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Journal articles on the topic 'Soil aggregates'
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1
Gijsman, AJ, and RJ Thomas. "Aggregate size distribution and stability of an oxisol under legume-based and pure grass pastures in the eastern Colombian savannas." Soil Research 33, no. 1 (1995): 153. http://dx.doi.org/10.1071/sr9950153.
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This study evaluated soil aggregate size distribution and stability of an Oxisol under improved grass-only or grass-legume pastures, established in previously native savanna. Three grass-legume combinations were included at various stocking rates. In all treatments and soil layers, soils were well aggregated, having more than 90% of their weight in macroaggregates (>250 �m). The addition of legumes to pastures did not affect the soil aggregate size distribution, although aggregates showed somewhat more stability against slaking. An increase in stocking rate negatively affected both average aggregate size and aggregate stability. Aggregates showed little or no dispersion of clay particles in any treatment. A positive correlation was found between wet aggregate stability and hot-water extractable carbohydrate concentration, supporting the hypothesis that these carbohydrates equate with plant-derived or microbial polysaccharides which glue soil aggregates together. It is suggested that determination of hot-water extractable carbohydrates may serve as a useful indicator of small differences in aggregate stability, even when these differences are not evident in the stability measurement itself.
2
Ben-Hur, M., G. Yolcu, H. Uysal, M. Lado, and A. Paz. "Soil structure changes: aggregate size and soil texture effects on hydraulic conductivity under different saline and sodic conditions." Soil Research 47, no. 7 (2009): 688. http://dx.doi.org/10.1071/sr09009.
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Hydraulic conductivity of soil is strongly dependent on soil structure, which can be degraded during wetting and leaching. It was hypothesised that this structural degradation is dependent on initial aggregate size distribution and soil texture. The general aim of this study was to investigate the effects of aggregate sizes and soil textures, and their interactions, on the structural degradation and saturated hydraulic conductivity (Ks) of smectitic soils under different saline and sodic conditions. The studied soils were clay and loamy sand soils with low (~4.5) or high (~10) exchangeable sodium percentages (ESP), and with aggregate sizes in the ranges: (i) <1 mm (small aggregates); or (ii) 2–4 mm (large aggregates). The Ks values of the samples in a column after slow or fast pre-wetting were determined by means of a constant head device. Different wetting rates and leaching under various saline and sodic conditions had no effect on the Ks of the loamy sand; however, the Ks values of this soil with large aggregates were an order of magnitude greater than those of the soil with small aggregates. In contrast, in the clay soil with large aggregates, the Ks values after fast pre-wetting were significantly smaller than those after slow pre-wetting, probably because of aggregate slaking. No significant effects of the wetting rates on Ks were found in clay soil with small aggregates. An increase in the ESP in the clay soil decreased the Ks by a factor of 1.5 for the large aggregates and by an order of magnitude for the small aggregates, mainly as a result of increased clay swelling. Leaching the clay soil with deionised water significantly decreased the Ks values, partly because of clay dispersion. Although significant structural degradation of the clay soil occurred during leaching, the Ks values were smaller in the soils with small aggregates than in those with large aggregates, indicating the importance of the initial aggregate size on Ks even in soils that are prone to structural damage.
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Thai, Saven, Tomáš Davídek, and Lenka Pavlů. "Causes clarification of the soil aggregates stability on mulched soil." Soil and Water Research 17, No. 2 (March 4, 2022): 91–99. http://dx.doi.org/10.17221/151/2021-swr.
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Soil aggregates have great effects on soil properties and soil functions. Mulching (organic inputs) has been known as a factor influencing soil aggregate stability. Our study aimed to reveal the causes of the higher stability of soil aggregates under organic mulches. The primary soil characteristics such as organic carbon (Cox), humus quality (E4/E6), potential wettability index (PWI), and aromaticity index (iAR) were determined. The Cox was measured using rapid dichromate oxidation, and E4/E6 was measured using the UV-Vis spectrophotometry. The PWI and iAR were determined according to the intensity of selected bands in diffuse reflectance infrared spectra. Results showed that mulched plots contained higher Cox content in aggregates in comparison with whole soil. This indicates that the carbon was stabilized within the aggregates and sequestrated into the soil. The iAR was significantly higher after using the organic mulches, the aliphatic components of the organic matter thus contribute more to the aggregates stabilization. The PWI of aggregates was found to be higher after applying these mulches than in soil. Organic mulches are therefore able to reduce the wettability of the aggregates and also to protect the aggregate from dispersion with water.
4
Hanna Radziuk and Marcin Świtoniak. "Time of aggregate destruction as a parameter of soil water stability within an agricultural hummocky moraine landscape in northern Poland." Bulletin of Geography. Physical Geography Series, no. 23 (December 6, 2022): 49–62. http://dx.doi.org/10.12775/bgeo-2022-0009.
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Slaking is a rapid wetting of soil aggregates that affects their stability in the face of the effects of water. The aggregate’s stability has an indirect influence on soil functioning through its minimising of soil erosion. Testing slaking is very simple, does not need additional complicated equipment and could be done for any point. Testing was performed for natural air-dry aggregates (7–10 mm) sampled from the arable layers of four different types of soils within a young hummocky moraine landscape: Eutric Regosol (Protocalcic), Haplic Luvisol (Protocalcic), Albic Luvisol, Mollic Gleysol. The soil tests were performed on a soil-erosive catena located in Chełmno Lake District (Northern Poland) from the tops of hummocks and from the shoulder to bottom part of depressions. The test results demonstrated a significant decrease in aggregate stability from Mollic Gleysol to Eutric Regosols (Protocalcic) – that is, from colluvial soils at depressions to completely eroded hummock-top soils. However, 75% of all aggregates in Eutric Regosols were unstable when time of aggregate destruction was less than 300 sec. Oppositely to Eutric Regosols laying on hummock tops, 70% of aggregates of Mollic Gleysols in depressions were water stable. The mean time for aggregate destruction for each soil from hummock-top to depression was 209 sec. for Eutric Regosol, 375 sec. for Haplic Luvisol, 616 sec. for Albic Luvisol and 772 sec. for Mollic Gleysol. The main soil properties that affected the time of aggregate destruction are clay content (very strong negative correlation; r=–0.72); soil organic carbon content (strong positive correlation; r=0.69), and content of secondary carbonates (strong negative correlation; r=–0.69).
5
Wang, Jingjing, Kunliang Shu, Siyu Wang, Chang Zhang, Yanchun Feng, Ming Gao, Zhonghe Li, and Hongguang Cai. "Soil Enzyme Activities Affect SOC and TN in Aggregate Fractions in Sodic-Alkali Soils, Northeast of China." Agronomy 12, no. 10 (October 18, 2022): 2549. http://dx.doi.org/10.3390/agronomy12102549.
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Soil enzymes strongly affect soil organic carbon (SOC) and nitrogen (TN) storage. However, few studies have focused on their relationships in aggregates, especially in sodic-alkali agricultural fields. In the current study, we hypothesized that the impact of soil enzymes on SOC and TN were different within aggregates for their heterogeneous distribution. Soils collected from the surface (0–20 cm) and subsurface (20–40 cm) layers of sodic-alkali agricultural fields in the northeast of China were separated via the dry sieve method into macro-aggregates (>2000 μm), meso-aggregates (250–2000 μm), and micro-aggregates (<250 μm). SOC, TN, microbial biomass carbon (MBC) and nitrogen (MBN), and C- and N-cycling enzymes, namely amylase (AMY), invertase (INV), β-glucosidase (GLU), catalase (CAT), β-N-acetylglucosaminidase (NAG), and urease (URE) in soil aggregates were tested and analyzed. High content of SOC and TN were observed in macro- and meso-aggregates in both layers, with the largest amount detected in meso-aggregates. The highest values of MBC and MBN were observed in meso-aggregates, followed by micro-aggregates for MBC and macro-aggregates for MBN. Soil enzymes were distributed heterogeneously in soil aggregates, where the activities of AMY, INV, and URE in both layers were in the order of meso-aggregates > macro-aggregates > micro-aggregates. The same trend was followed by NAG of surface soils, while in the subsurface soils, NAG activities increased with the increasing aggregate sizes. NAG activities in both layers decreased with decreasing aggregate sizes. The GLU activity rose with the decreasing aggregate sizes in both layers, contrary to CAT. Enzyme activities affect SOC and TN in soil aggregates, for NAG, INV, GLU, and URE are closely related to SOC and TN across aggregate sizes. The test indices mentioned above in the surface layer were higher than those in the subsurface layer. These results indicate that biophysical processes associated with C- and N-cycling enzymes may be vital to the SOC and TN sequestration within soil aggregates in sodic-alkali agricultural fields.
6
Liu, Yufei, Xiaoxu Fan, Tong Zhang, Xin Sui, and Fuqiang Song. "Effects of atrazine application on soil aggregates, soil organic carbon and glomalin-related soil protein." Plant, Soil and Environment 67, No. 3 (March 1, 2021): 173–81. http://dx.doi.org/10.17221/594/2020-pse.
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Atrazine is still widely used in China. Atrazine residue (1.86–1 100 mg/kg) in the soil has exceeded the allowable limit (1.0 mg/kg), affecting soil structure and soil aggregate composition. To understand the long-term application of atrazine on soil aggregates and the binding agent, four treatments were established in cornfield planted since 1998, including without atrazine applied (AT<sub>0</sub>), atrazine applied (28% atrazine, 1 200–1 350 mL/ha/year) once a year from 2012 to 2018 (AT<sub>6</sub>, 167 mg/kg), from 2008 to 2018 (AT<sub>10</sub>, 127.64 mg/kg) as well as from 2002 to 2018 (AT<sub>16</sub>, 102 mg/kg) with three replications. Along with the increase of atrazine application time, the mass fraction of soil aggregates > 5 mm and 2–5 mm decreased significantly while the mass fraction of soil aggregates 0.5–2 mm and < 0.5 mm increased gradually, and the change of aggregate binding agents contents were the same as that of aggregates. The contents of soil organic carbon (SOC) and glomalin-related soil protein (GRSP) in the aggregates > 5 mm and 2–5 mm were significantly negatively correlated with the years of atrazine application. Our results show that although atrazine residue in the soil does not increase with the increased yearly application, its concentration is still markedly higher than the permitted limit value and seriously affected the content of SOC and GRSP of aggregates > 2 mm, which can lead to a decrease of soil aggregate stability and soil quality.
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Liu, Man, Guilin Han, Zichuan Li, Qian Zhang, and Zhaoliang Song. "Soil organic carbon sequestration in soil aggregates in the karst Critical Zone Observatory, Southwest China." Plant, Soil and Environment 65, No. 5 (May 27, 2019): 253–59. http://dx.doi.org/10.17221/602/2018-pse.
