Abstract:The turnover of soil inorganic carbon (SIC) is considered slowly and its role in carbon sequestration and climate change is limited. Therefore, the role of SIC in croplands to the global carbon cycle is rarely investigated. In recent years, more evidences have indicated that the turnover rate of SIC is much faster than was thought. This suggests that its roles in stabilizing soil fertility, global carbon pool, and regulating the concentration of carbon dioxide (CO2) in the atmosphere should not be ignored. Therefore, we have reviewed recent advances on SIC in croplands, paying special emphasis on the important role of SIC in sequestrating carbon and buffering soil pH. SIC loss in China induced by agricultural production, especially the application of nitrogen (N) fertilizers affects the health of croplands by accelerating soil acidification and increasing the risk of heavy metals pollution. Soils in the transition zones between the North and the South China (Qinling Huaihe River), brown soil and alluvial soil in the Shandong Peninsula, black soil and chernozem in Northeast China, have low carbonates and a vulnerable pool of SIC that is easily lost. Thus, we suggest that these regions should be designated as SIC loss vulnerable zones. For further studies, the following topics should be considered (i) understanding the fates of SIC and interactions of soil organic carbon-CO2- Ca-SIC in cropland induced by agricultural production, especially adding N fertilizers; (ii) SIC roles in carbon soil balance and cycle; and (iii) regular monitoring of the SIC content in the vulnerable zones. Also, for a sustainable reduction of SIC loss induced by soil acidification, the following measures should be considered: adequate application of N fertilizers, combining the application of N fertilizers with organic fertilizer and nitrification inhibitors and replacing the ammonium bearing fertilizers with nitrate fertilizer.

Abstract:Healthy soil is the key to healthy food production and maintenance of the multifunctionality of the soil ecosystem. It is also the cornerstone of agriculture green development. Identifying the status of soil health and systematically carrying out soil health diagnosis are the basis of cultivating healthy soil and improving soil productivity. However, in the past, a large number of indicators and evaluations have been developed based on an individual soil function (e.g. soil productivity) , while other soil functions were largely ignored. Soil biological indicators are still underrepresented in soil health assessment, and the dynamic monitoring of soil processes is not sufficiently conducted. In pursuit of sustainable development goals and with the requirement of agriculture green development, the indicator system and evaluation approaches of soil health have been greatly improved. Thus, the establishment of multi-objective coordinated soil health assessment has become the hotspot and the frontier. This paper summarizes the selection principle in the indicator system of soil health. The importance of soil biological indicators in soil health evaluation is analyzed. The advances, advantages, disadvantages and application areas of the Chinese soil health assessment method, Cornell Comprehensive Assessment of Soil Health, New Zealand SINDI, the framework of Soil Navigator, Soil Management Assessment Framework are expounded. Finally, the pathways to improve the soil health evaluation system are put forward. It is necessary to build a big data platform for integrated soil-crop management based on the regional ecological conditions. A multi-objective coordinated soil health assessment for different regions and crop systems should be established through the participation of multi-actors with the development of soil biological indicators. A long-term and whole-process dynamic monitoring system should be established in combination with rapid testing and intelligent information technologies. This will provide important support for agriculture green development.

Abstract:Soil health has become a hot topic in soil science. Scientific assessment of soil health is fundamental to soil management and the achievement of sustainable development goals. Soil health assessment is challenging because of the multiple properties and ecosystem services. In this paper, the development of the concept and the traditional health assessment indicators, including physical, chemical and biological indicators, and their connotation were summarized. Also, the commonly used soil health assessment frameworks and their applicability were introduced while the general procedure of soil health assessment was summarized. This study also pointed out that the future soil health assessment in China should enhance the weight of carbon pool index, biological index and environmental index. Thus, the paper aims to lay a foundation for the establishment of a soil health assessment method that conforms to China's national conditions.

Abstract:Soil is an essential component of the Earth's critical zone, offering series of essential ecosystem services (i.e. agricultural production, plant growth, animal habitat, biodiversity, carbon sequestration, and environmental quality) . Soil stands for a nexus of the whole natural ecosystem. Enhancing soil health is vital to achieving sustainable development goals; therefore, scientific researchers have paid much attention to that over the world. Cultivated land and grassland are currently the most extensive land-use types on the Earth, accounting for 12% and 26% of the ice-free land, respectively. Also, these two crucial components consist of the Mountain-River-Forest-Farmland-Lake-Grass System theory. Therefore, keeping up the soil health status of these two land-use patterns has significant meaning for holding the whole natural ecosystem healthy and achieving sustainable development goals. In recent decades, the research focusing on the soil health of these two land-uses types is progressive worldwide. China is also relatively vibrant in this research field; however, the achievements have not made a difference. Additionally, a unified soil health assessment system has not yet been established at the national level. In this paper, firstly, the connotation and evolution of “soil health” was sorted out comprehensively. Then, focusing on the cultivated land and grassland, we highlighted the recent hotpots and advances in soil health globally. Secondly, we outlined several soil health assessment systems in different countries and sketched out series of fundamental works on soil health maintenance in China. Finally, we pointed out the new insights in the future to improve soil ecosystem functions and maintain the soil health of cultivated and grassland soils in China.

Abstract:Soil analysis is the tool for understanding the soil. However, the conventional chemical analysis methods have been difficult to meet the requirements of mass information deprived from modern soil science. Laser-induced breakdown spectroscopy (LIBS) is one of the novel tools which reflects the elements atomic peaks in the soil with the advantages of less pre-processing, rapid, in situ, real-time and multielement monitoring. Moreover, each spectrum was recognized as a fingerprint of soil sample due to its unique characteristic. The current study aimed to provide a critical review of LIBS in soil analytical studies. Firstly, the principle of LIBS, the main factors in spectral recording and the chemometrics methods for spectra processing were introduced; then the applications in qualitative and quantitative soil analysis during the last decade were elaborated. Some of the soil analysis recorded with LIBS include soil identification, prediction of soil nutrients; soil heavy elements detection, and soil elements distribution studies at nano- and mesoscale. Lastly, the main challenges of the LIBS techniques in soil analysis were discussed and we highlighted the prospects and application of LIBS in future research.

Abstract:Tungsten has been listed as an emerging contaminant by the United States Environmental Protection Agency (EPA). Tungsten can accumulate in soils through multiple avenues, creating potential damages to soil and biological ecosystems. However, our understanding of the occurrence, biogeochemical cycling and ecological risk of soil tungsten are limited. Based on previous research progresses and our experimental data, this paper systematically summarizes the content levels of tungsten in typical soils, tungsten’s environmental interface behaviors, as well as its accumulations and health risks to biological ecosystems. Finally, we highlight scientific problems and key research directions for future studies and call for more attention on the (i) ecological and environmental risks, (ii) biogeochemical processes, and (iii) risk management and remediation of soil tungsten.

