Formation of Tianwen-1 landing crater and mechanical properties of Martian soil near the landing site

After landing in the Utopia Planitia,Tianwen-1 formed the deepest landing crater on Mars,approximately 40 cm deep,exposing precious information about the mechanical properties of Martian soil.We established numerical models for the plume-surface interaction(PSI)and the crater formation based on Computational Fluid Dynamics(CFD)methods and the erosion model modified from Roberts’Theory.Comparative studies of cases were conducted with different nozzle heights and soil mechanical properties.The increase in cohesion and internal friction angle leads to a decrease in erosion rate and maximum crater depth,with the cohesion having a greater impact.The influence of the nozzle height is not clear,as it interacts with the position of the Shock Diamond to jointly control the erosion process.Furthermore,we categorized the evolution of landing craters into the dispersive and the concentrated erosion modes based on the morphological characteristics.Finally,we estimated the upper limits of the Martian soil’s mechanical properties near Tianwen-1 landing site,with the cohesion ranging from 2612 to 2042 Pa and internal friction angle from 25°to 41°.

Thunderstorm and Lightning Activities over Western Pacific,Northern Indian Ocean and South China Sea Along with Their Adjacent Lands

The Lightning Imaging Sensor(LIS)and Radar Precipitation Feature(RPF)data are used to investigate the activities and properties of lightning and thunderstorms over a region including the Western Pacific,northern Indian Ocean and the South China Sea along with their adjacent lands.The lands feature significantly more frequent lightning flashes and thunderstorms than the oceans,especially the open oceans.The highest densities of lightning and thunderstorm occur over the Strait of Malacca and the southern foothills of the Himalayas.Over the ocean regions,the Bay of Bengal and the South China Sea are characterized by relatively frequent lightning and thunderstorm activities.Larger average spatiotemporal size and optical radiance of flashes can be found over the oceans;specifically,the offshore area features the most significant flash duration,and the open ocean area is characterized by the greatest flash length and optical radiance.The smallest average values of flash properties can be found over and around the Tibetan Plateau(TP).The oceanic thunderstorms tend to have a significantly larger horizontal extent than the continental thunderstorms,with the former and latter having the average area of the regions with radar reflectivity larger than 20 dBZ,generally over 7000 km^(2) and commonly below 6000 km^(2),respectively.The TP thunderstorms show the smallest horizontal extent.Meanwhile,the oceanic thunderstorms exhibit greater 20 dBZ but smaller 40 dBZ top heights than the continental thunderstorms.The average flash frequency and density of the oceanic thunderstorms are typically less than 5 fl min^(-1) and 0.3 fl 100 km^(-2) min^(-1),respectively;in contrast,the corresponding values of continental thunderstorms are greater.It is explored that the regions associated with strong convective thunderstorms are more likely to feature small-horizontal-extent and low-radiance flashes.

Impacts of Changes in Structure of Rural Land Property Rights on Agricultural Performance

In the reform process of the rural land property rights system,the incentive mechanism of the rural land property rights system has a crucial impact on the production activities of rural economic entities.Due to the different rights structures of the property rights system in different social and economic development stages,the land rights and interests enjoyed by rural economic subjects are different,and the degree of incentives for farmers is also different.This difference in incentives affects farmers investment in agricultural production factors,which in turn affects agricultural performance.This paper analyzes the incentive impacts of the structure of rural land property rights on the changes of farmers land rights and agricultural performance since the founding of the People s Republic of China,in order to further deepen the reform of the land system,protect the rights and interests of farmers,promote the modernization of agriculture and rural areas,and explore the realization form and operation mechanism of the rural collective land system in the new era.