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Soil organic carbon (SOC) sequestration in aggregates under land use change have been widely concerned due to intimate impacts on the sink (or source) of atmospheric carbon dioxide (CO<sub>2</sub>). However, the quantitative relationship between soil aggregation and SOC sequestration under land uses change has been poorly studied. Distribution of aggregates, SOC contents in bulk soils and different size aggregates and their contributions to SOC sequestration were determined under different land uses in the Puding Karst Ecosystem Observation and Research Station, karst Critical Zone Observatory (CZO), Southwest China. Soil aggregation and SOC sequestration increased in the processes of farmland abandonment and recovery. SOC contents in micro-aggregates were larger than those in macro-aggregates in restored land soils, while the opposite results in farmland soils were obtained, probably due to the hindrance of the C-enriched SOC transport from macro-aggregate into micro-aggregate by the disturbance of agricultural activities. SOC contents in macro-aggregates exponentially increased with their proportions along successional land uses. Macro-aggregates accounted for over 80% on the SOC sequestration in restored land soils, while they accounted for 31–60% in farmland soils. These results indicated that macro-aggregates have a great potential for SOC sequestration in karst soils.
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Wang, Yunqiu, Muhammad Shahbaz, Mostafa Zhran, Anlei Chen, Zhenke Zhu, Yehia Galal Mohamed Galal, Tida Ge, and Yuhong Li. "Microbial Resource Limitation in Aggregates in Karst and Non-Karst Soils." Agronomy 11, no. 8 (August 10, 2021): 1591. http://dx.doi.org/10.3390/agronomy11081591.
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Karst is a widespread ecosystem with properties that affect the microbial activity and storage and cycling of soil organic carbon. The mechanisms underlying microbial resource availability in karst, which limit the microbial growth and activity in soil aggregates, remain largely unknown. We assessed the microbial resource limitations using exoenzymatic stoichiometry and key extracellular enzyme activities in bulk soil and aggregates in karst and non-karst forest soils. Soil organic carbon, total nitrogen, and microbial biomass carbon and nitrogen were significantly higher in bulk soil and the aggregate fractions in karst forests. However, the microbial biomass accumulation was higher in finer aggregates than in macroaggregate fractions. This may be attributed to the surface area of finer aggregates that increase the microbial C accumulation. In karst forests, the activity of extracellular enzymes β-d-glucosidase, β-N-acetylglucosaminidase, α-glucosidase, and α-d-1,4-cellobiosidase was two to three times higher in microaggregates (0.053–0.25 mm) and mineral fractions (<0.053 mm) than in macroaggregates. This coincided with the distribution of microbial biomass carbon and phosphorus in finer aggregate fractions. The microorganisms in bulk soil and aggregates in karst forests were largely co-limited by carbon and phosphorus and rarely by nitrogen and only by phosphorus in non-karst soils. The microbial phosphorus limitation in non-karst soils was alleviated in finer soil aggregates, while these fractions reflected slightly higher. microbial C limitations than bulk and other aggregates in karst forests. The patterns of microbial resource limitations in the bulk and aggregate fractions in karst ecosystems reflected the regulation of enzyme activity and soil organic carbon accumulation in finer aggregate fractions but not in other aggregates.
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Urbanek, Emilia, Rainer Horn, and Alwin J. M. Smucker. "Tensile and erosive strength of soil macro-aggregates from soils under different management system." Journal of Hydrology and Hydromechanics 62, no. 4 (December 1, 2014): 324–33. http://dx.doi.org/10.2478/johh-2014-0034.
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Abstract Reduced soil tillage practices are claimed to improve soil health, fertility and productivity through improved soil structure and higher soil organic matter contents. This study compares soil structure stability of soil aggregates under three different tillage practices: conventional, reduced and no tillage. The erosive strength of soil aggregates has been determined using the abrasion technique with the soil aggregate erosion chambers (SAE). During abrasion soil aggregates have been separated into the exterior, transitional and interior regions. The forces needed to remove the material from the aggregate were calculated as erosive strength and compared with the tensile strength of the aggregates derived from crushing tests. The relationship between aggregate strength and other soil properties such as organic carbon and hydrophobic groups’ content has also been identified. The results show that erosive and tensile strength of soil aggregates is very low in topsoil under conventional and reduced tillage comparing with the subsoil horizons. Negative correlation was found between the content of organic carbon, hydrophobic compounds and erosive aggregate strength which suggests that the stabilising effect of soils organic carbon may be lost with drying. The positive relationship between the tensile strength and erosive strength for aggregates of 8-5 mm size suggests that the total strength of these aggregates is controlled by the sum of strength of all concentric layers
10
Eynard, Anna, Thomas E. Schumacher, Michael J. Lindstrom, Douglas D. Malo, and Robert A. Kohl. "Wettability of soil aggregates from cultivated and uncultivated Ustolls and Usterts." Soil Research 42, no. 2 (2004): 163. http://dx.doi.org/10.1071/sr03029.
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Soil organic matter can modify the interaction of clay minerals with water, limiting the rate of water intake of swelling clays and stabilising soil aggregates. Soil structural stability and organic C content usually decrease with cultivation. Faster wetting increases stresses on aggregates and decreases stability. Aggregate wettabilities of prairie soils under 3 different management systems (grassland, no-till, and conventional-till) were compared in the Northern Great Plains of the USA. Six Ustolls and 2 Usterts were selected as replications along the Missouri River. Wettability was measured as water drop penetration time (WDPT) and as rate of water intake under 30 and 300 mm tension. At low tension, aggregates from both cultivated fields and uncultivated grasslands showed similar wettability. Water intake in grass aggregates was attributed to a greater amount of stable pores relative to cultivated aggregates. In cultivated aggregates, slaking created planes of failure that allowed rapid water entry. Differences of wettability between management systems at 300 mm tension (in Ustolls, grasslands had greater wettability than cultivated soils, 0.24 v. 0.17 g water/h.g dry soil) and between soil orders (Usterts had longer WDPT than Ustolls, 2.9 v. 1.7 s) were explained by both clay and organic C contents. Simple measurements of aggregate wettability may be effectively used for soil quality characterisation. Aggregate wettability is a desirable property for agricultural soils when it is related to stable porosity, as may be found in high organic matter soils (e.g. grasslands). Wettability is excessive when fast aggregate wetting results in aggregate destruction as observed in low organic matter cultivated soils.
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Das, Bappa, Debashis Chakraborty, Vinod K. Singh, Pramila Aggarwal, Ravender Singh, and Brahm S. Dwivedi. "Effect of Organic Inputs on Strength and Stability of Soil Aggregates Under Rice-Wheat Rotation." International Agrophysics 28, no. 2 (April 1, 2014): 163–68. http://dx.doi.org/10.2478/intag-2014-0004.
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Abstract The study aims to elucidate the impact of organic inputs on strength and structural stability of aggregates in a sandy loam soil. Tensile strength, friability and water stability of aggregates, and the carbon contents in bulk soil and in large macro (>2 mm), small macro (0.25-2 mm), micro (0.053-0.25 mm) and silt+clay size (<0.053) aggregates were evaluated in soils from a long-term experiment with rice-wheat rotation at Modipuram, India, with different sources and amounts of organic C inputs as partial substitution of N fertilizer. Addition of organic substrates significantly improved soil organic C contents, but the type and source of inputs had different impacts. Tensile strength of aggregates decreased and friability increased through organic inputs, with a maximum effect under green gram residue (rice)-farmyard manure (wheat) substitution. Higher macroaggregates in the crop residue- and farmyard manure-treated soils resulted in a higher aggregate mean weight diameter, which also had higher soil organic C contents. The bulk soil organic C had a strong relation with the mean weight diameter of aggregates, but the soil organic C content in all aggregate fractions was not necessarily effective for aggregate stability. The soil organic C content in large macroaggregates (2-8 mm) had a significant positive effect on aggregate stability, although a reverse effect was observed for aggregates <0.25 mm. Partial substitution of nitrogen by organic substrates improved aggregate properties and the soil organic C content in bulk soil and aggregate fractions, although the relative effect varied with the source and amount of the organic inputs.
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Yang, Caidi, Upendra M. Sainju, Chao Li, Xin Fu, Fazhu Zhao, and Jun Wang. "Long-Term Chemical and Organic Fertilization Differently Affect Soil Aggregates and Associated Carbon and Nitrogen in the Loess Plateau of China." Agronomy 13, no. 6 (May 25, 2023): 1466. http://dx.doi.org/10.3390/agronomy13061466.
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Fertilizer sources may have variable effects on soil aggregation, aggregated-associated C and N, and wheat yield. A 34-year field experiment was performed to evaluate the influences of chemical and organic fertilization on soil aggregates and associated carbon and nitrogen under winter wheat in a Cumulic Haplustoll of the Loess Plateau, China. Treatments included unfertilized control (CK), inorganic N fertilizer (NF), inorganic P fertilizer (PF), inorganic N and P fertilizer (NP), organic manure (M), inorganic N fertilizer plus manure (NM), inorganic P fertilizer plus manure (PM), and inorganic N plus P fertilizers plus manure (NPM). Compared to CK, long-term fertilization significantly increased the proportion of soil macro-aggregates, mean weight diameter (MWD), and geometric mean diameter (GMD), but decreased the proportion of micro-aggregates and fractal dimension, especially fertilizer plus manure. Compared to CK, manure treatments (M, NM, PM, and NPM) had a better improvement on soil organic carbon (SOC), soil total nitrogen (STN), particle organic C, and microbial biomass C in all aggregates than the fertilizer alone. The SOC in different aggregates increased with the increased aggregate size, which was because the larger aggregates formed by the binding of the smaller aggregates and organic matter. PON increased in NM and NPM, and MBN was more sensitive to N fertilizer. The C/N ratio in bulk soil and aggregates decreased with fertilization, especially in fertilizer with manure and in macro-aggregates. The improved soil structure was related to the increased SOC and STN, which was proved by the positive correlations among SOC and STN with macro-aggregates and MWD. A correlation analysis also showed that the contribution rate of SOC and STN in macro-aggregates was positively associated with the macro-aggregate and stability. Therefore, the sequestration of C and N in soil was related to aggregate size and was mainly affected by larger aggregates. The results demonstrated that fertilizer with manure improved the soil structure and fertility better than fertilizer alone, thus increasing crop yield.
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Yang, Chao, Jingjing Li, and Yingjun Zhang. "Soil aggregates indirectly influence litter carbon storage and release through soil pH in the highly alkaline soils of north China." PeerJ 7 (October 29, 2019): e7949. http://dx.doi.org/10.7717/peerj.7949.
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Background Soil aggregate-size classes, structural units of soil, are the important factors regulating soil organic carbon (SOC) turnover. However, the processes of litter C mineralization and storage in different aggregates-size classes are poorly understood, especially in the highly alkaline soils of north China. Here, we ask how four different aggregate sizes influence rates of C release (Cr) and SOC storage (Cs) in response to three types of plant litter added to an un-grazed natural grassland. Methods Highly alkaline soil samples were separated into four dry aggregate classes of different sizes (2–4, 1–2, 0.25–1, and <0.25 mm). Three types of dry dead plant litter (leaf, stem, and all standing dead aboveground litter) of Leymus chinensis were added to each of the four aggregate class samples. Litter mass loss rate, Cr, and Cs were measured periodically during the 56-day incubation. Results The results showed that the mass loss in 1–2 mm aggregates was significantly greater than that in other size classes of soil aggregates on both day 28 and day 56. Macro-aggregates (1–2 mm) had the highest Cr of all treatments, whereas 0.25–1 mm aggregates had the lowest. In addition, a significant negative relationship was found between Cs/Cr and soil pH. After incubation for 28 and 56 days, the Cs was also highest in the 1–2 mm aggregates, which implied that the macro-aggregates had not only a higher CO2 release capacity, but also a greater litter C storage capacity than the micro-aggregates in the highly alkaline soils of north China.