Abstract:The soil resources in islands of the South China Sea are very scarce and precious. However, limited studies have been conducted on the island soils in this region to establish soil series. Thus, the purpose of this study was to systematically setup soil series for this region. 【Method】A systematic soil survey was conducted in 2020 on13 islands of the Xisha Islands, which has the most abundant soil resources in the South China Sea. Specifically, one typical soil profile was selected from the islands of Yongxing, Zhaoshu, Beidao, Nanshazhou and Jinqing, while two typical soil profiles were selected from Ganquan. Information on soil formation factors, profile morphological characteristics, and soil physicochemical properties was observed or measured. 【Result】The parent materials of the seven soil profiles were dead corals and shells. Of all the soils studied, twopedons only had Mollicepipedon, threepedons had Ochric epipedon, and twopedons had Orchric and Cambic horizons. All the sevenpedons had Udic moisture regime, Hyperthermic temperature regime and Lithological characteristics of coral debris sands while sixpedons had Phosphic property. Thus, (i) the pedon in Jinqing and onepedon in Ganquan islands were classified as soil subgroup Phosphic Carbonati-Udic Cambosols, (ii) the pedons in the islands of Yongxing, Zhaoshu, Nansha and North were classified as subgroup Phosphic Udic-Orthic Primosols, and (iii) the second soil profile in the Ganquan island was classified as subgroup Carbonatic Udic-Orthic Primosols. Finally, four soil families were identified and six soil series were established which included Jinqingdao Series, Ganquandao Series, Yongxingdao Series, Zhaoshudao Series, Nanshazhou Series, and Ganquandaodi Series. In brief, Jinqingdao Series, Ganquandao Series, Yongxingdao Series, Zhaoshudao Series and Nanshazhou Series are distributed in the lacustrine depression in the islands, covered by vegetation and is the habitats of birds, where soil organic carbon and phosphorus contents are high due to the accumulation of plant litters and bird droppings. Similarly, Ganquandi Series is distributed in the bare sea dike around the islands where soil organic carbon and phosphorus contents are very low due to limited vegetation coverage and little bird droppings. 【Conclusion】The seven typical soil profiles belonged to two soil orders, two soil suborders, two soil groups and three soil subgroups, and could be divided into four soil families and six soil series. These results can provide basic information for guiding sustainable utilization of soil resources and eco-environmental protection, and also offer support for effective natural resource governance over Xisha Islands.

Abstract:【Objective】In Chongqing, changes in soil morphological characteristics of Stagnic Anthrosols derived from calcareous mudstone are not obvious from top to bottom of the soil profile in most cases. However, this phenomenon is not always so for Stagnic Anthrosols derived from limestone. Given that the reason for this difference is not clear, there is a need for further studies in this area. Therefore, this paper discusses the occurrence and evolution characteristics; types and causes of calcareous mudstone and limestone soils under rice-planting conditions, to improve the accuracy of the systematic classification and spatial distribution prediction. 【Method】Field soil surveys were conducted to identify six Stagnic Anthrosols profiles of different slope positions (mesoslope, baseslope and footslope) on limestone and calcareous mudstones and to obtain soil-forming conditions and soil morphological characteristics of the profiles. Soil samples were collected from the profiles by horizon for analysis of physical and chemical properties. According to the “Keys to Chinese Soil Taxonomy (3rd ed.)”, diagnostic horizons and diagnostic characteristics for the tested soils were determined, and the soils were attributed and named in Chinese Soil Taxonomy level by level. The soil genesis of the tested soils is discussed based on the characteristics of organic carbon mineralization. 【Result】From the mesoslope to footslope, there was very few rust mottles on the structural plane of Stagnic Anthrosols derived from calcareous mudstone (CS), and the vertical differentiation of free iron was not obvious. However, there was very few to many rust mottles on the structural plane of Stagnic Anthrosols derived from limestone (LS), and the distribution was different in different slope positions. Especially in the acid soil of the baseslope, the lower layer of free iron accumulated significantly. This showed that there were differences in iron migration characteristics between the Stagnic Anthrosols derived from the different types of parent rocks. The accumulation of organic carbon mineralization (C₁₅) of CS was significantly (P<0.05) lower than that of LS at the same slope position. The lower amount of easily mineralized organic carbon made it difficult to reduce the high valent iron in CS. Given that iron migration in the profiles was not observable, the typical soils of CS at different slope positions were classified as Typic Hapli-Stagnic Anthrosols. From the mesoslope to footslope, the C₁₅ of LS increased gradually, with C₁₅ of footslope being significantly (P<0.05) higher than that of other slope positions. Combined with the influence of slope position on water condition, the typical soils from the mesoslope to footslope were classified as Typic Hapli-Stagnic Anthrosols, Typic Fe-accumuli-Stagnic Anthrosols and Typic Gleyi-Stagnic Anthrosols. 【Conclusion】The concentration of easily mineralized organic carbon is a key factor in determining whether slope position can cause different types of Stagnic Anthrosols derived from calcium-rich mother rock. Also, some of the Stagnic Anthrosols derived from limestone have anthro-recalcification, but cannot be classified into the subcategory of “Recalcaric” based on the current standards. Therefore, it is suggested that the retrieval requirements for the adjective “Recalcaric” of the subcategory of Stagnic Anthrosols be revised.