GIS-Based Assessment of Soil Chemical and Physical Properties as a Basis for Land Reclamation in Toshka Area, Aswan, EGYPT

The accurate assessment of soil properties is a crucial factor for composing and implementing reclamation plans. The main objective of this study was to evaluate soil chemical and physical properties and calculate the chemical and fertility index for assisting land reclamation in Toshka area. The Toshka area is located between latitudes 31°32'N and 31°36'N and longitudes 32°40'E and 32°60'E. GIS was used to select 16 sites. The results revealed the soil has undesirable characteristics. The soil pH ranged from slightly alkaline to moderately alkaline. Furthermore, it was characterized as saline (with a ECe of 4.65 - 11.45 dS⋅m−1) and moderately calcareous soil (with CaCO3 at 11.85% - 17.20%). The soil had a low soil organic matter content which did not exceed 0.18%. The soil was dominated by a sandy loam texture (62.50%) followed by a sandy clay loam texture (18.75%). The bulk density, total soil porosity and saturated hydraulic conductivity values varied with 1.38 - 1.55 Mg⋅cm−3, 41.85% - 48.45% and 1.20 - 3.34 cm⋅h−1, respectively. The chemical index ranged from low to moderate quality. The correlations between the parameters osculated between negative and positive. Therefore, the soil may be reclaimed if the soil properties are improved and crop selection is optimized for this soil.

Reform Paths of Rural Land Property Rights System in the Context of Agricultural Modernization

The reform of rural land property rights system can promote large-scale and intensive agricultural production,improve the quality of laborers,improve agricultural production efficiency,increase farmers'income,and effectively promote the development of agricultural modernization.In the context of the reform of the"separation of three powers",the rural land property rights system still has problems in terms of ownership,use rights,disposal rights,and income rights,which affect the healthy development of agricultural modernization.In this situation,it is necessary to further clarify the subject of rural land ownership,thoroughly improve the right to use rural land,vigorously improve the right to dispose of rural land,effectively protect the right to benefit from rural land,and deeply promote the reform of the rural land property rights system in order to effectively promote the development of agricultural modernization.

Effects of land-use patterns on soil microbial diversity and composition in the Loess Plateau,China

In the Loess Plateau of China,land-use pattern is a major factor in controlling underlying biological processes.Additionally,the process of land-use pattern was accompanied by abandoned lands,potentially impacting soil microbe.However,limited researches were conducted to study the impacts of land-use patterns on the diversity and community of soil microorganisms in this area.The study aimed to investigate soil microbial community diversity and composition using high-throughput deoxyribonucleic acid(DNA)sequencing under different land-use patterns(apricot tree land,apple tree land,peach tree land,corn land,and abandoned land).The results showed a substantial difference(P<0.050)in bacterial alpha-diversity and beta-diversity between abandoned land and other land-use patterns,with the exception of Shannon index.While fungal beta-diversity was not considerably impacted by land-use patterns,fungal alpha-diversity indices varied significantly.The relative abundance of Actinobacteriota(34.90%),Proteobacteria(20.65%),and Ascomycota(77.42%)varied in soils with different land-use patterns.Soil pH exerted a dominant impact on the soil bacterial communities'composition,whereas soil available phosphorus was the main factor shaping the soil fungal communities'composition.These findings suggest that variations in land-use pattern had resulted in changes to soil properties,subsequently impacting diversity and structure of microbial community in the Loess Plateau.Given the strong interdependence between soil and its microbiota,it is imperative to reclaim abandoned lands to maintain soil fertility and sustain its function,which will have significant ecological service implications,particularly with regards to soil conservation in ecologically vulnerable areas.

Ecological effect of the plantation of Sabina vulgaris in the Mu Us Sandy Land,China