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Doetterl, S., J. T. Cornelis, J. Six, S. Bodé, S. Opfergelt, P. Boeckx, and K. Van Oost. "Soil redistribution and weathering controlling the fate of geochemical and physical carbon stabilization mechanisms in soils of an eroding landscape." Biogeosciences 12, no. 5 (March 4, 2015): 1357–71. http://dx.doi.org/10.5194/bg-12-1357-2015.
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Abstract. The role of eroding landscapes in organic carbon stabilization operating as C sinks or sources has been frequently discussed, but the underlying mechanisms are not fully understood. Our analysis aims to clarify the effects of soil redistribution on physical and biogeochemical soil organic carbon (SOC) stabilization mechanisms along a hillslope transect. The observed mineralogical differences seem partly responsible for the effectiveness of geochemical and physical SOC stabilization mechanisms as the mineral environment along the transect is highly variable and dynamic. The abundance of primary and secondary minerals and the weathering status of the investigated soils differ drastically along this transect. Extractable iron and aluminum components are generally abundant in aggregates, but show no strong correlation to SOC, indicating their importance for aggregate stability but not for SOC retention. We further show that pyrophosphate extractable soil components, especially manganese, play a role in stabilizing SOC within non-aggregated mineral fractions. The abundance of microbial residues and measured 14C ages for aggregated and non-aggregated SOC fractions demonstrate the importance of the combined effect of geochemical and physical protection to stabilize SOC after burial at the depositional site. Mineral alteration and the breakdown of aggregates limit the protection of C by minerals and within aggregates temporally. The 14C ages of buried soil indicate that C in aggregated fractions seems to be preserved more efficiently while C in non-aggregated fractions is released, allowing a re-sequestration of younger C with this fraction. Old 14C ages and at the same time high contents of microbial residues in aggregates suggest either that microorganisms feed on old carbon to build up microbial biomass or that these environments consisting of considerable amounts of old C are proper habitats for microorganisms and preserve their residues. Due to continuous soil weathering and, hence, weakening of protection mechanisms, a potential C sink through soil burial is finally temporally limited.
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Doetterl, S., J. T. Cornelis, J. Six, S. Bodé, S. Opfergelt, P. Boeckx, and K. Van Oost. "Soil redistribution and weathering controlling the fate of geochemical and physical carbon stabilization mechanisms in soils of an eroding landscape." Biogeosciences Discussions 11, no. 11 (November 26, 2014): 16227–68. http://dx.doi.org/10.5194/bgd-11-16227-2014.
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Abstract. It has been suggested that eroding landscapes can form C sinks or sources, but the underlying mechanisms are not fully understood. Our analysis aims to clarify the effects of soil redistribution on physical and biogeochemical soil organic carbon (SOC) stabilization mechanisms along a hillslope transect. The observed mineralogical differences seem partly responsible for the effectiveness of geochemical and physical SOC stabilization mechanisms as the mineral environment along the transect is highly variable and dynamic. The abundance of primary and secondary minerals and the weathering status of the investigated soils differ drastically along this transect. Extractable iron and aluminum components are largely abundant in aggregates, but show no strong correlation to SOC, indicating their importance for aggregate stability but not for SOC retention. We further show that pyrophosphate extractable soil components, especially manganese, play a role in stabilizing SOC within non-aggregated mineral fractions. The abundance of microbial residues and measured 14C ages for aggregated and non-aggregated SOC fractions demonstrate the importance of the combined effect of geochemical and physical protection to stabilize SOC after burial at the depositional site. Mineral alteration and the breakdown of aggregates limit the protection of C by minerals and within aggregates temporally. The 14C ages of buried soil indicate that C in aggregated fractions seem to be preserved more efficiently while C in non-aggregated fractions is released, allowing a re-sequestration of younger C with this fraction. Old 14C ages and at the same time high contents of microbial residues in aggregates suggest that microorganisms either feed on old carbon to build up microbial biomass, or that these environments consisting of considerable amounts of old C are proper habitats for microorganisms and preserve their residues. Due to continuous soil weathering and, hence, weakening of protection mechanisms, a potential C sink through soil burial is finally temporally limited.
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Gao, Hailong, Liping Qiu, Yanjiang Zhang, Liaohong Wang, Xingchang Zhang, and Jimin Cheng. "Distribution of organic carbon and nitrogen in soil aggregates of aspen (Populus simonii Carr.) woodlands in the semi-arid Loess Plateau of China." Soil Research 51, no. 5 (2013): 406. http://dx.doi.org/10.1071/sr12250.
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The distribution and turnover of organic carbon (OC) and nitrogen (N) associated with aggregates in soils is critical for understanding the behaviour of C and N in soils. We collected soil samples from aspen (Populus simonii Carr.) woodland in the semi-arid Loess Plateau of China to investigate the distribution of aggregate-associated OC and N. The distribution of aggregates and aggregate-associated OC and N were measured, and OC and N stocks in each aggregate fraction were calculated. Across the sites and soil depths, microaggregates and the silt + clay fraction dominated the distribution of soil aggregates, which varied with site. Organic C and N accumulated mainly in the macro- and micro-aggregate fractions in loamy soils but in the silt + clay fractions in sandy soils. The OC and N stocks in the bulk soil of aspen woodland were determined by the OC and N stocks associated with silt + clay fraction. The results of this study indicate that soil texture may play an important role in assessing the distributions of soil OC and N in both bulk soils and aggregate size fractions in aspen woodland, especially in semi-arid regions. Furthermore, the establishment of aspen woodland would result in greater accumulation of OC and N in loam soils than in sandy soils.
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Schlotter, D., and H. Schack-Kirchner. "Intra-aggregate CO<sub>2</sub> enrichment: a modelling approach for aerobic soils." Biogeosciences Discussions 9, no. 10 (October 24, 2012): 14795–822. http://dx.doi.org/10.5194/bgd-9-14795-2012.
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Abstract. CO2 concentration gradients inside soil aggregates, caused by the respiration of soil microorganisms and fungal hyphae, might lead to variations in the soil solution chemistry on a mm-scale, and to an underestimation of the CO2 storage. But, up to now, there seems to be no feasible method for measuring CO2 inside natural aggregates with sufficient spatial resolution. We combined a one-dimensional model for gas diffusion in the inter-aggregate pore-space with a cylinder diffusion model, simulating the consumption/production and diffusion of O2 and CO2 inside soil aggregates with air- and water-filled pores. Our model predicts that for aerobic respiration (respiratory quotient = 1) the intra-aggregate increase in the CO2 partial pressure can never be higher than 0.9 kPa for siliceous, and 0.08 kPa for calcaric aggregates, independent of the level of water-saturation. This suggests that only for siliceous aggregates CO2 produced by aerobic respiration might cause a high small-scale spatial variability in the soil solution chemistry. In calcaric aggregates, however, the contribution of carbonate species to the CO2 transport should lead to secondary carbonates on the aggregate surfaces. As regards the total CO2 storage in aerobic soils, both siliceous and calcaric, the effect of intra-aggregate CO2 gradients seems to be negligible. To assess the effect of anaerobic respiration on the intra-aggregate CO2 gradients, the development of a device for measuring CO2 on a mm-scale in soils is indispensable.
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Schlotter, D., and H. Schack-Kirchner. "Intra-aggregate CO<sub>2</sub> enrichment: a modelling approach for aerobic soils." Biogeosciences 10, no. 2 (February 25, 2013): 1209–18. http://dx.doi.org/10.5194/bg-10-1209-2013.
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Abstract. CO2 concentration gradients inside soil aggregates, caused by the respiration of soil microorganisms and fungal hyphae, might lead to variations in the soil solution chemistry on a mm-scale, and to an underestimation of the CO2 storage. But, up to now, there seems to be no feasible method for measuring CO2 inside natural aggregates with sufficient spatial resolution. We combined a one-dimensional model for gas diffusion in the inter-aggregate pore space with a cylinder diffusion model, simulating the consumption/production and diffusion of O2 and CO2 inside soil aggregates with air- and water-filled pores. Our model predicts that for aerobic respiration (respiratory quotient = 1) the intra-aggregate increase in the CO2 partial pressure can never be higher than 0.9 kPa for siliceous, and 0.1 kPa for calcaric aggregates, independent of the level of water-saturation. This suggests that only for siliceous aggregates CO2 produced by aerobic respiration might cause a high small-scale spatial variability in the soil solution chemistry. In calcaric aggregates, however, the contribution of carbonate species to the CO2 transport should lead to secondary carbonates on the aggregate surfaces. As regards the total CO2 storage in aerobic soils, both siliceous and calcaric, the effect of intra-aggregate CO2 gradients seems to be negligible. To assess the effect of anaerobic respiration on the intra-aggregate CO2 gradients, the development of a device for measuring CO2 on a mm-scale in soils is indispensable.
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Xiao, L., Y. Hu, P. Greenwood, and N. J. Kuhn. "The use of a raindrop aggregate destruction device to evaluate sediment and soil organic carbon transport." Geographica Helvetica 70, no. 2 (June 15, 2015): 167–74. http://dx.doi.org/10.5194/gh-70-167-2015.
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Abstract. Raindrop impact and subsequent aggregate breakdown can potentially change the movement behaviour of soil fractions and thus alter their transport distances when compared against non-impacted aggregates. In a given water layer, the transport distances of eroded soil fractions, and thus that of the associated substances across landscapes, such as soil organic carbon (SOC) and phosphorous, are determined by the settling velocities of the eroded soil fractions. However, using mineral size distribution to represent the settling velocities of soil fractions, as often applied in current erosion models, would ignore the potential influence of aggregation on the settling behaviour of soil fractions. The destructive effects of raindrops impacting onto aggregates are also often neglected in current soil erosion models. Therefore, the objective of this study is to develop a proxy method to effectively simulate aggregate breakdown under raindrop impact, and further identify the settling velocity of eroded sediment and the associated SOC. Two agricultural soils with different sandy and silty loam textures were subjected to rainfall using a raindrop aggregate destruction device (RADD). The aggregates sustained after raindrop impact were fractionated by a settling tube into six different classes according to their respective settling velocities. The same mass amount of bulk soil of each soil type was also dispersed and sieved into the same six classes, to form a comparison in size distribution. The SOC content was measured for each settled and dispersed class. Our results show the following: (1) for an aggregated soil, applying dispersed mineral grain size distribution, rather than its actual aggregate distribution, to soil erosion models would lead to a biased estimation on the redistribution of eroded sediment and SOC; (2) the RADD designed in this study effectively captures the effects of raindrop impact on aggregate destruction and is thus able to simulate the quasi-natural sediment spatial redistribution; (3) further RADD tests with more soils under standard rainfall combined with local rainfalls are required to optimize the method.
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Feng, Ming, Jian Xiang, Xiaofang Ji, and Jiang Jiang. "Larger Soil Water-Stable Aggregate May Exert a Negative Effect on Nutrient Availability: Results from Red Soil (Ultisol), in South China." Forests 14, no. 5 (May 9, 2023): 975. http://dx.doi.org/10.3390/f14050975.
