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To clarify the effects of weathered coal humic acid on water-stable aggregates and pore characteristics of reclaimed cambisol, this research analyzed the evolution characteristics of soil aggregates and pores. Effects of different humic acid dosages (0, 1%, 3%, and 5% by weight) and application period (1 year, 2 years, and 3 years) on soil aggregates and organic carbon components in soil water-stable aggregates were investigated. The results showed that it is advisable to have an addition of 5% weathered coal humic acid in reclaimed cambisol. The humic acid of weathered coal promoted the disintegration and transformation of water-stable aggregates and increased soil pore p > 75 μm. At 3 years, the structure of reclaimed soil was the most stable, with more robust connected pores, and the irregular pores increased. The humic acid of weathered coal has the potential to be used as an effective organic amendment for improving the quality of reclaimed cambisol. [ABSTRACT FROM AUTHOR]

Tillage modes and straw returning influence soil aggregate stability and the distribution of organic carbon (C) and nitrogen (N) in aggregates of different particle sizes. In the typical hilly regions of southwest China, the predominant soil type is purple soil, characterized by heavy texture and high stickiness, with relatively lower soil fertility compared to other soil types. The improper use of fertilizers and field management practices further exacerbates soil compaction. However, abundant straw resources in the region provide an opportunity for comprehensive straw utilization. The effective utilization of straw resources is of significant importance for stabilizing agricultural ecological balance, improving resource utilization efficiency, and alleviating ecological pressure. Previously, most studies have focused on the impact of different mechanized tillage systems on the physical and chemical properties of soil in hilly areas, while research on the preservation of water-stable aggregates' organic C and N content remains limited. In this study, the soil properties of fields under a winter pea–summer corn rotation for two years were studied with regards to the effects of straw returning on its water-stable aggregate distribution, macroaggregate content (R0.25), mean weight diameter (MWD), geometric mean diameter (GMD), and the organic C and N content in soil aggregates of different particle sizes and at different depths. The effects of five different tillage modes were assessed, namely rotary tillage with straw mixed retention (RTM), conventional tillage with straw burial retention (CTB), no-tillage with straw covered retention (NTC), subsoiling with straw covered retention (STC), and no-tillage without straw retention (NT). Based on the study results, under different tillage modes, straw returning effectively enhanced the soil organic carbon (SOC) and total nitrogen (TN) reserves at the plow layer (0–30 cm), SOC increased by 17.2% to 88%, and TN increased by 8.6% to 85.9%. At the same time, the content of 0.25–2 mm aggregates increased under the straw-return treatments under different tillage patterns. The NT treatment had the lowest R0.25 and MWD and GMD values for soil aggregates at different depths, which were significantly different (p < 0.05) from the other treatment modes. The correlation coefficients between SOC and soil aggregate stability indices ranged from 0.68 to 0.90, with most of them showing highly significant positive correlations (p < 0.01). In conclusion, straw returning under different tillage systems has improved soil aggregate stability and promoted soil structure stability. Specifically, the STC treatment has shown more pronounced effects on soil improvement in the upper soil layer of the hilly regions in southwest China, while the RTM treatment is beneficial for improving the lower soil layer. Therefore, the comprehensive experimental results indicate that the combination of STC and RTM treatments represents the most promising mechanized tillage and straw returning practices for the hilly regions in southwest China. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Mountain Research (10082786) is the property of Mountain Research Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Purpose: Saline sodic soils pose challenges for crop growth due to their high soil salinity, poor structure, and low nutrient content and effectiveness. As a result, there has been increasing interest in using straw return to the field as a means to enhance productivity. However, the impact of straw return and nitrogen fertilization on soil aggregates and nutrient dynamics in saline sodic soils has not been fully understood yet. Methods: The present study conducted a 3-year positional experiment to examine the effects of straw return (S0: 0, S1: 7 t ha−1) and nitrogen fertilization (N0: 0, N1: 150, N2: 250, and N3: 350 kg ha−1) on bulk density (BD), aggregate distribution, nutrient dynamics, and rice yield. Results: Straw return to the field promoted the transformation of aggregates into larger ones, resulting in increased aggregate stability. Additionally, it significantly reduced the BD by 8.5 to 10% and increased the soil organic carbon (SOC), nitrogen (N), phosphorus (P), and potassium (K) content of the aggregates. The 0.25–2 mm aggregates were found to be the major contributors to fertility enhancement. There were no significant differences in the structure of the aggregates and the nutrient levels between the N2 and N3 treatments. Straw return led to a significant increase in rice yield by 20.90 to 27.57%. However, the differences between the S1N2 and S1N3 treatments were not significant, indicating that S1N2 had better benefits. Regression analysis revealed that the optimum nitrogen application rate tended to decrease with the increase in years of straw return. Conclusion: The incorporation of straw and optimal nitrogen (quantity) into saline sodic soils can enhance soil structure and aggregate nutrients, particularly in 0.25–2 mm aggregates. This agronomic measure is viable in improving soil productivity which ultimately increases rice yield. [ABSTRACT FROM AUTHOR]

The composition and stability of soil aggregates are important characteristics for evaluating soil health. The objective of this study was to explore the effects of different restoration modes and secondary succession sequences of Korean pine on the stability of forest soil aggregates after clear cutting and their causes. The stability and composition of soil aggregates in 0–10 cm, 10–20 cm, and 20–40 cm were analyzed in four natural forests in the secondary succession sequence and a Pinus koraiensis plantation in the clear-cutting area of Liangshui National Nature Reserve, and the effects of forest community characteristics and cementing materials on these aggregates were explored. With the advancement of succession, the large soil water-stable aggregates and mechanical aggregates increased, and the stability increased. From the pioneer community to the top community, the proportion of macroaggregates in the soil mechanical aggregates in the 20–40 cm soil layer increased by 36%, while that in the water-stable aggregates in the 10–20 cm soil layer increased by 19%. Compared with plantation, the stability of soil aggregates in natural forests with a similar age was stronger. Water-stable aggregates were negatively correlated with bulk density, density, and porosity, and positively correlated with organic-matter-related cement. The volume of the dominant tree, litter yield, tree species diversity, biomass of various tree species, and litter biomass in the undecomposed layer were the key indicators affecting the stability of aggregates. In terms of restoration measures, natural restoration is better than plantations with a single tree species. In addition, succession makes forest soil aggregates more stable. The change of dominant tree species leads to changes in soil aggregate stability, and the effect of organic-related cementing material was stronger than that of iron oxide. [ABSTRACT FROM AUTHOR]

