Abstract:Urban green infrastructure is an effective way to solve many environmental issues caused by urbanization. As urban soils are generally not suitable for vegetation growth, a lot of soil resources needed for urban green infrastructure construction can only be excavated and transported from the exurban farmland and/or natural topsoil to urban areas, or in another way, urban soils are planted vegetation after fertilized with organic waste. These methods tend to be costly, destructive to arable land, induce large carbon emissions, and/or have a high cumulative risk of pollution. The huge amount of soil resources needed for the construction of urban green infrastructure is very scarce and this has to be addressed urgently. Constructed Technosols (CT) is a new soil created by using organic and inorganic solid wastes (including artefacts and also seminatural sediment and excavated deep soil-like things) for growing plants, which can be adjusted to meet the requirements of various vegetation types, land uses, site conditions (roof, balcony, street, etc.) in physicochemical properties and pollutant limit standards, and finally returned to the city for green infrastructure construction. CT can simultaneously alleviate the pressure of disposal of urban solid waste and solve the issue of soil shortage in urban green infrastructure construction. It features low carbon, low cost and low eco-impact, and can also produce economic benefits. In this paper, firstly, it was briefly stated the definition, classification and construction techniques of CT. And, the research status and advances mainly in terms of roles in plant growth, carbon capture, biodiversity protection, runoff pollutant removal, and artificial biological intervention of CT were presented. Then, it was briefly described the production of solid waste in China, and according to the current research and application situation, it was proposed the application potential (such as ornamental plant breeding and cultivation, sod production and urban farming etc. in addition to the park, green buffers, green roof and brownfield remediation like things) and advantages of CT. Finally, based on comprehensive research progress, some problems in CT research were pointed out and some insights and suggestions were put forward. Meaningful research on the ecological risk of pollutants in CT, biochar (hydrochar or pyrochar) application to CT, soil heterogeneity design for plant diversity, biological regulation of CT good for human health, promotion of environmental function for CT, and role of carbon sequestration by CT were proposed and supposed. It was aimed that comprehensive reutilization of urban solid waste and more eco-friendly low-carbon development of urban green infrastructure will be able to be promoted, urban carbon sequestration will increase, and urban ecological environment and people's health and well-being will be improved.

Abstract:Soil moisture is an important link for the exchange of water and heat processes between the surface and the atmosphere, and is of great significance to agricultural production, ecological planning, and water resources management. Microwave remote sensing has the advantages of not being affected by weather conditions and being able to better detect the soil information and trend of soil moisture change under vegetation coverage. Thus, it is a hot spot for accurate soil moisture retrieval by remote sensing. With the gradual increase in the number of Earth observation satellites, microwave detectors have developed from C-band to L-band, and soil moisture datasets have become more and more abundant. In this paper, the existing global-scale soil moisture products based on microwave remote sensing are summarized. It also analyzes and compares the principle, characteristics, application scope and key technological progress of active microwave remote sensing, passive microwave remote sensing, and active and passive microwave fusion in soil moisture retrieval. The advantage of active microwave remote sensing and passive microwave remote sensing is high spatial resolution and high temporal resolution, respectively. High spatial resolution can capture the subtle spatial information features of the surface, but it is limited by the complex relationship between soil moisture and backscattering coefficients, especially the interference of vegetation and surface roughness on the radar backscattering coefficient making retrieval of soil moisture inaccurate. Therefore, selecting different scattering models according to the actual situation and using multi-source data synergy are the current research hotspots to improve accuracy. This paper summarizes the active microwave soil moisture retrieval method into three types: mechanism model, empirical model and semi-empirical model according to the principle. We also considered the applicability and shortcomings at the same time. For instance, high temporal resolution can achieve global and large-scale soil moisture monitoring, but it is difficult to meet the actual research needs of small-scale or small-scale areas. In order to better match the measured data in space, four downscaling methods based on the geostatistical method, mathematical statistics method, data assimilation method and multi-source remote sensing data fusion method are proposed. Combining the advantages and disadvantages of the above two microwave remote sensing methods, researchers can rely on more abundant data sources and relatively mature observation technology to fuse and extract more moisture information and to improve the retrieval accuracy or obtain long-term series data. However, this method often has the problem of missing data due to factors such as revisit time, seasonal ice period or radio frequency interference, which has a great impact on the spatiotemporal continuity of the data. So, the interpolation methods based on time, space, and statistics have been employed to solve the missing value issues. In the current method, soil moisture retrieval shows good performance at small scales, but at the global scale, there will be many problems such as missing data, poor applicability, low retrieval accuracy, and too complicated retrieval processes. Improvements can be made by employing multiple observation methods (multi-polarization, multi-angle, multi-band), multi-temporal repeated observation, the introduction of new algorithms on the original model and data assimilation. The rapid development of long-term stable and high spatiotemporal resolution L-band microwave signals in the field of land remote sensing of Global Navigation Satellite System also provides a reference for the development of China's BeiDou Navigation Satellite System, showing its huge application potential.

Abstract:Saline-alkali land is one major medium-low yield land in China, it is increasingly important to improve the saline-alkali land in compensating decreasing cultivated land and ensuring the security of crop productivity. In China, the reclamation of saline-alkali land has always been attached great importance, while the increasing fresh water scarcity in saline-alkali area has become the crucial constrain in saline-alkali land utilization. In the current situation of the freshwater shortage, how to optimally regulate the movements of soil water, fertilizer and salt is the key scientific problem in sustainable utilization of saline-alkali land. Focusing on above scientific problems, numerous studies of fertile plough layer construction have been conducted in recent years to decrease soil salinity and increase the soil quality including organic fertilization, field tillage, water-saving irrigation, field coverage and saline water utilization etc., the fertile plough layer with the function of “salt control, fertilizer maintaining the water conservation” can be constructed in saline-alkali land. Meanwhile the natural movements of water, salt and fertilizer are significantly alerted in Soil Plant Atmosphere Continuum, and the aim of collaborative improvements of quality and capacity for saline alkali land can be realized. The above contents have increasingly become an important research direction in the sustainable utilization of saline-alkali land. The present study systematically summarizes the research progresses in the reclamation and fertile plough layer construction of saline-alkali land, and looks forward to the integrate regulation of soil water, fertilizer and salt and its synergistic relationship with plant growth under fertile plough layer construction in saline alkali land, in order to provide reference for the sustainable reclamation and utilization of saline-alkali land.

