Abstract:The characterization of soil hydraulic parameters and their heterogeneity is related to many scientific problems in soil and groundwater fields. Due to the limitation of time and sampling cost, the traditional experimental approaches cannot address this issue adequately. With the development of Internet of Things technology, the state variables related to soil water movement (such as water content and pressure head) can be acquired in real time through sensors. This has sparked some debates about how to estimate the soil hydraulic parameters using these measurements. Data assimilation methods can estimate the soil hydraulic parameters by integrating the measurements into numerical models. This paper systematically analyzes the uncertainty sources and measurement approaches of soil hydraulic parameters, expounds on the basic principles of several common data assimilation methods and their applications in soil hydraulic parameter inversion, and discusses the latest advances in data assimilation methods from aspects of computational efficiency and accuracy. Finally, the development direction of data assimilation methods is provided. The results show that the data assimilation methods can break through the limitation of the traditional experimental approach, and thus are suitable for the characterization of soil hydraulic parameters and their heterogeneity. However, limitations such as the strong nonlinearity of the unsaturated flow model, spatial heterogeneity of soil and sparsity of in-situ measurements do exist. It is, therefore, essential for us to unfold in-depth research on soil hydraulic parameter inversion from the aspects of supervised dimension reduction method, multi-source and multi-scale data fusion, and coupling of machine learning with physical mechanisms, thereby assisting agricultural soil and water management as well as the prevention, control, and remediation of pollution in agroecosystems.

Abstract:Global climate change and population growth exacerbate various biotic (e.g., infection of pathogens) and abiotic (e.g., drought, salinity, high temperature, etc.) stress in agricultural production, which impede plant growth, development and productivity by affecting plant morphology, physiological and biochemical characteristics as well as metabolic functions. Consequently, this affects crop yield and quality and seriously threatens agricultural sustainability. With the vigorous development of modern agriculture, beneficial microorganisms have attracted much attention due to their ability to improve soil quality and fertility, stress tolerance in crops, and their yield and quality. Besides, the proper use of microbial inoculum in agricultural production can achieve the effects of reducing the amounts of agrochemicals, reducing production costs, improving the quality of agricultural products, and protecting the ecological environment, which is also in line with the agricultural production goal of harmonious coexistence between humans and nature. In this review, the types and application effects of plant growth-promoting bacteria (PGPB) were briefly summarized, with emphasis on the analysis of PGPB's ability to produce phytohormone, fix nitrogen, facilitate the absorption and utilization of nutrients (phosphate and potassium solubilization and siderophore production), alleviate biotic and abiotic stress, regulate plant root architecture and rhizosphere microbial community structure. Moreover, the frontier science and technology of PGPB inoculum preparation and application methods in modern agriculture in recent years were systematically explored, and the application prospect and research direction of PGPB in future agricultural production were further discussed.

Abstract:【Objective】Improving the spatial prediction accuracy of soil attributes is of great significance for achieving accurate fertilization of farmland and protecting the ecological environment. 【Method】Soil organic matter (SOM) data was collected from 1773 samples from soil surface layer (0-20cm) of cultivated land in Luanping County, Hebei Province. The optimal environmental variables were screened through a stepwise regression analysis method. Multiple linear regression (MLR), ordinary kriging (OK), random forest (RF), Bayesian regularized neural network (BRNNBP), and the corresponding three integrated models combined with a geostatistical model (MLR-OK, RF-OK and BRNNBP-OK) were utilized to predict SOM content via the training set including 1426 sampling points. Also, the prediction accuracy of each method was compared with 347 sampling points of the testing set. Autocorrelation analysis was carried out based on the residual of the integrated model to evaluate the fitting effect of the model. 【Result】Results showed that the range of SOM content in the study area was 8.62～35.64 g·kg^-1, and the coefficient of variation was 20.26%, which showed a moderate spatial variation. High concentrations of SOM were mainly distributed in the northeast and southeast areas with higher altitudes, while relative low concentrations of SOM were mostly observed in the southwest and central valleys of the study area. Elevation, slope and temperature selected by stepwise regression were closely related to SOM content (P<0.001). The lowest average absolute error and the root mean square error of the BRNNBP-OK model were 2.162 g·kg^-1and 2.801 g·kg^-1, respectively. Compared with the OK, MLR, RF, BRNNBP, MLR-OK and RF-OK models, the goodness of fit of the BRNNBP-OK model increased by 1.84%～43.72%, making it an optimal model for SOM spatial prediction. Compared with the single model, the nugget coefficient of the integrated model residual was greater than 0.75, and the Moran's I was less than 0 and numerically closer to 0, indicating that the spatial autocorrelation of the integrated model residual was weakened and the residual presented a more discrete spatial distribution. At the same time, the accuracy of all models was significantly correlated with Moran's index of model residuals. 【Conclusion】In this study, the integrated model fitted more trends and the spatial aggregation of model residuals decreased and even tended to be discrete. Thus, the overall prediction accuracy of the integrated models was improved.

Abstract:【Objective】Soil quality problems often arise in the process of greenhouse agriculture pursuing economic benefits. There are also signs of soil quality changes in the Tibet Plateau greenhouse land, and the regional differentiation pattern of soil quality changes in the Lhasa Valley. The Lhasa Valley is the main distribution area of greenhouse plots on the Tibet Plateau. Nevertheless, there is limited research that integrates the physical and chemical properties of its soil to reflect overall soil quality changes in the facility farmland with a comprehensive index, and the overall soil quality changes and their regional differentiation patterns are not yet clear. 【Method】Taking the arable land soil samples as the references, this study collected 240 soil samples of greenhouse land and 112 soil samples of arable land. The texture, pH value, water-soluble total salt content, organic matter, total nitrogen, alkali-hydro nitrogen, total phosphorus, available phosphorus, total potassium, available potassium, and soil heavy metals elements (Cr, Ni, Cu, Zn, Pb, Cd, As, Hg) were determined. The comprehensive soil quality index and factor detector methods were used to study the soil quality changes and spatial differentiation characteristics of the greenhouse land soil in Lhasa Valley, and the main factors of soil quality changes in the greenhouse land soil were identified.【Result】The comprehensive soil quality indices of the Lhasa valley greenhouse land and the arable land soil were 0.36, and 0.43, respectively. The soil quality grades of 80% of both samples were distributed in V～III. The soil quality of the greenhouse land was relatively high on the sunny slopes within 930 m from the river at an altitude of 3, 700～3, 750 m in the area. Secondly, there were spatial differences in the degree of soil quality variation in the study area. The SQI of the greenhouse land decreased by 16.28% on average compared to that of the larger field farmland. Among them, soil quality in the Doilungdeqen county decreased most significantly, with an average decrease of 74.46%. At different depths, soil quality decreased most significantly in the range of 0～10 cm, in which the average decline was 6.5%, and the highest percentage of declining sample plots, at 66.67. Thirdly, there was spatial heterogeneity in soil quality changes in the greenhouse land affected by altitude and slope direction. With the increase of elevation and the change of soil quality from sunny slope to shady slope, the change of soil quality in the agricultural land facilities showed a significant trend of increase. Finally, analysis of the soil quality change factors in greenhouse land found that the soil quality change in the whole region was generally affected by changes in salt content, available potassium and cadmium content, and the explanatory power of all three could reach 20%.【Conclusion】Under the changing influence of salt accumulation, available potassium and cadmium content changes, the overall soil quality of the study area's greenhouse land showing a decreasing trend and varied significantly in different regions. This could provide a theoretical basis for the layout and development of greenhouse agriculture in the region.