In China, increasing the quantity and quality of total carbon and nitrogen stocks in sandy soil used for crop production is an important research issue. Soil amendment with pelletized straw could improve both soil physical structure and fertility in sandy soils, but these aspects remain understudied. The present pot and field experiments examined the dynamic changes in sandy soil water holding capacity, soil bulk density, soil total carbon and nitrogen stocks, and the distribution of water-stable aggregates and soil total carbon stocks related to aggregates across the following treatments: no fertilization (i.e., study control (CK)), normal fertilizer rate (NM), soil amendment at 150 Mg ha−1 (S150), manure amendment at 150 Mg ha−1 (M150), pelletized straw amendment at 75 Mg ha−1 (PS75), and pelletized straw amendment at 150 Mg ha−1 (PS150). The results show that the pelletized straw incorporation significantly increased water holding capacity and decreased soil bulk density. PS150 notably increased the large macroaggregates (>2000 μm) proportion and decreased the ratio of <250 μm aggregate size fractions in comparison with CK, NM, S150, and M150 at 0–20 and 20–40 cm soil depths. Compared with the CK treatment, the bulk soil carbon and nitrogen stocks in the 0–20 cm layers under the PS150 treatment were significantly increased by 85.2% and 302.9%, and in the 20–40 cm layers those increased by 136.4% and 257.1%, respectively. The PS150 treatment resulted in higher soil organic carbon (SOC) and particulate organic carbon content than the CK and PS75 treatments, whereas the PS75 treatment achieved maximum soil inorganic carbon content. The pelletized straw treatment increased the large macroaggregate-associated soil total carbon content at 0–20 and 20–40 cm soil depths. The maximum soil total carbon stocks were in the small macroaggregates (250 < WSA < 2000 μm) rather than in the large macroaggregate and microaggregates under the PS75 and PS150 treatments. Additionally, the pelletized straw and manure amendments increased the yield of silage corn, which was dependent on the increase in soil total carbon and nitrogen content in the macroaggregates, whereas the soil and manure amendments did not facilitate sandy soil aggregation and soil total carbon stock increases. In conclusion, PS150 was found to be the optimal amendment for maintaining sandy soil profile physico-chemical properties through macroaggregate stabilization. These results will be beneficial for arid and semi-arid regions, thus contributing to soil carbon and nitrogen conservation. [ABSTRACT FROM AUTHOR]

Organic amendments have been widely used in coastal saline–alkali soil remediation; however, the mechanisms involved and the interactions between organic and inorganic amendments are still unclear. In this work, furfural residue (particulate; C/N ratio: 51.87; O‐alkyl C + di‐O‐alkyl C: 42.35%, aromatic C: 40.89%) and black liquor (dissolved; C/N ratio: 3.11; O‐alkyl C + di‐O‐alkyl C: 32.20%, aromatic C: 28.32%) were tested to examine their effects on chemical properties, water‐stable aggregate fractions, chemical compositions of solid‐state soil organic matter (SOM), gloaming‐related soil protein contents, and microbial communities of coastal saline–alkali soil under a 400‐day incubation experiment. Furthermore, organic amendments mixed with mineral amendment (4:1) were employed to explore the interactions between organic and inorganic amendments. Furfural residue had stronger and longer effects on soil macroaggregate stability (~240 days, intense) than black liquor (~15 days, weak), and mineral amendment addition had a positive effect on the stability of microaggregates. Our results revealed that qualities (primary form, C/N ratio, and chemical composition) of organic amendment which can change microbial communities by increasing soil C/N ratio and effective chemical compositions of solid‐state SOM, are the key factors in promoting the rapid formation and longer stability of coastal saline–alkali soil aggregates. Moreover, inorganic amendment addition can further improve the formation and stability of microaggregates rather than those of macroaggregates. This study provided a much‐needed technical basis for remediation of coastal saline–alkali soil. [ABSTRACT FROM AUTHOR]

Soil aggregates and associated carbon (C) and nitrogen (N) stocks are important for soil organic matter (SOM) consequences and quality. The study is meant to understand the mechanisms of how fertilization management affects Cand Nstocks. Tobacco monocropping systems with four fertilizer treatments (0, 75, and 112kg Nha−1, and 60kg Nha−1 + manure) were established in 1998. After 19 years, crop monocrop and fertilization management redetermined soil aggregates and related indicators. The results showed the large aggregates proportion (LMP) and small macroaggregates proportion (SMP) varied inversely with changing season. The LMP gradually rose after the implementation of tillage while microaggregates gradually declined. By manure fertilizer, LMP and SMP were significantly higher than those in inorganic fertilizer treatments, while microaggregates proportion (MIP) and silt and clay proportion (SCP) were lower than in inorganic fertilizer treatments. Soil water-stable aggregate and their associated soil organic stocks are changed with growing season, and tillage practices would have potentially affected these indicators, while the proportion and soil organic stocks more quickly recovered in large aggregates by manure application. Therefore, the proper application of manure combined with chemical fertilizer would maintain soil quality in tobacco cultivation. [ABSTRACT FROM AUTHOR]