Abstract:【Objective】 Soil organic carbon (SOC) forms the basis of soil fertility, food production, and soil health, and plays a key role in climate change via mediating greenhouse gas emissions. Consequently, accurate characterization of SOC spatiotemporal dynamics is extremely important for the sustainable management of soil resources, ecosystem stability maintenance, and mitigation and adaptation to climate change. 【Method】 A total of 399, 413, and 407 cropland topsoil (0 ~ 20 cm) SOC data in 1980, 2000, and 2015 were collected from the southern Jiangsu Province of China, respectively, and the microbial-explicit SOC model MIMICS (Microbial-Mineral Carbon Stabilization) was used to model the spatiotemporal dynamics of SOC. The Sobol global sensitivity analysis was applied to identify the sensitive parameters of the MIMICS model, and then, two-parameter optimization schemes, one batch (using all SOC observations in a batch mode to optimize the parameters) and site-by-site (using SOC observations at individual sites to optimize the parameters site by site), were used to optimize the sensitive parameters of the MIMICS model through Markov Chain Monte Carlo (MCMC) approach, respectively. The coefficient of determination(R²), root mean squared error (RMSE), and mean absolute error (MAE) that were calculated from the independent validation of SOC in 2000 and 2015 were used to compare the performance of different parameter optimization schemes.【Result】Results show: (1) The net increment of SOC density between 1980 and 2000 was 0.89 kg·m^-2, while the net decrement was 0.44 kg·m^-2 between 2000 and 2015, representing a net increment of 0.45 kg·m^-2 over the period of 1980-2015; (2) The MIMICS model with parameters optimized by either One batch or site-by-site method can represent the overall trends in topsoil SOC dynamics during the period of 1980-2015, but the model with parameters optimized by the site-by-site method presents more local details on the variability of the SOC change rate; (3) Compared with the default parameter values and the One-batch optimized parameter values, the MIMICS model with site-by-site optimized parameter values had the best performance in modeling the spatiotemporal dynamics of SOC in the study area, with the RMSE decreasing by 22.2% (the independent validation in 2000) and 14.7% (the independent validation in 2015) in comparison with the MIMICS model with default parameter values. Yet, its prediction accuracy in 2015 was still relatively low (R² = 0.13, RMSE = 1.22 kg·m^-2). 【Conclusion】The optimization of sensitive parameters can improve the space-time SOC prediction accuracy of the MIMICS model, and the representation of local details on the spatiotemporal patterns of SOC dynamics. Although the MIMICS model with the spatially heterogeneous parameter values optimized by the site-by-site method had the best performance, its prediction accuracy in 2015 was still relatively low, which indicated that the MIMICS model still has limitations in representing the responses of SOC to anthropogenic activities such as changes in land use and agricultural management practices. Thus, further improvement of the MIMICS model structure and enhancing the spatiotemporal resolution of model input data are still significant challenges for regional scale modeling of SOC spatiotemporal dynamics through microbial-explicit SOC models.

Abstract:【Objective】Shajiang black soil is one of the major soil types with low or medium productivity in China and is mainly distributed in the Huai River North Plain. As the soil is high in clay content and its parent material is dominated by montmorillonite, it suffers from swelling/shrinkage, low infiltration and strong strength. Suitable tillage is widely considered an effective measure to improve soil structure. However, how tillage practice impacts the pore structure of Shajiang black soil is not clear. Therefore, the objective of this study was to assess the effect of different tillage practices on soil pore structure characteristics in Shajiang black soil. 【Method】Intact soil columns (20 cm height, 10 cm diameter) were sampled from three tillage treatments including no-tillage (NT), rotary tillage (RT) and deep ploughing (DP) at Longkang Farm in Anhui Province, and then were scanned using X-ray computed tomography at a voxel resolution of 60 m, and followed by saturated hydraulic conductivity (K_s) measurement. After reconstruction of CT images, characteristics of soil macropore (>60 m) morphology and networks were quantified with Image analysis. 【Result】Compared to no-tillage, rotary tillage and deep ploughing increased soil macroporosity by 192.7% and 261.1% (P < 0.05), respectively. Rotary tillage and deep ploughing significantly increased the hydraulic radius, compactness, fractal dimension and global connectivity of soil macropores (P < 0.05), but decreased the degree of anisotropy and Euler number (P < 0.05). The K_swas significantly improved under rotary tillage and deep ploughing. Deep ploughing improved soil structure and K_s better than rotary tillage did. A significant correlation was observed between K_s and macropore structure characteristic parameters (P < 0.05), in which the connected largest macroporosity was the highest (r=0.833**, P< 0.01). 【Conclusion】Deep ploughing enhanced pore hydraulic radius, connectivity and complexity, built a good soil pore morphology and network structure and consequently improved hydraulic conductivity and reduced structural obstacles of Shajiang black soil.

Abstract:【Objective】Biochar has been shown to improve soil physicochemical properties and enhance crop yields. The results of previous studies on soil temperature were inconsistent, the changes of crop emergence rate under the change of biochar application rate were not analyzed in detail, and the relationship between crop emergence rate and soil physicochemical properties such as soil bulk density, temperature and organic carbon was neglected. Thus, it is important to estimate the most appropriate application rate of biochar for improving soil physicochemical properties and crop yield to provide a basis for field management. 【Method】In this paper, a salinization soil in south Xinjiang was researched and field cotton and sugarbeet growth experiments were carried out in plots under different biochar treatments (0, 10, 50, and 100 t·hm^-2) and combined with drip irrigation mode under plastic mulching. The improvement extent and influences of biochar application on soil physicochemical properties and crop germination rates were detailed investigated at the biochar application rates. The relationship between germination rates and soil physicochemical properties was further investigated and compared. 【Result】The results showed that the fluctuations of daily air temperature and solar radiation directly affected the fluctuations of soil temperatures in various depths with biochar applications. The increase of biochar application amounts significantly reduced the soil bulk density at the 0-30 cm depths, in which cotton and sugar beet decreased by 0-0.32 and 0.04-0.25 g·cm^-3, respectively. The application of biochar at 100 t·hm^-2 significantly increased the soil temperature at the 5 cm depth at different growth stages of cotton and sugar beet, but the application of biochar at 10 and 50 t·hm^-2 only significantly increased the soil temperatures of the 5 cm depth at seedling and bolling stages of cotton. During the two experimental years of 2018 and 2019, biochar application have significantly increased the soil organic carbon content of cotton and sugar beet at the seedling and harvesting stages by 0.98-13.2 and 0.66-12.1 g·kg^-1 if the differences of planting year and growth periods were not considered, respectively. Also, the increase rate was 1.20-7.43 at the cotton seedling stage and 0.66 to 13.2 g·kg^-1 at the harvest stage if the differences of planting year and crops were not considered, respectively, and was proportional to the application rates at the seedling stage. The emergence rate of cotton and sugar beet both increased with the increased soil bulk density, and increased first and then decreased with the increased soil temperature. The optimum temperature range for cotton and sugar beet germination was 22 to 26 ℃. The germination rate increased first and then decreased with the increased soil organic carbon contents, indicating that the excess increase of soil organic carbon content caused by high biochar application rates inhibited crop germination. When the application amount of biochar was 10 t·hm^-2, the seedling emergence rates of cotton and sugar beet were greater than 0.7, which was higher than that of the other three biochar application rates. However, when the biochar application rate was greater than 10 t·hm^-2, the emergence rates of cotton and sugar beet were lower than that of the treatment without biochar application. 【Conclusion】Therefore, a biochar application amount of 10 t·hm^-2 is recommended as the optimal amount for cotton and sugar beet field management considering its comprehensive effects on improving soil properties and crop germination rate.