Abstract:【Objective】Soil total nitrogen(STN)plays an important role in terrestrial ecosystems, and hence is of great significance to mitigating the greenhouse effect and water eutrophication. Any slight changes in the STN pool will pose an important impact on global climate. It is, therefore, essential to make a precise estimation of STN density and storage in the effort to optimize nitrogen fertilizer management. However, so far most of the studies on estimation of STN have been done based on medium or small scale soil maps, and few have been reported to be based on provincial level detail soil databases. Consequently this study on STN estimation based on a provincial level soil database may help implement agricultural sustainable development with data support, and design agricultural management strategies.【Method】In this study, based on the most detailed soil database of Fujian Province, consisting of 3 082 sampling profiles and a 1: 50 000 soil map, analyses were carried out of spatial distributions of STN storage and density in the surface soil layer(0 ～ 20 cm)and soil profile(0 ～ 100 cm), in the bulk soil of the main types of soils of the Province as well as in the soils of different administrative divisions of the Province. The pedological knowledge based method, i.e, PKB, was used to correlate soil attributes with soil spatial data. So the 1: 50 000 scale soil map consisted of 247 969 soil patches and 3 082 soil profiles. 【Result】Results show that Fujian province has a total of 12.08 x 10⁶ hm² of soils. The STN density in the surface soil layer and soil profile of the province was averaged to be 0.35 kg·m^–2 and 0.97 kg·m^–2, respectively, while the STN storage was 42.06 Tg and 116.83 Tg, respectively. Analysis of the soils by prefecture shows that Nanping City was the highest, being 0.40 kg·m^–2 and Longyan followed, being 0.39 kg·m^–2 in STN density in surface soil, whereas Nanping City was the highest, being 1.19 kg·m^–2 in and Sanming City followed, being 1.11 kg·m^–2 in STN density in profile soil. Zhangzhou City was the lowest, being 0.24 kg·m^–2 and Xiamen City the next, being 0.27 kg·m^–2 in STN density in surface soil, whereas Zhangzhou City was the lowest, being 0.67 kg·m^–2 and Putian City the next, being 0.71 kg·m^–2 in STN density in profile soil. In terms of soil type, Mountain meadow soil was the highest, being 0.85 kg·m^–2 and Skeletal soil followed, being 0.57 kg·m^–2 in STN density in surface soil, whereas Mountain meadow soil was the highest, being 2.09 kg·m^–2 and Yellow soil followed, being 1.27 kg·m^–2 in STN in profile soil. Aeolian soil was the lowest, being by 0.11 kg·m^–2 and Latosolic red earth the next, being 0.17 kg·m^–2 in STN density in surface soil, whereas Aeolian soil was the lowest, being 0.27 kg·m^–2 and Latosolic red earth the next, being 0.53 kg·m^–2 in STN in profile soil. 【Conclusion】Consequently, the STN density in the surface and profile soil of Fujian demonstrates a declining trend from north to south, and from inland to coastal area, too. To sum up, the STN in Fujian Province varies significantly in spatial distribution. The findings in this study may be helpful in designing agricultural management strategies and controlling non-point source N pollution in the province.

Abstract:【Objective】As an active ground cover widely distributed in arid areas, biological crusts have an important impact on the nutrient cycle of desert ecosystems. At present, research on the nutrient effects of biological crusts is mostly concentrated on the plot scale. This study explores the spatial characteristics of biological crust nutrients at the regional scale. We aim to provide a reference for research methods on the nutrient characteristics of biological crusts at the regional scale and also provide a scientific evaluation for the ecological value of biological crust in a desert ecosystem. 【Method】The ecological restoration project carried out since 1959 has enabled the vegetation coverage in Mu Us to reach 40-50%, and biological crusts are widely distributed in this area as a sign of sandy land fixation. This study selected 146 sample points that cover the entire Mu Us Sandy land, and used geostatistics combined with multivariate statistical analysis to explore the spatial heterogeneity, distribution pattern and influencing factors of the soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP). 【Result】Biological crusts increased the nutrient content of the desert soil. The autocorrelation range of SOC and TP was relatively large, with variable ranges of 171.83 km and 147.78 km respectively, while the autocorrelation range of TN was relatively small. The nugget coefficients of SOC, TN, and TP were 53.3%, 49.86%, and 20.2%, respectively. SOC and TN exhibited moderately strong spatial autocorrelation, while TP exhibited strong spatial autocorrelation. The content of TP decreased from east to west, whereas the content of SOC and TN presented a high-low-high-low band distribution from east to west. Importantly, the main control variation factors of the three soil nutrients were different. The stepwise regression model of SOC introduced three variables, soil moisture (sm), surface downward shortwave radiation (srad), and normalized vegetation index (NDVI), while the stepwise regression model of TN introduced two variables, average temperature (Tas) and normalized vegetation index (NDVI). Additionally, wind speed (ws) and soil moisture (sm) were introduced into the stepwise regression model of TP as the first and second factors, respectively. 【Conclusion】Biological crusts in the Mu Us sandy land increased the nutrient content of desert soils. Three kinds of nutrient elements (TN, TP and SOC) showed spatial correlation and were directly or indirectly affected by vegetation conditions, surface water and heat balance, and other factors. On a regional scale, the nutrient content of soils under this biological crust was higher in the eastern part of the study area and lower in the southwest.

Abstract:【Objective】 Predicting and screening potential pesticide-contaminated sites timely and efficiently is important for controlling environmental pollution. 【Method】 Based on 46 pesticide sites samples published on the World Wide Web, the index system and method for rapid prediction of soil pollution in pesticide sites was established by a five-score analytic hierarchy process. 【Result】The predictive system was constituted with four factors: product characteristics, local climatic conditions, soil properties and site characteristics, including 11 characteristic indicators: product toxicity,product persistence, average annual temperature, average annual precipitation, average annual wind speed, light, soil texture, pH, organic matter content, production time and idle time. There is a significant linear correlation between the three indicators: production time level, product toxicity and durability level, and the soil pollution of the pesticide site. The linear comprehensive prediction accuracy of the three indicators is less than 65%. Also, the comprehensive judgment accuracy of the machine (SVM, BP) learning method combining 11 indicators is 82%, but all of them have significant limitations as they missed classified the severity of the contaminated sites. 【Conclusion】The comprehensive evaluation index value P≥0.6 is used as the prediction threshold of soil pollution in pesticide sites. The accuracy of the comprehensive prediction of the five score AHP is 91%, which is better than linear prediction and the machine learning method. It has the characteristics of low demand for key data, and efficient , and reflects the principle of“Implemented to the strictest standards without leaving a contaminated site”. It can be used for pre-diagnosis of soil pollution in various types of pesticide sites.