This study aims to investigate the effects of different straw returning amounts on soil aggregate stability and carbon pool change characteristics of wheat fields in dry loess tableland. Four treatments were set, including S0 (no straw returning), S1/2 (half of the straw returning), S1 (total straw returning), and S2 (two times straw returning), in the dryland winter wheat growing area of southern Shanxi Province, China. The composition and stability of soil aggregates were determined under different straw return rates over three consecutive years. A systematic investigation was made to clarify the Total Organic Carbon (TOC), Light Fraction Organic Carbon (LFOC), Heavy Fraction Organic Carbon (HFOC), Humin Carbon (HM-C), Humic Acid Carbon (HA-C), and Fulvic Acid Carbon (FA-C) in the soil and aggregates with different grain size. A relationship was also established between the organic carbon components in the aggregates of different grain sizes and the stability of aggregates. The results showed that the content of large macroaggregates (>0.25 mm) increased gradually, with the increase of straw returning amount, while the content of macroaggregates (<0.25 mm) and silt+clay (<0.053 mm) decreased gradually. Compared with the S0 treatment, the Mean Weight Diameters (MWD), Geometric Mean Diameter (GMD), and R0.25 increased by 14.7%, 22.2%, and 13.9% (P<0.05), respectively, indicating the higher stability of aggregates. The TOC content of the soil under the S2 treatment was the highest, which increased by 28.1% compared with the S0 treatment (P<0.05). The contents of soil organic carbon components under different treatments also increased significantly, with the increase of straw returning amount. Furthermore, straw returning increased the LFOC in the 0.053-0.25mm aggregate, and the HFOC in the 0.25-2 mm aggregate. In addition, the contents of HM-C, HA-C, and FA-C in the >0.25-2mm aggregate increased by 19.0%, 25.5%, and 14.9% (P<0.05), respectively, in the S2 treatment, compared with the S0. The ratio of humic to fulvic acid carbon (HA-C/FA-C) also increased, with the increase of straw returning amount. The variation of FA-C content in the silt+clay (<0.053 mm) was the main reason for the stability change of water-stable aggregates, which was 64.1% of the variation. Therefore, straw returning promoted the transformation from the water-stable micro-aggregate to large macroaggregates in the dry loess plateau, particularly for the higher stability of the aggregate. At the same time, straw returning increased the content of organic carbon and the components in the soil and aggregates. The degree of soil humification was improved significantly, as the straw returning amount increased. Two times the amount of straw returning performed the best on the soil organic carbon content and soil structure. The finding can also provide the theoretical basis for soil fertilizer cultivation in dry farmland. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Long-term frequent tillage would cause black soil degradation and serious soil erosion as soil microbial communities and soil structure are extremely sensitive to tillage process. However, there is no unified conclusion on the relationship between the distribution of soil water-stable aggregates (WSAs), and microbial community construction and diversity under long-term tillage in black soil during different seasons. In this study, we used wet-sieving method to evaluate the composition and stability of soil WSAs and employed Illumina MiSeq high-throughput sequencing technology to study the diversity, taxonomic composition and co-occurrence network properties of microbial community, comparing outcomes between uncultivated soil and long-term cultivated soil for 60 years in Keshan farm of Heilongjiang Province. The results showed that after long-term tillage, the proportion of larger than 1 mm WSAs reduced by 34.17–51.37%, and the stability of WSAs, soil pH, organic matter (OM), total nitrogen (TN) contents decreased significantly in all seasons (P < 0.05), while soil available phosphorus (AP) and available potassium (AK) contents increased remarkably (P < 0.05). The diversity of bacteria increased, while that of fungi decreased. Soil fungal communities were more susceptible to long-term tillage than bacterial and archaeal communities. Actinobacteria mainly exist in large WSAs (˃1 mm), and when their relative abundance is high, it is beneficial to improve the water-stability of black soil; while Proteobacteria and Gemmatimonadetes may exist in small WSAs (˂1 mm), whose high relative abundance will weaken the water-stability of black soil. The experimental results provide a scientific theoretical basis for sustainable utilization of black soil. [ABSTRACT FROM AUTHOR]

Soil aggregates are the anticipated organic carbon repository, and the stability of aggregate is vital for the efficacy of carbon sequestration. The stability and carbon content of soil aggregates in croplands are affected by nutrient management; however, the changes of aggregate organic carbon stability (AOCS) remain elusive under nutrient management with nature-based solutions. A total of 2035 observations from 269 peer-reviewed articles was compiled to elucidate the changes of AOCS, including aggregate stability, physically protected organic carbon content (i.e., aggregate-associated carbon), and the decomposability of aggregate organic carbon under nutrient management with nature-based solution. The AOCS was significantly improved with nature-based nutrient addition (biochar, manure, straw, and soil conditioner) in contrast to merely synthetic fertilization. Aggregate stability and physically protected organic carbon increased by 18.8–23.3 % and 20.5–34.3 %, respectively, while the decomposability of aggregate organic carbon decreased. Furthermore, the changes of ACOS traits were strengthened with prolonged nutrient management with nature-based solution. Notably, AOCS decreased with the high levels of synthetic nitrogen, in which the contents of aggregate organic carbon and recalcitrant organic carbon were reduced. The findings indicate that nutrient management with nature-based solution can enhance AOCS, therefore, the viable nature-based nutrients are desirable for carbon sequestration in worldwide croplands. • Nutrient management under nature-based solution (NbSNM) increased soil organic carbon. • NbSNM improved soil aggregate stability. • NbSNM increased physically protected organic carbon, particularly in macroaggregate. • NbSNM increased the recalcitrant carbon in aggregates. • Aggregate carbon stability was enhanced over time under NbSNM. [ABSTRACT FROM AUTHOR]

The present work screened four factors (i.e., tillage, initial soil water content (IWC), freezing–thawing (F–T) and drying–wetting (D–W) cycles) to examine the Mollisols aggregate size distribution and stability. Soils were sampled from no-till (NT) and conventional tillage (CT) treatments in the 0–10 cm soil layer and conducted 0/3/6/11 F–T and D–W cycles. Three different IWC values were considered: 130, 230, and 330 g/kg, and our trials set up four aggregate size classes: larger aggregate size fractions (LWSA, >1.00 mm), medium aggregate size fractions (MWSA, 0.25–1.00 mm), small aggregate size fractions (SWSA, 0.106–0.25 mm), and particles (PA, < 0.106 mm); and the mean weight diameter (MWD) was used to analyze water-stable aggregate stability (WAS). Significant decrease of LWSA and WAS in NT was observed in the snowmelt stage, but the opposite results occurred during the crop growth period. In the simulated experiment, significant interactive effects of tillage and IWC on LWSA and WAS were observed in the F–T and D–W cycles, which showed that LWSA and WAS elevated as the F–T and W–D cycle numbers and IWC increased for both NT and CT treatments exhibited negative correlation with WAS. The greater amount of LWSA in NT was observed than CT in the F–T cycles, while the opposite results were in W–D cycles. The SWSA fraction had a negative relation with LWSA for NT treatment, and the MWSA fraction had a contrary variation with LWSA for CT treatment. In either tillage treatment, PA was not greatly affected. We therefore suggested to evaluate size distribution and stability of the Mollisols aggregates by including tillage, IWC, F–T and W–D cycles. [ABSTRACT FROM AUTHOR]

Soil degradation threatens agricultural productivity and food supply, leading to hunger issues in some developing regions. To address this challenge, we developed a low-cost, highly efficient, and long-term stable soil improvement method. We chose polyvinyl alcohol (PVA), a commercially available polymer that is safe and non-degradable, to serve as a soil adhesive. We mixed PVA solution into the soil and applied a drying treatment to enhance the bonding between PVA and the soil, achieving highly water-stable soil. This PVA-stabilized soil exhibits low bulk density, high porosity, and high permeability, making it an ideal substrate for planting. In a germination test, the PVA-stabilized soil revealed a higher germination rate and growth rate compared to those of the non-treated soil. We believe this simple and efficient soil improvement method can restore degraded soil and contribute to sustainable agriculture.

