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【Objective】The present paper aimed to study the occurrence form of cadmium (Cd) accumulation in soil aggregates of Cd-contaminated brown calcareous soil matrices of paddy fields in the Karst area of northwestern Guangxi, and to provide data reference for safe rice production in this type of Cd-contaminated paddy fields in the region. 【Method】The sampled soil aggregates were separated into five aggregates as ＞ 2.000 mm, 1.000-2.000 mm, 0.050-1.000 mm, 0.074-0.250 mm and ＜0.074 mm, the composition of soil aggregates particle size, Cd content of different particle size aggregates and their main occurrence patterns from 0-20, 20-30, 30-50 and 50-80 cm depth profiles in the Karst area of northwest Guangxi were studied.【Result】The proportion of 0.250-1.000 mm size aggregates in each profile was stable, above 30.00%, with no significant difference between profiles (P＞0.05), the proportion of ＞2.000 mm size aggregates in the 0-20 cm soil profile (tillage layer) was the largest (40.20%), and as the depth of the profile increased, the proportion of ＞2.000 mm size aggregates decreased rapidly, and the proportion of ＜0.250 mm size aggregates showed a gradual increasing trend. Analysis of the Cd content of agglomerates of different particle sizes showed that, in 0-20, 20-30 and 30-50 cm soil profiles, Cd was mainly enriched in ＞2.000 mm particle size aggregates, with contents as high as 2.22, 1.66 and 0.95 mg/kg, respectively, and in the 50-80 cm soil profile, Cd was mainly enriched in 1.000-2.000 mm particle size aggregates. ＞2.000 mm particle size aggregates contributed most to the whole soil Cd content in the 0-30 cm soil layer. The occurrence form of Cd in the aggregates at different profile depths showed obvious differences, the proportion of Cd in aggregates of all particle sizes in the 0-20 cm profile was mainly in the organic matter binding state, with the smallest proportion of Cd in the exchangeable state (except for ＜0.074 mm particle size aggregates), and the proportion of Cd in the exchangeable state in the aggregates increased greatly with the increase of the depth of the profile, when the profile depth was increased to under 30 cm, the Cd in the aggregates mainly existed in carbonate bound state, and with minimal content in the residue lattice state.【Conclusion】In the typical Cd-contaminated brown calcareous soil matrices of paddy fields in the Karst area of northwestern Guangxi, the Cd is mainly enriched in aggregates of ＞2.000 mm and 1.000-2.000 mm particle size, the Cd in the aggregates of each particle size in the 0-20 cm tillage soil is mainly in the form of organic matter bound state, and with the smallest proportion in the form of exchangeable state. With the increase of the profile depth, the proportion of exchangeable Cd increases greatly, while the proportion of Cd in the stable form decreases significantly. Therefore, in the actual production process, it should focus on improving the content of large particle size soil aggregates and avoiding excessive intensive ploughing and deep tilling, reducing the exchangeable state Cd content in the ploughed soil, and ultimately reducing the risk of excessive Cd in rice during rice production. [ABSTRACT FROM AUTHOR]

[Objective] The present paper aimed to investigate the effects of microplastics on the structure and carbon, nitrogen, phosphorus stoichiometric characteristics of red soil with different levels of iron enrichment, and to provide theoretical basis for guiding the improvement of soil quality and pollution management in red soil areas. [Method] Using subtropical red soil as the research object, low density polyethylene (M0, M1, M2) with 0, 0.1%, 1.0% mass and iron (Fe0, Fe1, Fe2) with 0, 10 and 20 g/kg mass were added through indoor cultivation experiments to simulate the pollution level of microplastics and the degree of iron enrichment in red soil. The distribution characteristics of water stable aggregates and the stoichiometric characteristics of carbon, nitrogen and phosphorus in red soil polluted by microplastics under different iron enrichment conditions were studied. [Result] Under the condition of Fe0o, compared with M0, the aggregate content (WSA), mean weight diameter (MWD) and geometric mean diameter (GMD) of M1 with particle size > 0.25 mm decreased, and the WSA, MWD and GMD of M2 increased significantly; Under Fe0, conditions, there was no significant difference in the stability indicators of aggregates among M0, M1 and M2; Under Fe2 conditions, both M1 and M2 significantly reduced the WSA, MWD and GMD of soil aggregates. In terms of carbon, nitrogen and phosphorus content and their stoichiometric characteristics, M1 and M2 under Fe0 conditions could significantly increase soil organic carbon content (SOC); Under Fe0, and Fe2 conditions, microplastic treatment had no significant effect on SOC. The total nitrogen content (TN) of the soil decreased significantly under Fe0, and Fe1, conditions, while microplastic treatment had no significant effect on TN under Fe2 conditions; The total phosphorus content (TP) of the soil showed M0 > M1 > M2. The changes in soil nutrients ultimately led to a significant increase in C/N, C/P and N/P of all microplastic treatments (except for Fe0, M1, Fe2 M1 and Fe2 M2). [Conclusion] The effects of different treatments on the stability of soil aggregates vary. Under the current existing red soil conditions, low micro plastic pollution can reduce the stability of soil aggregates, while high micro plastic pollution can increase the stability of soil aggregates. Under relatively light iron rich red soil conditions, both low and high microplastic pollution have no significant impact on the stability of soil aggregates. Under relatively high iron rich red soil conditions, both low and high microplastic pollution can reduce the stability of soil aggregates. M0reover, the changes in soil aggregate structure under different treatments led to significant differences in the stoichiometric characteristics of carbon, nitrogen and phosphorus in the soil. Overall, microplastic pollution can significantly improve the C/N, C/P and N/P of red soil. [ABSTRACT FROM AUTHOR]

