ecological restoration in degraded ecosystems.

Abstract:【Objective】 Moso bamboo is a typical type of forest resource widely distributed in South China. Its expansion, however, has caused a number of ecological problems, especially emission of soil N₂O and CO₂ in the groves as affected by nitrogen deposition, which has rarely any research papers, let alone in-situ field observation data. 【Method】In this study, the static chamber technique was used to monitor N₂O and CO₂ emission rates, cumulative N₂O and CO₂ emissions and their responses to simulated nitrogen deposition in pure moso bamboo forest, moso bamboo - Japanese cedar mixed forest and pure Japanese cedar forest in Lushan Mountain, Jiangxi Province. 【Result】Results show: (1) the content of NH₄⁺-N, content of NO₃^--N, and pH in the mixed forest soil was 14.39 mg•kg^-1, 8.65 mg•kg^-1, and 4.88, respectively, significantly higher than their respective ones in the Japanese cedar forest soil (i.e. 9.75 mg•kg^-1, 5.58 mg•kg^-1 and 4.05), but the former (236.5 mg•kg^-1) was much lower than the latter (382.0 mg•kg^-1) in DOC content; (2) the cumulative N₂ O emission in the mixed forest (393.6 mg•m^-2) was significantly higher than that in the moso bamboo forest (202.5 mg•m^-2) and that in the Japanese cedar (192.8 mg•m^-2), while the cumulative CO₂ emission in the mixed forest (4 655 g•m^-2) was significantly higher than that in the Japanese cedar forest (2 815 g•m^-2); and (3) simulated nitrogen deposition had no significant effect on CO₂ emission rate and cumulative CO₂ emission in the three types of forest soils, but significantly increased cumulative N₂O emission in the Japanese cedar forest soil and mixed forest soil. 【Conclusion】 All the findings indicate that the soils varied in physicochemical property and N₂O and CO₂emission characteristics with the expansion of moso bamboo. Expansion of moso bamboo did increase N₂O and CO₂ emission from the soils to a certain extent. However, when the expansion completed, like in the moso bamboo forest, emissions of N₂O decreased significantly, while emission of CO₂ did not change much. Meanwhile, nitrogen deposition promoted N₂O emission from the Japanese cedar forest soil (no bamboo intruding) and the mixed forest soil (early stage of moso bamboo expansion), but had no significant effect on CO₂emission. It is, therefore, suggested that in management of moso bamboo expansion in subtropical China under future meteorological conditions, it is essential to take into account effects of composition and structure of the ecosystem and other various affecting factors.

Abstract:【Objective】In order to make effective use of aquatic plants wildly growing in the Taihu Lake Valley, composting is an important way. This study is to investigate effects of using aquatic plant compost as manure on wheat yield and soil nutrient status with a view to promoting effective utilization of aquatic plant residues. 【Method】A field experiment was carried out for four years successively from 2012 to 2016 in the Taihu Lake region, preparing compost of aquatic plant residues as manure to substitute part of the N fertilizer (mineral urea) applied to a wheat field to explore effects of the substitution on wheat yield, NPK uptake, contents of soil NPK and soil pH. The field experiment was designed to have six treatments, different in substitution rate (0, 20%, 40%, 60%, 80% and 100%), but the same in N supply. Grain yield of wheat, nitrogen, phosphorus and potassium uptake by the plant, contents of soil total nitrogen, soil available phosphorus, soil readily available potassium and soil pH value in the top soil layer were monitored. 【Result】Results show that compared to Treatment M0U100 (application of mineral urea alone), Treatments M20U80 and M40U60 (20% and 40% of mineral urea substituted by the compost, respectively) was 14.0% and 13.5%, respectively, higher in total cumulative wheat grain yield, however, the increment decreased in magnitude with the substitution rate increasing over 40%, and Treatment M60U40 was even significantly lower than Treatment M0U100 in N content in shoot and N uptake. The substitution significantly increased P and K concentrations in the grain. However, with rising substitution rate, crop uptake of P and K exhibited a trend of rising first and then declining. After four years the practice, the contents of soil total nitrogen, soil available phosphorus and potassium, and soil pH in the plough layer were all higher than in the control, showing a trend of the higher substitution rate, the more significant, the increase. 【Conclusion】In summary, to improve the grain yield of wheat meanwhile maintain the soil fertility, Treatment 40%, that is, to apply compost of aquatic plant residue as manure to substitute 40% of the mineral urea to be applied is the optimal option, which can increase yield and phosphorus and potassium utilization efficiency of the crop, and contents of nitrogen, phosphorus and potassium in the soil, and also alleviate soil acidification. Therefore, the practice of applying mineral urea and a proper amount of compost of aquatic plant residue as substitute is an economical and environment-friendly fertilization technology in the Taihu Lake region.