This study explored the effects of different soil amendments—a calcium preparation（GZJ）, furfural residue（KQZ）, and weathered coal（FHM）on the improvement of moderately saline-alkali coastal soil and maize growth therein. The effects of the treatments on the physicochemical properties of the soil and on maize plant height, chlorophyll content（SPAD）, and yield were studied via pot experiments, and the experimental dosage of each treatment was as follows：GZJ1（15 t·hm-2）, GZJ2（22.5 t·hm-2）, KQZ1（30 t·hm-2）, KQZ2（45 t·hm-2）, FHM1（30 t·hm-2）, and FHM2（45 t·hm-2）. The results showed that the three amendments significantly increased the cation exchange capacity（CEC） of saline-alkali soil by 17.53%~49.45%, compared to when no amendments were added. Three amendments reduced soil bulk density and salt content while two different doses of furfural slag and high levels of weathered coal reduced soil bulk density significantly by 7.80%~12.06%. Two different doses of weathered coal and a low dose of the calcium preparation reduced the soil salt content significantly by 13.19%~19.33%. In addition, the calcium preparation and furfural residue significantly increased the quantity of water-stable aggregates（0.25~0.5 mm and 0.5~1 mm, respectively）, increasing these by 5.36~6.59 percentage points and 1.92~ 2.81 percentage points, respectively. The quantity of micro-aggregates（<0.25 mm）was decreased by 9.93~11.52 percentage points. The best treatment to improve the physicochemical properties of saline-alkali soil was KQZ1（30 t·hm-2 of furfural residue）. Furfural slag and weathered coal significantly increased the plant height and SPAD of maize at different stages. The height of the maize plant at maturity increased by 9.71%~13.09% and the SPAD at jointing stage increased by 10.13%~16.44%. The three amendments increased the number of grains per ear and yield per plant by 15.97%~37.43% and 25.86%~49.65%, respectively; Once again, treatment KQZ1 had the best effect. The calcium preparation, furfural slag, and weathered coal all improved the moderately saline-alkali coastal soil and the kernel number and yield of maize. However, there was no significant difference between the three kinds of amendments in different dosages. The comprehensive effect of improvement with the use of furfural slag was better than those with the use of weathered coal and the calcium preparation; and treatment KQZ1（30 t·hm-2）had the best comprehensive improvement effect among the furfural slag treatments. [ABSTRACT FROM AUTHOR]

The poly-γ-glutamic acid super-absorbent polymer (γ-PGA SAP) is an environmentally friendly material. Five different γ-PGA SAPs contents based on weight, including 0% (CK), 0.05% (T1), 0.10% (T2), 0.15% (T3), and 0.20% (T4), were added to the soil in this study. The results showed that cumulative infiltration decreased by 32.4% (T1), 39.2% (T2), 51.0% (T3), and 52.0% (T4) at 90 min and the field capacity was increased by 18.7% (T1), 26.0% (T2), 37.8% (T3), and 58.3% (T4) compared with the CK. The cumulative evaporation of the different treatments with γ-PGA SAPs was 17.1% (T1), 23.5% (T2), 24.4% (T3), and 25.3% (T4) higher than that of the CK at the end of the evaporation experiment. The evaporation experiment lasted 96 h (CK), 132 h (T1), 144 h (T2), 180 h (T3), and 312 h (T4) to progress from field capacity to a soil water content of 10%. Adding γ-PGA SAPs to the soil significantly increase the water-stable aggregate content below 0.25 mm when the γ-PGA SAP addition exceeded 0.10%. So reasonable utilization of γ-PGA SAP can improve water use efficiency and improve soil structure in semi-arid areas. [ABSTRACT FROM AUTHOR]

The paper is devoted to the development and performance testing of a soil conditioner based on leonardite humic substances (LHS) modified with 3-aminopropyltriethoxysilane (APTES). The modified HS were obtained by adding APTES to LHS solution at different mass ratios of LHS and APTES, followed by the investigation of siloxane structures using 31Si NMR spectroscopy. The Urbic Technosol was used as a model soil. The size and amount of water-stable soil aggregates were estimated using wet sieving and laser diffraction, respectively. Toxicity was evaluated by monitoring microbial substrate-induced respiration (SIR) and seedling bioassay. Laboratory column experiments demonstrated an increase in water-stability of the 3–5 mm soil aggregates after LHS-APTES application. Field tests showed an increase in the average weighted diameter of micro aggregates (from 59 to 73 μm) and water-stable macroaggregates (from 1.6 to 2.9 mm) due to the LHS-APTES amendment. A substantial increase in SIR from 5 to 9 mg CO2 (kg h)−1 was detected. Better survival of seedlings was observed. The obtained beneficial results indicate that APTES-modified HS can be successfully used as a soil conditioner. The formation of extended siloxane networks was suggested as the main mechanism of the observed improvement in the structure of the amended soils.

This study investigated the effects of three contrasting soil management regimes and different nutrient treatments on the distribution of water-stable aggregates (>2, 1–2, 0.5–1, 0.25–0.5, and 0.25 mm) and mean weight diameter (MWD) at 0–10 and 10–20 cm soil horizons compared with Cropping, whereas Fallow yielded lower values of above two parameters. Abandonment increased SOC and TN contents in all aggregate sizes by 17–62% and 6–60%, respectively, at 0–10 cm soil layer compared with Cropping. Conversely, Fallow decreased SOC and TN contents in all aggregates by 7–27% and 7–25%, respectively. Nevertheless, the three soil management regimes presented similar SOC contents in all aggregates at 10–20 cm soil horizon. Only Cropping showed higher TN content in >0.5 mm aggregates than the two other regimes. Consequently, Abandonment enhanced the partitioning proportions of SOC and TN in >1 mm macro-aggregates, and Fallow promoted these proportions in micro-aggregates compared with Cropping. Under Cropping, long-term fertilization did not affect the distribution of aggregates and MWD values compared with those under CK, except for NPK treatment. Fertilizer treatments enhanced SOC and TN contents in aggregates at all tested soil depths. However, fertilization did not affect the partitioning proportions of SOC and TN contents in all aggregates compared with CK. Comprehensive results showed that different soil management regimes generated varied patterns of SOC and TN sequestration in loess soil. Abandonment enhanced soil aggregation and sequestered high amounts of SOC and TN in macro-aggregates. Long-term amendment of organic manure integrated with NPK maintained soil aggregate stability and improved SOC and TN sequestration in all aggregates in loess soil subjected to dryland farming.