Abstract:【Objective】 Biochar applied in soil plays an important role in improving soil moisture and soil fertility. To explore effects of kind and incorporation depth of biochars on soil water movement and nutrient interception, an in-lab experiment was conducted. 【Method】 The experiment was designed to have a stable water potential, three kinds of biochars (biochar derived from rice husk, biochar derived from maize straw, and biochar derived from bamboo), two incorporation depths (10 cm and 20 cm), and a control plot of bare purple soil. During the experiment, water movement, total nitrogen (TN) loss and total phosphorus (TP) loss were monitored and changes in soil structure observed. 【Result】 Results show that application of biochars altered soil pore structure, which, together with the specific surface area and particle size distribution of biochars, affected the movement of soil water. The application of biochars reduced soil bulk density, to a varying extent relative to kind of the biochars applied. Among the three, rice husk biochar was the highest in the effect of reducing bulk density, and only rice husk biochar significantly increased total soil porosity and saturated soil water content. Rice husk biochar significantly promoted advance of the wetting front and enhanced soil water infiltration. The rice husk biochar incorporated into the soil 10 cm deep showed the greatest effect of promoting water infiltration in the biochar-soil layer and did not have much effect on water leakage, and when into the soil 20 cm deep, it promoted water leakage and increased saturated hydraulic conductivity. Maize straw biochar is the highest in specific surface area and in total pore volume, thus having a strong ability to retain soil water. Maize straw biochar does not have particles more than 1 mm in size. Once incorporated, it did not have much effect on soil total porosity, but did reduce soil saturated water content, thus inhibiting soil water migration. Maize straw biochar incorporated into the soil 20 cm deep showed the most significant inhibitory effect on water leakage. Bamboo biochar did not have much effect on wetting front movement and infiltration process, but did inhibit water leakage process when incorporated into the soil 20 cm deep. Moreover, it was found that rice husk biochar reduced total phosphorous loss, but increased total nitrogen loss; maize straw biochar did not have much effect on total nitrogen loss, but did have some effect of reducing total phosphorous loss; and bamboo biochar adsorbed nitrogen but enhanced total phosphorous loss. 【Conclusion】 When planning to incorporate biochars into the soil, rice husk biochar incorporated into the soil 10cm deep is the best choice, for it can effectively reduce surface runoff and total phosphorous loss, but it should be remembered that it can increase total nitrogen loss, too. Maize straw biochar incorporated into the soil 20 cm deep can reduce soil water migration rate, thus effectively inhibiting soil water leakage and total phosphorous loss, so it is the best choice for use in sandy soil and other highly permeable soils. Bamboo biochar has less impact on water infiltration and leakage than rice husk biochar and maize straw biochar, and does increase TP loss, thus making it the worst choice for use in farmlands.

Abstract:【Objective】 Sand-layered soil is widely distributed in the Hetao Irrigation District of Inner Mongolia, and its water and salt migration processes are more complicated than that in a homogeneous soil. Therefore, this study was designed to investigate the effects of different thresholds of drip irrigation on water and salt re-distribution in a sand-layered soil profile and on crop growth and water use.【Method】A two-year field experiment was conducted in a sand-layered soil field at the Hetao Irrigation District during spring maize growing seasons in 2017 and 2018. For this soil profile, the depth between 60~100 cm was sand-layer. The experiment included 5 irrigation thresholds under mulched drip irrigation, which controlled the threshold values of soil matric potential (SMP) at –10 kPa(S1), –20 kPa(S2), –30 kPa(S3), –40 kPa(S4), and –50 kPa(S5)respectively, for spring maize planting. The soil volumetric water content, water storage, salt distribution and storage in 0~120 cm soil profile, and maize grain yield and water use efficiency were analyzed. 【Result】The presence of sand layer affected the water and salt movement in the soil profile. This resulted in a significant difference in the vertical distribution of water and salt in the soil profile. The soil volumetric water content was relatively lower in the root layer between 0~60 cm depth, but higher in the sand layer between 60~100 cm depth. The soil volumetric water content in the sand layer was always kept around the level of field water capacity during maize’s growing seasons. Due to the water movement in the soil profile, more salt was concentrated in the sand layer. The abrupt transition points of distribution of water and salt in the profile appeared at an upper boundary of the sand layer. These distribution characteristics of water and salt were consistent during different growth periods. Besides, different thresholds of drip irrigation significantly affected the distribution and storage of soil moisture and salinity in different soil layers. At higher soil volumetric water content, the lowest soil EC_1:5(electrical conductivity of 1:5 soil/water extract) were observed in the root layer. Nevertheless, the difference between the soil moisture content and salt content in the sand layer and below was not significant. The grain yields of maize treated with S1, S2, and S3 were significantly higher than those of S4 and S5 (P<0.05), but the difference among the former three was not significant. Also, the water use efficiency (WUE) of maize increased first and then decreased with the decrease in irrigation thresholds, and S3 had the highest WUE. 【Conclusion】Lower irrigation thresholds favored grain yield relative to higher thresholds. Considering the water and salt environment in the root layer and WUE, it is suggested that the threshold of irrigation should be –30 kPa when cropping spring maize in this sand-layered field using mulched drip irrigation.

Abstract:【Objective】Theoretically, surface electrochemical properties of bulk soil can be well characterized by streaming potential measurement. Since the streaming potential measurement is usually adopted to measure the zeta potential of charged solid with large size (e.g. bulk soil) . Nevertheless, commercial streaming potential apparatus is cumbersome to operate and expensive. This limits the application and development of streaming potential measurement in soil research.【Method】In this study, a laboratory-made streaming potential apparatus was developed to measure the zeta potential of simulated bulk soil. Packed quartz grains and Fe oxide-coated quartz grains column were used to mimic the porous structure and surface electrochemical characteristics of bulk soil. The zeta potentials of quartz grains in NaCl electrolytes with different ionic strength (0.01, 0.05, 0.1, 0.5, 1.0, 2.0, and 5.0 mmol·L^–1) were measured by the streaming potential measurement. Also, using this self-made streaming potential apparatus, we measured the zeta potentials of quartz grains and Fe oxide-coated quartz grains in electrolytes with same ionic strength (20 μS·cm^–1) but different pHs (4.4, 5.2, 6.1, 6.6, 6.9, 7.7, and 8.0) . In addition, the zeta potentials of colloidal quartz in different pH’s electrolytes measured by traditional electrophoresis measurement was used to verify the accuracy of the streaming potential measurement.【Result】The results show that, with increasing ionic strength, the zeta potential of quartz grains measured by steaming potential measurement became less negative due to compression of the diffusion layer of the electric double layers on charged solid surfaces at higher electrolyte concentrations. Similarly, with increasing electrolyte pH, the zeta potentials of both quartz and Fe oxide-coated quartz grains measured by steaming potential measurement decreased because of the greater deprotonation effect of functional groups on the surface of quartz and Fe oxide-coated quartz grains. When Fe oxide was adsorbed on the quartz surface, the zeta potential of Fe oxide-coated quartz grains was higher than that of uncoated quartz grains. This was because of charge neutralization between positively charged Fe oxide and negatively charged quartz grains. The measured IEP (isoelectric point) of the Fe oxide-coated quartz grains was between the IEPs of quartz grains and Fe hydroxide. There was a good consistency between the zeta potentials of quartz grains measured by streaming potential and the zeta potentials of quartz colloids measured by electrophoresis measurement.【Conclusion】The results obtained by using the laboratory-made streaming potential measurement apparatus are consistent with the theoretical prediction and electrophoresis measurement. Also, the structure of the laboratory-made streaming potential apparatus is simple, its operation is convenient, and the cost to build this apparatus is low compared to commercial apparatus. Thus, the streaming potential measuring apparatus used in this study can be used as a powerful tool to conduct studies in the field of soil electrochemistry.