Vegetation restoration through artificial plantation is an effective method to combat desertification,especially in arid and semi-arid areas.This study aimed to explore the ecological effect of the plantation of Sabina vulgaris on soil physical and chemical properties on the southeastern fringe of the Mu Us Sandy Land,China.We collected soil samples from five depth layers(0-20,20-40,40-60,60-80,and 80-100 cm)in the S.vulgaris plantation plots across four plantation ages(4,7,10,and 16 years)in November 2019,and assessed soil physical(soil bulk density,soil porosity,and soil particle size)and chemical(soil organic carbon(SOC),total nitrogen(TN),available nitrogen(AN),available phosphorus(AP),available potassium(AK),cation-exchange capacity(CEC),salinity,p H,and C/N ratio)properties.The results indicated that the soil predominantly consisted of sand particles(94.27%-99.67%),with the remainder being silt and clay.As plantation age increased,silt and very fine sand contents progressively rose.After 16 years of planting,there was a marked reduction in the mean soil particle size.The initial soil fertility was low and declined from 4 to 10 years of planting before witnessing an improvement.Significant positive correlations were observed for the clay,silt,and very fine sand(mean diameter of 0.000-0.100 mm)with SOC,AK,and p H.In contrast,fine sand and medium sand(mean diameter of 0.100-0.500 mm)showed significant negative correlations with these indicators.Our findings ascertain that the plantation of S.vulgaris requires 10 years to effectively act as a windbreak and contribute to sand fixation,and needs 16 years to improve soil physical and chemical properties.Importantly,these improvements were found to be highly beneficial for vegetation restoration in arid and semi-arid areas.This research can offer valuable insights for the protection and restoration of the vegetation ecosystem in the sandy lands in China.

Effects of Artificial Vegetation Restoration on Soil Physicochemical Properties in Southern Edge of Mu Us Sandy Land

[Objective] This study aimed to investigate the artificial vegetations on soil physicochemical properties of sandy land. [Method] The soil physicochemical proper- ties in five representative lands respectively covered by Artemisia ordosica, Salix cheilophila, Hedysarum scoparium, Populus simonii and Amorpha fruticosa, all of which were planted artificially at the same year were measured in the present study, using a bare soil as the control. [Result] Artificial vegetation improved the soil physicochemical properties by different extents in the lands covered by different plants. The soil physicochemical properties such as bulk density under A. Fruticosa and H. Scoparium were improved greatly. The frequency distribution of soil particle size under artificial vegetations exhibited a bimodal curve. The average soil particle size under A. fruticosa was the smallest, and the soil was very poorly sorted. The soil nutrients in the sandy land were not significantly improved by artificial vegeta- tion. [Conclusion] Artificial vegetation has a certain impact on soil properties in sandy land, as it greatly improves the soil physical properties but not the chemical properties.

Studies of Soil Physical Property on Different Abandoned Lands in the Minqin Oasis,Downstream of the Shiyang River

The vast area of farmland was abandoned at downstream of the Shiyang River because of decreased water recourse. To ensure the ecological safety of Minqin Oasis and to provide management basis for the abandoned land, soil physical properties were observed and studied. The authors analyzed land with abandonment time of 1 year, 2 years, 3 years, 4 years, 5 years, 8 years, 15 years, 24 years and 31 years. Samples were took at the 0-40 cm layer of soil to measure the bulk density, porosity and grain composition of soil in the different abandoned lands. Results showed that the tendency of clay content was decreasing, conversely, the fine sand increased at the layer of 0-10 cm of different abandoned lands.The changes of grain content reached a peak at the fourth year after the land was abandoned, then varied slightly. The variation of grain content of abandoned land was obvious with the extension of the abandonment year. The soil bulk density decreased and porosity increased with the extension of the abandonment year. The difference of porosity and soil bulk density at the range of 0-40 cm of different abandoned land decreased after the land abandoned for 3 years. The quality of soil was decreased, while the soil permeability was improved. The soil physical properties changed obviously in 3 to 4 years after abandonment, so it is the key time for land management.

Effects of different plantation types on soil properties after vegetation restoration in an alpine sandy land on the Tibetan Plateau, China

Large areas of Artemisia ordosica Krasch., Caragana korshinskii Kom., and Caragana intermedia Kuang and H. C. Fu plantations were established on moving sand dunes in the Gonghe Basin （northeastern Tibetan Plateau） for vegetation restoration. Elevating our understanding of the changes in soil characteristics after the establishment of different plantation types can be useful in the context of combating deserdfication. To assess the effects of these plantation types on the restoration of sandy land, we measured soil physical-chemical properties at four depths （0-5, 5-10, 10-20, and 20-50 cm） in each of the three plantation types and also in non-vegetated moving sand dunes （as control sites）. Generally, the establishment of A. ordosica, C korshinskii and C intermedia plantations on sand dunes has greatly ameliorated soil quality in the Gonghe Basin. Specifically, relative to the moving sand dunes, shrub plantation has increased the silt and clay contents, total porosity and water holding capacity, soil organic matter, total nitrogen, total phosphorus and total potassium contents. The calculated soil quality index suggested that in the Gonghe Basin, C. intermedia is the best choice for soil amelioration. In all the three plantation types, soil amelioration mainly occurred in the shallow depths.

