DISPERSION OF SOIL PARTICLES BY SONIC VIBRATION1

Dispersion of soil particles is achieved without use of oxidants, acids, or peptizing reagents, by subjecting an aqueous suspension of the soil sample (10 g soil, 25 ml water) to sonic vibration at 13 to 15°C using a Raytheon (9 kc, 50 w) vibrator. Studies using soils of widely different textures and organic matter contents showed that the dispersion caused by sonic vibration for 30 min, as evaluated by pipette analysis for < 2 μ material, was similar to that obtained by chemical methods currently used for dispersion of soils. The dispersion effected by ultrasonic vibration of soil-water suspensions using a probe-type vibrator (18–20 kc, 60 w) is comparable to that achieved by sonic vibration. The vibration method of dispersing soil particles yields stable suspensions and is effective with highly calcareous soils and with soils containing large amounts of montmorillonite and organic matter. It permits dispersion of soil particles without dissolution of more than trace amounts of organic or inorganic material and does not significantly affect the pH or conductivity of the soil suspension.     

紫色土发育成的水稻土微团粒结构中有机－无机复合体的性质

This paper deals with characteristics of organo-mineral complexing of microaggregates in the paddy soils developed from purple soils in Sichuan, China. Results show that the contents of organic matter in microaggregates are in the order of 1-0.25 mm > smaller than 0.05 mm > 0.05-0.25 mm. But the organic matter in 1-0.01 mm microaggregates accounts for 68.1%-78.7% of that in soil. The organic matter in < 0.05 mm microaggregates is complexed humus on the whole, of which the degree of organo-mineral complexing varies between 96.1% and 99.5%, which is higher than that of the soil or > 0.05 mm microaggregates. The contents of loosely combined humus and the ratios of loosely and tightly combined humus markedly decline with the size of microaggregates. Flesh soil humus formed from semi-decomposed organic material or organic manure added is combined first with < 0.001 mm clay, and then aggregated with other organic and mineral particles to form larger microaggregates, in which the aging of humus happens at the same time; whereas organic matter of the light fraction is mainly involved in the formation of > 0.05 mm microaggregates.     

Soil organic matter distribution and microaggregate characteristics as affected by agricultural management and earthworm activity

Stable microaggregates can physically protect occluded soil organic matter (SOM) against decomposition. We studied the effects of agricultural management on the amount and characteristics of microaggregates and on SOM distribution in a marine loam soil in the Netherlands. Three long‐term farming systems were compared: a permanent pasture, a conventional‐arable system and an organic‐arable system. Whole soil samples were separated into microaggregates (53–250 µm), 20–53 µm and < 20 µm organo‐mineral fractions, sand and particulate organic matter, after complete disruption of macroaggregates. Equal amounts of microaggregates were isolated, irrespective of management. However, microaggregates from the pasture contained a larger fraction of total soil organic C and were more stable than microaggregates from the two arable fields, suggesting greater SOM stabilization in microaggregates under pasture. Moreover, differences in the relative contribution of coarse silt (> 20 µm) versus fine mineral particles in the microaggregates of the different management systems demonstrate that different types of microaggregates were isolated. These results, in combination with micromorphological study of thin sections, indicate that the great earthworm activity under permanent pasture is an important factor explaining the presence of very stable microaggregates that are relatively enriched in organic C and fine mineral particles. Despite a distinctly greater total SOM content and earthworm activity in the organic‐ versus the conventional‐arable system, differences in microaggregate characteristics between both arable systems were small. The formation of stable and strongly organic C‐enriched microaggregates seems much less effective under arable conditions than under pasture. This might be related to differences in earthworm species' composition, SOM characteristics and/or mechanical disturbance between pasture and arable land.     