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Soil aggregates are the basic units of soil, which regulate soil carbon cycling and nutrient availability through the protective effect of soil aggregates on soil organic matter. It is still uncertain whether larger aggregates are more conducive to soil nutrient availability in red soil. This study explored the regulation of soil aggregates on soil nutrient availability by studying the distribution of soil aggregates, nutrient concentrations, nutrient availability and organo-mineral bonds in soil aggregates in a low-productivity Chinese fir forest, in south China. We sampled the 0–10 cm soil with nine repeated plots and analyzed the soil aggregate structure, total nutrients, available nutrients and organo-mineral bonds of soil aggregates. The results showed that the contribution of >2 mm soil aggregates to soil nutrients was highest, because the mass of >2 mm soil aggregates accounted for about 50% of the total mass of aggregates and was much higher than that of other aggregates. The availability (available nutrient/total nutrient) of nitrogen, phosphorus and potassium increased with decreases in soil aggregate size, indicating that soil aggregates with a larger particle size were more averse to nutrient availability. Strong organo-mineral bonds accounted for more than 80% of the total organo-mineral bonds in the soil aggregates of each size, and the proportion of weak organo-mineral bonds in the soil aggregate increased with decreases in the soil aggregate size. There was a significant negative correlation between the size of soil aggregates and the proportion of weak organo-mineral bonds in soil aggregates. The availability of carbon, nitrogen, phosphorus and potassium in soil aggregates was positively correlated with the proportion of weak organo-mineral bonds. These results suggest that Fe/Al oxides may play an important role in regulating nutrient availability, especially in red soil. A higher proportion of strong organo-mineral bonds in larger soil aggregates may exert a stronger negative effect on the accessibility of microorganisms to organic matter and result in a lower nutrient availability. In conclusion, this study shows that larger-sized soil macroaggregates may exert a negative effect on nutrient availability, owing to a higher proportion of strong binding bonds, which can better prevent microorganisms from mineralizing organic matter into effective nutrients in red soil.
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Cavael, Ulrike, Philipp Tost, Katharina Diehl, Frederick Büks, and Peter Lentzsch. "Correlations of Soil Fungi, Soil Structure and Tree Vigour on an Apple Orchard with Replant Soil." Soil Systems 4, no. 4 (December 3, 2020): 70. http://dx.doi.org/10.3390/soilsystems4040070.
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The soil-borne apple replant disease (ARD) is caused by biotic agents and affected by abiotic properties. There is evidence for the interrelation of the soil fungal population and soil aggregate structure. The aim of this study conducted between March and October 2020 on an orchard in north-east Germany was to detect the correlations of soil fungal density, soil structure and tree vigour under replant conditions in a series of time intervals. By using the replant system as the subject matter of investigation, we found that replanting had an impact on the increase of soil fungal DNA, which correlated with a mass decrease of large macro-aggregates and an increase of small macro- and large micro-aggregates in the late summer. Increased proportions of water-stable aggregates (WS) with binding forces ≤ 50 J mL−1, decreased proportions of WS > 100 J mL−1 and a decrease of the mean weight diameter of aggregates (MWD) emphasised a reduction of aggregate stability in replant soils. Correlation analyses highlighted interactions between replant-sensitive soil fungi (Alternaria-group), the loss of soil structure and suppressed tree vigour, which become obvious only at specific time intervals.
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Yi, Chenxu, Jing Zhu, Liuhuan Chen, Xiangtang Huang, Rong Wu, Hongling Zhang, Xuanyu Dai, and Jianhong Liang. "Speciation of Iron and Aluminum in Relation to Phosphorus Sorption and Supply Characteristics of Soil Aggregates in Subtropical Forests." Forests 14, no. 9 (September 4, 2023): 1804. http://dx.doi.org/10.3390/f14091804.
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Phosphorus (P) is one of the main limiting nutrients in subtropical forest soils. Both soil type and aggregate structure affect the P sorption capacity of soil; thus, determining soil P supply and leaching characteristics. However, the mechanism of their interactions on soil P sorption and leaching at an aggregate level remains unclear. We classified soil aggregates from red soils and limestone soils in a subtropical forest via wet-sieving and carried out P isothermal sorption experiments. The P sorption maximum (Qm), P sorption strength (KL, KF), P sorption index (PSI) and maximum buffer capacity (MBC) were obtained by fitting to Langmuir and Freundlich isotherm equations. Moreover, different P fractions were determined to estimate the degree of P sorption saturation (DPS) of aggregates. The results showed that the Qm of the two soils were similar, but the sorption strength (KL, KF) and MBC of the limestone soil were higher than those of the red soil. Higher contents of free iron (Fe) oxide and amorphous aluminum (Al) oxide in the limestone soil may enhance the P sorption capacity and, thus, reduce P availability, resulting in a higher total P retention capacity than in the red soil. A higher content of complex Fe in red soil may reduce P sorption and, therefore, play a role in maintaining the supply capacity of soil-available P. The 0.25–0.5 mm aggregates of the two soils had the largest MBC among all aggregate sizes, and their P sorption and buffering capacity were stronger than other aggregates. The DPS of different aggregate sizes were all low, indicating that the soils of subtropical forests were in a state of P deficiency; thus, the risk of P leaching was low. The <0.1 mm aggregate in red soil had relatively high DPS and significantly lower PSI than the other aggregate sizes, indicating that it was more prone to P leaching. The results provide further insight into forest management to improve P availability and reduce P leaching in subtropical forest soils.
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Li, Ying, Zhanming Ma, Yutao Liu, Zilong Cui, Qiuyu Mo, Can Zhang, Haiyan Sheng, Wen Wang, and Yongkun Zhang. "Variation in Soil Aggregate Stability Due to Land Use Changes from Alpine Grassland in a High-Altitude Watershed." Land 12, no. 2 (February 1, 2023): 393. http://dx.doi.org/10.3390/land12020393.
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Land use change affects soil aggregate composition and stability, which impacts soil structure and health. To reveal how land use change impacted soil aggregates of alpine grassland in a high-altitude watershed, soil samples from 161 sites including alpine grassland, cropland and abandoned land were selected to measure and analyze the distribution of aggregate fractions (macro-aggregates, micro-aggregates, silt+clay), soil aggregate stability (mean weight diameter, geometric mean diameter, fractal dimension, etc.) and related soil properties (soil organic carbon content, soil particle composition, etc.) in the Huangshui River watershed of the Qinghai–Tibet Plateau. The results showed: (1) As alpine grasslands were converted to croplands and croplands to abandoned lands, the proportion of macro-aggregates and the aggregate stability index showed a trend of first decreasing and then increasing (p < 0.05), indicating that tillage and abandonment have significant influences on soil aggregate structure. (2) Compared with temperate grassland, alpine grassland had richer soil organic carbon, and a higher ratio of macro-aggregates and aggregate stability. (3) Soil organic carbon and sand content had distinct influences on the fractions and stability of aggregates during land use change. These results suggested that cultivation can substantially reduce the soil aggregate stability in alpine grassland, whereas abandonment can effectively improve soil aggregate structure.
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Tang, F. K., M. Cui, Q. Lu, Y. G. Liu, H. Y. Guo, and J. X. Zhou. "Effects of vegetation restoration on the aggregate stability and distribution of aggregate-associated organic carbon in a typical karst gorge region." Solid Earth 7, no. 1 (January 27, 2016): 141–51. http://dx.doi.org/10.5194/se-7-141-2016.
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Abstract. Land use changes have a major impact on soil structure and soil nutrients. The influences of vegetation restoration on aggregate stability and soil carbon storage have been studied extensively, but the distribution of aggregate-associated carbon is not yet understood. The objective of this work was to study the influences of vegetation restoration on aggregate stability and distribution of soil organic carbon (SOC) associated with water-stable aggregates (WSAs) in a karst gorge region. The experiment was carried out in 2012 and included four land use types: bare land (BL), grassland (GL), shrubland (SL), and woodland (WL). Soil samples were collected from the 0–20, 20–40, and 40–60 cm depths, and aggregates were separated by a wet-sieving method. Aggregate stability and aggregated-associated SOC were determined, and the relationships between water-stable aggregation with SOC were examined. The results showed that total SOC and SOC associated with WSAs of various sizes were the highest at a soil depth of 0–20 cm. In addition, the SOC contents of the WSAs increased as the soil aggregate sizes decreased. The SOC contents of the WSAs < 0.25 mm were highest except in the bare land, and the SOC contents of the aggregates < 0.25 mm comprised the majority of the total aggregate SOC contents. The aggregates were dominated by particles with sizes > 5 mm under dry-sieving treatment, while aggregates were predominantly comprised of WSAs < 0.25 mm under wet-sieving treatment. At a soil depth of 0–60 cm, the mean weight diameter (MWD), geometrical mean diameter (GMD), and fractal dimensions (D) of the dry aggregates and water-stable aggregates in the different types of land were ranked, in descending order, as WL > GL > SL > BL. The contents of WSAs > 0.25 mm, MWD, and GMD increased significantly, in that order, and the percentage of aggregate destruction (PAD) and fractal dimensions decreased significantly as the soil aggregate stability improved. SOC contents increased after vegetation restoration, and the average SOC content of WL was 2.35, 1.37, and 1.26 times greater than that in the BL, GL, and SL, respectively. We conclude that woodland and grassland facilitated WSA stability and SOC protection; thus, promoting the natural restoration of vegetation by reducing artificial disturbances could effectively restore the ecology and prevent soil erosion in karst regions.
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Riveras-Muñoz, Nicolás, Steffen Seitz, Kristina Witzgall, Victoria Rodríguez, Peter Kühn, Carsten W. Mueller, Rómulo Oses, Oscar Seguel, Dirk Wagner, and Thomas Scholten. "Biocrust-linked changes in soil aggregate stability along a climatic gradient in the Chilean Coastal Range." SOIL 8, no. 2 (December 7, 2022): 717–31. http://dx.doi.org/10.5194/soil-8-717-2022.
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Abstract. Biological soil crusts (biocrusts) composed of cyanobacteria, bacteria, algae, fungi, lichens, and bryophytes stabilize the soil surface. This effect has mainly been studied in arid climates, where biocrusts constitute the main biological agent to stabilize and connect soil aggregates. Besides, biocrusts are an integral part of the soil surface under Mediterranean and humid climate conditions, mainly covering open spaces in forests and on denuded lands. They often develop after vegetation disturbances, when their ability to compete with vascular plants increases, acting as pioneer communities and affecting the stability of soil aggregates. To better understand how biocrusts mediate changes in soil aggregate stability under different climate conditions, we analyzed soil aggregate samples collected under biocrust communities from four national parks in Chile along a large climatic gradient ranging from (north to south) arid (Pan de Azúcar, PA), semi-arid (Santa Gracia, SG), Mediterranean (La Campana, LC) to humid (Nahuelbuta, NA). Biocrust communities showed a stabilizing effect on the soil aggregates in dry fractions for the three northern sites and the wet aggregates for the southernmost site. Here, permanent vascular plants and higher contents of organic carbon and nitrogen in the soil control aggregate stability more than biocrusts, which are in intense competition with higher plant communities. Moreover, we found an increase in stability for aggregate size classes < 2.0 and 9.5–30.0 mm. The geometric mean diameter of the soil aggregates showed a clear effect due to the climatic gradient, indicating that the aggregate stability presents a log-normal instead of a normal distribution, with a trend of low change between aggregate size fractions. Based on our results, we assume that biocrusts affect the soil structure in all climates. Their role in aggregate stability is masked under humid conditions by higher vegetation and organic matter contents in the topsoil.