Flue-cured tobacco production in China is typically over-fertilised and mono-cropped. To understand how this agronomic management affects soil structure and organic matter, this study investigated the effect of rotation, fertilizer rate, and manure amendment on the proportion of water stable aggregates and aggregate-associated soil organic carbon (SOC) and total soil nitrogen (TSN) concentrations and stocks in tobacco production. Two tobacco management systems (Tobacco monoculture and Tobacco-rice rotation) with four fertilizer treatments (0, 75, and 112 kg N/ha, and 60 kg N/ha + manure) were established in 1998. After 18 years, soil aggregation and aggregate-associated SOC and TSN were significantly affected by rotation and fertilizer management. Compared to tobacco monoculture and current fertilizer management, rotation and manure amendment increased macroaggregate (>250 μm) proportion and geometric mean diameter and decreased the proportion of microaggregates and silt-clay sized fractions (<250 μm). Simultaneously, rotation and manure amendment increased macroaggregate-associated SOC and TSN stocks at the expense of the microaggregate and silt-clay size class and their associated SOC and TSN stocks. Rotation and/or manure treatment can maintain satisfactory physico-chemical soil properties through macroaggregate stabilization in tobacco production, which contributes to conserving SOC and TSN stocks. [ABSTRACT FROM AUTHOR]

Agriculture wastes returning to soil is one of common ways to reuse crop straws in China. The returned straws are expected to improve the fertility and structural stability of soil during the degradation of straw it selves. The in situ effect of different straw (wheat, rice, maize, rape, and broad bean) applications for soil aggregate stability and soil organic carbon (SOC) distribution were studied at both dry land soil and paddy soil in this study. Wet sieving procedures were used to separate soil aggregate sizes. Aggregate stability indicators including mean weight diameter, geometric mean diameter, mean weight of specific surface area, and the fractal dimension were used to evaluate soil aggregate stability after the incubation of straws returning. Meanwhile, the variation and distribution of SOC in different-sized aggregates were further studied. Results showed that the application of straws, especially rape straw at dry land soil and rice straw at paddy soil, increased the fractions of macro-aggregate (> 0.25 mm) and micro-aggregate (0.25-0.053 mm). Suggesting the nutrients released from straw degradation promotes the growing of soil aggregates directly and indirectly. The application of different straws increased the SOC content at both soils and the SOC mainly distributed at < 0.53 mm aggregates. However, the contribution of SOC in macro- and micro-aggregates increased. Straw-applied paddy soil have a higher total SOC content but lower SOC contents at > 0.25 and 0.25-0.053 mm aggregates with dry land soil. Rape straw in dry land and rice straw in paddy field could stabilize soil aggregates and increasing SOC contents best. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the effects of soil conditioners on the structure stability of degraded soil. Biomass ash, lime, lime with zeolite, biological fertilizer and peat ash, mixed with chemical fertilizer were selected as soil conditioners. A pot experiment with degraded clay loam soil (a Cambisol) was carried out. The stability of soil aggregates was analyzed by the Le Bissonnais method. The results showed that macro-aggregates (>0.25 mm) of biomass ash treatment in fast wetting test stayed stable compared with others. The higher mean weight diameter and geometrical mean diameter in biomass ash treatment indicated a high stability from external forces. From this study, the stability of soil aggregates was improved by the addition of biomass ash in degraded soil effectively, but more attention should be paid on soil slope protection during heavy-rain seasons. [ABSTRACT FROM PUBLISHER]

Structure is the most striking, visual aspect of vertisol morphology. The type and degree of structure development in a vertisol provides a digest of its genesis, constituent properties and agriculture management potential. The present study includes the results of the investigations of aggregate composition and water stability of structural aggregates in all horizons (Ap, A, AC, C) of 7 vertisol profiles formed over tertiary clayish and pyroclastic sediments in the central part of Macedonia (Štip, Probištip and Ovče Pole valleys). The main objectives were to determine and compare aggregate composition and water stability of structural aggregates of vertisols which have been used as long-term arable fields (6 of the analyzed profiles) or as pasture (1 profile). The most represented fraction of aggregates in the process of dry sieving of the soil samples is the fraction of cloddy macro-aggregates (>10 mm), which is the most unfavourable from the agricultural point of view. Micro- aggregates fraction (

Mycorrhization-induced secretion of glomalin-related soil protein (GRSP) is known to contribute in improving soil fertility and aggregate stability. But, there is hardly any evidence that exogenous GRSP could produce the similar type of response. The present study was, therefore, carried out to extract easily extractable GRSP (EE-GRSP) from citrus rhizosphere soils and evaluate the response at 1/4, 1/2 and full strength EE-GRSP solutions watered into the rhizosphere of 27-year-old Satsuma mandarin (Citrus unshiu) grafted on the rootstock of Poncirus trifoliata. After ~5 months, exogenous EE-GRSP treatments produced significantly positive responses on endogenous EE-GRSP, difficultly-extractable GRSP (DE-GRSP), total GRSP production and soil organic carbon (SOC) content. A significantly positive correlation of these endogenous GRSP fractions with SOC indicated an active participation of GRSP on soil C pool. Exogenous GRSP showed a key role in binding water-stable aggregate (WSA) at 2–4, 1–2, 0.5–1, and 0.25– 0.5 mm size and enhancing WSA stability through changes in mean weight diameter (MWD). A stronger correlation of EE-GRSP and total GRSP with MWD was observed than DE-GRSP fraction. On the other hand, exogenous EEGRSP showed a positive effect on soil phosphatase activity, and soil endogenous EE-GRSP was significantly and positively correlated only with neutral phosphatase. Our studies suggest that exogenous EE-GRSP could be used as an effective regulator to affect soil fertility and soil structure within citrus rhizosphere.

By breaking up soil, tillage often disrupts mycorrhizal extraradical mycelium (ERM). In a core having four windows covered with 37-μm mesh in a perspex box, trifoliate orange ( Poncirus trifoliata ) seedlings were colonized with an arbuscular mycorrhizal (AM) fungus, Funneliformis mosseae . The core was rotated weekly at 180° around vertical axes, in order to simulate ERM disruption. After 13 such rotations, root mycorrhizal colonization, soil hyphal length inside and outside the core, and plant biomass were substantially reduced. On the other hand, mycorrhizal inoculation without disruption of ERM (static core) was associated with significant increase in biomass production, compared with disruption of ERM (rotating core). Disruption of ERM (rotating core) inhibited the production of easily-extractable glomalin-related soil protein (EE-GRSP) and total GRSP (T-GRSP) inside the core under mycorrhization, due to breakdown of ERM. Mycorrhization markedly increased soil organic carbon content, distribution of water-stable aggregate (WSA) at 0.5–4 mm size and mean weight diameter (MWD), whereas core rotation showed a negative effect on MWD and the percentage of WSA within 1–4 mm size under mycorrhization and within 0.25–2 mm size under non-mycorrhization. It was proposed that soil tillage, in terms of the core rotation, strongly disrupted ERM network, which adversely influenced EE-GRSP and T-GRSP production and plant growth under mycorrhization, subsequently weakening the GRSP functioning on WSA stability. [ABSTRACT FROM AUTHOR]