The impact of land use on soil properties in a karst agricultural region of Southwest China: a case study of Xiaojiang watershed, Yunnan

Supported by RS and GIS, the land use change from 1982 to 2003 were analyzed and the impacts of land use changes on pH value, organic matter, total N, total P, total K, available N, available P, and available K in soil of Xiaojiang watershed, a typical karst agricultural region of Yunnan Province, Southwest China were assessed. The following aspects are concluded. （1） The total land use converted during the past 20 years in Xiaojiang watershed covers an area of 610.12 km^2, of which 134.29 km^2 of forestland was converted into cultivated land, and 210 km^2 of.unused land was converted into cultivated land. （2） The rapid growth of population and the economic development were the main driving forces of land use change. （3） With the change in land use, the soil properties have been changed significantly. The pH, organic matter, total N, total P, total K, available N, available P and available K in soil in 1982 were 6.3, 38.02 g·kg^-1, 1.86 g·kg^-1, 1.63 g·kg^-1, 10.94 g·kg^-1, 114.42 g·kg^-1, 11.65 mg·kg^-1 and 64.69 mg·kg^-1g, respectively; and those in 2003 were 6.73, 25.26 g·kg^-1, 1.41 g·kg^-1, 0.99 g·kg^-1, 12.6 g·kg^-1, 113.43 mg·kg^-1, 11.11 mg·kg^-1 and 151.59 mg·kg^-1, respectively. Pared samples t-test of the tested indices of soil properties indicate that those indices have changed significantly during the last 20 years. But the soil properties changed differently, due to the differences in land use change. （4） Also, with the change in land use and management measures of soil, the modifications in soil properties which developed from carbonate rocks were more sensitive than those in the soil developed from sandstone.

Eddy properties in the Pacific sector of the Southern Ocean from satellite altimetry data

Mesoscale eddies play a key role in the ocean dynamics of the Southern Ocean, and eddy response to the climate changes has also been widely noted. Both eddy kinetic energy（EKE） and eddy detection algorithm are used to study the eddy properties in the Pacific sector of the Southern Ocean. Consistent with previous works,the maps of the EKE illustrate that higher energy confines to the Antarctic Polar Frontal Zone（APFZ） and decreases progressively from west to east. It also shows that the most significant increase in the EKE occurs in the western and central parts of the Pacific sector, where the baroclinicity of the Antarctic Circumpolar Current（ACC） is much stronger. Statistical eddy properties reveal that both of the spatial pattern and interannual variation of the EKE are primarily due to the eddy amplitude and the eddy rotational speed, rather than the eddy number or the eddy radius. In general, these results furtherly confirm that anomalous westerly wind forcing associated with the positive Southern Annular Mode（SAM） index enhances the Southern Ocean eddy activity by strengthening the eddy properties.

Comparison of soil physico-chemical properties under different land-use and cover types in northeastern China's Horqin Sandy Land

The Horqin Sandy Land of northeastern China was originally a grassland with plenty of water and lush vegetation dominated by palatable grass species along with sparsely scattered woody species. However, it has experienced severe desertification in recent decades due to its fragile ecology together with inappropriate human activities. Currently, the landscape of the Horqin Sandy Land is dominated by irrigated croplands and sand dunes with different degrees of vegetation cover, as the region has become the most important part of the semiarid agro-pastoral ecotone of northern China. In this study, we compared soil physical and chemical properties under different land-use and cover types （irrigated cropland, rainfed cropland, sandy grassland, fixed dunes, and mobile dunes）. We found that soil particle size distribution; organic C, total N, and total mineral element, microelement, and available microelement and nutrient contents; pH; CEC; and bulk density differed significantly among the land-use and cover types. In general, soil quality was highest in the cropland, intermediate in the sandy grassland, and lowest in the dunes. The most important soil quality attribute, soil organic carbon （SOC） storage, decreased in the fol-lowing order： irrigated cropland （5,699 g/m^2） 〉 sandy grassland （3,390 g/m^2） 〉 rainfed cropland （2,411 g/m^2） 〉 fixed dunes （821 g/m^2） 〉 mobile dunes （463 g/m^2）. SOC was significantly positively correlated with a large proportion of the other soil physico-chemical parameters. Our results suggest that the key issue in restoration of the degraded soils will be to increase SOC storage, which would also create a high potential for sequestering soil C in desertified areas of the Horqin Sandy Land.