Abstract:【Objective】 Soil surface is the main place for various chemical and biochemical processes in soils and most of the negative charges are concentrated here. The five electrochemical characteristics, surface potential, surface charge density, surface electric field strength, specific surface area, and surface charge, deeply affect a series of physical and chemical processes in soils. Therefore, an accurate understanding of the electrochemical properties of soil surface has extensive and profound significance for the prevention and control of soil erosion, soil management and regulation, vegetation restoration and reconstruction in karst areas. However, it is still unclear how soil surface charge properties evolve with environmental factors change in different succession stages of rocky desertification.【Method】 In this study the method of combined analysis of surface properties was applied to measure surface potential, surface charge density, surface electric field strength, specific surface area, and surface charge of the soils varying in different rocky desertification grades in Anshun area. Correlation and redundancy analyses were used to explore the effects of soil environmental factors on its surface electrochemical properties. 【Result】 Soil surface charge density, surface electric field strength, specific surface area, and surface charge decreased with the increase in rocky desertification intensity, and the variation range was 0.34 C·m^–2～0.42 C·m^–2, 4.85×10⁸ V·m–1～5.86×10⁸ V·m–1, 47.11 m²·g^–1～ 53.16 m²·g^–1, 16.86 cmol·kg^–1～22.82 cmol·kg^–1, respectively. Also, the soil surface potential increased with the increase in rocky desertification intensity and the variation range was –113.74 mV～–115.10 mV. Soil clay, sand, amorphous alumina, and humic acid were the main factors affecting soil surface electrochemical properties change, and the interpretation rates were 48.3%, 38.1%, 13.0% and 12.0%, respectively. The effects of soil particle size composition, organic matter composition, and metal oxides on soil surface electrochemical characteristics were as follows: soil clay > sand > silt, humic acid > organic carbon > fulvic acid, and amorphous alumina > free iron oxide > amorphous iron oxide. 【Conclusion】 Our study revealed that during the succession of karst rocky desertification, soil physical properties, chemical properties, and oxide content changed significantly, and this led to changes in soil surface electrochemical properties.

Abstract:【Objective】As the most dynamic and bioavailable fraction of the soil carbon pool, dissolved organic matter (DOM) plays important roles in a wide range of biogeochemical processes in the environment. The interaction of soil minerals with DOM would induce structural fractionation of the DOM at the mineral/water interface, thereby influencing long-term preservation and biogeochemical processes of the DOM in the soil. Ferrihydrite, a poorly crystalline iron oxide, is known to be highly reactive to DOM in the soil owing to its high specific surface area and abundant reactive binding sites. it is widespread in the environment and can associate with DOM through either adsorption or co-precipitation. However, so far, few studies have been reported on structural fractionation of DOM at the ferrihydrite/water interface induced by co-precipitation at the molecular level. 【Method】To explore molecular fractionation of DOM at the ferrihydrite/water interface during its co-precipitation process, this study prepared ferrihydrite-DOM complex separately in solutions different in C/Fe ratio via co-precipitation and adopted the technology of combining ultraviolet (UV) spectrum with electrospray ionization Fourier transform ion cyclotron resonant mass spectrometry (ESI-FT-ICR-MS) to probe changes in DOM composition after co-precipitation ended. Species of carbon and Fe in the complex were determined with the aid of X-ray photoelectron spectroscopy (XPS) and Fe K edge XAS.【Result】Results show that Fe in the complex existed mainly in the form of ferrihydrite, of which the proportion gradually decreased from 95.9% to 68.0% with the increase in initial carbon/iron (C/Fe) ratio of the solution. UV and ESI-FT-ICR-MS analysis collectively revealed that during the co-precipitation process, ferrihydrite fixed in priority aromatic components high in molecular weight and rich in oxygen (mainly combustion-derived condensed polycyclic aromatic- and vascular plant-derived polyphenols-like substances) in the DOM, leaving aliphatic components in the solution. The lower the solution in C/Fe ratio, the higher the molecular fractionation in degree. This feature is basically consistent with what has been reported about the fractionation induced by adsorption, which indicates that no matter whether in the process of adsorption or co-precipitation, ferrihydrite tends to fix DOM components high in molecular weight and aromaticity, thus leading to changes in chemical composition of the DOM as well as surface properties of the ferrihydrite, which will in turn affect sorption, transportation and transformation processes of the contaminants therein. In addition, this study was the first to find that ferrihydrite varied dynamically with the reaction in time in selectivity to structure of the DOM, that is, combustion-derived condensed polycyclic aromatics were preferentially fixed in the ferrihydrite-DOM complex, and with the reaction going on, vascular plant-derived polyphenols-like substances followed.【Conclusion】The findings in this study are expected to be able to help understand in depth the mechanism of molecular fractionation that affects geochemical behavior of DOM in the environment via co-precipitation during the process of ferrihydrite formation.

Abstract:【Objective】Greenhouse vegetable production in China has played an important role in ensuring market vegetable supply and increasing the income of farmers. As in the greenhouse vegetable production, a high rate of fertilizer was applied, the production brings about a series of environmental problems, such as soil degradation and increased risk of greenhouse gas emission, which undermines the sustainability of the greenhouse vegetable production. In the lower reaches of the Yangtze River, the problem of non-point source pollution and labor shortage the greenhouse vegetable production faces are prominent. It has become an urgent need to have some labor-saving, efficiency-enhancing, and environment-friendly fertilization techniques. Fertigation is a technology that can save both water and fertilizer, improve fertilizer utilization efficiency, and reduce greenhouse gas emission. Fertigation is mainly applied in greenhouses in the water-deficient areas in North China, and no so common in the lower reaches of the Yangtze River. So little is available in the literature about the effects of fertigation on emission reduction and efficiency improvement in this area. 【Method】 In this study, a field experiment, designed to have three treatments, i.e. CK (no N fertilizer applied) , SF (chemical fertilizer broadcast) and DF (fertigation) , was conducted in Yixing, Jiangsu. Tomato (Solanum lycopersicum) was grown in a row of plastic greenhouses. In Treatment SF, chemical fertilizer was broadcast three times, one base application and two topdressings, making up a total of 225 kg·hm^–2 nitrogen (N) , and in Treatment DF, 225 kg·hm^–2 fertilizer was divided into five portions applied with irrigation separately as topdressing. Then, yield, N use efficiency, ammonia volatilization rate, and soil soluble N were measured for each treatment and systematically analyzed. 【Result】 Results show that fertigation significantly improved N use efficiency, and reduced soil ammonia volatilization rate and cumulative ammonia emissions, as compared with the treatment with fertilizer broadcast at the same N application rate. Treatment DF increased N use efficiency from 23.92% to 40.89% and was 71.10% higher than Treatment SF, and reduced cumulative ammonia emission from 37.25 kg·hm^–2 to 3.07 kg·hm^–2, and the ammonia loss rate from 16.56% to 1.36% during the entire tomato growth period. In Treatment CK, SF and DF, the mean NO₃^–-N residue in soil was 32.18, 45.70, and 67.06 mg·kg^–1, and the mean NH₄⁺-N residue in the 0-50 cm soil layer was 3.07, 8.27, and 19.27 mg·kg^–1, respectively. Fertigation significantly reduced the soil NO₃^–-N residues by 31.85% as compared to the treatment of fertilizer broadcast. However, it increases the risk of N leaching to some extent. 【Conclusion】 Fertigation is an efficient method combining irrigation and fertilization, which can significantly improve N use efficiency and reduce ammonia volatilization loss and soluble N residues, when applied to greenhouse vegetable fields in the lower reaches of the Yangtze River. All the findings of the research may serve as a scientific basis for extrapolation of the technique of fertigation in the Lower Yangtze River Region.