Abstract:【Objective】Under the background of high-intensity soil resource utilization, digital soil mapping has become an effective method to obtain and characterize soil information quickly, efficiently and accurately. The accuracy and reliability of soil spatial prediction and digital mapping are restricted by multiple factors, such as soil sample size, sampling strategy, prediction model, the complexity of geomorphology and soil-forming environment in the target region, and quality of covariate data. 【Method】Choosing Henan Province as the study region, we applied five of the most representative machine learning (ML) algorithms to spatially predict and digitally map the topsoil pH of croplands. Afterwards, the impact of different sample sizes and sampling methods on the performance of the chosen ML models and the prediction accuracy of topsoil pH were compared. 【Result】The results showed that: (1) When the soil sample size increased from 200 to 2 000, the performance of all ML models and prediction accuracy of topsoil pH showed a general trend of rapid increase regardless of the sampling method. When sample size reached and exceeded 2 000, the performance of most ML models tended to be stable, and the prediction accuracy of topsoil pH increase rapidly slowed down, suggesting that a soil sample size of 2 000 might be the sample size threshold for these ML models to predict the topsoil pH of croplands in this area. (2) The performance of the five ML models and their topsoil pH prediction accuracy was significantly different. The tree-based ML models, namely Random forests (RF) and Cubist performed best. No matter which sampling method was used, when the sample size was more than 2 000, the archived coefficient of determination (R²) of the two models could be stable between 0.75 and 0.80, and the RMSE could be kept below 0.50. (3) When the soil sample size was large enough, the sampling method had little impact on the ML model performance. Also, the topsoil pH prediction accuracy and the sampling method gradually highlighted when the soil sample size was less than 2 000. Comparatively, Conditioned Latin hypercube sampling (clhs) had advantages when the sample size was small. When the sample size was 1 000, clhs sampling method could still keep the R² of random forest and Cubist prediction at about 0.80. Even when the sample size was as small as 200, the R² archived by all five ML models under the clhs sampling method was above 0.55. (4) The uncertainty analysis showed that 73.9% of the observed values of topsoil pH of the validation samples fell into the 90% Prediction Interval (PI) of the random forest model, indicating that the reliability of the model was slightly overconfident, but it was within the acceptable range. In addition, the data indicated that the uncertainty of model prediction was not significantly correlated with sample size. 【Conclusion】Tree-structured machine learning models Random Forest and Cubist stand out in this case. Improving the spatial prediction and digital mapping accuracy of soil target variables cannot be achieved simply by expanding the scale of sample points and increasing the density of sample points. It is necessary to improve the model prediction performance and covariate data quality at the same time. When the sample size is large enough, the sampling strategy has little effect on the performance of the ML model and the prediction accuracy of surface soil pH; when the sample size is smaller than a certain threshold, the sampling method has a significant impact on the model performance and prediction results.

Abstract:【Objective】 Wind activity and aeolian dust transportation are key terrestrial processes in dryland ecosystems. Biocrusts are photoautotrophic communities that consist of cyanobacteria, actinomycetes, mosses, green algae, fungi, and other organisms. As an important living skin and pioneer communities developing on surface soil in drylands, biocrusts strongly influence most soil processes (hydrological, ecological, biological, and chemical processes) and have a variety of essential ecological functions. Although biocrusts are usually relatively thin (a few millimeters or centimeters at most), these organisms have unique micro-structures which could positively influence the formation of aeolian soil parent material. In order to further explore the aeolian sedimentary effects of biocrusts on soil parent material, we conducted this study to understand the effects of biocrusts on dustfall retention and soil fixation, as well as their influencing factors.【Method】 In the north of Chinese Loess Plateau, the biocrusts developed on aeolian and loessal soils were sampled, and the analyses and simulated experiments were carried out in the laboratory. The amount of dustfall retention and soil fixation of biocrusts at different developmental stages (cyano crust, mixed crust, and moss crust) were measured. The variations of dustfall retention amount under different wind speeds, dustfall grain sizes, and dustfall amount were explored. We also explored the key influencing factors.【Result】 The dustfall retention amount of biocrusts was 1.1～4.8 times higher than that without biocrusts, and it increased with the developmental stages of biocrusts from cyano crust to moss crust. On average, the erosion reduction of biocrusts was 19.5～4892 t·km^-2·a^-1under 1～8 m·s^-1 wind speeds. Moreover, the dustfall retention amount increased with increasing soil water content, and these increases were positively correlated with wind speed. It was found that the dustfall retention amount was increased by 4.9%, 53.1%, 59.6%, and 72.3%, respectively, under 5～8 m·s^-1 wind speeds when relative water content increased from 0 to 80%. Additionally, the dustfall retention amount was also significantly and positively correlated with the surface roughness of biocrusts. Similarly, the soil fixation amount of biocrusts also increased along with their developmental stages from cyano crust to moss crust. The soil fixation amount of moss crust was 1.4 times higher than that of cyano crust. At the same developmental stage, the soil fixation amount of biocrusts on aeolian sandy soil was significantly (F=30.74, P<0.003) higher than that on loessal soil. Furthermore, the soil fixation amount was positively correlated with the thickness of biocrusts and negatively correlated with the surface roughness. It firstly increased and then decreased with increasing soil water content.【Conclusion】 These findings show that biocrusts can significantly retain dustfall and fix soil due to their root, mycelium, exudates, and pore structures, and these biocrust functions are of great significance for the aeolian sedimentary process of soil parent material, the pedogenic process of primitive soil, and the primary succession of dryland ecosystem in the Chinese Loess Plateau. Additionally, this study demonstrates the important effects of biocrusts on the formation of aeolian soil parent material, and their key influencing factors are surface roughness, developmental stages, and water content of biocrusts. Therefore, it is essential to pay attention to the biocrust effects on dust retention and soil fixation in arid and semiarid climate regions.