Effect of Reclamation Time and Land Use on Soil Properties in Changjiang River Estuary,China

The objective of this study is to analyze soil physical and chemical properties,soil comprehensive functions and impact factors after different years of reclamation.Based on the survey data taken from 216 soil sampling points in the Fengxian Reclamation Area of the Changjiang (Yangtze) River Estuary,China in April 2009 and remotely sensed TM data in 2006,while by virtue of multivariate analysis of variance (MANOVA),geo-statistical analysis (GA),prin-cipal component analysis (PCA) and canonical correspondence analysis (CCA),it was concluded that:1) With the in-crease in reclamation time,soil moisture,soil salinity,soil electric conductivity and soil particle size tended to decline,yet soil organic matter tended to increase.Soil available phosphorous tended to increase in the early reclamation period,yet it tended to decline after about 49 years of reclamation.Soil nitrate nitrogen,soil ammonia nitrogen and pH changed slightly in different reclamation years.Soil physical and chemical properties reached a steady state after about 30 years of reclamation.2) According to the results of PCA analysis,the weighted value (0.97 in total) that represents soil nutrient factors (soil nitrate nitrogen,soil organic matter,soil available phosphorous,soil ammonia nitrogen,pH and soil particle size) were higher than the weighted value (0.48 in total) of soil limiting factors (soil salinity,soil elec-tric conductivity and soil moisture).The higher the F value is,the better the soil quality is.3) Different land use types play different roles in the soil function maturity process,with farmlands providing the best contribution.4) Soil physi-cal and chemical properties in the reclamation area were mainly influenced by reclamation time,and then by land use types.The correlation (0.1905) of the composite index of soil function (F) with reclamation time was greater than that with land use types (-0.1161).

Changes in soil carbon stocks and related soil properties along a 50-year grassland-to-cropland conversion chronosequence in an agro-pastoral ecotone of Inner Mongolia,China

Land use change significantly influences soil properties. There is little information available on the long-term effects of post-reclamation from grassland to cropland on soil properties. We compared soil carbon （C） and nitrogen （N） storage and related soil properties in a 50-year cultivation chronosequence of grassland in the agro-pastoral ecotone of Inner Mongolia. Field surveys on land use changes during the period of 1955-2002 were conducted to build a chronosequence of cropland of different ages since the conversion from grassland. The results showed that soil C and N storage, soil texture, and soil nutrient contents varied with land use types and cropland ages （P〈0.01）. In the 0-30 cm soil layer, the soil organic carbon （SOC） density was significantly lower in the crop- lands （3.28 kg C/m2 for C50 soil） than in the grasslands （6.32 kg C/m2）. After 5, 10, 15, 20, 35, and 50 years of crop planting （years since the onset of cultivation）, the SOC losses were 17%, 12%, 19%, 47%, 46%, and 48%, respec- tively, compared with the grasslands. The soil total nitrogen （TN） density of the grasslands was 65 g N/m2, and TN density of the cropland soil was 35 g N/m2 after 50 years of crop planting. Both the SOC and TN densities could be quantitatively determined by a negative exponential function of cropland age （P〈0.0001, R2=0.8528; P〈0.0001, R2=0.9637）. The dissolved organic carbon （DOC） content, pH value were decreased; and the soil bulk density and soil available potassium （AK） content, clay content, and sand content were increased since the conversion of grassland into cropland during the 50-year period. Our results show soil nutrients were higher in grassland than in cropland. The conversion of grasslands to croplands induced a loss of soil C storage and changes of related soil properties. The reclamation time of cultivated soil （cropland age） had significant effects on soil properties in the study area.