Abstract:【Objective】Soluble organic nitrogen (SON) is one of the most active components of the soil nitrogen pool in farmland and plays an important role in nitrogen transformation and ecological environment security. As SON is highly mobile, it is prone to get lost with runoff or leaching, and thus, and hence affect water quality. 【Method】To provide a theoretical basis for rational fertilization in paddy fields, prevention and control of non-point source nitrogen pollution from paddy fields and improvement of the theory of nitrogen cycling, a field experiment, designed to have the following treatments, all equivalent in nutrient content, i.e. CK (application of chemical fertilizer only), CMV1 (application of chemical fertilizer plus incorporation of milk vetch at 15 000 kg·hm^–2); CMV2 (application of chemical fertilizer plus incorporation of milk vetch at 30 000 kg·hm^–2); and CMV3 (application of chemical fertilizer plus incorporation of milk vetch at 45 000 kg·hm^–2), was carried out to explore dynamics, migration and loss of SON and dissolved organic nitrogen (DON) in grey-mud field soils. Soil samples from the treatments were analyzed for SON, respectively, using the hot water extraction method. SON concentrations were calculated by deducting TSN from the sum of SIN in the extracts. 【Result】During the growing period of rice, SON content in the 0-60 cm soil layer varied in the range from 2.09 to 22.32 mg·kg^–1, showing a trend of “increasing - decreasing - increasing - decreasing to stable”. In the treatments the SON concentration was 140.95% and 364.44%, higher in the 0-20 cm soil layer, respectively, than in the 20-40 cm soil layer and the 40-60 cm soil layer, and 92.75% higher in the 20-40 cm soil layer than in the 40-60 cm soil layer. It is quite obvious that incorporation of Chinese milk vetch during the growth period of rice is beneficial to accumulation of SON in the soil (0-60 cm). In SON concentration in the 0-60 cm soil layer during the rice growth period, Treatment CMV1, CMV2 and CMV3 was 5.57%, 10.11% and 21.39%, respectively, higher than CK. Total loss of DON from the grey-mud fields under different fertilization treatments ranged from 18.33-58.55 kg·hm^–2, accounting for 46.52%-50.16% of the TSN. Of the total loss, 3.77-37.85 kg·hm^–2 was attributed to runoff, while 14.5-18.02 kg·hm^–2 to leaching. Moreover, leaching of DON between soil layers was delayed to some extent. Compared with CK, Treatment CMV1, CMV2 and CMV3 was 16.90, 31.09 and 37.52 kg·hm^–2, respectively, lower in DON loss.【Conclusion】Incorporation of milk vetch can increase the accumulation of SON in the 0-60 cm soil layer of the grey-mud field and promote the migration of SON. However, the effects decline with soil depth. DON is one of the important forms of nitrogen loss in paddy fields. Incorporation of milk vetch can reduce DON loss and then mitigate non-point source N pollutant from the paddy fields. The environmental impact of the loss of DON from paddy fields is worthy of attention. If only the loss of inorganic nitrogen with leaching of paddy soil solution is considered, the total nitrogen loss from paddy fields will be underestimated.

Abstract:【Objective】¹⁵N isotope techniques have been widely used in investigating soil and water nitrogen transformation. The ¹⁵N isotopic composition of NO₃^–, NH₄⁺ and N₂O are key data for this type of study. These gas or liquid samples are usually stored before their concentrations or before ¹⁵N abundance are determined. Nevertheless, improper storage processes may induce changes in these samples. However, the effect of storage conditions on the ¹⁵N isotopic composition of the gas or liquid samples has not been well defined. 【Method】The influence of storage container, temperature, sample pretreatment, time and other factors on the ¹⁵N abundance of gaseous and liquid samples were studied in this paper. 【Result】The stable storage time of N₂O samples in aluminum foil air bags is very short, and its δ¹⁵N values significantly changed after 10-day storage. Also, the δ¹⁵N values were stable in a screw-top vacuum vial + butyl septa and clamp headspace vial + butyl septa for about 200 days. For soil extracts with natural abundance, the δ¹⁵N values of NO₃^– kept stable for about 10 days when refrigerated at 4 ℃ and frozen at –20 ℃, but its δ¹⁵N values of NH₄⁺ remained stable for about 60 days and no more than 10 days when frozen at –20 ℃ and refrigerated at 4 ℃, respectively. Besides, for ¹⁵N enriched soil extracts, the ¹⁵N abundance of NO₃^– was stable for about 160 days, while the ¹⁵N abundance of NH₄⁺ was only stable for about 30 days in –20 ℃ and less than 10 days in 4 ℃. For river samples, δ¹⁵N values of NO₃^– and NH₄⁺ were only stable for about 10 days no matter whether the samples were refrigerated at 4 ℃ or frozen at –20 ℃.【Conclusion】 Our results highlight the importance of storage conditions on ¹⁵N abundance of gas and liquid samples, and provides scientific guidance for proper storage conditions when adopting ¹⁵N isotope techniques.