Abstract:【Objective】To provide a basis for an advanced study on the impacts of biochar on soil carbon and nitrogen cycling, the effects of residence time after isotope labeling on the δ¹³C and δ¹⁵N values of rice aboveground and underground tissues and biochars derived from these two tissues were studied.【Method】Rice plants were labeled with ¹³Cand ¹⁵N by pulse labeling of ¹³C-CO₂ and foliar fertilization of ¹⁵N-urea, respectively. The residence time of 4 h, 6 h and 24 h was set after ¹⁵N isotope labeling. The labeled rice plants were divided into aboveground and underground tissues and four biochars were produced by pyrolyzing these two tissues at 300℃ and 500℃, respectively. The δ¹³C and δ¹⁵N values of rice tissues and their biochars were determined by isotope mass spectrometry.【Result】With the increase in residence time, δ¹³C values of the aboveground tissues of rice plants gradually decreased from 872‰ to 578‰, while the δ¹³C values of the underground tissues gradually increased from 226‰ to 869‰. Unlike with the δ¹³C, the δ¹⁵N values in the aboveground tissues of rice plants first increased then decreased, and the maximum(1 764‰)occurred at the residence time of 6 h, while δ¹⁵N values in the underground tissues first decreased and then increased. Overall, compared to rice tissues, the δ¹³C and δ¹⁵N values of the biochars decreased by 52.1% and 15.9%, respectively. Moreover, both the δ¹³C and δ¹⁵N values of the biochars were highest at the residence time of 24 h, especially for the 300℃ biochar. With the increase in residence time, the reduced proportion of the δ¹³C of hot water extractable dissolved organic carbon when compared with that of the residual solid increased from 4.14% to 11.0% for the 300℃ biochar, while it decreased from 32.3% to 18.9% for the 50 ℃ biochar. This indicates that increase in the residence time decreased and increased the uniformity of ¹³C of the 300℃ and 500℃ biochars, respectively.【Conclusion】Our results demonstrate that the effects of residence time after labelling on δ¹³C and δ¹⁵N values of the rice plants were different, and the biochars did not retain the isotopic signature of the raw rice tissues. Residence time and pyrolysis temperature together affected the uniformity of ¹³C in rice biochars.

Abstract:【Objective】After receiving precipitation, exposed rock surface in a rocky desertification area exposed to bedrock is easy to form rock surface flow, which carries organic and inorganic substances on the rock surface to the surrounding soil. This has a significant impact on the change of soil nutrients at the rock-soil interface. 【Method】 This study was designed to investigate the effect of rock surface flow on the leaching and input of nitrogen and phosphorus in the soil at the rock-soil interface. Three plots: fallow land (one-year rock surface flow), abandoned irrigated grassland (five-year rock surface flow), and sloping farmland (no/little rock surface flow) with obvious bedrock exposure, were chosen. We chose three special shapes of the rock surface, namely convex, straight, and concave, at different horizontal distances from the rock surface and soil layer to study the variation characteristics of total nitrogen and total phosphorus in the soil at rock-soil interfaces and non-rock-soil interfaces. 【Result】 The results indicated that rock surface flow contributed either to the input or leaching of nitrogen and phosphorus in the 0-10 cm surface of the rock-soil interface soil. However, it had a minimal effect on nitrogen and phosphorus in the 10-20 cm deep rock-soil interface soil. The intensity of the leaching and input of nitrogen and phosphorus in the surface soil of the rock-soil interface formed by different rock surface shapes followed concave > straight > convex. In the 1-year fallow land, under the action of rock surface flow, the influence of rock surface flow formed by concave rock surface on soil nitrogen at the rock-soil interface was mainly manifested as leaching, while flat and convex rock surfaces exhibited input effects. Also, the effects of rock surface flow with different shapes on soil phosphorus at the rock-soil interface showed leaching. For the 5-year rock surface flow, the result depicted mainly an input phenomenon. 【Conclusion】These results can provide a scientific basis for further understanding the influence of exposed rock on soil characteristics of the karst ecosystem.

Abstract:【Objective】The study aimed to assess and determine the P loss risk in red soil profiles of sloping upland and paddy fields based on the variation of soil phosphorus storage capacity (SPSC). 【Method】The soil samples were collected from different pedogenic horizons in peanut uplands and paddy fields which were located at the top, middle and bottom of the slope in Sunjia small watershed, Ying tan, Jiangxi province of China. The profile variation characteristics of total P(TP), soil available P(Olsen-P), P saturation rate (PSR), P sorption index (PSI) and SPSC of tested soils were analyzed. Also, the effects of soil total carbon, total nitrogen, iron-aluminum oxides, pH, Eh and bulk density (BD) on the P loss risk of red soil profiles at different slope positions were evaluated. 【Results】Soil TP and Olsen-P of the surface layer in peanut uplands and red paddy fields were significantly higher than those in the bottom layers and the profile variations of TP and Olsen-P in paddy fields were significantly higher than those in peanut uplands. Compared with the Ap1 layer, the PSI of peanut upland in the subsurface soils increased significantly by 33.1%~146%, and the PSI decreased with the increase of profile depth, but the PSI of paddy fields increased significantly with the increase of profile depth. The soil PSR of peanut upland and paddy field(except PF-M)decreased gradually with the increase of profile depth, while the variation ranges of SPSC were -89.2~298.3 mg·kg^-1 and -138.1~101.1 mg·kg^-1, respectively. The SPSC values of PU-T and PU-M were all positive, and they decreased with the increase of profile depth. Also, the SPSC value of all pedogenic horizons in PU-B(except Ap2)were all negative. The SPSC values of pedogenic horizons in PF-T (except Brs), PF-M (except Ap1), and PF-B were negative, and they changed significantly with the increase of profile depth. 【Conclusion】Based on the assessment of soil phosphorus storage and its environmental loss risk in sloping red soil profiles by SPSC theory, the migration and transport signs of soil P in peanut upland along the profile and slope position are obvious. Once soil Olsen-P > 27.6 mg·kg^-1, the risk of soil P loss in the peanut upland profiles will increase sharply, and control measures should be taken in time. The risk of P loss exists in each soil profile of the paddy fields, thus, proper management practices should be implemented during the application of P fertilizer.