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Haskevych, Oksana. "Aggrenic changes of the structural state of greyic luvic phaeozems of the Holohory-Kremenets range." Visnyk of the Lviv University. Series Geography, no. 51 (December 27, 2017): 111–19. http://dx.doi.org/10.30970/vgg.2017.51.8743.
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The article describes the structural and aggregate state of Greyic Luvic Phaeozems of the Holohory-Kremenets Range. Comparison of structural and water resistance indicators for soils of different nature of use has been performed. In particular, the soils under forest vegetation, arable land and grassland were taken into account. All soils differ in the degree of anthropogenic load, primarily mechanical pressure, which is reflected in the change in the physical state of soils. According to the results of the analysis of the structural and aggregate soil composition, the indicators of water-resistance of the macrostructure of the arable layer of soils have been determined. Soils under forest vegetation and grassland have been established to be characterized by a close distribution of structural aggregates by fractions, in particular, the predominance of lumpy elements (62.27–76.80 % of air-dry aggregates). In the arable horizon of cultivated soils, the share of aggregates with the size of 10–0.25 mm (53.96 %) is increasing. Water-resistant aggregates of soils under forest and grassland are usually 10–0.25 mm in size (59.9–68.14 %), whereas in arable soils they make less than 0.25 mm. At the same time, arable Greyic Luvic Phaeozems are characterized by a higher coefficient of structurality in the arable and subsurface layer, while the water resistance index of the soil structure is lower compared with analogues under forest and herbaceous vegetation. Key words: Greyic Luvic Phaeozems structural and aggregate soil composition, macrostructure, coefficient of structurality, water-resistance index, soil aggregates.
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Wang, Enheng, Richard M. Cruse, Xiangwei Chen, and Aaron Daigh. "Effects of moisture condition and freeze/thaw cycles on surface soil aggregate size distribution and stability." Canadian Journal of Soil Science 92, no. 3 (March 2012): 529–36. http://dx.doi.org/10.4141/cjss2010-044.
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Wang, E., Cruse, R. M., Chen, X. and Daigh, A. 2012. Effects of moisture condition and freeze/thaw cycles on surface soil aggregate size distribution and stability. Can. J. Soil Sci. 92: 529–536. Freeze/thaw cycles can affect soil aggregate stability, which in turn impacts wind and water erosion. The objectives of this laboratory study were: (1) to determine the effect of variable freeze/thaw cycles and soil water conditions on aggregate size distribution and stability; and (2) to evaluate differences in aggregate size distribution and stability between disturbed soil and undisturbed soil cores as affected by freeze/thaw cycles and soil water conditions. Surface soil was collected before freezing in late fall of 2009. Aggregates isolated from disturbed soil or intact soil cores were subjected to a factorial combination of 3 gravimetric water content treatments: 0.15 m3 m−3, 0.23 m3 m−3 or 0.30 m3 m−3, and 3 freeze/thaw treatments: 0, 3, or 9 cycles. A freeze/thaw cycle involved soil freezing at –10∘C for 24 h, followed by thawing at 5∘C for 24 h. Most aggregate size classes were affected significantly (P<0.05) by freeze/thaw cycles except for wet-sieved aggregates >5 mm. Dry-sieved aggregates were relatively more sensitive to the freeze/thaw treatment than wet-sieved aggregates. The mean weight diameter (MWD) of dry-sieved aggregates was significantly (P<0.05) greater at 0.30 m3 m−3 than 0.15 m3 m−3 water content, but the opposite trend was observed for MWD of wet aggregates and aggregate stability. There was a significant (P<0.05) response of the MWD in dry-sieved aggregates to the interactive freeze/thaw×water content effect that differed for aggregates obtained from disturbed soil and those in the undisturbed soil core, but not for the MWD of wet-sieved aggregates and aggregate stability.
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Hoosbeek, M. R., J. M. Vos, E. J. Bakker, and G. E. Scarascia-Mugnozza. "Effects of free atmospheric CO<sub>2</sub> enrichment (FACE), N fertilization and poplar genotype on the physical protection of carbon in the mineral soil of a polar plantation after five years." Biogeosciences 3, no. 4 (November 3, 2006): 479–87. http://dx.doi.org/10.5194/bg-3-479-2006.
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Abstract. Free air CO2 enrichment (FACE) experiments in aggrading forests and plantations have demonstrated significant increases in net primary production (NPP) and C storage in forest vegetation. The extra C uptake may also be stored in forest floor litter and in forest soil. After five years of FACE treatment at the EuroFACE short rotation poplar plantation, the increase of total soil C% was larger under elevated than under ambient CO2. However, the fate of this additional C allocated belowground remains unclear. The stability of soil organic matter is controlled by the chemical structure of the organic matter and the formation of micro-aggregates (within macro-aggregates) in which organic matter is stabilized and protected. FACE and N-fertilization treatment did not affect the micro- and macro-aggregate weight, C or N fractions obtained by wet sieving. However, Populus euramericana increased the small macro-aggregate and free micro-aggregate weight and C fractions. The obtained macro-aggregates were broken up in order to isolate recently formed micro-aggregates within macro-aggregates (iM-micro-aggregates). FACE increased the iM-micro-aggregate weight and C fractions, although not significantly. This study reveals that FACE did not affect the formation of aggregates. We did, however, observe a trend of increased stabilization and protection of soil C in micro-aggregates formed within macro-aggregates under FACE. Moreover, the largest effect on aggregate formation was due to differences in species, i.e. poplar genotype. P. euramericana increased the formation of free micro-aggregates which means that more newly incorporated soil C was stabilized and protected. The choice of species in a plantation, or the effect of global change on species diversity, may therefore affect the stabilization and protection of C in soils.
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Kausch, M. F., and C. E. Pallud. "Modeling the impact of soil aggregate size on selenium immobilization." Biogeosciences Discussions 9, no. 9 (September 6, 2012): 12047–86. http://dx.doi.org/10.5194/bgd-9-12047-2012.
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Abstract. Soil aggregates are mm- to cm-sized microporous structures separated by macropores. Whereas fast advective transport prevails in macropores, advection is inhibited by the low permeability of intra-aggregate micropores. This can lead to mass transfer limitations and the formation of aggregate-scale concentration gradients affecting the distribution and transport of redox sensitive elements. Selenium (Se) mobilized through irrigation of seleniferous soils has emerged as a major aquatic contaminant. In the absence of oxygen, the bioavailable oxyanions selenate, Se(VI), and selenite, Se(IV), can be microbially reduced to solid, elemental Se, Se(0), and anoxic microzones within soil aggregates are thought to promote this process in otherwise well aerated soils. To evaluate the impact of soil aggregate size on selenium retention, we developed a dynamic 2-D reactive transport model of selenium cycling in a single idealized aggregate surrounded by a macropore. The model was developed based on flow-through-reactor experiments involving artificial soil aggregates (diameter: 2.5 cm) made of sand and containing Enterobacter cloacae SLD1a-1 that reduces Se(VI) via Se(IV) to Se(0). Aggregates were surrounded by a constant flow providing Se(VI) and pyruvate under oxic or anoxic conditions. In the model, reactions were implemented with double-Monod rate equations coupled to the transport of pyruvate, O2, and Se-species. The spatial and temporal dynamics of the model were validated with data from experiments and predictive simulations were performed covering aggregate sizes between 1 and 2.5 cm diameter. Simulations predict that selenium retention scales with aggregate size. Depending on O2, Se(VI), and pyruvate concentrations, selenium retention was 4–23 times higher in 2.5-cm-aggregates compared to 1-cm-aggregates. Under oxic conditions, aggregate size and pyruvate-concentrations were found to have a positive synergistic effect on selenium retention. Promoting soil aggregation on seleniferous agricultural soils, through organic matter amendments and conservation tillage, may thus help decrease the impacts of selenium contaminated drainage water on downstream aquatic ecosystems.
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Kausch, M. F., and C. E. Pallud. "Modeling the impact of soil aggregate size on selenium immobilization." Biogeosciences 10, no. 3 (March 1, 2013): 1323–36. http://dx.doi.org/10.5194/bg-10-1323-2013.
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Abstract. Soil aggregates are mm- to cm-sized microporous structures separated by macropores. Whereas fast advective transport prevails in macropores, advection is inhibited by the low permeability of intra-aggregate micropores. This can lead to mass transfer limitations and the formation of aggregate scale concentration gradients affecting the distribution and transport of redox sensitive elements. Selenium (Se) mobilized through irrigation of seleniferous soils has emerged as a major aquatic contaminant. In the absence of oxygen, the bioavailable oxyanions selenate, Se(VI), and selenite, Se(IV), can be microbially reduced to solid, elemental Se, Se(0), and anoxic microzones within soil aggregates are thought to promote this process in otherwise well-aerated soils. To evaluate the impact of soil aggregate size on selenium retention, we developed a dynamic 2-D reactive transport model of selenium cycling in a single idealized aggregate surrounded by a macropore. The model was developed based on flow-through-reactor experiments involving artificial soil aggregates (diameter: 2.5 cm) made of sand and containing Enterobacter cloacae SLD1a-1 that reduces Se(VI) via Se(IV) to Se(0). Aggregates were surrounded by a constant flow providing Se(VI) and pyruvate under oxic or anoxic conditions. In the model, reactions were implemented with double-Monod rate equations coupled to the transport of pyruvate, O2, and Se species. The spatial and temporal dynamics of the model were validated with data from experiments, and predictive simulations were performed covering aggregate sizes 1–2.5 cm in diameter. Simulations predict that selenium retention scales with aggregate size. Depending on O2, Se(VI), and pyruvate concentrations, selenium retention was 4–23 times higher in 2.5 cm aggregates compared to 1 cm aggregates. Under oxic conditions, aggregate size and pyruvate concentrations were found to have a positive synergistic effect on selenium retention. Promoting soil aggregation on seleniferous agricultural soils, through organic matter amendments and conservation tillage, may thus help decrease the impacts of selenium contaminated drainage water on downstream aquatic ecosystems.
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Ushkova, D. A., U. A. Konkina, I. V. Gorepekin, D. I. Potapov, E. V. Shein, and G. N. Fedotov. "Stability of Arable Soil Aggregates: Experimental Determination and Normative Characteristics." Почвоведение, no. 2 (February 1, 2023): 203–10. http://dx.doi.org/10.31857/s0032180x22600834.