Effects of compost on the chemical composition of SOM in density and aggregate fractions from rice–wheat cropping systems as shown by solid‐state 13C‐NMR spectroscopy

The 4‐year application of pig‐manure compost (PMC) to crop fields in Jiangsu significantly increased organic‐C and total N concentrations compared to chemical fertilization and control treatment. To identify the soil processes that led to these changes, ¹³C cross‐polarization magic‐angle spinning nuclear‐magnetic resonance (¹³C CPMAS NMR) and dipolar‐dephasing nuclear‐magnetic‐resonance spectroscopy (DD NMR) were conducted on soil organic matter (SOM) fractions separated by wet‐sieving and density fractionation procedures. This allowed characterization of the SOM quality under three contrasting fertilizer regimes. The results indicate that PMC application can alter the distribution of functional groups and improve alkyl C‐to‐O‐alkyl C ratios compared to chemical‐fertilizer treatment (CF). Alkyl C contents were increased from macroaggregate fractions (> 2 mm) to microaggregate fractions (0.05–0.25 mm) for all treatments, suggesting that recalcitrant material accumulates in the microaggregate fractions. The O‐alkyl C contents were decreased from macroaggregate fractions (> 2 mm) to microaggregate fractions (0.05–0.25 mm) under CF and PMC treatments, while no consistent trend was found for the control (NF) treatment. The alkyl C‐to‐O‐alkyl C ratios in macroaggregates were lower than those in microaggregates, indicating that the degrees of SOM decomposition were lower in macroaggregates compared to microaggregates. In all aggregate‐size classes, the amount of organic matter appeared to depend on the fertilization regime. This study provides useful information regarding the buildup of organic material in soil from long‐term manure‐compost enrichment.     

Soil microaggregation as influenced by uncharged organic conditioners

Abstract

To assess the interaction of water soluble stabilizing agents with soil particles, soil microaggregation was studied after treatments with two uncharged organic conditioners, Polyvinyl alcohols (PVAs) and Dextrans, of different molecular weight. The size distribution of microaggregates (diameter <250 pm) was determined on two soils of low organic matter contents with differing texture by means of a laser light technique. PVAs and Dextrans modified the microaggregate size distribution, increasing the proportion of >75 μm aggregates. The extent of this modification increased with the molecular weight of the conditioners and, for the same molecular weight, decreased with increasing amount of conditioner used. The aggregating effect of PVAs was stronger on particles smaller then 5 μm, which formed microaggregates in the range 10–100 μm which were not broken down even by ultrasonication. S.E.M. micrographs of soil aggregates confirmed the results reported above. PVAs and Dextrans appeared to produce a more porus structure with more aggregates of about 100 μm size, both in the clay soil and, to a lesser extent, in the sandy soil.     

Effects of long-term compost and fertilizer application on stability of aggregate-associated organic carbon in an intensively cultivated sandy loam soil

The study examined the influence of compost and mineral fertilizer application on the content and stability of soil organic carbon (SOC). Soil samples collected from a long-term field experiment were separated into macroaggregate, microaggregate, and silt + clay fractions by wet-sieving. The experiment involved seven treatments: compost, half-compost N plus half-fertilizer N, fertilizer NPK, fertilizer NP, fertilizer NK, fertilizer PK, and control. The 18-year application of compost increased SOC by 70.7–121.7%, and mineral fertilizer increased by 5.4–25.5%, with no significant difference between control soil and initial soil. The C mineralization rate (rate per unit dry mass) in microaggregates was 1.52–2.87 mg C kg⁻¹ day⁻¹, significantly lower than in macroaggregate and silt + clay fractions (P < 0.05). Specific C mineralization rate (rate per unit SOC) in silt + clay fraction amounted to 0.48–0.87 mg C g⁻¹ SOC day⁻¹ and was higher than in macroaggregates and microaggregates. Our data indicate that SOC in microaggregates is more stable than in macroaggregate and silt + clay fractions. Compost and mineral fertilizer application increased C mineralization rate in all aggregates compared with control. However, compost application significantly decreased specific C mineralization rate in microaggregate and silt + clay fractions by 2.6–28.2% and 21.9–25.0%, respectively (P < 0.05). By contrast, fertilizer NPK application did not affect specific C mineralization rate in microaggregates but significantly increased that in silt + clay fractions. Carbon sequestration in compost-amended soil was therefore due to improving SOC stability in microaggregate and silt + clay fractions. In contrast, fertilizer NPK application enhanced SOC with low stability in macroaggregate and silt + clay fractions.     