Abstract:【Objective】The mechanisms of evaporation and infiltration during the processes of precipitation on soil layers is still not clear. Thus, this study was designed to investigate the spatial variations of soil water isotopes from deep vadose zones(>18 m)of pear orchard and farmland plots in the North China Plain. 【Method】Stable isotopes(δD and δ¹⁸O)in soil water, soil water content and soil texture were explored in the pear orchard and farmland plots of the North China Plain. 【Result】Results showed that the local meteoric water line(LMWL)was established as δD = 6.07δ¹⁸O-5.76(R²=0.86). The δD and δ¹⁸O of soil water from different soil layers fell below the LMWL, indicating that soil water replenished from precipitation experienced strong evaporation. Except for pear orchard(I), the coefficient of variation(CV)of soil water isotopic values was in the order of shallow layer>middle layer> deep layer, indicating that the δD and δ¹⁸O of shallow soil water fluctuated greatly. This implies that shallow soil water was more impacted by precipitation and evaporation compared with other soil layers. As the profile depth increased, the effect of precipitation and evaporation gradually became weaker. The larger isotopic CV of deep soil water in pear orchard(I)indicated deep soil water was affected by groundwater at this sampling site. The d-excess values of shallow soil water were greater in pear orchard plots than those in farmland plots, indicating that the evaporation intensity of shallow soil layers was less in the pear orchard plots than in farmland plots. The obvious isotopic enrichment(δD and δ¹⁸O)was observed in the soil layer of 0.25-0.5 m, which was associated with soil texture stratification and hindered infiltration into deep soil layers. This resulted in enriched soil water accumulating in the soil layer. The phenomenon of isotopic depletion was found in the soil layers(2-5 m)from the pear orchard plots and resulted from preferential flow induced by pear roots. 【Conclusion】The remarkable spatial differences of isotopic variations in soil layers were observed in the pear orchard and farmland plots, indicating that the infiltration processes of soil water differed in various land-use patterns of the North China Plain. The preferential flow of soil water during the infiltration processes was dominated in the pear orchard plots. These findings provide a theoretical basis for understanding the relationship between water movement, nitrogen migration and transformation, and groundwater quality in the deep vadose zone of the North China Plain.

Abstract:【Objective】Iron oxides are important cementitious substances in soil aggregates, which mainly exist in soil clay particles. This study aimed to reveal the transformation of iron oxides in soil aggregates and their enrichment characteristics in clay fractions of different particle sizes under the conditions of returning Chinese milk vetch to the field and applying chemical fertilizers.【Method】Four treatments including a single application of Chinese milk vetch (MV), a single application of chemical fertilizer (F100), Chinese milk vetch applied with chemical fertilizer(MV+F100)and Chinese milk vetch combined with 80% of chemical fertilizer (MV+F80) were selected. Soil aggregates (>250, 53～250 and 2～53 μm) and clay particles (<2 μm) were separated by wet sieving and centrifugation, and the content of iron oxides in soil aggregates and their clay particles with different treatments was determined. Also, the relationship between iron oxides and the stability of aggregates was analyzed.【Result】(1) Compared with MV and F100, the content of >250 μm aggregate was increased and the content of 53-250 μm aggregate was decreased, and the mean weight diameter (MWD) and geometric mean diameter (GMD) were increased by 8.2% to 20.5% and 4.1% to 8.5%, respectively. (2) Compared with MV, the combined application of Chinese milk vetch and chemical fertilizer significantly increased the contents of amorphous iron(12.7%-55.6%, 52.4%-54.9% and 45.9%-48.6%)in aggregates of various sizes, clay particles of 2～53 μm and free clay particles. The enrichment rates of amorphous iron in >250 and 53～250 μm aggregates were decreased (32.8%～36.8% and 17.2%～28.4%). Compared with F100, the content and enrichment rate of amorphous iron in 2～53 μm aggregates and clay of aggregates were significantly reduced (3.5%～21.3%, 29.2%～30.4% and 10.9%～26.9%). (3) The content of >250 μm aggregates was positively correlated with the content of non-crystalline iron and activation degree of iron in the clay of aggregates, and positively correlated with the enrichment rate of amorphous iron and the content of free iron in aggregates. The MWD and GMD were significantly positively correlated with the content of >250μm aggregates, and significantly negatively correlated with the content of <2μm aggregate. The free iron in the clay of >250 and 2～53μm aggregates and free clays was the most important factor influencing the MWD and GMD.【Conclusion】Combined application of Chinese milk vetch with chemical fertilizer could increase the content of iron oxide in the clay of different aggregates and promote the formation of >250μm aggregates, thus, enhancing the stability of aggregates.

Abstract:【Objective】Planting catch crops in a protected vegetable field during the fallow season is an important practice to reduce the leaching loss of important nutrients. However, few studies have been done on catch crops with high nitrogen and phosphorus leaching control efficiency in frequent rainfall areas.【Method】This research set up five planting catch crop treatments(sorghum treatment, maize treatment, ryegrass treatment, purslane treatment and collard treatment)and a fallow treatment to study the effect of different kinds of catch crops on nitrogen and phosphorus leaching, NO₃^--N and NH₄⁺-N content and soil microorganism.【Result】The results showed that compared with fallow treatment, sorghum, maize, ryegrass, purslane and collard treatments significantly reduced nitrogen leaching by 12.6, 26.6, 27.4, 28.9 and 26.8 kg·hm^-2 and phosphorus by 0.10, 0.05, 0.04, 0.04 and 0.13 kg·hm^-2, respectively. The nitrogen and phosphorus control efficiency was as follows; purslane＞ryegrass＞collard＞maize＞sorghum, and collard＞sorghum＞maize＞purslane＞ryegrass, respectively. The nitrogen control rates of ryegrass, purslane and collard reached 52.3%, 55.1% and 51.2%, respectively, which were nearly twice higher than the nitrogen control rates of sorghum and maize. This may be because the ryegrass, purslane and collard treatments had a certain coverage in the early fallow period(21 days), which reduced the leaching volume by 23.5%, 17.1% and 26.7% compared with fallow treatment. In contrast, sorghum and maize treatments had poor coverage in the early fallow period, hence there was no significant difference in leaching volume between sorghum and maize treatments and fallow treatment. In addition, the NO₃^--N content in the surface soil(0-20 cm)of ryegrass, purslane and collard treatments was 40.1-52.8 mg·kg^-1, while in the surface soil of sorghum and maize treatments it was 67.8-72.7 mg·kg^-1. Besides, compared with sorghum and maize treatments, ryegrass, purslane and collard treatments also significantly increased the abundance of nirS type denitrifying bacteria in surface soil and nosZ type denitrifying bacteria in rhizosphere soil, which may enhance the denitrification process in soil. This may be one of the mechanisms for high nitrogen leaching control efficiency.【Conclusion】In general, ryegrass, purslane and collard as the catch crops of protected vegetable field in areas with frequent rainfall can significantly reduce nitrogen and phosphorus leaching, and collard has the best effect on nitrogen and phosphorus comprehensive control.