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Soil stability in modern soil physics is divided into two directions: water stability and resistance to mechanical influences (compression, wedging). Both soil properties in water-saturated soil are based on the rupture of intra-aggregate interparticle bonds, however, no standard physically justified values have been proposed to characterize the stability of aggregates. The purpose of the article is to substantiate the physical concept of stability of soil aggregates and to propose a single methodological method for quantifying stability as a normative soil characteristic. A high-performance method has been developed based on the dissection of linearly arranged water-saturated aggregates using blades under controlled load. The main stages of the technique are vacuuming of aggregates to eliminate the uncontrolled influence of trapped air, saturation of aggregates in vacuum with water and subsequent determination of the aggregates stability to penetration of blades. Experimental stability values (mN/aggregate) were obtained for 17 soils, which made it possible to form normative ranges for mountainous arable heavy loamy soils: sod-podzolic – 17–19, gray forest –27–29, chernozems – 34–37 mN/agr and a number of other soils, which makes it possible to apply the obtained value as a soil characteristic of the stability of aggregates. The possibility of using the stability values as a methodological basis for monitoring soil stability and degradation, quantitative directions for assessing the state of physical characteristics of soil aggregates (first their main parameter, their stability) is discussed. Taking into account the highly correlative dependence of the proposed stability characteristic on the water stability values obtained by the Savvinov method (85%) and the high performance of the stability determination method (the proposed method is about 20 times more productive than the Savvinov method), the possibilities of using the method and the obtained values of the stability of aggregates as a general physical characteristic and a separate well for quantifying water stability are discussed.
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Li, Jingjing, Chao Yang, Xiaoli Liu, Hanzhong Ji, and Xinqing Shao. "Soil aggregate size influences the impact of inorganic nitrogen deposition on soil nitrification in an alpine meadow of the Qinghai–Tibet Plateau." PeerJ 8 (January 7, 2020): e8230. http://dx.doi.org/10.7717/peerj.8230.
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Background Ammonium (NH4+) and nitrate (NO3−) are two inorganic forms of nitrogen (N) that are deposited from the atmosphere into soil systems. As the substrate and product of soil nitrification, these two forms of inorganic nitrogen will affect or be affected by the soil net nitrification rate (Nr). Our knowledge regarding soil nitrification is mainly derived from studies with bulk soil. However, soil is composed of different aggregate fractions, which may have an important impact on Nr. Methods In 2017, we collected soil samples from an alpine meadow of the Qinghai–Tibet Plateau and separated them into four soil aggregates (2–4, 1–2, 0.25–1, and <0.25 mm) using the dry sieving method. The four soil aggregate sizes amended with the 2 N deposition forms (NH4+-N and NO3−-N) were then incubated at 25 °C for 28 days, and the soil aggregates for each treatment were collected on day 0, 7, 14, 21, and 28 to determine the NO3−-N concentration. The soil Nr and contribution of soil aggregates to the nitrification rate in the bulk soil were calculated. Results There were differences in the physicochemical properties of the soil aggregates. The addition of N and aggregate size had strong effects on soil Nr, which were significantly increased under high levels of NH4+ addition across all soil aggregates. The Nr during the 4 week incubation period differed among aggregate sizes. Nr in the 2–4 mm aggregates was higher than in the other aggregates, which was correlated with the maximum values of the soil porosity observed in the 2–4 mm aggregates. Furthermore, almost half of the soil was composed of aggregates of <0.25 mm, indicating that the <0.25 mm aggregates made a higher contribution to the nitrification rate in the bulk soil than the other aggregates, even though these aggregates had a lower nitrification ability. Overall, our study revealed that the soil nitrification rate was influenced by both the N addition and soil aggregates, and that the 2–4 mm aggregates had a dominant effect on the response of soil N transformation processes to future nitrogen deposition in the alpine meadow.
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Meng, Miaojing, Chong Li, Youpeng Zhao, Jie Lin, Xin Liu, Zhaohui Jia, and Jinchi Zhang. "Long-Term Forest Conversion Affects Soil Stability and Humic Substances in Aggregate Fractions in Subtropical China." Forests 13, no. 2 (February 18, 2022): 339. http://dx.doi.org/10.3390/f13020339.
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Soil aggregates are the basic structural components of soil, which are important factors that can predict erosion resistance. However, few researchers have investigated the effects of forest conversion on the stability of soil aggregates, particularly in subtropical forests. In this study, soils from various depths (0 to 30 cm) were collected from four forest types (transformed from broadleaved forests (BMF) to combined coniferous broadleaved (CBMF), Chinese fir (FF), and bamboo forests (BF)) to determine the impacts of forest conversion on the physical and chemical properties of soil, water-stable soil aggregates, and aggregate-associated humic substances. The results showed that forest conversion had no effects on the soil’s physical properties, or the humic substances in bulk soil, but had significant effects on soil aggregates. In addition, the conversion of broadleaved forest to Chinese fir forest increased the soil stability, and to bamboo forest, decreased the soil stability. Finally, the soil’s physicochemical properties were closely related to aggregate-associated humic substances. In summary, specific forest management measures should be applied to strengthen the positive impacts and reduce the negative impacts associated with forest conversion.
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Bieganowski, A., M. Ryżak, and B. Witkowska-Walczak. "Determination of soil aggregate disintegration dynamics using laser diffraction." Clay Minerals 45, no. 1 (March 2010): 23–34. http://dx.doi.org/10.1180/claymin.2010.045.1.23.
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AbstractA new practical and precise method for determining soil aggregate stability is described. Four air-dry aggregate fractions (<0.25, 0.25–0.5, 0.5–1.0 and 1.0–2.0 mm) were added to thoroughly stirred water in a Mastersizer 2000 laser diffractometer. The suspension obtained was passed directly through the measuring system. The dynamics of median (equivalent diameter d50) particle-size distribution decrease (interpolated with a logarithmic function) was assumed to be the measure of soil aggregate stability. In order to show the applicability of the new method, the results obtained (for selected and diverse soils) were compared with those from the wet sieving standard method. The main conclusion is that the proposed method is convenient and can be successfully used for the estimation of soil aggregate stability. Moreover, it has wider application because standard sieving methods are restricted to aggregates >0.25 mm whereas, with the use of the laser diffraction method, smaller aggregates can be measured. The energy delivered to the aggregates in the process of aggregate disintegration is more reproducible in the method described here. The method also provides an opportunity to verify that the soil aggregates are completely destroyed (lack of the changes of the median value shows the end of soil aggregate disintegration).
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Yang, Songyu, Boris Jansen, Samira Absalah, Rutger L. van Hall, Karsten Kalbitz, and Erik L. H. Cammeraat. "Lithology- and climate-controlled soil aggregate-size distribution and organic carbon stability in the Peruvian Andes." SOIL 6, no. 1 (January 27, 2020): 1–15. http://dx.doi.org/10.5194/soil-6-1-2020.
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Abstract. Recent studies indicate that climate change influences soil mineralogy by altering weathering processes and thus impacts soil aggregation and organic carbon (SOC) stability. Alpine ecosystems of the Neotropical Andes are characterized by high SOC stocks, which are important for sustaining ecosystem services. However, climate change in the form of altered precipitation patterns can potentially affect soil aggregation and SOC stability with potentially significant effects on the soil's ecosystem services. This study aimed to investigate the effects of precipitation and lithology on soil aggregation and SOC stability in the Peruvian Andean grasslands, and it assessed whether occlusion of organic matter (OM) in aggregates controls SOC stability. For this, samples were collected from soils on limestone and soils on acid igneous rocks from two sites with contrasting precipitation levels. We used a dry-sieving method to quantify aggregate-size distribution and applied a 76 d soil incubation with intact and crushed aggregates to investigate SOC stability's dependence on aggregation. SOC stocks ranged from 153±27 to 405±42 Mg ha−1, and the highest stocks were found in the limestone soils of the wet site. We found lithology rather than precipitation to be the key factor regulating soil aggregate-size distribution, as indicated by coarse aggregates in the limestone soils and fine aggregates in the acid igneous rock soils. SOC stability estimated by specific SOC mineralization rates decreased with precipitation in the limestone soils, but only minor differences were found between wet and dry sites in the acid igneous rock soils. Aggregate destruction had a limited effect on SOC mineralization, which indicates that occlusion of OM in aggregates played a minor role in OM stabilization. This was further supported by the inconsistent patterns of aggregate-size distribution compared to the patterns of SOC stability. We propose that OM adsorption on mineral surfaces is the main OM stabilization mechanism controlling SOC stocks and stability. The results highlight the interactions between precipitation and lithology on SOC stability, which are likely controlled by soil mineralogy in relation to OM input.
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NG, CHIU-ON, and CHIANG C. MEI. "Effects of a semipervious lens on soil vapour extraction." Journal of Fluid Mechanics 341 (June 25, 1997): 385–413. http://dx.doi.org/10.1017/s002211209700565x.
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We describe a theory for the removal of volatile organic chemicals from an unsaturated soil stratum consisting of highly porous coarse sand layers sandwiching a thin and semipervious lens. Each soil layer is modelled as a periodic array of spherical aggregates formed by solid grains and immobile water trapped by surface tension. Volatile chemicals are vaporized in the mobile air in pores between aggregates, dissolved in the intra-aggregate water, and adsorbed on the surface of soil grains. Using the effective transport equations derived for the aggregated soils, we consider shallow layers with sharp contrast in physical properties. An asymptotic analysis is developed for an axisymmetric geometry, yielding quasi-one-dimensional governing equations for individual layers. At the leading order the flow and the vapour transport are horizontal in the coarse layers but vertical in the semipervious lens. Numerical results are presented for a simple example to demonstrate the significance of the lens permeability, diffusivity and retardation factor, and the aggregate diffusivity in the coarse layers, on the vapour transport during the stages of contamination and air-venting.
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KAY, B. D., and A. R. DEXTER. "INFLUENCE OF AGGREGATE DIAMETER, SURFACE AREA AND ANTECEDENT WATER CONTENT ON THE DISPERSIBILITY OF CLAY." Canadian Journal of Soil Science 70, no. 4 (November 1, 1990): 655–71. http://dx.doi.org/10.4141/cjss90-068.
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The percentages of spontaneously dispersed clay, Ms, and mechanically dispersed clay, Mm, in a suspension of a given ionic strength were hypothesized to be controlled by the specific area of exposed aggregate surfaces and the dispersibility of clay per unit specific aggregate surface area. This hypothesis was evaluated using different sized aggregates collected in 1988 from wheat-fallow and continuous pasture rotations established in 1925 on a red-brown earth in southern Australia. Aggregates which were initially air-dry were wetted to matric water potentials ranging from −10 to −0.3 kPa, then placed in distilled water and Ms and Mm measured. Ms increased, as hypothesized, with increasing surface area of aggregates. However, the spontaneously dispersed clay per unit surface area of aggregates increased with increasing size of aggregates and increasing antecedent soil water content. The effect of water content was greatest in the larger aggregates of the less stable wheat-fallow soil. Mm was approximately 12 times larger than Ms and increased with increasing initial aggregate size and increasing antecedent water content. The sensitivity of Mm to water content was greatest on the least stable soil. Calculations showed that the higher values of Mm on unstable soils were due to both larger exposed aggregate surface areas and higher dispersibility of the clay on these surfaces. Keywords: Soil structure, aggregate stability, dispersion
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Radziuk, Hanna, and Marcin Świtoniak. "The Effect of Erosional Transformation of Soil Cover on the Stability of Soil Aggregates within Young Hummocky Moraine Landscapes in Northern Poland." Agronomy 12, no. 11 (October 22, 2022): 2595. http://dx.doi.org/10.3390/agronomy12112595.