Carbon mineralization in soil size fractions after various amounts of aggregate disruption

Aggregates (1–2mm) were subjected to shaking, increasing intensities of ultrasonification, or a peroxide treatment and then physically fractionated into sand-, silt- and clay-size fractions. CO₂ evolution was measured during a 20-day incubation of the sand-, silt- and clay-size fractions and was used to assess the decomposability of the organic matter within aggregates and associated with these size fractions.
All of the size fractions showed a large increase in the amount of readily decomposable C when the ultrasonic energy input increased from 300 to 500 J ml⁻¹ and disruption of microaggregates occurred. The data suggest that some readily decomposable organic matter is sequestered within microaggregates and protected from microbial attack.
Following complete dispersion, the C mineralized (mg C g⁻'C) upon incubation was greatest in the sand particles and least in the clay. The levels of potentially mineralizable C ( C ₀) in the sand-size fraction increased with increased dispersion energy whereas the mineralization rate (k) remained about the same. The levels of C₀ in the clay-size fraction decreased and the estimates of k increased abruptly upon the disruption of micro-aggregates.     

Application of Soil Fractionation Methods to the Study of the Distribution of Pollutant Metals

Three agricultural Fluvisols polluted by sewage sludge were dispersed by shaking in water or in organic solvent for particle size and density separations. The perturbations caused by the ultrasonic treatment were discussed. Only the carbonate particles were disrupted to very fine particles. The pollutant metals were not displaced by the treatments, except perhaps Cd that is partly soluble in water and in other solvents. We discussed the relationship between soil constitution and major element chemical analyses. We obtained enough different fractions by using the ultrasonic and other dispersion treatments and by fractionating versus two physical parameters (i.e. particle size and density), for a correlation study between the contents of major and trace elements. We found that Cu was the only element to be more concentrated in the “free” organic matter. Other metals were more concentrated within an organo-mineral compartment, containing evoluted organic matter, fine clay and hydrous oxides. No pollutant metals were associated with carbonates, feldspars, and quartz. Other less general features were discussed.     

How does sonication affect the mineral and organic constituents of soil aggregates?—A review

Application of ultrasound to disperse soil aggregates has been critical in enabling researchers to separate and analyze aggregate building blocks that include organic and mineral particles as well as mineral associated organic matter. But the forces generated in the process may also alter the dispersion products and, thus, potentially interfere with the interpretation of experimental results. This review summarizes present knowledge on experimental conditions that may lead to physical damage and chemical modifications of aggregate building blocks. The energy level at which physical disintegration of organic particles could be detected was as low as 60 J mL^–1. Physical damage of sand‐ and silt‐sized mineral particles was observed to commence at energy levels exceeding 700 J cm^–3. No evidence was found for the disintegration of particles within the clay‐size fraction of soils even though studies analyzing pure minerals such as kaolinite revealed particle breakage after application of energy amounts > 12,000 J cm^–3. Here we outline a strategy to minimize artifacts such as physical damage of mineral or organic particles resulting from ultrasonication by adopting a stepwise dispersion protocol involving successively higher energy levels, accompanied by a sequential separation of organic and mineral compounds.     

甘肃景电灌区土壤团聚体特征研究

本文对甘肃景电灌区土壤团聚体组成及其稳定性进行了研究。结果表明,土壤团聚性很差,团聚体以非水稳性为主,稳定性很低。粘粒对于团聚体的形成和稳定性影响最大,显示土壤中粘粒物质是目前这一地区土壤结构形成的最为重要的胶结物质。碳酸钙对于团聚体形成的胶结作用次之,有机质由于含量低,其胶结作用最小,但是有机质对于团聚体稳定性的影响大于碳酸钙的影响,易溶性盐使团聚体的数量和稳定性降低,土壤微团聚体研究表明,土壤     

TOWARDS AN ABSOLUTE MEASUREMENT OF SOIL STRUCTURAL STABILITY USING ULTRASOUND

Calibrations enabled controlled application of a range of known dispersive energies to a selected soil sample. The corresponding levels of dispersion were measured in terms of the weight fraction of particles <2 μm equivalent spherical diameter produced, and are used to define a dispersion characteristic for the test soil. Interpretation of this characteristic in terms of a microaggregate theory provides the energy value associated with complete ‘primary dispersion’ of microaggregates, which under normal field conditions is a direct practical measure of soil stability. This leads to a definition of the specific stability index (σ) of a soil which for the gleyed brown earth used in this work has the value (25±3) J g^?1.     