Abstract:【Objective】Sugar-clay aggregates play important roles in the transformation of nutrient elements such as phosphorus in soils. However, few studies have paid attention to the initial formation of microaggregates and subsequent adsorption of phosphorus mediated by the molecular weight of sugar in the nanoscale.【Method】In this experiment, a model clay, laponite, and representative sugars including glucose and dextran with different molecular weights were selected to serves the research objects. The formation of aggregates mediated by sugars with different molecular weights was observed by Raman spectroscopy and atomic force microscopy (AFM), and then the differences in interactions of laponite and sugar with different molecular weights were measured by single molecular force spectroscopy (SMFS). Finally, the content of phosphorus adsorbed by microaggregates was compared via the measurement of sorption isotherms of phosphate by laponite or sugar-laponite complexes.【Result】The molecular weight of sugar was important for interaction with laponite and the size of sugar-clay microaggregates increased with molecular weight, suggesting stronger interactions of laponite with the sugars. Phosphate adsorption was increased for sugar-laponite microaggregates compared to laponite because of an increase in the content of hydroxyl and surface Zeta potential of microaggregates. Also, the amount of phosphate adsorbed was observed to decrease with an increase in the molecular weight of sugar due to the greater particle size of high-molecular-weight sugar-laponite microaggregates.【Conclusion】The results showed that sugars with high molecular weight promoted the formation of microaggregates but disfavored the adsorption of phosphorus by microaggregates. These nanoscale observations will provide a new method and theoretical basis for understanding the biogeochemical cycle of phosphorus involved in microaggregates in soils.

Abstract:【Objective】In calcareous soils, iron (Fe) generally exists in the form of oxides or hydroxides, which is not conducive to plant absorption and utilization, thus frequently causing Fe deficiency in plants. In flooded acidic soils, such as paddy soil, due to conditions of irrigation and drainage and alternate cultivation of water and drought, the redox potential of the soil is low and ferric Fe is reduced to be ferrous. The ferrous Fe is readily absorbed and utilized, resulting in excessive Fe absorption by plants. Fe deficiency and excess are limiting factors affecting rice yield and quality. Fe deficiency leads to chlorosis and reduces plant growth while Fe overload is toxic for plants, with a typical symptom of leaf bronzing. Several transcriptome analyses have been performed to investigate the responses under Fe stress. However, a comprehensive dissection of the entire Fe-responsive profile at the protein level is still lacking. It is necessary to analyze the rice responses under Fe deficiency and Fe excess using proteomic analysis. 【Method】 In this study, a label-free proteomic analysis was performed on rice shoots grown in Fe-deficient (0 μmol·L^-1), Fe-sufficient (40 μmol·L^-1), and Fe-excess (350 and 500 μmol·L^-1) conditions. 【Result】Results showed that 130, 157 and 118 differentially accumulated proteins (DAPs) were identified under Fe deficiency and two concentrations of Fe excess stresses, respectively, compared with Fe sufficient conditions. Gene ontology enrichment analysis of the DAPs revealed that primary metabolic process, organonitrogen compound metabolic process, response to stimulus, and oxidative stress responses were significantly enriched under both Fe deficiency and excess stresses. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that DAPs under Fe deficiency and Fe excess were commonly enriched in metabolic processes like the ribosome, photosynthesis, and oxidative phosphorylation. Notably, the abundance of proteins involved in phenylpropanoid biosynthesis and biosynthesis of cofactors was mainly affected by Fe deficiency, while the abundance of proteins involved in the biosynthesis of amino acids was mainly influenced by Fe excess. Under Fe excess stress, the abundance of enzymes involved in amino acid metabolism was decreased, indicating a reduction in the content of plant-synthesized amino acids. However, the increased abundance of transketolase involved in photosynthesis and secondary metabolism probably reduced the inhibitory effect induced by Fe stress. Ribosomal proteins S16, Os03g0798600 and RPL17 may play important roles in response to Fe deficiency and Fe excess stresses, but the exact functions of these proteins under Fe stress are still unknown. Several novel proteins which may play potential roles in rice Fe homeostasis were also predicted in this study. 【Conclusion】Overall, our results indicate both Fe deficiency and Fe excess stresses affected photosynthesis and ribosomal metabolism. The synthesis of phenylpropane was mainly affected by Fe deficiency, while amino acid metabolism was mainly affected by Fe excess in the shoots of rice. The findings will provide some information for the exploration of key factors for the efficient absorption and utilization of Fe.

Abstract:【Objective】It is of great importance to clarify the current regional distributions and influencing factors of soil available iron (Fe), manganese (Mn), copper (Cu) and zinc (Zn) concentrations. This will improve understanding of the soil micronutrient supply abilities and guarantee high-yield and high-quality wheat in major wheat production regions of China.【Method】During 2016 to 2021, a successive 6-year in situ farm survey was conducted in combination with the collection of topsoil (0-20 cm) samples from 1 314 randomly selected farmland fields in 17 major wheat production provinces and regions in China. The soil-available Fe, Mn, Cu and Zn concentrations were determined to evaluate their abundance and deficiency status based on China’s classification criteria for soil-available micronutrients. Also, it was quantified the contribution of main soil chemical properties on Fe, Mn, Cu and Zn availabilities by random forest analysis.【Result】Results showed that the soil available Fe ranged from 1.8 to 611.9 mg·kg^-1, with an average of 49.1 mg·kg^-1, and 8.9% of samples had lower soil available Fe than the Fe deficiency threshold of 4.5 mg·kg^-1. Soils with relatively low available Fe were usually observed in the provinces of Shanxi, Shaanxi and Gansu in northern and northwestern wheat production regions, while high-Fe soils were found in southwestern and middle and lower Yangtze River wheat regions. Also, soil available Mn ranged from 0.1 to 176.2 mg·kg^-1, with an average of 22.1 mg·kg^-1, and 6.9% of samples exhibited lower soil available Mn than the Mn-deficient threshold of 5.0 mg·kg^-1. Mn-deficient soils were mainly distributed in Shanxi, Shaanxi, Gansu provinces and Inner Mongolia Autonomous Region in northern and northwestern wheat growing regions, while soils with high and very high available Mn often occurred in southwestern and middle and lower Yangtze River wheat regions. Soil available Cu ranged from 0.1 to 10.8 mg·kg^-1, with an average of 1.9 mg·kg^-1, and only 1.8% of samples had lower available Cu than the Cu-deficient critical value of 0.5 mg·kg^-1. Soil available Zn ranged from 0.1 mg·kg^-1 to 26.0 mg·kg^-1, with an average of 1.4 mg·kg^-1, and 14.3% of samples’ available Zn was lower than the Zn deficiency threshold of 0.5 mg·kg^-1. Zn-deficient soils were mainly found in Shanxi, Shaanxi, Gansu provinces and Inner Mongolia Autonomous Region of northern and northwestern wheat production regions, and higher Zn concentrations were mainly observed in soils of Yunnan and Guizhou provinces of southwestern wheat regions. Among the investigated soil chemical properties, the pH was the most important influencing factor to available Fe and Mn, and available Fe contributed to the highest Cu availability, and available phosphorus, followed by Cu, was found to be the leading factor for soil available Zn in major wheat production regions of China. 【Conclusion】 There were large regional variations in the soil-available Fe, Mn, Cu, and Zn concentrations in China’s wheat fields. Deficiencies of soil available Fe, Mn and Zn were serious problems on calcareous soils in the northern part, and higher supplies of these micro-elements occurred in the southern part, while almost all of the wheat fields were not identified as Cu-deficient soil in China.