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Aggregate stability is a crucial factor in predicting the development of the erosion process, and it is particularly important in landscapes with high heterogeneity of soil cover, such as young hummocky moraine uplands. The objective of the presented work was to estimate the influence of erosion on the properties of aggregates and analyze the variation of aggregate stability under different erosion-related alterations of soil cover. The conducted research indicates that erosion has led to a deterioration of the quality of soil structure in the upper parts of the slopes, which in turn may intensify the slope processes leading to faster truncation of the pedons. Both the differentiation of the soils themselves and the stability of the aggregates were very strongly linked to erosive transformations. The tops of the hills and the upper parts of the slopes are covered with completely or strongly eroded soils in which the aggregates have the least favorable characteristics. Due to the smallest amount of humus and the highest clay content, the soils have the largest share of soil clods, which are aggregates larger than 7 mm that may have formed in dry conditions (soil drought). The plow horizons of most eroded Eutric Regosols and strongly eroded Luvisols have very poor water resistance, similar to that of the subsoils. The main factor determining the low aggregate stability of Eutric Regosols is the number of secondary carbonates that lead to a rise in soil dispersion. Strongly eroded Haplic Luvisols have a low resistance to water due to relatively high clay content (20–26 percent). The higher stability of aggregates in soils with colluvial materials (Albic Luvisols, Mollic Gleysols, Endogleic Phaeozems) depends mainly on soil organic carbon content. The results showed the necessity for adaptation of land management practices to .real condition and heterogeneity of soil cover.
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Hoosbeek, M. R., J. M. Vos, and G. E. Scarascia-Mugnozza. "Increased physical protection of soil carbon in the mineral soil of a poplar plantation after five years of free atmospheric CO<sub>2</sub> enrichment (FACE)." Biogeosciences Discussions 3, no. 4 (July 5, 2006): 871–94. http://dx.doi.org/10.5194/bgd-3-871-2006.
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Abstract. Free air CO2 enrichment (FACE) experiments in aggrading forests and plantations have demonstrated significant increases in net primary production (NPP) and C storage in forest vegetation. The extra C uptake may also be stored in forest floor litter and in forest soil. After five years of FACE treatment at the EuroFACE short rotation poplar plantation, the increase of total soil C% was larger under elevated than under ambient CO2. However, the fate of this additional C allocated belowground remains unclear. The stability of soil organic matter is controlled by the chemical structure of the organic matter and the existence of protection offered by the soil matrix and minerals. Fresh litter entering the soil enhances microbial activity which induces the binding of organic matter and soil particles into macro-aggregates. As the enclosed organic matter is decomposed, microbial and decomposition products become associated with mineral particles. This association results in the formation of micro-aggregates (within macro-aggregates) in which organic matter is stabilized and protected. FACE and N-fertilization treatment did not affect the micro- and macro-aggregate weight, C or N fractions obtained by wet sieving. However, Populus euramericana increased the micro- and small macro-aggregates weight and C fractions. The obtained macro-aggregates were broken up in order to isolate recently formed micro-aggregates within macro-aggregates (iM-micro-aggregates). FACE increased the iM-micro-aggregate weight and C fractions. This study reveals that: 1) Species has an effect on the formation of macro-aggregates. The choice of species in a plantation or the effect of global change on species diversity, may therefore affect the stabilization and protection of soil C in aggregates. And 2) Increased atmospheric CO2 concentration increases the stabilization and protection of soil C in micro-aggregates formed within macro-aggregates. This mechanism increases the C sink of forest soils under increasing atmospheric CO2 concentration.
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Fér, Miroslav, Martin Leue, Radka Kodešová, Horst H. Gerke, and Ruth H. Ellerbrock. "Droplet infiltration dynamics and soil wettability related to soil organic matter of soil aggregate coatings and interiors." Journal of Hydrology and Hydromechanics 64, no. 2 (June 1, 2016): 111–20. http://dx.doi.org/10.1515/johh-2016-0021.
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Abstract The organo-mineral coatings of soil aggregates, cracks, and biopores control sorption and macropore-matrix exchange during preferential flow, in particular in the clay-illuvial Bt-horizon of Luvisols. The soil organic matter (SOM) composition has been hypothesized to explain temporal changes in the hydraulic properties of aggregate surfaces. The objective of this research was to find relations between the temporal change in wettability, in terms of droplet infiltration dynamics, and the SOM composition of coated and uncoated aggregate surfaces. We used 20 to 40 mm sized soil aggregates from the Bt2 horizon of a Haplic Luvisol from loess that were (i) coated, (ii) not coated (both intact), and (iii) aggregates from which coatings were removed (cut). The SOM composition of the aggregate surfaces was characterized by infrared spectroscopy in the diffuse reflection mode (DRIFT). A potential wettability index (PWI) was calculated from the ratio of hydrophobic and hydrophilic functional groups in SOM. The water drop penetration times (WDPT) and contact angles (CA) during droplet infiltration experiments were determined on dry and moist aggregate samples of the three types. The decrease in the CA with time was described using the power function (CA(t) = at−b). For dry aggregates, the WDPT values were larger for coated as compared to uncoated regions on the aggregate surfaces, and increased with increasing PWI value (R2 = 0.75). The a parameter was significantly related to the WDPT (R2 = 0.84) and to the PWI (R2 = 0.64). The relations between the b parameter and the WDPT (R2 = 0.61) and the PWI (R2 = 0.53) were also significant. The WDPT values of wet soil aggregates were higher than those of dry aggregates due to high water contents, which limited the droplet infiltration potential. At the wet aggregate surfaces, the WDPT values increased with the PWI of the SOM (R2 = 0.64). In contrast to dry samples, no significant relationships were found between parameters a or b of CA(t) and WDPT or PWI for wet aggregate surfaces. The results suggest that the effect of the SOM composition of coatings on surface wettability decreases with increasing soil moisture. In addition to the dominant impact of SOM, the wettability of aggregate surfaces could be affected by different mineralogical compositions of clay in coatings and interiors of aggregates. Particularly, wettability of coatings could be decreased by illite which was the dominant clay type in coatings. However, the influence of different clay mineral fractions on surface wettability was not due to small number of measurements (2 and 1 samples from coatings and interiors, respectively) quantified.
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Li, Jiangwen, Xihao Wei, Shouqin Zhong, En Ci, and Chaofu Wei. "A New Idea to Improve the Test Method of Soil Aggregate Stability for Soils with a Texture Gradient." Agronomy 13, no. 5 (April 23, 2023): 1192. http://dx.doi.org/10.3390/agronomy13051192.
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It is of great significance to determine soil aggregate stability in predicting agricultural production conditions and soil erosion risk. However, the problem exposed in the process of evaluating soil aggregate stability cannot be ignored: Can the effects of different mechanisms on the degree of soil aggregate breakdown be distinguished by selecting ethanol and water as dispersion media? Based on this question, natural soils with a gradient in soil textures of silty loam to loamy clay were used as the test materials. Deionized water, ethanol and hexane were employed as soaking solutions to quantitatively analyze the extent to which the aggregates were dispersed in static disintegration experiments. The results suggested that the soil hydrophilicity (SH) of six soils with a texture gradient were >1 by comparing the aggregate breakdown index (ABI) of soils undergoing ethanol and hexane dispersion. This indicated that the hydrophilic group (-OH) contained in ethanol interacted with the hydrophilic surfaces of the soil particles. Therefore, the soil hydrophilicity (hydration) should be determined by comparing the ABI values undergoing hexane and water dispersion. From silty loam to loamy clay, the average contribution of hydration to aggregate fragmentation decreases, and the process of aggregate breakdown with different textures is characterized by size selectivity. When the soil aggregates were fragmented into 2–0.25 mm aggregate fractions, for silty loam and sandy clay loam, 0.002–0.02 mm and <0.002 mm particles were preferentially moved; for clay loam and loamy clay, >0.002 mm particles were preferentially moved. When the soil aggregates were fragmented into <0.25 mm aggregate fractions for soils with different textures, the 0.002–0.02 mm and <0.002 mm particles all exhibited preferential migration characteristics. This work provides an idea for improving the methods of aggregate stability measurements in the future.
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Udom, Bassey, Joshua Ogunwole, and Chima Wokocha. "Aggregate characteristics and aggregate-associated soil organic carbon and carbohydrates of soils under contrasting tree land use." SAINS TANAH - Journal of Soil Science and Agroclimatology 18, no. 2 (December 26, 2021): 126. http://dx.doi.org/10.20961/stjssa.v18i2.53615.
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<p><span>Protection of soil organic carbon and acid-hydrolyzable carbohydrates in aggregate-size fractions is important for appraising soil degradation and aggregation under land use types. Aggregate-associated soil organic carbon (SOC) and acid-hydrolyzable carbohydrates (R-CHO) in bulk soils and aggregate-size fractions of a sandy loam soil under Alchornea bush, Rubber, Oil palm and Teak plantations in southern Nigeria were studied. Results revealed significant differences in aggregate-associated SOC and R-CHO, bulk densities, total porosity, soil organic carbon stock and aggregate stability among the land use types. Greater SOC was stored in macro-aggregates >0.25 mm, while greater R-CHO was occluded in micro-aggregates <0.25 mm (p<0.05). The highest mean weight diameter (MWD) was 1.01 mm in Alchornea soils and 0.92 mm in Oil palm plantation at 0-15 cm topsoil. Soil organic carbon stock in 0-15 cm topsoil was 77.7, 81.8, 92.2, and 67.5 kg C ha<sup>-1</sup> in Alchornea, Rubber, Oil palm, and Teak soils, respectively. Relationships showed a positive linear correlations between MWD and SOC (r = 0.793, p < 0.05) and R-CHO (r = 0.789. p < 0.05). Alchornea bush and Oil palm plantation increased macro-aggregate formation and macro-pores >5 µm, therefore they have greater potentials to boost protection of SOC in soil macro-aggregates.</span></p>
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Bronswijk, J. J. B., and J. J. Evers-Vermeer. "Shrinkage of Dutch clay soil aggregates." Netherlands Journal of Agricultural Science 38, no. 2 (June 1, 1990): 175–94. http://dx.doi.org/10.18174/njas.v38i2.16603.
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Shrinkage characteristics and COLE and PLE values of undisturbed natural aggregates of clay soils from the Netherlands were measured. The course of the shrinkage process upon drying varied strongly between soils, and very often the measured characteristics diverged from the theoretical curve. Some Dutch clay soils are amongst the strongest swelling and shrinking soils in the world, with volume decreases of aggregates up to 49% between saturation and oven-dryness, and 42% between saturation and a pressure head of -16 000 cm. Potential subsidence of a Dutch field soil due to shrinkage is up to 15 cm. In some Netherlands clay soil, as a result of normal shrinkage, the aggregates remain saturated throughout the whole year; only inter-aggregate pores such as shrinkage cracks, contain air. (Abstract retrieved from CAB Abstracts by CABI’s permission)
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Sui, Yue-yu, Xiao-guang Jiao, Xiao-bing Liu, Xing-yi Zhang, and Guang-wei Ding. "Water-stable aggregates and their organic carbon distribution after five years of chemical fertilizer and manure treatments on eroded farmland of Chinese Mollisols." Canadian Journal of Soil Science 92, no. 3 (March 2012): 551–57. http://dx.doi.org/10.4141/cjss2010-005.