Clay mineralogy differs qualitatively in aggregate‐size classes: clay‐mineral‐based evidence for aggregate hierarchy in temperate soils

Clay minerals have a major role in soil aggregation because of their large specific surface area and surface charges, which stimulate interactions with other mineral particles and organic matter. Soils usually contain a mixture of clay minerals with contrasting surface properties. Although these differences should result in different abilities of clay minerals regarding aggregate formation and stabilization, the role of different clay minerals in aggregation has been seldom evaluated. In this study, we took advantage of the intrinsic mineral heterogeneity of a temperate Luvisol to compare the role of clay minerals in aggregation. First, grassland and tilled soil samples were separated in water into aggregate‐size classes based on the aggregate hierarchy model. Then, clay mineralogy and organic C in the aggregate‐size classes were analysed. Interstratified minerals containing swelling phases accumulated in aggregated fractions compared with free clay fractions under the two land‐uses. The accumulation increased with decreasing aggregate size from large macroaggregates (> 500 µm) to microaggregates (50–250 µm). Carbon content and carbon‐to‐nitrogen ratio followed the opposite trend. This fully supports the aggregate hierarchy model, which postulates an increasing importance of mineral reactivity in smaller aggregates than in larger aggregates in which the cohesion relies mostly on physical enmeshment by fungal hyphae or small roots. Consequently, differences in the proportion of the different 2:1 clay minerals in soils can influence their structure development. Further research on the links between clay mineralogy and aggregation can improve our understanding of mechanisms of soil resistance to erosion and organic matter stabilization.     

Chemical contamination in upper horizon of Haplic Chernozem as a transformation factor of its physicochemical properties

Purpose

The effect of Cu, Zn, and Pb high rates on the physical properties and organic matter of Haplic Chernozem (Clayic) (A1 horizon 0–20 cm) under model experimental conditions was studied.

Materials and methods

In a model experiment, soil samples of Haplic Chernozem (Clayic) were artificially contaminated with 2000 mg/kg of Cu, Zn, and Pb acetates added separately. The particle-size fraction, the microaggregates distribution, the structural status, the total content and fractional and group composition of organic matter, physico-mechanical properties were determined in soil without metals and soil contaminated with metals.

Results and discussion

At the soil contamination with Cu, Zn, and Pb, the content of organo-mineral colloids increased, which results to the increasing of the clay fraction content by 4.5% compared to the control. The analysis of the microaggregate size composition of the studied soil shows that the content of coarser aggregates (1–0.25 mm) increases and the content of finer (0.05–0.001 mm) aggregates decreases after the addition of HMs and correspond to the HMs series: Cu → Zn → Pb. A significant decrease in the coefficient of water stability in the control from 3.0 to 1.4–1.5 in the contaminated treatments. The structural status (estimated from total agronomically valuable aggregates) changes from excellent to good. The addition of Cu, Zn, and Pb to the soil affects the quantitative composition of organic matter. The contents of free and sesquioxide-bound humic acids and free fulvic acids increased. The contamination with Zn and Pb causes the aliphatization of organic matter.

Conclusions

Under conditions of model experiment, the contamination of Haplic Chernozem (Clayic) with high rates of Cu, Zn, and Pb leads to changes of the microaggregates distribution, the structural status, and the qualitative composition of organic matter.

