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

Abstract:Soils evolve in space and time and soil changes are coupled with the changes in climate and environment, rock weathering and biogeochemical cycling. A better understanding and accurate quantification of soil spatio-temporal variation not only act as a basic research task of soil science but also are prerequisite for scientifically evaluating and reasonably maintaining soil functions. The main objective of this study was to review the recent studies on spatio-temporal soil variation. Dozens of latest related publications were reviewed, of which the topics included soil formation and evolution, soil morphology, soil survey, soil classification, digital soil mapping and soil degradation. It is anticipated that main scientific issues may include the simulation of coupling processes between soil and environment within the framework of earth surface system, precise modeling of the soil-landscape, and the data fusion and assimilation of multisource soil information. Based on the analysis, future priority areas of soils in space and time studies may include the soil formation and evolution driven by Critical Zone processes, digital soil mapping at various scales, the principle and technology for soil information acquisition based on multi-sensors, a complete and detailed national even global soil inventory and its sharing platform, and the processes of regional soil resource degradation and the recovery of soil functions.

Abstract:With the problem of environmental deterioration becoming increasingly conspicuous and the impact of anthropic activities on soil formation getting more and more intense in recent decades, it is, therefore, essential to intensify the researches on the impact so as to explain processes of and changes in magnetism in modern soils. Hydragric Anthrosols (paddy soils) are defined as Anthrosols, and their formations are affected by human activities in various ways. Tillage and anthrostagnic moisture regimes are two major factors that control characteristics of the soil formation processes. However, so far only some scattered rather than systematic studies have been reported on how human activities induce changes in soil magnetism. Therefore, this paper is oriented to review or summarize all the findings of researches in this field, including characteristics of the evolution of parameters of magnetism in Hydragric Anthrosols, mechanisms of the formation and transformation of magnetic minerals and their responses to soil forming factors. Magnetic minerals in paddy soils, on one hand, inherit some of the features of their original soils and on the other, have undergone a series of apparent changes under the impacts of paddy cultivation. Water regime controlled the soil magnetic characteristics in the early stage of paddy soil formation, however, all different types of paddy soils could eventually develop into profiles similar in structure of magnetic susceptibility after long-term paddy cultivation. Most of the ferrimagnetic minerals and hematite in the anthrostagnic epipedon tended to reduce into goethite, lepidocrocite and/or their hydrated forms within a short term, while in the hydragric horizons (subsoils), the changes of magnetic minerals were more complicated and duration of artificial submergence and reduction degree were the major factors controlling changes of the ferrimagnetic minerals. In appropriate environment, Fe2 got oxidized slowly, thus forming ferrimagnetic minerals, which may represent one mechanism for enhancement of magnetism in the subsoil. Ferrimagnetic minerals in clays in the paddy soil were susceptible to breakage, while newly formed ferromagnetic minerals were concentrated in soil aggregates of the clay fraction. In paddy soils, periodic submergence made it difficult for the soil to develop drought-stressed environment that could dehydrate ferrihydrite into hematite, which was usually reduced first in contrast to goethite under reducive conditions. Goethite and lepidocrocite often coexisted in paddy soils and their relative contents depended mainly on soil environment. Human activities affected or governed the formation and transformation of magnetic minerals in the paddy soil mainly through their impacts on natural soil forming factors (i.e., climate, organism, parent material, relief, time). However, the impacts reduced in degree with paddy cultivation going on. In the end, the paper summarized shortages and problems existing in current studies and prospected for directions of future researches in hope to help development of environmental magnetism.

Abstract:Soil chronosequences are valuable tools for investigating rates and directions of soil evolution and their modeling as well as for testing theories of pedogenesis. To obtain reliable results, the establishment of soil chronosequences must consist of two critical processes, i.e. quantitative identification of parent material uniformity or lithologic discontinuities (LDs) between and within profiles of the chronosequence, and identification of age of the soils with numerical or geochronometric dating methods and surface exposure (relative) dating methods. In this paper, types and constructing procedures of soil chronosequences, and in detail, the detection methods of parent material uniformity or LDs as well as age dating techniques are reviewed, with a view to providing detailed references for correct construction of soil chronosequences and better understanding the effects of the time factor on soil development. In addition, this paper discusses the significance of the chronosequence approach in pedogenesis research.

Abstract:Content and morphotype of phyoliths was studied in a soil chronosequence consisting of five soil profiles developed from basalt ranging in age from 10 000 years to 6.12 million years in tropical Leiqiong area. It was found that 1) the content of phytoliths in the soils, ranging from 1.54 to 21.95 g kg-1, was high in the surface horizon and decreased with the depth in profile; its drop was sharp from entisols to ferrosols and less significant from ferrosols to ferralsols, and then leveled off after entering ferrosols; 2) originated mainly from poaceae and palmae, the phytoliths ranged from 5 to 130 µm in size and appeared in 12 shapes, e.g. spherical echinate, dumbbell, fan, rectangular, square, saddle, hat, rod, tapered, crenate, round and others; The phytolith samples were all > 0.5 in warmth index, indicating the study area has basically been under a warm climate since 6.12 Ma.

