Aging shapes the distribution of copper in soil aggregate size fractions

As the basic unit of soil, aggregates are considered as a stable soil organic ( SOC ) pool. Changes in organic subtract due to straw addition induce variations in soil microbial community or activity, which may effect the C sequestration in aggregates. Most of the previous studies on soil microorganisms assessment was done at large scale i.e. larger quantities of soil, however, few studies on SOC is known in aggregate size fractions. This study investigated the effects of soil aggregate size on the distribution of microorganism and SOC, and the relationship of microorganism and C sequestration inside aggregate size fractions with 13C-labelled straw addition. Soil samples were collected from 0-15 cm and classified into 5 aggregates sizes classes ( &#65310;5 mm, 2-5 mm, 1-2 mm, 0.25-1 mm and &#65308;0.25 mm ), and the graded aggregates were incubated for 180 days at 20&#160;&#176;C, with or without&#160;13C-labelled straw residue. The incorporation of 13C into the five aggregate size fractions was analyzed.After incubation, the SOC, DOC and ROC contents were increased more rapidly and significantly in aggregate ( &#65310;5 mm ) than that in aggregate ( &#65308;5 mm ) under straw addition, with the same trend of new carbon derived from straw. The total PLFAs was increased most significantly in aggregate ( &#65310;5 mm ), especially fungi and negative bacteria ( G- ), while the positive bacteria ( G+ ) increased slightly in aggregate ( &#65308;0.25 mm ), with no significant change in total PLFAs. The proportion of bacteria in total microorganism increased gradually, as the aggregate size increased in straw treatment. The results imply that aggregate ( &#65310;5 mm ) have more space for C sequestration and greater contribution to new carbon turnovering in soil than other small aggregates, and it gradually tended to be bacterial with the enrichment of carbon. In addition, the SOC contents were strongly related to the amount of fungi and G- in aggregate ( &#65308;5 mm ), while related to G+ in aggregate ( &#65308;0.25 mm ) under straw addition.

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Total mercury distribution among soil aggregate size fractions in a temperate forest podzol

Spanish Journal of Soil Science ◽

10.3232/sjss.2018.v8.n1.05 ◽

2018 ◽

Vol 8 ◽

Author(s):

Antía Gómez Armesto ◽

Lucía Bibián-Núñez ◽

Claudia Campillo-Cora ◽

Xabier Pontevedra-Pombal ◽

Manuel Arias-Estévez ◽

...

Keyword(s):

Temperate Forest ◽

Aggregate Size ◽

Fine Sand ◽

Soil Aggregate ◽

Coarse Sand ◽

Coarse Silt ◽

Fine Silt ◽

Size Fractions ◽

Total Hg ◽

Sand Size

This study determined the distribution of total Hg (HgT) among aggregate size fractions in the A, E, Bh and Bs horizons of a representative temperate forest podzol. The aggregate distribution was dominated by the coarse sand size fraction (average of 55%) followed by fine sand (29%), fine silt (10%), coarse silt (4%) and clay (2%). In general, HgT mean values increased as the aggregate size become smaller: clay (170 ng g-1) > fine silt (130 ng g-1) > coarse silt (80 ng g-1) > fine sand (32 ng g-1) > coarse sand (14 ng g-1). Total Hg enrichment in clay-sized aggregates ranged from 2 to 11 times higher than the values shown by the bulk soil (< 2 mm). The accumulation of HgT in the finer size aggregates was closely related to total organic C, Na-pyrophosphate extracted C, metal (Al, Fe)-humus complexes and Al and Fe oxyhydroxides. Indeed, these parameters varied significantly (p < 0.05) with the aggregate size and their highest values were found in the finer fractions. This suggested the role of these soil compounds in the increase of the specific surface area per mass unit and negative charges in the smallest aggregates, favouring Hg retention. Mercury accumulation factor (HgAF) values reached up to 10.8 in the clay size aggregates, being close to 1 in sand size fractions. Regarding Hg enrichment factors (HgEF), they were < 4 (“moderate pollution” category) in most of the horizons and aggregate sizes. Grain size mass loading (GSFHg) revealed that finer fractions had a higher Hg loading than their mass fractions, with a notable contribution of fine silt which made up > 50% of HgT in Bh and Bs horizons. The potential ecological risk index (PERIHg) increased as the aggregate size decreased, with the highest values in the illuvial horizons (45-903) and lowest in the E horizon (3-363). Heterogeneous distribution of Hg in the soil aggregate size fractions must be considered for Hg determination for purposes such as critical loads, background values or environmental risk indices. In addition, Hg accumulation in finer aggregates could be of concern due to its potential mobility in forest soils, either transferred by leaching to groundwater and freshwaters or mobilized by runoff in surface horizons.