Abstract:【Objective】The sustainable and safe utilization of agricultural soil is of great significance to effectively improve the quality of the agricultural soil environment, and to ensure the quality and safety of agricultural products and human health.【Method】Taking Zhejiang Province, one of the most developed areas in the Yangtze River Delta, as an example, the main problems and development trends of agricultural land soil environment were analyzed, and the theory and method of sustainable and safe utilization of agricultural land soil were studied. During the 13th Five-year Plan period, based on the survey results of agricultural land soil pollution in Zhejiang Province at a scale of 1: 50 000 over the years, provincial pilot demonstrations focusing on the control of heavy metal cadmium pollution in agricultural land were carried out in Wenling City and Tonglu County. The methods of pollution source analysis and prevention, multi-dimensional agricultural safety utilization technology screening and application, and safe disposal of over-standard crop straws were comprehensively adopted to form a batch of agricultural land soil pollution comprehensive treatment technology models with significant regional characteristics, high-efficiency control effects, and independent intellectual property rights, which are suitable for mild to moderate and moderate to severe cadmium pollution.【Result】The main results were as follows: (1)Atmospheric deposition source is one of the main external input sources of Cd in the agricultural land ecosystem, accounting for about 24%-59% of the total input.(2)58 varieties with low accumulation(mainly Yongyou 538)were screened out, 20 passivation materials with calcareous substances as the main, and 10 leaf resistance control materials with silicon and selenium as the main were selected.(3)The safe utilization technology mode of rice/wheat rotation, which is suitable for light and moderate Cd polluted agricultural land can effectively reduce the available state of Cd in soil by more than 20%-50%. The production and remediation technology mode which is suitable for moderate and severe Cd polluted agricultural land, mainly with hyperaccumulators, can effectively reduce the total amount of Cd in soil by more than 30% and the available state of Cd in soil by more than 50%.【Conclusion】This paper innovatively puts forward the general idea and technical route of sustainable and safe utilization of heavy metal polluted agricultural land soil. It also summarizes the experience and strategy of sustainable and safe utilization of heavy metal polluted agricultural land soil, to provide a demonstration model and technical reference for the safe utilization of contaminated agricultural land soil in China.

Abstract:【Objective】This study aimed to effectively, rapidly, and cost-effectively purify wastewater and repair soil from lead pollution.【Method】The remediation effect of a lead-remediation material(superparamagnetic micro nano Fe₃O₄@ Ca₁₀(PO₄)₆(OH)₂functional material, MFH)on Pb²⁺ in wastewater and polluted soil was studied in terms of dosage, initial concentration of Pb²⁺, adsorption time, pH, ionic strength and organic matter concentration.【Result】The results showed that the adsorption of Pb²⁺ in solution by MFH satisfies the pseudo-second-order kinetic model. The adsorption equilibrium was reached in about 10 min, and the maximum adsorption capacity was 181.6 mg·g^-1; at pH 2.00～5.00. Also, the removal rate of Pb²⁺ in the pH range decreased with the increase of pH while an increase in ionic strength of the solution inhibited the removal rate of Pb²⁺ by MFH. Nevertheless, an increase in the organic matter content in the reaction system effectively improved the removal rate of Pb²⁺ by MFH. MFH showed a good lead-removal effect when applied to lead-contaminated soils in farmland and industrial parks. The addition of heavy metal activator EDTA can significantly improve the removal effect of MFH on lead in soil. In slightly lead-contaminated farmland soil, the total amount of lead removed was 102.74 μg·g^-1. After experimentation, the recovery rate of MFH from soil was over 88% by using a magnetic rod, while the recovery rate of MFH regeneration performance was 89.49%. Importantly, the magnetic properties and specific surface area of the regenerated MFH recovered well, suggesting that MFH had a good recovery and regeneration ability.【Conclusion】Therefore, MFH is a good material for the decontamination of lead- contaminated wastewater and soils and its usage is promising given that it can easily be recovered with its basic properties intact.

Abstract:【Objective】Soil fertility is significantly influenced by plough layer thickness. However, it is still not clear how the transformation and fate of fertilizer nitrogen (N) in fluvo-aquic soils would be affected by plough layer thickness. 【Method】In this study, a soil column simulation experiment in the field was conducted throughout three crop cultivations. The experiment was performed in a completely randomized design with six treatments including two plough layer thicknesses (15 and 25 cm) and three soil textures (sandy loam, sandy clay loam and loamy clay). A ¹⁵N-labeled tracer technique was used to evaluate the dynamics of fertilizer-derived organic N, fixed NH₄⁺ and mineral N in 0-40 cm soil layer and the fate of fertilizer N in soil-crop systems. 【Result】 The transformation of fertilizer N in soil-crop systems was significantly affected by plough layer thickness, and showed the same varying tendency among different textural soils. The residual fertilizer N existed mainly in the form of organic N, which accounted for more than 83% of the total residual fertilizer N and played a pivotal role in the storage and supply of fertilizer N. Increasing plough layer thickness degraded the conversion of fertilizer N to fixed NH₄⁺ pool, while increased the stocks of fertilizer-derived organic N in 0-40 cm soil layer. In the current season after fertilizer N was applied, the average value of fertilizer-derived organic N stock in soils with 25 cm plough layer thickness (PLT-25) was averagely 8.9% higher than that in soils with 15 cm plough layer thickness (PLT-15). The stocks of fertilizer-derived mineral N under PLT-25 treatments were also higher than that under PLT-15 treatments in the current and subsequent crop cultivations; promoting the fertilizer N uptake by crops. The N use efficiency under PLT-25 treatments in the first two crop cultivations was about 8.0% higher than that of PLT-15 treatments, while the current seasonal loss rate and cumulative loss rate of fertilizer N were 12.3% and 9.1% lower, respectively. The stocks of fertilizer-derived organic N in sandy clay loam and loamy clay were significantly (P < 0.05) higher than that in sandy loam, while the trend was the opposite for the stocks of fertilizer-derived fixed NH₄⁺. And the fertilizer-derived mineral N stock was usually to be higher in sandy loam. Overall, the percentage of recovery of applied fertilizer N in crops and soil under sandy loam treatment was significantly (P < 0.05) lower than that in sandy clay loam and loamy clay. Also, the percentage of cumulative loss of fertilizer N in sandy loam was 20.4% and 18.2% higher than that in sandy clay loam and loamy clay, respectively. 【Conclusion】The fluvo-aquic soils with higher sand content have lower fertilizer N storage capacity, restricting the enhancing of N use efficiency. For fluvo-aquic soils with different textures, increasing plough layer thickness could improve the annual N use efficiency and the residual amount of applied fertilizer N in the current season. This, could be released for crop uptake in the subsequent crop cultivation. In typical fluvo-aquic soil areas, increasing the plough layer thickness may be a potential means for regulating the transformation and fate of applied fertilizer N, increasing fertilizer N retention, enhancing the fertilizer N uptake by crops and minimizing fertilizer N loss in soil-crop systems.