Abstract:【Objective】As one of the most important food crops in China, rice (Oryza sativa L.) is the staple food for more than half of the country’s population. With the development trend of global warming and frequent occurrence of extreme weather such as sustained high temperature, drought on farmland is becoming a more frequent and urgent problem. Thus, this study seeks to clarify the effects of drought stress on rice at different growth stages, the regulation of potassium on drought stress and its mechanism, and to provide a theoretical basis for the management of potassium and efficient water use in rice.【Method】A two-factor pot experiment of K and water treatments at different periods was carried out in 2021. Potassium management was two levels of 0.15 (+K) and 0 (-K) g·kg^-1 soil (calculated as K₂O), moisture management was four levels of drought stress at the tillering stage (TD), drought stress at booting stage (BD), drought stress at milking stage (MD) and well-watered treatment (WW), to explore the effects of K fertilizer on rice yield and physiological characters under drought stress at different growth stages. 【Result】Results showed that drought stress significantly decreased rice yield. Compared with the WW treatment, TD, BD and MD treatments decreased rice yields by 53.9%, 45.2%, and 7.6% under K deficient conditions, respectively, while under K sufficient conditions, rice yields reduced by 28.3%, 16.5% and 5.9%, respectively. The degree of influence of drought stress on yield in different growth stages was: TD > BD > MD, and K deficiency aggravated the negative impact of water deficit on rice yields. Similarly, drought stress also caused a decrease in canopy transpiration rate, leaf water potential, leaf net photosynthetic rate, and limited dry matter accumulation. Compared to the WW treatment corresponding to the same period, TD and BD treatments reduced leaf biomass by an average of 42.9% and 31.2%, respectively. The stem sheath biomass decreased by 43.8% and 38.0%, respectively, and the effect of water deficiency on biomass in different growth stages was: TD > BD. Potassium deficiency resulted in a reduction in net photosynthetic rate, leaf area and chlorophyll content, which restricted the ability of plants to receive light radiation and produce dry matter. Compared with the K-sufficient treatment, the leaf biomass of the TD and BD and WW treatments at the same stages decreased by 52.6%, 32.7%, 42.1%, and 31.2%, respectively. Also, under potassium deficient conditions, stem sheath biomass decreased by 55.3%, 63.6%, 52.2%, and 28.0%, respectively. Drought stress exacerbated the negative effects of potassium deficiency. 【Conclusion】Our results indicated that drought stress could limit the net photosynthetic rate and leaf water potential, resulting in the reduction of rice yield, which affects the tillering stage and booting stage more than the milking stage. Potash application significantly increased leaf area, increased chlorophyll content, enhanced the ability of rice to intercept light radiation, improved rice photosynthetic efficiency, and increased rice dry matter accumulation, while reducing canopy transpiration rate, improving water use efficiency, alleviating the decline of leaf water potential, thereby enhancing the drought resistance of crops.

Abstract:【Objective】Cadmium (Cd) is a harmful element to the human body and can cause many serious diseases. At present, many soils are faced with serious Cd contamination. For example, the soil in Yunnan Province highly polluted by Cd, and necessary steps need to be taken to remedy this situation. The application of biochar to soils is a common way to remedy soil Cd contamination, therefore, this research is designed to study the properties of biochar from different plant sources and evaluate their application effect on Cd pollution in the Dongchuan area, Yunnan Province. 【Method】The isothermal adsorption-desorption and adsorption kinetic characteristics of rice straw biochar (RBC), wheat straw biochar (WBC), corn straw biochar (MBC), hemp straw biochar (HBC), sesbania biochar (TBC) and peanut shell biochar (PBC) were studied; Through pot experiments, the effects of the above biochar on Cd fraction in Cd-contaminated soil and Cd uptake by Lactuca sativa L. in Dongchuan were analyzed. 【Result】Fitting results of adsorption models showed that Langmuir adsorption isotherm and the pseudo-second-order model could better simulate the adsorption process of Cd by biochar. TBC’s maximum saturated adsorption capacity was the highest, 37.1 mg·g^-1 in the isothermal adsorption model and 27.9 mg·g^-1 in the adsorption kinetic model, respectively. The desorption rates of WBC, RBC and TBC were lower than those of MBC, HBC and PBC, and no more than 10% under each concentration gradient. Fourier transform infrared spectroscopy (FTIR) analysis showed that TBC contained more oxygen-containing functional groups (OH-, C=O etc.). Also, the XRD analysis showed the biochars were mainly composed of C and Si elements, while different biochars also had some different elements (e.g. Fe, Mn etc.). Compared with the treatment without biochar (CK), WBC, MBC, HBC, TBC and PBC treatments significantly reduced the content of soil available Cd. Among them, the maximum decrease was observed for TBC (24.32%). At the same time, the Cd fraction changed from an acid soluble state to a reducible state, oxidizable state and residual state. Compared with the treatment without biochar, WBC, MBC, HBC and TBC treatments significantly reduced the Cd content in the aboveground parts of Lactuca sativa L. (P<0.05), and the maximum decrease occurred in HBC (26.40%). In addition, WBC and HBC treatments significantly reduced the translocation factors of Cd in Lactuca sativa L., which were 0.662 0 and 0.692 8 respectively. The results of ABT (aggregated promoted tree) analysis showed that soil soluble organic carbon (DOC) and soil pH were the main influencing factors of soil available Cd, with a significant negative correlation, and the contribution rates were 33.0% and 21.9% respectively. 【Conclusion】In conclusion, all the biochars from different plant sources can reduce the availability of Cd in Cd-contaminated soil in Dongchuan, change the Cd fraction in soil, and reduce the absorption and transport of Cd by plants. There are differences between different biochars. Moreover, TBC can be selected to remedy Cd-contaminated soil in the Dongchuan area through the results of the isothermal adsorption test, adsorption kinetics test and pot experiments.

Abstract:【Objective】Soil colloids, especially water-dispersible colloids (WDC), as pollutant carriers, play important roles in heavy metal adsorption, migration, and biological absorption. The purpose of this study was to explore the effect of exogenous rice straw and redox change on the distribution of heavy metals in the aqueous phase of the soil and water-dispersible colloids. 【Method】In this study, soil microcosm experiments were conducted for 70 days, in which 0-40 days was the reduction period, and 41-70 days was the oxidation period. The experiment comprised two treatments: (i) no straw added (CK), (ii) rice straw added (1% of the soil weight, S). The different chemical parameters in the aqueous phase of the soil were comprehensively compared, and the particle size classification and elemental composition of WDC during the redox process were characterized by asymmetrical flow field-flow fractionation (AF4) coupled to UV and ICP-MS (AF4-UV-ICP-MS) method. 【Result】The results showed that in anaerobic conditions, exogenous rice straw increased aqueous concentrations of dissolved organic carbon (DOC), arsenic (As), iron (Fe), manganese (Mn), calcium (Ca), potassium (K), silicon (Si), aluminum (Al), and magnesium (Mg), while it decreased aqueous redox potential (Eh) and the concentrations of copper (Cu) and lead (Pb). In aerobic conditions, exogenous rice straw increased aqueous concentrations of Pb. Results from AF4-UV-ICP-MS indicated that the size of WDC was mainly distributed at three size ranges, 0.3-3 kDa, 3-40 kDa, and 130 kDa-450 nm with different complexes of organic matters, inorganic clay minerals, and ferriferous minerals. A significant proportion of heavy metals in the aqueous phase were bound to WDC particles, which indicated that WDC played an important role in the environmental behavior of these pollutants. WDC with different particle sizes tended to combine different kinds of heavy metals. Exogenous rice straw affected the distribution of heavy metals in WDC particles and this effect was related to the nature of the elements. Also, exogenous rice straw promoted the transformation of Fe and As from WDC state to the dissolved state, while promoting the transformation of cadmium (Cd) and Cu from dissolved state to the WDC state. 【Conclusion】Water-dispersible colloids were important carriers for heavy metals in the aqueous phase of the soil. Exogenous rice straw and redox change affected the behavior of WDC associated heavy metals related to the nature of elements. This study is important as it reveals the interface mechanism of how agricultural activities affect the migration, transformation, and bioavailability of heavy metals.