Abstract:【Objective】 The aim of this study is to explore reasonable nitrogen (N) fertilizer management mode in Fluvo-aquic soil of the Huanghuai Plain, in an attempt to provide certain theoretical and technical basis for accomplishing the goal of zero growth in consumption of chemical fertilizer in China. 【Method】A stationary field experiment was carried out in Fengqiu of Xinxiang, Henan Province, a typical grain crop growing region of China, from October 2015 to September 2017. Then experiment was designed to have four treatments on N fertilizer application, concerning mode, i.e. Treatment T1 (application of loss control urea once as basal), Treatment T2 (application of conventional urea split as basal and topdressing), Treatment T3 (application of loss control urea as basal and conventional urea as topdressing), and Treatment T4 (application of conventional urea as basal and loss control urea as topdressing), and four N application rates for each treatment, i.e. (0, 80, 160 and 240 kg·hm^-2). All the treatments, except Treatment T1, received 60% the fertilizer as basal and 40% as topdressing at the jointing stage of winter wheat and at the flaring stage of summer maize.【Result】 Results showed that average grain yield per crop, average annual yield, and average annual economic benefit increased first and then decreased with rising N application rate, but average nitrogen use efficiency (NUE) declined gradually all the way. Among the treatments, Treatment T1 160 kg·hm^-2 in rate was the highest in yield and economic benefit. In addition, it was also found that Treatment T1 varied sharply from all the other three (T2, T3 and T4), which did not between themselves, in wheat grain yield, annual yield, annual crop output and annual economic benefit. Furthermore, analysis of the economic benefits of the two years showed that, Treatment T1 was lower in labor cost than all the others, the same in N application rate, because it saved the labor for topdressing, and moreover it was relatively high in yield. So among the treatments, Treatment T1 was relatively higher in, economic benefit. 【Conclusion】 Based on the equation of analog curve between yield and N rate, it is found that the application of loss control urea 160~173 kg·hm^-2 in application rate, is relatively suitable to the studied area where rural labor is quite limited, and hence has a vast prospect of extrapolation.

Abstract:【Objective】Nowadays, application of straw directly or after it is pyrolyzed into biochar is the main practice of straw resource utilization. However, how application of straw directly or after it is pyrolyzed into biochar affects transformation of nitrogen is still not clear.【Method】A field experiment was carried out to explore effect of the application on transformation of fertilizer N in calcareous cinnamon soil and its possible mechanism. Sorghum uptake, residual in soil and losses of fertilizer N were studied using the ¹⁵N isotope technique. The experiment was designed to have three treatments: NPK (chemical fertilizer only), NPK+B (chemical fertilizer with straw biochar), and NPK+S (chemical fertilizer with straw). 【Result】Sorghum nitrogen absorption rate, soil N retention rate, and N loss rate in the experiment was determined to be 18.4%~24.9%, 22.7%~35.5% and 46.1%~52.4%, respectively. Compared with NPK, NPK+B and NPK+S was 2.20 and 6.53 (P<0.05) percentage point respectively lower in sorghum nitrogen absorption rate and 3.40 and 6.28 (P<0.05) percentage point lower in N loss rate, but 5.58 (P<0.05) and 12.80 (P<0.05) percentage point higher in soil N retension rate. Besides, NPK+B and NPK+S was 23.5% (P<0.05) and 4.3% respectively higher than NPK in content of soil organic carbon, 2.8% and 19.4% higher in soil labile organic carbon, 25.0% and 13.4% higher in population of soil bacteria, and 29.4% and 161.1% higher in population of fungi. Moreover, NPK+S was 103.7% and 72.8% higher than NPK+B and NPK in AWCD (Average well color development) value after 96 hours of incubation. 【Conclusion】In conclusion, application of straw or straw-derived biochar may reduce nitrogen absorption rate of sorghum, increase N retention rate, and lower N loss rate in the calcareous cinnamon soil. Application of straw significantly increases soil labile organic carbon, soil microbial population and metabolic activity, which in turn improves nitrogen transformation from nitrogen fertilizer to soil nutrient, and consequently reduces N loss rate. Straw returning or application o straw directly is an effective measure to improve availability of nitrogen fertilizer to the crop in the calcareous soil and promote reasonable utilization of the straw resources.