【Objective】The aims of the present paper is to explore the spatial variation and stability of soil aggregates at different soil depths under different years of the deep turning measure. 【Method】The soil of the deep turning measure（2014） was used as a control, and the soil aggregates of 0-20, 20-40, 40-60 cm soil depths were continuously sampled and monitored based on the years of deep turning（2014-2020）. The changes of soil aggregates, particle size distribution patterns and stability of soil aggregates with the age of deep turning were analyzed. 【Result】 WR0.25 was more sensitive to the response to deep turning than DR0.25, which was significantly lower than DR0.25; WR0.25 generally increased with the age of deep turning and decreased with the increase of soil depth; Under deep flipping, WR0.25 was more sensitive to the response of deep turning than DR0.25, and the content of WR0.25 decreased with the increase of soil depth and increased with the increase of deep turning age; MWD showed no obvious overall change with the increase of deep turning age in 0-20 cm soil layer, 20-40 cm soil layer showed a gradual increase trend with the increase of deep turning age, MWD in 40-60 cm soil layer showed an increasing trend with the increase of deep turning age after 1-5 years of deep turning, and MWD gradually decreased after 6-7 years of deep turning. PAD showed a tendency to increase with the increase of soil depth and decrease with the increase of deep turning age. WR0.25, PAD and MWD showed a significant correlation（P<0.05）, in which WR0.25 showed a significant negative correlation with PAD, the correlation coefficient R was-0.750, WR0.25 showed a significant positive correlation with MWD, the correlation coefficient R was 0.866, and the PAD and MWD showed a significant negative correlation relationship, and the correlation coefficient R was-0.795.【Conclusion】The deep turning measure directly acted on the structure of soil aggregates, and the recombination of aggregate content components led to the hierarchical differentiation of the original tillage soil, which was manifested as two-level differentiation of the surface layer and the bottom layer, and the water stability aggregates had greater variation and more sensitive hierarchical response. The deep turning effect makes the soil surface and bottom layer achieve spatial displacement and mixing, resulting in the homogenization of the original layers of each soil layer, and with the increase of the deep turning age, the distribution pattern of soil aggregates tends to gradually converge and the stability gradually increases. [ABSTRACT FROM AUTHOR]

[ Purpose] The present paper aimed to study the physical properties, soil enzyme activities and their correlation characteristics of wild Bletilla striata soil in different producing areas in Guizhou, so as to provide a theoretical basis for realizing high yield and quality of B. striata artificial cultivation. [ Method] 8 soil sample plots for the wild B. striata were collected in Guizhou province to detect and analyze the soil physical and enzyme activity index characteristics and the correlation between them. [ Result]The soil density was between 2. 06 -2. 55 g/ cm³ with weak variation. The soil texture was mainly clay loam and sandy loam. In most soils, the proportion of the > 0. 25 mm size soil water-stable aggregates reached 70% . The distribution of the soil water-stable aggregates size fraction were different, 2 - 5 mm size fraction was the dominant size fraction in 4 soil plots, < 0. 25 mm size fraction was the dominant size fraction in 3 soil plots. The dominant size fraction of soil micro-aggregate was 0. 25 -0. 05 mm size fraction. The activities of urease, acid phosphatase and sucrase in soil were significantly different with strong variation. The activities of catalase in soil were not significantly different with weak variation. Soil enzyme activity was strongly influenced by the soil density, soil aggregates and microaggregates. There was a significant positive correlation between urease and acid phosphatase, which could promote each other. [Conclusion] Guizhou wild B. striata has strong adaptability to soil environment. It mainly grows in sandy soil or clay with soil clay content less than 25 %, and some wild B. striata can also grow in clay with soil clay content more than 30% ; Soil specific gravity, soil aggregates and micro aggregates are important factors affecting soil enzyme activity of B. striata. The suitable soil specific gravity is 2. 06 - 2. 55 g/ cm³, the dominant particle size is 2 - 5 mm or < 0. 25 mm, and loam is the best soil texture; Urease and acid phosphatase can promote each other. [ABSTRACT FROM AUTHOR]

[Objective] The present paper aimed to explore the impact of different farming methods on soil physical properties in Aksu area.[Method] The soil under five typical farming methods including wheat field, single-cropping jujube orchard, jujube-wheat intercropping garden, wasteland single-cropping jujube orchard, and abandoned land were collected in Aksu area, and the main physical characteristics were studied through field investigation and indoor analysis.[Result] Compared with farmland wheat fields and abandoned land, the soil bulk density of jujube orchard and jujube-wheat intercropping orchard is reduced, and soil porosity, aggregate stability, and soil moisture content are correspondingly improved; soil wet sieve aggregate composition under different farming methods. They are mainly 2-0.25 mm intermediate aggregates, with a content of 38.95%-53.74%.After the farmland was converted into a jujube orchard or a jujube-wheat intercropping orchard, the content of soil aggregates over 0.25 mm increased significantly (P<0.05), and both soil MWD and GMD showed an increase. After the abandoned land was converted into a jujube orchard, the content of soil powder + clay aggregates dropped by 5.25%-43.86%.The content of soil macroaggregates, intermediate aggregates and microaggregates showed an increase, with the increasing range of 9.07%-64.92%, 0.49%-4.19% and 0.72%-20.11%, respectively. [Conclusion] Compared with farmland wheat fields and abandoned land, jujube orchards and jujube-wheat intercropping gardens are beneficial to the stability of soil aggregates and can promote the formation of good soil structure. [ABSTRACT FROM AUTHOR]