Physical Properties,Morphology and Petrological Characteristics of Pumices from the Central Indian Ocean Basin

About 400 pumice clasts collected from the Central Indian Ocean Basin（CIOB）were studied for their morphology and were classified based on their shape and size.A majority of the samples range between1 cm and 36 cm and in the Zinggs shape diagram plot in the equant and oblate fields.The Corey Shape Factor for most of the samples is close to 0.7,which is common for volcaniclastic material. The physical properties such as density,specific gravity,void ratio,porosity,moisture content and degree of saturation,were determined for 30 pumice samples.Density varies from 0.21 to 0.74 g/cm^3 specific gravity 1.84 to 3.27,void ratio 2.21 to 10.67,porosity 67%to 91%,moisture content during sinking 0.44 to 2.35 and degree of saturation varies from 26.5%to 86%.Binocular and electron microscopy studies reveal that 60%of the vesicles are elongated,30%are spherical and 10%are fibrous.Petrography of the pumices exhibits vitrophyric texture with phenocrysts of feldspars and clinopyroxenes.X-ray diffractrogram and mineral analyses confirm plagioclase to be a major phase, while quartz and orthoclase are not uncommon.Todorokite is commonly present in the ferromanganese oxide coating present over some of the pumices.This paper also delves into some details concerning the controversial origin of the pumices and glass shards in the CIOB.

Rapid Climatic Change during Past 60 ka Recorded in NE Indian Ocean and Its Correspondence from South China Land

According to the marine records from the Bay of Bengal, northeastern Indian Ocean, and the continental records from the South China, the authors make a detailed discussion in this paper about the correlation between them and their implication of rapid climatic change. The marine records show its good response to the high latitudes both for cold events and for warm ones while the continental records mainly mirror those cold Heinrich events corresponding to the North Atlantic but bear strongly a local color in reflecting warm events. The authors assume that the heat transmission style may cause the unbalanced coupling relationship.

Assessment of several typical physical properties of reclaimed farmland filled with Yellow River sediment in Jining, China

Land subsidence caused by underground coal mining is one of the most prominent environment problems in China. The reclamation of mining subsidence land with Yellow River sediment was considered to be feasible, but its effectiveness needs to be verified. An integrated reclamation technology with Yellow River sediment was evaluated using a comparison of actual crop production soil profile analysis in Jining City, China. The results indicated that reconstructed soil profile of the reclaimed farmland was less effective in retaining water and in supporting plant growth than that of the unaltered farmland. Some measures are proposed, such as reducing the drainage velocity to allow sedimentation and retention of the clay and silt, changing the techniques of filling the Yellow River sediment and increasing the organic matter content in the soil layers to improve the capacity to retain water in the reclaimed farmland.

Effects of land uses on soil physic-chemical properties and erodibility in collapsing-gully alluvial fan of Anxi County,China

the National Key Technologies R＆D Program of China during the 12th Five-Year Plan period （2011BAD31B00）

Effect of Land Use on Soil Properties in Debris Flow Bottomland:A Case Study at Xiaojiang Basin, Yunnan

In order to understand the effect of different land use on soil physics and nutrients properties of the debris flow bottomland, a case study at Daqing gully （in Xiaojiang Basin, Yunnan） was conducted in 2004. Soil samples were taken at depth of 0-10,10-20,20-40,40-60,60-80 cm under three land use patterns crop bottomland （CL）, forest bottomland （FL）, and barren bottomland（BL）. The results showed that the developing bottomland to CL promoted soil toaccumulate total phosphorus （TP） and available phosphorus （AP）, pH value transferred from neutral to alkalescency, and organic matter decreased significantly. Furthermore, the contents of total nitrogen （TN） and available nitrogen （AN） in CL were lower than that of FL and BL because the growth of crops consumed more nutrients in soil. The results also showed that the contents of TP, AP and available potassium （AK） in soil were positively correlated with soil particle.