Abstract:【Objective】Mixed culture technology of soil suspension and culture medium, high-throughput sequencing, and conventional analysis methods were used to study the influence of long-term fertilization on inorganic phosphorus (P) mobilization in soil. 【Method】Soil samples were collected from the plots of a 15-year-long experiment regarding crop cultivation and fertilization in Zunyi City, China. The treatments included (i) fallow soil (Control), (ii) consecutive flue-cured tobacco cultivation plus the application of only chemical fertilizers (C-CF), (iii) consecutive flue-cured tobacco cultivation plus the application of chemical fertilizers in combination with manures (C-CFM), (iv) flue-cured tobacco-maize rotation plus the application of only chemical fertilizers (R-CF), and (v) flue-cured tobacco-maize rotation plus the application of chemical fertilizers in combination with manures (R-CFM). The soil collected from the long-term fertilization test site was divided into two parts. A part of the soil sample was used for the mixed culture technology of soil suspension and culture solution. The method involved preparing the soil suspension (soil: sterile water = 1: 100) and then diluting it to 10^-5 with sterile water. 200 mL diluent was taken and inoculated into NBRIP (National Biological Research Institute phosphate growth medium) solid medium with Ca₃ (PO₄)₂, FePO₄ and AlPO₄ as phosphorus sources. After incubation at 30 ℃ for 2 days, the number of colonies with a phosphorus dissolving circle was observed. Then, another 200 mL 1: 100 soil suspension was taken and inoculated in 50 mL NBRIP liquid medium with Ca₃ (PO₄)₂, FePO₄ and AlPO₄ as phosphorus sources for 16 days. At 12, 24, 48, 72, 96, 120 and 144 hours after inoculation, the culture medium was drawn, and the pH, soluble inorganic phosphorus content, and organic acid content were determined. The other part of soil samples was sent to Meggie Biological Company for high-throughput sequencing to study the effect of long-term fertilization on the relative abundance of enzyme synthesis pathway related to organic acid synthesis. 【Result】The number of cultivable microorganisms (bacteria, fungi, actinomycetes and inorganic phosphate bacteria) in flue-cured tobacco-maize rotation, application of organic fertilizer and Control soil increased, and the population diversity increased. When the soil suspension was inoculated in a microbial culture medium, the content of available phosphorus was higher in the flue-cured tobacco-maize rotation than in consecutive flue-cured tobacco cultivation. Also, the available phosphorus was higher in the application of chemical fertilizers in combination with manures and Control than when only chemical fertilizers were applied; among which R-CFM was the highest and C-CF was the lowest. In the mixture, hydrogen ions were significantly correlated with dissolved Ca₃ (PO₄)₂, and organic acids were significantly correlated with dissolved FePO₄ and AlPO₄. This indicates that compared with pure culture technology of phosphorus-mobilizing microbes, soil suspension culture can not only reflect the phosphorus-mobilizing characteristics of microorganisms but also be closer to the complex phosphorus solubilization status of soil microbial flora. In high-throughput sequencing, the relative abundance of the synthetic pathways of citrate (Si) -synthase, protein glucose dehydrogenase and malate synthase in the soil of R-CFM was significantly higher than that of other treatments. 【Conclusion】 Optimal crop cultivation and scientific fertilization are conducive to the activation of soil inorganic phosphorus, and R-CFM can be promoted as a flue-cured tobacco demonstration cultivation model for widespread promotion in Zunyi tobacco areas. Soil suspension culture can be used as an extension of pure microbial liquid culture as (a) it is closer to the complex phosphorus solubilization status of soil microbial flora, (b) effectively characterizes the ability of PMM to activate inorganic phosphorus, and (c) supplements the deficiencies of pure microbial liquid culture technology. The difference in the relative abundance of enzyme synthesis pathways related to the synthesis of organic acids also explains the reason for rational crop rotation and combined application of chemical fertilizers and manures to promote the activation of soil inorganic phosphorus from the perspective of molecular biology.

Abstract:【Objective】 Prevention and control measures of soil erosion can restore forest vegetation and improve soil quality, and hence affect the soil microbial community structure. Soil microbes play an important role in soil substance recycling. Thus, it is of great significance to explore changes in soil biochemical processes and to study the effects of typical prevention and control measures of soil erosion on the interactions between soil microbial community. Ecological network analysis can be used to reveal microbial interactions and microbial network structure. However, it is still unclear how prevention and control measures of soil erosion affect the microbial interaction network in Pinus massoniana plantation. There are few researches exploring soil microbial interactions and the changes in environmental factors caused by agricultural engineering measures and vegetation planting. 【Method】 In this paper, a one-year field experiment was carried out in Pinus massoniana plantation of the Institute of Soil and Water Conservation of Shaoyang City (111°22'E, 27°03'N), Hunan Province, China. The experiment was designed to have three treatments, one for digging fish-scale pits and planting grass, one for digging fish-scale pits and planting grass and shrubs and another for a control check without any measure; three replicates were conducted for each treatment. One year later, soil samples were collected from the three treatments, separately, for analysis of soil physicochemical properties and DNAs. The 16S rRNA and 18S rRNA Illumina MiSeq high-throughput sequencing technology was used to determine the soil microbial community structure under different treatments, and the random matrix method was used to construct the microbial network. 【Result】After implementation of prevention and control measures of soil erosion, soil microbial community composition changed as the relative abundance of Chloroflexi significantly decreased and that of Proteobacteria and Acidobacteria significantly increased. Ecological network analysis showed that the total nodes, total links, average connective degree, and the modularity of the microbial network increased. This indicated an increase in the microbial network scale and complicated microbial interactions. Three microbial networks were dominated by negative interactions (60.59%～67.49%), and the competition between species was strengthened after the implementation of the two measures. Parts of the microbial communities of Chloroflexi, Actinobacteria, and Proteobacteria played an important connecting role in the microbial network of the study area. Also, some key microbial communities with low relative abundance (< 1%) played a key role in the establishment of the microbial network. The average path distance of microbial networks became longer after the implementation of the measures. This means that the response rate of microbial action slowed down and the stability of the community structure was improved. Additionally, the measure of digging fish-scale pits and planting grass and shrubs was more effective than digging fish-scale pits and planting grass. Soil bulk density (R² = 0.465, P < 0.05), pH (R² = 0.377, P < 0.05) , soil organic matter (R² = 0.383, P < 0.05), and total nitrogen (R² = 0.545, P < 0.01) had significant influence on bacterial community structure while soil water content (R² = 0.485, P < 0.05) had a significant influence on fungal community structure. 【Conclusion】After implementation of prevention and control measures of soil erosion (i) soil microbial community structure changed, (ii) the microbial network scale, interaction and stability increased, and (iii) the competition within soil microbial communities became more intensive.