Abstract:【Objective】 Application of Se fertilizer is an important agronomic rice Se biofortification measure, and is usually done in two ways, i.e. foliar spray (FS) and application in soil (SA). However, as affected by the way of Se application, Se absorption and translocation of Se into rice grain varies in mechanism. Therefore, it is of great practical significance to study the differences between the two Se application methods in effect on Se absorption and translocation and nutritional quality of rice. 【Method】 A pot experiment was conducted to study mechanisms of FS and SA affecting Se biofortification and nutritional quality of rice grains. 【Result】 Results show that the two methods did not vary much in effect on rice growth. The same in Se application rate, the two methods both increased Se content in rice shoot and grain significantly. However, the content of Se in rice shoot and grain was 8.9 and 5.3 times as high in SA as in FS, respectively, which indicates that SA could more effectively increase Se content in rice grain than FS. But the distribution coefficient of Se in grain was 2 times higher in FS than in SA, which demonstrates that the mechanism of transporting Se from leaf into grain was more effective than that from root to grain. However, no significant effect on Se form in rice grains relative to Se application method, which indicates that Se application methods affected only transport, rather than assimilation of Se in rice. SA could significantly increase the contents of magnesium (Mg), sulfur (S), iron (Fe), manganese (Mn) and zinc (Zn) in rice grain. Compared with the control (No Se applied), SA and FS was 8% and 4.5% higher in content of crude protein in rice grain, respectively, which shows that Se can improve nutritional quality of rice, and the effect of SA was more significant than that of FS. Meanwhile, Se application can also increase the content of serine (Ser) and tyrosine (Tyr) as compared with CK, and, the effect on Tyr was more significant in SA than that in FS or 1.15 times as higher in the former than in the latter. 【Conclusion】Therefore, considering cost-effectiveness, SA is better than FS in applying selenate, for it improves more significantly Se content and nutritional quality of rice grains.

Abstract:【Objective】Contributions of fertilization to crop yield and soil fertility are key parameters in evaluating whether the fertilization practices are reasonable or not. In order to provide some scientific basis for decision-making in fertilizing and developing sustainable agriculture in the Heilu soil region of the Loess Plateau, this paper tried to explore in-depth contribution of fertilization to crop yield and soil fertility in a long-term stationary field experiment in the region, relative to treatment.【Method】The long-term experiment, which has been carried on since 1978, was designed to have six treatments, that is, CK (no fertilizer), N (single chemical fertilizer of N), NP (chemical fertilizers of N and P), SNP (straw and chemical fertilizers of N and P), M (single organic manure) and MNP (organic manure and chemical fertilizers of N and P).【Result】Results show that accumulative yields of wheat and maize were significantly and positively related to the number of years the crops had been cultivated in all the treatments with determination coefficients R² being all higher than 0.95. The crop of maize and wheat in treatment MNP, SNP, NP and M reached 8 856, 7 089, 7 226, 7 043 kg·hm^-2 and 4 916, 3 747, 4 132 and 3 868 kg·hm^-2, respectively, in mean annual yield, significantly higher than that in the control (CK). However, among the four treatments, treatments SNP, M and MNP were similar to or higher than treatment NP. The relationships between the contribution of N fertilizer and P fertilizer to accumulative yield and the number of years of cultivation could be well fitted by quadratic concave function and convex function, respectively. In treatments NP and SNP, the contribution was significantly and positively related to the number of years of cultivation, reaching 3 407 and 2 191 kg·hm^-2, respectively with maize 429 and 208 kg·hm^-2 respectively with wheat, in accumulative yield. Treatments MNP and SNP significantly increased the contents of soil organic matter and total nitrogen, while treatments CK and NP slightly increased the content of soil organic matter only, and treatment NP almost had no impact on soil total nitrogen. Treatment NP significantly increased soil Olsen-P content, while treatment MNP significantly increased the content of soil Olsen-P content and the content of available potassium, as well.【Conclusion】All the findings listed above suggest that long-term balanced application of chemical fertilizers, application of organic manure, application of chemical fertilizers coupled with straw returned, and application of chemical fertilizer in combination of organic manure all can increase crop yields and improve soil fertility quality, that the suitable fertilizer application rate should be N 90 kg·hm^-2 and P₂O₅ 75 kg·hm^-2, and that in fields where straw returning is adopted, P fertilizer could be applied once every two years in the Heilu soil area of the Loess Plateau, China.