Abstract:As the second most abundant element in the Earth crust after oxygen, the transfer and transformation of silicon (Si) are one of the most important processes of soil formation and evolution. Biological processes are known to play significant roles in soil formation and mineral weathering. Especially, plants can take up dissolved silicon (DSi) and deposit it to produce silicified structure as phytolith, a kind of biogenic silicon (BSi). In this paper, a chronosequence including seven basalt-derived soil profiles in northern Hainan Island was studied. The extraction of BSi was conducted following a wet extraction procedure, in which heavy liquid of ZnBr2 (2.35 g cm-3) was used to separate phytoliths from other heavy mineral fractions. Results showed that contents of BSi in the soils varied widely from 2.9 to 54.0 g kg-1. The highest concentration of BSi occurred in the surface horizon of profile HE09, a young soil on basalt, while the lowest was found in the B2 layer of HE11, an older soil in the sequence. In general, the contents of BSi, OC and TN are high in the surface horizon of soil profiles and decrease rapidly with depth. This phenomenon is prominent in topsoil, especially from surface to 40 cm. The finding implies that the accumulation of BSi in topsoil is mainly due to BSi release from organic matter during its decomposition. During soil development, these soils became progressively more weathered, with base cations depleting, clay fraction increasing and pH decreasing. Furthermore, a linear correlation between BSi and TSi was found for all soil samples, indicating that BSi determines to a certain extent the whole Si cycles during soil development. In the initial stage of soil development, DSi from weathering of primary minerals may contribute to the conservation of BSi, while with time, continuous high rainfall and depletion of cations leads to leaching or recycling of BSi faster than plants can bring it to the surface. As a result, the contents of BSi may maintain a relatively stable state with the function of biogenic pump in the soil-plant system. In conclusion, BSi is playing a very important role in tropical soil formation and evolution, especially in the biogeochemical cycles of Si.

Abstract:Soil chronosequence is a valuable means in investigating rates and directions of pedogenic evolution. A soil chronosequence consisting of one tract of mudflat and five paddy soils of different rice cultivation ages were selected for this study. Ages of the paddy fields were estimated according to the literature available indicating the time when the polder was built up to reclaim the mudflat into paddy fields. The objectives of this study were to evaluate lithologic discontinuity (LDs) of the parent material in the inter-and intra-profiles of the chronosequence, and to verify relative ages of the fields by making use of various soil attribute parameters. Results show that low variation coefficient was associated with clay-free silt and Ti/Zr ratio of the silt fraction between horizons, suggesting no LDs in the studied profiles, that is to say, the profiles of the chronosequence have developed from a relatively homogeneous parent material.The clay-free silt and Ti/Zr ratio of the silt fraction are the most useful parameters in identifying LDs in this study. In order to establish a well-dated chronosequence, CaCO3 content, magnetic susceptibility and differentiation degree of free iron oxide in the profiles were used to assess soil relative ages and they were shown as good indicators of soil age and development. However, these parameters in the 500a soil profile have an odd tendency along the sequence, so it should be excluded from the chronosequence when a reliable comparison of soil changes is desired.

Abstract:Magnetic properties can be simply,rapidly and accurately measured,and their pedogenetic implications are significant.In this study,63 soil samples collected from 11 subgrade soil profiles distributed in the downtown area of Nanjing were tested for low-frequency susceptibility,frequency dependent susceptibility,free iron oxide,active iron oxide,particle size distribution,organic carbon,pH and calcium carbonate equivalents.Results show that magnetic mineral and soil-forming processes were highly diversified due to heterogeneity of parent materials and artificial input.Magnetic minerals were mainly derived from fly ash,automobile exhaust and so on High pH and carbonate content retarded formation of fine magnetic minerals in urban en vironment.Magnetic susceptibility combined with other pedogenetic properties is very useful in illustrating the soil-forming processes in urban areas.

Abstract:With the study of physical,chemical,morphological and mineralogical properties of three pedons of typical albic soils from the Three River plain of Heilongjiang Province,we discussed the pedogenetic characteristics.The profiles were found to be lithologically countinuous by the comparsion of Zr/Sr and Ti/Zr ratio within the pedons.The albic soils study was characterized by a mollic epipedon,an ablic E horizon and a thick argillic horizon.Through this study,it was indicated that lessivage was a dominant pedogenetic process.Pedogenic Fe Mn nodules were found abundant in Ah and E horizons and were apparently forrned by weathering of Fe-Mn primary minerals,and the nodules may have developed in situ.The maximum amounts of pyrophosphate extractable Fe and AI appeared it Bt2 horizons were smaller than the values required for podzols.Vermiculite,which had not previously been recognized,dominated the clay fraction of albic soils.The clay mineral assemblage was qualitatively similar but quantitively differentiated throughout the profile.Finally,we suggested that the albic soils could be classified as mollie planosols in the FAO-UNESCO system and Typical Argialbolls in Soil Taxonomy.

Abstract:Alfisols are important soils in China. They occupy about 1.25 million km2 or about 13% of the land area. Dark brown forest soils, burozems, yellow-brown earths, and drab soils in temperate China are identified as four major great soil groups. According to the criteria given by soil Taxonomy, these soils should belong to Alfisols. Additionally, Baijiang soil is identified as a special kind of Alfisols, probably Albaqualfs. These are mostly forested soils with a return of organic matter, estimated at 5-13t/ha/yr, to the soils from a mixed temperate forest. In terms of elemental bio-cycling Ca is prominent.In a comparison of 30 profiles, the average rate of clay (B/A) was 1.47 for cryoboralfs and Eutroboralfs: 1.88 for Hapludalfs and 2.53 for Paleudalfs. From Eutroboralfs to Paleudalfs there was a difference of 7 times in the average gain (or loss) in clay during soil development. Hapludalfs, Cryoboralf and associated Cryaquepts differ considerably in the moisture regimes, but the amount of water is always enough to cause a significant leaching. During the weathering and pedogenetic processes-TiO2, Mgo and Fe2O3 are accumulated, respectively, in both A and Bt horizons; But SiO2 and Al2O3, tend to be leached from the solum.