Abstract:【Objective】Guangdong is a major province of vegetable production and consumption in China, and is also an important vegetable production base for Hong Kong, Macao, and the "Southern Vegetables and Northern Transportation". Therefore, rapid diagnosis and assessment of soil heavy metal pollution is the premise of soil pollution prevention and control and risk management. This study aimed to investigate the applicability of in situ and ex situ portable X-ray fluorescence spectroscopy (PXRF) for rapid detection of heavy metals in greenhouse vegetable production soils of Guangdong Province and to diagnose and evaluate heavy metal pollution in greenhouse vegetable production soils based on portable X-ray fluorescence spectroscopy. 【Method】A total of 110 greenhouse vegetable production soil sampling sites and 26 open-field soil sampling sites were set up in the study area. PXRF was used in situ to rapidly detect soil heavy metal contents (Cd, Cu, Cr, Pb, Zn, As, Ni and Hg). The accuracy of the PXRF method was verified by analyzing the correlation between the values of soil heavy metals measured by the PXRF and the traditional laboratory analysis and based on this, the soil heavy metal pollution status was quickly diagnosed. The risk of soil heavy metal pollution was evaluated by the single factor pollution index and the Nemerow composite pollution index method. 【Result】The results indicated that: (1) the concentrations of Cd, Cu, Cr, Pb, Zn, As and Ni detected by the ex situ PXRF method were significantly correlated with those determined by traditional laboratory methods (P < 0.01), and the R² were 0.69, 0.50, 0.56, 0.58, 0.47, 0.54 and 0.62, respectively. Also, the results of in situ determination of Pb and As in soil by the PXRF method were significantly correlated with those by traditional laboratory methods (P < 0.01), and the R² were 0.73 and 0.74, respectively. (2) When the soil moisture content was 150 g·kg^-1-200 g·kg^-1, the results of in situ determination of Cr, Pb, Zn and As in soil by the PXRF method were significantly correlated with those by traditional laboratory methods (P < 0.01), and the R² were 0.77, 0.94, 0.72 and 0.93, respectively.(3)Soil Cd and Cu pollutions were prominent in greenhouse vegetable production soils of Guangdong Province. The point exceeding rates were 20.9% and 10.0%, respectively, according to the Soil Environmental Quality Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018). In addition, the average content of Cd in greenhouse vegetable production soil was 0.21 mg·kg^-1, which was 1.2 times greater than that in open-field soil. The contents of Cd, Cu, Cr, Pb, Zn, As and Ni in the greenhouse vegetable production soil in the Pearl River Delta were generally higher than those in other areas.(4)The single pollution index of Cd, Cu, Cr, Pb, Zn, As, Ni and Hg were all less than 1, and the order was Cd > Cu > Pb > Zn > Cr > As > Ni > Hg. The mean value of the Nemerow comprehensive pollution index was 0.69. From the overall average, the degree of soil heavy metal pollution was at a clean level.【Conclusion】In summary, PXRF is an effective method for the rapid diagnosis of heavy metal pollution in greenhouse vegetable production soils in Guangdong Province. Furthermore, Cd and Cu can be quickly identified as the primary pollution elements with high risk in greenhouse vegetable production soils of Guangdong Province. The results of this study will serve as a reference for the evaluation of soil environmental quality and sustainable development of greenhouse agriculture.

Abstract:【Objective】Reductive soil disinfestations (RSD) is an effective agriculture practice to conquer continuous cropping obstacles by the elimination of soil-borne pathogens, degradation of allelochemicals, improvement of soil microbial community structure, and restoration of soil microbial functions. However, the effects of RSD practice on the stability of the mono-cropped soil microbial community are still unknown. Moreover, the relationship between soil microbial community stability and functions also needs to be studied. Therefore, this study was oriented to explore the relationship between the stability and function of soil microbial communities driven by reductive soil disinfestation.【Method】A field experiment, designed to have four treatments, i.e. CK (control without soil treatment); SB (RSD incorporated with 15 t·hm^-2 organic substrate with C/N ratio of 122); BD (RSD incorporated with 15 t·hm^-2 organic substrate with C/N ratio of 19); and SB+BD (RSD incorporated with 15 t·hm^-2 organic substrates containing both high and low C/N ratios with equal mass), was carried out in a lisianthus mono-cropped soils in Shiping County, Yunnan Province. Biolog microplate method, quantitative real-time PCR, and high-throughput sequencing were used to analyze the microbial community stability, microbial metabolic activity and function diversity, and the abundance of nitrogen-related functional genes.【Result】Results showed that RSD significantly reduced the stability of bacterial community composition and abundance as compared to CK, with the effects of SB+BD treatment being stronger than that of SB and BD treatment, whereas it had no significant effect on the stability of fungal community composition and abundance. Also, RSD significantly enhanced the stability of interactions between bacterial and fungal communities, and SB and BD treatments had greater effects on the improvement of stability of the interaction between microbial communities than SB+BD treatment. Regression analysis indicated that the stability of interaction relationship of soil microbial community was closely related to the stability of microbial composition and abundance. In addition, correlation analysis showed that soil microbial community stability was highly correlated with its activity, carbon metabolic function and denitrification capacity.【Conclusion】Collectively, reductive soil disinfestation can improve the stability of interactions between microbial taxa by reducing the stability of microbial community composition and abundance, thereby promoting the restoration of soil microbial activity and improvement of community ecological function.