     

Variation of intra‐aggregate organic carbon affects aggregate formation and stability during organic manure fertilization in a fluvo‐aquic soil

The aggregate formation and stability are controlled by the dynamics of soil organic matters (SOM), but how it is related to SOM chemical composition within different‐sized aggregates is largely unknown during manure fertilization. In this study, the variations of intra‐aggregate organic carbon (OC), including intra‐particulate organic matter (iPOM) and mineral‐associated organic matter, were quantitatively and qualitatively analysed, and then, their effects on aggregate formation and stability were assessed under four treatments: control (CK), mineral fertilizer (NPK), reduced manure (30%M) and manure fertilizers (M). Manure application (M) significantly increased macroaggregate proportion, mean weight diameter (MWD), and OC contents within different‐sized aggregates compared to CK, NPK, and 30%M. The OC accumulation of macroaggregate in M was attributed to OC content increase in silt plus clay subfraction rather than iPOM with more labile organic groups; oppositely, in microaggregate it was located in the relatively stable fine iPOM. The macroaggregate formation and stability were controlled by the fine iPOM within macroaggregates, whose abundant polysaccharide‐C and aliphatic‐C after manure fertilization advanced the microbial growth except for Gram‐positive bacteria, which further promoted macroaggregate formation and stability. The free silt plus clay fraction also affected macroaggregate formation and stability, and its polysaccharide‐C derived from microorganisms or decomposing SOM was positively associated with MWD and macroaggregate proportion. Because polysaccharide‐C can be easily associated with mineral particles, further improving micro‐ or macroaggregation. We conclude that continuous manure fertilization could increase labile SOM accumulation within aggregates and then facilitate microbial growth, which collectively are responsible for aggregate formation and stabilization.     

The effect of organic matter on the difference between particle-size distribution data obtained by the sedimentometric and laser diffraction methods

Particle-size distribution in dispersed sediments, soils, atmospheric dust, and other natural objects is their fundamental characteristic. The methods of sedimentometry (the pipette method) and laser diffraction have been applied to study particle-size distribution in a typical chernozem of Kursk oblast from the Alekhin Central Chernozemic Reserve. The content of the clay fraction as determined by the method of laser diffraction is three to five times lower than the clay content determined by the traditional pipette method. One of the reasons for such a great difference in the results obtained by two different methods is related to the low density of the solid phase of the particles of soil organic matter that have the size corresponding to the fine and medium silt fractions. Owing to this, they fall into the category of the clay fraction during the traditional sedimentometric analysis. The initially water-stable aggregates of 0.25–0.5 mm in size are subjected to several stages of their breakdown under the impact of ultrasonic dispersion with the detachment of small particles from their surface layers. The remaining aggregates have different resistance to ultrasonic treatment. After the long-term ultrasonic dispersion, the most stable microaggregates still exist in the soil mass. These microaggregates may only be decomposed to elementary soil particles after the addition of sodium pyrophosphate.     

STRUCTURAL FEATURES OF AGGREGATES IN SOME EAST ANGLIAN SILT SOILS

Samples from field plots of silty soils in East Anglia, which were high and low in organic matter, were subjected to mild ultrasonic vibration. In soils high in organic matter particles in the 2–20 μm or 20–50 μMm size range contained most humified organic matter, whereas in soils low in organic matter, most was present in the clay sized fraction. Scanning electron micrographs of the ultrasonically separated particles showed that those from the high organic matter soils had more extensive surface coatings. Clean fragments were left after peroxide and calgon dispersion treatment.     

连续施肥20年后棕壤团聚体分布和碳储量变化

利用两种不同分离方法(干筛法与湿筛法)对耕作施肥20年后棕壤的团聚体组成、团聚体有机碳含量以及有机碳储量进行了研究。结果表明:棕壤团聚体以0.25～1mm团聚体为主。与长期不施肥比较,除0.25～1mm粒级外长期施用氮磷化肥使风干团聚体和水稳性团聚体中较大团聚体和微团聚体数量下降,降低了各级风干团聚体中有机碳积累,增加了水稳性团聚体中有机碳积累;长期施用有机肥较大团聚体和微团聚体数量增加及其相连的有机碳含量和储量均增加;长期有机无机肥配施大团聚体数量下降,微团聚体数量增加,有机碳含量均增加,大团聚体碳库储量下降,微团聚体碳库储量增加。由此可见长期施有机肥土壤结构改善,固C潜力增加。长期高量有机肥与无机肥配施可能有利于土壤固碳,但不利于作物生长。     

Influence of soil properties on the aggregation of some Mediterranean soils and the use of aggregate size and stability as land degradation indicators