Abstract:【Objective】The combined application of woody peat and straw has the potential to rapidly increase soil organic matter (SOM) and crop yield. However, how the application proportion of woody peat and straw affects crop yield and its microbiological mechanism remains unclear. 【Method】A field experiment was designed, based on the application of straw and activator (RJ). Then, a was comparative analysis of the effects of the ratio of woody peat and straw at 2: 1 (RJM1), 3: 1 (RJM2), and 4: 1 (RJM3) on soil physicochemical properties, bacterial community composition and rice yield was carried out, and compared with the control (CK) without any organic matter. At the same time, based on co-occurrence networks, the path analysis model was used to elucidate the potential relationship between specific bacterial flora and crop yield under different treatments. 【Result】The results showed that the rice yield of RJM1, RJM2, and RJM3 was similar, and their average yield was 16.09% and 31.46% higher than that of RJ and CK, respectively. The soil physicochemical properties of the five treatments were divided into three different groups (P < 0.01). The first group was RJM2+RJM3, which was characterized by remarkably increased pH, SOM, dissolved organic carbon (DOC), available phosphorus (AP) and available potassium (AK) contents. The second group was RJ+RJM1, which was characterized by significantly increased nitrate-nitrogen (NO₃^--N) and dissolved organic nitrogen (DON). The third group was CK. The average content of SOM, DOC, and AP in RJM2+RJM3 was 29.69%, 22.65%, and 23.95% higher than those of RJM1, respectively, which indicates that RJM2+RJM3 has the potential of rapidly increasing the content of soil organic matter. The bacterial community composition between RJM2 and RJM3 was similar, and was mainly influenced by soil pH, SOM and DOC, while they were significantly different from RJM1. Module 1 of key ecological clusters within the bacterial co-occurrence network had a direct and significant positive effect on rice yield, in which soil physicochemical properties indirectly affected crop yield by directly and significantly affecting module 1 properties. The improvement of yield was mainly affected by the relative abundance and community composition of module 1, while module 2 and module 3 had no significant effect on rice yield. RJM2+RJM3 significantly increased the abundance of Gaiellaceae unidentified, Nocardioidaceae unidentified, Terracoccus, Comamonadaceae unidentified, WD2101 unidentified, and Sphingobacteriales unidentified, which were positively correlated with rice yield. Also, RJM1 significantly increased the abundance of the other five species mentioned above, except Sphingobacteriales unidentified, which indicates that RJM2+RJM3 could stimulate more dominant species that were positively correlated with crop yield than RJM1. Meanwhile, the sustainability of increasing rice yield in RJM1 was lower than RJM2+RJM3 because the SOM content of RJM1 was not significantly different from that of CK and RJ. 【Conclusion】Combining the above results with economic benefits, RJM2, the application ratio of woody peat to straw 3: 1, is recommended as an appropriate ratio that can rapidly improve SOM and crop yield at the same time.

Abstract:【Objective】The objective of this study was to clarify the status of soil nutrient accumulation in the peach orchard of Taihu Watershed. It aimed to provide a guide for the green production mode of peach orchard. 【Method】In this study, a total of 66 soil samples were collected from 33 juicy peach orchards, with different cultivation years in the four main planting towns. Combined with field research and laboratory analysis, the fertilizer input status, soil nutrient content and ecological stoichiometry characteristics were analyzed. 【Result】The results showed that the average total nutrient inputs was N 527 kg·hm^-2, P₂O₅ 362 kg·hm^-2 and K₂O 545 kg·hm^-2, and the proportion of organic inputs were 27.8%, 15.4% and 15.6% respectively. Here chemical fertilizer was mainly NPK compound fertilizer, while the types of organic fertilizer applied mainly included rapeseed cake, livestock manure, and composting straw. Over-application of fertilizer could aggravate soil acidification and nutrient accumulation, soil pH in 0-20 cm and 20-40 cm soil layers of planted >10 years peach orchard both decreased by more than 1.5 units, which belonged to strongly acidic soil (4.5<pH<5.5). According to the 2^nd National Soil Survey of soil fertility classification standards, soil organic matter, total nitrogen, phosphorus and potassium in 0-20 cm and 20-40 cm soil layers reached level 3 or above, and the C: N, C: P and N: P ratios in 0-20 cm soil layer decreased with an increase of cultivation years. Soil alkali-hydrolytic nitrogen, available phosphorus and potassium of planted >10 years peach orchard reached level 1. The soil NO₃^--N concentration of the peach orchard was up to 19.3-33.1 mg·kg^-1. The annual apparent surplus of N, P₂O₅, K₂O were 343 kg·hm^-2, 238 kg·hm^-2 and 240 kg·hm^-1, respectively. 【Conclusion】The excessive nutrient input in the peach orchard has aggravated soil acidification and nutrient accumulation. A high concentration of nitrogen and phosphorus accumulated in the soil might increase the environmental loss risk. Therefore, it is necessary to put forward a green production model for the peach production.

Abstract:【Objective】This study aimed to analyze the change of phosphorus fixation capacity and release potential in different occurrence layers of red paddy soil, to clarify the release mechanism of fixed phosphorus (P), and to evaluate the loss risk of P in red paddy soil with different planting years.【Method】Soil samples were collected from the bottom to the top of three typical red paddy fields in Yingtan, Jiangxi Province. These paddies included a mid-phase paddy field (MP), a new paddy field (NP) and an old paddy field (OP). Based on the adsorption-desorption experiment and structural equation model, the variation differences and influencing factors of phosphorus retention capacity (PSI), maximum capacity of soil fixed phosphorus (MCSP) and the release potential of the soil were analyzed.【Result】With the increase of pedogenic horizons depth, PSI and MCSP of red paddy soil gradually increased, and the order of their changes were: MP > NP > OP and NP > MP > OP. The desorption capacity of electrostatically adsorbed state P (CaCl₂-P) of OP, MP and NP profiles and the desorption capacity of specific adsorbed state P (EDTA-P) in the OP profile gradually decreased with the increasing profile depth. Also, the EDTA-P in MP (except Ap₁ layer) and NP profiles and residual P (Red-P) in soil pedogenic horizons followed an opposite trend. With the increase of profile depth, the CaCl₂-P/EDTA-P in the pedogenic horizons of the OP profile increased, which was significantly higher than that in the MP and NP profiles. The adsorption-desorption capacity of phosphorus in red paddy soil is mainly affected by SOM (soil organic matter), TP (total phosphorus), pH and iron-aluminum oxides. The interaction between SOM, TP, pH and iron-aluminum oxides jointly regulates the number of phosphorus adsorption sites and the strength of adsorption-desorption capacity in red paddy soil.【Conclusion】In this research, it was found that the Ap layer of red paddy soils was characterized by the weak capacity of the soil P sorption and strong capacity of P desorption and a high risk of soil P loss. Meanwhile, Br and C layers showed a stronger soil P sorption capacity and a weaker P desorption capacity, and a higher soil P fixation capacity than the Ap layer. Compared with the profile of OP, the exogenous P adsorbed in pedogenic horizons of NP and MP was more easily converted to the specialized adsorption state and residual state P, thus, resulting in a reduced risk of soil P loss. The risk of P loss in the OP profile was relatively higher than its counterparts, and timely regulatory measures are needed.