Abstract:【Objective】This study aimed to understand the key processes that drive the changes in diversity and community assembly of arbuscular mycorrhizal (AM) fungi in greenhouse ecosystem.【Method】Soil samples were collected during different growth stages (i.e., fallow period, flowering stage, fruiting stage) of tomatoes in a greenhouse. Illumina MiSeq high-throughput pyrosequencing was performed to investigate the changes in taxonomic and phylogenetic diversity and community structure of AM fungi. The relative importance of stochastic and deterministic processes in structuring AM fungal community at different growth stages was analyzed by phylogenetic structure analysis.【Result】Results showed that both taxonomic and phylogenetic diversity of AM fungi varied significantly across different growth stages. Compared with the fallow period, OTU richness, Shannon diversity, Pielou evenness, phylogenetic diversity (PD) and mean pairwise phylogenetic distance (MPD) of AM fungi significantly decreased by 42.82% - 59.18%、43.25% - 48.31%、17.46% - 25.40%、57.14% - 67.86% and 50.00%, respectively, during the flowering and fruiting stages. In addition, the relative abundance of Glomus was promoted in the growing period, whereas the relative abundance of Claroideoglomus and Paraglomus decreased. Also the relative abundance of Archaeospora followed a unimodal pattern. Results of permutational multivariate analysis of variance (PERMANOVA) and non-metric multidimensional scaling analysis (NMDS) showed that, based on both taxonomic and phylogenetic data, the community structure of AM fungi in tomato soils during the fallow period was significantly different from that of the growing period, while the difference in community composition between the flowering and fruiting stage was not significant. According to the phylogenetic structure analysis, we found that the mean net relatedness index (NRI) across all samples was equal to zero at the fallow period, indicating phylogenetic random of AM fungal community, whereas the mean NRI was significantly greater than zero in both the flowering and the fruiting stages, indicating phylogenetic clustered. These results suggest that the primary ecological process structuring communities shifted from a stochastic process at early succession to a deterministic process at the tomato growing stage when local environmental filtering increased, which inference was also supported by the neutral community model (NCM) results. Mantel test showed that soil pH, soil nutrients (SOC, total NPK, and Olsen-P) and salt content, as well as soil temperature and humidity, significantly affected the seasonal changes of AM fungal community.【Conclusion】The highly intensive production stress in the greenhouse vegetable ecosystem promoted the transformation of the primary ecological process of AM fungal community assembly from a random process to a deterministic process, leading to a decrease in diversity and a change in community structure. Our results reveal the degradation of soil quality and the evolution of the microbiome in the process of greenhouse vegetable cultivation.

Abstract:【Objective】Revealing soil microbial community stability of different long-term fertilization strategies is helpful to guide field fertilization management and ensure soil health and sustainable development of agroecosystems. 【Method】Based on the long-term stationary field experiment on nutrient balance in the Fengqiu National Agro-ecological Experimental Station of the Chinese Academy of Sciences, the experiments of drought disturbance and rewet recovery were carried out on three different fertilization strategies of Fluvo-aquic soils. The microbial community stability (resistance and recovery) was quantified and compared in terms of dehydrogenase activity, bacterial alpha diversity, key taxa, community structure and molecular ecological network. 【Result】Compared with no fertilization (CK) and mineral NPK fertilizers (NPK), organic manure plus mineral NPK fertilizers (OM) significantly increased the resistance and recovery of the microbial community. After rewet treatment, soil alpha diversity recovered faster than community function and structure. Soil alpha diversity, the abundance of key taxa and network topology parameters recovered to the initial level, while dehydrogenase activity and community structure did not recover completely. 【Conclusion】This study quantified and compared the microbial community stability of three different fertilization strategies from a variety of microbial community response indexes. The results showed that the application of organic manure plus mineral NPK fertilizers could significantly improve the stability of the microbial community, which is a good fertilization management strategy to ensure the soil health and sustainable development of the farmland ecosystem.

Abstract:【Objective】Masson pine forest (Pinus massoniana Lamb.) is a typical ectomycorrhizal (ECM) dominant forest. However, in recent years, the ecological service function of the Masson pine forest decreased due to pine wood nematode disease, and the Masson pine forest was gradually replaced by an Arbuscular mycorrhizal (AM) dominant broadleaved forest. However, it remains unclear what influence could be exerted by the changes of dominant mycorrhizal types on soil organic carbon accumulation during the conversion of Masson pine forest to broadleaf forest in the subtropical region. 【Method】In this study, the biomass of ECM fungi and AM fungi were determined by high-performance liquid chromatography (HPLC) and neutral lipid fatty acids (NLFA), respectively. At the same time, phospholipid fatty acids (PLFAs) technology was used to study the characteristics of the microbial community. The content of glomalin-related soil protein (GRSP) and the activities of soil extracellular enzymes was also determined in Masson pine and broadleaved forests in Jiande County, Zhejiang Province.【Result】The results showed that: AM fungi-dominated (AMD) broadleaved forest replaced ECM fungi-dominated (ECMD) Masson pine forest, soil organic carbon in AM fungi dominated broadleaved forest was significantly enhanced by 36.81%, microbial carbon use efficiency (CUE) significantly increased by 53.85%, and AM fungal biomass significantly increased by 25.57%. Moreover, compared with ECM fungi-dominated forests, the biomass of ECM fungi in AM fungi-dominated forests decreased significantly by 45.04%. The Masson pine forest, which was dominated by ECM fungi, was subjected to more severe microbial nitrogen limitation. Phospholipid fatty acids analysis showed that the gram-positive bacteria (G⁺) and the ratio of gram-positive bacteria to gram-negative bacteria (G⁺/G^-) in Masson pine forest dominated by ECM fungi compared with the broadleaved forest dominated by AM fungi were significantly decreased by 21.47% and 6.46%, respectively. Redundancy analysis (RDA) results showed that there were significant differences in microbial community structure between forests dominated by AM fungi and ECM fungi (P<0.05), in which AM fungal biomass (R²=0.48, P=0.002) and soil organic carbon content (R²=0.47, P=0.003) were significantly correlated with the variation of microbial community structure (P<0.05).【Conclusion】The decrease of GRSP and the different recruit of microbial groups by different mycorrhizal fungi types were important reasons for the reduction of soil organic carbon content in forests dominated by ECM fungi compared to AM fungi dominated forests. Therefore, the substitution of broadleaved forest for Masson pine forest in the subtropical region increased the content of forest soil organic carbon and improved the function of the forest carbon sink.

Abstract:【Objective】Soil aggregate organic carbon and extracellular enzymes play an important role in improving soil structure and carbon sequestration, which are easily affected by agronomic management practices. In order to study the effects of long-term straw returning combined with chemical fertilization on organic carbon components and extracellular enzymes in soil aggregates, a 35-year field positioning experiment was carried out. 【Method】The field experiment was designed to have three treatments in a rice-wheat rotation system: no chemical fertilizer (CK), chemical fertilizer only (NPK), and straw plus chemical fertilizer (NPKS). The contents of soil organic carbon (SOC) and its labile components (dissolved organic carbon (DOC), easily oxidizable organic carbon (EOC) and microbial biomass carbon (MBC)) in soil aggregate were analyzed, as well as the activities of extracellular enzymes related to carbon cycle (β-1, 4-Glucosidase (BG), β-1, 4-Xylosidase (BX) and β-D-Cellobiohydrolase (CBH)). 【Result】The contents of SOC, DOC and MBC in >0.25 mm aggregates were significantly higher than those in <0.25 mm aggregates, and their contents of NPKS treatment were the highest. This showed that NPKS promoted soil macro-aggregates organic carbon regeneration. The values of MBC/SOC and DOC/SOC in each particle size aggregate were relatively stable, which indicated that dynamic change trends of MBC and DOC were consistent with that of SOC. Thus, MBC and DOC could be used as sensitive indexes to evaluate soil organic carbon. The 2-0.25 mm aggregates were the main carriers of extracellular enzymes, and their activities in NPKS treatment were the highest. However, the enzymes activities in >2 mm aggregates had no significant difference among treatments. The soil organic carbon components and extracellular enzymes in soil aggregates promoted each other, in which the contents of SOC, DOC and MBC in aggregates were mainly affected by CBH, followed by BG; while EOC was only positively affected by CBH. These two extracellular enzymes (CBH and BG) could promote soil organic carbon turnover and the interaction was enhanced in 2-0.25 mm aggregate. 【Conclusion】Long-term application of straw returning combined with chemical fertilizer could increase organic carbon regeneration and turnover rate, and increase soil organic carbon content, which is an important agronomic way for sustainable carbon sequestration in paddy soil.