Few studies have examined direct impacts of intensive tillage on soil structural stability in hillslope landscapes. In this experiment, we performed simulation tillage within the steep hillslope landscape of the Sichuan Basin, China, i.e., 20-time consecutive tillage by hoeing in a short time interval (3 days) under no rainfall. The 137 Cs tracing was used to demonstrate tillage erosion/deposition in soil profiles and landscape positions. A wet-sieving method was used to determine mean weight diameter (MWD) and geometric mean diameter (GMD) as indices of soil aggregate stability. Soil organic matter (SOM) was also determined just before and after hoeing tillage implementation. The greatest changes in 137 Cs inventory due to 20-operation tillage were observed at 1 and 20 m slope positions, with a decrease of 100% at the 1 m position and an increase of 50.58% at the 20 m position compared with pre-tillage. The <0.25 mm water-stable aggregates after 20-operation tillage increased by 32.62–42.14% (mean 36.98%) for all slope positions compared with those of pre-tillage. After 20-operation tillage, the great differences in MWD and GMD values were found at the upper slope positions (1 m), with decreases of 35.01% and 39.24%, respectively, and at the lower slope positions (15 and 20 m), with decreases of 14.17–24.79% and 20.37–29.63%, respectively, as compared to pre-tillage. However, MWD and GMD values remained unchanged at the middle slope position (10 m). This result suggests that apparent changes in soil structural properties occur close to the upslope and downslope boundaries of the field and the middle slope acts as a conveyor belt. On the whole, simulated tillage markedly increased the CV values of MWD and GWD by 96.80% and 86.15%, respectively, compared with those of pre-tillage, implying that intensive tillage causes a great within-field spatial variability of soil aggregate stability. Soil aggregate stability can be affected by both the disruption caused by the act of tillage and the loss of surface soil and incorporation of subsoil through intensive tillage. Our results indicate that intensive tillage has a twofold influence: aggregate redistribution due to the soil transfer process and the mechanical breakage of macroaggregates. It is suggested that the use of reduced tillage is not only an effective alternative for diminishing soil erosion, but also a viable strategy for improving soil structure on the hillslopes. [ABSTRACT FROM AUTHOR]

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A study was conducted to evaluate the effects of different land uses and soil-management systems (LU and SMS) on key soil physicochemical indicators [aggregate stability, distribution of soil organic carbon (SOC), and nitrogen (N) in aggregate fractions] and to interpret significance of long-term cultivation of agroforestry plantations [Prosopis julifloraL. (AFP) andCasuarina equisetifoliaL. (AFC)], horticultural plantations [(Tamarindus indica(HI) andSyzygium cumini(HJ)], and rice–wheat system (RW) in sodic soil of the Indo-Gangetic plain. Soil samples collected from the different LU and SMS plots were analyzed. The barren sodic soil (BSS) exhibited the least mean weight aggregate diameter (0.21), whereas AFP recorded the greatest (0.59). Total N content in surface soil under RW system was about the same as AFP, AFC, HI, and HJ and significantly greater than BSS. Across the LU and SMS except BSS, microaggregates recorded a narrower C/N ratio than macro- and mesoaggregates. [ABSTRACT FROM PUBLISHER]

Based on the field survey and laboratory analysis, this paper studied the soil aggregate stability and soil organic carbon characteristics in Quercus variabilis and Pinus tabulaeformis plantations in Beijing area. In the two plantations, the contents of soil macro-aggregates decreased with soil depth. In P. tabulaeformis plantation, soil macro-aggregates (>0. 25 mm) occupied the majority, accounting for 71% -77% of the total; whereas in Q. variabilis plantation, no significant difference was observed in the contents of soil macro-aggregates and micro-aggregates (⩽0. 25 mm), which accounted for 51% -58% and 42% -49%, respectively. Both the mean mass diameter and the geometrical mean mass diameter of the soil aggregates in P. tabulaeformis plantation were significantly higher than those in Q. variabilis plantation, and the fractal dimension (D) of the soil water-stable aggregates in P. tabulaeformis plantation was lower than that in Q. variabilis plantation, suggesting that P. tabulaeformis plantation was more favorable for the soil aggregate stability than Q. variabilis plantation. Also in the two plantations, the organic carbon content in soil water-stable aggregates decreased with soil depth. The organic carbon content in soil macro-aggregates was significantly higher in P. tabulaeformis plantation (58%-83%) than in Q. variabilis plantation (49%-66%). It was suggested that in Beijing area, P. tabulaeformis plantation was more beneficial to the soil organic carbon protection, as compared with Q. variabilis plantation. [ABSTRACT FROM AUTHOR]

Structure is the most striking, visual aspect of vertisol morphology. The type and degree of structure development in a vertisol provides a digest of its genesis, constituent properties and agriculture management potential. The present study includes the results of the investigations of aggregate composition and water stability of structural aggregates in all horizons (Ap, A, AC, C) of 7 vertisol profiles formed over tertiary clayish and pyroclastic sediments in the central part of Macedonia (Štip, Probištip and Ovče Pole valleys). The main objectives were to determine and compare aggregate composition and water stability of structural aggregates of vertisols which have been used as long-term arable fields (6 of the analyzed profiles) or as pasture (1 profile). The most represented fraction of aggregates in the process of dry sieving of the soil samples is the fraction of cloddy macro-aggregates (>10 mm), which is the most unfavourable from the agricultural point of view. Microaggregates fraction (<0.25 mm) is barely present, which means that in the dry state nearly all micro-aggregates and mechanical elements are associated in larger structural aggregates. The researched soils are characterized by different water stability of the structural aggregates. In the process of wet sieving, except surface horizon of the vertisol under natural vegetation, the cloddy macro-aggregates showed the greatest instability. With decrease of the dimension their stability increases so micro-aggregates have the highest water stability. [ABSTRACT FROM AUTHOR]