Abstract:【Objective】pH and oxygen were the key limiting factors for the ammonia oxidation activity of archaea. The law of competition and adaptation of different archaea ecotypes (soil archaea and marine archaea) to pH and oxygen in complex soils are still unclear.【Method】Ammonia-oxidizing archaea (AOA) was selected as the marine archaea Group1.1a-associated with acid forest soil with pH = 5.40, and the active ammonia-oxidizing archaea were selected as the soil archaea Group 1.1b-associated with alkaline paddy soil with pH = 8.02. After adjusting the pH and oxygen concentration of the mixed soil, a stable isotopic probe microcosm indoor culture experiment was set up to analyze the intensity of soil nitrification. Also, quantitative PCR and 454 high-throughput sequencings were employed to study the effect of different pH and oxygen conditions on the number of soil ammonia-oxidizing archaea and bacteria and also the types of active ammonia-oxidizing microorganisms present.【Result】Compared with zero time, the contents of nitrate nitrogen and ammonium nitrogen had no change at pH3.8; At pH6.0 and 7.6, nitrate nitrogen content increased by 23 times and 19 times, respectively, and the ammonium nitrogen content decreased significantly. The results show that after the soil samples were mixed, there was no nitrification at pH 3.8, while strong nitrification occurred at pH 6.0 and 7.6. Also, the nitrification in a high-oxygen environment was stronger than that in a low-oxygen environment. After substrate culture, the number of oxidizing archaea was increased significantly; DNA-SIP shows that the active ammonia oxidizing archaea with pH 6.0 and 7.6 were almost all soil archaea Group 1.1b.【Conclusion】 This study reveals that pH rather than oxygen is the main factor affecting nitrification. Although oxygen also has a certain effect on nitrification; in neutral and alkaline soil, soil archaea lineage has greater activity in high O₂ and low O₂ environment and have more adaptive capacity than marine lineage.

Abstract:【Objective】 Although hexachlorocyclohexane (HCH) has been banned as pesticide in agriculture for decades, its residue, still high in concentration, has been frequently observed in soil due to its property of persistentcet, So it remains to be an important task to well elucidate how HCH affects soil microbial communities in diversity and structure, and a topic of great significance to ecological health of the agro-environment systems. 【Method】In this work, a greenhouse experiment was conducted, in red and purple soils grown with wheat, spiked with HCH at a rate of 0, 600, or 1 500 g•hm-2. Soil bacterial community structure and diversity in the soils were determined using the high throughput sequencing technique. Total DNA in the soil samples were extracted using the Power Soil DNA Isolation Kit, a product of from MOBIO and tested with 1% agarose gel electrophoresis for quality. Compositions of the soil microbial communities were characterized with the sequencing technique.【Result】Alpha index analysis revealed that HCH significantly increased diversity of the bacterial community in the red soil, while no significant effect was observed in the purple soil at the beginning of the wheat cultivation. However, after 42 days of cultivation, no significant differences were found between the soils spiked with HCH and CK in soil bacterial community diversity in the soils. Analysis of bacterial community compositions showed that Proteobacteria and Actinobacteria were the dominant phyla at the phyluma level, and HCH increased the diversity of Actinobacteria and Acidobacteria in the red soil, while Proteobacteria and Acidobacteria were the dominant ones in the purple soil. Relative abundance of Bradyrhizbium in red the soil increased with the spiking rate of HCH, and its abundance did about 150% and 180% in the soils spiked with 600 and 1 500 g·hm^–2 HCH, as compared ing with that in the control treatment. However, in the purple soil, relative abundance of the nitrogen-fixing bacteria decreased with the addition of HCH.【Conclusion】The residue of HCH obviously induced the changes in diversity and structure of the of soil bacterial community in the soils, and the impact was more obvious in the red soil than in the purple soil. The findings provide a basis for understanding of the micro-ecological effects and safety assessment of HCH in the soil environments.

Abstract:【Objective】The stability of biochar provides a basis for a better understanding of its potential to sequestrate soil carbon(C). This study aimed to study the stability of rice straw biochar in a Zelkova serrata plantation soil under in situ conditions and to explore the relationship between the stability of biochar, its chemical properties, soil temperature, and soil moisture content.【Method】Two biochars were produced by pyrolyzing rice straw at 300 ℃ and 500 ℃. By using ¹³C isotope, the stability of the biochars in soils was examined through 182 d in situ experiments in a Zelkova serrata plantation.【Result】The cumulative decomposition of 300 ℃ and 500 ℃ biochars was 10.5 and 3.65 g·m^–2, respectively, during the entire experiment. The results of double-exponential fitting indicated that the mean residence time of the recalcitrant C in 300 ℃ and 500 ℃ biochars were 99.8 a and 302 a, respectively. The decomposition rate of 300 ℃ biochar was significantly positively correlated with surface soil temperature(P = 0.034, r = 0.417, n = 26)but not for 500 ℃ biochar(P = 0.549, r = 0.123, n = 26). This indicated that the effect of soil temperature on biochar stability depends on its pyrolysis temperature.【Conclusion】To sum up, this study demonstrated that biochar produced at 500 ℃ is more stable than biochar produced at 300 ℃ through in situ experiments, and provides basic data for further study on biochar stability.

Abstract:This study was conducted to explore effects of biochar-based fertilizer on physiology and nitrogen uptake of flue-cured tobacco and nitrogen balance in the yellow soil－flue-cured tobacco system, which will provide certain scientific guidance for optimizing nitrogen management in the yellow soil of the tobacco-planting areas in Guizhou and reducing pollution in the ecological environment of the farmland of tobacco-planting areas in Guizhou. A field experiment, carried out with flue-cured (Yunyan 87)in yellow soil for the study, was designed to have three treatments, i.e. no nitrogen (CN), conventional fertilizer (CF), biochar-based fertilizer (BF). Results show that Treatment BF significantly increased soil urease activity, root length and surface area, glutamine synthase and glutamate synthetase activities in leaves, and nitrogen uptake of flue-cured tobacco. Treatment BF was significantly 35.06%and 14.24% higher than Treatments CN and CF in nitrogen uptake of flue-cured tobacco, respectively. Treatment BF was the highest in activity, volume and dry biomass of root and yield of flue-cured tobacco, and significantly higher than Treatment CN. Nitrogen surplus was obviously detected in the yellow soil－flue-cured tobacco system in all the treatments, the nitrogen input was mainly the initial soil inorganic nitrogen, while the nitrogen output mainly consisted of soil inorganic nitrogen residue and nitrogen uptake of flue-cured tobacco. Treatment BF increased inorganic nitrogen residue in the 0-20 cm soil layer. Moreover, Treatment BF significantly decreased nitrogen apparent loss by 44.42 kg·hm^–2, and decreased nitrogen surplus by 37.70 kg·hm^–2, and significantly increased nitrogen apparent recovery efficiency by 16.15%. Therefore, the reasonable application of biochar-based fertilizer is an effective way to optimize management of nitrogen in the yellow soil and protect ecological environment of tobacco-planting areas in Guizhou.