Abstract:【Objective】A reasonable supply of magnesium is an important guarantee for high-quality tobacco production. The current soil magnesium fertilizer application in tobacco growing areas is mainly determined according to the level of soil available magnesium content and its spatial distribution. However，the practical impact of the ratio of soil available calcium content to available magnesium content（Ca/Mg ratio）on magnesium supply is rarely considered. 【Method】Taking Bijie tobacco growing area as an example，the level of available magnesium content，Ca/Mg ratio and spatial distribution contours were obtained based on a large number of soil samples. Then，the suitable grade zoning of magnesium fertilizer was delimited through graphic superposition and grid operation. 【Result】The results showed that the average content of soil available magnesium in Bijie tobacco growing area was 278.1 mg· kg^-1. The content shows great fluctuation in space，which was caused by the parent rock，soil type，elevation and topographic location. Also，the average Ca/Mg ratio in this area was 14.5，and was at a high level. Moreover，the spatial fluctuation of the ratio was also large，and mainly related to the spatial distribution of soil-forming parent rock and soil types. From spatial interpolation contours of available magnesium content，the areas with high content were mainly concentrated in the east and southwest，while areas with low content were mainly distributed in the middle north and northwest. The available magnesium content was dominated by the suitable grade，which accounted for 69% of the whole area. Moreover，the area of lacking and rich grades accounted for 19.0% and 10.5% respectively，and the areas of extremely lacking and extremely rich grades were both small. From the distribution of soil Ca/Mg ratio，the study area was dominated by two grades of 10～20 and 5～10，while areas covering > 20 and < 5 were relatively small. On the whole，the Ca/Mg grades were characterized by interphase distribution in space. In the application grade map of soil magnesium fertilizer obtained from available magnesium content and Ca/Mg ratio，the most suitable application areas were mainly concentrated in the north-central，southeast and northwest regions. Also，the unsuitable grades were mainly distributed in some parts of the southwest and northeast，while the areas of extremely unsuitable grade were very small，and mainly scattered in the southwest. Among all the grades，the areas of suitable and more suitable grades of magnesium fertilizer application accounted for 69.0% and 10.5% respectively. The unsuitable application area accounts for 19.0%，while the proportion of extremely suitable and extremely unsuitable areas account for only 1.3% and 0.2% respectively. 【Conclusion】The results indicate that the Ca/Mg ratio of soil is an important factor to be considered when formulating the application scheme of magnesium fertilizer. If the influence of the Ca/Mg ratio on soil magnesium supply is not considered，the appropriate grade zoning of magnesium fertilizer will have a large deviation，which will have an adverse effect on soil fertilization in tobacco growing areas. It can be seen that comprehensive consideration of soil available magnesium content and Ca/Mg ratio is an important prerequisite for scientifically formulating regional magnesium fertilizer application scheme.

Abstract:【Objective】The periphytic biofilms widely distributed between the water-soil interface are key hot areas and necessary places for material migration and energy exchange in the paddy ecosystem. However, few studies have paid attention to the community characteristics and regulatory functions of the paddy periphytic biofilm. The purpose of this study is to further understand the function of periphytic biofilm biological phosphorus capture. 【Method】This study selects the periphytic biofilms in the main rice areas in China, covering three rice planting areas in the South China, the middle and lower reaches of the Yangtze River, and the Northeast China. The composition and structure of periphytic biofilms communities are analyzed using high-throughput sequencing technology, combined with PLS-PM and regression analysis to reveal factors affecting the capture of phosphorus by periphytic biofilms around the paddy field.【Result】There are significant differences in soil physical and chemical properties in different paddy regions (P<0.05). The phosphorus capture capacity of the periphytic biofilms in main rice regions in China showed an increasing trend from north to south and west to east. There are significant differences in the composition of the periphytic biofilms community of paddy fields in different regions (P<0.05). At the genus level, the periphytic biofilms in South China are dominated by prokaryotic microorganisms such as Acinetobacter and Proteiniclasticum and eukaryotic microorganisms such as Gregarina and Adriamonas. The periphytic biofilms in the middle and lower reaches of the Yangtze River are mainly prokaryotic microorganisms such as Bacillus and Cloacibacterium and eukaryotic microorganisms such as Gregarina and Vermamoeba. In the Northeast, periphytic biofilms are composed of prokaryotic microorganisms dominated by Flavisolibacter and Anaerolinea and eukaryotic microorganisms dominated by Adriamonas and Vermamoeba. It was found that the physical and chemical properties of soil (especially soil organic carbon and pH of floodwater) correlated with the diversity of the periphytic biofilms community. The microalgae in the periphytic biofilms in South China play a certain role in promoting the capture of phosphorus, while the phosphorus accumulating bacteria in the periphytic biofilms in the northeast have a positive effect on the capture of phosphorus.【Conclusion】This study provides deep insight into the understanding of the composition and structure of the periphytic biofilms and their regulation in the phosphorus cycle in paddy fields through analysis of the phosphorus capture capacity of periphytic biofilms in paddy fields in different regions of China. Also, this study provides a theoretical basis for the future development of biotechnology to recycle surplus phosphorous in paddy fields.

Abstract:【Objective】Nitrifiers play an important role in the process of farmland soil nitrogen transformation. A study on the distribution of nitrifying microorganisms in aggregates will help to reveal the interaction mechanism between soil structure, microorganisms and soil nutrient cycling.【Method】The changes in soil aggregate properties and nitrification potential (N_P) in maize monoculture (M-M) and maize peanut rotation (M-P) were compared, and the abundance and community composition of different nitrifying functional genes in soil aggregates were evaluated by quantitative PCR and high-throughput sequencing.【Result】Compared with M-M, M-P significantly increased pH, NH₄⁺ and total carbon (TC) in soil aggregates. M-P also significantly enhanced N_P, but the aggregate size had no significant effect on N_P. The abundance of the AOB amoA gene was higher in M-P and also more abundant in smaller aggregates. The distribution pattern of AOA and comammox amoA genes was opposite to that of AOB, indicating that AOB can better adapt to the micro-environment of smaller aggregates, while AOA and comammox tended to dominate in larger aggregates. In addition, compared with M-M, the difference in AOA/AOB and comammox/AOB ratio between M-P aggregates decreased, indicating that rotation promoted an even distribution of soil nitrifiers among different aggregate sizes. By further analysis of the nitrifying community based on the 16S rRNA gene sequencing, the results showed M-P increased the proportion of Nitrolancea-like NOB and Candidatus Nitrosocosmicus-like AOA, decreased the proportion of Nitrospira-like NOB, and had no significant effect on AOB compositions. The aggregate size only had a significant effect on the proportion of Nitrosospira-like AOB. NH₄⁺ content and pH were the main factors affecting soil N_P and the nitrifying microbial community structure among soil aggregates. N_P was positively correlated with AOB amoA gene abundance and negatively correlated with AOA amoA gene abundance. However, in terms of community composition, Nitrosospira-like AOB, Candidatus Nitrosocosmicus-like AOA and Nitrospira-like NOB all showed positive correlations with N_P.【Conclusion】Soil aggregate size and cropping system can greatly affect the distribution of nitrifying microorganisms in soil aggregates. However, nitrifying microorganisms have different adaptation mechanisms among aggregates. This study provides a theoretical support for improving the ecological adaptation mechanism of soil nitrifying microorganisms in the micro-environments under Gramineae-Legume rotation.