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Sui, Y.-y., Jiao, X.-g., Liu, X.-b., Zhang, X.-y. and Ding, G.-w. 2012. Water-stable aggregates and their organic carbon distribution after five years of chemical fertilizer and manure treatments on eroded farmland of Chinese Mollisols. Can. J. Soil Sci. 92: 551–557. Water-stable aggregates are the foundation for both water and fertility conservation and nutrient release in the soil. We investigated the effects of 5 yr of different fertilizer treatments (chemical fertilizer and fertilizer+manure) on water-stable aggregates and their organic carbon distribution patterns within five different simulated erosion levels (removal of 0, 5, 10, 20, and 30 cm of topsoil) in an eroded Black soil of northeast China. Water-stable aggregates greater than 0.25 mm in size and aggregate-associated-carbon (AAC) contents in the aggregates were greater in the soils with fertilizer+manure application than those with chemical fertilizers alone. Both water-stable aggregates and AAC contents declined (P<0.05) gradually as soil removal depth increased. The decline in aggregates larger than 1 mm with increased erosion depth was greater in the fertilizer-only application than that in the fertilizer+manure application. The minimum value was found in the case of 30 cm topsoil removal under the fertilizer-only application. Significant correlations (P<0.05) between water-stable aggregates greater than 1 mm and soil organic carbon (SOC) were observed in the soil with fertilizer+manure application. A significant positive correlation was observed between SOC and all different aggregate classes with both chemical fertilizer and fertilizer+manure applications. AAC within large aggregates and SOC contents were significantly higher in the fertilizer+manure treatment than in the fertilizer-only treatment. The study shows that water-stable aggregates (>1 mm) can be used as an indicator in evaluating the influence of carbon transformation on soil quality. The increases in SOC by cattle manure application to eroded Black soil might be responsible for the larger size aggregate formation.
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Gorban, V. A., J. L. Poleva, N. A. Bilova, S. O. Hunko, and O. V. Kotovych. "Mechanisms of influence of forest ecosystems on the aggregate composition and water stability of soil aggregates in the semi-arid area of southeast Ukraine." Regulatory Mechanisms in Biosystems 15, no. 1 (February 20, 2024): 148–58. http://dx.doi.org/10.15421/022422.
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Modern processes of climate change are accompanied by a number of negative factors, which include aridization, desertification, soil degradation and erosion. The research was were carried out on the territory that is the southern border of the distribution of the late glacial phase of the Dnieper glaciation (Middle Pleistocene, 100–230 thousand years ago). The influence of forest ecosystems on the aggregate composition and water stability of soil aggregates, the features of which determine the protection of soils from erosion and other degradation processes in semiarid conditions, was assessed. It has been established that luvic chernozems of forest ecosystems are characterized by an increased content of aggregates of fractions 2–3, 1–2 and 0.5–1.0 mm, as well as water-stable aggregates of fractions > 5, 0.5–1.0 and 0.25–0.5 mm in the 0–20 cm layer compared to ordinary chernozems of steppe ecosystems. The content of soil organic matter is a determining factor on which the aggregate composition and content of water-stable aggregates in luvic chernozems of forest ecosystems depends. The existence of close direct relationships has been established between the content of soil organic matter and the content of aggregates of the 0.5–1.0 mm fraction, as well as between the content of soil organic matter and the content of water-stable aggregates of fractions 3–5, 2–3 and 1–2 mm in chernozems of steppe and forest ecosystems. The existence of close direct relationships between the sand content and the content of water-stable aggregates of fractions 3–5 and 2–3 mm was revealed. The established increase in the content of soil organic matter and sand in luvic chernozems of forest ecosystems compared to ordinary chernozems of steppe ecosystems is the reason for the improvement in the aggregate composition and the increase in the content of water-stable aggregates. This is a key aspect of increasing the resistance of soils in forest ecosystems to various negative factors, such as desertification, degradation, wind and water soil erosion.
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Zádorová, T., O. Jakšík, R. Kodešová, and V. Penížek. " Influence of terrain attributes and soil properties on soil aggregate stability." Soil and Water Research 6, No. 3 (September 19, 2011): 111–19. http://dx.doi.org/10.17221/15/2011-swr.
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The study on the relationship between the soil aggregates stability assessed using water stable aggregate (WSA) index and the selected terrain and soil properties was performed on a morphologically diverse study site in Chernozem soil region of Southern Moravia. Soil analyses and detailed digital elevation model processing were the main methods adopted in the study. The soil structure stability is negatively influenced by the soil material removal from the steep parts of the back-slope and re-deposition of the mineral loess material at the base of the slope. The highest aggregates stability was identified in the upper flat parts of the study plot, undisturbed by erosion processes, and at the concave parts of the back-slope with intensive accumulation of organic matter. Statistical analysis showed a significant dependence of aggregates stability on organic carbon content and plan curvature index.
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Fuller, L. G., and Tee Boon Goh. "Stability-energy relationships and their application to aggregation studies." Canadian Journal of Soil Science 72, no. 4 (November 1, 1992): 453–66. http://dx.doi.org/10.4141/cjss92-038.
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The objective of this study was to develop a method to describe aggregate stability-energy relationships using ultrasonic dispersion and to examine the role played by carbohydrate in soil aggregation. Aggregate size fractions (ASF) from three soils were sonified, and dispersed clay and solubilized carbohydrate measured at energy levels ranging from 0 to 1000 kJ L−1. Study soils included an Orthic Black, Orthic Dark Gray, and Orthic Gray Luvisol, representing the change from a prairie ecosystem to an aspen-forest ecosystem. Ultrasonic dispersion of aggregated clay resulted in characteristic "stability curves" for each ASF which obeyed a first-order decay curve and provided two parameters describing the release of clay from soil aggregates with increasing levels of applied energy: the "stability constant" k and the E1/2 value, which are analogous to a first-order rate constant and half-life, respectively. E1/2 values ranged from 51 to 502 kJ L−1.These values were smallest for the Ae horizon of the Orthic Gray Luvisol and greatest for the macroaggregates of the Ahe horizon of the Orthic Dark Gray. Carbohydrates solubilized upon aggregate destruction generally constituted a minor proportion (10%) of the total ASF carbohydrate, indicating that most of the carbohydrate was strongly adsorbed to surfaces. The development of a stability-energy relationship for aggregates provides a means to study the role of binding agents, such as carbohydrate, in the aggregation process. Key words: Aggregates, ultrasonic dispersion, clay, carbohydrate
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Zhang, Han, Yongzhen Huang, Yahui Lan, Yaqin He, Shengqiang Wang, Chenyang Jiang, Yuhong Cui, Rongyuan Fan, and Shaoming Ye. "Mixed Chinese Fir Plantations Alter the C, N, and P Resource Limitations Influencing Microbial Metabolism in Soil Aggregates." Forests 15, no. 4 (April 21, 2024): 724. http://dx.doi.org/10.3390/f15040724.
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Assessing the limitations of microbial metabolic resources is crucial for understanding plantation soil quality and enhancing fertility management. However, the variation of microbial resource limitations at the aggregate level in response to changes in stands remains unclear. This research explores carbon (C), nitrogen (N), and phosphorus (P) limitations affecting microbial metabolism in bulk soils and aggregates in two mixed and one pure Chinese fir stands in subtropical China, analyzing resource limitations concerning soil carbon, nutrients, and microbial indicators. The results revealed that microbes in all aggregates of the pure stands and in the micro aggregates (<0.25 mm) of the three stands were relatively limited by C and P. In contrast, microbial metabolism was more N-limited in macroaggregates (>2 mm) and small aggregates (2–0.25 mm) in the mixed stands. Additionally, in the mixed stands the proportion of soil macroaggregates increased, and that of micro aggregates decreased, resulting in a shift from C and P limitation to N limitation for bulk soil microbial metabolism. Redundancy analysis identified soil aggregate organic carbon and nutrient content as the main factors affecting microbial resource limitation, rather than their stoichiometric ratios. Pathway analysis further confirmed that soil nutrients and their stoichiometric ratios indirectly influenced soil microbe resource limitation by regulating microbial biomass, microbial respiration, and extracellular enzyme activities. Thus, the impact of mixed plantations on soil nutrients and microbial activity at the aggregate level may be crucial for maintaining land fertility and achieving sustainability.
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Potapov, D. I., I. V. Gorepyokin, G. N. Fedotov, V. S. Shalaev, and Yu P. Batyrev. "Selection of conditions for studying intraaggregate connections influence on water stability of soil aggregates." FORESTRY BULLETIN 25, no. 4 (August 2021): 52–58. http://dx.doi.org/10.18698/2542-1468-2021-4-52-58.
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The search for approaches to assessment the water resistance of soil aggregates is conducted using the modified Andrianov method. It is shown that the kinetic equation of the first-order reaction could be applied to describe the aggregates destruction in standing water. Methods of formal kinetics at the same time are just partially applicable for the description of soil aggregates destruction because of a significant change in the reaction rate constant over time. In particular, the average constant of reaction rate is convenient for water resistance comparison of different aggregates samples. It is established that the main factors that determine the speed of aggregate destruction are trapped air, gases produced by anaerobic microorganisms as well as intra-aggregate connections and the velocity of water entering the aggregates. In the course of the conducted experiments, it is shown that water resistance assessment should perform on wet aggregates under the normal atmospheric pressure. It allows neutralizing the influence of trapped gases of microbial origin and providing the domination of intra-aggregate connections that sustain water resistance in wet aggregates of real soils.
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Qu, Jun Feng, Min Tan, Yu Le Hou, Meng Yu Ge, An Ni Wang, Kun Wang, Jin Xia Shan, and Fu Chen. "Effects of the Stability of Reclaimed Soil Aggregates on Organic Carbon in Coal Mining Subsidence Areas." Applied Engineering in Agriculture 34, no. 5 (2018): 843–54. http://dx.doi.org/10.13031/aea.12829.
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Abstract. Reclaimed soil aggregates play a critical role in the accumulation of soil organic carbon. The purpose of this article is to investigate the effects of reclaimed soil aggregate development on organic carbon and explore changes in reclaimed agricultural soil over time in a coal mining subsidence area. Adjacent to the control sample plot (CKN), six sample plots of different reclamation time series: 2001 (R15), 2003 (R13), 2005 (R11), 2007 (R9), 2009 (R7), and 2011 (R5) were collected. Soil analyses included aggregate fractionation and organic carbon. Over time, the distribution characteristics of water-stable aggregates in reclaimed soil gradually improved. The concentration of organic carbon in reclaimed soil increased with aggregate size, and the organic carbon concentration of all aggregates increased with reclamation age. As the number of reclamation years increased, organic carbon also increased, first in the free light fraction (fLF) and later in mineral-bound carbon (mineral-C). Accumulation of organic carbon was related to the development of soil aggregates. The formation and carbon sequestration of reclaimed soil aggregates was consistent with the conceptual model of “aggregate turnover.” The transformation and accumulation of organic carbon was consistent with the physical protection mechanism of soil organic carbon. Keywords: Aggregate, Coal mining subsidence area, Reclaimed soil, Soil organic carbon.