Soil aggregation in relation to other soil properties was studied along a climatological transect in the Southeast of Spain. Three sites were selected along this transect ranging from semiarid to subhumid climatological conditions. The aggregate size distribution, the macro and microaggregate stability of the superficial soil horizon and their relations with other soil properties were analysed. Large aggregates (>10, 10–5, 5–2 mm) were present in highest proportions in the most arid of the studied areas. These large aggregates were associated with high values of water-stable microaggregates; however, they did not improve soil structure and are related to high bulk densities and low water retention. Aggregates 1–0.105 mm were positively correlated to medium, fine, very fine sand and silt fractions and to organic matter. Aggregates <0.105 mm were positively correlated to organic matter and clay content. Small aggregate sizes (1–0.105 and <0.105 mm) had a positive influence on soil water retention and they seem a good indicator of soil degradation.Water stability of microaggregates showed a positive correlation with clay content while the stability of the macroaggregates depended on the organic matter content when the organic matter content was greater than 5 or 6%. Below that threshold the carbonate content was strongly correlated with aggregate stability. A general conceptual scheme of associations between aggregate size distribution, water-stable microaggregation and textural characteristics for the area was developed.The land use history affecting soil overlaps the pattern of climatological situations and has to be taken into account. Aggregate size distribution and stability can be used as indicator of soil degradation, but not as a unique parameter.     

黄土区不同施肥对土壤颗粒及微团聚体组成的影响

采用野外采样与室内分析方法,运用颗粒体积分形理论,研究了15年长期不同施肥处理对黄土区农田土壤颗粒组成、 微团聚体分布及有机碳的影响。结果表明,施肥处理对020 cm土层影响较大,不同施肥处理土壤颗粒及微团聚体的优势粒级均为0.02~0.05 mm。有机肥（M）、 磷肥（P）、 有机肥和氮肥配施（MN）、 有机肥、 氮肥和磷肥配施（MNP）处理可显著提高020 cm土层0.1~0.2 mm土壤颗粒的百分含量,有机肥和磷肥配施（MP）以及MNP处理有利于该土层大粒径土壤微团聚体的形成。氮肥和磷肥配施（NP）处理的土壤分散率最大,M处理最小。不同施肥处理土壤颗粒体积分形维数差异不显著。相关性分析表明, 020 cm及2040 cm土层土壤颗粒体积分形维数与粘粒（0.002 mm）和细粉粒 （0.002~0.02 mm） 呈极显著正相关,与粗粉粒 （0.02~0.05 mm） 和细砂粒 （0.05~0.2 mm）极显著负相关; 土壤团聚度与0.05 mm各粒径土壤团聚体显著或极显著负相关,与 0.05 mm各粒径土壤团聚体显著或极显著正相关。020 cm土层土壤有机碳与0.01~0.05 mm各粒径土壤团聚体显著或极显著负相关,与0.1~0.5 mm各粒径土壤团聚体极显著正相关。     

Microaggregates in agricultural soils and their size distribution determined by X-ray attenuation

Understanding mechanisms of microaggregate formation in soils requires knowledge of their exact size distribution. With this in mind, we have used X‐ray attenuation to determine the size distributions of microaggregates and primary particles in the range 0.2–63 μm, with a resolution of 100 size increments. Ten arable and grassland soils with organic C contents ranging from 14.7 to 37.7 g kg^?1 were analysed. They were subjected to ultrasound at 52 J ml^?1 which destroyed most aggregates > 63 μm to give microaggregates in the size range 1–63 μm. The size distribution of microaggregates differed significantly from that of primary particles and was largely independent of their organic C content. Microaggregates were most abundant in 19 of the 100 size increments, contributing to 92% of the major peaks of the size distribution. These preferred increments differed from those of primary particles, but the order for the two was similar. Further analysis of the size distribution revealed a larger mean weight diameter of microaggregates, depending on the size distribution of primary particles. The results suggest a major effect of the size distribution of primary particles on microaggregation, whereas land use seems to have a negligible effect. The proportion of mechanically dispersible clay decreased with increasing C content and indicates structural stability at the microscale.