Abstract:【Objective】The process of nitrite-dependent anaerobic methane oxidation (n-damo) catalyzed by Candidatus Methylomirabilis oxyfera (M. oxyfera) -like bacteria links both the carbon and nitrogen cycles, and has attracted great attention in recent years because of its potential role acting as a microbial methane sink. This process has been reported to be a novel pathway for controlling methane emissions from paddy ecosystems. Elevated atmospheric CO₂ concentration can indirectly affect the structure and function of soil microbial communities. However, the response of n-damo to e[CO₂] is poorly known. This study aims to explore the response of n-damo activity, and the community composition and abundance of M. oxyfera-like bacteria to e[CO₂] in a paddy ecosystem.【Method】Here, ambient CO₂ treatment (CK) and a slow increase of atmospheric CO₂ treatment (EC: an increase of 40 μL·L^-1 per year above CK until 160 μL·L^-1) were set up based on the CO₂ automatic control platform with open-top chambers. The stable isotope tracer experiment, quantitative PCR and high-throughput sequencing were employed to investigate the n-damo activity, abundance, diversity and community composition of M. oxyfera-like bacteria in paddy soils across three key rice growth stages (tillering, jointing and flowering stages) under different CO₂ treatments.【Result】The results showed the occurrence of n-damo activity and the presence of M. oxyfera-like bacteria in the studied paddy soils. It was found that the n-damo activity ranged from 0.31 to 5.09 nmol CO₂ g^-1·d^-1, and the abundance of M. oxyfera-like bacteria varied between 7.51×10⁶ and 5.49×10⁷copies g^-1. Furthermore, EC treatment stimulated the n-damo activity and abundance of M. oxyfera-like bacteria, particularly at the jointing stage, in which the activity and abundance were increased by 137.9% and 96.0%, respectively. In addition, EC treatment significantly changed the community composition and diversity of M. oxyfera-like bacteria, and the diversity was increased under EC treatment. Correlation analyses showed that the soil dissolved organic carbon content, ammonium content, nitrate content and water content all had significant impacts on the community structure of M. oxyfera-like bacteria. The variations in soil dissolved organic carbon content and inorganic nitrogen content under EC treatment could probably cause the change of n-damo activity and the abundance of M. oxyfera-like bacteria.【Conclusion】Elevated atmospheric CO₂ promoted the n-damo activity and M. oxyfera-like bacterial abundance and significantly changed the community structure of M. oxyfera-like bacteria in a paddy ecosystem. In addition, the changes of soil dissolved organic carbon content, inorganic nitrogen content and water content greatly affected the n-damo activity and community structure of M. oxyfera-like bacteria. Taken together, our results showed a positive response of n-damo to the slow increase of atmospheric CO₂ concentration.

Abstract:【Objective】This study was designed to explore the impact of a new rice-shrimp farming model (NRS) on soil fertility and microbial community composition in paddy field. 【Method】Three different farming treatments: new rice-shrimp farming model (NRS), traditional rice-shrimp farming model (TRS) and rice monoculture (CK) were set up, with CK as control. The paddy field physicochemical indexes and microbial diversity and community structure were determined by using the soil agrochemical analysis method and 16S rDNA amplicon high-throughput sequencing technology. 【Result】Compared with CK and TRS, NRS significantly improved the contents of soil organic matter, available K, available P and pH. NRS significantly increased the microbial diversity and species richness. A total of 32 phyla, 80 classes, 202 orders, 347 families and 491 genera of bacterial groups were detected in the paddy field of three models. The dominant bacterial phyla were Proteobacteria, Acidobacteriota, Chloroflexi, Verrucomicrobiota and Desulfobacterota. Compared with CK, NRS changed the composition of the soil microbial community. Among the bacterial dominant phyla, the relative abundances of Acidobacteria, Chloroflexi and Verrucomicrobiota were increased by 30.89%, 36.38% and 2.16%, while the relative abundance of Proteobacteria and Desulfobacteria decreased by 17.96% and 58.59%, respectively. Compared with TRS, NRS also changed the composition of the soil microbial community. Among the bacterial dominant phyla, the relative abundances of Desulfobacteria increased by 14.93%, while the relative abundance of Chloroflexi, Verrucomicrobiota, Proteobacteria and Acidobacteria decreased by 39.29%, 37.42%, 16.27% and 6.81%, respectively. Correlation analysis showed that soil organic matter, available potassium, available phosphorus, available nitrogen and pH were the main physicochemical factors affecting the structure of soil microbial community in paddy field. 【Conclusion】The new rice-shrimp farming model is conducive to improving soil fertility, significantly improving soil microbial diversity and altering microbial community structure. The results of this study have certain guiding significance and reference for the demonstration and promotion of the new rice-shrimp farming model.

Abstract:【Objective】This study aimed to illustrate the impacts of different tillage practices on chitin degrading microbial communities and chitinase activity in farmland black soil, and to explore the main environmental factors in driving a change in chitin degrading microbial communities and chitinase activity.【Method】Based on the long-term positioning platform of different tillage practices in black soil and the combination of fluorescence quantification and high throughput sequencing technology, this research intends to study the effects of long-term different tillage practices (Conventional tillage, No-tillage, Sub-soiling tillage, Moldboard plowing tillage) on chitin degrading bacteria harboring chiA gene abundance, microbial communities and chitinase activity in 0 - 40 cm soil layers.【Result】Results showed that no-tillage increased chiA gene abundance in the 0 - 20 cm soil layer. Lower chiA gene abundance, alpha diversity and proteobacteria relative abundance, and higher actinobacteria relative abundance in the 20 - 40 cm soil layer of no-tillage than other tillage practices. The abundance of chiA gene and microbial community structure was significantly affected by soil pH, mean weight diameter and nutrients. Compared with conventional tillage, the chitinase activity increased in 0 - 20 cm soil layer under no-tillage, and the chitinase activity was enhanced in 0 - 40 cm soil layer under sub-soiling tillage and moldboard plowing tillage. The simulation result of the structural equation modeling showed that chitinase activity was directly affected by the tillage practice, soil depth, mean weight diameter, organic carbon, total nitrogen, total phosphorus, chiA gene abundance, and actinobacteria relative abundance.【Conclusion】These results provide a theoretical basis for understanding the effect of different tillage practices on soil chitin degradation in black soil areas.