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A modeling approach to quantifying soil macroaggregate dynamics

Canadian Journal of Soil Science ◽

10.4141/s01-024 ◽

2002 ◽

Vol 82 (2) ◽

pp. 181-190 ◽

Cited By ~ 41

Author(s):

A F Plante ◽

Y. Feng ◽

W B McGill

Keyword(s):

Organic Matter ◽

Aggregate Size ◽

Soil Aggregate ◽

Size Fractions ◽

Significant Control ◽

Modeling Approach ◽

Growing Seasons ◽

Organic Matter Dynamics ◽

Aggregate Turnover ◽

Aggregate Dynamics

While several researchers have suggested that soil aggregate turnover is a significant control on organic matter dynamics, the quantification of soil aggregate dynamics has yet to be achieved. Quantification of soil aggregate turnover is essential to testing any hypothesis concerning the relationship between aggregate turnover and organic matter dynamics. The goal of the current work was to propose a modeling approach to the quantification of soil macroaggregate dynamics. The approach taken was to define model compartments representing water-stable soil aggregate size fractions and describing the flows between compartments using first-order kinetics. Soil aggregate data from a 2-yr field study on two contrasting soils were used to calibrate the model and yielded soil aggregate mean residence times ranging from 4 to 95 d, where aggregate dynamics were generally two to three times more rapid in a Gray Luvisol compared to a Black Chernozem. The model was subsequently used to predict the distribution of applied tracer spheres in water-stable aggregate size fractions from an initially free state. The models closely predicted the Dy "mean weight diameters" (Dy-MWD) after two growing seasons. While the models have several limitations, they offer the first attempt to quantitatively describe soil macroaggregate dynamics, which is essential to predicting the response in organic matter dynamics to changes in aggregate dynamics. Key words: Soil aggregation, macroaggregate turnover, tracer, model

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Tillage effects on humus composition and humic acid structural characteristics in soil aggregate-size fractions

Soil and Tillage Research ◽

10.1016/j.still.2021.105090 ◽

2021 ◽

Vol 213 ◽

pp. 105090

Author(s):

Batande Sinovuyo Ndzelu ◽

Sen Dou ◽

Xiaowei Zhang ◽

Yifeng Zhang ◽

Rui Ma ◽

...

Keyword(s):

Humic Acid ◽

Structural Characteristics ◽

Aggregate Size ◽

Soil Aggregate ◽

Size Fractions ◽

Humus Composition

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Soil aggregation and soil organic matter in conventionally and organically farmed Austrian Chernozems / Bodenaggregation und organische Substanz in konventionell und biologisch bewirtschafteten österreichischen Tschernosemböden

Die Bodenkultur Journal of Land Management Food and Environment ◽

10.1515/boku-2017-0004 ◽

2017 ◽

Vol 68 (1) ◽

pp. 41-55

Author(s):

Taru Sandén ◽

Georg J. Lair ◽

Jeroen P. van Leeuwen ◽

Guðrún Gísladóttir ◽

Jaap Bloem ◽

...

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Organic Carbon ◽

Fungal Biomass ◽

Aggregate Size ◽

Soil Aggregate ◽

Biological Properties ◽

Size Fractions ◽

Significant Difference ◽

Haplic Chernozems

Summary In order to study the soil aggregate distributions and soil organic matter (SOM), we sampled top- and subsoils in four intensively farmed croplands (two organic (Org-OB and Org-LA), and two conventional (Con-OB and Con-LA)) on Haplic Chernozems located in Marchfeld in the east of Vienna (Austria). Soil structure and SOM quantity, quality and distribution between free and occluded particulate organic matter and aggregate size fractions (<20 µm, 20-250 µm, 250-5000 µm) were studied by following a density fractionation procedure with low-energy ultrasound treatment. The relation of the soil physicochemical (e.g., particle size distribution, pH, organic carbon, total nitrogen) and biological properties (e.g., fungal biomass, active fungi) with stable soil aggregate size fractions and SOM was studied. The mean weight diameter (MWD) showed no significant difference between all studied sites and was between 3.8 mm and 10.0 mm in topsoils and between 6.7 mm and 11.9 mm in subsoils. In topsoils, the contents of calcium-acetate-lactate (CAL)-extractable P, active fungal biomass, dithionite-extractable Fe and sand were significantly positively correlated with the amount of the macroaggregates and with the MWD. We observed that most soil organic carbon, depending on soil texture, was stored in the microaggregate size classes <20 µm and 20-250 µm.

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