Abstract:【Objective】The objective of the study was to investigate effects of tillage on soil bacterial diversity and soil properties in upland under a wheat-bean rotation system.【Method】A long-term stationary field experiment was started on tillage in an upland in Central Gansu in 2001. The experiment was designed to have four treatments, i.e. Treatment T (conventional tillage), Treatment NT (no tillage), Treatment TS (conventional tillage with straw returned), and Treatment NTS (no tillage with straw mulched).【Result】Results show: 1) Compared with Treatment T, Treatments NTS and TS significantly increased the contents of soil organic carbon, soil total nitrogen, soil microbial biomass carbon and soil microbial biomass nitrogen in the 0~10 cm and 10~30 cm soil layers, especially Treatment NTS, which increased the contents of soil organic carbon, soil total nitrogen, soil microbial biomass carbon and soil microbial biomass nitrogen by 28.27%, 114.16%, 13.51% and 49.14%, respectively, in the 0~10 cm soil layer and by 39.86%, 98.05%, 10.78% and 40.72%, respectively, in the 10~30 cm soil layer; 2) Acidobacteria (26.42%), Proteobacteria (19.86%) and Actinomycetes (19.44%) were the main dominant groups of bacteria, accounting for 26.42%, 19.86% and 19.44%, respectively, of the total population of the soil bacterial community in the upland. Treatment NTS increased the abundance of the three groups by 35.11%, 33.77% and 30.17%, respectively; and 3) Compared with the traditional tillage, the three conservation tillage practices increased the soil microbial in the 0~30 cm soil layer in Observed-species index, Chao index, Shannon index and Simpson index, and the effect of treatment NTS was the most significant.【Conclusion】Therefore, conservation tillage practices such as no-tillage with straw mulching would not only increase soil carbon and nitrogen sequestration, improve abundance and diversity of the soil bacterial community and soil biological activity, but can also promote sustainable development of the agriculture in the dryland farming area of Central Gansu.

Abstract:【Objective】 In recent years, domestic and foreign scholars have conducted in-depth researches on modes of comprehensive farming of paddy fields, but with focus mostly on mixed cultivation of rice and fish or crab. There are a few studies done on the mode of rice- crawfish rotation, with focus leaning on technology and economy of the mode, rather than on its effects on evolution of the paddy soil per se in the paddy field. Therefore, this study was oriented to explore effects of rice-crawfish rotation relative to cultivation history on physical and chemical properties of the soil , in an attempt to elucidate how the soil evolves in physicochemical properties under long-term rice-crawfish rotation, and provide certain scientific basis for guiding farmland management under such a cultivation model.【Methods】In this study, paddy fields, similar in soil and irrigation/drainage conditions, were selected within the scope of an irrigation/drainage ditch. Soil samples were collected by layer in a paddy field under mono-cropping of mid-rice as CK and paddy fields under rice-crawfish rotation different in cultivation history ( 1, 7, 13 ,18 and 23 years. and labeled as CR1, CR7, CR13, CR18 and CR23, respectively) for analysis of soil pH, bulk density, porosity, total nitrogen, alkaline nitrogen, available phosphorus, available potassium, cation exchange capacity (CEC), and soil oxidizable organic carbon (ROC).【Results】Results show that long-term rice-crawfish rotation significantly reduced soil bulk density and increased non-capillary porosity, capillary porosity, and total porosity in the 0~20 and 20~40 cm soil layers, but did not have much effect in the 40~60 cm soil. In the paddy field, 1 year old in rotation, soil pH, total nitrogen, and oxidizable organic carbon content increased significantly, but available nutrient and cation exchange capacity did not as much. Compared with the paddy field 1 year old in rotation 1 a, the paddy fields, 7~13 years old in rotation, were significantly higher in soil pH and other indices, and the paddy fields over 13 years old in rotation, soil pH, total nitrogen and content of available nutrients increased the most significantly in the 0~20 cm soil layer, but did not change much in physical and chemical properties in the 20~60 cm soil layer. In terms of significance of the changes in soil pH and other indices in the 0~20 cm soil layer, the paddy fields displayed an order of 23 a> 18 a> 13 a> 7 a> 1 a> 0 (CK), and pH, total nitrogen, alkali-hydrolyzable nitrogen, available phosphorus and available potassium in the 20~40 cm and 40~60 soil layers had similar trends, though not so significant. 【Conclusion】Therefore, it can be concluded that long-term rice-crawfish rotation helps improve soil structure of the plough layer of the field, and increase soil buffering capacity, soil pH and contents of available nutrients, such as nitrogen, phosphorus, and potassium.

Abstract:【Objective】 Soil texture is one of the important physical propertries of soil, which seriously affects the water holding and ventilation characteristics of soil. It is significant to study the unified soil texture classification system.【Method】In view of the chaos phenomenon of using soil texture classification systems in China, the study introduces some important standards for grading of soil particles prevailing home and abroad, compares the characteristics of four soil texture classification systems, and retrospects the use of the experiment-CCCP’s Kazhinski system during the first phase of the Second National Soil Survey of China and the shift to the international system later, with focus on comparison of the standards for soil texture classification adopted by the nation and various departments in the country. 【Result】Nowadays, there is no such a soil texture classification system that can universally be used in China.【Conclusion】It is, therefore, recommended to use the American system .