We investigated whether the long-term application of compost from agricultural waste improved soil physical structure, fertility and soil organic matter (SOM) storage. In 2006, we began a long-term field experiment based on a rice-wheat rotation cropping system, having a control without fertilizer (NF) and three treatments: chemical fertilizers (CF), pig manure compost (PMC) and a prilled mixture of PMC and inorganic fertilizers (OICF). Following the harvest of wheat in 2010, the mean-weight diameter (MWD) of water-stable aggregates and the concentration of C and N in bulk soil (0-20 cm; <2 mm fraction) were significantly greater ( P < 0.05) in PMC and NF plots than in CF or OICF plots. Pig manure compost significantly increased the proportion of >5-mm aggregates, whereas CF significantly increased the proportion of 0.45- to 1-mm aggregates. The C and N contents of all density fractions were greater in PMC than in other treatments with levels decreasing in the following order: free particulate organic matter (fPOM) >occluded particulate organic matter (oPOM) > mineral-combined SOM (mineral-SOM). Solid-state 13C CPMAS NMR spectra showed that alkyl C/O-alkyl C ratios and aromatic component levels of SOM were smaller in PMC and OICF plots than in CF plots, suggesting that SOM in PMC and OICF plots was less degraded than that in CF plots. Nevertheless, yields of wheat in PMC and NF plots were smaller than those in CF and OICF plots, indicating that conditions for producing large grain yields did not maintain soil fertility. [ABSTRACT FROM AUTHOR]

Soil aggregate-size distribution and soil aggregate stability are used to characterize soil structure. Quantifying the changes of structural stability of soil is an important element in assessing soil and crop management practices. A 5-year tillage experiment consisting of no till (NT), moldboard plow (MP) and ridge tillage (RT), was used to study soil water-stable aggregate size distribution, aggregate stability and aggregate-associated soil organic carbon (SOC) at four soil depths (0-5, 5-10, 10-20 and 20-30 cm) of a clay loam soil in northeast China. Nonlinear fractal dimension (Dm) was used to characterize soil aggregate stability. No tillage led to a significantly greater aggregation for >1 mm aggregate and significant SOC changes in this fraction at 0-5 cm depth. There were significant positive relationships between SOC and >1 mm aggregate, SOC in each aggregate fraction, but there was no relationship between soil aggregate parameters (the proportion of soil aggregates, aggregate-associated SOC and soil stability) and soil bulk density. After 5 years, there was no difference in Dm of soil aggregate size distribution among tillage treatments, which suggested that Dm could not be used as an indicator to assess short-term effects of tillage practices on soil aggregation. In the short term, > 1 mm soil aggregate was a better indicator to characterize the impacts of tillage practices on quality of a Chinese Mollisol, particularly in the near-surface layer of the soil. [ABSTRACT FROM AUTHOR]

A study on the biomass of fine roots and its relationship with water-stable aggregates (WSA) was conducted in two herbaceous models, triploid Populus tomentosa + Lolium multiflorum (TL) and triploid P. tomentosa + natural grass (TN). Both of the model triploid P. tomentosa stands were four years old converted from agriculture. Unconverted steep slope farmland was used as a control site. Results showed that the biomass of fine roots (⩽ 1 mm) in different layers varied in the following descending order: upper layer, middle layer and lower layer, at approximate ratios of 50:30:20. The average annual biomass of fine roots in ryegrass was twice that of the mixed natural grass-forest land. The total amount of natural grass roots was 4.4 times that of the ryegrass model. Water-stable aggregates of the upper, middle and lower layers and the unconverted farmland did not show any significant differences, whereas the amounts of water-stable aggregates of big-particles in the upper and middle layers were much larger than those of unconverted lands. The amounts of water-stable aggregates of natural grass-forest lands (TN model) were higher than those of managed grass-forest lands (TL model). Two-way analysis of variance indicated that fine roots (≤ 1 mm) could significantly enhance water-stable aggregates and total water-stable aggregates. We conclude that the program of converting agricultural lands to forest-grass lands is an effective way in improving soil anti-erosion capability. [ABSTRACT FROM AUTHOR]

Abstract: In a controlled potted experiment, citrus (Poncirus trifoliata) seedlings were inoculated with three species of arbuscular mycorrhizal (AM) fungi, Glomus mosseae, G. versiforme or G. diaphanum. Two soil-water levels (ample water, −0.10MPa; drought stress, −0.44MPa) were applied to the pots 4months after transplantation. Eighty days after water treatments, the soils and the citrus seedlings were well colonized by the three AM fungi. Mycorrhizal fungus inoculation improved plant biomass regardless of soil-water status but decreased the concentrations of hot water-extractable and hydrolyzable carbohydrates of soils. Mycorrhizal soils exhibited higher Bradford-reactive soil protein concentrations than non-mycorrhizal soils. Mycorrhizas enhanced >2mm, 1–2mm and >0.25mm water-stable aggregate fractions but reduced 0.25–0.5mm water-stable aggregates. Peroxidase activity was higher in AM than in non-AM soils whether drought stressed or not, whereas catalase activity was lower in AM than non-AM soils. Drought stress and AM fungus inoculation did not affect polyphenol oxidase activity of soils. A positive correlation between the Bradford-reactive soil protein concentrations, soil hyphal length densities, and water-stable aggregates (only >2mm, 1–2mm and >0.25mm) suggests beneficial effects of the AM symbiosis on soil structure. It concluded that AM fungus colonization enhanced plant growth under drought stress indirectly through affecting the soil moisture retention via glomalin''s effect on soil water-stable aggregates, although direct mineral nutritional effects could not be excluded. [Copyright &y& Elsevier]

Soil cultivation influences organic carbon storage and soil structures. To evaluate the impact of different soil-management practices on soil organic carbon (SOC) pools and aggregate stability in black soils, SOC in whole soil, various size aggregates, and density-separated fractions from three long-term experiments (20 years) was examined. The three soil-management systems were grassland (GL), bare land (BL), and croplands. The croplands had two treatments: nitrogen and phosphorus fertilizer application (NP) and NP together with organic manure (NPM). The SOC in the 0- to 10-cm layer decreased in the order NPM>GL>NP>BL and also declined with the soil depth. The SOC of GL increased by 9.7% as compared to NP after 20 years of natural vegetation restoration. The SOC of NPM increased by 11% over NP after 13 years of organic manure application. The percentages of water-stable aggregate (>0.25 mm) (WSA>0.25mm) decreased in the order GL>BL>NPM>NP in the top 0- to 20-cm horizon. WSA>2mm, the most important fraction for carbon (C) storage in GL and NPM, accounted for 33 and 45% of the whole soil for GL in the depths of 0-10 and 10-20 cm, respectively, and 25 and 18% for NPM in the same soil layers. A significant positive correlation was found between the C stored in WSA>2mm and total SOC (r=0.81, P<0.05) and between the mean weight diameters (MWD) of aggregates and total SOC (r=0.78, P<0.05). Water-stable aggregate0.25-2mm was the largest fraction of WSA>0.25mm, ranging from 54 to 72% for the 0- to 10-cm layer and 46 to 71% for the 10- to 20-cm layer; thus these aggregates would play a major role in soil sustainability as well as the resistance to soil erosion. The organic carbon (OC) of heavy fraction (HF) accounted for 94-99% of the OC in the WSA0.25-2mm, whereas free particulate organic matter (fPOM) and occluded particulate organic matter (oPOM) contributed a minor fraction of the OC in the WSA0.25-2mm, suggesting that C sequestration in HF could enhance the stability of aggregates and C pools in black soil. [ABSTRACT FROM AUTHOR]

The article presents abstracts of several studies on environmental geochemistry. Some of the abstracts presented include "Biogeochemical Cycling of Nutrients in Karstic Catchments, Southwestern China: Linkages to Changes of Eco-Environments," by Congqiang Liu and "Emerging Organic Contamination in China," by Guibin Jiang and colleagues.