Abstract:【Objective】Changes in the dominant vegetation community will inevitably affect soil organic carbon (SOC) by altering the quantity of litter and root exudates during shrub encroachment. Thus, this study aimed to explore the response of different active organic carbon fractions in alpine grassland soils to invasion by different shrub species.【Method】Physicochemical fractionation method was used to divide soil organic carbon into non-protected carbon, physically-protected carbon, chemically-protected carbon and biochemically-protected carbon. It was analysed the contents of various organic carbon fractions and factors influencing their contents among four typical shrub-grassland and unshrub-encroached grassland on the east edge of Qinghai-Tibetan Plateau.【Result】The results showed that (1) Shrub encroachment has no significant effect on the SOC content of the surface soil(0-10 cm)in alpine grassland (P>0.05), but the content of organic carbon components was different. After Spiraea alpina and Sibiraea angustata shrubs encroached the grassland, the non-protected organic carbon and biochemically-protected organic carbon contents were significantly decreased (P<0.05) while the non-protected organic carbon content significantly decreased when Potentilla fruticose encroached the grassland. Also, the contents of physically-protected and chemically-protected organic carbon decreased significantly in Caragana microphylla encroached grassland (P<0.05), while the biochemically-protected organic carbon increased significantly (P<0.05). (2) SOC in both grassland and shrub patches soil were dominated by non-protected carbon pool, followed by resistant carbon pool (chemically-protected organic carbon and biochemically-protected organic carbon), while physically-protected organic carbon pool accounted for the least. (3) The contents of soil clay and total nitrogen were the main factors affecting the organic carbon fractions in alpine shrub-encroached grassland, with an explanation degree of 51.2%. 【Conclusion】The invasion of different shrub species had inconsistent effects on the content of different reactive organic carbon fractions. The soils of both unshrub grassland and shrub sample sites on the Tibetan Plateau were dominated by non-protected carbon. Thus, in the presence of external disturbances, the organic carbon pool in the area may become a source of carbon.

Abstract:【Objective】Although many studies have reported the effects of long-term fertilizer application on soil organic carbon composition, molecular structure and functional group, few studies revealed the relationships between soil organic carbon, organic carbon composition and organic carbon functional groups under long-term fertilization conditions. Therefore, a field experiment with a maize-cowpea cropping rotation was conducted. The experiment included three treatments, i.e., organic nitrogen (N)fertilizer (OM), inorganic N fertilizer (IF), and the combination of organic and inorganic N fertilizers (IF+OM). The effect of long-term (9 years) N fertilizer applications on organic carbon composition and molecular structure of soil aggregates were studied to reveal the accumulative mechanism of soil organic carbon. 【Method】The soil was divided into 4 components by dry sieving method: >2 mm, 2-0.25 mm, 0.25-0.053 mm, and <0.053 mm, and then the mean weight diameter (MWD) and geometric mean diameter (GMD) were analyzed. The physical isolation method was used to measure free light particulate organic carbon (fPOC), intra-microaggregate particulate organic carbon (iPOC), silt-clay sized fraction organic carbon within microaggregates (iSOC) and free silt-clay sized fraction organic carbon (fSOC), and nuclear magnetic resonance spectroscopy was used to determine the functional group structure of soil organic carbon. 【Result】The results showed that compared with IF treatment and OM treatment, IF+OM treatment significantly enhanced maize and cowpea yields after 9 years of continuous N fertilization. Moreover, compared with IF treatment, OM and IF+OM treatments significantly increased MWD and GMD, and the effect was more obvious under IF+OM treatment. This study shows that fPOC was the main component of the soil organic carbon fraction, ranging from 21.0 to 29.8 g·kg^-1. The combination of organic and inorganic N fertilizers significantly enhanced the contents of soil organic carbon, fPOC and iPOC by 30.0%, 41.9% and 23.5% relative to IF treatment, respectively, but had no significant effect on the contents of iSOC and iSOC. The type of N fertilizer significantly influenced the ratio of alkyl, alkoxyl and aromatic carbon, which in turn significantly influenced alkyl/alkoxyl carbon and aromaticity in the soil. Compared with IF treatment, the combination of organic and inorganic fertilizer N fertilizers significantly increased alkyl carbon contents, but decreased aromatic carbon. Multi-path analysis showed that the alkyl carbon/alkoxy carbon ratio, hydrophobicity, aromaticity, fPOC and iPOC carbon content were closely related to organic carbon content. 【Conclusion】In conclusion, long-term combined application of organic and inorganic N fertilizers results in increases in crop yields, promotes the transformation of soil fine aggregates to large aggregates, increases fPOC and iPOC contents, optimizes the structure of aggregates, enhances soil stability, and thus promotes soil carbon sequestration, increased organic carbon storage, and thus promotes soil carbon sequestration. These results reveal the improvement mechanism of long-term combined application of organic and inorganic N fertilizers on soil organic carbon content, which would provide a theoretical basis for improving cropland soil fertility and structure.

Abstract:To study the effects of deposition of atmospheric particulate matter (APM) on the properties of urban soils, the values of magnetic susceptibility (χ_lf) and heavy metals in the topsoils and road dust in the industrial, traffic, residential and agricultural areas of Baoshan District, Shanghai, were analyzed. The topsoils in the different functional areas of Baoshan District, Shanghai, commonly have significantly enhanced magnetic strength (χ_lf = 130.7×10^-8m³·kg^-1 on average) of about 86.2% higher than the local magnetic background. χ_lf of the road dusts nearby the topsoils in the different functional areas was even more significantly enhanced, which was 903.3×10^-8m³·kg^-1 on average. Likewise, heavy metal contents in the road dust were significantly higher than those in the nearby topsoils in the different functional areas. The contents of Cu, Zn, Pb, Cd, Ni, Cr, Co, Mn and Fe in the road dust were 3.4, 2.4, 4.7, 22, 1.5, 2.8, 1.2, 1.4 and 1.6 times of those in the topsoils on average, respectively. Moreover, χ_lfof the topsoils in the Baoshan District was extremely significantly correlated with the contents of Cu, Zn, Cd, Ni, Cr and Mn (P < 0.01), and also significantly correlated with Pb and Fe (P < 0.05). Likewise, χ_lfof the road dust was also significantly correlated with the content of Zn, Ni, Cr, Co, Mn and Fe (P < 0.01), and with Cu (P < 0.05). Nevertheless, such correlations in the different functional areas of the district are highly different. Those in the agricultural topsoils are not significant. The distinctive characteristics of the road dust in the studied areas suggested that the APM under the urban environment contain a certain amount of anthropogenic magnetic particles enriched in heavy metals. The long-term and continuous deposition of such magnetic pollutants has led to the enhancement of magnetic signals and heavy metal contents in urban topsoils synchronously, and also adversely impacted the properties of urban soils significantly.