Abstract:【Objective】Ca²⁺ produced by dissolution of desulfurized gypsum will react with carbon-containing anions (CO₃^2-, HCO₃^-) in the soil, and eventually CO₂ is absorbed and fixed as soil inorganic carbon. The inorganic carbon fixation of desulfurized gypsum in alkaline soil improvement is of great significance to achieving "carbon neutrality". 【Method】In this study, the 0-20 cm soil layer of desert alkaline soil in the Sangong River basin of Fukang, Xinjiang, was improved by using desulfurized gypsum as a calcium source. The changes in soil inorganic carbon (SIC) and soil inorganic carbon density (SICD) were investigated under different application rates of desulfurized gypsum at different times, so as to study the role of inorganic carbon sequestration in alkaline soil improvement. 【Result】The results showed that the application of desulfurized gypsum significantly reduced soil alkali damage (pH decreased) and increased soil salinity and inorganic carbon sequestration effect (SIC and SICD increased) (P<0.05). The optimal application rate of desulfurized gypsum was 30 t·hm^-2, when the pH of the improved soil layer was reduced to the lowest (8.24). The SIC increased by 0.93 g·kg^-1 and SICD increased by 0.29 kg·m^-2 (i.e., CO₂ fixation was 1.06 kg·m^-2) from 0 to 46 days after the improvement. The amount of desulfurized gypsum application was significantly positively correlated with SIC, SO₄^2- and Ca²⁺ (P<0.05) and negatively correlated with pH, CO₃^2-, HCO₃^- and Na⁺ (P<0.05) during the improvement process. Climatic factors had an effect on soil inorganic carbon sequestration; increasing relative humidity and precipitation suppressed the increase in SIC and SICD, while increasing wind speed, temperature and total solar radiation facilitated it. 【Conclusion】The results of this study provide direct evidence that the application of desulfurized gypsum to improve alkaline soils will increase the carbon sequestration potential of the soils.

Abstract:【Objectives】This study aimed to analyze the influence of the acidification environment on weathering products of the typical purple parent rock. The weathering products of purple parent rocks from the Suining Group (J₃s), Shaximiao Group (J₂s), and Penglaizhen Group (J₃p) were investigated under different acidification environments in the laboratory. 【Method】 The acid solutions used for acidification of purple parent rock samples were used to cycle soaking and simulate leaching experiment tests at pHs of 2.5, 3.5, 4.5, and 5.6. In addition, deionized water (pH = 7.0) was set as a control treatment (CK). 【Result】 The results showed that the exchangeable cations and content of total exchangeable cations of weathering products of these purple parent rocks decreased as the acidity of the acidifying solutions increased. The acid buffering capacity of weathering products had an extremely significant correlation with the content of the exchangeable K⁺, Na⁺, Ca²⁺, and Mg²⁺ and the content total of exchangeable cations (P < 0.01). Compared with the value at pH = 7.0 (CK), the total content of exchangeable cations of the weathering products of purple parent rock of the groups J₃s, J₃p, and J₂s in cycle soaking experiment tests decreased by 8.75%-18.21%, 10.83%-23.18%, and 5.85%-18.41%, respectively. When the amount of simulated rainfall at 24 times was compared with that at 12 times, the total content of exchangeable cations in J₃s, J₃p, and J₂s decreased by 1.77%-24.85%, 8.99%-25.75%, and 8.05%-25.66%, respectively. In addition, the exchangeable cations characteristics of the weathering products were Ca²⁺> Mg²⁺> Na⁺ > K⁺ under the same acidity treatment. 【Conclusion】The acid buffer capacity, exchangeable salt ions, and total salt of weathering products under the soaking treatment in this experiment were lower than under the leaching treatment. It can be seen that the transport of minerals or nutrients on the slopes of hilly areas is dominated by leaching, while the transport of minerals or nutrients on the plains is dominated by leaching. Therefore, acid deposition may accelerate the occurrence of soil erosion on slopes to some extent, which in turn leads to an acceleration of the plain side process.

Abstract:【Objectives】This study aimed to provide a scientific basis for optimizing appropriate film mulching practices to improve productivity and protect the environment in dryland farming.【Methods】A complete random two-factor field experiment was conducted in Pengyang, Ningxia Province to investigate the coupled effects of mulching (started in 2012) with different straw-derived carbon inputs on the soil aggregate characteristics, organic carbon content, and maize yield. Specifically, the mulching method was the main factor and the straw return form was the sub-factor. Six treatments were established as follows: straw return with film mulching (PS), biochar return with film mulching (PC), no-return with film mulching, straw return without mulching (TS), biochar return without mulching (TC), and no return without mulching.【Results】The results indicated that each straw and biochar return treatment significantly (P < 0.05) improved the soil aggregate distribution and stability of each particle size, and the aggregate content > 0.25 mm increased significantly (P < 0.05) by 47.32% on average. Compared with the no-mulching treatment, the mean weight diameter and geometric mean diameter of the soil particles increased by 9.19% and 4.15%, respectively, under the double ridge-furrow mulching treatments. The organic carbon content of the 0-60 cm soil layer increased significantly (P < 0.05) under each straw and biochar return treatment compared with the no-return treatments, where the contents were 2.60% and 2.73% higher under PC and TC than PS and TS, respectively. The aggregate organic carbon contents under each treatment increased as the aggregate particle size increased. Also, the straw and biochar return treatments significantly increased the organic carbon content of aggregates, whereas the contents decreased under double ridge-furrow mulching treatments. Structural equation modeling showed that the straw return form, mulching method, and soil organic carbon content could significantly promote yield increases, while the straw and biochar return treatments significantly increased (P < 0.05) the corn yield in film-mulched fields by 14.6% on average. However, the yield increase did not differ significantly between the straw return treatments and biochar return treatments.【Conclusion】In conclusion, double ridge-furrow mulching and straw carbon input treatments significantly improved the soil stability, soil organic carbon content, crop yield, and the coupled effect of the double ridge-furrow mulching and biochar return had a positive effect on improving the farmland soil quality and fertility.