We studied the effects of a saprophytic lignin-decomposing basidiomycete isolated from plant litter on soil aggregation and stabilization. The basidiomycete produced large quantities of extracellular materials that bind soil particles into aggregates. These binding agents are water-insoluble and heat-resistant. Water stability of aggregates amended with the fungus and the degrees of biodegradation of the binding agents by native soil microorganisms were determined by the wet-sieving method. The data demonstrated that aggregates supplemented with a source of C (millet or lentil straw) were much more water-stable and resisted microbial decomposition longer than when they were prepared with fungal homogenates alone. Moreover, retrieval of fungal-amended aggregates supplemented with millet during the first 4 weeks of incubation in natural soil exhibited more large aggregate fractions (>2 mm) than the ones supplemented with lentil straw. The possible relationship of the role of basidiomycetes in litter decomposition and soil aggregation is discussed. [ABSTRACT FROM AUTHOR]

The paper is devoted to the development and performance testing of a soil conditioner based on leonardite humic substances (LHS) modified with 3-aminopropyltriethoxysilane (APTES). The modified HS were obtained by adding APTES to LHS solution at different mass ratios of LHS and APTES, followed by the investigation of siloxane structures using 31Si NMR spectroscopy. The Urbic Technosol was used as a model soil. The size and amount of water-stable soil aggregates were estimated using wet sieving and laser diffraction, respectively. Toxicity was evaluated by monitoring microbial substrate-induced respiration (SIR) and seedling bioassay. Laboratory column experiments demonstrated an increase in water-stability of the 3–5 mm soil aggregates after LHS-APTES application. Field tests showed an increase in the average weighted diameter of micro aggregates (from 59 to 73 μm) and water-stable macroaggregates (from 1.6 to 2.9 mm) due to the LHS-APTES amendment. A substantial increase in SIR from 5 to 9 mg CO2 (kg h)−1 was detected. Better survival of seedlings was observed. The obtained beneficial results indicate that APTES-modified HS can be successfully used as a soil conditioner. The formation of extended siloxane networks was suggested as the main mechanism of the observed improvement in the structure of the amended soils. [ABSTRACT FROM AUTHOR]

Extreme precipitation regime under global change context is estimated to cause heavy rainstorms and longer drought intervals. Temporal variations of soil structure and erosion characteristics during and after heavy rainstorms were less investigated, particularly across a wide soil texture gradient. In this study, 15 soils were selected with clay content ranging in 12.9–38.2%. Soil erosion characteristics and enrichment ratios of organic carbon (ER OC) and nitrogen (ER N) were measured during 3 successive rainfall simulations at slope of 15° and intensity of 120 mm h−1. The water-stable aggregate distribution was measured for soils before and after rainfall and drying. The mean weight diameter (MWD) of water-stable aggregate remained unchanged before (1.476 ± 0.182) and after rainfall and drying (1.406 ± 0.135 mm), but decreased for soils with higher organic carbon contents. Soil erodibility (K factor) averaged in 0.018 ± 0.003, 0.011 ± 0.001 and 0.008 ± 0.001 in 3 successive rainfall events, with 42% and 27% decreases after each event, respectively (P < 0.05); and the decreases were greater for less aggregated soils or coarser textured soils. Stepwise regression showed that the <0.25 mm water-stable aggregate explained most variations of K and its dynamics. The ER OC and ER N were close to 1 and were not correlated with clay content or MWD (P > 0.05). The ER N decreased first and then remained stable, and ER OC was unchanged during successive rainfalls. These results indicated that soil texture or aggregation status affected soil erodibility and its temporal changes in successive rainstorms. Unlabelled Image • Extreme precipitation regime was simulated by successive rainstorms and drying. • Aggregate stability was not affected by rainfalls and drying regardless of texture. • Erodibility decreased in successive rainstorms especially in poorly aggregated soils. • ER OC and ER N were close to 1 regardless of texture and unaffected by sediment mass. [ABSTRACT FROM AUTHOR]

The glomalin-related soil protein (GRSP) is an important fraction of soil organic carbon (SOC) and soil nitrogen (N), and is important for stabilization of SOC and soil aggregates. However, the effects of natural restoration on the concentration and allocation of GRSP differ for different soil aggregate sizes, and how size further affects SOC and soil N restoration, and stabilization of SOC and soil aggregates is not well understood. Here, we present the first characterization of the distribution of GRSP fractions and soil nutrients in soil aggregates following natural restoration by choosing fields of 0, 7, 12, 17, 22, 32 years after cropland abandonment, and a natural grassland as reference. GRSP concentration increased most in microaggregates after 32 years of natural restoration. The processes of rapid accumulation of GRSP (22 to 32 years) occurred simultaneously with the formation of macroaggregates, reduction of microaggregates, and rapid increase of mean weight diameter (22 to 32-years). The soil aggregate stability and contents of GRSP, SOC, labile carbon, total N and phosphorus in each soil aggregate fraction significantly increased in the late stage of natural restoration (22 to 32 years). The most recalcitrant carbon fraction in microaggregates significantly increased between 7 and 32 years (0.887 g kg−1). Our study suggests that abandoning farmland is effective for the restoration of GRSP, soil nutrients and structure and that microaggregates promote the accumulation of recalcitrant carbon and increase the stability of SOC largely through its ability to retain GRSP. • Natural revegetation increased the stability of SOC in aggregates < 2 mm. • Large macroaggregates played an important role in TN, SOC and labile carbon accumulation. • GRSP facilitated the accumulation of SOC and TN, and promoted the increased soil aggregation. • Microaggregates increased recalcitrant carbon and the SOC stability largely by retaining GRSP. [ABSTRACT FROM AUTHOR]